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

Principal Investigator: B. Celikkol, K. Baldwin, J. Irish, M. R. Swift, I. Tsukrov

I. Accomplishments

A. Scheduled Tasks
Background: For the past eight 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 biomass capacity at the site; the two small systems were replaced with a larger four-bay grid mooring enabling the deployment of additional containment structures (Fredriksson et al., 2004 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. During 2006, the engineering component supported 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 2005 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
The OOA engineering team has been involved in the analysis of possible commercial size fish containment systems. Three systems have recently been investigated: (1) a low cost, submersible plastic net pen, (2) a rigid, fixed volume, spherical net pen, and (3) a small volume, high density net pen.

A Low Cost, Submersible, Plastic Net Pen: In 2005, a Phase II SBIR grant was awarded to JPS Industries UNH to develop a low-cost, submersible fish cage for open ocean aquaculture (Santamaria et al., 2005). This cage concept (see Figure 1) is a modified version of a traditional gravity cage. The upper rim 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 upper superstructure of the system. 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 and ballast chain (or deadweight anchor depending upon bottom conditions) will hang below the bottom rim. The weight and bridle arrangement provides a restoring force that helps maintain volumetric stability if the two rings above move relative to each other in waves and currents and during surface or submerging operations.

A 1:1.623 scale cage was first chosen to be built to help optimize construction, assembly and deployment techniques. This scale factor was chosen for two reasons: (1) it was important to have a cage size large enough that similar construction methods would be used on the full scale system and (2) to use the cage as a possible (future) grow-out and/or nursery net pen. The resulting cage had an overall diameter of 15.2 m (50 ft) and a volume of 1100 m3. In January 2006, the individual components were ordered and/or manufactured (see Santamaria et al., 2006a).

After construction of the metal fittings, the components were assembled and aligned, prior to shipping, at the JPS manufacturing plant, located in Bristol, New Hampshire. The cage rim was “dry-fitted” to insure that the components were compatible for future system construction. In June 2006, the cage system was shipped to and assembled at the New Hampshire Port Authority in Portsmouth, NH. Figures 2, 3 and 4 show the system under construction.

The cage (shown in Figure 5) was secured into the northwest bay of the submerged grid mooring system with four sets of Y-lines. Two 20,000 lbf capacity load cells and recorders were attached in the northeast and southwest lines. The load cells were bolted to a strongback and held a submersible data recorder. To measure the environmental conditions, a monitoring buoy, located approximately 150 m to the east of the submerged grid, was used. This buoy measures the waves, surface and subsurface currents, salinity, temperature and other environmental factors at the site. The buoy output data will be used to determine the forcing parameters acting on the cage. The cage was slated to remain at the surface for the duration of the deployment in order to experience maximum wave loading to test construction robustness.

In July 2006, the system underwent a series of hydrostatic tests. The tests were performed to determine the surfacing/submerging and vertical stability characteristics of the cage. The first sets of experiments examined the airlift and its capacity to lift in “stages.” The airlift was designed to surface in increments (~ 9 ft) allowing the cage to be used with fish that have air bladders (such as cod), providing the animal proper decompression time. The cage was submerged to its resting depth, approximately 8 to 9 m (28-30 ft), and is shown in the process of submerging in Figure 6.

Once the system came to equilibrium at the end of each stage, additonal water in the airlift was purged (using air hoses from the surface) in increments. This system worked well, and results of these tests can be found in Santamaria et al. (2006b). The cage system was recovered in November 2006 and is currently under an engineering review. The system components will be inspected, and any information gathered, such as fatigue on joints, wear points, etc., will be taken into consideration for the full scale system (slated to begin construction in spring 2007).

A Rigid, Fixed Volume, Spherical Net Pen: The second system investigated was developed by Ocean Farm Technologies, LLC called the “AquaPod” (see 2005 Progress Report). This system was deployed and placed in the UNH OOA submerged grid system in 2005. 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 2006, however, the data was re-analyzed to account for wake effects experienced during the tow. A new, updated velocity ­ drag curve was generated for use in predicting the system’s drag force under various current regimes. The results of this analysis were reported by DeCew et al. (2006a).

A Small Volume, High Density Net Pen: A third study was initiated between UNH and the American Soybean Association (ASA) to investigate a small volume, high density net pen. A numerical model of a prototype ASA cage system was constructed using a finite element program developed UNH called Aqua-FE. The aquaculture system was modeled to determine how the system will operate in normal and extreme environmental conditions.

