Publications (6)1.18 Total impact
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ABSTRACT: The University of New Hampshire (UNH) developed and maintained an offshore aquaculture test site in the Western Gulf of Maine, south of the Isles of Shoals in approximately 50 m of water. This site was designed to have a permanent moored grid to which prototype fish cages or surface buoys could be attached for testing new designs and the viability of the structure in the exposed Gulf of Maine. In 1999, the first moorings deployed consisted of twin single bay grids each capable of each securing one fish cage. These systems were maintained until 2003. To expand the biomass capacity of the site, the single bay moorings were recovered and a new four bay submerged grid mooring was deployed within the same foot print of the previous twin systems. This unique system operated as a working platform to test various structures, including surface and submersible fish cages, feeding buoys and other supporting equipment. In addition, the expanded capability allowed aquaculture fish studies to be conducted along with engineering and new cage/feeder testing. The 4 bays of the mooring system were located 15 meters below the surface. These bays were supported by nine flotation elements. The system was secured to the seafloor on the sides with twelve catenary mooring legs, consisting of Polysteel® line, 27.5 m of 52 mm chain and a 1 ton embedment anchor, and in the center, with a single vertical line to a 2 ton weight. To size the mooring gear, the UNH software package Aqua-FE was employed. This program can apply waves and currents to oceanic structures, predicting system motions and mooring component tensions. The submerged grid was designed to withstand 9 meter, 8.8 second waves with a 1 m/s collinear current, when securing four fish cages. During its seven year deployment, the site regularly experienced extreme weather events, most notably a storm with a 9 m significant wave height, 10 second dominate period in April 2007. The maximum currents at the site were ob- - served during internal solitary wave events when 0.75 m/s currents with 25 minute periods and 8 m duration were observed. The mooring was recovered in 2010 after 7 years of continuous deployment without problems. The dominate maintenance requirement of the mooring was the cleaning once a year of excessive mussel growth on the flotation elements and grid lines. No problems of anchor dragging or failure of mooring components were documented during the deployment. Upon recovery, critical mooring components were inspected and documented, focusing on items with wear or other areas of interest. The mooring proved to be a reliable, stable working platform for a variety of prototype ocean projects, highlighting the importance of a sound engineering approach taken in the design process.
Conference Paper: An Investigation of a Deployed Submerged Grid Mooring System[Show abstract] [Hide abstract]
ABSTRACT: The University of New Hampshire has a submerged four grid mooring system off the coast of New Hampshire. To better understand the deployed grid system, a finite element model was built and field measurements of static tensions were taken. The purpose of the finite element model was to better understand the sensitivity of the system to anchor placement. An individual anchor was moved around the designed deployment location to better understand the grid tensions distribution. To take field measurements in the submerged system, a diver deployable instrument was designed. Field measurements reflect upon the accuracy of anchor placement and the effectiveness of the grid
Conference Paper: Design of a 20-Ton Capacity Finfish Aquaculture Feeding Buoy[Show abstract] [Hide abstract]
ABSTRACT: A design for a 20-ton capacity buoy was developed to feed fish in four submerged cages at an exposed site south of the Isles of Shoals, New Hampshire, USA. The buoy was designed to contain all the equipment necessary to accomplish the feed dispensing tasks as well as have the strength and stability to remain on location in a variety of sea states. New feed handling and distribution systems were developed and tested. To evaluate seakeeping response a Froude scaled physical model was constructed and tested at the Ocean Engineering wave/tow tank at the University of New Hampshire (UNH). The mooring system was designed using the UNH developed finite element analysis program called Aqua-FE. The prototype buoy is now under construction, and is scheduled for deployment in late summer 2006
Conference Paper: Practical Applications of Numerical Modeling using Aqua-FE: A Case Study[Show abstract] [Hide abstract]
ABSTRACT: A numerical model of an American Soybean Association (ASA) cage system was constructed using a finite element program developed at the University of New Hampshire (UNH) called Aqua-FE. The small volume, high density aquaculture system was modeled to determine how the system will operate in normal and extreme environmental conditions. The goals of the study were to determine the maximum loads in the system during tropical storm conditions and determine a similar cage system's response under specified environmental criteria. The cage is currently deployed in Weitou Bay, China. The system consists of a 100 m<sup>3</sup> cage (2 m times 4.5 m times 7 m) secured in a single point mooring. The rigid HDPE cage is held to the mooring by two sets of bridle lines, attached to the upper and lower cage framework. Chain ballast hangs below the lower cage rim providing a restoring force. A deadweight anchor secures the system to the seafloor. A 90 kg float suspends the single point mooring and serves as a tie-up location for servicing vessels. Aqua-FE can apply wave and current loading on truss and buoy elements by utilizing the Morrison equation adopted for analysis of aquaculture net pen systems. The algorithm employs a nonlinear Lagrangian formulation to account for large displacements of structural elements. In addition, the unconditionally stable Newmark direct integration scheme is adopted to solve the nonlinear equations of motion. Hydrodynamic forces on the structural elements are calculated using the Morison equation modified to account for relative motion between the structural element and the surrounding fluid. Maximum loads in the mooring gear approached 56 kN during the storm events. When various current velocities were applied, the cage submerged to a maximum depth of 16.4 meters
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ABSTRACT: Aquaculture products are projected to play an important role in filling the global demand for seafood in the world marketplace. In the US, stiff resistance to near shore aquaculture sites (where most farms are located) will drive the industry to more exposed locations. In an effort to better understand open ocean aquaculture challenges, the University of New Hampshire (UNH) has been investigating the biological, engineering, environmental and economical issues. This overview focuses on the engineering approach utilized by UNH to determine aquaculture system loads, motions and operational logistics by utilizing a variety of tools including numerical and physical models and field experimentation. Numerical modeling is performed with Aqua-FE, a finite element analysis (FEA) program developed to study aquaculture type systems, MSC.MARC/Mentat, a FEA structural modeling program, and FLUENT, a computational dynamics program. Scaled physical model tests are performed in the UNH wave/tow tank. In addition, an extensive field program experiments with the use of biofouled net panels, telemetry and control systems, feed buoys, scaled cages and various environmental monitoring equipment. Biofouled net panels were tested to determine the blockage effect due to the biological growth. Feed buoys, with telemetry and control options, have been deployed and tested. A new 20 ton capacity feed buoy has been designed and is currently under construction. A scale, experimental, submersible net pen has been designed, built and deployed to determine the feasibility of various components. Environmental measurements are collected with a surface buoy and the data is transmitted to shore. The resulting information from these experiments can help move the near shore aquaculture industry to more exposed locations.
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ABSTRACT: A research prototype feed-buoy was developed to supply a submerged net pen at an exposed site south of the Isles of Shoals, New Hampshire, in the Gulf of Maine. The system, designed for a quarter-ton feed capacity, consists of a surface feed-buoy, rubber tether moorings attached to a submerged grid, a feed transfer hose, feed dispensing machinery, and telemetry/control components. The buoy is taut-moored above the cage by compliant members in order to allow for the tidal range and large storm waves. The feeding mechanism uses a small, electric powered pump to actively force feed slurry down to the cage. A wind generator and solar panels provide power to this pump, bilge pumps, and the telemetry/control system. The control system switches the power to the various pumps on a user-set schedule and also monitors the operation of the electric power system. A spread spectrum radio is used to send diagnostic and status information to shore and via Internet to the project manager. The high-stretch feed hose has integrated, spiral-wound conductive wires to transmit power down to, and receive data back from, instrumentation in the fish cage.
University of New Hampshire
Дарем, New Hampshire, United States
- Center for Ocean Engineering