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 (41-60)

41.  PIV Measurements of Wake Flow Characteristics behind a Rotating Cylinder.

Y.Y. GAO, Z.L. SUN, D.S. TAN, B.F. ZHANG, S.K. TAN.

Ocean College, Zhejiang University, Hangzhou, 310058, China.

Abstract :

The experimental investigation on the flow behaviour behind a rotating cylinder at low Reynolds number Re=300 was carried out in a recirculation water channel. A stepper motor was used to rotate the cylinder about its longitudinal axis, and the Particle Image Velocimetry (PIV) technique was used to capture the flow field behind the rotating cylinder. The instantaneous and ensemble-averaged pictures such as velocity and vorticity contours were analysed. The effect of frequency ratio Fr (Fr = fn/ fv, the ratio of the forcing frequency fn to the natural vortex shedding frequency fv) on the wake in the lee of the rotating cylinder was also examined. The findings of the study show that on the wake flow patterns are strongly dependent on Fr.

42. A Generalized 3D Numerical Wave Tank for Practical Wave-Structure Interactions in Steep Waves.

Debabrata Sen, Shivaji Ganesan.

Dept. of Ocean Eng. & Naval Architecture, IIT Kharagpur, Kharagpur, West Bengal 721302, India.

Abstract :

This paper presents development of a practical tool for wave-structure interactions based on a 3D numerical wave tank concept but with certain approximations in the treatment of the associated hydrodynamic problems of radiation and diffraction. The solution is in time domain and the method is versatile; it canincorporate influence of many subcomponents of a complex offshore platform, making it suitable for routine industry applications particularly for initial design stages. However, despite the simplified treatment of the interaction hydrodynamics, long-duration simulation of nonlinear interactions for a completely unrestrained floating body in a steep incident wave-field in general proves difficult as the solution tends to diverge. This problem is found to be associated with the evaluation of exact FK force on the instantaneous wetted surface rather than the relatively more complex and time-consuming interaction-hydrodynamic calculations. Some form of horizontal restraint is found to remove this problem. Results are presented to demonstrate that providing an artificial restriction on the horizontal motions enables longduration simulations to be performed. Such artificial restraints are however not needed if mooring lines are present.

43.  The development of shoulder cavitation when a vehicle flying through water surface.

Y. Ma, X.W. Liu, Z. Huang.

The Chinese Academy of Aerospace Aerodynamics, Beijing,China.

Abstract :

In the high-speed movement of a submarine-launched vehicle, a cavitation appears on the shoulder of the surface. The cavity collapses while the vehicle is moving fromthe water into the air, which has great effects on the surface load and the mechanical environment of the vehicle. In order to study this development of the shoulder cavitation, high-speed photography and canny edge detection technique have been adopted in the flow visualization experiment. After comparing and analyzing the record of the model location and attitude at each time, as well as the corresponding cavity profile image, some results about the shoulder
cavitation development have been found. There are three large-scale cavitation structures appear at the shoulder of the vehiclein the process of flying through water surface, and they are sheet cavitation, vortex cavitation and cloud cavitation respectively. The vapor-filled sheet cavitation appears firstly in the shape of irregular streaky structures and each streak begins from different position along the axis. The axis length of the sheet cavitation isclosely related to the velocity of the vehicle and the circumferential distribution of the streaks is random and discontinuous. Two modes have been found in the process of a sheet cavitation transferring to cloud cavitation. One is shedding from the tail of the sheetcavitation because of the re-entrant jet, and the other is from vortex cavitation, which is separated from the main sheet cavitation constantly with the vehicle moving in vertical direction under water.

44.  Convective instability and diffusion in isothermal ternary gas mixtures at various pressures and viscosity.

V.N. Kossov, O.V. Fedorenko, V. Mukamedenkyzy.

