TUHH Open Research (TORE)https://tore.tuhh.deTORE captures, stores, indexes, preserves, and distributes digital research material.Thu, 08 Jun 2023 19:37:19 GMT2023-06-08T19:37:19Z50501- The improvement of stochastic averaging method to solve the ship rolling response excited by narrow-band waveshttp://hdl.handle.net/11420/15339Title: The improvement of stochastic averaging method to solve the ship rolling response excited by narrow-band waves
Authors: Liu, Yaliu; Liu, Liqin; Maki, Atsuo; Dostal, Leo; Dostal, Leo
Abstract: The stochastic averaging method of energy envelope can accurately solve the random motion response under the excitation of white noise. The noise had to fulfill the condition of strong mixing which roughly means that the process has to be broad-band. However, the sea conditions in practical engineering conditions are narrow-band spectra. Research on applicability of the stochastic averaging method of energy envelope shows that for narrow-band excitation, the damping of the system and excitation intensity should be small, and the excitation bandwidth should be large. Based on the above background, the improvement of stochastic averaging method of energy envelope under narrow-band waves is studied. The phase angle θ is introduced to characterize the relationship between kinetic energy and potential energy of the system. The drift coefficients and diffusion coefficients are averaged with respect to the period of θ. When the excitation frequency is in the lock-in field, large parametric rolling appears. The stationary probability density function (PDF) of the roll angle obtained by solving the Fokker-Planck-Kolmogorov (FPK) equation compares well with Monte Carlo simulation in the lock-in field. The improved method can relax the limitation of broad-band excitation required by stochastic averaging method. It can also consider both the nonlinear damping and nonlinear restoring force of roll motion. Therefore, the improved method is an efficient way to calculate the nonlinear roll response of ships in real sea conditions.
Tue, 01 Aug 2023 00:00:00 GMThttp://hdl.handle.net/11420/153392023-08-01T00:00:00Z
- Non-stationary probability of parametric roll of ships in random seashttp://hdl.handle.net/11420/6078Title: Non-stationary probability of parametric roll of ships in random seas
Authors: Dostal, Leo; Kreuzer, Edwin
Abstract: We analyze the problem of parametric roll in random seas, where the random wave excitation is modeled by anon-white stationary stochastic process. This process is derived from a spectral description of the random seaway using a traveling effective wave. The method of stochastic averaging is applied, such that the fast oscillatory dynamics of roll is averaged over the roll period. This procedure yields equations for the drift and diffusion of the roll energy. With these equations the non-stationary probability density of roll energy is obtained by solving the corresponding Fokker-Planck equation using a finite difference approach. The results can be used to improve ship hull design as well as for controller design to encounter the occurrence of parametric roll resonance.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/11420/60782013-01-01T00:00:00Z
- Theoretical estimation of roll acceleration in beam seas using PDF line integral methodhttp://hdl.handle.net/11420/7539Title: Theoretical estimation of roll acceleration in beam seas using PDF line integral method
Authors: Maki, Atsuo; Dostal, Leo; Maruyama, Yuuki; Sakai, Masahiro; Sugimoto, Kei; Fukumoto, Yusuke; Umeda, Naoya
Abstract: The prevention of excessive roll acceleration is one of the fundamental requirements of an oceangoing vessel at sea. In this paper, aiming at this requirement, we propose a new theoretical method for calculating roll angular acceleration, called “PDF line integral method.”. This paper presents the derivation of this method and a numerical comparison with Monte Carlo simulation (MCS) results; also, its validity is shown. Although the utilized GZ curve (restoring curve) exhibits strong asymmetricity, the proposed method can provide for such a condition. With only the information of roll and roll rate joint probability density function (PDF), this method can approximately calculate the roll angular acceleration, which is a high-order differential property. In addition, a relatively good agreement is achieved between the theory and MCS results.
Wed, 01 Sep 2021 00:00:00 GMThttp://hdl.handle.net/11420/75392021-09-01T00:00:00Z
- First passage time of nonlinear diffusion processes with singular boundary behaviorhttp://hdl.handle.net/11420/5430Title: First passage time of nonlinear diffusion processes with singular boundary behavior
Authors: Dostal, Leo; Namachchivaya, Navaratnam Sri
Abstract: New theorems for moments of the first passage time of one dimensional nonlinear stochastic processes with an entrance boundary xe are formulated. This important class of one dimensional stochastic processes results among others from approximations of the energy or amplitude of second order nonlinear stochastic differential equations. Since the diffusion of a stochastic process vanishes at an entrance boundary, xe is called a singular point of the stochastic process. The theorems for the moments of the first passage times are validated based on existing analytical results. In addition, the first passage times of a forced and damped Mathieu oscillator, as well as a nonlinear stochastic differential equation, which is important for the determination of dangerous ship roll dynamics, are calculated. The proposed analytical expressions for the moments of the first passage times can be calculated very fast using standard quadrature formulas.
Tue, 23 Jun 2020 00:00:00 GMThttp://hdl.handle.net/11420/54302020-06-23T00:00:00Z
- A comparative study of the stochastic averaging method and the path integration method for nonlinear ship roll motion in random beam seashttp://hdl.handle.net/11420/2760Title: A comparative study of the stochastic averaging method and the path integration method for nonlinear ship roll motion in random beam seas
Authors: Chai, Wei; Dostal, Leo; Naess, Arvid; Leira, Bernt J.
Abstract: In this paper, the energy-based stochastic averaging method and the path integration method are applied to study the stochastic response of the nonlinear roll motion in random beam seas. Specifically, the Markov diffusion theory is applied to describe the random roll motion such that the probabilistic properties of the ship roll motion are governed by the Fokker–Planck (FP) equation. The stochastic averaging method focuses on the roll energy envelope process and reduces the difficulty in calculating the stochastic response via a dimensional reduction of the original system. In contrast, the path integration method is based on the Markov property of the original dynamical system and provides approximate solutions to the FP equation by linking the explicitly known local solutions. Although the stochastic averaging technique is well established in the study of the stochastic responses of various dynamical systems, its accuracy for determining the high-level roll response has not yet been a focus of study. This paper aims to provide a comparative study for the performance of the two above-mentioned methods; additionally, the advantages and shortcomings of using each method for studying the nonlinear roll motion in beam seas are demonstrated by practical calculations.
Sat, 01 Dec 2018 00:00:00 GMThttp://hdl.handle.net/11420/27602018-12-01T00:00:00Z
- Study on the behavior of weakly nonlinear water waves in the presence of random wind forcinghttp://hdl.handle.net/11420/4268Title: Study on the behavior of weakly nonlinear water waves in the presence of random wind forcing
Authors: Dostal, Leo; Hollm, Marten; Kreuzer, Edwin
Abstract: Specific solutions of the nonlinear Schrödinger equation, such as the Peregrine breather, are considered to be prototypes of extreme or freak waves in the oceans. An important question is whether these solutions also exist in the presence of gusty wind. Using the method of multiple scales, a nonlinear Schrödinger equation is obtained for the case of wind-forced weakly nonlinear deep water waves. Thereby, the wind forcing is modeled as a stochastic process. This leads to a stochastic nonlinear Schrödinger equation, which is calculated for different wind regimes. For the case of wind forcing which is either random in time or random in space, it is shown that breather-type solutions such as the Peregrine breather occur even in strong gusty wind conditions.