The system consists of a 100 m3 cage (2 m x 4.5 m x 7 m) secured by a single point mooring (see Figure 7 and Figure 8). The cage’s main structure was constructed of HDPE pipe with galvanized steel fittings. Chain ballast hangs below the lower cage rim providing a restoring force. The net chamber is formed by attaching net panels to the cage framework. The cage’s framework and netting provide a system with a fixed volume, capable of withstanding deformations due to currents and waves. The rigid cage is held to the mooring by two sets of bridle lines, attached to the upper and lower cage framework (Figure 8). A single deadweight anchor secures the system to the seafloor. A buoy (880 N maximum buoyancy force) suspends the single point mooring and serves as a tie-up location for servicing vessels.

A simulation was performed under typhoon-type conditions to predict the maximum stresses in each major component. Using information provided by the ASA, waves with a significant wave height of 5 meters and a dominant period of 9.6 seconds were used as input. A JONSWAP spectrum was used to represent this storm. A 1.5 m/s current in the same direction as the waves was also applied to encompass worst case conditions. The maximum tensions in the mooring gear were predicted for this storm event. A representative time series of anchor chain tensions can be seen in Figure 9. The stud-link chain had maximum tension of 55.6 kN. Other results showed that tensions in the lower bridle lines also tended to be larger than those in the upper bridle lines, with tensions in the lower bridle lines reaching over 15 kN. When the system loads were compared to minimum breaking loads (M.B.L.) for similar equipment, the safety factors proved to be adequate. The cage, in this storm condition, sunk to a mean, steady state depth of 4.8 m. The full set of results, including a detailed description of the input parameters, investigated elements and load comparisons, is reported by DeCew et al., (2006b).

PROGRESS ON TASK #2: ANALYSIS OF CAGE MOORING GRID SYSTEMS
Over the last year, mooring systems have been investigated using both numerical modeling and field measurements. Calculations were completed using the UNH finite element computer program Aqua-FE. One application was a large salmon farm having surface cages moored using a 20-bay grid system. In addition, a measurement program to determine actual deployed geometry and line tensions at the OOA site was completed.

Investigation of a Near-Shore Salmon Farm: A direct result of the OOA project’s numerical modeling efforts and expertise in the field led to UNH being awarded a Saltonstall-Kennedy Grant (# NA03NMF4270183) entitled “Engineering Design and Analysis for More Secure Salmon Net Pen Systems.” The objective of the project was 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 targeted the program area to establish more secure cages to reduce farmed fish escapement. In addition to this objective, the work investigated the feasibility of expanding salmon farming operations into more exposed areas in an effort to reduce environmental and multi-use issues.

The project was completed this year, and information was obtained on a variety of important aquaculture engineering related fronts, such as the load distribution throughout the farm, environmental conditions present at the site and water velocity fluctuations throughout the farm. In-situ measurements and numerical modeling methods were employed. In addition, this information led to new approaches in modeling large complex systems, as well as ways to investigate the structural integrity of high density polyethylene cage rims. The results of this study can be found in Fredriksson et al. (2006a), while velocity reduction issues are discussed below in PROGRESS ON TASK #4: IMPROVED NUMERICAL MODELING TECHNIQUES.

Line Tension in the OOA Grid/Mooring System: The four-bay mooring system designed and deployed by UNH in August 2003 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 three and a half years, there was still a lack of understanding regarding the actual deployed geometry and load distribution. The concern was that grid depth and line tension would be sensitive to the deployed anchor locations. Anchors that were not positioned correctly could have reduced reserve holding capacity or result in problems with snap loads.

The sensitivity of grid and anchor line static tensions to the placement of a single corner anchor was computed using Aqua-FE as described by Rice et al. (2006) and Rice (2006). The analysis indicated that discrepancies of 3 m in anchor position could result in anchor/grid line tension changes on the order of 7 kN. Since the design tensions were 11 kN for grid lines and 14 kN for anchor lines, variations on this order were regarded as significant. A field program was initiated in which four load cells were installed in two anchor lines and two grid lines attached to the northeast grid corner. Deployment was difficult, and data acquired from this instrumentation was found to be unreliable.

Since tension measurements were needed and it was clear that more than four locations would be of interest, a new, portable line tension meter was designed, built, calibrated and used to make key tension measurements (Rice et al., 2006 and Rice, 2006). The mobile tension meter, shown in Figure 10, was diver operated. The meter was placed so that the line was against the two wheels directly over the jack. The ram with load cell was jacked against the line deforming it by a prescribed amount. The load cell compression force was related to line tension from calibration results. Field measurements of selected grid and anchor tensions were made on April 6, 2006 with the results shown on Figure 11. Though differences between measurement and design tensions exist, the discrepancies do not compromise the functionality or safety of the system.

PROGRESS ON TASK #3: FEED BUOY DEVELOPMENT
Twenty-Ton Feed Buoy Program: A 20-ton capacity feed buoy is under construction to remotely feed an increased biomass of growing fish stock. Due to the buoy’s cost, a unique collaborative arrangement was established between Ocean Spar (formerly 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) were used for the design and analysis of the system. In 2005, the design was completed, the external feed transfer system tested and seakeeping experiments conducted using a scale physical model (see 2005 Progress Report and Turmelle et al., 2006).