Institute of Experimental and Theoretical Physics, al-Farabi Kazakh National University, al-Farabi av., 71, Almaty, 050040, Kazakhstan

Abstract :

An experimental study of the instability ofmechanical equilibrium in gas systems 0.4300 C3H8+ 0.5700 He– 0.4300 C3H8+ 0.5700 CH4and 0.4300 C3H8+ 0.5700 He– 0.4200 C3H8+ 0.5800 Ne, where the diluent gas is present, subject to the pressure and viscosity is performed. It is shown that the intensity of convective flows is less in more viscous mixtures. Linear stability theory is applied to determine the boundary of transition from the state of diffusion to the region of the concentration convection. The experimental data are in good agreement with the theoretical results.

45. Experimental study on dynamics of buoyant jets and plumes in linearly stratified environment.

Harish N & Sridhar Balasubramanian.

Department of Mechanical Engineering, IIT Bombay, Mumbai, Maharashtra, India.

Abstract :

Many geophysical and engineering flows in nature encounter stratification, i.e. density or temperature variation along height. The presence of stratification alters the turbulent mixing behavior, thus posing a challenging fluid dynamics problem having important consequences in modeling of such flows. Here, the entrainment dynamicsof vertical turbulent buoyant jet/plume into a linearly stratified medium for varying Brunt vaisala frequency (N) is presented by criticallyanalyzing the development of largescale and small-scale flow patterns. The experimental facility for this study consists of two square acrylic tanks. One of them is the main tank, which is linearly stratified ( ∂ρ/∂z < 0) with the help of water and commercial salt. The second tank is the mixing tank that is filled with water. The fresh water is injected into the stratified tank to study the plume dynamics. The ensuing evolution of buoyant jet is studied using high resolution camera and commercial dye, and bulk flow parameters are obtained. The experiments were carried out for three different values of N. High resolution camera visualization was used to measure various bulk parameters governing the flow dynamics. Firstly, the spreading height (Zs), defined as the height at which the plume traps in the linearly stratified medium and starts moving horizontally, was measured and compared for different values of N. Secondly, radial intrusion of plume (Rp) is defined as the radius of plume in the neutral buoyant layer, when plume starts moving horizontally was measured and studied for different N. The effect of different N on maximum height of the plume (Zm ) was also studied and compared. Additionally, the plume thickness was also measured & different regimes were demarcated based on the plume propagation rate.

 

46.  Cross-flow transverse force and yaw moment ona semi-displacement vessel with forward speed and drift angle.

Babak Ommani, Odd M. Faltinsen.

Department of Marine Technology, Norwegian University of Science and Technology, Marine Technology Centre Trondheim, NO-7491, Norway.

Abstract :

The hydrodynamic transverse force and yaw moment acting on a semi-displacement vessel with forward speed and drift angle are studied. Following the Froude-hypothesis, the forces are decomposedinto forward-flow potential and cross-flow viscous parts. The cross-flow problem is solved using a 2D+t approximation, disregarding the free-surface effects by applying the rigid surface condition. The evolution of the 2D ship sections in a start-up flow is considered inthe calculations. Finite volume method is used to discretize and solve the Navier-Stokes equations in the fluid domain. Slender body theory is used to extract the viscous part of the obtained transverse force. The results are compared to the simplified cross-flow model presented in [1]. In particular, the distribution of forces due to the cross-flow separation along the ship, and its effect on the obtained yaw moment are considered. A semi-displacement model tested at INSEAN towing tank [2], is chosen as a test-case. The cross-flow corrections are applied to the potential forward-flow results for the drift force and moment from [1] and compared with experimental data ([2]). The results are presented for a set of Froude numbers and two drift angles. The measured values of vessel’s sinkage, trim and heel angles at different drift angles and Froude numbers are adopted from experiments. The importance of the cross-flow-vortex and the freesurface interactions are addressed, as well as the performance of the present method incapturing the behavior of the viscous drift force and moment.

47.  Evaluation of roll damping for PCTCs considering the center of roll motion.

S. LEE, J. HWANG, J. CHOI, H. LEE.

HMRI, Hyundai Heavy Industries Co., Ltd., 1000 Bangeojinsunhwan-doro, Dong-gu, Ulsan, 682-792, Korea.

