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Table 1

Open Ocean Aquaculture Engineering

CINEMar/Open Ocean Aquaculture Annual Progress Report for the period 1/01/05 through 12/31/05

Principal Investigator: M.R. Swift, B. Celikkol, K. Baldwin, D. Fredriksson, I. Tsukrov

I. Accomplishments

A. Scheduled Tasks
Background: For the past seven years, the University of New Hampshire (UNH) has operated an open ocean aquaculture site in 52 meters of water approximately 10 km from the New Hampshire coast in the United States. The site is permitted to perform research related to the operational, engineering, biological and environmental aspects of open ocean aquaculture (OOA). To support the research, two independent 600 m3 Sea Station™ fish cages (SS600) were analyzed and deployed at the site in 1999 using separate, robust mooring systems (see Tsukrov et al., 2000; Fredriksson et al., 2000; Baldwin et al., 2000). For over four years, these systems were the focus of an intense engineering and operational analysis program. From the engineering perspective, studies were conducted to investigate the dynamics so that numerical and physical modeling techniques could be developed to cost-effectively engineer and specify equipment suitable for deployment (see Palczynski, 2000; Tsukrov et al., 2003; Fredriksson et al., 2003a; 2003b).

More recently, an effort was made to expand bio-mass capacity at the site; the two small systems were replaced with a larger four grid mooring enabling the deployment of additional containment structures (Fredriksson et al., 2004a and Fredriksson et al. 2005). The new mooring system also allows auxiliary equipment, such as feeding platforms (Rice et al., 2003; Fullerton et al., 2004), to be installed at the site. The intent is to approach commercial level operations so that proper economic assessments can be initiated. Even though the techniques and engineering methods are being developed, engineering challenges still have to be overcome to create the technological basis for commercial scale aquaculture.

Objectives: To address these challenges, the goal of the OOA project has been set to establish a commercial scale facility at the Isles of Shoals site. The engineering component supports this collective goal by pursuing the following objectives,

  1. Investigation of commercial scale fish cage systems.
  2. Analysis of cage mooring grid systems.
  3. Feed buoy development including design and control/telemetry.
  4. Improved numerical modeling techniques
  5. Investigation of increased cage net drag due to biofouling
  6. Development of an operations center.
  7. Investigation of exterior-interior cage flow regimes.

These objectives represent a continuation of previous work performed (see the OOA Engineering 2004 Progress Report). In the following section, a brief description of each of these studies is included.

B. Progress on Tasks
PROGRESS ON TASK #1: INVESTIGATION OF COMMERCIAL SIZE SYSTEMS
As part of the proposed work, the Center for Ocean Engineering (COE) at UNH has been involved in the analysis of possible commercial size fish containment systems. Two systems have recently been investigated: (1) a low cost, submersible plastic net pen, and (2) a rigid, fixed volume, spherical net pen.

A Low Cost, Submersible, Plastic Net Pen: JPS Industries, a NH manufacturing company, worked with UNH to obtain a Small Business Innovation Research (SBIR) project to work on the first system. This investigation was based in part on experience gained evaluating other commercially available cage systems (see, for example, DeCew et al. 2005). During Phase I of this study, a low-cost, submersible fish cage for open ocean aquaculture was investigated. Hydrostatic tests and numerical, physical and structural modeling were performed on two conceptual, gravity-type designs (OOA Engineering 2004 Progress Report and Santamaria et al., 2004). During this study, a finite element structural analysis showed that the pipe configuration of one of the designs would fail at 8,230 lbf, 58% below the specified design criteria of 20,000 lbf. In addition, during assembly of a 1:10 scale model cage, various construction concerns were raised such as component compatibility (when mass produced), tolerances of parts, and needed equipment for assembly. Therefore the design was modified to increase the structural integrity and simplify the assembly of the system. This cage/mooring concept is shown in Figure 1. Phase II of the SBIR program was awarded in September 2005. During the initial stages of this study, system hydrostatics were again analyzed. The objective was to fine-tune the lift mechanism using buoyancy in the top pipe framework as well as an airlift positioned below the cage.

This cage concept (see Figure 2) is a modified version of a traditional gravity cage. However, the cage structure has been modified to ease the transportability, construction, and maintenance of the system. It consists of 12 sections of dual High Density Polyethylene (HDPE) pipes secured with metal fittings. These fittings cap each end of the pipe sections and are bolted together to form the shape of the system. They also support the handrail stanchions, triangular stays (supporting the lower rim and ballast) and provide net attachment locations. A bottom “ring,” which supports the lower half of the net chamber, is constructed in the same manner, however, only one length of pipe is used between the fittings. A bridle, airlift and ballast chain (or deadweight anchor depending upon bottom conditions) will hang below the bottom rim.

Two variable buoyancy/ballast configurations (to raise and lower the cage) are currently being investigated (see Figure 1). The first will be located within one section of the upper rim pipes. This configuration was tested in the Phase I portion of the SBIR program with the scale model cage. Although the geometry of the cage is now different, the concept is similar and tested well. The second system will be located in an airlift below the lower rim. This airlift (to be used on a 1:1.623 scale model) was recently constructed and tested in the UNH large engineering tank (see Figure 3).

The tank was designed to allow surface filling (even with the tank at depth) and to provide precise control of vertical position. Filling the tank in “stages” will allow the system to offset precise weights. By understanding the geometry of the tank, the distance between each valve, and the ballast weight characteristics, the cage system can rise in set increments, important when dealing with fish with swim bladders. A 1:1.623 scale cage (having a diameter of 50 ft) is scheduled to be constructed in the coming months. Once this scale cage is deployed, both ballast systems will be tested to determine the optimal configuration and insure the cage system’s stability in the water column.

