CINEMar/Open Ocean Aquaculture Annual Progress Report for the period 1/01/03 through 12/31/03
Principal Investigator(s): B. Celikkol, M.R. Swift, K. Baldwin, I. Tsukrov, D.W. Fredriksson
I. Accomplishments
A. Scheduled Tasks
Background: As environmental and utilization issues put pressure on existing near shore aquaculture facilities, the need to move operations into more exposed sites is becoming necessary. The technologies required to perform economic open ocean aquaculture, however, are still in the process of being developed. The University of New Hampshire (UNH) operates 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. To support the research, two independent 600 m3 Sea Station™ fish cages (SS600) were designed 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).
Recently, in an effort 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. 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 develop the technological basis for commercial scale open ocean 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:
- Investigation of commercial-scale fish cage systems.
- Expansion of the existing mooring grid system at the OOA site.
- Feed buoy development including design, control/telemetry and modeling.
- Web-based control of operations.
- Finite element modeling improvements.
These objectives represent a continuation of previous work performed (see Baldwin et al., 2003 or the OOA Engineering progress report for 2002). In the following section, a brief description of each of these studies is included. Since the results are extensive, references are incorporated where applicable.
B. Progress on Tasks
PROGRESS ON TASK #1: Investigation of Commercial Size Systems
The SADCO Shelf© Submersible Fish Cage: The initial investigation of the SADCO Shelf© fish cage and mooring system (Figure 1) was performed in 2002 (see previous progress report for 2002 and DeCew, 2002). Following completion of testing, a second set of tests, using the physical model, were conducted to verify motion and load data previously obtained. This was necessary to reduce noise obtained in the load measurements. New load cells were constructed and the data was processed using a cross-spectral technique, which can reduce noise. Using the cross-spectral technique, uncorrelated noise associated with line tension measurements is cancelled in the calculation, usually providing a better estimate. The new results can be found in DeCew et al. (2004).
In general it was found that the SADCO fish cage showed favorable dynamical characteristics that are typical of a highly damped system. The cage did not produce large motion responses. The Response Amplitude Operators (RAOs) for motion were calculated and exhibited no resonant condition peaks within the wave excitation range of 0.05 to 0.45 Hz. In heave and surge, the system generally decreased in response as the frequencies increased, with RAOs below one in most cases (Figure 2). In heave and pitch, RAOs approached one at low frequencies indicating wave contouring behavior. At high frequencies, responses were small indicating that inertia and damping are inhibiting cage motion. Results of the physical model tests also show that the cage maintains volumetric stability. Unlike traditional gravity type cages, which have a tendency to deform in large waves, the SADCO system kept its shape due to the triangular tension lines running the length of the cage.
The tensions present in the mooring system were also favorable. In general, the numerical and physical models predicted anchor and bridle line tension responses to be below 5 kN/m (Figure 3). Thus typical mooring tensions would be on the order of 25 kN or less for an extreme 10 m high wave. In fact, the embedment anchors used to hold the present 600 m3 cage (1/5 the volume) must sustain loads which are several times larger. The numerical and physical models indicate that, from the wave mechanics point of view, the SADCO design has many positive attributes.
PROGRESS ON TASK #2: Expansion of Mooring System Grid
Work also continued to expand the bio-mass capacity at the site. In the previous progress report for 2002, various multi-grid mooring configurations were investigated for possible deployment (Kurgan, 2003). Due to space allocation, growth potential, marine mammal considerations and structural integrity, a submerged, four-cage grid mooring system was designed, analyzed and deployed at the OOA Demonstration Site. A schematic of the system is shown on Figure 4s.
The mooring system concept was designed to accommodate four fish cages and/or feeding systems while maintaining the 30 acre permit boundaries. It incorporates a grid that is submerged at a depth of approximately 15 meters (about 37 meters above the bottom) and consists of nine nodes (4 corners, 4 sides, and 1 center). Four sets of bridle lines connect the cages to the submerged grid. The grid is anchored to the bottom using 12 mooring legs each incorporating co-polymer rope and a chain catenary. Tension in the system is maintained using flotation at the nine nodal locations. Due to the 12 anchor design, flotation elements at the corners are larger than those at the grid sides to accommodate the weight of chain for 2 anchor legs. During the deployment process, the anchors are set to form the required geometry, which submerges the flotation elements down to the desired depth and lifts chain up off the bottom. The chain catenary in the anchor legs provides necessary compliance to the system.
