TUHH Open Research (TORE)https://tore.tuhh.deTORE captures, stores, indexes, preserves, and distributes digital research material.Mon, 12 Apr 2021 15:58:20 GMT2021-04-12T15:58:20Z50411- Forced response of low-frequency pendulum mechanismhttp://hdl.handle.net/11420/4737Title: Forced response of low-frequency pendulum mechanism
Authors: Starossek, Uwe
Abstract: A strongly nonlinear pendulum mechanism is considered in which the restoring force is approximately a cubic function of the displacement variable. Its free oscillation frequency is approximately proportional to the amplitude of oscillation and distinctly lower than that of a simple pendulum. The mechanism has therefore been named infra-pendulum. The forced undamped oscillation response of the mechanism to non-harmonic periodic loading is studied under the assumption of small displacements. The loading function is derived from the free oscillation response whose time course follows a Jacobi elliptic function. It is chosen such that exact analytical solutions are obtained for the steady-state response and the amplitude-frequency relation. The equation describing the amplitude-frequency relation is a cubic polynomial equation. Its solutions are presented. The general approach of using non-harmonic periodic loading functions is transferable to other types of nonlinear oscillators.
Wed, 05 Feb 2020 09:15:49 GMThttp://hdl.handle.net/11420/47372020-02-05T09:15:49Z
- Eccentric-wing flutter stabilizer for long-span bridgeshttp://hdl.handle.net/11420/4736Title: Eccentric-wing flutter stabilizer for long-span bridges
Authors: Starossek, Uwe
Abstract: An aerodynamic device for preventing bridge flutter is presented. It consists of wings positioned along the sides of, and fixed relative to, the bridge deck. Flutter suppression efficiency is high provided the lateral eccentricity of the wings is large. It is a passive device without moving parts. This is an advantage over active or passive devices with moving parts, which meet resistance due to reliability concerns. Results of a numerical study are presented in which the critical wind speed for flutter onset of a bridge without wings and with wings mounted in various configurations was determined. Furthermore, first results of wind tunnel tests are reported and a cost estimate is given.
Wed, 05 Feb 2020 09:13:09 GMThttp://hdl.handle.net/11420/47362020-02-05T09:13:09Z
- Active vibration control of an oscillator with two translational degrees of freedom using centrifugal forces created by two eccentrically rotating masseshttp://hdl.handle.net/11420/2653Title: Active vibration control of an oscillator with two translational degrees of freedom using centrifugal forces created by two eccentrically rotating masses
Authors: Bäumer, Richard; Starossek, Uwe
Abstract: An active mass damper for vibration control of an oscillator with two translational degrees of freedom is presented along with the corresponding closed-loop control algorithm. The damper consists of two eccentrically rotating masses. In a preferred mode of operation, the masses rotate in opposite directions with a mostly constant angular velocity about a single axis. The resulting force is a harmonic control force. Its direction is determined by the relative angular position of the masses. In previous research, a similar control algorithm for vibration control of a single degree of freedom oscillator has been proven to be effective. In this paper, the control algorithm is augmented such that it can be applied to an oscillator with two translational degrees of freedom. Various state variables are introduced and a feedback control algorithm is developed. The presented algorithm ensures that the rotational motion of the masses is smooth and that the control force has the required orientation. The algorithm is verified experimentally with a test setup for the damping of free vibrations and numerically for stochastically forced vibrations. Finally, the device is compared with a conventional active mass damper. It is shown that the power demand and the energy consumption of the presented device are smaller than those of the conventional active mass damper.
Tue, 07 May 2019 10:09:05 GMThttp://hdl.handle.net/11420/26532019-05-07T10:09:05Z
- Pancake-type collapse : energy absorption mechanisms and their influence on the final outcomehttp://hdl.handle.net/11420/6182Title: Pancake-type collapse : energy absorption mechanisms and their influence on the final outcome
Authors: Lalkovski, Nikolay; Starossek, Uwe
Abstract: Since the World Trade Center disaster in 2001, various theories have been proposed as to what caused the observed rapid collapse progression ending in the total collapse of both towers. According to the theory now widely accepted, the columns in the aircraft impact zone lost their load-bearing capacity due to the effects of fire. As a result, the upper part of the building fell over the height of at least one story. The resulting impact forces greatly exceeded the buckling load of the columns near the impact zone, which led to the release of a new portion of potential energy. It was also shown that the energy absorbed by the columns during buckling was significantly less than the potential energy released during this process. This led to the conclusion that the total collapse was inevitable once initial failure occurred. However, there are some examples of buildings, in which the columns of an entire story failed and no collapse progression occurred. Such cases were observed in the 1995 earthquake in Kobe, Japan. There were also some failed controlled demolition attempts, in which a progressive collapse to be triggered by the destruction of vertical load bearing elements in lower levels did not occur. No significant deformations of vertical elements were observed in these cases. This raises the question if there are energy absorption mechanisms other than column buckling that may play a role in the structural response to initial failure. Numerical simulations of simple systems are presented showing that there are such mechanisms indeed and that column buckling is not the only possible way to absorb the energy at impact. An analytical approach based on a simplified model is also described. © 2013 American Society of Civil Engineers.
Tue, 26 May 2020 09:09:03 GMThttp://hdl.handle.net/11420/61822020-05-26T09:09:03Z
- An analytical study on the bending moment acting on the girder of a long-span cable-supported bridge suffering from cable failurehttp://hdl.handle.net/11420/2647Title: An analytical study on the bending moment acting on the girder of a long-span cable-supported bridge suffering from cable failure
Authors: Shoghijavan, Mohammad; Starossek, Uwe
Abstract: In this study, the structural behavior of a long-span cable-supported bridge after the sudden rupture of one of its axial cables is of concern. Cable failure produces large bending moments on the girder of the bridge. Henceforth, the focus of this study is to find the “maximum bending moment” on the girder due to the cable failure. For this purpose, an analytical approach based on differential equations of the system will be used. Then, an approximation function for a simplified bridge model in a cable-loss scenario will be derived. The use of the least squares method is also applied to minimize the error of the approximation function. The proposed approximation function has been checked by numerical models, and its good accuracy has been proven. The results show that by increasing the ratio of the bending stiffness of the girder to the axial stiffness of the cables, cable failure produces a larger bending moment on the girder.
Tue, 07 May 2019 09:56:51 GMThttp://hdl.handle.net/11420/26472019-05-07T09:56:51Z
- Structural Robustness of Long-Span Cable-Supported Bridges in a Cable-Loss Scenariohttp://hdl.handle.net/11420/2652Title: Structural Robustness of Long-Span Cable-Supported Bridges in a Cable-Loss Scenario
Authors: Shoghijavan, Mohammad; Starossek, Uwe
Abstract: This study concerns the structural behavior of long-span cable-supported bridges after the sudden rupture of a cable. The load carried by the failed cable must be redistributed to the remaining structure. The cable adjacent to the failed cable receives most of the redistributed load and becomes the critical member. The aim of this study is to find the stress increase ratio of this member. To do this, an analytical approach based on differential equations of the system is used. Then, an approximation function for a simplified bridge model in a cable-loss scenario is derived. The least-squares method is also used to minimize the error of the approximation function. The proposed approximation function has been checked by numerical models, and its accuracy has been proven. The results show that due to increases in the ratio of the bending stiffness of the girder to the axial stiffness of the cables, the stress increase ratio of the critical cable decreases.