Work during 2006 included conducting a Request for Proposal (RFP) process and awarding a construction contract, as well as continued physical and computer modeling. The RFP process generated acceptable bids; a builder was selected, and construction has begun. Components were purchased and transported to the buoy construction site and dry fit into position. Physical modeling was done to test an alternate “Upper” mooring attachment. The wave tank tests performed were the same type as the previous model tests. Computer modeling consisted of simulating the buoy and mooring system dynamics using the UNH finite element analysis program Aqua-FE. The computer and physical model test data were compared with favorable results. Slight modifications to the mixing chamber design were made to incorporate easier cleaning of the internal surfaces. In addition, supervision of buoy construction was performed utilizing six site visits to the fabrication site in Weldon, New Brunswick, Canada.

Request For Proposal / Construction: The bid from Aquaculture Engineering Group Inc. (AEG) was accepted by UNH on February 13, 2006. Construction began in early March at AEG’s fabrication facility in Weldon, NB, Canada. At this time (December 2006) the major buoy hull components have been completed and welded into one assembly (see Figure 12). Another inspection trip is planned for later in the month of December 2006.

Construction has been behind schedule due to components arriving late to the fabrication facility. These delays have predominately been the result of component manufacturer’s not completing and shipping parts on time. These delays have resulted in the completion date for the buoy being pushed back until the spring of 2007.

Components required for the buoy’s functioning were purchased and shipped to the fabrication site. These items included major items such as: feed storage silos (four), fuel tanks (two), generator, mixing chamber, and flex-augers (four). Numerous small items were also purchased and delivered to the site.

While the fabrication process has moved forward, there have been problems. One major component, feed storage silos, was not manufactured to the tolerances that were provided by the manufacturer upon purchase. The silo’s diameter was larger than specified and would not fit in the holes that were in the intermediate decks. As a fix, these holes were enlarged to allow the insertion of the large diameter silos into position. Figure 13 shows the silos in the buoy as well as one flex auger mounted in position.

In an effort to remedy some of these delays, the control and telemetry electronics design and installation work was outsourced to AEG. Originally, UNH was to complete the electronics installation and testing after arrival in New Hampshire. Under the new plan, the buoy will be able to go straight into service potentially saving time.

At the time of writing the major fabrication is complete. Ballast concrete has been poured into the ballast can (see Figure 14) and major interior components have been installed (including silos, feed pump and flex-augers). Most of the major and minor machinery, tank and plumbing components are at the buoy’s location, ready for installation. Electronics installation is expected to commence before the end of the calendar year.

Mixing Chamber Design Improvements: The mixing chamber design (see Figure 15) was altered in an effort to allow easier access to the internal section of the mixing chamber. These design changes included the addition of two screw-out deck plates, with clear windows, as well as modifications to the top cap. The screw-out deck plates allow visible access to the internal section of the mixing chamber. The feed-water interaction can be observed while feeding operations are being conducted. The deck plates will allow viewing of different flow inlet control plates that are to be used during testing. The top cap diameter was increased to allow access, once removed, to both internal and external sections of the mixing chamber. Having access to both sections will allow easier maintenance and cleaning operations.

In an effort to minimize testing of the external feeding system while installed in the buoy, the mixing chamber was tested in New Hampshire before shipment to Canada. The mixing chamber was constructed to allow the changing of flow inlet control plates. Two separate tests were performed (see Figure 16). These tests resulted in the final design of the flow control plates. These plates were installed into the mixing chamber and shipped to Canada for installation into the buoy.

Control and Telemetry: This larger feed buoy requires an expanded controlling system. The approach used in previous buoys (see 2004 and 2005 Progress Reports) could have been expanded to the larger buoy, but it was based on a development approach, rather than a more off-the-shelf standard industrial controller approach. The decision was made to follow the standard industrial controller approach, and have AEG design and install the control system while they were building the 20-ton feed buoy, rather than UNH installing it after delivery.

This new approach has several advantages. The hardware is standard and easily replaced if a failure should occur. AEG is using this approach in their salmon fisheries, and could easily adapt their controlling software to the new system. One downside is that the new system requires a much higher level of power, and therefore requires the generator to be functional for any operation. Batteries will keep the controlling computer (a standard notebook PC) operational between times that the generator is running.

Utilizing the experience with previous feed buoys, a document was prepared and reviewed with AEG, which specifies the wiring code compliances and the items to be controlled/monitored. This approach was very useful as it outlined the work to be done and the software approach for AEG. The power system is critical to the operation of any function of the feed buoy, and an outline of the power distribution is given in Table 1. The document also stated that all wiring for the buoy will be completed in compliance with the US NFPA 2005 National Electric Code and all wiring will retain specific ratings for watertightness.

