Experimental and FNPT-RANS Investigations Into Gap-Excitation and Vortex Dynamics in a Rectangular Moonpool Interacting With Focused Waves

2021 ◽  
Author(s):  
Shaswat Saincher ◽  
John Wesly Gongalla ◽  
P. Vineesh ◽  
V. Sriram
Keyword(s):  
Research Effort ◽  
Body Wave ◽  
Wave Structure ◽  
Ocean Engineering ◽  
Regular Waves ◽  
Wave Characteristics ◽  
Wave Elevation ◽  
Series Of Experiments ◽  
Research Gap ◽  
Wave Structure Interaction

Abstract Moonpools are designed to provide a calm environment for lowering of equipment from ships. Considerable research effort has been invested towards understanding water column excitation within a moonpool. However, most recent investigations consider regular waves. The nature of interaction between focused waves and a moonpool is not well-understood; the present work strives to fill this research gap. A series of experiments have been carried out in a 22 m long glass flume in the Department of Ocean Engineering at IIT Madras. Two identical cuboidal boxes were affixed with a 0.15 m gap representing a rectangular moonpool. Focused waves based on a constant steepness spectrum were generated in 0.6 m water depth by a piston-type wave-paddle. The focusing point was set at the center of the moonpool and wave-focusing experiments were performed with and without the twin-body. Wave elevation at various locations along the flume was measured using five wave-gauges. Next, the experiments were numerically replicated using the in-house codes IITM-FNPT2D (for inviscid wave generation) and IITM-RANS3D (for fully viscous wave-structure interaction). Gap-excitation at the instant of focusing has been quantified and correlated with focused wave characteristics and with dynamics of spanwise vortices generated at the edges of the moonpool.

Wave Interaction With an Infinite Long Horizontal Elliptical Cylinder

2011 ◽  
Author(s):  
Hao Song ◽  
Longbin Tao
Keyword(s):  
Wave Interaction ◽  
Wave Structure ◽  
Offshore Structures ◽  
Elliptical Cylinder ◽  
Ocean Engineering ◽  
Parallel Side ◽  
Matrix Differential Equations ◽  
Unsteady Loading ◽  
Matrix Differential ◽  
Wave Structure Interaction

Wave-structure interaction in ocean engineering is a major source of unsteady loading and vibration of offshore structures including platforms, risers and long cables. Many efforts focus on vertical structures in which solution procedures can usually be simplified in the plane of mean free surface as the variable in the direction of gravity can be separated. In this paper, wave interaction with an infinite long horizontal elliptical cylinder is solved by a semi-analytical method, namely, the scaled boundary finite-element method (SBFEM). The solution domain is divided into two bounded domains and two unbounded domains with parallel side-faces. The governing partial differential equation (Helmholtz equation) is weakened and transformed to ordinary matrix differential equations in radial direction and are then solved analytically by SBFEM.

Application of Semi-Empirical Probability Distributions in Wave-Structure Interaction Problems

2012 ◽  
Author(s):  
Amir H. Izadparast ◽  
John M. Niedzwecki
Keyword(s):  
Probability Distribution ◽  
Wave Structure ◽  
Random Variable ◽  
Ocean Wave ◽  
Ocean Engineering ◽  
Structure Interaction ◽  
Wide Range ◽  
Empirical Probability ◽  
Semi Empirical ◽  
Wave Structure Interaction