Sat, 01 Feb 2020 00:00:00 GMThttp://hdl.handle.net/11420/42682020-02-01T00:00:00Z
- Predictability of vibration loads from experimental data by means of reduced vehicle models and machine learninghttp://hdl.handle.net/11420/8452Title: Predictability of vibration loads from experimental data by means of reduced vehicle models and machine learning
Authors: Dostal, Leo; Grossert, Helge Johannes; Dücker, Daniel-André; Grube, Malte; Kreuter, Daniel; Sandmann, Kai; Zillmann, Benjamin; Seifried, Robert
Abstract: Nowadays electric cars are in the spotlight of automotive research. In this context we consider data based approaches as tools to improve and facilitate the car design process. Hereby, we address the challenge of vibration load prediction for electric cars using neural network based machine learning (ML), a data-based frequency response function approach, and a hybrid combined model. We extensively study the challenging case of vibration load prediction of car components, such as the traction battery of an electric car. We show using experimental data from Fiat 500e and VWeGolf cars that the proposed ML approach is able to outperform the classical model estimation by means of ARX and ARMAX models. Moreover, we evaluate the performance of a hybrid-ML concept for combination of ML and ARMAX. Our promising results motivate further research in the field of vibration load prediction using machine learning based approaches in order to facilitate design processes.
Mon, 28 Sep 2020 00:00:00 GMThttp://hdl.handle.net/11420/84522020-09-28T00:00:00Z
- The effect of random wind forcing in the nonlinear Schrödinger equationhttp://hdl.handle.net/11420/2933Title: The effect of random wind forcing in the nonlinear Schrödinger equation
Authors: Dostal, Leo
Abstract: The influence of a strong and gusty wind field on ocean waves is investigated. How the random wind affects solitary waves is analyzed in order to obtain insights about wave generation by randomly time varying wind forcing. Using the Euler equations of fluid dynamics and the method of multiple scales, a random nonlinear Schrödinger equation and a random modified nonlinear Schrödinger equation are obtained for randomly wind forced nonlinear deep water waves. Miles theory is used for modeling the pressure variation at the wave surface resulting from the wind velocity field. The nonlinear Schrödinger equation and the modified nonlinear Schrödinger equation are computed using a relaxation pseudo spectral scheme. The results show that the influence of gusty wind on solitary waves leads to a randomly increasing ocean wave envelope. However, in a laboratory setup with much smaller wave amplitudes and higher wave frequencies, the influence of water viscosity is much higher. This leads to fluctuating solutions, which are sensitive to wind forcing.
Tue, 02 Jul 2019 00:00:00 GMThttp://hdl.handle.net/11420/29332019-07-02T00:00:00Z
- Comparative study of the path integration method and the stochastic averaging method for nonlinear roll motion in random beam seashttp://hdl.handle.net/11420/1943Title: Comparative study of the path integration method and the stochastic averaging method for nonlinear roll motion in random beam seas
Authors: Chai, Wei; Dostal, Leo; Naess, Arvid; Leira, Bernt J.
Abstract: In this work, the path integration method and the energy-based stochastic averaging method are introduced in order to study the stochastic responses of ship roll motion in random beam seas. Based on the Markov property of the dynamical system, the path integration (PI) method provides approximate solution to the governing Fokker-Planck (FP) equation. On the other hand, the stochastic averaging method leads to a dimension reduction of the original system, but the essential behavior is retained. Then numerical solution or even analytical solution of the low-dimensional FP equation can be obtained. Since the principles of the above two stochastic methods are different, a comparative study is valuable and noticeable. The accuracy and performance of each method are evaluated with the assistance of Monte Carlo simulation (MCS).
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/11420/19432017-01-01T00:00:00Z
- Nonlinear model parameter identification for ice-induced vibrationshttp://hdl.handle.net/11420/1863Title: Nonlinear model parameter identification for ice-induced vibrations
Authors: Dostal, Leo; Lourens, Eliz-Mari; Metrikine, Andrei
Abstract: The problem of level ice interacting with compliant structures is addressed, where the ice loads can depend on the dynamical behavior of the structures. We are interested in a special type of ice-induced vibration, known as frequency lock-in, and characterized by having the dominant frequency of the ice forces near a natural frequency of the structure. It is shown that accurate estimates of the model parameters for the well-known Määttänen's model for ice-induced vibrations can be obtained from measurements of the structural vibrations and the ice velocity. Määttänen's model uses a state-dependent piecewise nonlinear function for the ice crushing strength, which leads to nonlinear negative damping in the equations of motion of the considered structure. The identification is achieved by means of an Unscented Kalman Filter using simulated noisy measurements of the structural behavior.
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/11420/18632017-01-01T00:00:00Z
- Non-standard stochastic averaging of large-amplitude ship rolling in random seashttp://hdl.handle.net/11420/3347Title: Non-standard stochastic averaging of large-amplitude ship rolling in random seas
Authors: Dostal, Leo; Kreuzer, Edwin; Namachchivaya, Navaratnam Sri
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/11420/33472012-01-01T00:00:00Z
- Probabilistic approach to large amplitude ship rolling in random seashttp://hdl.handle.net/11420/1562Title: Probabilistic approach to large amplitude ship rolling in random seas
Authors: Dostal, Leo; Kreuzer, Edwin
Abstract: For a vessel in open seas, the sudden indirect excitation of roll motions due to waves from the front or rear leads to dangerous situations, sometimes even capsizing. We derive a general non-linear model, which is appropriate for the analysis of parametric excited roll motions in head or following random seas. The irregular waves are modelled in terms of a continuous time autoregressive moving average process. The resulting model of stochastic differential equations is investigated numerically by Local Statistical Linearization. The necessary stochastic moments and their derivatives are computed using Itoˆ’s differential rule and Gaussian closure.
Fri, 30 Sep 2011 00:00:00 GMThttp://hdl.handle.net/11420/15622011-09-30T00:00:00Z
- Theoretical and experimental study of a pendulum excited by random loadshttp://hdl.handle.net/11420/10854Title: Theoretical and experimental study of a pendulum excited by random loads
Authors: Dostal, Leo; Pick, Marc-André
Abstract: Results on the behaviour of a pendulum which is parametrically excited by large amplitude random loads at its pivot are presented, including a novel experimental case study. Thereby, it is dealt with a random excitation by a non-white Gaussian stochastic process with prescribed spectral density. Special focus is devoted to stochastic processes resulting from random sea wave elevation and the question whether random sea waves can lead to rotational motion of the parametrically excited pendulum. The motivation for such an experimental study is energy harvesting from ocean waves.