Abstract :

According to the increasing number of pure car and truck carriers (PCTC), interests in the roll damping of PCTC are on the rise. One of the most general ways to increase the roll damping of ship is to attach bilge keels and the roll damping should be accurately evaluated to determine adequate bilge keel design. In this study, free roll decay tests were carried out in calm water to evaluate the roll damping of PCTC. A new procedure was established to obtain the roll damping coefficients accurately. The pivot point of the towing device was located at a height corresponding to the axis of roll center in order not to interfere theroll motion. From the comparative experiments, the roll damping isfound to be significantly dependent on the pivot point of the towing device and a proper consideration is needed to obtain accurate roll damping.

48.  Theoretical and Numerical Analyses of the ventilation mass’s similarity for finite-length cavities based on volume criteria.

X. Chen, Y. Chen, C.J. Lu, etc.

MOE Key Laboratory of Hydrodynamics, SJTU, Shanghai, China.

Abstract :

For an underwater moving body using artificial ventilation technique, the determination of the scaling law for the ventilation mass is a key step in model tests. In this paper, based on cavity volume criteria four similarity parameters including the natural cavitation number, the ventilated cavitation number, the Froude number, and the Strouhal number are introduced for analyses. From the assumption of finite-length cavities without evident breakage and leakage, the scaling law for mass flux of the ventilated gas is derived. It is directly concerning with not only the geometry scale but also the saturated vapor pressure and the pressure in cavity. In addition, for a given non-rolling underwater vehicle the ventilated cavitating flows are simulated for different scale and ventilation mass by numerical methods. Comparing the theoretical prediction with the numerical simulation, a conclusion can be drawn as follow. The scaling law for the ventilation mass proposed in the present work basically reflects the main flow mechanisms, and has a high precision.

49.  One numerical approach on the ventilated cavitating flow with the two-fluid multiphase flow model.

Jingjun Zhou, Rongrong Li, Kun Tan.

705 Research Institute, China Shipbuilding Industry Corporation, xi’an, China.

Abstract :

In order to quantitatively predict the ventilated cavitating flow and understand the structure of flow field in the ventilated cavity, one numerical method based on the two-fluid multiphase flow model was adopted and in which the SST and DES turbulence model are used separately for steady and unsteady simulations. By comparing the simulating results with experimental data in the water tunnel, the method proposed in this paper can accurately simulate the gas leakage way and the cavity stability. The method in this paper is of important value of engineering.

50.  The Radiation Hydrodynamics Equations and the developed Program coupled Neutron Mass Transport Effect.

Zhenying Hong, Xiangdong Lu, Bo Yang.

Institute of Applied Physics and Computational Mathematics, Department 6,NO.2. Fenghaodong Road, Haidian, Beijing, China.

Abstract :

The neutron has more long mean free path than ion and electron in the considered media. Therefore they can carry the mass, momentum, energy from the media to affect the state of the system. In the D-T fusion target of ICF, scattering neutron source, stellar system, the neutron density is similar to material density. Therefore the change of media mass by neutron transport cannot be ignored. It is very important to study the effect of neutron mass transport to radiation hydrodynamics and to construct the coupled equations for radiation hydrodynamics considering neutron effect. Based on the research of the professor Zuqia Huang and the professor Chengan Liu, we give the radiation hydrodynamics equations coupled neutron mass transport effect and develop corresponding program. We considerthe quality conservation equation, momentum conservation equation, energy conservation equation and give some additional factors in these equations. The additional factors contain transport information about neutron flux. These factors may reflect the impact of the neutron mass migration to the hydrodynamic equations. Based the coupled equations, we developed a corresponding program and consider the multi-physics coupling processes and their relationship. To validate the program and analyze this problem, we construct two models to study this effect to hydrodynamic.

51.  Simulation of a fast speed boat motion in regular waves with help of CFD.

D. Nikushchenko, V. Zverkov.

Faculty of Naval Architecture and Ocean Engineering, St. Petersburg State Marine Technical University, Lotsmanskaya Str. 10, St. Petersburg, 190008, Russia.