Mooring system geometry, subsurface flotation and pretension requirements were specified using analytical techniques, which included standard chain catenary equations and the method of joints. The four-grid bays, each having an area of 4225 m2, are tensioned by 5 subsurface floats of 11.1 kN and four subsurface floats with a net buoyancy of 3.22 kN. The minimum resulting static tension in the system is 6.01 kN.
Mooring gear and ground tackle were sized, in part, by modeling the designed system using the Aqua-FE finite element program. The model included representations of potential sets of mooring gear and four Sea Station™ submersible cages (totaling 7200 m3 of containment volume). Numerical simulations were performed using a wave height of 9 meters, wave period of 8.8 seconds and depth averaged current of 1 m/s as input coming from the northeast. Results of the model simulations provided information regarding the distribution of loads throughout the mooring system (see Figure 5). The results of the simulations were also utilized to develop a design load condition so mooring components could be specified (Fredriksson et al., 2004). The design load was used to specify mooring components, which consist of twelve 1-ton drag embedment anchors, 15 shots of 48-mm chain, 1720 meters of co-polymer, 48-mm 8-plait rope, nine subsurface floats all held together using 70, 38-mm galvanized shackles. The large diameter line, coupled with the static tension of the system, help reduce the risk of marine mammal entanglement at the site.
The location of the mooring grid within the permitted site was determined using bottom topography information obtained courtesy of Center for Coastal and Ocean Mapping /Joint Hydrographic Center (CCOM/JHC). A three-dimensional representation of the mooring grid is shown superimposed on the bottom topography in Figure 6. The gear was successfully deployed the first week of July, 2003, using the F/V Nobska operated by Stommel Fisheries from Woods Hole, MA. In the second week of July 2003, the two SS600 cages used with the previous mooring, containing Atlantic halibut (Hippoglossus hippoglossus) and haddock (Melanogrammus aeglefinus) were connected to the new grid (the F/V Nobska is shown on Figure 7 deploying the mooring gear). A previously constructed feed platform was then attached to one of the SS600 cages containing the haddock the following week. In August, a new submersible SS3000 cage was deployed. Shortly thereafter approximately 30,000 Atlantic cod (Gadus morhua) were transferred from a shore side facility into a nursery net located inside of the cage. For more details, refer to the operational progress report.
PROGRESS ON TASK #3: Feed Buoy Development
Quarter-Ton Feed Buoy
Background: An automated feeding system needed to be developed since reliable methods of supplying regulated feed to fish in submerged cages in the open ocean environment were not commercially available in the United States. While specialized feed boats, barges and buoys are typically used presently for large arrays of surface cages located in sheltered waters, relatively little has been done for submerged net pens in extreme wave, tide range and current environments. A research prototype feed buoy was developed to supply a submerged cage at the open ocean aquaculture site. The system, designed for a quarter-ton feed capacity, consists of a surface buoy, moorings attached to the submerged grid, a feed transfer hose, feed dispensing machinery, and telemetry/control components. The buoy is taut-moored above the cage by compliant members to provide flexible response to tides and waves. The feed buoy described here may be regarded as one of a series of feed buoys under development, increasing in size as design methods are improved.
Design criteria included the ability to operate remotely at the OOA site between re-supply and maintenance trips. Therefore automated feed dispensing, power supply, control and communication systems were developed. The operational plan for the quarter-ton system is to supply feed to one of the SS600 cages while moored in the submerged configuration. The mooring system had to accommodate the tides and extreme waves, as well as the kinematics of two bodies dynamically responding to environmental forcing.
The first part of the development approach established the basic design concept for the buoy shell, ballasting, component arrangement plan and mooring configuration. Next, the internal components including feed storage, feed dispensing, power supply, control and telemetry were designed and fabricated. Mooring specifications were determined iteratively employing a finite element model to analyze the overall system dynamics and a physical scale model to characterize the buoy seakeeping response.
