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 (81-100)

81.  Hydrodynamic Optimization of a TrisWACH.

C. Yang, F. Huang, H.Y. Kim, H.Y. Kim.

School of Physics, Astronomy and Computational Sciences, George Mason University, Fairfax, VA 22030, USA.

Abstract :

A new methodology for hydrodynamic optimization of a TriSWACH is developed, which considers not only the positions of the side hulls but also the shape of the sidehulls. In order to account for the strong near-field interference effects between closelyspaced multihulls, an integrated hydrodynamic computational tool that consists of a potential-flow based simple CFD tool and an Euler/RANS/Navier-Stokes based advanced CFD tool has been further developed and integrated into a practical multi-objective hydrodynamic optimization tool. The other components of this hydrodynamic optimization tool consist of a hull shape representation and modification module and an optimization module. This enhanced multi-objective hydrodynamic optimization tool has been applied to the hydrodynamic design optimization of the TriSWACH for reduced drag by optimizing the side hulls only. A new methodology is developed to optimize side hull forms so that the TriSWACH has a minimal drag for a wide speed range and for various side hull positions. Two sets of the side hulls are developed and used for the design of two optimal TriSWACH models. Model tests are carried out for two optimal TriSWACH models at Webb Institute for validations. Substantial drag reductions have beenobtained for a wide range of speed.

82.  Natural frequency of 2-dimensional horizontal cylinders heaving on free surface.

S.J. Lee, J. Song.

Department of Naval Architecture & Ocean Engineering, Chungnam National University, Gung-dong Yuseong-gu, Daejeon, S. Korea.

Abstract :

Following the recent studies on the natural frequency of heaving circular cylinder, this deals with a similar investigation on 2-dimensional heaving cylinders of Lewis form. Well-known method,ie the Ursell-Tasai method was applied to get hydrodynamic forces, and in turn they were used to obtain motion characteristics including the natural frequency of the cylinder. A few frequencies, each of which can be regarded as the natural frequency of the heaving cylinder, are defined, computed, compared and discussed. It is found that the frequency corresponding to the minimum of the added mass can be used as a first approximation to the heave natural frequency for cylinders of beam-draft ratio less than 2.5.

83.  The combining effects of inlet guide vanes and blade setting angles on performance of axial-flow pump system.

W.M. Feng, Q. Cheng, C.G. Zhou, Z.W. Guo.

School of Water Resources and Hydropower Engineering, Wuhan University, Hubei, China.

Abstract :

The combining effects of variable-inlet guide vanes and blade setting angles on performance of axial flow pump system are investigated. The commercial software FLUENT is used to simulate the performance. The results show that for each blade setting angle, pump performance is improved by adjusting the angles of inlet guide vanes from positive value to negative value. For different blade setting angles, the angles of inlet guide vanes producing the highest efficiency are different. Although the efficiency ranges of adjusting either the angles of inlet guide vanes or blade setting angles are limited, the combining effects of both methods can broaden the high efficiency region of axial flow pump.

84.  The characteristic analysis of propeller disturbed flow field.

Chen Ke, Qian Zheng-Fang, Jiang Jing-Wei,Ma Cheng, Cai Hao-Peng.

Naval Armament Academy, Beijing, 100161, China.

Abstract :

The panel method was used to predict the wake flow field of propeller. According to Green’s formula, integral equation of the surface velocity potential of propeller could be derived, then solve it by discrete method of the panel method. Some quadrilateral hyperbolic panels were distributed on the blade, propeller hub and wake surface, and the source-sink and the dipole was evenly distributed on the panels. According to integral equation, the strength of the dipole and the source-sink could be solved by combining with Kutta condition and kinematics boundary condition, Morino formula was used to solve induced velocity to the flow field by the source-sink and the dipole which were evenly distributed. The induced velocity of propeller in the wake flow field after the propeller was calculated, then analyzed the constitution and pulsating character of the induced velocity of propeller.

85.  Numerically Calculating Method for the Unsteady Hydrodynamic performance of Podded Propellers.

Qian Zheng-Fang, Chen Ke, Ma Cheng, Cai Hao-Peng, Jiang Jing-Wei.

Naval Armament Academy, Beijing, 100161, China.
Naval University of Engineering,Wuhan,430033,China.