Tue, 01 Oct 2019 00:00:00 GMThttp://hdl.handle.net/11420/108542019-10-01T00:00:00Z
- Study of weakly nonlinear water waves subjected to stochastic wind excitationhttp://hdl.handle.net/11420/5416Title: Study of weakly nonlinear water waves subjected to stochastic wind excitation
Authors: Hollm, Marten; Dostal, Leo
Abstract: The behavior of deep-water gravity waves under the effect of wind and viscosity is studied. It is analyzed, how random wind affects the Peregrine breather, which is considered as a possible prototype of extreme waves in the oceans. Using the Euler equations of fluid dynamics and the method of multiple scales, the nonlinear Schrödinger equation and the modified nonlinear Schrödinger equation are obtained for the case of nonlinear deep water waves forced by random wind. For modeling the wind forcing of ocean waves, Miles’ theory is extended to include time varying random wind velocity processes, which leads to stochastic partial differential equations. For different regimes of stochastic wind it is shown that perturbed versions of the Peregrine solution occur also under strong gusty wind conditions and lead to extreme waves as well. Moreover, the improved modeling using the modified nonlinear Schrödinger equation does not considerably change this behavior.
Sun, 01 Sep 2019 00:00:00 GMThttp://hdl.handle.net/11420/54162019-09-01T00:00:00Z
- Pendulum energy converter excited by random loadshttp://hdl.handle.net/11420/2693Title: Pendulum energy converter excited by random loads
Authors: Dostal, Leo; Korner, Kevin; Kreuzer, Edwin; Yurchenko, Daniil
Abstract: We present new solutions for the dynamics of a pendulum energy converter which is vertically excited at its suspension point. Thereby, we deal with a random excitation by a non-white Gaussian stochastic process. We formulate the pendulum energy converter as a weakly perturbed Hamiltonian system. The random process across the energy levels of the Hamiltonian system is then approximated by a Markov process, which is obtained by stochastic averaging. This procedure leads to analytical results for the energy of the pendulum motion, which are used for analyzing the required probability of reaching higher energy states of the pendulum energy converter in order to maximize the harvested energy.
Thu, 01 Mar 2018 00:00:00 GMThttp://hdl.handle.net/11420/26932018-03-01T00:00:00Z
- Almost Sure Stability Analysis of Parametric Roll in Random Seas Based on Top Lyapunov Exponenthttp://hdl.handle.net/11420/11043Title: Almost Sure Stability Analysis of Parametric Roll in Random Seas Based on Top Lyapunov Exponent
Authors: Dostal, Leo; Kreuzer, Edwin; Sri Namachchivaya, Navaratnam
Abstract: Stability analysis of the upright position of a ship in random head or following seas is presented. Such seas lead to parametric excitation of roll motion due to periodic variations of the righting lever. The development of simple criteria for the occurrence of parametric induced roll motion in random seas is of major interest for improvement of the international code on intact stability provided by the International Maritime Organization. The stability analysis in random seas is based on the calculation of the top Lyapunov exponent using the fact, that a negative top Lyapunov exponent yields no roll motion. With this findings, roll motion can be excluded for specific sea states.
Sat, 01 Dec 2012 00:00:00 GMThttp://hdl.handle.net/11420/110432012-12-01T00:00:00Z
- Analysis of Nonlinear Stochastic Ship Dynamics Under Extended Wave Modelinghttp://hdl.handle.net/11420/11044Title: Analysis of Nonlinear Stochastic Ship Dynamics Under Extended Wave Modeling
Authors: Dostal, Leo; Kreuzer, Edwin
Abstract: Analytical criteria for risk assessment of ships in random seas are important for the development of new intact stability criteria and also for the first design stage, where many ship designs have to be compared. The analysis is performed by Stochastic Averaging. The results are compared to those obtained by Monte Carlo simulations. We use extended wave modeling by means of two independent stochastic processes realizing a traveling wave with random phase and amplitude corresponding to a prescribed sea spectral density. The righting lever curve in waves is approximated by a polynomial, while quasistatic equilibrium of the analyzed ship in waves is assumed
Wed, 01 Dec 2010 00:00:00 GMThttp://hdl.handle.net/11420/110442010-12-01T00:00:00Z
- Surf-Riding Threshold of Ships in Random Seashttp://hdl.handle.net/11420/11042Title: Surf-Riding Threshold of Ships in Random Seas
Authors: Dostal, Leo; Kreuzer, Edwin
Abstract: A possible stability failure in ship dynamics is surf-riding of the ship in waves followed by broaching-to. In order to exclude broaching one thus seeks to prevent the ship from surf-riding. We analyze the surf-riding problem of a ship in random seas as a weakly perturbed Hamiltonian system, where the excitation owing to irregular sea waves is modeled as a Gaussian process. Then, an approximation of the probability of surf-riding in irregular sea waves is obtained using the stochastic Melnikov's method, by which means transitions from the asymmetric periodic surging motion to the surf-riding equilibrium are identified.
Sun, 01 Dec 2013 00:00:00 GMThttp://hdl.handle.net/11420/110422013-12-01T00:00:00Z
- Reduction of nonlinear dynamical systems excited by random loadshttp://hdl.handle.net/11420/11040Title: Reduction of nonlinear dynamical systems excited by random loads
Authors: Dostal, Leo
Fri, 01 Nov 2019 00:00:00 GMThttp://hdl.handle.net/11420/110402019-11-01T00:00:00Z
- Numerical Computation of Parametric Induced Roll Motions in Random Seashttp://hdl.handle.net/11420/11045Title: Numerical Computation of Parametric Induced Roll Motions in Random Seas
Authors: Dostal, Leo; Kreuzer, Edwin
Abstract: For a vessel in open seas, the sudden appearance of roll motions due to waves from the front or rear leads to dangerous situations up to capsizing. The equations of motion used to analyze the roll motion include the righting lever curve. This curve is set up by means of hydrostatic calculations and approximated by polynomials for further analysis. The irregular waves are modeled in terms of a continuous-time ARMA process. The resulting model of stochastic differential equations is investigated numerically by Local Statistical Linearization. The necessary stochastic moments and their derivatives are computed using Itô's differential rule and Gaussian closure.
Tue, 01 Dec 2009 00:00:00 GMThttp://hdl.handle.net/11420/110452009-12-01T00:00:00Z
- Power generation of a pendulum energy converter excited by random loadshttp://hdl.handle.net/11420/11049Title: Power generation of a pendulum energy converter excited by random loads
Authors: Dostal, Leo; Pick, Marc-André
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/11420/110492017-01-01T00:00:00Z
- Providing opportunities for individual practice and assessment in a large undergraduate mathematics coursehttp://hdl.handle.net/11420/11053Title: Providing opportunities for individual practice and assessment in a large undergraduate mathematics course
Authors: Gleßmer, Mirjam Sophia; Seifert, Christian; Dostal, Leo; Konchakova, Natalia; Kruse, Karsten
Abstract: many universities, undergraduate courses of fundamental subjects such as mathematics are taught to students enrolled in many different course programs. Since the fundamental subject is then taught without using examples from the students’ main subjects, this often results in low student motivation in the fundamental subject and lacking knowledge and skills of this subject even when necessary for the understanding of the students’ main subject. At Hamburg University of Technology, this applies to first year mathematics, which is taught in the same course to 1300 students enrolled in 12 different engineering study programs.