Once the main power is on and distributed to the various supply lines, the system can start controlling the various components - the main one being the feeding process. However, once the generator is powered up, the system will continuously monitor a long list of diagnostic outputs from the generator, and take emergency actions if there is any problem. This includes alerting the shore control center of any problems. Also, the system supplies power for 12 interior lights, three bilge pumps and two fresh air blowers.

In addition to controlling the various processes the controller needs to monitor a large number of sensors (Table 2) to insure that there is nothing wrong in the buoy. The controller is programmed to take a set action in case of any problem and alert the shore control center. In addition, during the feeding process the controller monitors the level of feed, controls the rate of feeding, checks for high level in the feed hopper and high pressure in several places in the feed hose system to determine if any problem, such as blockage occurs, and again take a predetermined responsive action.

Finally, every hour the system checks the feed buoy status (Table 3) if another action is occurring or not, to provide information to the control center on the system status. Also, when the feed buoy is actively performing a programmed action, these quantities are monitored to insure that everything is going well, and again responsive action is taken in case a problem exists (such as a blown breaker).

The telemetry of the feed buoy status and the changing of scheduled actions is a critical part of the system. The feed buoy is capable of operating on its own without direct control from shore, but monitoring what things are occurring is important to regular scheduled feeding to optimize fish growth and well being. Success with standard 900 MHz Spread Spectrum radios in the past will be utilized. Also, we have procured some newer technology radios still operating at 900 MHz with increased bandwidth for shore-based control of the offshore system.

Physical Modeling: In an effort to minimize the pitch response that was observed in previous wave model tests (see 2005 Progress Report), a second set of tests was conducted. This series of wave tests used a higher “Upper” mooring attachment location, closer to the center of gravity of the buoy (see Figure 17). The original tests were conducted using the “Lower” mooring attachment. The buoy physical model was altered with the addition of two new mooring attachment points.

The modified buoy was tested during December 2005 and January 2006 in the UNH wave/tow tank. The wave tests were conducted over the same range of wave profile inputs as that of the original. The purpose of the wave testing was to compare the Heave, Surge and Pitch Response Amplitude Operators (RAOs) between the two mooring attachment locations. The RAOs are defined as the ratio of the buoy response to the wave forcing. All tests were analyzed using the same procedures.

Comparisons showed that both mooring attachment locations resulted in similar wave response. For both locations, the buoy is a wave follower with respect to vertical motion, and for large waves should not have severe reactions to the wave spectra that are normally observed at the expected buoy location. The changes in the RAO values for the different mooring attachment points did not justify the significant design changes that would arise from moving the buoy mooring attachment point. The mooring location on the buoy will remain at the “Lower” attachment point.

Numerical Modeling: Aqua-FE modeling of the 20-ton buoy design was performed to optimize modeling procedures for large, solid floating bodies. Predicted heave and pitch natural frequencies were compared favorably with those obtained from physical scale model tests as discussed in PROGRESS ON TASK #4: IMPOVED NUMERICAL MODELING TECHNIQUES below.

The optimized Aqua-FE feed buoy representation was then used to design the mooring system. Due to space limitations in the UNH wave/tow tank, the full mooring system could not be set up for physical experiments. Aqua-FE was applied to the full system, including the cage and site grid, and was used to model the response to large amplitude storm waves combined with current. The present design of the feed buoy mooring consists of a four legged system separate from the UNH OOA grid system (see Figure 18). The feed buoy was not moored directly to the grid system for two reasons: the grid was not designed to hold a large surface buoy, and the grid’s purpose is to serve as an independent scientific/engineering platform. The northeast grid corner was chosen for the buoy location in order to minimize the distances from the buoy to the cages to keep feed hose lengths as short as possible as well as have the mooring legs that leave the site be parallel to the navigation LORAN lines. The buoy could not be located inside the grid due to the interference of the mooring with grid cage surfacing operations. A large scope (6:1) was desired for the mooring to minimize the downward force that would be exerted on the buoy with a tight mooring.

The Aqua-FE analyses were performed using multiple wave heights, periods, and currents. The majority of the analyses were done using a design wave that has the following parameters: 9.0 m wave height, 8.8 second period, and a 1 m/s current that is constant with depth and in the direction of the wave train. Using the design wave and a worst-case scenario, one mooring leg taking the entire load of the wave forcing, the maximum tension that was found in a single anchor leg was 282 kN. This tension value is serving as the basic criterion for choosing and acquiring mooring gear. With the present mooring design the buoy’s watch circle will be a maximum/minimum straight line distance of 72/49 meters from the northeast grid corner. Hose/support lengths from the buoy to the grid will be specified to accommodate these extremes.