Tue, 07 May 2019 10:08:49 GMThttp://hdl.handle.net/11420/26522019-05-07T10:08:49Z
- Simplified flutter prediction for bridges with bluff cross-sectionhttp://hdl.handle.net/11420/326Title: Simplified flutter prediction for bridges with bluff cross-section
Authors: Starossek, Uwe
Abstract: Wind-induced flutter of bridges occurs as coupled torsional and vertical oscillation, or uncoupled torsional oscillation. Bridges with bluff, non-streamlined sections are prone to torsional flutter. Prediction of torsional flutter on the basis of measured aerodynamic derivatives essentially corresponds to the prediction of coupled flutter, although, compared to the latter, it can be largely simplified. The theoretical background is discussed and the given formulae are checked against empirical data. It is found that simplification is recommendable only up to a certain degree.
Thu, 10 Apr 2008 08:04:34 GMThttp://hdl.handle.net/11420/3262008-04-10T08:04:34Z
- Reduction of dynamic cable stiffness to linear matrix polynomialhttp://hdl.handle.net/11420/325Title: Reduction of dynamic cable stiffness to linear matrix polynomial
Authors: Starossek, Uwe
Abstract: For the dynamic stiffness of a sagging cable subject to harmonic boundary displacements, frequency-dependent closed-form analytic functions can be derived from the corresponding continuum equations. When considering such functions in stiffness matrices of composed structures, however, these matrices become frequency dependent, too - a troublesome fact, especially in regards to the eigenvalue difficulties is described whereby an analytic dynamic stiffness function is reduced to a linear matrix polynomial; the matrices of this polynomial are of any desired order. The reduction corresponds to a mathematically performed transition from a continuum to a discrete-coordinate vibrating system. In structural dynamic applications (dynamic cable stiffness), the two resultant matrices correspond to a static stiffness matrix and a mass matrix. Beyond the particular problem focused on, the method may be applied to all kinds of analytic impedance functions. In every case, the resultant matrices can easily be considered within the scope of a linear matrix-eigenvalue problem.
Thu, 10 Apr 2008 08:02:40 GMThttp://hdl.handle.net/11420/3252008-04-10T08:02:40Z
- Dynamic cable stiffness and dynamic interaction between cable and beamhttp://hdl.handle.net/11420/424Title: Dynamic cable stiffness and dynamic interaction between cable and beam
Authors: Kutterer, Mathias; Starossek, Uwe
Abstract: Closed-form expressions for the dynamic stiffness functions of a damped cable and a damped, axially prestressed beam element are given. A dynamic damping phenomenon of a single cable is described. For a multiply-guyed mast, dynamic response functions are evaluated. Influence of cable dynamics is investigated. In case of internal resonance, the dynamic stiffness function of a cable decreases and may become negative. Nevertheless, the response function for the composed system is favourably influenced by cable vibration. This effect is quantified by means of a stochastic analysis of the system response to random excitation. The study is restricted to linear theory; validity of linear theory is discussed.
Mon, 13 Oct 2008 08:03:22 GMThttp://hdl.handle.net/11420/4242008-10-13T08:03:22Z
- Alternating the twin rotor damper between two modes of operation to eliminate small vibrationshttp://hdl.handle.net/11420/1982Title: Alternating the twin rotor damper between two modes of operation to eliminate small vibrations
Authors: Bäumer, Richard; Terrill, Richard; Starossek, Uwe
Abstract: In previous research, the twin rotor damper (TRD), an active mass damper, was presented. In a preferred, energy-efficient mode of operation, the continuous rotation mode, two eccentric control masses rotate with constant angular velocities about two parallel axes in opposite directions. The resulting centrifugal forces combine into a directed harmonic control force that can be used for the control of structural vibrations. In another, more power-demanding mode of operation, the swinging mode, both control masses oscillate about certain angular positions. For both modes of operation, corresponding control algorithms have been developed. Furthermore, it has been found that the continuous rotation mode is not efficient for the damping of small vibrations, whereas the swinging mode can bring small vibrations to rest. In this paper, a control algorithm is presented, which uses the continuous rotation mode for large vibrations and the swinging mode for small vibrations. To validate the control algorithm, the TRD is numerically and experimentally applied on a single degree of freedom oscillator. The efficiency of the algorithm is studied for free vibrations.
Tue, 22 Jan 2019 13:56:15 GMThttp://hdl.handle.net/11420/19822019-01-22T13:56:15Z
- Eccentric-wing flutter stabilizer for bridges – Analysis, tests, design, and costshttp://hdl.handle.net/11420/2646Title: Eccentric-wing flutter stabilizer for bridges – Analysis, tests, design, and costs
Authors: Starossek, Uwe; Ferenczi, Tamas; Priebe, Jürgen
Abstract: A device is presented that aims at preventing bridge flutter. It consists of wings positioned along the sides of, and fixed to, the bridge deck. Flutter suppression effectiveness is high provided the lateral eccentricity of the wings is large. It is a passive aerodynamic device that is presumably more cost-efficient than other passive measures or devices. Moreover, it does not contain moving parts. This is an advantage over devices with moving parts, which meet resistance due to reliability and durability concerns. Wind-tunnel tests were performed in which the flutter speed of a bridge deck sectional model without wings and with wings mounted in various configurations was measured. The experimental results are presented and compared with the results of flutter analyses using finite aeroelastic beam elements. Using the analytical approach, also the effect of the distribution of the wings along the length of a bridge was studied to optimize this distribution. Preliminary design studies for the wings and their support structures as well as quantity and cost estimates are presented. For a representative example bridge and wing configuration, an increase of 22% of flutter speed is reached at a cost increase of 2.5%.
Tue, 07 May 2019 09:53:26 GMThttp://hdl.handle.net/11420/26462019-05-07T09:53:26Z
- How to increase the flutter speed of a bridgehttp://hdl.handle.net/11420/8718Title: How to increase the flutter speed of a bridge
Authors: Starossek, Uwe
Mon, 08 Feb 2021 10:24:43 GMThttp://hdl.handle.net/11420/87182021-02-08T10:24:43Z
- Twin Rotor Damper for Human-Induced Vibrations of Footbridgeshttp://hdl.handle.net/11420/6073Title: Twin Rotor Damper for Human-Induced Vibrations of Footbridges
Authors: Terrill, Richard Douglas; Bäumer, Richard; Van Nimmen, Katrien; Van Den Broeck, Peter; Starossek, Uwe
Abstract: Footbridges often have a lightweight and slender design. As a result, they tend to be susceptible to human-induced vibrations. In this paper, the application of the twin rotor damper (TRD), an active mass damper consisting of two eccentrically rotating masses, for the control of human-induced footbridge vibrations is presented. A proof-of-concept prototype is developed for a real-world slender steel footbridge that is sensitive to human-induced vibrations. First, a numerical study is performed to design a TRD to mitigate human-induced vibrations. Based on these results, a TRD prototype was designed and built. Second, the performance of the TRD is evaluated on-site. The response of the footbridge to human-induced loading is measured under both uncontrolled and controlled conditions and compared to corresponding numerical simulations. The measurements confirm the results of the numerical simulations. They show that the TRD prototype is able to effectively damp human-induced vibrations of a real-world footbridge and validate the TRD design.