We here present our approach to solving this dilemma: Opportunities for individual practice and feedback tailored to the needs of students of the different study courses, such that students apply mathematical concepts in the context of their main subject. This helps them to see the relevance of the content which might otherwise be perceived as bothersome and irrelevant, thereby increasing student motivation. Providing additional practice opportunities also increases perceived student self-efficacy, in turn enhancing motivation.
We discuss our strategies to enhance student motivation as well as potential pitfalls and vicious circles and how to avoid them.
Mon, 08 Aug 2016 00:00:00 GMThttp://hdl.handle.net/11420/110532016-08-08T00:00:00Z
- Assessment of extreme rolling of ships in random seashttp://hdl.handle.net/11420/11041Title: Assessment of extreme rolling of ships in random seas
Authors: Dostal, Leo; Kreuzer, Edwin
Abstract: The goal of our analysis is to improve intact stability criteria for ships. For this, we develop analytical formulas for mean first passage times of critical roll amplitudes of ships travelling in long crested random seas with an arbitrary wave encounter angle. Starting from a model for coupled heave-pitch-roll motion, we average the fast oscillatory dynamics of roll over the roll period, which yields equations for drift and diffusion of roll energy. The results are used to calculate the desired mean first passage times. Finally, we apply the proposed theory to a sample ship design.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11420/110412014-01-01T00:00:00Z
- Ship capsizing analysis in random seas using non-standard stochastic averaginghttp://hdl.handle.net/11420/11052Title: Ship capsizing analysis in random seas using non-standard stochastic averaging
Authors: Dostal, Leo; Kreuzer, Edwin; Namachchivaya, Navaratnam Sri
Abstract: We study the dynamics of a ship in random seas as a perturbation of a Hamiltonian system. The random process across the energy levels of the Hamiltonian system is approximated by a Markov process, which is obtained by stochastic averaging. The noise due to wave excitation is a real stationary stochastic process. This is an extension to previous results where white noise excitation was used.
Fri, 01 Jul 2011 00:00:00 GMThttp://hdl.handle.net/11420/110522011-07-01T00:00:00Z
- Individualisierung von Großveranstaltungen. Oder: Wie man Ingenieurstudierenden die Mathematik schmackhaft machthttp://hdl.handle.net/11420/11149Title: Individualisierung von Großveranstaltungen. Oder: Wie man Ingenieurstudierenden die Mathematik schmackhaft macht
Authors: Gleßmer, Mirjam Sophia; Seifert, Christian; Dostal, Leo; Konchakova, Natalia; Kruse, Karsten
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/11420/111492016-01-01T00:00:00Z
- Conception of online e-assessment exercises for math courses with elements from mechanical engineeringhttp://hdl.handle.net/11420/11145Title: Conception of online e-assessment exercises for math courses with elements from mechanical engineering
Authors: Kruse, Karsten; Dostal, Leo; Gleßmer, Mirjam Sophia; Konchakova, Natalia; Seifert, Christian
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/11420/111452016-01-01T00:00:00Z
- Hydrodynamic Forces Acting on Cylindrical Piles Subjected to Wind-Forced Random Nonlinear Water Waveshttp://hdl.handle.net/11420/12050Title: Hydrodynamic Forces Acting on Cylindrical Piles Subjected to Wind-Forced Random Nonlinear Water Waves
Authors: Hollm, Marten; Dostal, Leo; Seifried, Robert
Abstract: A novel approach for the computation of hydrodynamic forces due to random nonlinear water waves acting on a cylindrical pile is presented. This approach is based on paths of fluid particles underneath of solutions to the nonlinear Schrödinger equation (NLS). This is computationally very efficient compared to the determination of the corresponding solutions of the Euler equations or even of the Navier–Stokes equation.In this chapter, specific solutions of the NLS, such as solitons, are considered in the presence of gusty wind. Using a spectral scheme for the numerical computation, the corresponding velocity potential is obtained. Depending on the corresponding wave envelope, the wave kinematics, the particle trajectories, and the forces acting on a submerged cylindrical pile are computed. Thereby, the equation of Morison is used for the computation of the hydrodynamic forces. With this, also effects of random wind on particle trajectories and forces are studied in detail. With the presented new approach it is possible to determine very efficiently the loads on structures that are exhibited to complicated random nonlinear ocean waves.
Sat, 01 Jan 2022 00:00:00 GMThttp://hdl.handle.net/11420/120502022-01-01T00:00:00Z
- Theoretical estimation of joint probability density function of roll angle and angular acceleration in beam seas using PDF line integral methodhttp://hdl.handle.net/11420/12099Title: Theoretical estimation of joint probability density function of roll angle and angular acceleration in beam seas using PDF line integral method
Authors: Maki, Atsuo; Dostal, Leo; Maruyama, Yuuki; Sasa, Kenji; Sakai, Masahiro; Sugimoto, Kei; Fukumoto, Yusuke; Umeda, Naoya
Abstract: So far, we have developed a calculation method for roll angular acceleration and its derivative, which is a jerk. In this study, using the probability density function (PDF) line integral method and the joint PDF (JPDF) of roll angle and angular rate, we obtain a theoretical method for the evaluation of the two properties. In particular, the estimation method of acceleration is considered crucial, as the angular acceleration is directly related to inertial forces or moments of onboard objects. Moreover, to consider the strength of container stacks, as well as the lashing strength of cargo and track on board, a separate evaluation of roll angle and roll angular acceleration is insufficient. Further, although the new-generation intact stability criteria for excessive acceleration have been discussed by the International Maritime Organization, the evaluation of JPDF of roll angle and roll angular acceleration could contribute to the efficient evaluation of the safety of crews on board. Meanwhile, no JPDF of roll angle or angular acceleration has been calculated for an arbitrary nonlinear system so far, and there is no doubt that it is a challenging problem. In this study, by applying and extending the idea of the PDF line integral method, we proposed a method for evaluating the JPDF of roll angle and angular acceleration.
Tue, 01 Mar 2022 00:00:00 GMThttp://hdl.handle.net/11420/120992022-03-01T00:00:00Z
- Study on the interaction of nonlinear water waves considering random seashttp://hdl.handle.net/11420/10921Title: Study on the interaction of nonlinear water waves considering random seas
Authors: Hollm, Marten; Dostal, Leo; Fischer, Hendrik; Seifried, Robert
Abstract: The nonlinear Schrödinger equation plays an important role in wave theory, nonlinear optics and Bose-Einstein condensation. Depending on the background, different analytical solutions have been obtained. One of these solutions is the soliton solution. In the real ocean sea, interactions of different water waves can be observed at the surface. Therefore the question arises, how such nonlinear waves interact. Of particular interest is the interaction, also called collision, of solitons and solitary waves.
Using a spectral scheme for the numerical computation of solutions of the nonlinear Schrödinger equation, the nonlinear wave interaction for the case of soliton collision is studied. Thereby, the influence of an initial random wave is studied, which is generated using a Pierson-Moskowitz spectrum.
