Numerical Investigation of Heaving Hydrodynamic Behavior of a Single Cylinder and a Dual Coaxial-Cylinder System Using CFD

2020 ◽  
Author(s):  
Pengfei Zhi ◽  
Xinshu Zhang ◽  
Ke Chen ◽  
Ronald W. Yeung
Keyword(s):  
Outer Cylinder ◽  
Mesh Size ◽  
Computer Code ◽  
Coaxial Cylinder ◽  
Hydrodynamic Performance ◽  
Hydrodynamic Coefficients ◽  
Hydrodynamic Behavior ◽  
Time Step ◽  
Cfd Models ◽  
Free Decay

Abstract In this paper, we apply a CFD computer code to study the hydrodynamic behavior of a stand-alone cylinder and a dual coaxial-cylinder system (DCCS) via free-decay motion tests. The geometric proportions of a stand-alone cylinder and the inner and outer cylinder of the DCCS are chosen to be the same as those in [1] and [2], respectively, as ocean wave-energy converter (WEC) devices. Overset mesh based on the commercial code ‘Star-CCM+ 11’ is used to simulate the free-decay motion of the two systems. Five parameters chosen for the CFD implementation are: turbulence model, initial displacement, time step, number of prism layers and mesh size. Results obtained from using different values of these parameters are compared so as to confirm the validity of choices made. The hydrodynamic performance of the stand-alone cylinder and outer cylinder in the DCCS are compared with the experimental results to assess and validate the CFD models. In addition, the heave hydrodynamic coefficients, namely, the added mass and total damping, and ‘resonance’ frequency of the stand-alone cylinder and those of the inner cylinder of the DCCS, with the outer cylinder being fixed, are obtained by using the CFD procedure. The hydrodynamic coefficients of another stand-alone cylinder with the same dimensions as the inner cylinder of the dual-coaxial cylinder are also obtained by simulations. The vorticity-contour plots for the stand-alone cylinder and the outer cylinder in the DCCS in free-decay motion are presented and analyzed. Finally, the results of the three cases are compared to examine the effect of the outer cylinder on the heave hydrodynamic coefficients of the inner cylinder.

Motion Response Control of the DWSC Spar Based on State-Space Model

2012 ◽  
Author(s):  
Xiaochuan Yu ◽  
Jeffrey Falzarano
Keyword(s):  
State Space ◽  
Transfer Functions ◽  
State Space Model ◽  
Development Program ◽  
Naval Research ◽  
Hydrodynamic Coefficients ◽  
Time Step ◽  
Response Control ◽  
Motion Response ◽  
Space Model

In 2007, the Office of Naval Research (ONR) started a technology development program called STLVAST (Small to Large Vessel At-Sea Transfer), in order to develop ‘enabling capabilities’ in the realm of logistic transfer (i.e. stores, equipment, vehicles) between a large transport vessel and a smaller T-craft ship, using a Deep Water Stable Crane (DWSC) spar between them. In this paper, the equation of motions of the single DWSC spar is initially expressed as the standard state-space model. Then the ODE solver of Matlab is directly employed to obtain the motion responses at each time step. Two levels of approximation of hydrodynamic coefficients are considered in this study. One is the Constant Coefficient Method (CCM), and the other one is the Impulse Response Function (IRF) method, with fluid memory effects considered. WAMIT software is used to calculate the hydrodynamic coefficients, including the added mass, radiation damping, IRF, the first order and second order waves loads transfer functions, etc. The motion response control is achieved by assuming the thrusters can provide the optimal feedback force derived from Linear Quadratic Regulator (LQR) method.

scholarly journals Numerical Method of Fabric Dynamics Using Front Tracking and Spring Model

2013 ◽  
Vol 14 (5) ◽  
pp. 1228-1251 ◽  
Author(s):  
Yan Li ◽  
I-Liang Chern ◽  
Joung-Dong Kim ◽  
Xiaolin Li
Keyword(s):  
Upper Bound ◽  
Mesh Size ◽  
Front Tracking ◽  
Time Step ◽  
Mass System ◽  
Ode System ◽  
Spring System ◽  
Fabric Surface ◽  
Mass Spring ◽  
Eigen Frequency

