Proceedings of the 11th International Conference

on Hydrodynamics (ICHD 2014)

October 19 – 24, 2014Singapore
Editors: TAN Soon Keat, WANG Xikun, GHO Wie Min & Joy CHUA

Session Papers (21-40)

21. The response of hydrodynamics to Caofeidian Project in 2012.

C.P. Kuang, J.W. Qi, M.T. Jiang, etc.

Department of Hydraulic Engineering, Tongji University, No. 1239, Siping Road
Shanghai, 200092, China.

Abstract :

Caofeidian is located in the west of Bohai Bay, the eastern coast of north China. Caofeidian owns the predominant natural conditions for the construction of a deep water harbor and marine industry. The large scale reclamation and construction of Caofeidian started in 2003 and are still busily underway. The reclamation of Caofeidian has been mainly completed by 2012, including Caofeidian approach jetty, foreland area, coal terminal and so on. The reclamation and construction of the project change the hydrodynamic environment greatly, which will in turn influence the design and construction of the project. In this paper, a two-dimensional numerical flow model of Caofeidian harbor was established with Delft3D, which has been widely used for hydrodynamic simulation in coastal area. This model was validated with the measured data both in tidal current velocity and directions in 2012. The validated model was used to simulate flow fields in Caofeidian coastal area with 2012 project and without project. Comparison and analysis of the characteristics in flow fields are made between the two scenarios, results indicate that: 1) The tidal current in Caofeidian coastal area which flows eastward during the flood tide and westward during the ebb tide shows the characteristic of reversing current. 2) The tidal current velocities are relatively bigger in front of the foreland, and are relatively smaller in harbor basin and near the coast with 2012 project. 3) With 2012 project, the tidal current velocities in front of Caofeidian foreland are larger than that without project. However, in the west foreland, west and east branch of south Laolonggou and basins of Caofeidian harbor, the flow becomes weak after the project.

22.  Application of different design and analysis tools for a propeller in axial cylinder.

S.Gaggero, G.Tani, C. Vaccaro, M. Viviani, etc.

Department of Electrical, Electronic, Telecommunication Engineering and Naval Architecture (DITEN), University of Genoa, Italy - Address: Via Montallegro 1 – 16145 Genova.

Abstract :

In present work, two propeller analysis tools, namely a panel code and a RANS solver, are applied for the evaluation of mechanical characteristics and cavitation behavior of two CP thrusters in axial cylinder, for which experimental results are available, in terms of propeller mechanical characteristics in absence of cavitation and ofcavitation behavior (cavitation extension and thrust and torque breakdown). The comparison of numerical results allows to underline merits and shortcomings of the two approaches and to define possible ways for their improvement, in view of their possible applications in the design loop.

23.  Analysis on wave actions on two closely spaced floating boxes.

Yong Liu, Lin Lu.

Shandong Provincial Key Laboratory of Ocean Engineering, Ocean University of China, Qingdao 266100, China.

Abstract :

Closely spaced maritime structures with narrow gaps subject towater waves may result in extremely large amplitudes of fluid resonance in gaps and wave forces on structures. In this study, an idealized case of two rectangular boxes with different widths and drafts in linear waves is considered. An analytical solution for the present problem is developed using the matched eigenfunction expansions. An artificial resistance force, which results in two dissipative boundary conditions, is introduced in order to model the practical wave energy dissipation. The free surface elevation in gap and the wave forces on boxes are presented. The analytical solutions are confirmed by the comparisons with available experimental data, multi-domain boundary element method solutions and CFD results. Some useful results associated with gap resonance are provided.

24.  Numerical and theoretical analysis on the collapse effect of the partial cavitation around decelerating underwater vehicle.

Y. Chen, C.J. Lu, X. Chen, J. Li, J.Y. Cao, Z.X. Gong.

School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University,
800 Dongchuan Road, Shanghai, 200240, China。

Abstract :

In the present work, the collapse regimes of the cavitation occurring on the underwatervehicles navigating with deceleration were numerically investigated. The cavity collapse process can be classified into two types: periodic oscillation and damped oscillation. In each type the evolution of the total mass of vapor in cavity are found to have strict correlation with the pressure oscillation in far field. The two types are different in the intensity and bandwidth of the pressure peaks. By defining the equivalent radius of cavity, we introduce the specific kinetic energy of collapse and demonstrate that its change-rate is in good agreement with the pressure disturbance. It is also found that the drag presents corresponding oscillations. We numerically investigated the influence of angle of attack on the collapse effect. The result shows that when the vehicle decelerates, an asymmetric-focusing effect of the pressureinduced by collapse occurs on its pressureside. We analytically explained such asymmetric-focusing effect. The theoretical model we proposed shows capability in reflecting the evolution of the pressure difference between both sides of the vehicle.