Mon, 25 Jan 2021 00:00:00 GMThttp://hdl.handle.net/11420/109212021-01-25T00:00:00Z
- Towards reinforcement learning-based control of an energy harvesting pendulumhttp://hdl.handle.net/11420/3365Title: Towards reinforcement learning-based control of an energy harvesting pendulum
Authors: Cyr, Caralyn; Dostal, Leo; Dücker, Daniel-André; Kreuzer, Edwin
Abstract: Harvesting energy from the environment, e.g. ocean waves, is a key capability for the long-term operation of remote electronic systems where standard energy supply is not available. Rotating pendulums can be used as energy converters when excited close to their eigenfrequency. However, to ensure robust operation of the harvester, the energy of the dynamic system has to be controlled. In this study, we deploy a light-weight reinforcement learning algorithm to drive the energy of an Acrobot pendulum towards a desired value. We analyze the algorithm in an extensive series of simulations. Moreover, we explore the real world application of our energy-based reinforcement learning algorithm using a computationally constrained hardware setup based on low-cost components, such as the Raspberry Pi platform.
Sat, 01 Jun 2019 00:00:00 GMThttp://hdl.handle.net/11420/33652019-06-01T00:00:00Z
- Theoretical determination of roll angular jerk of ships in irregular beam seas using PDF line integral methodhttp://hdl.handle.net/11420/10942Title: Theoretical determination of roll angular jerk of ships in irregular beam seas using PDF line integral method
Authors: Maki, Atsuo; Dostal, Leo; Maruyama, Yuuki; Sakai, Masahiro; Sugimoto, Kei; Fukumoto, Yusuke
Abstract: The time derivative of acceleration is called a jerk, which is an important property to evaluate ride comfort in elevators, cars, and so on. Likewise, evaluation of motion sickness or ride comfort on a vessel could be achieved by this jerk property in the future. In this paper, we utilize the PDF Line Integral Method (PLIM), which was newly contrived in our previous research, for calculating not only roll angular acceleration but also roll angular jerk. The derivation of this theory, as well as numerical comparison with Monte Carlo simulation (MCS) results, are presented. Although the utilized restoring curve (GZ curve) exhibits strong asymmetricity, the proposed method successfully calculates roll angular jerk for such a condition. Since roll angular jerk is a high-order differential property, the biggest advantage of PLIM is that it only requires the information of roll and roll rate joint probability density function (PDF) to provide the PDF of jerk.
Tue, 01 Mar 2022 00:00:00 GMThttp://hdl.handle.net/11420/109422022-03-01T00:00:00Z
- Investigation of the dynamics of a multibody wave energy converter excited by regular and irregular waveshttp://hdl.handle.net/11420/13680Title: Investigation of the dynamics of a multibody wave energy converter excited by regular and irregular waves
Authors: Hollm, Marten; Dostal, Leo; Höhne, Joshua; Yurchenko, Daniil; Seifried, Robert
Abstract: The dynamics and the performance of a novel multibody wave energy converter is investigated, which is based on inclined single modules connected to a frame. The frame floats on the sea surface and the modules each move translationally along inclined guidance rods. Direct-drive linear generators or rotation based generators convert the relative translational motion between the frame and the modules into electrical power. This paper studies the conditions which influence the performance of the converters in regular and irregular waves. Different design layouts are investigated numerically, whereby the wave excitation is modeled by a random non-white Gaussian stochastic process.
Thu, 01 Dec 2022 00:00:00 GMThttp://hdl.handle.net/11420/136802022-12-01T00:00:00Z
- Enhanced estimation method and approximation method of the PDF of roll angular acceleration and jerk in beam seashttp://hdl.handle.net/11420/13741Title: Enhanced estimation method and approximation method of the PDF of roll angular acceleration and jerk in beam seas
Authors: Maki, Atsuo; Dostal, Leo; Maruyama, Yuuki; Sasa, Kenji; Sakai, Masahiro; Umeda, Naoya
Abstract: So far, the authors have established the theoretical estimation method of the Probability Density Function (PDF) of roll angular acceleration and jerk with the use of PLIM (PDF Line Integral Method), and estimations of the PDF of these properties were successfully achieved. PLIM, on the other hand, necessitates numerical integration along the complex shaped integral path. The integral path, in particular, becomes challenging in the calculation of the jerk property. However, if the restoring term is only represented by a linear component, then explicit expressions of PDF of roll angular acceleration can be obtained using the nonlinearization technique. It is noteworthy that the form of the nonlinear damping component does not constrain the applicability. This paper aims to show the derivation of the theoretical result and comparison with Monte Carlo Simulation (MCS) results. Furthermore, using the current form of the acceleration PDF, the PDF of roll angular jerk was obtained. The variance of roll angular rate determines the PDF form of the acceleration, which is the method's main advantage.
Tue, 15 Nov 2022 00:00:00 GMThttp://hdl.handle.net/11420/137412022-11-15T00:00:00Z
- Theoretical determination of asymmetric rolling amplitude in irregular beam seashttp://hdl.handle.net/11420/10940Title: Theoretical determination of asymmetric rolling amplitude in irregular beam seas
Authors: Maki, Atsuo; Dostal, Leo; Maruyama, Yuuki; Sakai, Masahiro; Katayama, Toru; Sugimoto, Kei; Fukumoto, Yusuke; Umeda, Naoya
Abstract: A methodology for predicting the probability density function of roll motion for irregular beam seas is developed in the author’s previous research. In this paper, two methods for the prediction of the probability density function (PDF) of the rolling amplitude are examined. One of these methods is an approach based on a non-Gaussian PDF with the use of the equivalent linearization and the moment method, which has been used by Maki in the field of naval architecture. In the framework of this method, the instantaneous joint PDF of the roll and roll rate can be calculated. Thereby, the transformation from the joint PDF to the PDF of the total energy H is necessary. In this paper, the transformation from the joint PDF of instantaneous roll and rate to the PDF of H was conducted. The other method is the energy-based stochastic averaging method, whereby the PDF of the total energy H is determined from which the roll amplitude is calculated. It is noteworthy that the proposed theory aims to predict the PDF of the amplitude of the vessel due to wind or flooding. For such conditions, the restoring curve (GZ curve) has asymmetricity. To take into account this asymmetricity, a new theory for the transform of the PDF of the total energy H to the PDFof amplitude is proposed. The obtained theoretical results show almost complete agreement, and both of the two theoretical methods i.e., the energy-based stochastic averaging method and the non-Gaussian PDF method with the use of the equivalent linearization and moment method, show equivalent prediction performance even in the asymmetric condition.