AbstractWe use front tracking data structures and functions to model the dynamic evolution of fabric surface. We represent the fabric surface by a triangulated mesh with preset equilibrium side length. The stretching and wrinkling of the surface are modeled by the mass-spring system. The external driving force is added to the fabric motion through the “Impulse method” which computes the velocity of the point mass by superposition of momentum. The mass-spring system is a nonlinear ODE system. Added by the numerical and computational analysis, we show that the spring system has an upper bound of the eigen frequency. We analyzed the system by considering two spring models and we proved in one case that all eigenvalues are imaginary and there exists an upper bound for the eigen-frequency This upper bound plays an important role in determining the numerical stability and accuracy of the ODE system. Based on this analysis, we analyzed the numerical accuracy and stability of the nonlinear spring mass system for fabric surface and its tangential and normal motion. We used the fourth order Runge-Kutta method to solve the ODE system and showed that the time step is linearly dependent on the mesh size for the system.

scholarly journals Estimation of Optimal Time Step and Compare with of ODE Solver of MATLAB Package of RLC Circuit using Numerical Methods

1970 ◽  
Vol 7 (1) ◽  
pp. 67-73 ◽  
Author(s):  
Sheikh Md Rabiul Islam
Keyword(s):  
Mesh Size ◽  
Paper Analysis ◽  
Optimal Time ◽  
Time Step ◽  
Minimum Error ◽  
Optimal Output ◽  
Runge Kutta Method ◽  
Rlc Circuit ◽  
Matlab Package ◽  
Theoretical Results

In this paper analysis of a RLC circuit model that has been described optimal time step and minimize of error using numerical method. The goal is to reach the optimal time response due to the input for which optimal output response reaches a minimum error and also compared with ODE solver of MATLAB packages for the different cell (mesh) size of the RLC model. Table is constructed of the model to evaluate optimal time step and also CPU time into the simulation using MATLAB 7.6.0(R2008a).The values of register, capacitor and inductor as well as electromagnetic force are obtained through the mathematical relations of the model. The general analysis of the RLC circuit due to the optimal time step and minimum error is developed after several analysis and operations. The theoretical results show effectiveness of optimized of the model. Keywords: Optimal time step; MATLAB; Trapezoidal; Implicit Euler; Runge-Kutta method; RLC circuit. DOI: http://dx.doi.org/10.3329/diujst.v7i1.9650   Daffodil International University Journal of Science and Technology Vol.7(1) 2012 67-73

A Finite-Element Solution of Thermal Distortion with Applications to Thrust Bearings

1984 ◽  
Vol 28 (04) ◽  
pp. 282-289
Author(s):  
James H. Ma
Keyword(s):  
Finite Element ◽  
Hot Spot ◽  
Mesh Size ◽  
Computer Code ◽  
Development Project ◽  
Element Space ◽  
Element Mesh ◽  
Data Set ◽  
Mechanical Responses ◽  
Nonlinear Temperature

A finite-element code to account for thermal expansion in a solid was developed for the Independent Research and Independent Exploratory Development project "Tribology of Sliding Surface Bearings." The program is based on a two-dimensional model using a second or higher-order interpolation function in the element space that will allow a diverse temperature field, such as a steep nonlinear temperature gradient, to be prescribed in a solid body. The computer code has a definite advantage over certain finite-element systems that are commercially available. Many accept only a constant, or averaged, temperature input into their element space. With the new capabilities, complex thermal mechanical responses under severe temperature gradients can be readily analyzed. For instance, the hot spot in a ship's landing deck due to the concentrated heat load, such as those generated by high-temperature jet exhaust, can be more realistically represented by the elements of current development. The element mesh size and the input data set are more manageable.

Experimental Testing and Numerical Modeling of Small-Scale Boat With Drag-Reducing Air-Cavity System

2021 ◽  
Author(s):  
Jeffrey M. Collins ◽  
Phillip R. Whitworth ◽  
Konstantin I. Matveev
Keyword(s):  
Adaptive Mesh Refinement ◽  
Experimental Testing ◽  
Hydrodynamic Performance ◽  
Small Scale ◽  
Video Monitor ◽  
Data Logger ◽  
Time Step ◽  
Experimental Conditions ◽  
Air Cavity ◽  
Air Supply