25.  Computing the free surface hydrodynamic coefficients of high speed blended wing body vehicle based on semi-relative reference frame and implicit VOF method.

X.C. Wu, Y.W. Wang, C.G. Huang, Z.Q. Hu, R.W Yi.

Key Laboratory for Mechanics in Fluid Solid Coupling Systems,Institute of Mechanics, Chinese Academy of Sciences, Hai dian District North Fourth Ring Road No.15, Beijing, China.

Abstract :

The interference of wave systems under the condition of high speedis more significant with the blended wing body vehicle with large square coefficient, which shows a different dynamic distribution from the traditional vehicle. In this paper, the implicit VOF method is adopted to simulate the wave resistance of high speed blended wing body vehicle, and a semi-relative reference frame method is proposed to compute the hydrodynamic coefficients, which combines the rotating reference frame and added momentum source method. In the semi-relative reference frame method, the computational domain is separated into two parts, one part is adopted the rotating reference frame and the other part is set an inertial frame. With the coordinate transformation of the rotation center from the rotating arm tank to the blended wing body vehicle, just one mesh is needed with different drift and rotating arm tank radius. Navigational speed, drift angle and rotating arm tank radius are computed to get the effect to the free surface hydrodynamic coefficients.

26.  Study On The Reverse Advancing Collapse Phenomenon At Cavitation Bubbles Closure In Underwater Vertical Launching Process.

Y.W. Wang, C.G. Huang, X. Fang, X.C. Wu, T.Z. Du, X.X. Yu.

Key Laboratory for Mechanics in Fluid Solid Coupling Systems, Institute of Mechanics, Chinese Academy of Sciences, Haidian District North Fourth Ring Road No.15, Beijing, China.

Abstract :

In a typical experiment of underwater vertical launching process, cavitation bubbles are generated in the low pressure regions on the vehicle in the water and collapse when the projectile runs through the free surface. The overall evolutions of cavitation are obtained including bubble growth and collapse through the free surface. A new collapse phenomenon which advanced from tail to head of the axisymmetric projectile was observed in an underwater launching experiment, which is different from usual collapse phenomena and rarely observed in water tunnel tests. During this process, cavities shrink to the upstream quickly with high impact pressure produced, and fast re-entry jets are formed which induced strong instabilities in the following. Analysis indicates that this phenomenon is relative to the rapid changes of vehicle speed and the cavitation number. Thin cavitation bubbles are generated when the vehicle accelerates rapidly, and then fast condensation of vapor occurs and forms an additional body force at the cavity closure in the deceleration phase. As a result, large velocity pointing to the wall is generated, and the liquid water layer continues to move towards the wall and impact as an internal collapse.

27.  Numerical simulation for unsteady propeller performance with inclined shaft propeller arrangement using CFD.

P. Kaewkhiaw, J. Ando.

Department of Maritime Engineering, Graduate School of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.

Abstract :

Inclined shaft propeller arrangements are found in ship maneuvering, high speed ship's propellers and so on. Flow field around the propeller blades with inclined shaft propeller are unsteady due to the cross flow component to influx of the shaft direction. Therefore the realistic flow around inclined shaft propeller is important for actual efficiency of propeller. This paper presents numerical calculation results of propeller performance with inclined shaft propeller arrangement using a Reynolds Averaged Navier-Stokes (RANS) solver. The domains and propeller geometric data are generated withautomated mesh generation technique. Grid independency in the present computation method was verified in advance. The calculation results have been validated for two different model propellers, DTMB P4990 and P4679. The P4990 began steady state form straight shaft condition and advanced to inclined shaft propeller with 4.8° and 8.8°. In two inclined shaft angles, the calculated time accurate of thrust and torque coefficients have been compared with experimental data. The DTMB P4679 operated with 7.5° shaft inclination are fully unsteady calculation was conducted byinclined flow condition. The calculated pressure distributions on the pressure and suction side on the blades have been compared with measured values.

28.  Influence of different gas-injection conditions on ventilated cloud cavitation.

X.X. Yu, Y.W. Wang, C.G. Huang, T.Z. Du, X.C. Wu, L.J. Liao.

Key Laboratory for Mechanics in Fluid Solid Coupling Systems,Institute of Mechanics, Chinese Academy of Sciences, No.15 Bei Si Huan Xi Road, Beijing, China.

