PREDICTION OF THE DYNAMIC RESPONSE OF A SHIP IN HEAD WAVES USING OPENFOAM TOOLBOX

2021 ◽  
Vol 162 (A1) ◽  
Author(s):  
J Yao
Keyword(s):  
Dynamic Response ◽  
Dynamic Responses ◽  
Navier Stokes ◽  
Design Stage ◽  
Offshore Platforms ◽  
Computational Domain ◽  
Marine Structures ◽  
Time Step ◽  
Head Waves ◽  
The Right

Ships and marine structures, such as oil tanker, offshore platforms, etc., usually face extreme seaway environment in real situation. If under the action of strong waves large amplitude motions will occur, with the result that they may not work as usual or even lose stability. Thus, it is of great importance to access their dynamic responses under such bad conditions at the initial design stage, so as to ensure normal usage and safety. Herein, the original RANS (Reynolds-Averaged Navier- Stokes) solver based on OpenFOAM Toolbox has been extended to predict dynamic responses of ships and marine structures in waves. A new “inlet-velocity boundary condition” was implemented to generate waves. A damping term for wave absorption was added to the right-hand side of RANS equations in order to avoid wave reflection from the boundary where waves leave the computational domain. The related numerical methods are described in this paper. The purpose of this paper is to present a validation of the approach used. The prediction of the dynamic response of a ship in head waves was the focus. Five cases with different wave lengths and heights were considered. The predicted results, i.e. time histories of total resistance, heave and pitch, were compared with available experimental data and analysed. In addition, due to current experience it is very necessary that effort is devoted to determining appropriate grid and time step, so as to ensure the quality of waves generated.

Prediction of the Dynamic Response of a Ship in Head Waves Using OpenFOAM Toolbox

2020 ◽  
Vol 162 (A1) ◽  
Author(s):  
J Yao
Keyword(s):  
Dynamic Response ◽  
Dynamic Responses ◽  
Navier Stokes ◽  
Design Stage ◽  
Offshore Platforms ◽  
Computational Domain ◽  
Marine Structures ◽  
Time Step ◽  
Head Waves ◽  
The Right

Ships and marine structures, such as oil tanker, offshore platforms, etc., usually face extreme seaway environment in real situation. If under the action of strong waves large amplitude motions will occur, with the result that they may not work as usual or even lose stability. Thus, it is of great importance to access their dynamic responses under such bad conditions at the initial design stage, so as to ensure normal usage and safety. Herein, the original RANS (Reynolds-Averaged Navier-Stokes) solver based on OpenFOAM Toolbox has been extended to predict dynamic responses of ships and marine structures in waves. A new “inlet-velocity boundary condition” was implemented to generate waves. A damping term for wave absorption was added to the right-hand side of RANS equations in order to avoid wave reflection from the boundary where waves leave the computational domain. The related numerical methods are described in this paper. The purpose of this paper is to present a validation of the approach used. The prediction of the dynamic response of a ship in head waves was the focus. Five cases with different wave lengths and heights were considered. The predicted results, i.e. time histories of total resistance, heave and pitch, were compared with available experimental data and analysed. In addition, due to current experience it is very necessary that effort is devoted to determining appropriate grid and time step, so as to ensure the quality of waves generated.

scholarly journals Coupled dynamic response of a three-column mini TLP

2010 ◽  
Vol 6 (2) ◽  
pp. 52-61 ◽  
Author(s):  
Anitha Joseph ◽  
Lalu Mangal ◽  
Precy Sara George
Keyword(s):  
Finite Element ◽  
Dynamic Response ◽  
Wave Force ◽  
Dynamic Responses ◽  
Design Stage ◽  
Force Model ◽  
Diffraction Radiation ◽  
Offshore Platforms ◽  
Scaled Model ◽  
Geometric Configurations

For the development of deepwater marginal fields, many new platform concepts and designs are on the anvil. The mini TLP is a proven concept in this regard wherein an optimised conventional TLP system economically and efficiently serves in developing small marginal deepwater reserves. Various new geometric configurations and designs of mini TLPs are reported in the literature. This paper presents a new geometric configuration which could be a better alternative to an existing configuration. A 3-column mini TLP is designed and its platform-mooring coupled dynamic behaviour is investigated and compared with an existing 4-column mini TLP. The numerical investigation is carried out for the 1:56 scaled model using a finite element computer program suitable for compliant offshore platforms. A combination wave force model with diffraction-radiation loading on large members and Morison loading on slender members is adopted for computing the non-linear dynamic response of the structure. The effects of parameters such as pretension in tethers and wave approach angle have been studied. The results obtained are compared with published results of the 4-column mini TLP. It is found that the dynamic responses of the 3-column mini TLP are close to the 4-column mini TLP with relatively higher surge and tether tension.  Accounting for this in the design stage, the newly designed structure could be a promising candidate which can be used as an alternative to the 4-column mini TLP. Reducing the number of columns from four to three has added advantages in terms of cost and time during fabrication, installation and maintenance of the platform. Keywords: Deepwater structures; Coupled dynamics; Finite element method; Mini TLP; Nonlinear dynamicanalysis. DOI: 10.3329/jname.v6i2.2789