Ocean engineers are routinely faced with design problems for coastal and deepwater structures that must survive a wide range of environmental conditions. One of the most challenging problems in the field of ocean engineering is the accurate characterization and modeling of the interaction of ocean waves with these offshore structures. The random characteristic of ocean environment requires engineers to consider the effects of random variability of the pertinent variables in their predictive models and design processes. Thus, for ocean engineering purposes, one needs to have accurate estimates of the probability distribution of the key random variables that will be used in sensitivity studies, reliability analysis, and risk assessment in the design process. In this study, a family of semi-empirical probability distribution is developed based on the quadratic transformation of linear random variable assuming that the linear random variable follows a Rayleigh distribution law. The estimates of model parameters are obtained from two moment based parameter estimation methods, i.e. method of moments and method of linear moments. The studied semi-empirical distribution can be applied to estimate the probability distribution of a wide range of non-linear random variables in the fields of ocean wave mechanics and wave-structure interaction. As examples, the application of the semi-empirical model in estimation of probability distribution of: a) ocean wave power, b) ocean wave crests interacting with an offshore structure is illustrated. For this purpose, numerically generated timeseries and experimentally measured data sets are utilized.

scholarly journals Wave-Structure Interaction for a Stationary Surface-Piercing Body Based on a Novel Meshless Scheme with the Generalized Finite Difference Method

Mathematics ◽  
2020 ◽  
Vol 8 (7) ◽  
pp. 1147
Author(s):  
Ji Huang ◽  
Hongguan Lyu ◽  
Chia-Ming Fan ◽  
Jiahn-Hong Chen ◽  
Chi-Nan Chu ◽  
...  
Keyword(s):  
Finite Difference ◽  
Finite Difference Method ◽  
Difference Method ◽  
Wave Structure ◽  
Second Order ◽  
Computational Domain ◽  
Ocean Engineering ◽  
Time Step ◽  
Structure Interaction ◽  
Wave Structure Interaction

The wave-structure interaction for surface-piercing bodies is a challenging problem in both coastal and ocean engineering. In the present study, a two-dimensional numerical wave flume that is based on a newly-developed meshless scheme with the generalized finite difference method (GFDM) is constructed in order to investigate the characteristics of the hydrodynamic loads acting on a surface-piercing body caused by the second-order Stokes waves. Within the framework of the potential flow theory, the second-order Runge-Kutta method (RKM2) in conjunction with the semi-Lagrangian approach is carried out to discretize the temporal variable of governing equations. At each time step, the GFDM is employed to solve the spatial variable of the Laplace’s equation for the deformable computational domain. The results show that the developed numerical method has good performance in the simulation of wave-structure interaction, which suggests that the proposed “RKM2-GFDM” meshless scheme can be a feasible tool for such and more complicated hydrodynamic problems in practical engineering.

Modelling of Wave-Structure Interaction of a Cylinder in Regular Sea Waves With Vessel Motions Using Coupled Transient CFD and Diffraction Methodology

2015 ◽  
Author(s):  
David Jia ◽  
Paul Schofield ◽  
Joanne Shen ◽  
Jim Malachowski
Keyword(s):  
Steady State ◽  
Hollow Cylinder ◽  
Cfd Simulation ◽  
Traditional Approach ◽  
Wave Structure ◽  
Sea Waves ◽  
Regular Waves ◽  
Structure Interaction ◽  
Added Masses ◽  
Wave Structure Interaction

This paper is a continuation of our previous paper [1] (OMAE2014-23225) where we did a parametric study for wave-structure interaction of a hollow cylinder in regular sea waves without vessel motions. The effect of waves and current on the motion of the cylinder and the associated forces were evaluated using a state-of-the-art methodology [2] (OMAE2013-11569) for predicting the motions and loads of subsea equipment and structures during offshore operations. In this paper, we extend the solution to include wave – structure interaction in regular sea waves and vessel motions. The 5th order Stokes regular waves in CFD and vessel motions are included in the modeling. This methodology couples the transient CFD with a hydrodynamic motion analysis after diffraction analyses, instead of relying on the traditional approach which uses simplified equations or empirical formulae to estimate hydrodynamic coefficients [3], or using steady-state CFD simulation on stationary equipment and structures to predict drag and added masses on submerged structures. The time domain diffraction simulation is coupled with a multiphase CFD simulation of subsea equipment and structures in waves. A transient CFD model with rigid body motions for the equipment and structures calculates added masses, forces and moments on the equipment and structures for the diffraction analysis, while the diffraction analysis calculates linear and angular velocities for the CFD simulation. In this paper, simulations are performed to investigate effect of the vessel motions on the motion of a hollow cylinder in regular sea waves. The results are compared with that from the traditional approach. This coupled methodology has potential applications in analyses of the motions of subsea equipment and structures in waves during offshore operations. The results in this paper show wave-structure interaction of a hollow cylinder in regular sea waves, and the effect of vessel motions on the motion of the cylinder. The results provide better understanding of structure motion in regular waves with vessel motions using this coupled methodology. The coupled methodology eliminates the inaccuracy inherited from assumed or calculated hydrodynamic properties that are obtained by using simplified equations or empirical formulations, or by using steady-state CFD analyses in traditional decoupled approaches. The results show that the coupled physics of regular sea waves, vessel motions and cylinder motion is captured by using this methodology. The coupled physics is not captured by the traditional approach.