Abstract :

A numerical method has been developed for predicting the unsteady hydrodynamic forces acting upon a propeller mounted on a pod. The method is based on a vortex lattice method for the propeller blades and a surface panel method for the pod. The unsteady velocities induced by propeller blades are time-averaged at the control points on the pod surface, while the propeller is considered to operate in a spatially inhomogeneous inflow due to the presence of the pod and the hull. Numerical computations are carried out for a 4-bladed propeller mounted on a pod, without and with the hull. The steady thrust and torque measured in a cavitation tunnel are used to partly validate the present method. The effect of pod on unsteady propeller forces and moments are discussed based on numerical results.

86.  Probability Sensitivity Analysis of Extreme Second-order Roll Motion Predictions for A Turret Moored FPSO.

Young Jun Son, Joong Soo Moon, Woo Seung Sim, Hyun Soo Shin.

Advanced Technology Institute, Hyundai Heavy Industries Co., Ltd, Ulsan, 682-792, Korea.

Abstract :

In the design of FPSOs (Floating, Production,Storage and Offloading) in harsh environments, the second-order roll behavior is one of major concerns to operators. For the sake of safe and cost-effective design, the extreme response prediction is inevitable. However, this prediction inherently contains uncertainty originated from the probabilistic approach. In the present paper, probabilistic sensitivities of extreme second-order roll motion predictions have been investigated for a turret-moored FPSO. Time domain simulations for representative storms are performed to take account of second-order responses. Applying the peak over threshold approach, which is also referred to as the storm based approach, extreme responses are determined with respect to the probability distributions and the number of data to fit. Comparing the results, it is found that the extreme responses are sensitive to the probabilistic variables. Recognizing the probabilistic uncertainty for predicting extreme second-order roll motions will help to understand their nature and achieve the safe and cost-effective designs of floating production systems.

87.  Utilizing CFD as a tool for sump model design.

I.H. Ibrahim, A. Gulam, R.A. Latip.

Adzaan Consulting PTE LTD, Singapore.

Abstract :

In this study, we present the results of Computational Fluid Dynamics (CFD) simulationson two geometrical designs: a rectangular trench-like sump and a general circular sump. The performance of these sump designs are verified with guidelines by the British Hydrodynamic Research Association (BHRA) as well as the Hydraulic Institute (ANSI – HI 9.8). These guidelines include the presence of surface and submerged vortices, swirl flow through the pumps and air bubbles entrainment. In addition to these parameters, the collection of wastewater scum has also been traditionally identified as potential problems by sump designers. By coupling Lagrangian Particle Tracking (LPT) in the multiphase model, a viable CFD tool for the prediction of wastewater scum is employed. Although it is not claimed that CFD can replace physical modelling, the exercise shows that CFD is a powerful tool to supplement the experience and hydraulic expertise of the pumping station designer.

88.  Added Mass and Damping Coefficients for a uniform flexible barge using VoF.

J.H.Kim, P.A.Lakshmynarayanana, P.Temarel.

Department of Naval Architecture and Ocean Engineering, Seoul National University, Gwanak-gu, Seoul, South Korea.

Abstract :

The main aim of this paper is the numerical investigation of the effect of domain size and mesh density on modeling the three dimensional (3-D) the radiation problem using RANS CFD software. The solution for the radiation forces and moments, namely the added mass and damping coefficients, is obtained by imposing a simple harmonic oscillation to a marine structure floating in still water at the relevant mode shape. A uniform barge is used to illustrate the investigation, with the relevant symmetric mode shapes provided from the Euler beam theory. The hydrodynamic coefficients for symmetric oscillations of the barge are evaluated using an inviscid flow model in STAR-CCM+. These include the rigid body motions of heave and pitch and the 2- and 3-node distortion mode shapes. A range of mesh densities, between 1.1M and 9.6 M, are used to examine their effects with particular reference to low and high frequencies and the cross-coupling hydrodynamic coefficients between rigid and distortion modes. The influence of the damping zone on the solution is also examined. The RANSCFD predictions are compared with the results from a three-dimensional potential flow boundary element method, allowing for hull distortions.

89. Design and Analysis of a Flow-through Bag Aquaculture System.

D. K. Das, N.J. Bhat.

Marine and Offshore Technology, Centre ofInnovation, Ngee Ann Polytechnic, 535 Clementi Road, 599489, Singapore.