Tue, 01 Mar 2022 00:00:00 GMThttp://hdl.handle.net/11420/109402022-03-01T00:00:00Z
- Localized stationary seismic waves predicted using a nonlinear gradient elasticity modelhttp://hdl.handle.net/11420/10967Title: Localized stationary seismic waves predicted using a nonlinear gradient elasticity model
Authors: Dostal, Leo; Hollm, Marten; Metrikine, Andrei; Tsouvalas, Apostolos; Dalen, Karel N. van
Sat, 01 Jan 2022 00:00:00 GMThttp://hdl.handle.net/11420/109672022-01-01T00:00:00Z
- Performance increase of wave energy harvesting of a guided point absorberhttp://hdl.handle.net/11420/11805Title: Performance increase of wave energy harvesting of a guided point absorber
Authors: Hollm, Marten; Dostal, Leo; Yurchenko, Daniil; Seifried, Robert
Abstract: The dynamics of a novel wave energy converter based on a guided inclined point absorber are investigated. Thereby, it is studied through simulations and experiments whether different inclination angles of the guided point absorber lead to larger motion amplitudes and velocities in regular and irregular waves, from which energy can be harvested. For that, different simulations and experimental setups are analyzed in the presence of wave forcing. In the case of irregular waves a random non-white Gaussian stochastic process based on a sea spectrum is used. It is shown that the inclination angle has a significant influence on the energy harvesting output. Based on this insight, a simple control strategy is introduced in order to further increase the energy harvesting output.
Wed, 02 Mar 2022 00:00:00 GMThttp://hdl.handle.net/11420/118052022-03-02T00:00:00Z
- Practical method for evaluating wind influence on autonomous ship operationshttp://hdl.handle.net/11420/13751Title: Practical method for evaluating wind influence on autonomous ship operations
Authors: Maki, Atsuo; Maruyama, Yuuki; Dostal, Leo; Sakai, Masahiro; Sawada, Ryohei; Sasa, Kenji; Umeda, Naoya
Abstract: The autonomous operations of marine vehicles have recently attracted significant attention. In particular, automation of harbor operations, such as autonomous docking or berthing, is a challenging target. In low-speed harbor operations, the external disturbance of wind is a non-negligible factor. Therefore, the stochastic behavior of gusty wind should be considered in numerical simulations. This study presents a practical computational scheme for generating random wind velocity fields. In the proposed method, the von Kármán’s spectrum [1] and Hino’s wind speed spectrum [2] were fitted by a degree of freedom (1DoF) filter driven by the Wiener process. The corresponding Itô’s equation had the form of the Ornstein–Uhlenbeck process. By employing the analytical solution of the Ornstein–Uhlenbeck process, the wind process was successfully generated without time series repetition. Furthermore, the wind speed and direction processes were also generated from the measured drift and diffusion terms. The spectra of these numerical results are consistent with the observed spectra.
Sat, 01 Jan 2022 00:00:00 GMThttp://hdl.handle.net/11420/137512022-01-01T00:00:00Z
- Application of linear filter and moment equation for parametric rolling in irregular longitudinal waveshttp://hdl.handle.net/11420/13655Title: Application of linear filter and moment equation for parametric rolling in irregular longitudinal waves
Authors: Maruyama, Yuuki; Maki, Atsuo; Dostal, Leo; Umeda, Naoya
Abstract: Parametric rolling is one of the dangerous dynamic phenomena. To discuss the safety of a vessel when a dangerous phenomenon occurs, it is important to estimate the probability of certain dynamical behavior of the ship with respect to a certain threshold level. In this paper, the moment values are obtained by solving the moment equations. Since the stochastic differential equation (SDE) is needed to obtain the moment equations, the autoregressive moving average (ARMA) filter is used. The effective wave is modeled using the 6th-order ARMA filter. In addition, the parametric excitation process is modeled using a non-memory transformation obtained from the relationship between GM and wave elevation. The resulting system of equations is represented by the 8th-order Itô stochastic differential equation, which consists of a second-order SDE for the ship motion and a 6th-order SDE for the effective wave. This system has nonlinear components. Therefore, the cumulant neglect closure method is used as higher-order moments need to be truncated. Furthermore, the probability density function of roll angle is determined using moment values obtained from the SDE and the moment equation. Here, two types of the probability density function are suggested and have a good agreement.
Mon, 12 Sep 2022 00:00:00 GMThttp://hdl.handle.net/11420/136552022-09-12T00:00:00Z
- Analytical and semi-analytical solutions of some fundamental nonlinear stochastic differential equationshttp://hdl.handle.net/11420/1883Title: Analytical and semi-analytical solutions of some fundamental nonlinear stochastic differential equations
Authors: Dostal, Leo; Kreuzer, Edwin
Abstract: We are interested in perturbed Hamiltonian systems in a plane, which are damped and excited by an absolutely regular non-white Gaussian process. We use two methods for the determination of analytical and semi-analytical solutions to such nonlinear stochastic differential equations (SDE). The first method is based on a limit theorem by Khashminskii, from which a class of methods was derived known as stochastic averaging. From the drift and diffusion of the resulting averaged process, probability density functions and mean exit times can be easily obtained. The second method enables the determination of a Gaussian mixture representation for probability density functions of SDE's. This method was proposed by Pradlwarter and is known as Local Statistical Linearization. The error evolution of such Gaussian mixture shows promising results for further research.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/11420/18832016-01-01T00:00:00Z
- Design and optimization of a wave energy converter for drifting sensor platforms in realistic ocean waveshttp://hdl.handle.net/11420/12846Title: Design and optimization of a wave energy converter for drifting sensor platforms in realistic ocean waves
Authors: Harms, Julius; Hollm, Marten; Dostal, Leo; Kern, Thorsten Alexander; Seifried, Robert
Abstract: One of the biggest challenges in converting wave energy is to enable the use of low frequency waves, since the highest waves in typical sea states have low frequencies, as can be seen from the corresponding wave spectra, such as the Pierson–Moskowitz or JONSWAP spectra. In this paper, we show that this challenge is indeed achievable for the operation of small autonomous drifting sensor platforms. We present the design and optimization of a compact wave energy converter that freely floats in random sea waves. An optimization of the dynamical behavior as well as the electromagnetic power take-off is conducted based on simulations and experiments. The platform has compact dimensions of 50 cm draft and 50 cm diameter, which leads to special requirements for size and appearance. To meet these requirements, a two-body self-reacting point absorber is designed and a flux switching permanent magnet linear machine is developed for the power take-off. The developed system is validated by experiments in a wave flume and the linear generator is analyzed on a test bench. A coupled model is used to simulate and optimize the corresponding mechanical system, which leads to an increased output power from below 10 mW for the simulated initial setup to a power output of more than 100 mW in the simulation. Simulations and experiments are performed for regular and random waves in order to provide realistic approximations of the total output power.