Fri, 08 May 2020 05:41:03 GMThttp://hdl.handle.net/11420/60732020-05-08T05:41:03Z
- Optimum design of long-span cable-supported bridges using robustness indexhttp://hdl.handle.net/11420/2677Title: Optimum design of long-span cable-supported bridges using robustness index
Authors: Shoghijavan, Mohammad; Starossek, Uwe
Abstract: The target of this study is to use a practical method for the optimization of cable distance in cable–supported bridges using the robustness index. The proposed optimization method minimizes the cost of the bridge construction and guarantees a certain level of robustness. The reserve-based robustness index, applied in this study, considers the redistribution of forces after the failure of structural elements. For finding the optimum distance of cables, a simplified bridge model is considered. Cable-loss scenarios are considered in the design process and the dynamic effect of cable rupture is taken into account. Then, the critical design load of the cables and the maximum bending moment acting on the girder after the cable failure are calculated and incorporated into the bridge design. The effect of other influential factors, such as the bending stiffness of the girder and the axial stiffness of the cables, on the optimum design of the system is also investigated.
Tue, 21 May 2019 11:57:25 GMThttp://hdl.handle.net/11420/26772019-05-21T11:57:25Z
- Brückendynamik : Winderregte Schwingungen von Seilbrückenhttp://hdl.handle.net/11420/363Title: Brückendynamik : Winderregte Schwingungen von Seilbrücken
Authors: Starossek, Uwe
Abstract: Gegenstand der Abhandlung ist das dynamische Verhalten von Brücken. Besonderes Augenmerk liegt auf dem Phänomen winderregte Flatterschwingung und auf der Konstruktionsgattung Seilbrücke. Ziele sind das Verstehen der Schwingungsmechanismen, die Verifizierung und Verbesserung bekannter Nachweisverfahren, wo erforderlich die Schaffung neuer mechanisch-mathematischer Kalküle und Aussagen zu einem dynamisch vorteilhaften Entwurf. Die Methodik umfaßt vergleichendes Literaturstudium, analytisches und numerisches Rechnen sowie - hierauf beruhend - klärende Diskussion. Vorausgesetzt werden fast durchweg kleine Verschiebungen (lineare Theorie), Berechnungen erfolgen im Frequenzbereich. Die Bestimmung der Luftkräfte geht vom ebenen instationären Strömungsfeld aus.
Die aerodynamischen und aeroelastischen Grundzusammenhänge werden am zweidimensionalen System erörtert. Dies beinhaltet eine Diskussion der klassischen Flattertheorie der ebenen Platte. (...)
Der rechnerische Flatternachweis allgemeinerer, linienförmig räumlicher Systeme erfordert eine theoretische Untersuchung der Aeroelastik des Biege-Torsions-Balkens. Sowohl die Methode des differentiellen Gleichgewichts als auch die Finite-Element-Methode werden angewendet. Letzteres führt auf die Entwicklung zweier aeroelastischer Balkenelemente.
Zur Erfassung der dynamischen Seil-Balken-Interaktion, erforderlich für die Berechnung zusammengesetzter Systeme, wird die dynamische Steifigkeitsmatrix des gedämpften Einzelseils hergeleitet. Ihre Elemente sind analytische Funktionen der Schwingungsfrequenz. Sie werden auf lineare Matrizenpolynome abgebildet, was eine erleichterte numerische Lösung des Eigenwertproblems ermöglicht.
Die gewonnenen Erkenntnisse werden auf reale Brückensysteme und insbesondere auf Schrägkabelbrücken übertragen. In Verbindung mit einer Diskussion der sogenannten Systemdämpfung und alternativ vorgeschlagenen Begriffsbildungen erfolgt eine Beschreibung systemeigener, dynamisch vorteilhafter Mechanismen. In einer numerischen Studie an einem Vielseilsystem wird die Beeinflussung des Flatterverhaltens durch die Nichtaffinität der Eigenformen untersucht.; The dynamic behavior of bridges is investigated, with special attention paid to the phenomenon of wind-induced flutter vibration and to the design family "cable-supported bridges". The aim is to understand the mechanisms of vibration, to verify and to improve known methods of calculation, to create new mechanical-mathematical tools where necessary and to make statements with regard to a dynamically advantageous design. The research method comprises comparative study of relevant publications, analytical and numerical calculation, and, based thereupon, clarifying discussion. Generally, small displacements are assumed (linear theory); calculations are effected in the frequency domain. Determination of aerodynamic forces proceeds from the assumption of plane instationary stream.
In the discussion of aerodynamic and aeroelastic basic relations, attention is focussed on the two-dimensional system. A review of the classical theory of flutter of a flat plate (aerofoil) is included, and a simplified arithmetical method for its execution is given. The applicability of the classical theory to bridges is investigated. An empirically modified theory of flutter makes use of measured aerodynamic coefficients (nonstationary derivatives). Available measuring methods are described and compared, and the applicability of the modified theory is investigated. Further discussion is dedicated to nonlinear aerodynamics and to dynamic-aeroelastic response behaviour.
Flutter calculation for more general systems, i.e. line-like three-dimensional systems, requires theoretical investigation of the aeroelastics of a beam with freedom to bend and twist. The approach by partial differential equations, as well as the finite-element concept, are applied. The latter leads to the development of two aeroelatic beam elements.
In order to account for the dynamic interaction between cables and other system elements (necessary for the calculation of composed systems), the dynamic stiffness matrix of a damped cable is derived. Its coefficients are analytical functions of the frequency of motion. They are subsequently represented by linear matrix polynomials, which facilitates the numerial solution of eigenvalue problems.
The acquired findings are applied to real bridge systems and, in particular, to cable-stayed bridges. In connection with the so-called system damping and alternatively proposed terms, a description of system inherent, dynamically advantageous mechanisms is given. By means of a numerical flutter study on a multi-cable system, the influence of non-affinity of mode shapes on the flutter behaviour is investigated.