Design Configuration: The external appearance and major dimensions of the feed buoy are shown on the left side of Figure 8, while the arrangement plan of the hopper, batteries, pumps and other internal systems are shown on the right side of Figure 8. Based on a previous design described by Rice (2003), the main body consists of a 1.5 meter diameter aluminum cylinder. A two-foot diameter cylinder extends downward and supports an open 1 meter diameter “bucket” at the base. Ballast in the form of brick-shaped lead ingots was placed in the bucket and covered by an aluminum grate.
Reserve buoyancy is provided in the form of an eight-inch thick Surlon‰ foam flotation collar. The center of gravity of the overall designed weight of 20 kN is below the center of buoyancy. The resulting metacentric height of 0.49 meters indicates a substantial reserve righting moment. Extra buoyancy and righting moment were viewed as essential for safety of maintenance personnel as well as buoy survivability in the event of severe storms, icing conditions or loss of watertight integrity.
The buoy mooring system, shown in Figure 9, consists of two tethers to grid corner points and a compliant feed hose to the top of the cage. Each tether consists of 2.5 cm diameter elastomeric members in parallel for part of the overall tether length. The remaining portion is made up of a single, 89 kN capacity, braided nylon rope. The feed hose is high-stretch rubber with an inside diameter of 7.6 cm. Initial values for member lengths were established in a preliminary static, kinematic analysis, which included extremes in water level range (3 meters for the tide and 4.72 meters for the wave amplitude). The system was designed to remain taut with the buoy at the level of low tide in the trough of the wave, yet be within the operational elastic limits of the hose and tether while the buoy is at the high tide, wave crest level. Final design specifications were arrived at after consideration of several alternatives subject to computer modeling of the buoy-cage-grid mooring storm response.
Feed Storage and Distribution: Feed pellets are loaded into the buoy through the top hatch and stored in the hopper shown in Figure 8. The fiberglass hopper holds 2.2 kN of feed. Beneath the feed hopper, a rotary drum valve is used to meter out the desired amount of pellets per feeding. The valve rotates at a constant rate; therefore by changing the duration of feeding or the cup size of the drum, the proper amount of feed will be delivered to the submerged fish cage. The feed pellets drop through an open ball valve into a small chamber of water, where a wash down pump forces the water/feed slurry down through the hose to the cage.
Power Supply, Control and Telemetry: The buoy is powered by both solar and wind energy (see Figure 10). Two 60 watt solar panels provide electricity during clear, sunny days and a wind generator provides power during moderate wind. These systems charge two 24-Volt, 105 amp-hour battery banks. Additionally, a backup set of charging cables were attached to the buoy to allow for emergency charging if the solar and the wind power failed.
A CF-1 microcontroller (located in a pressure cylinder) with a load distribution panel controls the systems inside the buoy. A flexible system was designed to allow the microcontroller to monitor all of the system voltages and currents that control the feeding operation. The controller is also interfaced with two spread-spectrum radio systems to allow for land-based remote control and data acquisition. The first of these systems contains two 900 MHz serial (RS-232) radios that allow for direct monitoring and control of the CF-1 controller. The system was designed and programmed to allow for land-based upgrading of the control programs/feed schedules without having to be at the site. The second radio system consists of a set of 2.4 GHz 802.11b radios used for live video monitoring from two cameras strategically placed within the fish cage to view feeding behavior. This second system has not yet been proven to work consistently from land, but has become invaluable while on a nearby research vessel for monitoring operations within the submerged cage.
Additionally, a SeaBird temperature and salinity measuring instrument is installed in the submerged cage and is interfaced with the CF-1 computer system to allow biologists to monitor the temperature and salinity from within the cage with a 15-minute sampling resolution. Both the instrument data and the video stream are transmitted to the buoy through the conductors embedded in a custom-made, high-stretch feed hose wall. This feed hose, with embedded conductors, has proven to be very useful for acquiring data remotely and such a system will be employed in future feed systems.
A web-based control center is currently being developed so that the status of the buoy can be monitored and to change the feeding schedules remotely through internet access. Presently, the control center has the ability to monitor position, environmental and system diagnostic data streaming, but plans are in the works to develop a robust web-based user interface.