A Rigid, Fixed Volume, Spherical Net Pen: The second system investigated was developed by Ocean Farm Technologies, LLC (see Figure 4) called the “AquaPod”. This system was deployed and placed in the UNH OOA submerged grid system. Prior to mooring the cage, however, a tow test was performed measuring the drag force and fluid velocity outside and inside the cage system (to investigate flow reduction). In addition to the drag and current measurements, mooring line loads and cage motion will be investigated while the cage is deployed at the OOA site.

The 500 m3 cage was constructed of 80 triangular panels, connected with galvanized hardware, forming a chamber with a diameter of 9.75 m (32 ft). Unlike traditional cage designs, the AquaPod’s net is integrated within each triangular panel. This combination forms a rigid superstructure protecting the fish and reducing net deformation due to waves and currents. The net is constructed of 16 gauge (2 mm diameter) vinyl coated galvanized wire. Due to the system’s structural components (fiberglass reinforced polyethylene), the cage is neutrally buoyant, with approximately 0.15 m (6 in) of freeboard (not including mooring components).

The cage was towed out to the site with the R/V Meriel B. To record the drag of the system, a 12,000 lbf load cell was attached to a 600 ft tow line (leading to the cage). Two sets of water velocity data were measured. A Marsh-McBirney electro-magnetic current meter was located on the tow vessel to measure the water velocity outside the cage. An Aquadopp acoustic-doppler current meter was also placed inside the cage system to measure any water velocity reduction due to blockage of the structure. Figure 5 and Figure 6 show the cage tow and Marsh-McBirney current meter set-up.

The cage system was brought to 5 velocity levels (constant vessel engine RPM) over 15 minutes. Each velocity level was held for approximately 2 - 3 minutes. The load cell measured loads from approximately 1600 lbs at 0.75 knots to 8200 lbs at 2.18 knots. Figure 7 displays the resulting load and velocity versus time for one of the tests. In addition, the flow reduction due to the blockage of the net and cage structure was found to range from 40 ­ 60%. This data, paired with the advances in the numerical modeling (see TASK #4), will allow more precise predictions of this cage system in oceanic environments.

PROGRESS ON TASK #2: GRID MODELING AND MEASUREMENTS
Over the last year, several new cage and mooring system options have been discussed. To investigate the feasibility of some of the new “proposed” concepts, additional model simulations were conducted to assess the holding capacity of the UNH grid mooring as well as other mooring configurations. Calculations were completed using the UNH finite element computer program Aqua-FE. In addition, a measurement program to determine actual deployed geometry and line tensions at the OOA site was initiated.

UNH 4-Cage Grid System with an AquaPod Cage: One scenario considered was an investigation of the 4 cage grid system with the quarter-ton feed buoy, one 3000 m3 Sea Station (SS3000), one 600 m3 Sea Station (SS600), and one 500 m3 experimental AquaPod cage (similar to the design described as part of TASK #1 called the “AquaPod” cage system developed by Ocean Farm Technologies). The constructed model is shown in Figure 8. In the model, the AquaPod cage has an overall diameter of 9.75 m (32 ft). The net on the cage has a twine diameter of 2 mm, a square length of 25.4 mm (1”), resulting in a solidity of 16%. Simulations were performed using the present grid configuration with the pennant weights on the 2 Sea Station cages modeled as fixed points. The waves and currents approached the system from the northeast. A 9 meter wave with an 8.8 second period and a 1 m/s current was used as input.

Results of the numerical model simulation focused on the six anchor legs deployed in the north and east direction. The grid lines were also analyzed because these components play a role in the distribution of loads through the system. The load distribution throughout the mooring lines is shown in Figure 9. The largest load experienced by the system was 124.3 kN (27,950 lbf) on the eastern anchor line. This anchor only reaches 71% of the nominal design load (177 kN or 40,000 lbf) of the system. Therefore, the mooring system can handle the 500 m3 AquaPod cage and associated mooring gear.

Investigation of a Near-Shore Salmon Farm: A direct result of the UNH Open Ocean Aquaculture’s numerical modeling efforts and expertise in the field was the awarding of a Saltonstall-Kennedy Grant (# NA03NMF4270183) in 2003 entitled “Engineering Design and Analysis for More Secure Salmon Net Pen Systems.” The objective of the project is to work with Heritage Salmon at their twenty-cage site in Broad Cove near Eastport, ME to evaluate the structural integrity of their deployed system for offshore application. The approach specifically targets the site area to establish more secure cages to reduce farmed fish escapement. In addition to this objective, the work investigates the feasibility of expanding salmon farming operations into more exposed areas in an effort to reduce environmental and multi-use issues.

The fish farm at the Broad Cove site near Eastport ME consists of twenty, 100-m circumference high-density polyethylene (HDPE) surface gravity cages (see Figure 10). The prevailing weather (winds, waves and currents) is typically from the west and south. The cage and mooring components that show the most wear are therefore in the southwest corner of the system.

Focusing on the gear located on the southwest corner of the cage and mooring system, a series of load cells, current meters and a wave measurement instrument were installed. Five 90 kN capacity load cells were deployed on the three southwest chain anchor legs, as well as the west and south chain anchor legs. The load cells are bolted to a strongback and shackled to the links of the anchor leg chain and connected to a submersible data logger. Four 45 kN capacity load cells were placed on the southern Y-lines that connect the grid corners to the cage. These load cells are connected to data loggers that are strapped to stanchions of the southwest cage. To measure the waves that occur at the site, a wave measuring Acoustic Doppler Current Profiler (ADCP) was deployed outside of the grid and mooring system. The ADCP is deployed in an upward looking configuration using a subsurface mooring with an instrument frame and flotation. In addition to the ADCP, a Nortek, Aquadopp and a MAVS-3 current meter were deployed on the seaward side and on the internal side of the southwest cage, respectively.

