scholarly journals A Semi-Analytical Model for Studying Hydroelastic Behaviour of a Cylindrical Net Cage under Wave Action

2021 ◽  
Vol 9 (12) ◽  
pp. 1445
Author(s):  
Mingyuan Ma ◽  
Hong Zhang ◽  
Dong-Sheng Jeng ◽  
Chien Ming Wang
Keyword(s):  
Analytical Model ◽  
Least Squares Method ◽  
Structural Parameters ◽  
Free Water ◽  
Wave Theory ◽  
Porous Membrane ◽  
Wave Forces ◽  
Different Depths ◽  
Net Cage ◽  
Net Cages

In the present study, a semi-analytical model based on the small-amplitude wave theory is developed to describe the wave fields around a single gravity-type cylindrical open fish net cage. The cage may be submerged to different depths below the free-water surface. The fish cage net is modelled as a flexible porous membrane, and the deflection of the net chamber is expressed by the transverse vibration equation of strings. The velocity potential is expanded in the form of the Fourier–Bessel series and the unknown coefficients in these series are determined from matching the boundary conditions and the least squares method. The number of terms for the series solution to be used is determined from convergence studies. The model results exhibit significant hydroelastic characteristics of the net cages, including the distribution properties of wave surface, pressure drop at the net interface, structural deflection, and wave loading along the cage height. In addition, the relationships between wave forces on the net cage with hydrodynamic and structural parameters are also revealed. The findings presented herein should be useful to engineers who are designing fish cage systems.

scholarly journals Finite Element Analysis of the Effect of Currents on the Dynamics of a Moored Flexible Cylindrical Net Cage

2021 ◽  
Vol 9 (2) ◽  
pp. 159
Author(s):  
Zhongchi Liu ◽  
Sarat Chandra Mohapatra ◽  
C. Guedes Soares
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Numerical Model ◽  
Analytical Model ◽  
Structural Response ◽  
Wave Theory ◽  
Design Parameters ◽  
Element Analysis ◽  
Net Cage ◽  
Comparison Of The Results

A numerical model associated with wave–current interactions with a moored flexible cylindrical cage was developed based on the finite element method. An analytical model was formulated under the linearised wave theory and small structural response, and a semi-analytical solution was obtained using the Fourier Bessel series solution and least squares approximation method, along with a matching technique. The numerical results from the finite element analysis of the horizontal displacements for different design parameters under a uniform current were compared with the analytical model solutions. It was seen that they had a good level of agreement with their results. The effects of different current speeds and time on the cage shapes were analysed from the finite element results. Further, the mooring forces on the flexible cage for different values of the cage height and cage radius were also presented. The comparison of the results indicated that the numerical model results could be used with confidence in the design of a flexible cylindrical net cage for applications to offshore aquacultures.

Retrofitting of Floating Bridges With Perforated Outer Cover for Mitigating Wave-Induced Responses

2018 ◽  
Author(s):  
K. G. Vijay ◽  
T. Sahoo
Keyword(s):  
Structural Parameters ◽  
Domain Boundary ◽  
Wave Theory ◽  
Hydrodynamic Characteristics ◽  
Wave Forces ◽  
Vertical Force ◽  
Integer Multiple ◽  
Bridge Structures ◽  
Floating Bridges ◽  
Wave Induced

An investigation has been carried out based on multi-domain boundary element method to analyze the mitigation of wave-induced hydrodynamic loads on a pair of floating rectangular bridges by retrofitting the structures with external porous plates. The study is based on the assumptions of small amplitude water wave theory in finite water depth with the characteristics of wave-body interactions remain unaltered along the bridge. Wave past porous structure is modelled using Darcy’s law. Various hydrodynamic characteristics are studied by analyzing the wave forces acting on the floating bridges and the retrofitted porous structures for different wave and structural parameters. With the introduction of a retrofit, the horizontal force on the bridge reduces irrespective of wave and structural parameters, whilst vertical force increases under certain conditions. Moreover, when the distance between the bridges is an integer multiple of half of the wavelength of the incident waves, both the bridges experience optima in horizontal and vertical wave forces, with both these forces being 180° out of phase. The present study is expected to be useful in the design of efficient bridge structures which will reduce wave-induced hydrodynamics loads on the structure and thus enhance the service life of floating bridges.