Thu, 01 Sep 2022 00:00:00 GMThttp://hdl.handle.net/11420/128462022-09-01T00:00:00Z
- Workshop: Adaptive Structures At Shore 2022 : 23rd & 24th of May 2022, Hamburg, Germany : conference proceedingshttp://hdl.handle.net/11420/13132Title: Workshop: Adaptive Structures At Shore 2022 : 23rd & 24th of May 2022, Hamburg, Germany : conference proceedings
Authors: Grabe, Jürgen; Wiltshire, Karen; Haase, Walter; Nitschke, Andreas; Fofonova, Vera; Keßler, Silvia; Wüchner, Roland; Düster, Alexander; Trieu, Hoc Khiem; Seifried, Robert; Rung, Thomas; Bletzinger, Kai-Uwe; Gescher, Johannes; Smarsly, Kay; Dragos, Kosmas; Dücker, Daniel-André; Pick, Marc-André; Ieropoulos, Ioannis; Schwarz, Niklas; Rutner, Marcus; Heitmann, Christian; Roubos, Alfred; Argyriadis, Kimon; Klein, Marco; Dostal, Leo; Stender, Merten; Abdel-Maksoud, Moustafa; Goseberg, Nils
Abstract: Die Weltbevölkerung wächst und gleichzeitig werden die Ressourcen immer knapper. Einen großen Anteil daran hat das Bauwesen. Die Lösung für ressourceneffizientes Bauen, sei es auf dem Wasser oder an Land, sehen Expertinnen und Experten in anpassungsfähigen, so genannten adaptiven Strukturen. Sie beschreiben die Idee, wie künftig für mehr Menschen ressourcenschonend und emissionsfrei gebaut werden kann. Dabei soll nicht nur mehr Wohnraum mit weniger Material geschaffen werden, sondern auch der Energieverbrauch gesenkt und der Nutzerkomfort gesteigert werden. Über den neuesten Stand der Technik diskutieren Expertinnen und Experten aus Wissenschaft und Wirtschaft am 23. und 24. Mai im Rahmen des Workshops „Adaptive Structures at Shore“ an der Technischen Universität Hamburg.
In unterschiedlichen Fachvorträgen geht es einerseits darum, welche Auswirkungen beispielsweise Wind und Wasser auf Kaimauern oder schwimmende Bauwerke haben, oder inwiefern eine hohe Verkehrslast Brücken beansprucht. Dabei stellt sich die Frage, wie Bauwerke nachhaltig auf entsprechende Herausforderungen optimiert und angepasst werden können und inwiefern dabei Modellierungen und Simulationen helfen können. Der interdisziplinäre, englischsprachige Workshop wird durch das TU-Institut für Geotechnik und Baubetrieb organisiert und richtet sich an Interessierte unterschiedlicher Fachbereiche aus Wissenschaft, Wirtschaft und Verwaltung.; Adaptive structures at shore provide an opportunity to minimize the resource consumption and the impact on the marine ecosystems through an efficient adaptation to changing boundary conditions. A combination of impact prediction, monitoring and material resistance estimation, numerical modelling, and innovative design is the key to success. The workshop “Adaptive Structures at Shore 2022” hosted by Hamburg
University of Technology (TUHH) brings together international scientists and professionals to discuss the latest developments in the field
and to explore synergies.
Mon, 23 May 2022 00:00:00 GMThttp://hdl.handle.net/11420/131322022-05-23T00:00:00Z
- A nonlinear gradient elasticity model for the prediction of seismic waveshttp://hdl.handle.net/11420/13744Title: A nonlinear gradient elasticity model for the prediction of seismic waves
Authors: Dostal, Leo; Hollm, Marten; Metrikine, Andrei; Fărăgău, Andrei; Dalen, Karel N. van
Abstract: We present a novel equation of motion for a nonlinear gradient elasticity model. Thereby, higher-order gradient terms are introduced to capture the effect of small-scale soil heterogeneity/micro-structure. Using a newly established finite difference scheme, corresponding solutions including stationary waves are determined. In comparison with a commonly used model for nonlinear seismic waves, which has leading derivatives of second order, the solutions of the novel equations are much smoother. This allows much more accurate numerical computations as well as more realistic predictions of the seismic waves.
Fri, 01 Jul 2022 00:00:00 GMThttp://hdl.handle.net/11420/137442022-07-01T00:00:00Z
- Dynamical analysis of a multibody wave energy converter excited by random waveshttp://hdl.handle.net/11420/13742Title: Dynamical analysis of a multibody wave energy converter excited by random waves
Authors: Hollm, Marten; Dostal, Leo; Höhne, Joshua; Seifried, Robert
Abstract: The dynamics of a novel multibody wave energy converter based on inclined single modules connected to a frame are investigated, on which generators convert the corresponding relative motion into electrical power. Thereby, it is studied under which conditions the inclined individual modules perform the largest relative motions in regular and irregular waves. For this, different setups are analyzed in the presence of wave excitations, which is generated by a random non-white Gaussian stochastic process.
Fri, 01 Jul 2022 00:00:00 GMThttp://hdl.handle.net/11420/137422022-07-01T00:00:00Z
- The applicability of stochastic averaging method to solve the ship rolling response excited by narrow-band waveshttp://hdl.handle.net/11420/12194Title: The applicability of stochastic averaging method to solve the ship rolling response excited by narrow-band waves
Authors: Liu, Yaliu; Liu, Liqin; Dostal, Leo; Lu, Jiang
Abstract: In this paper, a single-degree-of-freedom rolling equation under parametric excitation is established. Based on strip theory, the righting arm is calculated by numerical simulation with different roll angles, wave heights, and phase angles of the wave position. Then the least square method is used to obtain an analytical expression of the righting arm. The stochastic averaging method of energy envelope is used to calculate the ship rolling response under random excitation. Compared with the Monte Carlo solution, the accuracy of stochastic averaging method under different sea conditions is evaluated. The results show that with the decreasing of the hydrodynamic damping, the peak factor or the excitation intensity of the considered JONSWAP sea spectrum, the accuracy of the stochastic averaging method increases. As a result, conditions for applicability of the stochastic averaging method of energy envelope for practical engineering problems are given. A very efficient way to analyze the roll response of ships in random seas is when stochastic averaging and Monte Carlo simulations are used hand in hand.
Sun, 01 May 2022 00:00:00 GMThttp://hdl.handle.net/11420/121942022-05-01T00:00:00Z
- Improved stochastic averaging method using Hamiltonian for parametric rolling in irregular longitudinal waveshttp://hdl.handle.net/11420/9696Title: Improved stochastic averaging method using Hamiltonian for parametric rolling in irregular longitudinal waves
Authors: Maruyama, Yuuki; Maki, Atsuo; Dostal, Leo; Umeda, Naoya
Abstract: Using the stochastic averaging method, the probability density function (PDF) of roll motion for parametric rolling in irregular waves is obtained. In this paper, the stochastic averaging method using Hamiltonian proposed by Dostal is used, and the PDF of roll amplitude and Hamiltonian are derived from the equations of roll motion. In addition, the asymptotic behavior of PDF is investigated to improve the accuracy of the calculation. Furthermore, to improve the applicability of this method, the simulation-based stochastic method is proposed. Compared to the results of the stochastic averaging method proposed by Roberts and Dostal, the results using this improved method show a good agreement. The results are examined for parametric excitation using white noise as well as colored noise. Moreover, the relationship between the scale parameter and the PDF is theoretically analyzed and formulated.