The monitoring data sets are being used to characterize the site and to provide environmental forcing and validation data for computer simulations. The simulations are being conducted using two finite element computer-modeling programs. The results of the computer modeling simulations are being used to evaluate reliability of the existing fish farm site, to predict cage/mooring performance in more exposed environments, and to design secure fish cage/mooring systems. These models will provide quantified data sets that can be used to identify potential failure locations. Design changes can then be implemented to reduce damage and farmed fish escapement.

A computer model of the 20-cage grid system has been built using the fluid-structure interaction program Aqua-FE (see Figure 11). Preliminary simulations are being performed using data from the waves-ADCP and the Aquadopp current meter as input. Anchor leg load tension results from the simulations are being compared to data sets acquired from the load cells. Mooring component tension results will be used as input to the second computer model (MSC.Mentat) to determine the yield strength characteristics and structural integrity of the surface gravity cages (see Figure 12).

It is important to have this information, prior to deployment of equipment in exposed areas, to establish more secure systems to reduce farmed fish escapement, liability risks and determine if existing equipment can be used in offshore locations. Although this research is on-going, progress has been summarized in the following reports by Fredriksson et al. (2003c), Fredriksson et al. (2004b) and Fredriksson et al. (2004c).

Load Cell Measurements in the OOA Grid/Mooring System: The four-grid mooring system designed and deployed by UNH has been the foundation of all OOA site work. It acts as a false bottom so that buoys and cages can be attached to a well known position without having to deploy new moorings or anchors in relatively unknown locations. The grid also allows for diver access to cage and buoy hardware for inspection and attachment that would otherwise be inaccessible. While this grid mooring has worked well during the last two and a half years, much is still not understood about the actual deployed geometry and load distribution. To better understand the deployed grid and its sensitivity to anchor locations, load cells are being incorporated into the northeast corner of the grid.

While plans were to deploy four load cells onto the two anchor and two grid lines attached to the northeast grid corner, other operational work has hindered progress. As a result, an outside contractor, Pepperell Cove Marine, was contracted to deploy these load cells. At this time, scheduling and weather has allowed for three of the four load cells to be deployed. Also, this preliminary work has revealed that grid tensions are somewhat higher than anticipated. While designed grid tensions were 2,000 ­ 3,000 lbs, divers using a four-ton come-a-long had difficulty pulling these lines slack. This indicates that tensions are most likely over 6,000 lbs and could be as high as 10,000 lbs. While the cause of this is unknown, it is suspected that extra stretch in the anchor and grid lines resulted in the anchor line scope being higher than designed. Since the anchors would have more horizontal pull due to increase scope, greater tension would result.

Once all four load cells are in place, monitoring of the grid will commence. This will likely take place during the spring of 2006 so this information can be used in planning the possible grid reinforcement during the summer of 2006.

PROGRESS ON TASK #3: FEED BUOY DEVELOPMENT
Twenty-Ton Feed Buoy Design, Modeling and Construction: A 20-ton capacity feed buoy is under development to remotely feed an increased biomass of growing fish stock. Due to the buoy’s cost, a unique collaborative arrangement was established between Net Systems, Inc, the OOA operations/infrastructure group and the OOA engineering team. SBIR Phase II funding was secured through a successful Net Systems/UNH proposal, while OOA infrastructure resources were committed for acquiring system hardware. OOA engineering personnel funds (labor) are being used for the design and analysis of the system. Last year the basic design configuration and major systems were identified (see the 2004 Progress Report). In 2005, the design was completed, the external feed transfer system tested and seakeeping experiments conducted using a scale physical model. Construction is expected to commence early in 2006. An update of the progress is provided below.

Tasks necessary to complete the 20-ton buoy design included a finite element analysis on the mooring plate attachment design. Buoy scantlings were proposed based on experience with similar sized vessels and verified using strength of materials analyses. External feed transfer design proceeded systematically with a series of full scale prototype tests. A suitable pump and controller for the external feeding system were purchased for testing with the external feed transfer system. The completed design (see Figure 13 for an external view) was documented in large scale engineering drawings and a specification list. The design seakeeping response was evaluated using a Froude scaled physical model in the UNH wave/tow tank. To select a builder, a Request for Proposal document was completed and distributed by the Purchasing Office of the University System of New Hampshire (USNH)

The 20-ton buoy design was based on input gathered from OOA operations, Net Systems and potential builders during the design process. The completed design was detailed on large scale engineering drawings and components were defined in a specifications list. Major components include the steel shell, framing and decks; concrete ballast; four feed silos; internal feed transfer augers; external feed transfer mixing chamber and pumps; generator, and control system (see Figures 13-16). The buoy’s feed capacity is 20 tons; the buoy’s steel structure weighs approximately 25 tons; the concrete ballast weighs 24.4 tons, and the onboard equipment weighs 14.6 tons. Thus, the fully loaded total weight is 84 tons.

The interior is filled with components to allow the buoy to feed fish in submerged cages. Important internal components include a radio, diesel generator, feed hopper, mixing chamber, batteries and computers housed in the buoy upper structure (see Figure 14). A mechanical flex-auger is located beneath each silo (4 total) and is capable of transferring feed pellets through a flexible pipe up to the central collection hopper in the superstructure. Below the hopper is the mixing chamber where water is introduced, creating a mixture which is piped down centrally to the main external feed transfer pump on the inside base of the buoy. The mixture is then pumped through selection valves to one of four exits located on the buoy bottom ­ each connected by feed hose to one of four possible cages.