Quarter-Ton Feed Buoy: Until the 20-ton feed buoy becomes operational, remote feeding is being conducted using the previously developed quarter-ton capacity feed buoy (see Fullerton et al., 2004). The quarter-ton feed buoy controller was upgraded last year to provide increased control: programs running longer than an hour, selection from several on-board feeding programs to increase feeding flexibility and for automatic downloading of new scheduling and feeding control files. This year the feed buoy was recovered, the controller serviced and redeployed and the last year’s updates tested. After the usual minor problems due to the disassembly and reassembly of the system, it is now successfully feeding the fish and reporting back system diagnostics and status.

PROGRESS ON TASK #4: IMPROVED NUMERICAL MODELING TECHNIQUES
The UNH OOA project continuously upgrades, modifies, or evaluates its numerical modeling capabilities using a variety of methods. In 2006, the Aqua-FE code underwent two verification studies dealing with a large near-shore salmon farm (see Investigation of a Near-Shore Salmon Farm above) and a newly developed 20-ton capacity feed buoy (see PROGRESS ON TASK #3: FEED BUOY DEVELOPMENT above).

Farm Modeling: In 2005, the Aqua-FE code was modified to allow for horizontal current velocity changes. The original code did not allow for any increases or reduction in current. When modeling was performed, the same environmental conditions were applied to all of the elements, regardless of wake effects or blockage that may be occurring due to objects such as nets or pen components. This approach has worked reasonably well when applied to small farms in open ocean conditions where limited velocity reduction occurs (Fredriksson et al., 2005). The examined 20 cage, near shore farm (Fredriksson et al., 2006a) showed evidence of a significant horizontal current reduction (Fredriksson et al., 2006b), and it was hypothesized that the change in current within the farm would significantly affect the loads calculated by the model. Therefore, this code modification was necessary.

A numerical model of the farm was constructed and run under similar environmental conditions present at the site. Although a direct comparison between the field measurements and the model simulation results was difficult due to many uncontrollable variables existing in-situ, the values compared reasonable well. For the fouled net load case with velocity reduction, the south anchor leg mean predicted tension was within 7.2% of the measured mean values. However, when comparing the same parameters for the west anchor, the predicted tension was significantly higher than the measured value. The comparison for the clean net condition showed that the measured west southwest and south southwest anchor tensions were within 22% of those predicted with the model incorporating velocity reduction. The results of the other anchor leg comparisons varied.

One explanation for the differences could be related to the geometric properties of the 26- leg mooring grid. In the numerical model, each leg pre-tension characteristic is estimated using an ideal deployed configuration. During fish farm operations, high horsepower vessels are used to set the legs by throttle control. Therefore, it is unlikely that the actual farm is evenly pre-tensioned in the ideal configuration. Evidence of this is apparent from examining the load cell data sets obtained from the western anchor leg during the clean net deployment where values appeared to be high. It was known from the field crew that this leg was stretched out considerably more than the other anchor legs. In addition, other unknown variables that can affect system tension included location of the load cell (e.g. along a chain catenary) and daily operations by personnel at the site such as pen adjustments, anchor re-alignments, etc. The velocity reduction scheme used as model input was another variable that affected the comparison. Though not thoroughly discussed here, the flow field characteristics at external and internal locations of the farm were complicated to describe, especially at this relatively shallow site having extreme tides.

Nevertheless, enabling horizontal flow reduction to be simulated in the numerical model provided insight to the tension distribution in the mooring lines of the large fish farm. Without reduction, numerical predictions for anchor leg tensions on the load bearing side of the farm were greater than when reduction was employed. On the “slack” side of the farm, the opposite was true, since the higher velocities allowed more set back. Both sets of results indicated that for diagonal, on-coming currents, the critical anchors are at middle locations. The results also showed that the grid components, in the ideal geometric case, effectively distribute loads throughout the farm. The intent in this study, however, was to incorporate a mechanism to model the velocity reduction in the numerical routine and to assess the benefits. When the measured data set values were compared to the calculated results, trends were evident. Employing the velocity reduction knowledge does enable a better tension estimate, though not exact. This can have implications when specifying gear and safety factor using the numerical model and therefore must be considered. The full results can be found in Fredriksson et al. (2006a).

Surface Buoy Modeling: A second verification study was performed comparing physical modeling results with predicted numerical modeling data. The 20-ton capacity feed buoy physical model underwent free release heave and pitch tests to determine its motion response (see 2005 Progress Report). In an effort to better understand the numerical modeling capabilities when representing large solid bodies (such as the feed buoy), the same tests were performed in Aqua-FE. The buoy was constructed in Aqua-FE with 380 elements and 75 nodes, and is shown in Figure 19 (stiffener elements removed for clarity).

