Hydrodynamic coefficients of a floater near a partially reflecting seawall in the presence of an array of caisson blocks

2021 ◽  
pp. 1-23
Author(s):  
K G Vijay ◽  
Santanu Koley ◽  
Kshma Trivedi ◽  
Chandra Shekhar Nishad
Keyword(s):  
Wave Scattering ◽  
Structural Parameters ◽  
Wave Force ◽  
Vertical Force ◽  
Hydrodynamic Coefficients ◽  
Floating Structure ◽  
Surface Gravity Wave ◽  
Damping Coefficients ◽  
Half Wavelength ◽  
Scattering And Radiation

Abstract In the present study, surface gravity wave scattering and radiation by a freely floating rectangular buoy placed near a partially reflecting seawall and in the presence of an array of caisson blocks are analyzed. Various hydrodynamic parameters related to the wave scattering and radiation, such as the added mass and radiation damping coefficients, correspond to sway, heave and roll motions of the floating buoy, horizontal force, vertical force and moment acting on the floating structure, and horizontal wave force acting on the partially reflecting seawall are studied for a variety of wave and structural parameters. The study reveals that the resonating pattern in various hydrodynamic coefficients occurs for moderate values of the wavenumber. Further, when the distance between the floater and the sidewall is an integral time of half wavelength, the resonating behavior in the sway, heave and roll added masses, and associated damping coefficients appears, and the aforementioned hydrodynamic coefficients change rapidly around this zone. These resonance phenomena can be diminished significantly with appropriate positioning of the floater with respect to the sidewall and in the presence of partially reflecting seawall.

Motion Responses of Floating Structures Near Small Islands

2015 ◽  
Author(s):  
Peng Yang ◽  
Xuekang Gu ◽  
Chao Tian ◽  
Xiaolong Liu
Keyword(s):  
Water Depth ◽  
Wave Force ◽  
Wave Pattern ◽  
Far Field ◽  
Small Islands ◽  
Hydrodynamic Coefficients ◽  
Floating Structure ◽  
Floating Structures ◽  
Seabed Topography ◽  
Motion Responses

The seabed topography near small islands is usually in rugged state, and the water depth can be changed from tens of meters to a few meters in a short distance. Far field waves advancing towards the shore will experience a complex evolution on the shoal. In this environment, the hydrodynamic responses of a floating structure will be largely affected by the non-uniform wave pattern and changeable seabed, and might be quite different from the general responses of a platform in waves with uniform water depth. In this paper, a coupling hydrodynamic model of floating structures and reef topography was established; the incident wave force, diffraction force, radiation hydrodynamic coefficients, motions of a floating structure were calculated. The model was validated by comparing the predicted results with that of model tests. It is indicated that complex seabed topography has a significant influence on the hydrodynamic responses of the floating structure. Moreover, the motions are increased obviously in certain wave periods, with reference to that in far field waves.

scholarly journals Mooring Drag Effects in Interaction Problems of Waves and Moored Underwater Floating Structures

2020 ◽  
Vol 8 (3) ◽  
pp. 146
Author(s):  
Cheng-Tsung Chen ◽  
Jaw-Fang Lee ◽  
Chun-Han Lo
Keyword(s):  
Water Waves ◽  
Degrees Of Freedom ◽  
Wave Force ◽  
Wave Forces ◽  
Linear Potential ◽  
Floating Structure ◽  
Mooring Lines ◽  
Wave Fields ◽  
Present Solution ◽  
Scattering And Radiation

In contrast to either considering structures with full degrees of freedom but with wave force on mooring lines neglected or with wave scattering and radiation neglected, in this paper, a new analytic solution is presented for wave interaction with moored structures of full degrees of freedom and with wave forces acting on mooring lines considered. The linear potential wave theory is applied to solve the wave problem. The wave fields are expressed as superposition of scattering and radiation waves. Wave forces acting on the mooring lines are calculated using the Morison equation with relative motions. A coupling formulation among water waves, underwater floating structure, and mooring lines are presented. The principle of energy conservation, as well as numerical results, are used to verify the present solution. With complete considerations of interactions among waves and moored structures, the characteristics of motions of the structure, the wave fields, and the wave forces acting on the mooring lines are investigated.