Wed, 25 Jun 2008 09:01:12 GMThttp://hdl.handle.net/11420/3632008-06-25T09:01:12Z
- An analytic comparison regarding steady-state damping performance between the twin rotor damper and a dynamic vibration absorberhttp://hdl.handle.net/11420/2136Title: An analytic comparison regarding steady-state damping performance between the twin rotor damper and a dynamic vibration absorber
Authors: Bäumer, Richard; Terrill, Richard; Starossek, Uwe
Abstract: © Springer International Publishing AG 2018. A novel active mass damper, the twin rotor damper (TRD), was presented in previous research, including control algorithms for monofrequent vibrations. In this paper, the steady-state damping performance is evaluated by applying a harmonic excitation force to a single degree of freedom (SDOF) oscillator with and without the action of the damping device. Using the velocity of the SDOF oscillator as feedback, adequate steady-state damping performance can be achieved with the TRD by setting the control force of the TRD in antiphase to the velocity of the SDOF oscillator. An analytic solution describing the steady-state damping performance is derived. The analytic solution allows for the comparison with a dynamic vibration absorber (DVA) of comparable size (stroke) and control mass. The analytic comparison shows that the TRD achieves greatly better damping performance than the DVA.
Wed, 13 Mar 2019 11:55:52 GMThttp://hdl.handle.net/11420/21362019-03-13T11:55:52Z
- Active vibration control of a three degree of freedom oscillator using two eccentrically rotating masseshttp://hdl.handle.net/11420/2130Title: Active vibration control of a three degree of freedom oscillator using two eccentrically rotating masses
Authors: Terrill, Richard; Bäumer, Richard; Starossek, Uwe
Abstract: © Springer International Publishing AG 2018. An active mass damper utilizing rotating masses to damp the vibrations of an oscillator with two translational degrees of freedom in a horizontal plane and one rotational degree of freedom about a vertical axis is presented along with a corresponding closed-loop control algorithm. The damper consists of two masses rotating about a single vertical axis, powered by two actuators. In a preferred mode of operation, these masses rotate with a nearly constant and equal angular velocity in opposite directions, thus producing a harmonic control force in a single horizontal direction. By varying the relative angular position of the rotating masses, this control force can be directed in an arbitrary direction and used to damp the translational motion. In previous research, a control algorithm was derived for this purpose. The rotational degree of freedom can additionally be controlled by producing a moment by imposing angular accelerations on the rotating masses. In this paper, the previous control algorithm is augmented such that the rotational degree of freedom is additionally controlled. The augmented control algorithm is verified with help of numerical simulations.
Wed, 13 Mar 2019 11:54:53 GMThttp://hdl.handle.net/11420/21302019-03-13T11:54:53Z
- Structural robustness of long-span cable-supported bridges segmented by zipper-stoppers to prevent progressive collapsehttp://hdl.handle.net/11420/2651Title: Structural robustness of long-span cable-supported bridges segmented by zipper-stoppers to prevent progressive collapse
Authors: Shoghijavan, Mohammad; Starossek, Uwe
Abstract: This paper investigates the structural behaviour of a long-span cable-supported bridge segmented by zipper-stoppers after the sudden rupture of some of its cables. Increasing the robustness of the structural system through segmentation is a possible approach to prevent progressive collapse in bridges due to cable failure. In this concept, zipper-stoppers, at the segment borders, are strong components with the multiple of the load bearing capacity of usual members and are designed to arrest a zipper-like collapse in the segment where the initial damage occurred. For finding the "stress increase ratio" of the zipper-stopper, an analytical approach based on differential equations of the system will be used. Then, an approximation function for a simplified bridge model in a cable-loss scenario will be derived. The proposed approximation function has been checked by numerical models, and its good accuracy has been proven.
Tue, 07 May 2019 10:08:39 GMThttp://hdl.handle.net/11420/26512019-05-07T10:08:39Z
- Ein Beitrag zum Brückenflattern: Nachweis am ebenen Ersatzsystem und Einfluß des Profilshttp://hdl.handle.net/11420/352Title: Ein Beitrag zum Brückenflattern: Nachweis am ebenen Ersatzsystem und Einfluß des Profils
Authors: Starossek, Uwe
Abstract: Dynamisch-aeroelastische Instabilität von Brücken kann je nach Querschnittsausbildung als gekoppeltes Biege-Torsions-Flattern oder als entkoppeltes Torsionsflattern auftreten. Zu ersterem neigen Brücken mit plattenähnlichem, zu letzterem Brücken mit nichtplattenähnlichem Profil. Ein rechnerischer Nachweis des Torsionsflatterns auf der Grundlage gemessener aerodynamischer Beiwertfunktionen entspricht im Prinzip dem Nachweis des gekoppelten Flatterns, kann gegenüber diesem aber weitgehend vereinfacht werden. Die theoretischen Grundlagen für den Nachweis gekoppelten Flatternsen am ebenen Ersatzsystem und den vereinfachten Nachweis entkoppelten Torsionsflatterns werden erörtert. Weiterhin werden Kriterien für eine Klassifizierung in plattenähnliche und nichtplattenähnliche Querschnitte angegeben. Da plattenähnliche Profile in der Regel höhere kritische Windgeschwindigkeiten ermöglichen, können die angegebenen Kriterien als Entwurfsregeln benutzt werden.; Wind-induced flutter of bridges occurs as coupled torsional and vertical oscillation or uncoupled torsional oscillation. Bridges with streamlined, plate-like cross-section are prone to coupled flutter; bridges with bluff, non-streamlined section tend to torsional flutter. Prediction of torsional flutter on the basis of measured aerodynamic derivatives essentially corresponds to the prediction of coupled flutter, although, compared to the latter, it can be largly simplified. The theoretical background for the prediction of coupled flutter by means of generalized 2-degree-of-freedom systems and the simplified prediction of uncoupled torsional flutter is discussed. Furthermore, criteria for the classification of cross-sections as plate-like sections are given. These sections generally provide higher critical wind speeds. The given criteria can therefore be used as design rules.
Thu, 19 Jun 2008 07:45:34 GMThttp://hdl.handle.net/11420/3522008-06-19T07:45:34Z
- Ein angepasstes Ermüdungslastmodell für stählerne Stabbogenbrücken mit freistehenden Bögenhttp://hdl.handle.net/11420/6583Title: Ein angepasstes Ermüdungslastmodell für stählerne Stabbogenbrücken mit freistehenden Bögen
Authors: Bransch, Martin; Priebe, Jürgen; Starossek, Uwe
Abstract: Bei vorhandenen stählernen Stabbogenbrücken mit freistehenden Bögen werden häufig seitliche Bogenschwingungen festgestellt. Diese resultieren aus kritischen Achsfolgeimpulsen überfahrender Lkw und Resonanz. Vielfach wird ein langes Nachschwingen beobachtet. Hieraus folgt eine große Ermüdungsbeanspruchung für den Bogen und die angrenzenden Bauteile, welche mit den Ermüdungslastmodellen aus den aktuell gültigen DIN‐Fachberichten unzureichend erfasst wird. Um bei Neuplanungen solcher Brücken die große Ermüdungsbeanspruchung zu berücksichtigen, wird hier ein erweitertes Ermüdungslastmodell zur Bemessung vorgeschlagen. Dieses wird ELM 3a genannt und in Anlehnung an die DIN‐Fachberichte aufgestellt. Für das ELM 3a werden ein anpassbarer Achsabstand und eine anpassbare Geschwindigkeit eingeführt, um die Bogenschwingung zu maximieren. In diesem Zusammenhang wird eine vereinfachte Impulsform für die Radlasten angegeben, die z. B. in einer FEM‐Berechnung verwendet werden kann.; Lateral arch vibrations are frequently observed at existing steel bowstring bridges. These result from critical axle arrangement loads of crossing trucks and resonance. A long post oscillation is often detected. Hence, a large fatigue load for the arch and the adjacent construction components exists, which is included in the actual standards insufficiently. An extended fatigue load model for structural design is presented to incorporate the large fatigue load while planning such bridges. It is called ELM 3a and is based on the fatigue load model 3 given in DIN Fachbericht 101. An adjustable distance between axles and an adjustable speed are introduced for the ELM 3a to maximize the lateral arch vibrations. A simplified impulse form is given for the wheel loads in this context, which can be used in an FEM calculation for example. © Ernst & Sohn;.