With the model complete, free-release tests were performed, similar to tests performed on the buoy physical model (see 2005 Progress Report). Heave and pitch tests were conducted at two different displacement conditions: load and light. The results of the analyses are shown in Table 4. The physical model and Aqua-FE model had similar damped natural periods with a maximum 13.3% difference. With smaller differences in other values, the Aqua-FE predictions generally agree with the results obtained from the physical model experiments.

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

= CD (1)

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 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 that was towed alongside a workboat. Thus, the catamaran served as the “carriage” for field measurements.

Field observations were processed by fitting a velocity-squared relationship 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. Methods and results were summarized by Swift et al. (2006).

PROGRESS ON TASK #6: DEVELOPMENT OF AN OPERATIONS CENTER
The original plan for the 20-ton feed system was to split the controlling hardware between the on-shore and on-site components. The system in the 20-ton feed buoy would control the feeding, video, lights, etc and monitor the feed buoy status. The user interface, which allows schedule changes, would be located in a PC on shore. However, the AEG approach, using industrial control components, locates the basic computing, and controlling hardware and software in the feed buoy. A telemetry link has to allow the display and control of the computer in the feed buoy. Therefore, the on-shore control center will be a computer that displays the screen of the computer in the feed buoy, and allows the user to modify the program as if he were in the feed buoy. The telemetry requirements for this will make interactions slower than with the previously developed systems. This component of the project will be addressed when the on-board controller is completed, and the telemetry component tested before delivery next spring.

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 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. Complex fluid dynamic problems are usually solved using some kind of computational fluid dynamics (CFD) software. We chose the widely used CFD software package called 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. In this study, drag tests of one-meter by one-meter net panels performed in the UNH tow tank are being used to assess those constants. The constants were found for a dense small mesh net with a solidity of 45 %, and three-dimensional models of the net panel were run for the same velocities as used in the tank. These results showed good agreement with the measured data. (FLUENT predictions for a net panel at normal incidence and a two-dimensional, cylindrical cage are illustrated in the 2005 Progress Report.)

During the past year, FLUENT predictions were made for net panels angled to the incident flow and compared with measurements made previously by others (Patursson et al., 2006a,b). Because angled net testing is critical for calibration of porous media tangential velocity coefficients, an angled net panel tow tank study has been initiated at UNH. The overall approach is to use net panel studies to obtain all empirical coefficients, apply the model to a gravity cage example, and validate by comparing predictions with tow tank data. Suitable data has been obtained using a 10 ft diameter by 6 ft high gravity cage towed at constant speeds in the U.S. Naval Academy’s 380 ft long by 26 ft wide by 16 ft deep tow/wave facility. Experiments carried out June 5­9, 2006 focused on measurements of the altered velocity field, particularly velocity reduction within the cage and in the wake region.

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, 53-67.

DeCew, J., S. Page, C.A. Turmelle, and J.D. Irish, (2006a) "Tow Test Results of an AquaPod Fish Cage," in Proc. Oceans06, Boston, MA.

DeCew, J, B. Celikkol, G. Rice, I. Tsurkov, (2006b) "Practical Applications of Numerical Modeling Using Aqua-FE: A Case Study, Proc. Oceans06, Boston, MA.

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, 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, 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), 117-270.

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), 77-94.

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.

Fredriksson, D.W., J. DeCew, J. Irish, V. Panchang, D. Li and I. Tsukrov (2006a)). SK Final Report. Project Title: Engineering Design and Analysis for More Secure Salmon Net Pen Systems. Grant # NA03NMF4270183.

Fredriksson, D.W., J. DeCew and J. Irish (2006b) “A Field Study to Understand the Currents and Loads of a Near Shore Finfish Farm”, Proc. Oceans06, Boston, MA.

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), 95-111.

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

Open Ocean Aquaculture Engineering 2005 Progress Report (2005) Annual Progress Report submitted to CINEMAR, NOAA, University of New Hampshire, Durham, NH, 30p.

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

Patursson, O., M.R. Swift, I. Tsurkov, K. Baldwin and K. Simonsen, (2006a) “ Modeling Flow Through and Around Nets Using FLUENT”, FLUENT CFD Summit, Monterey, CA.

Patursson, O., M.R. Swift, I. Tsurkov, K. Baldwin and K.Simonsen, (2006b)“ Modeling Flow Through and Around a Net Panel Using Computational Fluid Dynamics Software,” Proc. Oceans06, Boston, MA.

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, 197-203.

Rice, G., S. Boduch, J. DeCew, J.D. Irish, M.R. Swift and C.A. Turmelle (2006) “An Investigation of a Deployed Submerged Grid Mooring System,” Proc. Oceans06, Boston, MA.

