Development of a net pen system for aquaculture farming

1993 ◽  
Vol 20 (2) ◽  
pp. 189-200 ◽  
Author(s):  
Michael Isaacson ◽  
Norman Allyn ◽  
Gary Loverich
Keyword(s):  
Offshore Structures ◽  
Mooring Line ◽  
Wave Forces ◽  
Prototype System ◽  
Ocean Engineering ◽  
Fish Farms ◽  
Juan De Fuca ◽  
Prototype Structure ◽  
Structure Strength ◽  
Juan De Fuca Strait

The present paper describes a study carried out to verify a new net pen system which has been developed for aquaculture farming at exposed coastal sites. The structure is based on the use of spar buoys rather than rigid floats to support the net. A prototype structure has been deployed in Juan de Fuca Strait, and a verification of the system is described. This has involved an assessment of the environmental conditions and hydrodynamic loading for the structure, strength and fatigue analyses, and a calibration of wave conditions and mooring line forces with respect to prototype measurements. Overall, the system has been found to perform very well. Recommendations are made for monitoring the prototype system and for carrying out a refined verification of the system based on additional data. Key words: aquaculture, fish farms, hydrodynamics, ocean engineering, offshore structures, waves, wave forces.

Wave–current effects on large offshore structures

1989 ◽  
Vol 16 (4) ◽  
pp. 543-551 ◽  
Author(s):  
Michael Isaacson ◽  
John Baldwin
Keyword(s):  
Potential Flow ◽  
Offshore Structures ◽  
Wave Forces ◽  
Ocean Engineering ◽  
Viscous Effects ◽  
Offshore Structure ◽  
Time Stepping ◽  
Waves And Currents ◽  
Flow Effects ◽  
Interaction Problem

The various effects that influence loads acting on a large offshore structure due to the combination of waves and currents are reviewed. These may be broadly associated with potential flow effects and viscous effects. The potential flow effects are nonlinear and may generally be investigated by perturbation or time-stepping methods. Viscous effects include the onset of flow separation, which affects the validity of the assumed potential flow, as well as steady and oscillatory forces. The fluid mechanics of the complete wave–current–structure interaction problem are not yet well understood and areas in need of additional research are identified. Key words: currents, drag, drift forces, hydrodynamics, ocean engineering, offshore structures, waves, wave forces.

Nonlinear wave forces on a circular cylinder

1989 ◽  
Vol 16 (2) ◽  
pp. 182-187 ◽  
Author(s):  
Michael Isaacson ◽  
Qi-Hua Zuo
Keyword(s):  
Circular Cylinder ◽  
Nonlinear Wave ◽  
Perturbation Methods ◽  
Wave Force ◽  
Offshore Structures ◽  
Wave Forces ◽  
Ocean Engineering ◽  
Time Stepping ◽  
Wave Effects ◽  
Accuracy And Stability

Nonlinear wave forces on a surface-piercing vertical circular cylinder are considered using a time-stepping method previously developed which is based on Green's theorem. Possible improvements in the efficiency, accuracy, and stability of the method are considered. Results based on this method are compared with those obtained previously using perturbation methods as well as with experimental results. It is found that the time-stepping method adopted here is quite reasonable. Wave force coefficients are given as functions of the governing parameters of the problem and the importance of nonlinear wave effects on the forces is assessed. Key words: hydrodynamics, ocean engineering, offshore structures, waves, wave forces.

Moored structures in waves and currents

1996 ◽  
Vol 23 (2) ◽  
pp. 418-430 ◽  
Author(s):  
Michael Isaacson ◽  
John Baldwin
Keyword(s):  
Numerical Models ◽  
Mooring Line ◽  
Wave Forces ◽  
Ocean Engineering ◽  
Hydrodynamic Analysis ◽  
Floating Structures ◽  
Added Masses ◽  
Waves And Currents ◽  
Wave Heights ◽  
Exciting Forces

The present paper provides a brief review of the analysis of moored floating structures in waves and currents. A hydrodynamic analysis is required in order to predict wave and current effects on floating structures, and corresponding numerical models for determining transmitted and reflected wave heights, added masses, damping coefficients, and wave exciting forces are summarized. A mooring analysis is required in conjunction with the hydrodynamic analysis in order to calculate the restraint provided by the mooring system, as well as the structure motions, mooring line and anchor loads, and mooring line configurations. Various aspects of static, dynamic, and nonlinear responses are discussed and illustrated with example applications. Key words: coastal engineering, currents, floating structures, hydrodynamics, mooring forces, ocean engineering, wave forces, waves.