Wave Induced Deformation and Stress Responses in HDPE Circular Net Cage: A Numerical Approach

2012 ◽  
Vol 217-219 ◽  
pp. 2299-2303
Author(s):  
Jian Hang Du ◽  
Zhen He ◽  
Feng Lin Yan ◽  
Guo Yan Yu
Keyword(s):  
Stress Responses ◽  
Peak Stress ◽  
Numerical Approach ◽  
Wave Forces ◽  
Response Characteristics ◽  
Simulation Testing ◽  
Net Cage ◽  
Dynamics Response ◽  
Net Cages ◽  
Wave Induced

A 3D numerical model was developed to analyze the deformation and stress characteristics of HDPE material circular net cage exposed to waves, using the finite element method (FEM). The total wave forces acting on the structure were evaluated with method combining analytical and numerical, and served as boundary conditions during the simulation. Testing cases were performed eventually based on the actual conditions in Zhanjiang bay. The results show that wave height is an important factor that affects the dynamics response characteristics of net cages as well as the working conditions of the cages in sea environment, and the peak stress of the flotation structure always occurs at the mooring points. We also suggest that the net cages that constructed inside Zhanjiang Bay may not fail even during the storm process when in normal working condition.

Analytical investigation of nonlinear heave-coupled response of tension leg platform

2018 ◽  
Vol 233 (3) ◽  
pp. 699-713
Author(s):  
Mohammad Reza Tabeshpour ◽  
Reza Hedayatpour
Keyword(s):  
Degrees Of Freedom ◽  
Structural Response ◽  
Wave Theory ◽  
Equation Of Motion ◽  
Analytical Investigation ◽  
Response Analysis ◽  
Wave Forces ◽  
Tension Leg Platform ◽  
Heave Motion ◽  
Diffraction Effects

Having deep view in structural response of tension leg platform is important issue not only for response analysis but also for engineering design. Coupling between surge and heave motions of tension leg platform is such a problem. Here, tension leg platform motions are considered only in surge and heave degrees of freedom without pitch effect. The coupled term of heave is a nonlinear differential equation. Because the focus of this article is on this term, therefore, Duffing equation of motion in the surge direction is linearized. The wave forces are calculated using Airy’s wave theory and Morison’s equation, ignoring the diffraction effects. Current force also can be very important in dynamic analysis of tension leg platform. Because it affects the term of heave that is coupled with surge. It is shown that the effect of surge motion coupling on heave motion is very important in large displacement of surge motion in many sea states. The main result is that the coupling effects appeared in some frequencies such as heave and surge frequency, twice the frequency of wave, twice the natural surge frequency, and summation and difference of frequency of wave and surge frequency.

Modeling of Tuned Liquid Damper With Submerged Nets

1999 ◽  
Vol 121 (3) ◽  
pp. 334-343 ◽  
Author(s):  
S. Kaneko ◽  
M. Ishikawa
Keyword(s):  
Analytical Model ◽  
Wave Theory ◽  
Damping Factor ◽  
Tuned Liquid Damper ◽  
Liquid Motion ◽  
Tuned Mass Dampers ◽  
Dissipation Energy ◽  
Structure Interaction ◽  
Cable Stayed Bridge ◽  
Optimal Damping

An analytical model for describing the effectiveness of tuned liquid damper (TLD) with submerged nets for suppressing horizontal vibration of structures is proposed. Dissipation energy due to the liquid motion under sinusoidal excitation is calculated based on nonlinear shallow water wave theory. In particular, the effects of hydraulic resistance produced by nets installed in a tank on the performance of TLDs are examined. The results of dissipation energy theoretically obtained are confirmed by experiments. To show the effectiveness of the proposed analytical model for TLD-structure interaction problems, the case in which TLD with nets is installed on top of a pylon of a cable-stayed bridge is described and the calculated results are compared with the actual experimental data. In the calculation, it is shown that the optimal damping factor, as is the case for tuned mass dampers (TMD), can be produced by the nets, and the effectiveness of TLD with nets are demonstrated.

Numerical Simulation of Flows Past Partially-Submerged Horizontal Circular Cylinders in Free Surface Waves

2013 ◽  
Author(s):  
Hans Bihs ◽  
Muk Chen Ong
Keyword(s):  
Free Surface ◽  
Surface Waves ◽  
Wave Theory ◽  
Circular Cylinders ◽  
Navier Stokes ◽  
Wave Forces ◽  
Linear Wave ◽  
Numerical Wave Tank ◽  
Linear Wave Theory ◽  
Free Surface Waves

Two-dimensional (2D) numerical simulations are performed to investigate the flows past partially-submerged circular cylinders in free surface waves. The 2D simulations are carried out by solving the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with the k-ω turbulence model. The level set method is employed to model the free-surface waves. Validation studies of a numerical wave tank have been performed by comparing the numerical results with the analytical results obtained from the linear-wave theory. Wave forces on the partially-submerged cylinders have been calculated numerically and compared with the published theoretical and experimental data under regular-wave conditions. The free-surface elevations around the cylinders have been investigated and discussed.