Rice, G. (2006) “Investigation of a Submerged Four-Bay Mooring System for Aquaculture”, M.S. Thesis, Ocean Engineering, University of New Hampshire, Durham, NH, 96p.

Santamaria, J., Monahan, C., Scott, J, Celikkol, B, Fredriksson, D., DeCew, J (2005). “Development of a Submersible Fish Cage for Open Ocean Aquaculture.” Small Business Innovation Research, SBIR Phase II Proposal.

Santamaria, J., Monahan, C., Scott, J, Celikkol, B, Fredriksson, D., DeCew, J (2006a). “Development of a Submersible Fish Cage for Open Ocean Aquaculture.” Small Business Innovation Research, SBIR Progress Report for the period between September 1, 2005 and February 1, 2006.

Santamaria, J., C. Monahan, J. Scott, B. Celikkol, D. Fredriksson, J. DeCew (2006b). “Development of a Submersible Fish Cage for Open Ocean Aquaculture.” Small Business Innovation Research, SBIR Progress report for period between February 1, 2006 and September 1, 2006.

Swift, M.R., D.W. Fredriksson, A.Unrein, B. Fullerton, O. Patursson and K. Baldwin. (2006) ”Drag Force Acting on Biofouled Net Panels”, Aquaculture Engineering, Vo. 35, 292-299.

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, 251 ­ 270.

Turmelle, C., M.R, Swift, B. Celikkol, M. Chambers, J. DeCew, D. Fredriksson, G. Rice, and K. Swanson (2006) “Design of a 20-Ton Finfish Aquaculture Feeding Buoy," Proc. Oceans06, Boston, MA.

C. Important Results or Findings
Results are incorporated above.

D. Difficulties Encountered
Due to delays in the delivery of essential components, the 20-ton capacity feed buoy will be finished during spring 2007 rather than fall 2006.

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
FLUENT 2006 CFD Summit: Patursson, O., M.R. Swift, I. Tsurkov, K. Baldwin and K. Simonsen, “Modeling Flow Through and Around Nets Using FLUENT”, May 22-24, 2006, Monterey, CA.

International Workshop on Open Ocean Aquaculture in Turkey: DeCew, J., “Utilizing Numerical and Physical Models to Analyze Aquaculture Structures” and Turmelle, C., “Design and Evolution of Feeder Systems at the University of New Hampshire”, August 17th-19th 2006. Canakkale, Turkey.

IEEE/MTS OCEANS 2006: As a means of presenting the work that is being done by the University of New Hampshire in the area of Aquaculture Engineering, the OOA effort organized and chaired a special interest session at the 2006 MTS/IEEE Oceans conference held in Boston, MA. A request was sent out to the community, and two sessions of papers were received and presented. In addition, some papers presented by the OOA effort were in other sessions. The following is a list of papers presented by the OOA effort:

Boduch, S.J. and J.D. Irish, “Aquaculture Feed Buoy Control - Part 1: System Controller,” Proc. Oceans06, Boston MA, Sept, 2006.

DeCew, J., S. Page, C.A. Turmelle, and J.D. Irish, “Tow Test Results of an AquaPod Fish Cage,” in Proc. Oceans06, Boston MA, Sept, 2006.

DeCew, J., B. Celikkol, K. Baldwin, S. Boduch, M. Chambers, D.W. Fredriksson, J.D. Irish, O. Patursson, G. Rice, M.R. Swift, I. Tsukrov and C.A. Turmelle, “Engineering Overview of the University of New Hampshire’s Open Ocean Aquaculture Project,” Proc. Oceans06, Boston MA, Sept, 2006.

DeCew, J, B. Celikkol, G. Rice, I. Tsurkov, “Practical Applications of Numerical Modeling Using AquaFE: A Case Study, Proc. Oceans06, Boston MA, Sept, 2006. Fredriksson, D.W., J. DeCew, and J.D. Irish, “A Field Study to Understand the Currents and Loads of a Near Shore Finfish Farm,” Proc. Oceans06, Boston MA, Sept, 2006.

Irish, J.D., S.J. Boduch and W. Paul, “Coil-cord Conductors on Elastic Moorings,” Proc. Oceans06, Boston MA, Sept, 2006.

Irish, J.D. and S.J. Boduch, “Aquaculture Feed Buoy Control - Part 2: Telemetry, Data Handling, and Shore-Based Control” Proc. Oceans06, Boston MA, Sept, 2006.

Patursson, O., M.R. Swift, I. Tsurkov, K. Baldwin, K. Simonsen, “ Modeling Flow Through and Around a Net Panel Using Computational Fluid Dynamics Software,” Proc. Oceans06, Boston MA, Sept, 2006.