Abstract :

To meet the growing demand of fishes, fish farmers in the city country of Singapore need an alternative method beyond the traditional sea based net-aquaculture method which is labour intensive and contamination prone. A novel method called Flow through bag aquaculture system has been proposed in which the net is replaced by a bag in the open sea. The bag will be used to hold fishes and treated water is pumped in, thereby closely controlling the water quality in the bag. The water containing the fish waste has to be then periodically released from a one-way valve in the bottom of the bag. In this study a design of the bag based on the constraints is proposed such that it has maximum volume, minimum drag resistance and also allows easy waste collection and release. Then a numerical simulation of the flow around the bag and the fluid structure interaction analysis to evaluate the feasibility of the bag under the effect of ocean current and waves is carried out. The maximum spring tide current velocity (1m/s) in the Straits of Johor is used for this analysis. A parametric study on the thickness of the bag verses deformation and stress concentration is also carried out. The required freeboard of the bag is then analysed for the ocean current with and without the waves. The recommendations made from the analysis were used to modify the final bag design and also decide the overall installation and reinforcements required for the bag. The bag has since been installed at a fish farm near Singapore and the method has been running successfully for over a year now.

90.  A model for inhomogeneous oscillations near the stopping angle in an inclined, granular flow.

D. S. Tan, P. Richard, J. T. Jenkins.

Department of Mechanical Engineering, National University of Singapore, Singapore 117575, Singapore.

Abstract :

Recent numerical simulations of inclined granular flow report that oscillations appear when the angle of inclination is near the stopping angle. These oscillations are of particular interest as they present a possible explanation for the ‘booming’ phenomenon – the production of low frequency sound during spontaneous avalanches in the desert. This paper presents an extension on an existing theoretical model for oscillations in a dense inhomogeneous flow of inelastic, frictional spheres down an inclined slope driven by a phase transition between ordered and random collisional states. The model involves a cubic relationship between the normalized pressure and the solid volume fraction that links the pressures of the random collisional and ordered collisional phases. The onset of oscillations occurs when the solid volume fraction increases, corresponding to a decrease in the inclination angle towards the stopping angle. Numerical simulations results show that the amplitude of the oscillations varies with depth in the flow and the system eventually settles into a steady flow, with an inhomogeneous solid fraction distribution.

91.  Numerical simulation of two-phase flows with the Consistent Particle Method.

M. Luo, C.G. Koh, M. Gao, W. Bai.

Department of Civil and Environmental Engineering, National University of Singapore, 1 Engineering Drive 2, 117576, Singapore.

Abstract :

A recently developed Consistent Particle Method (CPM) is extended to model two-phase flows characterized by high density ratio. Eliminating the use of kernel function, the CPM computes spatial derivatives by the Generalized Finite Difference (GFD) scheme which is based on Taylor series expansion. For two-phase flows, however, this scheme cannot be directly applied near the fluid interface because the abrupt discontinuity of fluid density results in large variation in pressure gradient. To resolve this problem, the formulation uses the normalized pressure gradient term, whose values are in the same order of magnitude in the two fluids across interface, leading to the two-phase version of CPM. The benchmark example of Rayleigh-Taylor instability and water-air sloshing in a closed tank are studied to demonstrate the performance of this method. Laboratory experiments are conducted to partially verify the numerical results.

92.  Recent advancement in Tendon Technology for Deepwater Application.

Z.Y. Tay, H.D. Nguyen, W.P. Wang.

Keppel Offshore and Marine Technology Centre, 31 Shipyard Road, Singapore 628130.

Abstract :

As exploration and production venture moves into the deepwater region, the design, operation, installation and maintenance of tendon become more challenging and current technologies are being seen as inadequate to meet future operational requirements. Hence, there is a need to search for alternative materials and technologies that could improve the operational performance of the tendons as well as provide a cost effective solution. This paper presents an overview of recent developments of tendon technology for deepwater applications. It highlights new techniques and key issues addressed during these developments including various effects of deepwater to the conventional tendon technology.

93.  Challenges and potential of extended tension leg platform in ultra-deepwater.

Z.Y. Tay, V.Z. Yordanov, V. Mihalev, A. Choudhary.

Keppel Offshore and Marine Technology Centre, 31 Shipyard Road, Singapore 628130.