Determination of the added masses and damping coefficients during coupled motions of two ships in shallow water parallel to the vertical wall

2021 ◽  
pp. 16-25
Author(s):  
В.Ю. Семенова ◽  
К.И. Баканов
Keyword(s):  
Shallow Water ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Hydrodynamic Coefficients ◽  
Damping Coefficients ◽  
Added Masses ◽  
Joint Motions ◽  
National Practice ◽  
Simultaneous Influence

В статье рассматривается определение коэффициентов демпфирования и присоединенных масс, возникающих при совместной качке двух судов в условиях мелководья параллельно вертикальной стенке на основании решения трехмерной потенциальной задачи. Определение гидродинамических коэффициентов осуществляется на основании методов интегральных уравнений и зеркальных отображений. Представленное решение в отечественной практике является новым. В статье приводятся результаты расчетов коэффициентов присоединенных масс и демпфирования, возникающих при качке двух одинаковых судов, расположенных лагом к волнению и параллельно вертикальной стенке в зависимости от изменения расстояний как между судами, так и между судами и вертикальной стенкой. Проводится исследование влияния различных фарватеров на величины гидродинамических коэффициентов, а именно: мелководного фарватера, мелководного фарватера с вертикальной стенкой, мелководного фарватера со вторым параллельно качающимся судном и мелководного фарватера с вертикальной стенкой и вторым судном. Таким образом, в работе учитывается одновременное влияния мелководья, вертикальной стенки и второго судна. Показано увеличение значений коэффициентов присоединенных масс и демпфирования при уменьшении расстояний между судами и между судами и вертикальной стенкой. Также показано значительное совместное влияние вертикальной стенки и второго судна на коэффициенты присоединенных масс и демпфирования по сравнению с другими видами стесненных фарватеров. The article discusses the determination of damping coefficients and added masses arising from the joint motions of two ships in shallow water conditions parallel to the vertical wall based on the solution of a three-dimensional potential problem. Determination of hydrodynamic coefficients is carried out on the basis of the methods of integral equations and mirror images. The solution presented in the national practice is new The article presents the results of calculating the coefficients of added masses and damping arising from the motions of two identical ships located lagged to the sea and parallel to the vertical wall, depending on the change in the distances between the ships and between the ships and the vertical wall. A study is being made of the influence of various waterways on the values ​​of hydrodynamic coefficients, namely: a shallow waterway, a shallow waterway with a vertical wall, a shallow waterway with a second parallel oscillating ship and a shallow waterway with a vertical wall and a second ship. Thus, the work takes into account the simultaneous influence of shallow water, vertical wall and the second ship. An increase in the values of the coefficients of added masses and damping with a decrease in the distances between ships and between ships and the vertical wall is shown. It also shows a significant combined effect of the vertical wall and the second ship on the added mass and damping coefficients in comparison with other types of constrained waterways.

scholarly journals Revisiting Theoretical Limits for One-Degree-of-Freedom Wave Energy Converters

2020 ◽  
pp. 1-11
Author(s):  
Nathan Tom
Keyword(s):  
Power Generation ◽  
Wave Energy ◽  
Degree Of Freedom ◽  
Upper And Lower Bounds ◽  
Complex Conjugate ◽  
Hydrodynamic Coefficients ◽  
Damping Coefficients ◽  
Wave Energy Converters ◽  
Heave Motion ◽  
Energy Converters