Fri, 03 Jul 2020 09:11:56 GMThttp://hdl.handle.net/11420/65832020-07-03T09:11:56Z
- Die Dynamik des durchhängenden Seileshttp://hdl.handle.net/11420/313Title: Die Dynamik des durchhängenden Seiles
Authors: Starossek, Uwe
Abstract: Die vorliegende Arbeit gibt einen Überblick über die analytischen Möglichkeiten zur Beurteilung des dynamischen Verhaltens von horizontal oder schräg gespannten Einzelseilen mit gravitationsbedingtem großen oder kleinen Durchhang.
Der Schwerpunkt liegt auf der linearen Theorie der freien Schwingungen und, hierauf aufbauend, auf der Berechnung des Antwortverhaltens bei dynamischer Querbelastung oder Schwingungsanregung durch die Aufhängepunkte.
Nach einem Exkurs in die nichtlineare Dynamik werden die praktisch relevanten Erregungskräfte behandelt und Beispielrechnungen durchgeführt.
Fri, 04 Apr 2008 07:56:06 GMThttp://hdl.handle.net/11420/3132008-04-04T07:56:06Z
- Boundary induced vibration and dynamic stiffness of a sagging cablehttp://hdl.handle.net/11420/312Title: Boundary induced vibration and dynamic stiffness of a sagging cable
Authors: Starossek, Uwe
Abstract: This paper sets forth the linear theory of boundary induced vibration of an extensible, sagging cable. A dynamic stiffness matrix is derived whose coefficients are functions of the frequeny of motion, and which is suitable for dynamic direct-stiffness analysis of complex systems. The study considers motion within the cable plane only. Viscous damping is taken into account.
Fri, 04 Apr 2008 07:53:31 GMThttp://hdl.handle.net/11420/3122008-04-04T07:53:31Z
- Flatternachweis von Brücken mittels Finiter Balkenelementehttp://hdl.handle.net/11420/354Title: Flatternachweis von Brücken mittels Finiter Balkenelemente
Authors: Starossek, Uwe
Abstract: Winderregtes Flattern von Brücken mit plattenähnlichem Querschnitt erfolgt in einer gekoppelten Biege-Torsions-Form. Sein rechnerischer Nachweis kann u.U. an einem ebenen Ersatzsystem geführt werden. Die hierfür erforderliche Generalisierung ist allerdings unmöglich oder äußerst konservativ, falls die Eigenformen der Biege- und Torsionsschwingungen stark nichtaffin sind. Dem Flatternachweis ist dann eine räumliche Modellierung zugrundezulegen. Die klassischen Verfahren des Flugzeugbaus zur Lösung des räumlichen Problems gehen von differentiellen Bewegungsgleichungen aus. Für Anwendungen des Brückenbaus erweist sich die Methode der Finiten Elemente als vorteilhafter. Es werden zwei Balkenelemente verschiedener Komplexität definiert und die entsprechenden Element-Matrizen angegeben. Aufstellen und Lösen der diskretisierten Bewegungsgleichungen wird beschrieben. Ergebnisse einer numerischen Studie werden vorgestellt und erörtert.; Wind-induced flutter of bridges with streamlined, plate-like cross-section occurs as coupled torsional and vertical oscillation. Prediction can possibly be facilitated by representing the spatial system by a generalized 2-DOF system. This, however, may be unadmissible or extremely conservative if the modes of torsional and vertical vibration differ strongly. In this case, flutter prediction should be based on spatial modeling. Classical methods of aircraft engineering for solving the spatial problem proceed from partial differential equations of motion. For applications in bridge engineering, the finite-element concept proves more efficient. In this paper, two beam elements of differenct complexity are defined, and correspondend matrices are given. Formulation and solution of the resulting MDOF equations of motion is described. Results of a numerical study are presented and discussed.
Thu, 19 Jun 2008 14:16:42 GMThttp://hdl.handle.net/11420/3542008-06-19T14:16:42Z
- Dynamic stiffness matrix of sagging cablehttp://hdl.handle.net/11420/303Title: Dynamic stiffness matrix of sagging cable
Authors: Starossek, Uwe
Abstract: The dynamic behavior of an extensible sagging cable is investigated. A dynamic stiffness matrix is presented whose coefficients are functions of the frequency of motion, and that is suitable for dynamic direct-stiffness analysis of composed systems such as cable-stayed bridges and guyed masts. The study is restricted to small displacements (linear theory) and considers motion within the vertical cable plane only. Viscous damping due to external fluid is taken into account. Trigonometrical solution functions with complex arguments are utilized, which implies a substantial simplification in the analysis of damped vibrations. By means of example calculations, stiffness functions are discussed and compared to the results of other authors. For tightly stretched inclined cables, utilization of the more accurate theory presented in this paper is indispensable.
Thu, 20 Mar 2008 13:37:57 GMThttp://hdl.handle.net/11420/3032008-03-20T13:37:57Z
- An energy approach for the active vibration control of an oscillator with two translational degrees of freedom using two auxiliary rotating masseshttp://hdl.handle.net/11420/1793Title: An energy approach for the active vibration control of an oscillator with two translational degrees of freedom using two auxiliary rotating masses
Authors: Bäumer, Richard; Terrill, Richard; Starossek, Uwe
Abstract: An active mass damper implementing two auxiliary masses rotating about a single axis is presented. This device is used for the vibration control of an oscillator performing translational motion in a plane (two translational degrees of freedom). In a preferred mode of operation, both auxiliary masses rotate with the same constant angular velocity in opposite directions. The resultant of the produced harmonic centrifugal forces is used for the vibration control. The direction of this control force can be altered by slightly varying the angular velocity of the auxiliary masses. Using an energy approach, a control algorithm was derived. The control algorithm ensures that the control force effectively damps the oscillator when it is displaced in a single, arbitrary direction. Numerical simulations were performed, showing that the presented device with the corresponding control algorithm effectively damps the vibrations on the oscillator.