The buoy profile is dimensioned (in inches) in Figure 15, which shows an external view of the machinery house, main cylindrical hull, conical chine level, and ballast can secured by gussets. Figure 16 is a vertical plane, cross-section view showing the relationship of internal systems with the buoy structural components such as framing and internal decks.

The buoy mass and hydrostatic analyses were continuously updated as the design was refined. Design weight increases demanded that new hydrostatic analyses be performed. Scantlings (vessel framing) and shell thicknesses were designed and analyzed using standard strength of materials calculations. A finite element analysis was performed on the mooring plate design to ensure structural integrity.

Survivability of the buoy was of major concern. Sufficient reserve freeboard and stability to resist ice loads were incorporated into the design. Foam floatation was also included into the design to allow positive buoyancy of the buoy in case of free flooding.

One area in particular that was focused on was the hull structure and ballast. The scantlings and internal decks were discussed at length with members of the engineering group as well as with representatives of Net Systems. Only large weight contributions were considered in the initial weight analysis. With additional major structures included in the design, further hydrostatic analyses could be performed. After every major weight component was incorporated into the design, a new hydrostatic analysis was performed. As a result of some of these refinements, the ballast weight was increased and configuration adjusted. This was to ensure one of the major design criteria items was satisfied - positive righting moment at all angles under all conditions.

The mixing chamber is a vital component in the design of the 20-ton feed buoy. This is where fish feed pellets will be introduced into water and pumped to the submerged net pens. Since this mixing chamber concept is new, a prototype was needed for testing to prove the concept. (A complete description of the inner and outer chambers, pipe layouts and pump locations is included in the 2004 Progress Report.) A full scale mixing chamber prototype was constructed at UNH and is shown in Figure 17.

After construction, a series of three mixing chamber tests were conducted. The initial test was to verify water levels and transport directions within the mixing chamber. The other two tests were to investigate modifications to the mixing chamber (as result of the first test) and to test a PRAqua fish pump.

The first test, on Jan. 19, 2005, showed that water levels were as designed and the flow traveled as intended. To minimize pellet damage (see 2004 Progress Report) it was decided that a fish pump would be the best option for a pump. Great Bay Aquaculture (GBA), located in Newington, NH, allowed us use their PRAqua fish pump for the mixing chamber feed tests. The PRAqua pump was one of the two types of pumps being considered for use in the 20-ton buoy. The second and third tests were conducted on March 4 and 5, 2005 at the GBA facility.

With the feed pump in the system, actual fish feed pellets were introduced into the mixing chamber. The feed exited the mixing chamber quickly, was pumped through the feed pump and was discharged into a water reservoir and caught in a net basket. The feed passed through the system with excellent results. The amount of damaged feed was minor. This confirmed the decision that a fish pump is necessary for the final feeding system design.

After the testing at GBA using the PRAqua pump, it was decided to obtain the other pump under consideration ­ a Wemco-Hidrostal fish pump. This was due to the PRAqua pump barely obtaining the desired flow under the design conditions. The pump reached the design goals as tested, but there was no reserve power to work against a head pressure increase. A head pressure increase is likely to occur in actual operation conditions based upon previous operational experience.

A Wemco-Hidrostal pump and Toshiba variable frequency controller were purchased for testing and eventual use in the final buoy. The pump and controller were delivered to UNH for testing in late April. The pump performed up to design specifications. Feed pellets were introduced into the mixing chamber and pumped through the feeding system. Minor pellet damage was visible. The overall results of the test were favorable. The external feeding system design, with the tested components, was completely acceptable.

A physical scale model was constructed for wave tank testing after the major design features were finalized (see Figure 18). The scale factor was determined by using a depth based approach. The ratio of tank depth to depth of water at the OOA site was used resulting in a scale factor of 1:20.7.

Free-release tests were conducted in the wave/tow tank from June 30 to July 1, 2005. Heave (vertical motion) and pitch (angular motion) tests were performed under two different loading conditions: load and light. The load case corresponds to a buoy with full feed and fuel, while the light case includes only the permanent structures on the buoy.

The data for both the heave and pitch tests were acquired using UNH’s optical positioning instrumentation and evaluation (OPIE) measurement system (Michelin and Stott, 1996). The OPIE system uses a digital camera, computer and processing software to track the motion of black dots placed on the white buoy. The data exported by OPIE was then further analyzed using Matlab® software. For each type of test and loading, a set of at least six tests were recorded. These were each analyzed and then averaged to yield the results shown in Table 1.

Wave tests were conducted in the wave/tow tank during July 14-19, 2005. The two loading conditions (load and light) were tested, as with the free-release tests. A total of 10 different regular (single frequency) wave inputs were used. Wave periods/frequencies bracketed common wind generated, storm and sea swell waves found at the OOA site. The purpose of the wave testing was to determine the heave, surge (horizontal motion) and pitch Response Amplitude Operators (RAOs). The RAOs are defined as the ratio of the buoy response to the wave forcing and were calculated for the buoy. At low frequencies, the buoy was observed to follow the wave vertical motion indicating a heave RAO around unity. In the frequency band where the buoy had a large heave RAO (greater than 1.5) the wave energy at the site is expected to be small. This occurred around the heave damped natural frequency of 0.274 Hz. Based upon the model tests, the buoy is a primarily a wave follower with respect to vertical motion and should not have very severe reactions to the wave spectra that are normally observed at the OOA site.