Application of Breather Solutions for the Investigation of Wave/Structure Interaction in High Steep Waves

2012 ◽  
Author(s):  
Günther F. Clauss ◽  
Marco Klein ◽  
Matthias Dudek ◽  
Miguel Onorato
Keyword(s):  
Real World ◽  
Wave Structure ◽  
Model Tests ◽  
Design Stage ◽  
Regular Waves ◽  
Freak Waves ◽  
Structure Interaction ◽  
Steep Waves ◽  
The Impact ◽  
Wave Structure Interaction

During the design process of floating structures, different specifications have to be aligned such as the range of application, the warranty of economical efficiency as well as the reliability and are an inevitable integral part of the evaluation process during the design stage. The validation of the performance by means of model tests in terms of sea state behavior and the associated local and global structural loads are an important milestone within this process. Therefore it is necessary to determine an adequate test procedure which covers all essential areas of interest. Thereby one field of interest are limiting criteria of the design such as maximum local and global loads as well as maximum accelerations due to the impact of extraordinarily high waves, at which the floating structure has to survive. Different alternatives are available to conduct model tests in high, steep waves — transient wave packages, regular waves, irregular waves with random phases or more sophisticated deterministic tailored irregular wave sequences such as reproductions from numerical simulations and real-world measurements. This paper introduces a new approach for the systematic investigation of wave/structure interaction in high, steep waves. Exact solutions of the nonlinear Schrodinger equation — the so called breather solutions — are implemented for the generation of extraordinarily high waves. Three types of breather solutions are investigated in the seakeeping basin and to cover the full range of interest, each solution has been used to generate freak waves at certain frequencies. To evaluate the applicability of breather solutions for model tests two types of ships — a LNG Carrier and a Chemical Tanker — are investigated in the seakeeping basin. The ships are segmented and connected with strain gauges to detect the vertical wave bending moment. Furthermore, green water probes are installed on deck to evaluate the local impact on the bow of the freak waves. The obtained results are compared to investigations in regular waves with certain frequency and steepness as well as in real-world freak wave reproductions.

scholarly journals Investigation of a Stochastic Inverse Method to Estimate an External Force: Applications to a Wave-Structure Interaction

2012 ◽  
Vol 2012 ◽  
pp. 1-25 ◽  
Author(s):  
S. L. Han ◽  
Takeshi Kinoshita
Keyword(s):  
External Force ◽  
Inverse Method ◽  
Inverse Function ◽  
Wave Structure ◽  
Dynamic Responses ◽  
Structure Interaction ◽  
External Forces ◽  
Interaction Problem ◽  
Wave Structure Interaction

The determination of an external force is a very important task for the purpose of control, monitoring, and analysis of damages on structural system. This paper studies a stochastic inverse method that can be used for determining external forces acting on a nonlinear vibrating system. For the purpose of estimation, a stochastic inverse function is formulated to link an unknown external force to an observable quantity. The external force is then estimated from measurements of dynamic responses through the formulated stochastic inverse model. The applicability of the proposed method was verified with numerical examples and laboratory tests concerning the wave-structure interaction problem. The results showed that the proposed method is reliable to estimate the external force acting on a nonlinear system.