Wed, 07 Nov 2018 06:51:30 GMThttp://hdl.handle.net/11420/17932018-11-07T06:51:30Z
- Cable dynamics - a reviewhttp://hdl.handle.net/11420/302Title: Cable dynamics - a review
Authors: Starossek, Uwe
Abstract: The history of the theory of cable vibrations from the 18th century to the present is reviewed. Basic equations of linear dynamics of an extensible sagging cable are presented. A dynamic stiffness function that can be derived from these equations is given. Limiting transitions lead to other well known results: The static equivalent modulus of elasticity given by Ernst as well as the natural frequencies of motion given by Irvine and Caughey can be inferred from this function. A discussion of dynamic-excitation mechanisms and of dynamic interaction between cables and other structural elements conclude this contribution.
Thu, 20 Mar 2008 13:34:34 GMThttp://hdl.handle.net/11420/3022008-03-20T13:34:34Z
- Closed-Form Steady-State Response Solution of the Twin Rotor Damper and Experimental Validationhttp://hdl.handle.net/11420/4399Title: Closed-Form Steady-State Response Solution of the Twin Rotor Damper and Experimental Validation
Authors: Bäumer, Richard; Starossek, Uwe
Abstract: In previous research, the twin rotor damper (TRD), an active mass damper, was presented including control algorithms for monofrequent vibrations. In a preferred mode of operation, the continuous rotation mode, two eccentric masses rotate in opposite directions about two parallel axes with a mostly constant angular velocity. The resulting control force is harmonic. Within this paper, the steady-state response of a single-degree-of-freedom (SDOF) oscillator subjected to a harmonic excitation force with and without the TRD is studied. A closed-form solution is presented and validated experimentally. It is shown that the TRD provides damping to the SDOF oscillator until a certain frequency ratio is reached. The provided damping is not only dependent on the design parameters of the TRD but also depends on the steady-state vibration amplitude. The solution serves as a powerful design tool for dimensioning the TRD. The analytical closed-form solution is applicable for other active mass dampers.
Fri, 17 Jan 2020 10:38:15 GMThttp://hdl.handle.net/11420/43992020-01-17T10:38:15Z
- Twin rotor damper for the damping of stochastically forced vibrations using a power-efficient control algorithmhttp://hdl.handle.net/11420/2484Title: Twin rotor damper for the damping of stochastically forced vibrations using a power-efficient control algorithm
Authors: Bäumer, Richard; Terrill, Richard Douglas; Wollnack, Simon; Werner, Herbert; Starossek, Uwe
Abstract: The twin rotor damper (TRD), an active mass damper, uses the centrifugal forces of two eccentrically rotating control masses. In the continuous rotation mode, the preferred mode of operation, the two eccentric control masses rotate with a constant angular velocity about two parallel axes, creating, under further operational constraints, a harmonic control force in a single direction. In previous theoretical work, it was shown that this mode of operation is effective for the damping of large, harmonic vibrations of a single degree of freedom (SDOF) oscillator. In this paper, the SDOF oscillator is assumed to be affected by a stochastic excitation force and consequently responds with several frequencies. Therefore, the TRD must deviate from the continuous rotation mode to ensure the anti-phasing between the harmonic control force of the TRD and the velocity of the SDOF oscillator. It is found that the required deviation from the continuous rotation mode increases with lower vibration amplitude. Therefore, an operation of the TRD in the continuous rotation mode is no longer efficient below a specific vibration-amplitude threshold. To additionally dampen vibrations below this threshold, the TRD can switch to another, more energy-consuming mode of operation, the swinging mode in which both control masses oscillate about certain angular positions. A power-efficient control algorithm is presented which uses the continuous rotation mode for large vibrations and the swinging mode for small vibrations. To validate the control algorithm, numerical and experimental investigations are performed for a single degree of freedom oscillator under stochastic excitation. Using both modes of operation, it is shown that the control algorithm is effective for the cases of free and stochastically forced vibrations of arbitrary amplitude.
Thu, 25 Apr 2019 13:04:54 GMThttp://hdl.handle.net/11420/24842019-04-25T13:04:54Z
- Eccentric-wing flutter stabilizer: analysis and wind tunnel testshttp://hdl.handle.net/11420/5476Title: Eccentric-wing flutter stabilizer: analysis and wind tunnel tests
Authors: Starossek, Uwe; Ziems, Hannah; Ferenczi, Tamas
Abstract: Adevice is presented that aims at preventing bridge flutter. It consists of wings positioned along the sides of, and fixed relative to, the bridge deck. Flutter suppression efficiency is high provided the lateral eccentricity of the wings is large. It is a passive aerodynamic device that is presumably more economical than other passive measures or devices. Moreover, it does not contain moving parts. This is an advantage over devices with moving parts, which meet resistance due to reliability concerns. The reasons of effectiveness of the device are outlined and results of a parametric flutter analysis are presented. Wind tunnel tests have been performed in which the critical wind speed for flutter of a bridge deck sectional model without wings and with wings mounted in various configurations was measured. The experimental results are presented and compared with the results of flutter analysis.
Wed, 25 Mar 2020 07:35:20 GMThttp://hdl.handle.net/11420/54762020-03-25T07:35:20Z
- Comparison of time domain and spectral fatigue analyses of an offshore jacket structurehttp://hdl.handle.net/11420/5473Title: Comparison of time domain and spectral fatigue analyses of an offshore jacket structure
Authors: Mohammadi, Said Fawad; Galgoul, Nelson Szilard; Starossek, Uwe
Abstract: The results obtained from a computationally excessive full-scale time domain analysis of an offshore jacket structure quantifies the errors resulting from the assumptions and simplifications made in spectral fatigue analysis. These findings also indicate that the simplifications involved lead not only to the well-known inaccuracy but also to a lower fatigue resistance. This paper shows the main causes of the inaccuracies of the spectral fatigue analysis and quantifies them. In addition, this paper verifies the efficacy of an approximation method suggested by Mohammadi et al. (2015) that drastically reduces the computational burden necessary to perform fatigue analyses in time domain.
Wed, 25 Mar 2020 07:01:30 GMThttp://hdl.handle.net/11420/54732020-03-25T07:01:30Z
- Vertical building collapse triggered by loss of all columns in the ground story−last line of defensehttp://hdl.handle.net/11420/5480Title: Vertical building collapse triggered by loss of all columns in the ground story−last line of defense
Authors: Lalkovski, Nikolay; Starossek, Uwe
Abstract: In multi-story buildings, one of the worst collapse types in terms of structural damage and loss of life is the pancake-type collapse, where some or all floors end up lying on top of each other like the layers of a pancake, with the floor contents crushed between them. Mostly observed after strong earthquakes, such collapses are triggered by loss of some or all vertical load bearing elements in some story−often the ground story. Once this occurs, the building part above the lost vertical elements−still intact−starts gaining downward velocity until it meets resistance from below. The ensuing impact forces often lead to collapse progression ending in total collapse. However, there are some examples of buildings in which the columns of an entire story failed and the collapse remained arrested after the subsequent impact. Such cases were observed in the 1995 Kobe earthquake and in the 1985 Mexico City earthquake. There have also been some failed controlled demolition attempts in which the intended total vertical collapse did not occur after letting a building collide with the ground by explosive removal of the vertical load bearing elements in the lowest stories. In an attempt to determine the factors which play the main role in arresting vertical collapse once initiated at the ground level, this paper studies the behavior of vertically falling multi-story building structures impacting a rigid surface representing the ground. A simplified analytical model of the problem is presented. Depending on the structural properties, several possible energy dissipation mechanisms, and−in case the collapse cannot be arrested at impact−collapse modes, are identified.