scholarly journals Stability of Finite Difference Discretizations of Multi-Physics Interface Conditions

2013 ◽  
Vol 13 (2) ◽  
pp. 386-410 ◽  
Author(s):  
Björn Sjögreen ◽  
Jeffrey W. Banks
Keyword(s):  
Stokes Equations ◽  
Normal Mode Analysis ◽  
Linear Equations ◽  
Mode Analysis ◽  
Navier Stokes ◽  
Computational Domain ◽  
Interface Conditions ◽  
Step Size ◽  
Time Step ◽  
Time Step Size

AbstractWe consider multi-physics computations where the Navier-Stokes equations of compressible fluid flow on some parts of the computational domain are coupled to the equations of elasticity on other parts of the computational domain. The different subdomains are separated by well-defined interfaces. We consider time accurate computations resolving all time scales. For such computations, explicit time stepping is very efficient. We address the issue of discrete interface conditions between the two domains of different physics that do not lead to instability, or to a significant reduction of the stable time step size. Finding such interface conditions is non-trivial.We discretize the problem with high order centered difference approximations with summation by parts boundary closure. We derive L2 stable interface conditions for the linearized one dimensional discretized problem. Furthermore, we generalize the interface conditions to the full non-linear equations and numerically demonstrate their stable and accurate performance on a simple model problem. The energy stable interface conditions derived here through symmetrization of the equations contain the interface conditions derived through normal mode analysis by Banks and Sjögreen in [8] as a special case.

Time-Domain Nonlinear Wave Making Simulation of the Catamaran Based on Velocity Potential Boundary Element Method

2010 ◽  
Author(s):  
Dakui Feng ◽  
Xianzhou Wang ◽  
Zhiguo Zhang ◽  
Yanming Guan
Keyword(s):  
Free Surface ◽  
Radiation Condition ◽  
Flow Fields ◽  
Design Stage ◽  
Hydrodynamic Characteristics ◽  
Outer Side ◽  
Surface Boundary ◽  
Computational Domain ◽  
Time Step ◽  
Surface Boundary Conditions

The catamaran is composed of two monohulls, the flow fields between the inner and outer side of each monohull are different, the bodies must be considered as lifting bodies. So it is very important to know the lifting effect on hydrodynamic characteristics of catamaran hull at the preliminary design stage of its hull form. The pressure Kutta condition is imposed on the trailing-surface of the lifting body by determining the dipole distribution, which generates required circulation on the lifting part. The method is based on Green’s second theorem. Rankine Sources and dipoles are placed on boundary surfaces. Time-stepping scheme is adopted to simulate the wave generated by the catamaran with a uniform speed in deep water. The values of the potential and position of the free surface are updated by integrating the nonlinear Lagrangian free surface boundary conditions for every time. A moving computational window is used in the computations by truncating the fluid domain (the free surface) into a computational domain. The grid regeneration scheme is developed to determine the approximate position of the free surface for the next time step. An implicit implement of far field condition is enforced automatically at the truncation boundary of the computational window, Radiation condition is satisfied automatically. The influences on the wave making resistance of the distance between the twin hulls of the Wigley catamaran on the hydrodynamic characteristics are discussed. The numerical results are presented compared with the existing simulation result. The method can be used to simulate the flow fields around the foil near free surface.