Correction factors for nonlinear runup and wave forces on a large cylinder

1994 ◽  
Vol 21 (5) ◽  
pp. 762-769 ◽  
Author(s):  
Michael Isaacson ◽  
Kwok Fai Cheung
Keyword(s):  
Experimental Studies ◽  
Diffraction Theory ◽  
Wave Force ◽  
Offshore Structures ◽  
Wave Forces ◽  
Correction Factors ◽  
Wave Loads ◽  
Wave Runup ◽  
Ocean Engineering ◽  
Simplified Approach

A recently developed numerical method for second-order wave diffraction is summarized and is used to develop a simplified approach to predicting nonlinear runup and maximum wave loads for large coastal and offshore structures subjected to regular waves. The perturbation method on which the method is based is extended to provide correction factors for the runup and maximum loads. These correction factors apply directly to the predictions of linear diffraction theory, and are independent of the wave height. The correction factors for runup, maximum force and maximum overturning moment are provided for a range of geometric parameters relating to the case of a large circular cylinder extending from the seabed to the free surface. Nonlinear runup and load maxima calculated by the correction factors are compared with the results of previous experimental studies; in general, favourable agreement is obtained. An example application of the proposed procedure is provided, the importance of nonlinear effects in the evaluation of runup and wave loads is discussed, and the limitations of the results are indicated. Key words: coastal structures, diffraction, hydrodynamics, ocean engineering, offshore structures, wave runup, wave force, waves.

Combined wave – iceberg loading on offshore structures

1996 ◽  
Vol 23 (5) ◽  
pp. 1099-1110 ◽  
Author(s):  
Ricardo Foschi ◽  
Michael Isaacson ◽  
Norman Allyn ◽  
Steven Yee
Keyword(s):  
Numerical Analysis ◽  
Offshore Structures ◽  
Wave Forces ◽  
Combined Effects ◽  
Ocean Engineering ◽  
First Order ◽  
Load Combination ◽  
Wave Parameters ◽  
Annual Probability ◽  
Verification Process

The Canadian Standards Association has developed and published a code for the design and construction of fixed offshore structures. This code has been subjected to a comprehensive verification process which has identified several issues warranting further study. One of these relates to the combined effects of wave and iceberg collision loading. At present, this combination is treated by the use of a load combination factor specified in the Code. The present paper describes a recent study which was undertaken to determine the appropriateness of the recommended value of the load combination factor. The study involves a numerical analysis in which loads due to waves alone, an iceberg alone, and an iceberg and waves in combination have been calculated for a range of iceberg and wave parameters. These results have been applied to a first-order reliability analysis in order to study the force levels corresponding to an annual probability of 10−4 or to the onset of global sliding with an annual probability of 10−4. The paper thereby makes recommendations for load combination factors applicable to combined wave–iceberg loading. Key words: hydrodynamics, icebergs, ocean engineering, offshore structures, wave forces, waves.

Wave and current forces on fixed offshore structures

1988 ◽  
Vol 15 (6) ◽  
pp. 937-947 ◽  
Author(s):  
Michael Isaacson
Keyword(s):  
Key Words ◽  
Recent Literature ◽  
Offshore Structures ◽  
Design Criteria ◽  
Wave Forces ◽  
Ocean Engineering ◽  
Detailed Survey ◽  
Ice Loads ◽  
Hydrodynamic Data ◽  
Design Construction

The Canadian Standards Association standard S471 "General requirements, design criteria, environment, and loads, Part 1 of the CSA code for the design, construction and installation of fixed offshore structures" contains an appendix "Wave and current loads." To compliment this appendix, the present paper provides a more detailed survey of this topic with a review of the recent literature and recommendations of hydrodynamic data needed in offshore design. In addition, hydrodynamic considerations in the calculation of earthquake and ice loads are mentioned. Key words: currents, current forces, hydrodynamics, ocean engineering, offshore structures, waves, wave forces.

Less=Moor: A Time-Efficient Computational Tool to Assess the Behavior of Moored Ships in Waves

2017 ◽  
Author(s):  
Yijun Wang ◽  
Alex van Deyzen ◽  
Benno Beimers
Keyword(s):  
Dynamic Response ◽  
Research Effort ◽  
Equations Of Motion ◽  
Line Tension ◽  
Mooring Line ◽  
Induced Response ◽  
Wave Forces ◽  
Computational Tool ◽  
The Time Domain ◽  
Nonlinear Equations Of Motion

In the field of port design there is a need for a reliable but time-efficient method to assess the behavior of moored ships in order to determine if further detailed analysis of the behavior is required. The response of moored ships induced by gusting wind and/or waves is dynamic. Excessive motion response may cause interruption of the (un)loading operation. High line tension may cause lines to snap, introducing dangerous situations. A (detailed) Dynamic Mooring Analysis (DMA), however, is often a time-consuming and expensive exercise, especially when responses in many different environmental conditions need to be assessed. Royal HaskoningDHV has developed a time-efficient computational tool in-house to assess the wave (sea or swell) induced dynamic response of ships moored to exposed berths. The mooring line characteristics are linearized and the equations of motion are solved in the frequency domain with both the 1st and 2nd wave forces taken into account. This tool has been termed Less=Moor. The accuracy and reliability of the computational tool has been illustrated by comparing motions and mooring line forces to results obtained with software that solves the nonlinear equations of motion in the time domain (aNySIM). The calculated response of a Floating Storage and Regasification Unit (FSRU) moored to dolphins located offshore has been presented. The results show a good comparison. The computational tool can therefore be used to indicate whether the wave induced response of ships moored at exposed berths proves to be critical. The next step is to make this tool suitable to assess the dynamic response of moored ships with large wind areas, e.g. container ships, cruise vessels, RoRo or car carriers, to gusting wind. In addition, assessment of ship responses in a complicated wave field (e.g. with reflected infra-gravity waves) also requires more research effort.