Wed, 25 Mar 2020 08:54:19 GMThttp://hdl.handle.net/11420/54802020-03-25T08:54:19Z
- Eccentric-wing flutter stabilizer - Simplified analysis and main findingshttp://hdl.handle.net/11420/3766Title: Eccentric-wing flutter stabilizer - Simplified analysis and main findings
Authors: Starossek, Uwe
Abstract: A device aiming at preventing bridge flutter is studied. It consists of fixed wings positioned with a large lateral offset along the edges of the bridge deck. The wings are attached to the bridge deck by means of lateral support structures. Flutter analyses for various kinds of bridges and wind-tunnel tests confirm the flutter-suppression effectiveness of the wings. They constitute a passive damping device without moving parts. This is an advantage over devices with moving parts, which meet resistance due to reliability and maintenance concerns. The main findings to date concerning analysis, flutter-suppression effectiveness, and cost-efficiency of the eccentric-wing flutter stabilizer are summarized. In addition, a simplified approach for the analysis of torsional flutter of a bridge equipped with this device is presented and applied to the first Tacoma Narrows Bridge. It is found that with relatively small effort the flutter stability of that bridge could have been substantially improved.
Mon, 11 Nov 2019 13:12:39 GMThttp://hdl.handle.net/11420/37662019-11-11T13:12:39Z
- Efficient fatigue assessment in the time domain in comparison to spectral fatigue analysis of an offshore jacket structurehttp://hdl.handle.net/11420/5472Title: Efficient fatigue assessment in the time domain in comparison to spectral fatigue analysis of an offshore jacket structure
Authors: Mohammadi, Said Fawad; Galgoul, Nelson Szilard; Starossek, Uwe
Abstract: Industry codes require inspections of critical joints within certain intervals to ensure the structural integrity of fixed offshore structures and suggest the use of spectral fatigue analyses to identify them. Inspections of fixed offshore platforms routinely show very few signs of degradation at the joints identified by the recommended computational methods, however. This illustrates the low degree of accuracy of these methods. The uncertainties involved in the fatigue assessment of fixed offshore structures have stimulated a continuous improvement of the techniques used to assess fatigue resistance. Industry codes have replaced early deterministic fatigue analyses with spectral techniques. These are considered less reliable but more efficient than approaches in the time domain, which are generally considered highly accurate but computationally unfeasible. This paper evaluates both the time and the frequency domain approach using a large platform as an example. The results obtained from a computationally excessive full-scale time domain fatigue assessment quantify the errors resulting from the assumptions and simplifications made in spectral fatigue analyses. These findings also indicate that the simplifications involved lead not only to the well-known inaccuracy but also to a lower fatigue resistance prediction. Our results confirm that spectral methods are very conservative for offshore structures, especially those that are sensitive to dynamic excitation. This excessive conservatism can lead to unnecessary and costly inspections. The analysis in the time domain, by comparison, is more accurate and recent developments show that methods based on approximation of fatigue damage exist that make fatigue assessments in the time domain computationally feasible. This paper shows the main causes of the inaccuracies of the spectral method and quantifies them. It also shows the advantage of using the approximated time domain fatigue analysis, which makes this method feasible for use during design projects. Performing fatigue analyses in the time rather than frequency domain increases the accuracy and the reliability of the results and extends the fatigue life of the joints of the structure since several conservative assumptions are eliminated.
Wed, 25 Mar 2020 06:38:53 GMThttp://hdl.handle.net/11420/54722020-03-25T06:38:53Z
- An efficient time domain fatigue analysis and its comparison to spectral fatigue assessment for an offshore jacket structurehttp://hdl.handle.net/11420/5471Title: An efficient time domain fatigue analysis and its comparison to spectral fatigue assessment for an offshore jacket structure
Authors: Mohammadi, Said Fawad; Galgoul, Nelson Szilard; Starossek, Uwe; Videiro, Paulo Mauricio
Abstract: Industry codes require inspections of critical joints within certain intervals to ensure the structural integrity of fixed offshore structures and suggest the use of spectral fatigue analyses to identify them. Spectral methods are considered less reliable but more efficient than approaches in the time domain, which are generally considered highly accurate but computationally unfeasible. This paper evaluates both the time and the frequency domain approaches using a large platform as an example. The results obtained from a, computationally demanding, full-scale time domain fatigue assessment are used as the standard to quantify the errors resulting from the assumptions and simplifications made in the spectral fatigue analysis. These results indicate, also, that the simplifications involved in spectral fatigue lead not only to the well-known inaccuracy but also to consistently lower fatigue lives. This excessive conservatism leads to unnecessary and costly inspections. This paper contributes to the literature in two important ways. First, it shows the main causes of the inaccuracies of the spectral method and quantifies them. Second, it proposes a novel approach for the time domain fatigue analysis which drastically reduces the computational burden, while maintaining a high degree of accuracy. Performing fatigue analyses in time rather than frequency domain increases the accuracy and the reliability of the results and extends the fatigue life of the joints of the structure since several conservative assumptions are eliminated.
Wed, 25 Mar 2020 06:01:14 GMThttp://hdl.handle.net/11420/54712020-03-25T06:01:14Z
- Exact analytical solutions for forced undamped duffing oscillatorhttp://hdl.handle.net/11420/5462Title: Exact analytical solutions for forced undamped duffing oscillator
Authors: Starossek, Uwe
Abstract: The steady-state response of an undamped Duffing oscillator to periodic external forces is studied. The forcing functions are chosen such that the time course of the displacement can be described by exact analytical expressions. The displacement and forcing functions are governed by Jacobi elliptic functions and thus are periodic but generally non-harmonic. The parameter of the elliptic functions is deliberately chosen. For certain parameter choices, exact analytical expressions are found for the frequency–amplitude relation.
Tue, 24 Mar 2020 10:43:00 GMThttp://hdl.handle.net/11420/54622020-03-24T10:43:00Z
- Active vibration control using centrifugal forces created by eccentrically rotating masseshttp://hdl.handle.net/11420/5481Title: Active vibration control using centrifugal forces created by eccentrically rotating masses
Authors: Bäumer, Richard; Starossek, Uwe
Abstract: The twin rotor damper (TRD) is a newly developed active mass damper. It is presented here along with respective closed-loop control algorithms. The greatest advantage of the device is its low power demand when operated in a preferred mode of operation, the continuous rotation mode. In this mode, two eccentric masses rotate in opposite directions about two parallel axes with a mostly constant angular velocity. The resultant force is harmonic and can be used for the control of structural vibrations. To study the effect of the TRD on a single degree-of-freedom (SDOF) oscillator, various state variables are introduced and a feedback control algorithm is developed for the continuous rotation mode of operation. For reaching and leaving the continuous rotation mode, ramp-up and ramp-down trajectories are developed. These trajectories are designed such that the power and energy demand as well as the mechanical wear on the device are minimized. The feedback control algorithm is validated on a test setup. The damping effectiveness and the low power and energy demands encourage further investigation of the device under stochastic loading and comparisons with other active mass dampers.