Abstract :

The aim of the present work is prediction of pitch and heave motions of a fast shipusing Reynolds averaged Navier-Stokes (RANS) simulations on a base of commercial CFD code NUMECA FINE/Marine. Correct prediction of forces and moments act to a boat in different environmental conditions is very important for design at all its stages for stability and maneuverability calculations. For now scaled models experimental investigation is the most popular way to investigate ship motions, but this way is enough expensive and takes much time. Besides, information obtained during model tests is very limited. Therefore nowadays CFD is very perspective alternative way for investigation of motion of ships. In the present work motor yacht and fishing boat hulls were used for simulations. Ship motions characteristics are investigated by decomposing the full problem into three parts: investigation of ship ahead motion in calm water, investigation of heave motion of ship with ahead speed, investigation of pitch motion of ship with forward speed. Investigations were performed using different models of turbulence. Researches of a ship motion in waves were performed in range ofship velocities and waves parameters. In case of calm water different values of boat speed were also simulated. Results obtained were compared with scale models tests in wide range of Froude numbers, wavelengths and amplitudes.

52.  A Numerical Study of Flexible Hydrofoil in Water Tunnel.

S.L. Hu, C.J. Lu, Y.S. He.

Department of Engineering Mechanics, ShanghaiJiao Tong University, 800 Dongchuan Road, 200240, Shanghai, China.

Abstract :

The closely coupled approach combined the Finite Volume Method (FVM) solver and the Finite Element Method (FEM) solver is applied to investigate the fluid-structure interaction (FSI) of a 3D cantilevered hydrofoil in water tunnel. In the no cavitation flow, the result indicates that the growth of the initial incidence angle and Reynolds number would improve the deformation of the foil, and the lift on the foil would be increased by the twist deformation. The normalized twist angle and displacement along the span of the hydrofoil for different incidence angles and Reynolds numbers is almost uniform. For the cavitation flow, it is shown that the small amplitude vibration of the foil has limited influence on the development of the partial cavity and the quasi two dimensional cavity shedding does not change the deformation mode of the hydrofoil, while the oscillation of the lift on the foil contain two frequencies which is associated to the cavity shedding and the first bend frequency of the hydrofoil.

53.  Cavitation performance of exposed bolt head fastener configurations.

W.A. Straka, J.J. Koncoski, And D.R. Stinebring.

Penn State University / Applied Research Laboratory, State College, PA 16804, United States.

Abstract :

Bolt fasteners in installations of submerged components such aspropellers that are exposed to the flow may cause cavitation and lead to performance and maintenance issuessuch as cavitation erosion. To help mitigate these issues, designers must understand and predict the cavitation performance of these exposed fasteners. In contrast to previous research that used generic shaped isolated surface irregularities, the current study systematically measured cavitation performance on actual standard hex head, socket head and button head fasteners over a number of mounting configurations including flow exposed, surface flush and surface recessed. The desinent cavitation data for each bolt type and mounting condition are collated into scaling equations involving Reynolds number and a characteristic length scale.

54.  Numerical Analysis on the Wind Pressure Characteristics of Combinatorial Hemisphere.

L.J. Yang, P.F. Zhu, X.P. Liu.

Navigation College, Dalian Maritime University, Linghai Road No.1, Dalian, Liaoning, China.

Abstract :

The wind pressure characteristics of combinatorial hemisphere must be complicated due to the spherical tank of Liquefied Natural Gas (LNG) carrier. Accurate wind pressure distribution plays a significant role in studying wind drag coefficient and ship maneuvering capability. In this paper, we focus on the effect of irregular shape and spacing ratio on the wind pressure characteristics of combinatorial hemispheric tank and we only consider the combinatorial hemispheric tank, without considering the ship body under deck. A CFD simulation is performed for flow around single combinatorial hemisphere and flow around two combinatorial hemispheres in tandem arrangement. The size of combinatorial hemisphere model is as the same as the real tank of LNG carrier. The flow simulations are at high Reynolds number of 6.0×107 and the velocity of wind is 18.256m/s. Large Eddy Simulation (LES) is employed to calculate the flow field. Firstly, to validate the capability of the numerical analysis method described in this paper, a simulation of flow around single hemisphere is performed, and the result is in good agreement with experimental data. Then based on this method, flow around single combinatorial hemisphere and flow around two combinatorial hemispheres in tandem arrangement have been simulated. Finally, the flow field structure and wind pressure distribution of combinatorial hemispheres were obtained and discussed. The result shows that the flow field structure of combinatorial hemisphere is more complicated than that of hemisphere and the spacing ratio is a key factor affecting wind pressure distribution and flow structure.