Abstract :

Cavitation occurs around high-speed underwater vehicles, inducing noises, vibration, etc. Gas-injection is an important method to adjust cavitating flow field. In this paper, dimensionless quantities are got though the dimensional analysis on ventilated cavitation. Among these dimensionless quantities, the ratios of mass flux and momentum flux of the gas-injection to those of the main flow are crucial in ventilated cloud cavitation. Numerical simulation is carried out on the effect of these two dimensionless quantities on ventilated cavitation. The results indicate that gas-injection mass flux has greater impact on the evolution of ventilated cavitation than momentum flux. As gas-injection mass flux increases, the form of gas entrainment changes from bubbles to air-layer. There is a tendency for the ventilated cavitation to become supercavitation when the gas-injection mass flux reaches critical value. Besides, increase of gas-injection mass flux can reduce the high pressure at the closure of the cavity and improve the pressure stability while it can also lead to the rise of drag of the vehicle. Gas-injection momentum flux has little effect on the evolution and pressure. Increase of gas-injection momentum flux can reduce drag of the vehicle.

29.  Significant Wave Height Retrieval from Synthetic Radar Images.

A. P. Wijaya & E. Van Groesen.

Department of Applied Mathematics, University of Twente, Drienerlolaan 5 Enschede, 7522 NB, The Netherlands.

Abstract :

In many offshore activities radar imagery is used to observe and predict ocean waves. An important issue in analyzing the radar images is to resolve the significant wave height. Different from 3DFFT methods that use an estimate related to the square root of the signal-to-noise ratio of radar images, in this paper we present a completely different approach. This approach is based on the intuitive observation that the shadowing of waves leads to a visibility that depends on the distance from the radar. We will show that for irregular waves the visibility depends in a characteristic way on the distance normalized by the peak wavelength, and on the ratio of radar height and significant wave height and only slightly on the details of the wave spectrum. By comparing the visibility of a specific sea with results of Monte Carlo simulations of sea states with various significant wave heights, the best LSM fit then determines the significant wave height. In this paper we restrict to long-crested waves and illustrate the method with various cases.

30.  Numerical Study on Open-Channel Bifurcations with Topographic Obstacles.

C. Zeng, P.J. Hu, L.L. Wang, C.W. Li, J. Zhou.

College of Water Conservancy and Hydropower Engineering, Hohai University,Nanjing, 210098, China.

Abstract :

In the present study, a 3D URANS model is developed by adopting the drag force method (DFM) to simulate the blocking effects of obstacles.  A quadratic law is used to relate the resistance effect to the squares of the flow velocity, and a large resist ance coefficient (frk) is used to restrict the flow into the obstacle. The experiments conducted by Mignot et al. were replicated with the present model.  The  impact  of  the  frk-value  on  the  flow  pattern,  water  surface  elevation  and  discharge  distribution  was  firstly verified.  The  results  show  that  the  change  in  discharge  distribution  by  the  presence  and  location  of  the  obstacles  can  be accurately  predicted,  although  the  fine  flow  features  around  the  obstacle  are  not  very  accurate. The drag force method is concluded to be effective and efficient to simulate the resistance effects of obstacles on flow distribution in street junctions.  The proposed model was used to numerically investigate the impact of the impact of the obstacle size on flow distribution. The results indicate the maximum change in discharge distribution induced by the different sized obstacle (L = W/6, W/4 & W/3) is nearly the same and around 15% of the inflow discharge.  When the obstacle located in the downstream main channel and in the middle of the junction, the obstacle impact is enhanced with greater size and Froude number.

31.  Modelling harbor resonance with an improved open boundary condition.

D. Liang, J. Zhang, J. Wang, H. Liu.

MOE Key Laboratory of Hydrodynamics, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.

Abstract :

In the numerical study of the flows in estuarine and coastal regions, the open boundaries are commonly encountered, which serve as the interface between the limited computational domain and the open sea.  Based on the shallow water equations and the method  of  characteristics,  a  generic implementation of  the  open  boundary  condition has been  examined  and demonstrated  in modelling the long wave dynamics in idealised harbors. The open boundary condition is devised for the solutions of fully nonlinear shallow water equations in the time domain.  In enforcing the non-reflecting boundary, the incident wave information is provided, whereas the reflected waves from inside the computational domain are allowed to escape from the boundary at the same time. The essence of its numerical implementation is to decouple the characteristic pointing inward the domain from the actual flow field inside. In  this way, the outgoing waves are allowed to  freely  leave  the  finite-sized domain, without any reflection at the open boundary. Compared with previous techniques, the present method includes extra terms in the derivation to include the effect of bed slope and the shape of the characteristic lines. A shock-capturing finite difference method has been used to solve the shallow water equations in the deviatoric format, but the open boundary algorithms constructed herein are generic and applicable to other numerical schemes. After being verified for the simple standing wave situation, this boundary condition is used to predict the wave resonance phenomena in idealised harbors of different shapes.