Numerical Modeling of Aerated Cavitation Using a Penalization Approach for Air Bubble Modeling Coupled to Homogeneous Equilibrium Model

2014 ◽  
Author(s):  
Petar Tomov ◽  
Sofiane Khelladi ◽  
Christophe Sarraf ◽  
Farid Bakir
Keyword(s):  
Fluid Flow ◽  
Mixture Model ◽  
Stokes Equations ◽  
Saturation Pressure ◽  
Homogeneous Mixture ◽  
Navier Stokes ◽  
Strain Rate Tensor ◽  
Computational Domain ◽  
Time Step ◽  
Homogeneous Mixture Model

Cavitation is a well-known physical phenomena occurring in various technical applications. It appears when the pressure of the liquid drops below the saturation pressure. Coupling aeration in a cavitating flow is a recent technique to control the overall effect of the cavitation. It is achieved by introducing air bubbles into the flow. In order to reveal and explore the behaviour of air gas in the vicinity of the cavitation region, the paper is oriented towards the physics of the colliding vapor phase bubbles and cavitating regions. The re-entrant jet may influence the dynamics of the bubbles as well as the frequency of cavitation separation. Therefore, a two-way coupling between the fluid flow and the introduced vapor is of capital importance. By penalizing the strain rate tensor in the Homogeneous Mixture Model, the two-way coupling has been achieved. The contact-handling algorithm is based on the projections of the velocity fields of the injected particles over the velocity field of the fluid flow. At each time step the gradient of the distance between the bubbles, is kept non-negative as a guarantee of the physical non overlapping. The bubbles’ collisions are considered as inelastic. The differential equations system is composed of the Navier-Stokes equations, implemented with the Homogeneous Mixture Model. A high-order Finite Volume (FV) solver based on Moving Least Squares (MLS) approximations is used. The code uses a SLAU-type Riemann solver for the accurate calculation of the low Mach numbers. The computational domain is a symmetrical 2D venturi duct with an 18°–8° convergent/divergent angles respectively.

FSI Numerical Simulation for Wind-Induced Dynamic Response of Tension Membrane Structures

2014 ◽  
Vol 1065-1069 ◽  
pp. 1069-1073
Author(s):  
Xin Lou ◽  
Zhen Hua Liu ◽  
Shuang Yang Song
Keyword(s):  
Numerical Simulation ◽  
Dynamic Response ◽  
Stokes Equations ◽  
Small Strain ◽  
Distribution Coefficients ◽  
Dynamic Responses ◽  
Wind Pressure ◽  
Navier Stokes ◽  
Membrane Structures ◽  
Navier Stokes Equations

In this paper, systemic FSI numerical simulations for wind-induced dynamic response of saddle-shaped tension membrane structures are performed using ADINA software, and the effects of some parameters such as inlet velocity, wind direction, span, rise-span ratio, tension stiffness and pre-stress of tension membrane are considered. The flow is modeled with the incompressible viscous Navier-Stokes equations and the standard κ-ω turbulence model, and the membrane is assumed as isotropic-linear-elastic material with large displacement and small strain. The rules of FSI numerical simulation for wind-induced dynamic responses of saddle-shaped tension membrane structures are summarized and the wind-induced dynamic coefficients and the wind pressure distribution coefficients are obtained which can be used in the design of membrane structures.

Comparative Studies on the Dynamic Performances of High Speed Turbocharger Rotor Supported on Oil-Free Bearings Versus Conventional Floating Ring Systems

2017 ◽  
Author(s):  
Rajasekhara Reddy Mutra ◽  
J. Srinivas
Keyword(s):  
Dynamic Response ◽  
High Speed ◽  
Equations Of Motion ◽  
Dynamic Modelling ◽  
Dynamic Responses ◽  
Effect Of Temperature ◽  
Time Step ◽  
Foil Bearing ◽  
Dynamic Performances ◽  
Bearing System

Present work focuses on the dynamic modelling of the dual-disc rotor supported on oil-free bearings idealizing a turbocharger rotor bearing system. The equations of motion of the rotor system are formulated and solved by finite element method to obtain the dynamic response of the system. The gas-foil bearing forces obtained from finite-difference approach at each time-step of solution. The same rotor model is used with the conventional floating ring bearing system where, the bearing forces are provided as displacement dependent time-varying oil and floating ring forces. As a practical environmental condition, the effect of temperature on the viscosity is studied using Dowson equation. The dynamic responses are illustrated both for rotor supported on both gas-foil and floating-ring type bearings. The effects of changes in bearing clearances on the overall dynamic characteristics of the rotor are reported. In order to utilize the gas foil bearing model, an identification study is performed to predict the operating clearance and air viscosity using dynamic response data.

scholarly journals Feasibility Study of Rans in Predicting Propeller Cavitation in Behind-Hull Conditions

2020 ◽  
Vol 27 (4) ◽  
pp. 26-35
Author(s):  
Yuxin Zhang ◽  
Xiao-ping Wu ◽  
Ming-yan Lai ◽  
Guo-ping Zhou ◽  
Jie Zhang
Keyword(s):  
Model Test ◽  
Turbulence Models ◽  
Tip Vortex ◽  
Navier Stokes ◽  
Design Stage ◽  
Step Size ◽  
Time Step ◽  
Tip Vortex Cavitation ◽  
Time Step Size ◽  
Sheet Cavitation