Wed, 25 Mar 2020 09:00:30 GMThttp://hdl.handle.net/11420/54812020-03-25T09:00:30Z
- Progressive collapse of structures – review and outlookhttp://hdl.handle.net/11420/4937Title: Progressive collapse of structures – review and outlook
Authors: Starossek, Uwe
Abstract: The difference between progressive collapse, related to mechanisms of collapse, and disproportionate collapse, related to design, is outlined. Various mechanisms of collapse are described, which helps to clarify conceptual relationships. Ordinary design procedures are inadequate for preventing disproportionate collapse. The reasons for this are explained. After defining the terms collapse resistance and robustness, a pragmatic design approach for achieving collapse resistance of general structures is outlined. In this approach, the design objectives are established in a decision-making process. Concerning design methods, segmentation is available in addition to alternative load paths. The former method can be preferable in case of large initial local failure. This pragmatic approach can be developed into model guidelines for the design of general structures against disproportionate collapse. In contrast, it is found that current design regulations apply only to buildings of small to medium size and not to structures in general.
Sun, 16 Feb 2020 19:56:43 GMThttp://hdl.handle.net/11420/49372020-02-16T19:56:43Z
- Reduktion analytischer Impedanzfunktionen auf lineare Matrizenpolynome am Beispiel der dynamischen Seilsteifigkeithttp://hdl.handle.net/11420/353Title: Reduktion analytischer Impedanzfunktionen auf lineare Matrizenpolynome am Beispiel der dynamischen Seilsteifigkeit
Authors: Starossek, Uwe
Abstract: Die dynamische Steifigkeit eines durchhängenden Seiles gegenüber harmonischen Randverschiebungen kann mit Methoden der Kontinuumsmechanik in geschlossener Form mittels analytischer Funktionen der Schwingungsfrequenz dargestellt werden. Eine Berücksichtigung derartiger Funktionen in den Steifigkeitsmatrizen zusammengesetzter Systeme macht diese Matrizen allerdings ebenfalls frequenzabhängig - ein besonders bei der Behandlung des Eigenwertproblems hinderlicher Umstand, da dieses nichtlinear wird. Durch die hier beschriebene Reduktion einer komplexen analytischen Impedanzfunktion auf ein konstantes Matrizenpaar beliebiger Ordnung werden derartige Schwierigkeiten behoben. Diese Abbildung entspricht einem nachträglichen Übergang von Kontinua auf diskrete Schwingungssysteme. In strukturdynamischen Anwendungen, wie z.B. für die hier betrachtete dynamische Seilsteifigkeit, entsprechen die beiden Ergebnismatrizen einer statischen Steifigkeitsmatrix und einer Massenmatrix. Die Berücksichtigung des resultierenden Matrizenpaares im Rahmen einer linearen Eigenwertaufgabe ist in jedem Fall problemlos möglich.; For the dynamic stiffness of a sagging cable subject to harmonic boundary displacements, frequency-dependent closed-form analytic functions can be derived from the corresponding continuum equations. By consideration of such functions in stiffness matrices of composed systems, however, these matrices become frequency-dependent, too a troublesome fact, especially with regard to the eigenvalue problem which becomes nonlinear. In this paper a method for avoiding such difficulties is described: A complex analytic impedance function is reduced to two constant matrices of any desired dimension. This reduction corresponds to a mathematically performed transition from a continuum to a discrete-coordinate vibrating system. In structural dynamics applications such as for dynamic cable stiffness the two resultant matrices correspond to a static stiffness matrix and a mass matrix. In every case, these matrices can easily be considered within the scope of a linear eigenvalue problem.
Thu, 19 Jun 2008 07:47:00 GMThttp://hdl.handle.net/11420/3532008-06-19T07:47:00Z
- Exact analytical solutions for forced cubic restoring force oscillatorhttp://hdl.handle.net/11420/5463Title: Exact analytical solutions for forced cubic restoring force oscillator
Authors: Starossek, Uwe
Abstract: A strongly nonlinear oscillator is considered in which the restoring force is a purely cubic function of the displacement variable. Its forced undamped oscillation response to non-harmonic periodic loading is studied. The loading function is derived from the free oscillation response whose time course follows a Jacobi elliptic function. It is chosen such that exact analytical solutions are obtained for the steady-state response and the amplitude–frequency relation. The equation describing the amplitude–frequency relation is a cubic polynomial equation. Its solutions are presented and further discussed by means of diagrams that illustrate the equilibrium of dynamic forces. Furthermore, results of a numerical study are presented concerning the stability of the identified analytical steady-state solutions. The numerical study also reveals the existence of a subharmonic steady-state response with a period three times the period of the loading function. The general approach of using non-harmonic loading functions is transferable to other types of nonlinear oscillators.
Tue, 24 Mar 2020 10:46:27 GMThttp://hdl.handle.net/11420/54632020-03-24T10:46:27Z
- Eccentric-wing flutter stabilizer for bridgeshttp://hdl.handle.net/11420/5461Title: Eccentric-wing flutter stabilizer for bridges
Authors: Starossek, Uwe
Abstract: A device is presented that aims at preventing bridge flutter. It consists of wings positioned along the sides of, and fixed relative to, the bridge deck. Flutter suppression efficiency is high provided the lateral eccentricity of the wings is large. It is a passive aerodynamic device that is more economical than other passive measures or devices. Moreover, it does not contain moving parts. This is an advantage over devices with moving parts that meet resistance due to reliability concerns. Results of a numerical study are presented in which the critical wind speed for flutter onset of a bridge without wings and with wings mounted in various configurations were determined. Preliminary wind tunnel test results are reported and a cost estimate is given.
Tue, 24 Mar 2020 10:37:40 GMThttp://hdl.handle.net/11420/54612020-03-24T10:37:40Z
- Prediction of bridge flutter through use of finite elementshttp://hdl.handle.net/11420/324Title: Prediction of bridge flutter through use of finite elements
Authors: Starossek, Uwe
Abstract: Wind-induced flutter of bridges with streamlined, plate-like cross-sections occurs as coupled torsional and vertical oscillation. Prediction can possibly be facilated by representing the spatial system by a generalized 2-DOF system. This may, however, be inadmissible or may lead to extremely conservative results if the modes of torsional and vertical vibration differ strongly. Flutter prediction should then be based on spatial modeling. Classical methods of aircraft engineering for solving the spatial problem proceed from differential equations of motion or make use of variational principles. For appliations in bridge engineering, the finite-element concept proves to be more efficient. In this paper, two beam elements of different complexity are presented. Formulation and solution of the resulting MDOF equations of motion are described. Results of numerical calculations are stated.
Wed, 09 Apr 2008 17:00:58 GMThttp://hdl.handle.net/11420/3242008-04-09T17:00:58Z