During the Summer 2005, OOA engineering and operations teams worked with USNH Purchasing to prepare an RFP package for outside fabrication of the buoy structure and installation of the major components. Two bids were received which exceeded the funding allocated. A search was immediately initiated to identify sources of additional funds and for broadening the competition. Having strengthened our position, we are presently conducting a second RFP process.

One-Ton Buoy Sinking and Recovery: On December 27, 2004, at 3:00 AM the 1-ton feed buoy’s control system sent warnings to shore that it appeared to be taking on water. (UNH’s 1-ton feed buoy has been described in the 2003 and 2005 Progress Reports.) That day there was subfreezing temperatures along with a 30-knot northeast wind, 1-knot surface current, and wave heights in excess of 20 feet. At 3:30 AM the buoy ceased communicating with shore altogether. One week later a crew went out to check on the buoy and discovered it was not at the surface. Several weeks later, a dive team was sent down to inspect the mooring lines and discovered the buoy lying on the bottom in 175 feet of water. The divers inspected the buoy carefully and looked inside of it but were unable to determine the cause of the failure in the poor visibility.

In early August of 2005, the 1-ton feed buoy was recovered by the US Coast Guard and brought to the Portsmouth Naval Shipyard for further inspection. After viewing the interior, it was theorized that an aluminum weld supporting the heavy rotary airlock dosing unit and mixing chamber broke free when the buoy was being buffeted around in the high sea state. In this scenario, the heavy stainless steel unit then broke the main feed line exiting the buoy down to the cage below the water line. This in turn allowed water to enter the buoy. Since the weld broke right below the feed silo, nothing restrained the feed from dispensing onto the buoy floor. The feed was still visible in the subfloor bilge area eight months after being submerged. The feed that filled the bilge area probably clogged the bilge pump and prevented it from pumping out the incoming water from the broken feed pipe.

There is no way of determining with absolute certainty that the events occurred in this manner. With the weather and sea state the way it was, many things may have contributed to the feed buoy’s termination. The above description has been the best determination of event chronology so far.

In any case, the experience emphasizes the importance of designing support structures to restrain heavy components against inertial loads as well as gravity. The inertial loads may be lateral as well as vertical. These factors have been taken into account in specifying supporting structures for components within the new 20-ton buoy design.

PROGRESS ON TASK #4: FINITE ELEMENT MODELING IMPROVEMENTS
Aqua-FE was originally developed to have the commercially available FEA pre-processing/post-processing program Mentat as its graphical user interface. This configuration has been successfully used by the OOA project to analyze various fish cage designs and corresponding mooring systems. Recently, the graphical user interface module Aqua-FEed was developed. This program has the capacity to create finite element meshes of truss-, beam- and buoy-type elements, prepare the environmental loading data, and prescribe the computational parameters in the input format of the Aqua-FE simulation software. The module is written in the programming language Python, and is compatible with any PC-based Windows operating system.

In addition, the computational efficiency of the Aqua-FE software was improved. Through a series of code modifications, the speed at which the program operates was increased. For example, a time savings of 40% was found when comparing the code with identical models of the same size in the same wave/current conditions.

The code was also modified to allow a horizontal change in water velocity. The original code applied the same environmental conditions to every submerged element in the model, regardless of wake effects or blockage that may be occurring due to objects such as net or cage components. This approach has worked well to date, due to the relatively small size farms and limited reduction of current velocities studied. However, this will not work for larger (more cages), near-shore systems (such as salmon farms) that have a varying current distribution throughout the site. The code was modified to account for this effect.

Two approaches were considered to account for horizontal velocity changes. The first was to develop a new element that incorporates a certain water particle velocity reduction. This approach was implemented with a certain degree of success, but only a single cage was modeled (Fredriksson et al., 2003b). This approach, however, doubles the number of element types. In addition, when there are multiple velocity reductions, this results on an excessive number of element types and reduces the efficiency of the program. The second approach was to allow multiple “current profiles” to be generated and applied to specific elements. Therefore, several different current profiles (for example, velocities of 1 m/s, 0.5 m/s 0.25 m/s) could be applied to different elements (three cages, each effected by a different current). This approach allows for a “horizontal current profile” feature to be used in Aqua-FE.

The program was modified to allow for up to 25 different profiles to be applied to various parts of the model. This would allow for a variety of profile application techniques to be investigated, and if needed, a large current reduction in a complex system. The code was modified to produce a specifically generated file which contains all the wave (height, length, phase) and current (velocity, depth) information for each profile. The program then assigns the proper profile to the associated element for processing. This repeats for each element at each time step. Modifying the code in this manner allows for the most versatile use of the model without compromising the efficiency of the program.

PROGRESS ON TASK #5: BIOFOULED NET PANEL DRAG
Measurements were made to assess the increase in drag on aquaculture cage netting due to biofouling. Because the drag force acting on fish cage netting constitutes a major mechanism by which wave and current loads are imparted to net pens (Palczynski, 2000; Fredriksson et al. 2003a), quantifying this mechanism is important to the design of open ocean aquaculture net pen systems Drag force was obtained by towing net panels, perpendicular to the incident flow, in experiments conducted in a tow tank and in the field. The net panels were fabricated from netting stretched within a one-meter-square pipe frame. The net solidity, actual thread projected area divided by outline area, was 0.121. They were towed at various speeds, and drag force was measured using a bridle-pulley arrangement terminating in a load cell. The frame without netting was also drag tested so that net-only results could be obtained by subtracting out the frame contribution. Measurements of drag force and velocity were processed to yield drag coefficient (CD) values defined by:

for which D = drag force; _ = density; AN = area normal to the flow, and V = velocity. This work was done in a collaborative study with EPaint who supplied the net panels as well as funding to help support the field work and data processing.

