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Item type:Publication, Access status: with files , Experimental and numerical investigation of free-running turning manoeuvres in extreme shallow waterThe precise prediction of ship manoeuvring behaviour in shallow water is essential for safe navigation and waterway design. To examine depth-induced changes in ship dynamics, the turning behaviour of the container ship DTC (Duisburg Test Case) was investigated at model scale (1:60) using combined free-running experiments and CFD simulations, with emphasis on extreme shallow water down to (Formula presented) .Free-running manoeuvres were conducted, with measurement of propeller thrust and rudder forces. The CFD model was verified by means of a grid convergence study for a complete turning manoeuvre and validated against experimental data, showing mean deviations of approximately 5% for key manoeuvring parameters, confirming its predictive capability.The results reveal a pronounced deterioration of steady turning performance with decreasing water depth. A reversal in port-starboard asymmetry occurs in shallow water, governed by depth-dependent changes in propeller-rudder interaction and wake distribution. Transient analysis further shows that initial turning ability increases slightly in the transition from (Formula presented) to 1.15, but deteriorates sharply at (Formula presented), identifying a critical threshold. These effects are linked to redistributions of hydrodynamic forces along the hull.The results highlight the coupled influence of water depth and speed, emphasizing the governing role of the depth Froude number on manoeuvring behaviour.Publicationtype: Journal Article25 17 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Analysis of the flow conditions between the bottoms of the ship and of the waterway(2020-03-01); ; A physical model test was performed, to which a scaled model (1:40) was designed and constructed to carry two Laser Doppler Velocimetry sensors and provide optical access at different locations along the hull to detect the stream close to bottom of the hull and resolving the boundary layer flow at the hull. The measurement campaign was conducted in a shallow water towing tank and included a range of water depths and ship speeds such that the influence of each became analysable. The purpose of the experiment is to provide validation data to further corroborate a numerical approach and to gain deeper insight in the flow conditions in the gap flow underneath the vessel in very shallow water. In addition the extension of the effect of propulsion on the dynamic sinkage and trim in very shallow water was checked. Even though for one particular ship design and restricted to model scale 1:40, the results are regarded a valuable basis for further investigations on this phenomenon.Publicationtype: Journal Article139 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Disequilibrium wall function in RANSE computation applied to flow conditions around ship’s hull marine 2019(2019-05); Through years of scaled physical model tests to predict ship induced wave loads on rip-rap and bank protection in channels and waterways at Federal Waterways Engineering and Research Institute, a comprehensive collection of squat measurements had grown and became foundation of some principal and systematic conclusions on the squat effect in shallow and restricted waters [1]. There was the observation of a significant increase of the trim angle when water depth to draft ratio is decreased to less than = 1.3. A change in the flow regime was suspected to be responsible for this effect [2]. To prove the assumption of different flow regimes the boundary layers in the gap between the hull’s bottom and the ground were further investigated. All the investigations so far have been in the scale 1:40 in accordance with Froude’s Law. Boundary layers and gap flow conditions heavily depend on the Reynolds’ Number and the turbulence degree. Unfortunately it is impossible to satisfy Reynolds’ and Froude’s Law for this scale and this experimental set-up at the same time. It was decided to bypass this quandary with an extension of the analysis by numerical simulation of the flow around the hull at full scale. In the scaled model tests, the occurrence of a coalescence of the two boundary layers, at the hull and the ground, in the aft third of the hull was observed. In terms of time and computing cost, computational fluid dynamics simulation of flow around a ship’s hull at full scale are not reasonably feasible without application of wall functions today. The flow condition in the boundary layer violates the basic assumption of local equilibrium which is common for the regular wall functions implemented in the CFD-Codes solving Reynolds Averaged Navier-Stokes Equations with turbulence models to close the system of equations for solving. To cope with the non-equilibrium condition in the boundary layer at the hull, the “Generalized Wall Functions” [3] were implemented in OpenFOAM [4] and applied to the numerical analysis of the flow conditions around the ship hull.Publicationtype: Conference Paper45