Abstract :

Tension leg platform (TLP) is a floating production system that is vertically moored to the sea floor by using the tendon technology. As the tendons are always in tension, the heaving motion of the TLP is very small as compared to other type of floaters. This enables the incorporation of dry tree solution which is low in operational cost (OPEX). To date, the world deepest TLP is built for the ‘Big Foot’ field in the Gulf of Mexico (GOM) up to a water depth of 1,581 m (5,187 ft).Water depth beyond this limit would be a great challenge to the TLP. In this article, the state of the art review of ultra-deepwater TLP will be presented and the challenges in the hull design, global performance, tendon design as well as the riser design will be addressed.

94.  The New Generation Semi-Submersible Drilling Tender (SSDT).

Aziz A. Merchant, Anis Hussain, Murthy Pasumarthy.

Keppel Offshore & Marine Technology Centre (Deepwater), Deepwater Technology Group (DTG), Keppel FELS (Engineering), Singapore.

Abstract :

The aim of this paper is to present the Semisubmersible Drilling Tender as the supreme drilling and well work-over alternative for shallow water and marginal field developments, and how advances in drilling tender design enables tender assisted drilling in deep-water areas will be discussed. In particular the six column KFELS SSDT design series is described, showing the latest development in semisubmersible tender and design. This paper examined the benefits of utilizing a six column semisubmersible drilling tender over conventional drilling rig configurations; in particular the advantages this configuration gives in terms of operational mobility and flexibility. Typical tender operations are discussed to give insight into the relationship between good tender design and operability, while aspects of hydrodynamic behavior and station keeping system are presented in more detail. As a world leader in the construction of offshore structures, Keppel FELS has a commendable track record in semisubmersible drilling tender design and construction. The near market, near customer strategy for achieving excellence and customer satisfaction will also be touched on.

95. Performance Analysis of Massively-Parallel Computational Fluid Dynamics.

J. Hawkes, S.R.Turnock, S.J. Cox, A.B. Phillips.

Fluid Structure Interactions (FSI),University of Southampton, UK & MARIN Academy, Maritime Research Institute Netherlands, Netherlands.

Abstract :

As modern supercomputers edge towards exascale, their architectures are becoming more parallel. In order for computational fluid dynamics (CFD) simulations to operate efficiently on newer machines, a complete harmony between hardware, software and numerical algorithms is required. In the work presented here, a typical CFD code is instrumented, and a strong-scalability study performed to identify areas of the execution which require improvement, using the well-known KVLCC2 test case. The effects of changing discretization schemes, mesh structure, turbulence models and linear solvers are all tested. The results show that data-exchange among cores and the inner-loop pre-conditioners both have a large impact on performance in a massively parallel environment, and should be the focus of future developments.

96.  Tidal-and density-driven flows in submerged vegetation.

W. Z. Kwong, V. P. Chua.

Department of Civil & Environmental Engineering, National University of Singapore, Singapore 119077, Singapore.

Abstract :

Aquatic plants are commonly found in estuarine environments that are driven by tides and river inflow. A three-dimensional model is employed to investigate the effects of tides and inflow on flow over submerged vegetation. The model is tidally forced at the downstream end and freshwater inflows are imposed at the upstream end. The model is run until the tidally-averaged velocity and salinity profiles achieve steady state. A comparison is made for runs that are unstratified with no tidal mixing, unstratified with tidal mixing and stratified with tidal mixing. Our results indicate stratification-induced changes to the tidally averaged velocity and turbulence profiles in the presence of vegetation. The velocity is enhanced at the top of the canopy and reduced at the salinity interface. The turbulent kinetic energy is reduced across the vertical with maximum at the top of the canopy. There are no significant changes to the tidally-averaged velocity and turbulence profiles for unstratified runs with/without tidal mixing.

97.  Prediction of Responses of Floating Production Systems using the Multi Gaussian Maximum Entropy Method.

U. Alibrandi, C.Y. Ma & C.G. Koh.

Department of Civil and Environmental Engineering, National University of Singapore, 1 Engineering Drive 2 117576, Singapore.