An Application of the Maximum Shear Strain Increment in Searching Sliding Surfaces

2013 ◽  
Vol 423-426 ◽  
pp. 1618-1622 ◽  
Author(s):  
Liu Yong Cheng ◽  
Jian Li ◽  
Shan Xiong Chen ◽  
Xiao Jie Chu
Keyword(s):  
Shear Strain ◽  
Least Squares Method ◽  
Limit Equilibrium ◽  
Quadratic Function ◽  
Strain Increment ◽  
Vertical Line ◽  
Sliding Surface ◽  
Maximum Shear Strain ◽  
Sliding Surfaces ◽  
Different Depths

A slope landslides generally at the place where the shear strain increment is the largest. This position is considered as the standard of defining sliding surfaces to assess the slope stability under the action of the foundation. A new method is proposed to determine the potential sliding surface, which is based on the largest shear strain increment. Firstly, the stress and strain in the slope were calculated by using the finite difference software-FALC3D. Secondly, a series of vertical line would be set in the calculating section. And then the discrete coordinates of the sliding surface, where the shear strain is largest on the vertical line, would be found through programming fish program. At last the position and shape of the sliding surface can be obtained through carrying on curve fitting of the discrete points by using the least squares method. The concept of this method is clear and can reflect the true form of the sliding surface through contrasting with the limit equilibrium method. Sliding surfaces of different depths and distances of slope are researched and a quadratic function is put forward which can describe the trends of glide direction. Three coefficients of the quadratic function were analyzed and the corresponding expression was obtained which can provide a reference to specification revision and engineering.

Calculation of Wave Forces Acting on a Cylinder With a Porous Plate Fixed Inside

2009 ◽  
Author(s):  
Weiguang Bao ◽  
Fenfang Zhao ◽  
Takeshi Kinoshita
Keyword(s):  
Body Surface ◽  
Porous Body ◽  
Porous Plate ◽  
Wave Theory ◽  
Wave Forces ◽  
Linear Wave ◽  
Normal Velocity ◽  
Wave Loads ◽  
Eigen Values ◽  
Eigen Function

To evaluate wave forces and to estimate the motion of breakwater, a circular cylinder is investigated based on the linear wave theory in the present work. The cylinder possesses a porous sidewall, an impermeable bottom and a horizontal porous plate inside that is fixed in the cylinder to work as obstruct and make wave dissipation more effectively. To simplify the problem, the Darcy’s fine-pore model is applied to the boundary condition on the porous body surface. The boundary value problem is solved by means of the eigen-function expansion approach. The fluid domain is divided into three regions and different eigen-function series are used. The so-called dispersion relation for the region inside the cylinder is quite different from a conventional one due to the existence of the porous plate. It leads to eigen values of complex number. To obtain solutions for the radiation problems, particular solution should be constructed to take account of the normal velocity appearing on the porous boundary. The wave loads are evaluated by integrating the pressure difference on two sides of the wetted body surface. The theoretical works are in good consistence with the experimental results. The Haskind relations are examined for the porous body. It is found that the damping coefficient consists of two parts. In addition to the component of conventional wave-radiating damping, exists a second component caused by the porous effects.

scholarly journals WAVE FORCES ON PILES OF VARIABLE DIAMETER

1982 ◽  
Vol 1 (18) ◽  
pp. 108
Author(s):  
Bernard LeMehaute ◽  
James Walker ◽  
John Headland ◽  
John Wang
Keyword(s):  
Wave Field ◽  
Intertidal Zone ◽  
Wave Theory ◽  
Wave Force ◽  
Wave Forces ◽  
Linear Wave ◽  
Inertial Effects ◽  
Linear Wave Theory ◽  
Variable Diameter ◽  
Wave Induced

A method of calculating nonlinear wave induced forces and moments on piles of variable diameter is presented. The method is based on the Morrison equation and the linear wave theory with correction parameters to account for convective inertial effects in the wave field. These corrections are based on the stream function wave theory by Dean (1974). The method permits one to take into account the added wave force due to marine growth in the intertidal zone or due to a protective jacket, and can also be used to calculate forces on braces and an array of piles.

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