scholarly journals Systematic review of evidence underpinning non-pharmacological therapies in dementia

2018 ◽  
Vol 42 (4) ◽  
pp. 361 ◽  
Author(s):  
Richard Olley ◽  
Andrea Morales
Keyword(s):  
Systematic Review ◽  
Sleep Disturbances ◽  
Research Effort ◽  
Evidence Base ◽  
Pharmacological Therapy ◽  
Sufficient Evidence ◽  
Behavioural Treatment ◽  
Significant Research ◽  
Research Gap ◽  
Meta Analyses

Objective Dementia is one of the most common illnesses worldwide, and is one of the most important causes of disability in older people. Currently, dementia affects over 35 million people around the globe. It is expected that this number will increase to 65.7 million by 2030. Early detection, diagnosis and treatment to control the principal behaviour symptoms may help reduce these numbers and delay the progression to more advanced and dangerous stages of this disorder with resultant increase quality of life for those affected. The main goal of the present systematic literature review was to examine contemporary evidence relating to non-pharmacological therapy in the treatment of dementia. Methods To achieve the study goal, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement was used. Results This study identified the five most common behaviours in patients with dementia as aggression, wandering, agitation, apathy and sleep disturbances. Two non-pharmacological therapies were the most studied treatment: music therapy and aromatherapy. Ten other non-pharmacological therapies were also identified, but these lack a sufficient evidence-base. Conclusion Although all the therapies identified could be used as part of the treatment of behavioural symptoms, there is insufficient evidence relating to the indications, appropriate use and effectiveness of these therapies to apply in each behavioural treatment. Thus, the present study has demonstrated a significant research gap. What is known about the topic? Despite the widespread use of many different types of therapies, there is limited evidence regarding the efficacy of non-pharmaceutical therapies deployed in the management of behaviours of concern manifested by some people who suffer with dementia in all its forms. What does this paper add? This systematic review examines contemporary evidence from the literature to determine whether there is an evidence base available that would underpin the use of these therapies. This report on a PRISMA systematic review of the available literature demonstrates that only two therapies have some evidence to underpin the use of these non-pharmaceutical therapies and that a significant research gap is exists. What are the implications for practitioners? The implications for practitioners is that significant research effort is required to determine the efficacy of many of the therapies that are currently deployed, and thus many of the therapies used lack an evidence base at this time.

scholarly journals Efficient Solution of the 3D Laplace Problem for Nonlinear Wave-Structure Interaction

2008 ◽  
Author(s):  
Harry B. Bingham ◽  
Allan P. Engsig-Karup
Keyword(s):  
Nonlinear Wave ◽  
Efficient Solution ◽  
Wave Structure ◽  
Finite Difference Schemes ◽  
Surface Boundary ◽  
Computational Domain ◽  
Problem Size ◽  
Structure Interaction ◽  
Nonlinear Wave Structure ◽  
Wave Structure Interaction

This contribution presents our recent progress on developing an efficient solution for fully nonlinear wave-structure interaction. The approach is to solve directly the three-dimensional (3D) potential flow problem. The time evolution of the wave field is captured by integrating the free-surface boundary conditions using a fourth-order Runge-Kutta scheme. A coordinate-transformation is employed to obtain a time-constant spatial computational domain which is discretized using arbitrary-order finite difference schemes on a grid with one stretching in each coordinate direction. The resultant linear system of equations is solved by the GMRES iterative method, preconditioned using a multigrid solution to the linearized, lowest-order version of the matrix. The computational effort and required memory use are shown to scale linearly with increasing problem size (total number of grid points). Preliminary examples of nonlinear wave interaction with variable bottom bathymetry and simple bottom mounted structures are given.

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