Chen W.-Q.,China Ship Scientific Research Center
Chuan Bo Li Xue/Journal of Ship Mechanics | Year: 2017
The water-exit cavity is simplified as the problem of the spherical cavity near the water surface, and the two-phase bubble dynamical model under the comprehensive effect of the unbounded atmosphere flow field and the bounded water flow field was established. The influence mechanism of the atmosphere density and flow to the collapse pressure of the water-exit cavity was also studied based this model. The research shows that when the cavity contracts to some small value, the nonlinear dynamic behavior of the cavity can make the perturbation of the atmosphere density and pressure amplified rapidly. Especially on the same initial conditions, the small perturbation of the atmosphere density can lead to an obvious increase of the collapse pressure at the same moment. © 2017, Editorial Board of Journal of Ship Mechanics. All right reserved.
Cui W.,China Ship Scientific Research Center |
Wang F.,China Ship Scientific Research Center |
Huang X.,Shanghai JiaoTong University
Marine Structures | Year: 2011
Marine structures such as ships and offshore platforms are mostly designed with damage tolerance and this design philosophy requires accurate prediction of fatigue crack propagation process. Now more and more people have realized that only a fatigue life prediction method based on fatigue crack propagation (FCP) theory has the potential to satisfy the accuracy requirement and to explain various fatigue phenomena observed. In the past several years, the authors' group has made some efforts in developing a unified fatigue life prediction (UFLP) method for marine structures. The key issue for this development is to establish a "correct" crack growth rate relation. In this paper the improvement of the crack growth rate model is dealt with first. A new crack growth rate model based on the concept of partial crack closure is presented. The capability of the model is demonstrated. Secondly, studies on the engineering approaches to determine the parameters in the new crack growth rate model are carried out and validated by comparing with the experimental results on a wide range of alloys. Thirdly, the preliminary studies on some significant problems such as load sequence effect are presented. Finally, further studies for the application of the UFLP method to the fatigue strength assessment of marine structures are pointed out. © 2011 Elsevier Ltd.
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.
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.
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.
Hu H.,China Ship Scientific Research Center
2016 IEEE/OES China Ocean Acoustics Symposium, COA 2016 | Year: 2016
Based on the simplified Third Order Shear Deformation Theory (TSDT), The sound radiation properties of a moderate laminated composite rectangular plate was deduced, In order to validate the proposed method, the result was compared with the finite element method. The advantages of TSDT was demonstrated by comparing the result with traditional CLPT (classical laminated plate theory) and FSDT (first shear deformation theory). And, by changing Youngs modulus; shear modulus; lamina thickness; and, fibre orientation angle, the main parameters and the variation in different frequency bands were obtained, this was a reference for underwater typical structure sound radiation and noise control. © 2016 IEEE.
Pan B.B.,China Ship Scientific Research Center |
Cui W.C.,China Ship Scientific Research Center |
Shen Y.S.,China Ship Scientific Research Center
Marine Structures | Year: 2012
In a previous study, a new empirical formula for the ultimate strength of the titanium alloy spherical pressure hulls of deep manned submersibles is recommended. This formula is mainly derived from the systematic finite element analyses of ANSYS. This paper introduces the further experimental verification of this new equation. Four small spheres of inner diameters 500 mm are tested to collapse. The collapse load range is predicted before the test and all the four final test results are within the range. The work shows that the predictions by the new equation are in well agreement with the experimental results. This suggests that the new equation can be used as the core equation to update current design rules. © 2012 Elsevier Ltd.
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.
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.
Pan B.,China Ship Scientific Research Center |
Cui W.,China Ship Scientific Research Center
Marine Structures | Year: 2010
The load-carrying capability of spherical shells under external pressure has been the subject of a long history and many theoretical and experimental studies have been carried out. However, from a comparative study on the design rules for the minimum thickness of the deep manned spherical shells from various classification societies, significant differences have been found. This indicates that these design rules need to be updated and unified like Common Structural Rules for tankers and bulk carriers. In order to lay a foundation for this target, a systematic study is carried out to develop a consistent calculation method for predicting the ultimate strength of spherical pressure hull under external pressure. This is the first paper of a series of three for reporting this study and in this paper, a critical review on the buckling and ultimate strength of spherical pressure hulls is carried out and further problems to be studied are identified. This could lay a solid foundation for the further study. © 2010 Elsevier Ltd.