Detailed Study on Breaking Wave Interactions With a Jacket Structure Based on Experimental Investigations

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Jithin Jose ◽  
Olga Podrażka ◽  
Ove Tobias Gudmestad ◽  
Witold Cieślikiewicz
Keyword(s):  
Wind Turbines ◽  
Wave Breaking ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Wave Forces ◽  
Breaking Wave ◽  
Offshore Wind Turbines ◽  
Wave Parameters ◽  
Wave Slamming ◽  
Breaking Wave Forces

Wave breaking is one of the major concerns for offshore structures installed in shallow waters. Impulsive breaking wave forces sometimes govern the design of such structures, particularly in areas with a sloping sea bottom. Most of the existing offshore wind turbines were installed in shallow water regions. Among fixed-type support structures for offshore wind turbines, jacket structures have become popular in recent times as the water depth for fixed offshore wind structures increases. However, there are many uncertainties in estimating breaking wave forces on a jacket structure, as only a limited number of past studies have estimated these forces. Present study is based on the WaveSlam experiment carried out in 2013, in which a jacket structure of 1:8 scale was tested for several breaking wave conditions. The total and local wave slamming forces are obtained from the experimental measured forces, using two different filtering methods. The total wave slamming forces are filtered from the measured forces using the empirical mode decomposition (EMD) method, and local slamming forces are obtained by the frequency response function (FRF) method. From these results, the peak slamming forces and slamming coefficients on the jacket members are estimated. The breaking wave forces are found to be dependent on various breaking wave parameters such as breaking wave height, wave period, wave front asymmetry, and wave-breaking positions. These wave parameters are estimated from the wave gauge measurements taken during the experiment. The dependency of the wave slamming forces on these estimated wave parameters is also investigated.

Experimental Investigation on the Dynamic Response of a Three Legged Articulated Type Offshore Wind Tower

2016 ◽  
Author(s):  
Chinsu Mereena Joy ◽  
Anitha Joseph ◽  
Lalu Mangal
Keyword(s):  
Dynamic Response ◽  
Wind Turbine ◽  
Renewable Energy Sources ◽  
Offshore Structures ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Experimental Investigations ◽  
Offshore Wind Turbine ◽  
Ocean Engineering ◽  
Study Results

Demand for renewable energy sources is rapidly increasing since they are able to replace depleting fossil fuels and their capacity to act as a carbon neutral energy source. A substantial amount of such clean, renewable and reliable energy potential exists in offshore winds. The major engineering challenge in establishing an offshore wind energy facility is the design of a reliable and financially viable offshore support for the wind turbine tower. An economically feasible support for an offshore wind turbine is a compliant platform since it moves with wave forces and offer less resistance to them. Amongst the several compliant type offshore structures, articulated type is an innovative one. It is flexibly linked to the seafloor and can move along with the waves and restoring is achieved by large buoyancy force. This study focuses on the experimental investigations on the dynamic response of a three-legged articulated structure supporting a 5MW wind turbine. The experimental investigations are done on a 1: 60 scaled model in a 4m wide wave flume at the Department of Ocean Engineering, Indian Institute of Technology, Madras. The tests were conducted for regular waves of various wave periods and wave heights and for various orientations of the platform. The dynamic responses are presented in the form of Response Amplitude Operators (RAO). The study results revealed that the proposed articulated structure is technically feasible in supporting an offshore wind turbine because the natural frequencies are away from ocean wave frequencies and the RAOs obtained are relatively small.

scholarly journals THE DYNAMIC RESPONSE OF OFFSHORE STRUCTURES TO TIME-DEPENDENT FORCES

1964 ◽  
Vol 1 (9) ◽  
pp. 29
Author(s):  
William S. Gaither ◽  
David P. Billington
Keyword(s):  
Degrees Of Freedom ◽  
Wind Waves ◽  
Offshore Structures ◽  
Time Dependent ◽  
Wave Forces ◽  
Ocean Bottom ◽  
Single Wave ◽  
Single Degree Of Freedom ◽  
The Many ◽  
Floating Objects

This paper is addressed to the problem of structural behavior in an offshore environment, and the application of a more rigorous analysis for time-dependent forces than is currently used. Design of pile supported structures subjected to wave forces has, in the past, been treated in two parts; (1) a static analysis based on the loading of a single wave, and (2) a dynamic analysis which sought to determine the resonant frequency by assuming that the structure could be approximated as a single-degree-of-freedom system. (Ref. 4 and 6) The behavior of these structures would be better understood if the dynamic nature of the loading and the many degrees of freedom of the system were included. A structure which is built in the open ocean is subjected to periodic forces due to wind, waves, floating objects, and due occasionally to machinery mounted on the structure. To resist motion, the structure relies on the stiffness of the elements from which it is built and the restraints of the ocean bottom into which the supporting legs are driven.

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