Clean nets were drag tested in the UNH 36.5 m long tow tank. The average drag coefficient based on net outline area (1 m2) was 0.181; average drag coefficient based on actual thread projected area was 1.49. Nets were then exposed to biofouling during the summer of 2004 at the UNH OOA site. Nine net panels were recovered on October 6, 2004 and immediately drag tested at sea to minimize disturbing the fouling communities. The majority of the growth (see Figure 19) was skeleton shrimp (Caprella sp.) with some colonial hydroids (Tubularia sp.), blue mussels (Mytilus edulus) and rock borer clams (Hiatella actica). Since the deployment depth was 15 m (commensurate with submerged cages at the site), no algae were present. The net panels had been subject to several different antifouling treatments applied by EPaint, so the extent of growth varied amongst the panels. Drag force measurements were made using a bridle-pulley-load cell configuration similar to that employed in the tow tank. Fixtures and instruments were mounted on an unpowered catamaran, shown in Figures 20 - 22, that was towed alongside a workboat. Thus, the catamaran served as the “carriage” for field measurements.

Field observations were processed during the Spring and Summer 2005, and the work was summarized by Swift et al. (2005a, b). A velocity-squared relationship was fitted to the force, velocity data for each net panel minimizing the mean square difference. Net drag coefficients were then found by subtracting the frame contribution and using Equation 1. Increases in net-only drag coefficient varied from 6% to 240% of the clean net values. The maximum biofouled net drag coefficient was 0.599 based on net outline area. Biofouled drag coefficients generally increased with solidity (projected area of blockage divided by outline area) and volume of growth. There was, however, considerable scatter attributed in part to different mixes of species present.

PROGRESS ON TASK #6: DEVELOPMENT OF AN OPERATIONS CENTER
In January of 2005 the operations team spent a month looking into the 1-ton buoy transmissions over the whole deployment and also leading up to its termination. Operationally, all of the controls and electronics running in the buoy were determined to be fully functional at the time of the failure. All of the alarms that were installed operated successfully and warning messages were sent to shore as programmed.

In February of 2005 the 1/4-ton feed buoy was recovered for an extensive overhaul. This posed a great opportunity to upgrade several of the monitoring and control capabilities of this feeder. One of the key upgrades was to the communications with instrumentation at the cage. The WHOI Gumby hose conductors were cleaned and thoroughly tested before being reterminated with new splices. The expanded communications capability now allows for monitoring of the cage depth along with water temperature at three points vertically and salinity at one point in the cage. Previously the system could only monitor water temperature and salinity at one point in the cage. Unfortunately, due to conductor degradation, the video system that formerly allowed for two cameras to be monitored in the cage had to be reduced to one video feed. A new video transmission system was developed, however, allowing for higher frame-rate feeds back to shore. The end result of the video upgrade allows for nearly continuous motion (high frame rate) video monitoring of the one camera back to campus with only a ten second lag between video capture and display.

The software controlling the buoy was also rewritten at this time and now allows for closer monitoring of feed operations and timing. The code was rewritten after the 1-ton feed buoy code model and greatly improves the speed of problem diagnostics.

PROGRESS ON TASK #7: EXTERIOR-INTERIOR CAGE FLOW REGIMES
To improve farming of fin fish in sea cages, it is important to know the flow environment around and inside the cage. For the engineering design of the cages, velocity shadowing (see TASK #4) is important due to the fact that the forces acting on the cage are highly dependent on current. On the environmental side, the flow environment around and inside the cages is an important factor for flushing rate, feeding, and dispersion of effluents from the cages.

One way to get more insight into this problem is to make calculations of the flow. The problem is not trivial to solve, since the main part of a fish farming cage usually is made out of net with many small meshes. Nontrivial fluid dynamic problems are usually solved using some kind of computational fluid dynamics (CFD) software. One of the widely used CFD software packages is FLUENT from Fluent Inc.

When creating a model of a fish farming cage, the number of elements in the net is too large to be modeled as solid bars, and the net has to be represented in some other way. Using a thin sheet of porous material to represent the net of the cage is a promising way to deal with this problem.

The pressure drop in the porous media in FLUENT is described as a function of current velocity through the media, which consists of a linear term and a squared term that have constants associated with them that need to be found either from experiments or from some analytical relationship. We chose to use drag tests of one-meter by one-meter net panels performed in the UNH tow tank to assess those constants. The constants were found for a dense small mesh net with a solidity of 45 %, and 3d models of the net panel were run (Figure 23) for the same velocities as used in the tank. These results showed good agreement with the measured data, and it was decided to continue and start creating a model of a cage.

A 2d model of a 30 m diameter circular cylinder of the same net material is shown in Figure 24. This simulation can be viewed as a simple model of a circular gravity type fish cage with the same diameter, which is quite common in the salmon farming industry. Note, however, that the solidity, and hence the velocity reduction of the net used, is much higher than what is common in fish farming cages. The fact that the simulation is 2d will also affect the result, and a 3d will probably give a different result.

CITED MATERIAL:
Baldwin, K., B. Celikkol, R. Steen, D. Michelin, E. Muller, P. Lavoie (2000). Open Aquaculture Engineering: Mooring and Net Pen Deployment. Mar. Tech. Soc. J. Washington D.C. Vol 34, No. 1 pp 53-67.

DeCew, J., D.W. Fredriksson, L. Bougrov, M.R. Swift, O. Eroshkin, and B. Celikkol (2005). "A Case Study of a Modified Gravity Type Cage and Mooring System using Numerical and Physical Models", IEEE Journal of Oceanic Engineering, Special issue on Open Ocean Aquaculture Engineering. Vol 30, No. 1, 47-58.