Abstract Hydrodynamic performance of ships can be greatly improved by the formation of air cavities under ship bottom with the purpose to decrease water friction on the hull surface. The air-cavity ships using this type of drag reduction are usually designed for and typically effective only in a relatively narrow range of speeds and hull attitudes and sufficient rates of air supply to the cavity. To investigate the behavior of a small-scale air-cavity boat operating under both favorable and detrimental loading and speed conditions, a remotely controlled model hull was equipped with a data acquisition system, video camera and onboard sensors to measure air-cavity characteristics, air supply rate and the boat speed, thrust and trim in operations on open-water reservoirs. These measurements were captured by a data logger and also wirelessly transmitted to a ground station and video monitor. The experimental air-cavity boat was tested in a range of speeds corresponding to length Froude numbers between 0.17 and 0.5 under three loading conditions, resulting in near zero trim and significant bow-up and bow-down trim angles at rest. Reduced cavity size and significantly increased drag occurred when operating at higher speeds, especially in the bow-up trim condition. The other objective of this study was to determine whether computational fluid dynamics simulations can adequately capture the recorded behavior of the boat and air cavity. A computational software Star-CCM+ was utilized with the VOF method employed for multi-phase flow, RANS approach for turbulence modeling, and economical mesh settings with refinements in the cavity region and near free surface. Upon conducting the mesh verification study, several experimental conditions were simulated, and approximate agreement with measured test data was found. Adaptive mesh refinement and time step controls were also applied to compare results with those obtained on the user-generated mesh. Adaptive controls improved resolution of complex shedding patterns from the air cavity but had little impact on overall results. The presented here experimental approach and obtained results indicate that both outdoor experimentation and computationally inexpensive modeling can be used in the process of developing air-cavity systems for ship hulls.

Numerical Simulation Study on the Recovery Process of Autonomous Underwater Vehicle

2021 ◽  
Author(s):  
Weigang Huang ◽  
Donglei Zhang ◽  
Jiawei Yu ◽  
Tao He ◽  
Xianzhou Wang
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Autonomous Underwater Vehicle ◽  
Flow Characteristics ◽  
Recovery Process ◽  
Underwater Vehicle ◽  
Hydrodynamic Performance ◽  
Time Step ◽  
Convergence Test ◽  
Motion Paths

Abstract AUV (Autonomous Underwater Vehicle) recovery is considerably influenced by the nearby flow field and simulations of AUV in different motion paths in the wake of a submarine with a propeller are presented in this paper. A commercial CFD solver STAR CCM+ has been used to research the motion and flow characteristics of AUV, which using the advanced computational continuum mechanics algorithms. The DARPA (Defense Advanced Research Projects Agency) SUBOFF Submarine (L1 = 4.356m) propelled with INSEAN (Italian Ship Model Basin) E1619 propeller is used in this study, and the self-propulsion characteristics of the propeller at an incoming flow velocity of 2.75m/s are obtained through numerical simulation and results are compared with the available experimental data to prove the accuracy of the chosen investigation methodology. A grid/time-step convergence test is performed for verification study. AUV (L2 = 0.4356m) is a smaller-scale SUBOFF without a sail, which approaches the submarine in different motion paths in the submarine wake at a relative speed combined with the dynamic overlapping grid technology. The hydrodynamic performance of the AUV when approaching the submarine and the velocity distribution of the surrounding flow field are analyzed, which provides a useful reference for underwater recovery of the AUV.

Influence of Basic Parameters for Fiber Reinforced Polymer Crushing Simulation

2016 ◽  
Author(s):  
Benoit Stalin ◽  
Dongyang Yang ◽  
Yong Xia ◽  
Qing Zhou
Keyword(s):  
Finite Element ◽  
Mesh Size ◽  
Fiber Reinforced Polymer ◽  
Physical Parameters ◽  
Large Element ◽  
Fiber Reinforced ◽  
Time Step ◽  
Reinforced Polymer ◽  
Simulation Results ◽  
The Impact