32. A practical system for hydrodynamic optimization of ship hull form using parametric modification function considering operational condition.

K.R. Pak, H.J. Kim, Y.C. Lee, etc.

Marine Research Institute, Samsung Heavy Industries Co., Ltd Daejeon, Korea.

Abstract :

This paper presents a practical system for hydrodynamic optimization of ship hull forms using parametric modification function considering operational condition of ship. The parametric modification function is based on the classical naval architect’s approach where the original ship geometry can be easily deformed by direct selection of well-known design parameters. These parameters are varied systematically one by one, maintaining all the other parameters constant. In order to reduce computational cost, this study suggests the optimization design process using two different fidelity solvers; low fidelity solver based on potential solve and high fidelity solver based on the RANS solve which is the computational evaluation system (SoLuTion) developed by Samsung Heavy Industry CO.(SHI). Hundreds of shapes can thus be explored efficiently, which provides a clear insight in trends and leads to a more effective hull form improvement procedure. This system for hull form optimization is now being used frequently at SAMSUNG in ship design process. For the purposes of illustration, the presented hydrodynamic optimization system is used to determine the optimum fore-hull form of a container ship by minimizing the resistance considering the operational condition.

33. Lagrangian particle simulation of lock-exchange flow.

M.Y. Lin.

Department of Civil Engineering, Chung Yuan Christian University, Chung Li 32023, Taiwan, China.

Abstract :

A Lagrangian particle method is proposed for the direct numerical simulations of gravity current in the lock-exchange configuration with relatively small density differences. The flow is generated in a plane channel filled with two fluids that are initially separated by a vertical gate. In this method, vorticity and concentration field are approximated by a set of particles. The gradient of density field and the Laplacian of density and vorticity are computed using the method of particle strength exchange. Simulations for different values of Grashof number are performed, exhibiting good agreement with the simulation results using high resolution spectral methods.

34.  Hydroelastic investigation on floating body near islands and reefs.

Chao Tian, Xinyun Ni, Xiaolong Liu, Yousheng Wu.

China Ship Scientific Research Center, No.222, East Shanshui Road, Wuxi, Jiangsu, 214082, China.

Abstract :

Very Large Floating Structures (VLFS) can be deployed near islands and reefs as a logistic base which can have various functions such as a floating harbor, accommodation, fishery processing, environment surveillance, aircraft landing and taking off, etc. in order to explore the natural and tourism resources in the ocean. In the past twenty years, extensive investigations have been carried out on the hydroelastic responses of VLFS in the deep open sea by researchers in US, Japan and China. However, study on the hydroelastic responses of VLFS near islands and reefs is still rarely reported. In addition to the complicated hydroelastic coupling effects between the hydrodynamic loads and structural dynamic responses, several other environmental effects should be taken into account when tackling the hydroelastic problems of floating structures near islands and reefs: the complex seabed profile, the non-uniform incident waves, non-linear wave excited forcesand dramatic increase on computational efforts and storage, etc. The theoretical investigation on the hydroelastic responses of VLFS deployed near islands and reefs are addressed in the present paper. Based on the three-dimensional hydroelastic analysis package THAFTS, the non-uniform wave propagation model, nonlinear wave forces and parallel fast computing techniques will be included to simulate the hydroelastic responses: motions, wave loads, distortions and stresses in the design stage and safety assessment of VLFS near islands and reefs.

35. Higher order synchronization outside primary lock-in of circular cylinder oscillating in streamwise.

L. Lu, G. Q. Tang, B. Teng, L.Cheng.

State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, 116024, China.

Abstract :

In this study, we present a new interesting phenomenon oftriple and quadruple locked modes outside the primary synchronization region by considering a cylinder oscillating in streamwise at Re = 200. For the low oscillating amplitudes, the numerical results show that the vortex shedding in the near wake is locked-on over three oscillating cycles of the cylinder while every four oscillating periods for the relatively high amplitudes. In addition, we find that the lift fluctuations are dominated by the frequency components of f*/ 3 (low oscillating amplitudes) and 3 f*/ 4 (high oscillating amplitudes) rather than f*/ 2 or f*for the primary synchronization region, where f* is the oscillating frequency of the circular cylinder.

36.  Numerical Simulation of Dam Breaking Flows by Overlapping Particle Method.

Z. Y. Tang, Y. X. Zhang, D. C. Wan.

State Key Laboratory of Ocean Engineering, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.

