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Luo H.,University of Lisbon | Wang H.,China Ship Scientific Research Center | Guedes Soares C.,University of Lisbon
Ocean Engineering | Year: 2012

This paper deals with the study of the slamming load and response of one complex 3D steel wedge with deadrise angle 22°. The stiffened panels on both sides of the wedge are made up of 9 longitudinal stiffeners and 5 transverse frames. In order to study the effect of flexibility on the elastic responses, the cross sections of the stiffeners and frames on each side were designed with different sizes. It is one segment of an idealized ship structure with V-shaped wedge bottom that was used in a series of free-drop experiments impacting still water. The acceleration, slamming pressures, and stress responses were measured. In this paper, one uncoupled method combining Wagner theory and the finite element method is presented to analyze this slamming problem for the 3D structure. The matched asymptotic theory is expanded to predict both the motion and the slamming pressure on the free-drop rigid body. Then slamming pressures are added on the finite element model to predict the transient structural responses. The numerical and experimental results of this slamming problem for a 3D structure are compared. Good agreement is achieved and the hydroelastic effects are discussed. © 2011 Elsevier Ltd All rights reserved. Source

Zhang Z.-R.,China Ship Scientific Research Center
Journal of Hydrodynamics | Year: 2010

The free surface flow of a modern container ship KCS without propeller was firstly simulated using three sets of grids. The computed results including resistance, wave elevation and flow field on propeller disk were compared with the experimental data in detail. Verification and validation of resistance and wave profile were performed using recommended procedures proposed by ITTC. Then the viscous flow around KCS with operating propeller behind was also simulated. Both body force approach and sliding mesh approach were applied to consider for the effect of propeller. The results of these two approaches were compared with the measured data. These numerical investigation shows that accurate prediction of propeller/hull interaction using CFD method is becoming feasible and the huge potential of CFD application in ship hydrodynamics performance prediction is demonstrated. © 2010 Publishing House for Journal of Hydrodynamics. Source

Cui W.,China Ship Scientific Research Center
Structural and Multidisciplinary Optimization | Year: 2011

Bi-Level Integrated System Collaborative Optimization (BLISCO) is a new multidisciplinary design optimization (MDO) method based on Bi-Level Integrated System Synthesis (BLISS) and Collaborative Optimization (CO). The key ideas of BLISCO are to replace compatibility constraint with the sum of coupled outputs as an integrated objective of subsystems and to decompose design variables into system design variables and subsystem design variables, while maintaining the collaborative mechanism of CO. One mathematical example and two engineering problems are used to test the effectiveness of BLISCO under the platform of iSIGHTTM. Results from the test cases show that BLISCO has satisfactory convergence, accurate result and reliable robustness. © 2010 Springer-Verlag. Source

Ji B.,Tsinghua University | Luo X.W.,Tsinghua University | Arndt R.E.A.,University of Minnesota | Peng X.,China Ship Scientific Research Center | Wu Y.,Tsinghua University
International Journal of Multiphase Flow | Year: 2015

Compared to non-cavitating flow, cavitating flow is much complex owing to the numerical difficulties caused by cavity generation and collapse. In this paper, the cavitating flow around a NACA66 hydrofoil is studied numerically with particular emphasis on understanding the cavitation structures and the shedding dynamics. Large Eddy Simulation (LES) was coupled with a homogeneous cavitation model to calculate the pressure, velocity, vapor volume fraction and vorticity around the hydrofoil. The predicted cavitation shedding dynamics behavior, including the cavity growth, break-off and collapse downstream, agrees fairly well with experiment. Some fundamental issues such as the transition of a cavitating flow structure from 2D to 3D associated with cavitation-vortex interaction are discussed using the vorticity transport equation for variable density flow. A simplified one-dimensional model for the present configuration is adopted and calibrated against the LES results to better clarify the physical mechanism for the cavitation induced pressure fluctuations. The results verify the relationship between pressure fluctuations and the cavity shedding process (e.g. the variations of the flow rate and cavity volume) and demonstrate that the cavity volume acceleration is the main source of the pressure fluctuations around the cavitating hydrofoil. This research provides a better understanding of the mechanism driving the cavitation excited pressure pulsations, which will facilitate development of engineering designs to control these vibrations. © 2014 The Authors. Source

Ji B.,Tsinghua University | Luo X.,Tsinghua University | Wu Y.,Tsinghua University | Peng X.,China Ship Scientific Research Center | Duan Y.,Tsinghua University
International Journal of Multiphase Flow | Year: 2013

Cavitating turbulent flow around hydrofoils was simulated using the Partially-Averaged Navier-Stokes (PANS) method and a mass transfer cavitation model with the maximum density ratio (ρl/ρv,clip) effect between the liquid and the vapor. The predicted cavity length and thickness of stable cavities as well as the pressure distribution along the suction surface of a NACA66(MOD) hydrofoil compare well with experimental data when using the actual maximum density ratio (ρl/ρv,clip=43391) at room temperature. The unsteady cavitation patterns and their evolution around a Delft twisted hydrofoil were then simulated. The numerical results indicate that the cavity volume fluctuates dramatically as the cavitating flow develops with cavity growth, destabilization, and collapse. The predicted three dimensional cavity structures due to the variation of attack angle in the span-wise direction and the shedding cycle as well as its frequency agree fairly well with experimental observations. The distinct side-lobes of the attached cavity and the shedding U-shaped horse-shoe vortex are well captured. Furthermore, it is shown that the shedding horse-shoe vortex includes a primary U-shaped vapor cloud and two secondary U-shaped vapor clouds originating from the primary shedding at the cavity center and the secondary shedding at both cavity sides. The primary shedding is related to the collision of a radially-diverging re-entrant jet and the attached cavity surface, while the secondary shedding is due to the collision of side-entrant jets and the radially-diverging re-entrant jet. The local flow fields show that the interaction between the circulating flow and the shedding vapor cloud may be the main mechanism producing the cavitating horse-shoe vortex. Two side views described by iso-surfaces of the vapor volume fraction for a 10% vapor volume, and a non-dimensional Q-criterion equal to 200 are used to illustrate the formation, roll-up and transport of the shedding horse-shoe vortex. The predicted height of the shedding horse-shoe vortex increases as the vortex moves downstream. It is shown that the shape of the horse-shoe vortex for the non-dimensional Q-criterion is more complicated than that of the 10% vapor fraction iso-surface and is more consistent with the experiments. Further, though the time-averaged lift coefficient predicted by the PANS calculation is about 12% lower than the experimental value, it is better than other predictions based on RANS solvers. © 2012 Elsevier Ltd. Source

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