This article investigates the influence of finite element model features on Fiber Reinforced Polymer (FRP) crushing simulation results. The study focuses on two composite material tube models using single shell modeling approach. The chosen material model is MAT58 (*MAT_LAMINATED_COMPOSITE_FABRIC) from the commercial finite element analysis software LS-Dyna. The baseline models geometry and material parameters come from a model calibration conducted for lightweight vehicle investigation. Five parameters are investigated. The mesh size and the number of integration point (NIP) are generic and ERODS, TSIZE and SOFT are the non-physical parameters of MAT58. This analysis aims at discuss the influence of these parameters on the simulation results focusing on the initial force peak and the average crush load, regarding results realism and instabilities such as large elements deformation and abnormal peak values. Also, the impact of the number of CPUs involved in the simulation calculation is presented. Recommendations are given to set the mesh size and the NIP. TSIZE value should be selected regarding the simulation time step. On the other hand, ERODS has to be adjusted manually. Both are determinant for simulation robustness. Further studies are proposed to find out the reasons of large element deformation.

Enhanced Verification for RELAP5-3D Parameter and Sensitivity Studies

2016 ◽  
Author(s):  
George L. Mesina ◽  
Nolan Anderson
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
User Interaction ◽  
Computer Code ◽  
Unintended Consequences ◽  
Physical Models ◽  
Case Processing ◽  
Time Step ◽  
Sensitivity Studies ◽  
Code Changes

The RELAP5-3D1 program solves a complex system of governing, closure and special process equations to model the underlying physics of nuclear power plants. For SQA (software quality assurance), the code must be verified and validated (V&V) to ensure proper performance before release to users. The physical models are validated against data from experiments and plants and verified against specifications for the computer code. In addition to physics, programs such as RELAP5-3D perform numerous other functions and processes that should also be checked to guarantee correct results. Functions include input, output, data management, and user interaction, while processes include restart, time-step backup, code coupling, and multi-case processing. Previous articles have covered the verification of the physical models, restart, and backup through extremely accurate and automated sequential verification applied on a comprehensive suite of test cases to ensure that code changes produced no unintended consequences. New developments have enabled the verification of multi-case and multi-deck processing. These features are frequently used in parameter and code sensitivity studies and therefore must be verified as working correctly. Both theory and application are presented.

Study on Hydrodynamic Performance of a Dish-Shaped Underwater Vehicle

2010 ◽  
Author(s):  
Yumin Su ◽  
Zhaoli Wang
Keyword(s):  
Numerical Method ◽  
Processing System ◽  
Least Square Method ◽  
Underwater Vehicle ◽  
Least Square ◽  
Hydrodynamic Performance ◽  
Hydrodynamic Coefficients ◽  
Post Processing ◽  
Motion Mechanism ◽  
Planar Motion Mechanism

A new kind of dish-shaped underwater vehicle was designed. The maneuverability of the dish-shaped underwater vehicle (UV) is predicted in this paper. Hydrodynamic coefficients of the vehicle were calculated in numerically. The numerical method applied is one of the tools available in the commercial computational fluid dynamics software FLUENT. The dynamic mesh system and post-processing system are adopted in the numerical method. By simulating numerically straight motion, inclined motion and planar motion mechanism (PMM) experiment, the hydrodynamic performance in different states were obtained. Based on the least square method, the hydrodynamic coefficients of maneuverability were obtained. The calculated results indicate that the numerical method is suitable.

Assessment of Latching Control for the Hemispheric Heaving Buoy Type Point Absorber With and Without Nonlinear Froude-Krylov Force Acting on the Buoy

2019 ◽  
Author(s):  
Sung-Jae Kim ◽  
Weoncheol Koo ◽  
Chul H. Jo
Keyword(s):  
Control Strategy ◽  
Potential Flow ◽  
Flow Theory ◽  
Hydrodynamic Performance ◽  
Hydrodynamic Coefficients ◽  
Damping Force ◽  
Hydraulic Power ◽  
Coulomb Damping ◽  
Point Absorber ◽  
Latching Control

Abstract In this study, a latching control strategy was utilized to increase the efficiency of a heaving buoy-type point absorber with a hydraulic Power take-off (PTO) system. For this purpose, the hydrodynamic performance of a floating buoy was analyzed based on the potential flow theory and Cummins equation. Nonlinear Froude-Krylov (FK) force according to instantaneous wetted surface of a buoy was calculated by a theoretical solution. The effect of the latching control on a point absorber was evaluated by considering PTO performance with hydrodynamic coefficients including nonlinear FK force. The hydraulic PTO system was modeled as an approximate coulomb damping force.

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