55.  Effect of regular seabed shape on the pressure distribution below hull bottom.

L.J. Yang, Z.Y. Qin, W.B. Zhang.

Navigation College, Dalian Maritime University, Linghai Road No.1, Dalian, Liaoning, China.

Abstract :

In this paper, we worked on the Effect ofregular seabed shape on pressure distribution below hull bottom in restricted water. Based on the computational fluid dynamics (CFD) technology, the flow field around the sailing ship and the seabed sailed was numerically simulated and analyzed. Firstly, a full-scale 3D model of training ship and a regular seabed were established. Secondly, computational domains of flow field were defined according to the above model; with the mesh dividing technology, the high precision hexahedron meshes of flow field were defined and the boundaries of flow field were defined. The Navier Strokes (N-S) equation, mass conservation equation and continuity equation was used tocalculation the variables of fluid. Then numerical simulation of the pressure distribution below hull bottom over two different position of regular object at seabed relative to ship hull was calculated by using ANSYS. In this case, the draft of the ship model was in full loaded condition. Finally, the distribution of the pressure below hull bottom was calculated at 1.3 of H/d ratio, full loading condition and sea speed. Based on the experimental result, it can be confirmed that: the pressure distribution below hull bottom can be affected by the uneven seabed; the pressure distribution is different with the change of the position of regular object at seabed relative to ship hull.

56.  Three-dimensional numerical modeling of wind-driven circulation in the Taihu Lake.

J. Zhou, Q.L. Yang.

College of Mechanics and Materials, Hohai University, Nanjing, 210098, China.

Abstract :

In aquatic basins such as shallow lakes and coastal regions, wind stress plays a major role in the formation of wind-driven current. In the present study, a three-dimensional numerical model was developed to simulate the wind-driven current in the Taihu Lake, P. R. China. The governing equations are the unsteady Reynolds-Averaged Navier-Stokes (RANS) equations in which the nonhydrostatic pressure distribution is included. Six existing formulae were used to estimate the drag coefficient (Cs) against the wind velocity. The model was firstly tested with a case of the wind-driven flow in an open channel. The numerical results are found to agree better with the analytical solution by adopting the formula proposed by Large and Pond [1]. Once the numerical model was verified, the model was used to generate typical circulation patterns for a variety of conditions in the Taihu Lake. The wind event of Mar 2000 was reproduced in particular due to the algae bloom. A good agreement was reached in the comparison of the calculated and measured water level at Xishan station. The numerical model is able to accurately predict the large-scale current circulation in Taihu Lake under a prevailing wind condition. It also suggests that the non-hydrostatic pressure distribution do not have any noticeable impact on the overall circulation pattern in the Taihu Lake. Moreover, the reasons of algae blooms at Meiliang Bay in 2000 were discussed based on the numerical results.

57.  Causal Representation of Wave Forces For Time-Domain Simulation of Maneuvering And Seakeeping Problems.

Gregory Vilensky, Dmitry Nikushchenko, Sergey Zaikov.

KM Tech LLC, Kongsberg Group, Rizhskaya Str. 1,St. Petersburg, 195196, Russia.

Abstract :

An  algorithm  for  the  time  domain  computation  of  wave  radiation  forces  which  does  not  require  calculation  of  Cummins’s retardation functions is formulated. Ease of numerical implementation, high computational speed and good tolerance to the input data irregularities make it an efficient modelling tool for real time ship simulators.  An extension of Cummins’s time-domain causal approach to the exciting force modelling is presented in the second part of the paper.