Abstract :

An overlapping particle technique (OPT) in the MPS (Moving Particle Semi-Implicit) framework is applied into a dam break flow. The basic idea of OPT is to distribute low-resolution particles in the whole domain and high-resolution particles in the local region. The whole flow field is first solved by the low-resolution particles and then it can provide the truncated boundary information to the high-resolution particles to recalculate the local concern domain, such that the computational cost can be reduced and the high-resolution can be maintained. In addition, an algorithm of generating particles and detecting the free surface particles is proposed. Validation is carried out against a 2D dam break flow. The results obtained by the OPT are compared with those using the traditional MPS method, and computational cost is analyzed. The results show the capability of the OPT in reducing the computational cost and providing a refine flow field in the concerned subdomain.

37. Parallel MPS Method for 3D Wave-body Interaction Flows.

Y.X. Zhang1, Z.Y. Tang, D.C. Wan, W.H. Huang.

State Key Laboratory of Ocean Engineering, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.

Abstract :

The presented study develops a parallel MPS (Moving Particle Semi-Implicit) method for simulation of 3D wave-body interaction flows. Parallelization is  implemented by means of MPI (Message Passing Interface) libraries. A domain decomposition strategy with dynamic load balancing is employed. Validation of the presented MPS method is carried out against a 3D dam break flow. Speed-up analysis shows an acceptable parallel efficiency. In addition, the numerical results of the wave height evolution are in agreement with experimental data. Finally, the presented MPS is applied to 3D wave-body flows, i.e. ship-wave interaction, where a mathematical hull, Wigley, interacting with regularwave, is investigated. Results suggest that the presented MPS method is capable of handling such complex practical flow problems.

38.  Partial validation and verification of the Neumann-Michell Theory of ship waves.

C.L. Zhang, F. Noblesse, D.C. Wan, F.X. Huang, C. Yang.

State Key Laboratory of Ocean Engineering, School of Naval Architecture, Ocean & Civil Engineering, Shanghai Jiao Tong University, Dongchuan Road 800, Shanghai, China.

Abstract :

The results of numerical studies directedtoward the verification and the validation of a practical method, called NeumannMichell theory, for evaluating the flow around a ship hull that steadily advances in calm water ofeffectively infinite depth and lateral extent are reported. Numerical predictions given by two completely independent numerical implementations of the theory, performed at the Shanghai Jiao Tong University and at the George Mason University, are compared with experimental measurements for four ship hull forms (the Wigley hull, and the Series 60, DTMB and KCS models) over the relatively wide
range of Froude numbers 0.1 ൑ F ൑ 0.45. The independent numerical results are found to be in good agreement on the whole, and to be consistent with experimental measurements.

39.  Cavitating Flow Simulation with Mesh Development using Salome Open Source Software.

V.H. Hidalgo, X.W. Luo And A. Yu, R. Soto.

State Key Laboratory of Hydro science & Engineering, Tsinghua University, Beijing 100084, China.

Abstract :

Cavitating flow simulation is very helpful for understanding the mechanism of cavitation in turbomachinery. However, the simulation accuracy may depend on the quality of mesh generation for computational domain source software Salome. The unsteady cavitating flow around a hydrofoil NACA 0015 is solved based on OpenFOAM, the results show that grid/mesh has important effects on the cavitating flow characteristics such ascavity revolution, vortex shedding. The comparison of cavitation flows among different mesh generation methods is conducted and it is noted that the cavitating flow with the structured mesh and well controlled node distribution can reproduce experimental resultsfairly well. Furthermore, mesh development using Salome greatly reduces calculation timeof the flows simulation.

40. Computational analysis of contra-rotating podded propulsors using a hybrid RANSE/BEM model.

D. Calcagni, F. Salvatore, R. Muscari, J. Sundberg, R. Johansson.

CNR-INSEAN, Via di Vallerano 139, Rome, 00128,Italy.

Abstract :

The paper presents a computational study of the hydrodynamic performance of unconventional ship propulsion configurations based on podded and contra-rotating propeller layouts. A Contra-Rotating Propeller Pod (CRP-Pod) and an Integrated Contrarotating Podded propeller (ICP) are addressed. Hull/propulsor interaction studies are performed by using a hybrid viscous/inviscid flow solver in which RANSE and BEM models are coupled by a general body-force/effective inflow technique. Numerical applications are performed to compare the two propulsive solutions in terms of hydrodynamic efficiency. A relatively higher performance of the CRP-Pod layout over the ICP is found. Numerical results are compared with available experimental data to analyse the capability of the proposed hybrid RANSE/BEM methodology to provide a correct characterization of the hydrodynamics of these unconventional and complex propulsor arrangements.