Estimation of Force Reduction on Ocean Structures With Perforated Members

2015 ◽  
Author(s):  
Srinivasan Chandrasekaran ◽  
Madhavi Natarajan ◽  
Lognath Radhakrishnan Sreeramulu
Keyword(s):  
Outer Cylinder ◽  
Wave Structure ◽  
Cylindrical Structure ◽  
Water Particle ◽  
Design Charts ◽  
Outer Cover ◽  
Force Reduction ◽  
Water Particle Kinematics ◽  
Existing Structure ◽  
Wave Structure Interaction

While retrofitting and rehabilitation are usually related to strengthening of members, the presented concept is a novel attempt as it addresses decrease in the encountered forces on the members. Presence of perforated members in ocean structures reduces the wave-structure interaction significantly; breakwaters with perforated members are classical examples of such kind. This concept of encompassing the perforated outer cylinder with inner existing structure is found to be most feasible rehabilitation concept as it does not demand replacement of any damaged members. The presence of outer perforated cover alters the water particle kinematics significantly and eventually this remains the reason for the force reduction mechanism. In this study, the variation of water particle kinematics along the depth of the cylinder is estimated on the cylindrical structure with and without perforated outer cover. Forces on the inner cylinder are quantified numerically and experimentally; experimental results show a close agreement with that of the numerical ones. Velocity variations along the water depth are quantified in the form of design charts, which shall be helpful for the practicing professionals while attempting for retrofitting or re-design. Force variations derived through numerical analyses, which are functions of the water particle kinematics along the depth shall be useful in the design offices for cylindrical members encompassed with perforated outer cover. Introduction of perforated member over the existing cylindrical structure showed a significant force reduction around 60% on an average for all the wave steepness indexes considered for the study, when compared to the force on the member without perforated cover.

Variations of Hydrodynamic Characteristics With the Perforated Cylinder

2014 ◽  
Author(s):  
Srinivasan Chandrasekaran ◽  
Madhavi Natarajan ◽  
Natarajan Chithambara Thanu
Keyword(s):  
Water Depth ◽  
Hydrodynamic Characteristics ◽  
Offshore Platforms ◽  
Wave Impact ◽  
Direct Wave ◽  
Water Particle ◽  
Design Charts ◽  
Perforated Cylinder ◽  
Outer Cover ◽  
Water Particle Kinematics

Presence of the perforated outer cover on the existing column members of offshore platforms reduces the direct wave impact on these members. Such applications are common in the coastal structures where perforated covers are provided on the seaside to dissipate the wave energy and to reduce the pressure on the members. Detailed studies on the variations of the hydrodynamic characteristics on the inner cylinder, encompassed by a perforated outer cover are scarce in the literature. Present study is focused the development of numerical model to investigate the variations in the water particle kinematics on the inner cylinder encompassed by perforated outer cover. Hydrodynamic characteristics are examined along the water depth through computation fluid dynamics (CFD) for perforation ratios (p%) varying in the range of 10 to 15%. Velocity profiles for different wave steepness are developed along with the design charts for the chosen perforation ratios. These design charts can be readily used for estimating the water particle kinematics for perforated members along the water depth.

Experimental Investigation of Dynamic Response of Tension Leg Platform With Perforated Members

2013 ◽  
Author(s):  
Vishruth Srinath ◽  
Srinivasan Chandrasekaran
Keyword(s):  
Dynamic Response ◽  
Wave Structure ◽  
Offshore Structures ◽  
Scale Model ◽  
Experimental Investigations ◽  
Cylindrical Structures ◽  
Structure Interaction ◽  
Near Shore ◽  
Outer Cover ◽  
Wave Structure Interaction

Perforated cylindrical structures are extensively used in near-shore breakwaters to reduce wave-structure interaction and scouring; however use of perforated members on floating offshore structures is not widespread. Current study investigates the influence of perforated members on the dynamic response of Tension Leg Platforms (TLP) through model testing. Detailed experimental investigations are carried out on the scale model of TLP with and without porous outer cover, under unidirectional regular waves. Based on studies conducted, it is shown that fluid-structure interaction is reduced in the presence of outer perforated covers; as a result, surge and pitch responses decrease.

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 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.

scholarly journals Wave–structure interaction in hybrid wave farms

2018 ◽  
Vol 83 ◽  
pp. 386-412 ◽  
Author(s):  
Siming Zheng ◽  
Yongliang Zhang ◽  
Gregorio Iglesias
Keyword(s):  
Wave Structure ◽  
Hybrid Wave ◽  
Structure Interaction ◽  
Wave Structure Interaction

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.

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