Abstract :

The dynamic analysis of a deepwater floating production systems has many complexities, such as the dynamic coupling between the  vessel and  the  lines, the  coupling  between the  first-order and  second-order  wave  forces,  several  sources of nonlinearities. These complexities can be captured by fully coupled time domain analyses. However  they require an enormous computational cost, especially for the evaluation of the extreme values, which are of great interest for practical reliability design purposes. In this  paper the non-Gaussian  probability density functions of the responses are  evaluated through a novel moment-based approach, based on the Maximum Entropy  principle. The application to a simplified 2 degrees-of-freedom model shows the accuracy and effectiveness of the presented procedure.

98  Drag Reduction in Water by Superhydrophobicity Sustained Leidenfrost Vapor Layers.

I U. Vakarelski, J. O. Marston, S. T. Thoroddsen, D. Y. C. Chan.

Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia.

Abstract :

One innovative approach to achieve drag reduction on a solid body moving in liquid is to introduce a lubricating gas layer between the body surface and the surrounding liquid. We demonstrate and quantify a highly effective hydrodynamic drag reduction technique that exploits the Leidenfrost effect to create continuous and robust lubricating vapor layer on the surface of a heated solid sphere moving in a liquid. When a perfluorinated liquid with low boiling point is used we show that such vapor layers can reduce the hydrodynamic drag by over 85%. These results appear to approach the ultimate limit of drag reduction possible by different methods based on gas-layer lubrication. To extend this approach to aqueous medium we use a nanoparticle coating to make a steel sphere surface superhydrophobic resulting in a reduced initiation temperature, and enhanced dynamic stability of the vapor layer. The vapor layer induces a gradual reduction of the dragcoefficient on heated spheres freely falling in water. In addition to the drag reduction we found that such vapor layer can also stabilize the sphere fall trajectory. The drag reduction is shown to operate in the Reynolds number range that spans the drag crisis in the absence of the vapor layer. The drag reduction and drag crisis moderation are attributed to the disruption of the viscous boundary layer by the vapor layer. The results of this study are expected to stimulate the ongoing efforts to develop effective and unexpansive drag reduction technologies based on the sustainability of vapor layer on textured superhydrophobic surfaces.

99.  Simulating water waves generated by underwater landslide with MPS and WC-MPS.

Mohammad Amin Nabian, Leila Farhadi.

Department of Civil and Environmental Engineering, The George Washington University, 2121 Eye Street, NW, Washington, DC 20052, USA.

Abstract :

Moving Particle Semi Implicit Method (MPS) is a mesh-free numerical approach which discretizes PDEs to provide approximations on the basis of integral interpolants. This method uses a fractional step method and splits each time step into two steps. In this paper, MPS method is used to solve inviscid Navier-Stokes equations in a fully Lagrangian form. The fluid is represented with particles and the motion of each particle is calculated through interactions with neighboring particles by means of a kernel function. Both the incompressible model and the weakly compressible model (WC-MPS) are considered in this paper and are used to simulate the water waves generated by submarine landslides. Landslides in this paper are simulated by a submerged rigid wedge sliding along an inclined plane into a water tank. As the wedge sinks, a wave and a vortex is formed. Water surface profile and pressure field are represented at different times and the results of incompressible and weakly compressible models are compared with each other. To confirm the accuracy, water surface profiles are compared with the experimental data, showing good agreement for both models.

100.  Modelling of oil-water flow patterns and pressure gradient in horizontal pipes.

T. Al-Wahaibi, Y. Al-Wahaibi, F. S. Mjalli, B. Al-Busaidi.

Petroleum and Chemical Engineering Department, Sultan Qaboos University, Muscat 123, Oman.

Abstract :

Quiet large number of studies is currently available in the literature on flow pattern and pressure drop in horizontal oil-water flow. However, very few studies have attempted to  develop a model that predicts the flow patterns and pressure gradient for oil-water flow. This is attributed to the complexity of the flow in oil-water flow. In this study, a new methodology is developed to predict the flow patterns and pressure gradients in horizontal oil-water pipes. AlWahaibi and Angeli (2009) entrained fraction model and phase inversion point are used to predict the flow pattern maps. The two-fluid model, homogenous model and a modified two-fluid model with entrainment are used to predict the pressure gradient. The performance of the model is tested against several experimental data. In general, however, the  predictions are very good taking into account the  diversity of conditions used in the  various works but most importantly the ambiguity that exists in defining the transitions between the different flow patterns.