AbstractThe propeller cavitation not only affects the propulsive efficiency of a ship but also can cause vibration and noise. Accurate predictions of propeller cavitation are crucial at the design stage. This paper investigates the feasibility of the Reynolds-averaged Navier–Stokes (RANS) method in predicting propeller cavitation in behind-hull conditions, focusing on four aspects: (i) grid sensitivity; (ii) the time step effect; (iii) the turbulence model effect; and (iv) ability to rank two slightly different propellers. The Schnerr-Sauer model is adopted as the cavitation model. A model test is conducted to validate the numerical results. Good agreement on the cavitation pattern is obtained between the model test and computational fluid dynamics. Two propellers are computed, which have similar geometry but slightly different pitch ratios. The results show that RANS is capable of correctly differentiating the cavitation patterns between the two propellers in terms of the occurrence of face cavitation and the extent of sheet cavitation; moreover, time step size is found to slightly affect sheet cavitation and has a significant impact on the survival of the tip vortex cavitation. It is also observed that grid refinement is crucial for capturing tip vortex cavitation and the two-equation turbulence models used – realizable k-ε and shear stress transport (SST) k-ω – yield similar cavitation results.

scholarly journals Numerical Investigation into the Effect of Damage Openings on Ship Hydrodynamics by the Overset Mesh Technique

2019 ◽  
Vol 8 (1) ◽  
pp. 11
Author(s):  
Xinlong Zhang ◽  
Zhuang Lin ◽  
Simone Mancini ◽  
Ping Li ◽  
Dengke Liu ◽  
...  
Keyword(s):  
Navier Stokes ◽  
Bottom Plate ◽  
Computational Domain ◽  
Time Step ◽  
Damage Scenario ◽  
Ship Hydrodynamics ◽  
Motion Responses ◽  
Damage Stability ◽  
Implicit Solver ◽  
The Difference

Damage stability is difficult to assess due to the complex hydrodynamic phenomena regarding interactions between fluid and structures. Therefore, a detailed analysis of the flooding progression and motion responses is important for improving ship safety. In this paper, numerical simulations are performed on the damaged DTMB 5415 ship at zero speed. All calculation are carried out using CD Adapco Star CCM + software, investigating the effect of damage openings on ship hydrodynamics, including the side damage and the bottom damage. The computational domain is modelled by the overset mesh and solved using the unsteady Reynold-average Navier-Stokes (URANS) solver. An implicit solver is used to find the field of all hydrodynamics unknown quantities, in conjunction with an iterative solver to solve each time step. The Volume of Fluid (VOF) method is applied to visualize the flooding process and capture the complex hydrodynamics behaviors. The simulation results indicated that two damage locations produce the characteristic flooding processes, and the motion responses corresponding to the hydrodynamic behaviors are different. Through comparative analysis, due to the difference between the horizontal impact on the longitudinal bulkhead and the vertical impact on the bottom plate, the bottom damage scenario always has a larger heel angle than the side damage scenario in the same period. However, the pitch motions are basically consistent. Generally, the visualization of the flooding process is efficient to explain the causes of the motion responses. Also, when the damage occurs, regardless of the bottom damage or the side damage, the excessive heel angle due to asymmetric flooding is often a threat to ship survivability with respect to the pitch angle.

Dynamic Responses of the Floating Cage System in Current and Waves

2012 ◽  
Author(s):  
Li Li ◽  
Shixiao Fu ◽  
Runpei Li
Keyword(s):  
Dynamic Response ◽  
Hydrodynamic Forces ◽  
Dynamic Responses ◽  
Wave Forces ◽  
Morison Equation ◽  
Time Step ◽  
Beam Elements ◽  
Cage System ◽  
Structural Deformations ◽  
Wave Conditions

In this paper, based on the Morison equation and FEM, we studied the dynamic responses of the floating cage system in currents and waves. The nets are modeled by truss elements, the current and wave forces are calculated based on the Morison equation at each time step. The floater is modeled by beam elements, and the hydrodynamic forces from wave and current are also calculated by Morison equations. The sinker is modeled by adding a circular mass bar on the bottom of the whole structure. The effects of the flexibility on the dynamic responses of the floater are investigated by studying the structural deformations of the floater. The dynamic response of the system in different current and wave conditions are studied as well.

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