58. Effect of Propeller Wash on Distribution of Natural Sedimentation around the Marina Bay Cruise Centre in Singapore.

M. Jain, H.H. Nguyen, E. Precht, T.M. Foster, C. Chung, E. Tan.

DHI Water & Environment (Singapore), CleanTech One, 1 Cleantech Loop #03-05, Singapore 637141, Singapore.

Abstract :

Extensive study was carried out to analyze the effect of propeller wash on the distribution of natural sedimentation around the container terminals in the vicinity of Marina Bay Cruise Centre in Singapore (MBCCS). Literature review had led to the basic understanding of the governing parameters influencing the propeller wash and its effect on the seabed. AIS data was used to understand the ship tracks, vessel traffic, type of vessel and the under keel clearance to the existing nearby terminals. Forces on the vessel along the track, during maneuvering, were quantified from a two dimensional desktop navigation study. These forces were then converted to estimate the bed shear stress of erosion and sediment resuspension due to propeller wash action. Field surveys were undertaken to collect the sediment flux data behind moving vessels to record the suspended sediment concentration (SSC) from the propeller action, which was further used to calibrate the SSC obtained from the empirical equations. DHI MIKE 21 hydrodynamic and morphology model was then applied to simulate larger scale effects of propeller wash on the seabed morphology, sedimentation and distribution of bed sediments from vessel movements at an existing container terminal nearby MBCCS. Finally the bathymetrydata was used to verify the results of the simulation.

59.  Analysis of fule tank baffles to reduce the impact generated from liquid sloshing.

G.H. Xu, J.J. Hu, X.K. Gu.

China Ship Scientific Research Center, Wuxi, 214082, Jiangsu, China.

Abstract :

The aim of this paper is to simulate liquid sloshing motions and impact loads on the inner hull in a tank. The simulations were conducted by using the computational fluid dynamics code based on finite volume method with the volume of fluid method and dynamic mesh techniques. 3D proportional numerical models were established for the sake of variousinner configurations of oil tanker hold, and simulations in different cases were carried out to analyze the effect of horizontal baffles and transverse bulkhead on restraining the liquid tank sloshing and reducing the impulse pressure. Some valuableconclusions were drawn and they are meaningful to evaluation of sloshing loads by formula.

60  Moisture Content Limit of Iron Ore Fines for the Prevention of Liquefaction in Bulk Carriers.

M.C. Munro, A. Mohajerani.

School of Civil, Environmental and ChemicalEngineering, RMIT University, Melbourne, Victoria, Australia.

Abstract :

In 2013, over 500 million tonnes of Iron Ore Fines (IOF) were transported around the world using bulk carriers, more than any other unrefined mineral. Since the holds of bulk carriers have notbeen designed to carry liquid, if liquefaction of IOF or other minerals occur it can cause the vessel carrying the cargo to list or even capsize. Since 2006, there have been at least eight reported bulk carrier incidents possibly caused by the iron ore cargo shifting. Currently, the only available parameter used to prevent this from occurring is the Transportable Moisture Limit (TML). The TML is the maximum gross water content that certain mineral cargoes may contain, while being loaded inbulk carriers, without being at risk of liquefying during transportation. The objective of this study is to compare the three test methods stated in the 2013 International Maritime Solid Bulk Cargoes Code (IMSBC Code), which are used to determine the TML of IOF. They are the Proctor/Fagerberg, Flow Table and Penetration test methods. The study alsocovers recent developments and advancements made in the field, which includes the Modified Proctor/Fagerberg test along with goethite content provisions, which are included in the 2013 draft individual schedule for IOF, and to be amended in the 2015 IMSBC Code. This study shows that the three test methods, stated in the 2013 IMSBC Code, which are used to determine the TML of minerals, are not appropriate for testing of IOF and that recent developments, such as the Modified Proctor/Fagerberg test along with goethite content provisions, permits IOF to be transported at higher moisture contents than if one of the previous three test methods were used.