Tue, 01 Mar 2022 00:00:00 GMThttp://hdl.handle.net/11420/96962022-03-01T00:00:00Z
- Stochastic averaging of roll-pitch and roll-heave motion in random seashttp://hdl.handle.net/11420/2545Title: Stochastic averaging of roll-pitch and roll-heave motion in random seas
Authors: Dostal, Leo; Kreuzer, Edwin; Namachchivaya, Navaratnam Sri
Abstract: Multi-degree-of-freedom ship motion and ship stability in random seas are of major interest for the development of new advanced intact stability criteria. The purpose of this research is to improve the safety of new ship designs, but the results are relevant also for other engineering systems involving multiple scales. We focus on roll-pitch and roll-heave motion in random seas. The random wave excitation is modeled by a non-white stationary process. This process is derived from a spectral description of the random seaway using traveling effective wave. © 2013 The Authors.
Tue, 02 Apr 2013 00:00:00 GMThttp://hdl.handle.net/11420/25452013-04-02T00:00:00Z
- Particle paths and hydrodynamic forces of random wind forced nonlinear ocean waveshttp://hdl.handle.net/11420/14232Title: Particle paths and hydrodynamic forces of random wind forced nonlinear ocean waves
Authors: Hollm, Marten; Dostal, Leo; Seifried, Robert
Abstract: The hydrodynamic forces of nonlinear deep water gravity waves acting on cylindrical offshore structures are studied. Thereby, the waves are excited by random wind and the corresponding effect on the particle paths and hydrodynamic forces is investigated. This is done for the Peregrine breather solution of the nonlinear Schrödinger equation, which is nowadays considered as a prototype of extreme waves in open seas. Using this theory, the loads on mechanical structures can be calculated efficiently. It is shown that the Peregrine breather can exist under strong and gusty wind conditions and the water particles experience a horizontal drift. This leads to a force with randomly increasing amplitude in time, whereby a mean wind velocity of 50km/h results in an increase of about 3%. The increase of hydrodynamic forces caused by the wind should therefore be considered for the construction of mechanical structures operating in the ocean.
Thu, 01 Sep 2022 00:00:00 GMThttp://hdl.handle.net/11420/142322022-09-01T00:00:00Z
- Probabilistische Analyse der nichtlinearen Dynamik von Schiffen im natürlichen Seeganghttp://hdl.handle.net/11420/11064Title: Probabilistische Analyse der nichtlinearen Dynamik von Schiffen im natürlichen Seegang
Authors: Dostal, Leo
Abstract: Die International Maritime Organization (IMO) verweist in ihren aktuellen Richtlinien zur Bewertung der Stabilität intakter Schiffe auf die Notwendigkeit von verbesserten Kriterien zur Bewertung der Schiffssicherheit unter Berücksichtigung des dynamischen Verhaltens im natürlichen Seegang. Aus dieser Notwendigkeit heraus werden in dieser Arbeit neue Wege zur Analyse der nichtlinearen Dynamik von Schiffen im natürlichen Seegang aufgezeigt. Der natürliche Seegang weist eine unregelmäßige Wasseroberfläche auf, die aus vielen Einflüssen resultiert, denen das Meer ausgesetzt ist. Diese Einflüsse können im Allgemeinen nur statistisch erfasst werden. Mit der vorgestellten Theorie ist es möglich, probabilistische Ergebnisse zur Vorhersage der Stabilität und der nichtlinearen Dynamik von Schiffen effizient zu bestimmen. Dabei werden funktionale Zusammenhänge bestimmt, mit denen die Gefährdung des Schiffes im natürlichen Seegang bewertet werden kann. Damit wird ein Beitrag zur Verbesserung der Sicherheit des Schiffes geleistet. Um dieses Ziel zu erreichen, werden bestehende Methoden weiterentwickelt. So ermöglicht eine neue Formulierung der stochastischen Mittelung der Energie eine einfachere Darstellung der stochastischen Differentialgleichung für die Energie der Schiffsdynamik. Gegenüber früheren Ergebnissen werden Anregungen durch nicht-weiße Gauß-Prozesse berücksichtigt, welche aus der Fluid-Struktur-Interaktion des Schiffes im natürlichen Seegang herrühren. Mit den Lösungen lassen sich stochastische Momente beliebiger Ordnung für Erstüberschreitungszeiten der Rollenergie effizient bestimmen. Diese Ergebnisse sind grundlegend und lassen sich auch für nichtlineare Schwinger anwenden, deren ungestörte Dynamik gegenüber der Dynamik der Anregung und Dämpfung dominiert.
Tue, 01 Mar 2016 00:00:00 GMThttp://hdl.handle.net/11420/110642016-03-01T00:00:00Z
- First passage times for nonlinear ship dynamics using Gaussian random fields and effective waveshttp://hdl.handle.net/11420/15334Title: First passage times for nonlinear ship dynamics using Gaussian random fields and effective waves
Authors: Dostal, Leo; Hollm, Marten; Maki, Atsuo
Abstract: It is important to know the mean time until critical roll motion occurs in various operating and sea conditions, in order to determine and ensure the safety of ship designs and operating ships. Since typical ocean waves are irregular, the forcing and roll response of the ship is considered to be a stochastic process of colored noise type. However, the simulation of the corresponding first passage times is very time consuming. Therefore, an approach for the determination of mean first passage times of critical roll motion of ships is proposed in this paper which needs much less computation time. This approach is based on explicit formulas for the roll energy of the ship. These formulas are used to determine the mean first passage times based on integral expressions, which were previously obtained. The resulting integral expressions can be computed very fast using standard quadrature formulas. Moreover, the underlying model for ship dynamics is extended by introducing a new effective wave for short-crested sea states. This is an extension to the improved Grim's effective wave concept.
Tue, 01 Aug 2023 00:00:00 GMThttp://hdl.handle.net/11420/153342023-08-01T00:00:00Z
- Estimation of acceleration probability density function for parametric rolling using PLIMhttp://hdl.handle.net/11420/15353Title: Estimation of acceleration probability density function for parametric rolling using PLIM
Authors: Maruyama, Yuuki; Maki, Atsuo; Dostal, Leo; Umeda, Naoya
Abstract: As previously reported, container loss due to severe roll angles and high acceleration is still a problem for container ships. In this paper, the roll's angular acceleration is explored. First, the acceleration is divided into two components. The PDF line integral method (PLIM) is used to obtain the probability density function (PDF) of each acceleration component. We point out that it is inappropriate to obtain the joint PDF of roll angle and rate via the standard transformation from roll energy to roll angle-roll rate. Furthermore, we suggest a method for calculating the joint PDF of roll angle and effective wave elevation. Although theoretically calculating the PDF of roll angular acceleration is attempted, the theory differs from the Monte Carlo simulation (MCS) result. Therefore, it is necessary to study an alternative way to obtain a reasonable PDF of roll angular acceleration. Finally, the PDF of cargo lateral acceleration is derived, showing that the proposed theory agrees well with the MCS result. In comparison to our previous results using the PLIM method, the computation of acceleration for large roll motion is much more difficult. This leads to new challenges.
Sat, 15 Jul 2023 00:00:00 GMThttp://hdl.handle.net/11420/153532023-07-15T00:00:00Z