Fredriksson, D.W., M.R. Swift, E. Muller, K. Baldwin and B. Celikkol. (2000). Open Ocean Aquaculture Engineering: System Design and Physical Modeling. Mar. Tech. Soc. J. Washington D.C. Vol 34, No. 1 pp 41-52.

Fredriksson, D.W., M.J. Palczynski, M.R. Swift, J.D. Irish and B. Celikkol. (2003a). Fluid Dynamic Drag of a Central Spar Cage in C.J. Bridger and B.A. Costa-Pierce, editors. Open Ocean Aquaculture: From Research to Commercial Reality. The World Aquaculture Society, Baton Rouge, Louisiana, United States. pp 151-168.

Fredriksson, D.W., M.R. Swift, I. Tsukrov, J.D. Irish and B. Celikkol. (2003b). Fish Cage and Mooring System Dynamics using Physical and Numerical Models with Field Measurements. Aqua Eng. Vol 27, (2), pp. 117-270.

Fredriksson, D.W., J. DeCew, J. Irish, V. Panchang, D. Li and B. Celikkol (2003c). SK Progress Report for the period between July 7, 2003 and December 31, 2003. Project Title: Engineering Design and Analysis for More Secure Salmon Net Pen Systems. Grant # NA03NMF4270183.

Fredriksson, D.W., J. DeCew, M.R. Swift, I. Tsukrov, M.D. Chambers, and B. Celikkol. (2004a). The Design and Analysis of a Four-Cage, Grid Mooring for Open Ocean Aquaculture. Aqua. Eng. Vol 32 (1) pp 77-94.

Fredriksson, D.W., J. DeCew, J. Irish, V. Panchang, D. Li and I. Tsukrov (2004b). SK Progress Report for the period between January 1, 2004 and June 30, 2004. Project Title: Engineering Design and Analysis for More Secure Salmon Net Pen Systems. Grant # NA03NMF4270183.

Fredriksson, D.W., J. DeCew, J. Irish, V. Panchang, D. Li and I. Tsukrov, (2004c). SK Progress Report for the period between July 1, 2004 and December 31, 2004. Project Title: Engineering Design and Analysis for More Secure Salmon Net Pen Systems. Grant # NA03NMF4270183.

Fredriksson, D.W., M.R. Swift, O. Eroshkin, I. Tsukrov, J.D. Irish and B. Celikkol, (2005) “Moored Fish Cage Dynamics in Waves and Currents”, IEEE Journal of Oceanic Engineering, Vol 30, No. 1, 28-36.

Fullerton, B. Swift, M.R., Boduch, S., Eroshkin, O. and G. Rice, (2004). Design and Analysis of an Automated Feed Buoy for Submerged Cages. Aqua. Eng. Vol 95 (1) pp. 95-111.

Open Ocean Aquaculture Engineering 2004 Progress Report (2004) Annual Progress Report submitted to CINEMAR, NOAA, University of New Hampshire, Durham, NH, 43p.

Michelin, D. and S. Stott (1996) “Optical Positioning, Instrumentation and Evaluation”, Ocean Projects Course Final Report, Tech 797, Sea Grant, Kingman Farm, University of New Hampshire, Durham, NH, 85 p.

Palczynski, M.J. (2000). Fish Cage Physical Modeling. M.S. Thesis, Ocean Engineering, University of New Hampshire, Durham, NH, 111 p.

Rice, G.A., M.D. Chambers, M. Stommel, O. Eroshkin. (2003). The Design, Construction and Testing of the University of New Hampshire Feed Buoy in C.J. Bridger and B.A. Costa-Pierce, editors. Open Ocean Aquaculture: From Research to Commercial Reality. The World Aquaculture Society, Baton Rouge, Louisiana, United States p. 197-203.

Santamaria, J., C. Monahan, J. Scott, B. Celikkol, D. Fredriksson and J. DeCew (2004). “Development of a Submersible Fish Cage for Open Ocean Aquaculture.” Small Business Innovation Research, Phase I Final Report. SBIR Proposal #04-4-11, Contract # DG133R-04-CN-0126.

Swift, M.R., D.W. Fredriksson, A. Unrein, B. Fullerton (2005a) ”Drag Force Acting on Biofouled Net Panels”, Final Report submitted to E Paint Corporation, Falmouth, MA, 11p.

Swift, M.R., D.W. Fredriksson, A.Unrein, B. Fullerton, O. Patursson and K. Baldwin. (2005) ”Drag Force Acting on Biofouled Net Panels”, Aquaculture Engineering, (Accepted for publication).

Tsukrov, I., Ozbay, M., Fredriksson, D.W., Swift, M.R., Baldwin, K., and Celikkol B., 2000. Open Ocean Aquaculture Engineering: Numerical Modeling. Mar. Tech. Soc. J. 34 (1), 29-40.

Tsukrov, I., Eroshkin, O., Fredriksson, D. W., Swift, M.R. and Celikkol, B., (2003) “Finite Element Modeling of Net Panels Using Consistent Net Element”. Ocean Eng. 30: pp. 251 ­ 270.

C. Important Results or Findings
Results are incorporated above.

D. Difficulties Encountered
Due to recent changes in the construction industry, the 20-ton feed buoy will be more expensive than anticipated. This challenge is being dealt with by careful allocation of resources and by a thorough search for the best value in outside fabrication. The sinking of the 1-ton buoy was a painful learning experience. The new buoy, however, will be designed for sufficient strength in all members requiring watertight integrity.

Dr. David Fredriksson left our team August 1, 2005 to assume a faculty position at the U.S. Naval Academy. Increased activity by both the PIs and engineering staff will be necessary to maintain productivity.