Rice, G., S. Boduch, J. DeCew, J.D. Irish, M.R. Swift and C.A. Turmelle, “An Investigation of a Deployed Submerged Grid Mooring System,” Proc. Oceans06, Boston MA, Sept, 2006.

Turmelle, C., M.R. Swift, B. Celikkol, M. Chambers, J. DeCew, D. Fredriksson, G. Rice, and K. Swanson, “Design of a 20-ton Finfish Aquaculture Feeding Buoy,” Proc. Oceans06, Boston MA, Sept, 2006.

Technology Partnership in Sustainable and Open Ocean Aquaculture: Baldwin, K. “Engineering Overview of the University of New Hampshire’s Open Ocean Aquaculture Project”, October 30th ­ November 2nd. Durham, NH, USA.

Strategic Collaboration Between SINTEF Fisheries and Aquaculture AS, University of New Hampshire (USA) and the Norwegian University of Science and Technology, Department of Cybernetics: Baldwin, K. and B. Celikkol, “Open Ocean Aquaculture Engineering”; Turmelle, C., “Feed Buoy Design and Engineering”; Rice, G., “Line Tension Measurement”; DeCew, J., “Utilizing Numerical and Physical Models for Open Ocean Aquaculture System Design”; Irish, J. and S. Bolduch, “Remote Monitoring”; Patursson, O., “Nets”; November 6th ­ 8th. Durham, NH USA.

Journal Articles
Swift, M.R., D.W. Fredriksson, A.Unrein, B. Fullerton, O. Patursson and K. Baldwin (2006) “Drag Force Acting on Biofouled Net Panels”, Aquaculture Engineering, Vol. 35, 292-299.

Theses
Rice, G. (2006) “Investigation of a Submerged Four-Bay Mooring System for Aquaculture”, M.S. Thesis, Ocean Engineering, University of New Hampshire, Durham, NH, 96p.

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,

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.
7. Optimal harvesting methodology and technology.
8. Fish biomass monitoring.

B. Brief work plan to accomplish these tasks.
Investigation of Commercial Scale Cages: Two systems will be investigated further: (1) the American Soybean Association small volume, high density cage, and (2) the SBIR large scale submersible system. The ASA cage and mooring system will be modeled to determine optimal buoyancy configuration and general response characteristics. As an ongoing part of the SBIR large scale system, the work plan includes:

  • Complete an engineering review of the deployed 1:1.6 scaled gravity cage
  • Process data from bridle line load cells and compare with numerical model predictions
  • Design and build a full scale prototype

Analysis of Mooring Grid: The work plan includes:

  • Perform computer simulations as needed to analyze mooring grid capacities for various scenarios

Feed Buoy Development: Working with the operations team, Ocean Spar and AEG, the work plan includes:

  • Supervise the construction of the 20-ton capacity feed buoy
  • Assemble and deploy the mooring and feed hose system
  • Work with AEG to bring the controller on-line with the basic programs for feeding, controlling other functions, monitoring and reporting system status
  • Complete checkout of the control system upon delivery so that its operation is understood and we can determine that it is functioning as designed
  • Learn how to program, modify and add features to the new control system
  • Test the various new telemetry systems and determine their capability
  • Add the environmental monitoring and the UNH monitoring system to the feed buoy as a “back-door” to observing the system status
  • Monitor and evaluate the entire 20-ton system when completed
  • Continue to support the quarter-ton buoy until the new feed buoy is on-line and actively feeding fish
  • Retire the quarter-ton buoy to back-up status

Numerical Modeling Development: The work plan for the numerical modeling effort includes:

  • Apply and evaluate recent improvements in Aqua-FE

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

  • Reconfigure the Seacoast Science Center computer and radio system to support the new feed buoy radios
  • Establish a base station at UNH which will interface with the offshore controller

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

  • Calibrate FLUENT using data from angled one-meter-square net panels tests
  • Use the porous media option to construct a cage model to predict flow around and through the Naval Academy test cage, as well as compute the associated drag
  • Compare FLUENT predictions with tow tank data.

Optimal harvesting methodology and technology: Harvesting methodologies and technologies will be developed to minimize the use of divers and to make efficient harvesting of live fish possible. The work plan includes:

  • Incorporate an airlift into the SBIR full scale cage design with automated controls that will fill or purge surface supplied air depending upon the depth of the cage, ascent or descent rate and/or other user specified criteria.
  • Develop a second system to optimize harvesting techniques from irregular net pen shapes (such as the Net System’s SeaStation design) using a small volume cage to be provided by the American Soybean Association. This cage will be submerged to a controlled depth for coupling and partial fish harvesting.

Fish biomass monitoring: Development of a proof-of-concept system will be initiated. Tasks include:

  • Adapt the large body of work on wild fish stock assessment.

C. 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).