Abstract This work revisits the theoretical limits of one-degree-of-freedom wave energy converters (WECs). This paper considers the floating sphere used in the OES Task 10 WEC modeling and verification effort for analysis. Analytical equations are derived to determine bounds on displacement amplitude, time-averaged power (TAP), and power-take-off (PTO) force. A unique result found shows that the TAP absorbed by a WEC can be defined solely by the inertial properties and radiation hydrodynamic coefficients. In addition, a unique expression for the PTO force was derived that provides upper and lower bounds when resistive control is used to maximize power generation. For complex conjugate control, this same expression only provides a lower bound, as there is theoretically no upper bound. These bounds assist in comparing the performance of the floating sphere if it were to extract energy using surge or heave motion. The analysis shows because of differences in hydrodynamic coefficients for each oscillating mode, there are different frequency ranges that provide better power capture efficiency. The influence of a motion constraint on TAP while utilizing a nonideal power take-off is examined and found to reduce the losses associated with bidirectional energy flow. The expression to calculate TAP with a nonideal PTO is modified by the mechanical-to-electrical efficiency and the ratio of the PTO spring and damping coefficients. The PTO spring and damping coefficients were separated in the expression, allowing for limits to be set on the PTO coefficients to ensure net power generation.

A Study on Sensitivity of Maneuverability Performance on the Hydrodynamic Coefficients for Submerged Bodies

2000 ◽  
Vol 44 (03) ◽  
pp. 186-196
Author(s):  
Debabrata Sen
Keyword(s):  
Dynamic Model ◽  
Dynamic Models ◽  
Equations Of Motion ◽  
Inertial Force ◽  
Axisymmetric Body ◽  
Hydrodynamic Coefficients ◽  
Damping Coefficients ◽  
Simulated Trajectory ◽  
Linear Damping

Based on a constant-coefficient dynamic model, a study was made to determine the influence of various hydrodynamic coefficients on the predicted maneuverability quality of submerged bodies. Two types of geometries were considered, a submarine and an axisymmetric slender geometry. For the submarine, the equations of motion used were the revised standard submarine equations (Feldman 1979) while for the latter geometry a dynamic model was developed. From computer simulation of a few selected definitive maneuvers based on these two different dynamic models for the two geometries, the sensitivity of the simulated trajectory on changes in different coefficients was found. The results quantified in form of sensitivity values are presented. It is found that the typical measures from the maneuvers do not depend significantly on most of the nonlinear coefficients. The coefficients having significant effects on the trajectories are found to be the linear damping coefficients for the submarine and the linear inertial force coefficients for the axisymmetric body.

scholarly journals Experimental Investigation on Hydrodynamic Coefficients of a Column-Stabilized Fish Cage in Waves

2019 ◽  
Vol 7 (11) ◽  
pp. 418
Author(s):  
Zhao ◽  
Chen ◽  
Bi ◽  
Cui
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Drag Force ◽  
Inertial Force ◽  
Element Model ◽  
Wave Force ◽  
Hydrodynamic Coefficients ◽  
Horizontal Wave ◽  
Horizontal Wave Force ◽  
The Finite Element Model

This study on hydrodynamic coefficients of a column-stabilized fish cage under wave action plays an important role in the anti-wave design of cages. The regular wave test was used to study the horizontal wave force of the jacket and column-stabilized fish cage under different wave heights, periods, and incident angles; the finite element model of the jacket and the column-stabilized fish cage was established according to the test model. On the basis of the calculation of the finite element model, combined with the wave force obtained from the experiment, the hydrodynamic coefficients of the structure was fitted by the least squares method, and then the drag force, inertial force, and total force of the structure under different conditions were calculated. The results show that the hydrodynamic coefficients of the jacket and netting under the wave condition were more obvious with the change of the KC number and wave incident angles. And as the wave height increased, the drag force, the inertial force, and the proportion of the drag force to the horizontal wave force both increased. When the wavelength was large, the same trend occured as the wave period increased. When the wave incident angles were different, the forces of the jacket and the column-stabilized fish cage were always small in lateral low-frequency waves, which is consistent with the change law of hydrodynamic coefficients of the jacket and netting.