E. Anticipated Success in Meeting Project Objectives on Schedule
See Section II below.

F. Reports, manuscripts, and presentations resulting from the project
Reports and manuscripts have been incorporated in the body of the report as cited material. The engineering team has also been involved in several other related scientific activities including workshops, presentations at conferences and other open ocean aquaculture project activities. These other initiatives are summarized below.

Conferences and Workshops
Aquaculture America 2005: DeCew, J., “Response of the Deployed Open Ocean Aquaculture Cage”, January 19, 2005, New Orleans, LA.

Aquaculture Association of Canada: DeCew, J., “University of New Hampshire Engineering Activities Relating to Open Ocean Aquaculture”, July 4-6, 2005, St. Johns, Newfoundland, Canada.

IEEE/MTS OCEANS 2005: Chaffey, M., W. Paul, A. Hamilton, S. Boduch, "The Use of Snubbers as Strain Limiters in Moorings", September 2005, Washington, DC.

Open Ocean Aquaculture Engineering Workshop: Fredriksson, D., “Numerical Modelling of Structures” and Rice, G., “The Operation and Design of a Submerged Ocean Fish Farm”, August 14-18, Torshavn, Faroe Islands.

Journal Articles
DeCew, J., D.W. Fredriksson, L. Bougrov, M.R. Swift, O. Eroshkin, and B. Celikkol (2005). "A Case Study of a Modified Gravity Type Cage and Mooring System using Numerical and Physical Models", IEEE Journal of Oceanic Engineering, Special issue on Open Ocean Aquaculture Engineering. Vol 30, No. 1, 47-58.

Fredriksson, D.W., M.R. Swift, O. Eroshkin, I. Tsukrov, J.D. Irish and B. Celikkol, (2005) “Moored Fish Cage Dynamics in Waves and Currents”, IEEE Journal of Oceanic Engineering, Vol 30, No. 1, 28-36.

Swift, M.R., D.W. Fredriksson, A.Unrein, B. Fullerton, O. Patursson and K. Baldwin. (2005) ”Drag Force Acting on Biofouled Net Panels”, Aquaculture Engineering, (Accepted for publication).

Related Open Ocean Aquaculture Projects
Development of a Low Cost, Submersible Plastic Net Pen: Design, construction and testing of a submersible, gravity-type fish cage, JPS Industries, SBIR Phase II, NOAA.

Engineering for More Secure Salmon Net-Pen Systems: Field measurements and finite element modeling of an Eastport, ME salmon farm, NOAA/NMFS.

Offshore Semi-Autonomous Fish Feeding System: Development of a 20-ton capacity buoy for remote fish feeding, Net Systems SBIR Phase II, NOAA.

Drag Force Measurements of Biofouled Net Panels: Tow tank and at-sea measurements of clean and biofouled net panels, EPaint, SBIR Phase II, NOAA,

Fish Farm Design and Modeling: Design and Aqua-FE modeling of a submerged, 6-cage grid mooring off Kona, Hawaii, Kona Bluewater Farms and Net Systems.

Analysis of a High Density, Low Volume Cage: Aqua-FE modeling and design advising for the development of a small cage/mooring for Weitou Bay, China, American Soybean Association.

II. Tasks and Activities for Next Reporting period

A. Tasks for the next reporting period
Please note that many of the tasks and activities evolve throughout the year. A general guideline, however, is provided below.

  1. Investigation of commercial scale fish cage systems.
  2. Analysis of the mooring grid system at the OOA site.
  3. Feed buoy development including building, deployment and evaluation.
  4. Improved numerical modeling techniques.
  5. Development of an operations center.
  6. Investigation of exterior-interior cage flow regimes.

B. Brief work plan to accomplish tasks
Investigation of Commercial Scale Cages: As an ongoing part of the project, the workplan includes:

  • Continue to work with local industry to design, analyze and build new cage systems through the activity of the Small Business Innovation Research (SBIR) program.
  • Complete and deploy a 1:1.6 scale submersible gravity cage and evaluate performance
  • Design and build a full scale prototype

Analysis of Mooring Grid: The workplan includes:

  • Perform computer simulations as needed to analyze mooring grid capacities for various scenarios
  • Acquire and process data from the load cells installed in the grid.

Feed Buoy Development: Working with the operations team and Net Systems, the workplan includes:

  • Supervise the construction of the 20-ton capacity feed buoy
  • Design, assemble and install the control, power and telemetry
  • Design, assemble and deploy the anchoring and feed hose system
  • Deploy, monitor and evaluate the completed system

Numerical Modeling Development: The workplan for the numerical modeling effort includes:

  • Incorporate biological fouling characteristics in net elements
  • Incorporate velocity shadowing in Aqua-FE

Operations Center: The following tasks will be performed for development of the operations center.

  • Develop video for the 20-ton buoy system
  • Construct the diagnostic data system for archival capability

    Exterior-Interior Flow Regimes: The workplan for investigating flow around and through net pens will involve:

    • Calibrate the Fluent porous media model using drag data for one-meter-square net panels
    • Use the porous media option to construct cage models to predict flow around and through standard cage shapes, as well as compute the associated drag
    • Compare Fluent predictions with tow tank and field cage data.

    C. Anticipated concerns or difficulties
    No major concerns or difficulties are anticipated.

    III. Expenditures
    Expenditures to date are all within budget.



    • Copyright 2007, Atlantic Marine Aquaculture Center, Durham, NH 03824
    The Atlantic Marine Aquaculture Center is a partnership of the University of New Hampshire (UNH) and the National Oceanic and Atmospheric Administration (NOAA).