Inline and Vertical Wave Force Variation due to Burial of Submarine Pipeline in Random Wave Fields

2011 ◽  
Author(s):  
S. Neelamani ◽  
K. Al-Banaa
Keyword(s):  
Wave Force ◽  
The Other ◽  
Hydrodynamic Condition ◽  
Random Wave ◽  
Vertical Force ◽  
Submarine Pipeline ◽  
Other Hand ◽  
Sea Bed ◽  
Good For ◽  
Depth Of Burial

Marine pipelines encounter significant dynamic forces due to the action of waves. In order to reduce such forces, they are buried below the seabed. The wave force on the pipeline at any depth of burial for the given hydrodynamic condition depends on the properties of the sea bed soil. Physical model is used for assessing the hydrodynamic force on the pipeline for a wide range of random wave conditions, for different burial depths and in four types of soils. It is found that for all the four soil types, the horizontal force reduces with increase in depth of burial, whereas the vertical force generally increases up to certain depth of burial, mainly due to the significant change in the magnitude as well as the phase lag between the pore water pressures in the vertical direction. Among the soils, well graded soil is good for half burial of pipeline, since the least vertical force occurs for this soil. On the other hand, uniformly graded and low hydraulic conductivity soil attracts the maximum vertical force for half burial. On the other hand, such soil is good for full burial or further increase of burial, since it attracts less vertical force when compared to the other soils. The results of this study will help the submarine pipeline design engineers to select the minimum safe burial depth in a range of cohesion-less soil.

scholarly journals Coupled Vibration Analysis of Submerged Floating Tunnel System in Wave and Current

2018 ◽  
Vol 8 (8) ◽  
pp. 1311 ◽  
Author(s):  
Zhengyang Chen ◽  
Yiqiang Xiang ◽  
Heng Lin ◽  
Ying Yang
Keyword(s):  
Degrees Of Freedom ◽  
Natural Vibration ◽  
Structural Parameters ◽  
Wave Force ◽  
Natural Vibration Frequency ◽  
Governing Equations ◽  
Nonlinear Dynamic Response ◽  
Submerged Floating Tunnel ◽  
Installation Depth ◽  
Tunnel System

Submerged floating tunnel (SFT) is an innovative underwater structure for crossing long straits, which withstands the effects of water wave and current throughout its lifecycle. This paper proposes a theoretical approach to investigate the nonlinear dynamic response of the SFT tube-cable system under combined parametric excitation and hydrodynamic forcing excitations (i.e., wave and vortex-induced loading). Firstly, the governing equations of the SFT system considering the coupled degrees of freedom in the tube and cable are established based on the Hamilton principle and are solved numerically. Then, several representative cases are analyzed to reveal the dynamic characteristics of the SFT. Finally, some key parameters are discussed, such as the wave and current conditions and the structural parameters. The results show that when the flow velocity reaches a certain value, the vortex-induced vibration (VIV) of the anchor-cables will excite a strong resonance in the structure. The displacement amplitude of the SFT increases with the increase of the wave height. Gravity-buoyance ratio (GBR) of the tube and the inclined mooring angle (IMA) of the cables jointly determine the natural vibration frequency of the SFT. The influence of the wave force on the tube is limited when the installation depth of SFT is more than 40 m.

Observations of surface-gravity-wave scattering and dissipation by an isolated shoal related to a cuspate foreland

2019 ◽  
Vol 173 ◽  
pp. 43-55 ◽  
Author(s):  
Juan F. Paniagua-Arroyave ◽  
Peter N. Adams ◽  
Sabrina M. Parra ◽  
Arnoldo Valle-Levinson
Keyword(s):  
Gravity Wave ◽  
Wave Scattering ◽  
Surface Gravity ◽  
Surface Gravity Wave
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