Finite Element Analysis: The mooring system design was analyzed using the UNH-developed finite element analysis program, Aqua-FE. The Aqua-FE finite element computer program was developed specifically for open ocean aquaculture application and has been described by Gosz et al. (1996) and Tsukrov et al. (2000, 2003). The model uses a nonlinear Lagrangian formulation to account for large displacements of structural components made up of truss and buoy elements. The unconditionally stable Newmark direct integration scheme is adopted to solve the nonlinear equations of motion. Fluid dynamic forces on structural elements are calculated using the Morison equation modified to represent relative motion between the element and the surrounding fluid. Aqua-FE has recently been upgraded to include nonlinear material behavior, a feature that significantly improves modeling of the high-stretch, rubber hose. In the finite element model of the feed buoy/mooring system choices of density, diameter and length of elements comprising the feed buoy were made so that the model would have the same fluid drag, inertia and buoyancy as the actual feed buoy.
The purpose of the model simulations was to identify the optimal tether construction as well as generally characterize the motions and forces under average and extreme wave and current conditions. The tethers could be made stiffer with more parallel elastomeric members with the anticipated trade-off of reduced motion at the expense of higher forces. Shortening the overall unstretched tether length would increase pretension, reduce the tendency for the tether to go slack and snap, but increase forces in the extreme stretch portion of the oscillating range.
The dynamic performance of the feed buoy system with various mooring line designs was investigated using the numerical model for both typical and extreme environmental loading conditions. The typical condition was taken to be a 1.2 meters high wind wave with a 0.25 m/s current uniform with depth. The extreme condition consisted of a 9 meter wave with a period of 8.8 seconds in combination with a current that was two knots at the surface and decreased linearly with depth to 1 m/s at the bottom. The design wave is based on wave statistics for the site region in the Gulf of Maine as discussed by Fredriksson (2001). The wave and current directions were collinear, and cases were considered in which the direction was aligned with the grid edges and also along the grid diagonal. Figure 11 shows the system responding to an extreme condition.
Aqua-FE results indicated that during typical conditions, tether and hose forces were well below working levels, and the cage maintained a suitable position for feeding operations. The hose did not go so slack, therefore reducing the possibility of looping or kinking. Simulation results also indicate that the hose will not stretch to a point where the inside diameter was in any way constricted.
Under extreme conditions, the feed buoy invariably set back with the current and moved in a path following the wave trajectory assumed by the fluid particles. These excessive buoy excursions induced large loads within the elastic tethers and the hose. Increasing tether stiffness did not decrease movement significantly and only served to further increase the tether forces. For all alternative mooring designs considered, the maximum force on a single elastomeric member exceeded its desired working load of 0.89 kN.
This last result clearly indicated that the compliant mooring concept, while excellent for feed operation positioning and able to absorb extremes in water level, has a risk of failure during storms that may occur once every few years, particularly those with high currents. In view of the benefits of the system and the immediate need to feed fish occupying the cage, the risk was acknowledged. It was reasoned that should failure occur, it would be the tethers that would part leaving the buoy to tail off anchored by the stronger hose. When fair weather returned, the tethers could be replaced. In view of the insensitivity of the motion to tether stiffness, a comparatively compliant design was adopted consisting of two parallel 11 meter lengths of elastomeric members in series with 20 meters of nylon rope.
Physical Model Testing: To complement the computer modeling, a 1:15.2 scale model of the buoy was built for Froude-scaled wave tank testing. Free release tests were conducted to determine heave and pitch natural frequencies. The buoy model and a previously built Sea Station cage model (Palczynski, 2000) were used for wave response experiments. Similar free release tests were performed using this model as described in Fredriksson et al. (2003c). The models were set up to simulate the mooring configuration as designed. A series of single frequency tests were carried out in which heave and pitch motion was recorded. The normalized results, presented in the form of RAOs or transfer functions, characterize the wave response over the expected frequency range.
The physical model, was tested in UNH’s 36 meter long by 3.66 meter wide by 2.48 meter deep wave/tow tank. Experiments were carried out adjacent to a window in the side of the tank, so an Optical Positioning and Evaluation System (OPIE) could be used to measure buoy motion. As described by Michelin and Stott (1996), the OPIE system consists of a digital camera that records images at a user-set frequency, a dedicated computer with frame-grabber, and processing software programmed in MATLAB. Small black target dots are placed on the white painted model, and the model is illuminated so that the black dots stand out from the much lighter background. The software operates by tracking the black dots on each succeeding image. Each recording must be calibrated so that distances in number of pixels can be converted to conventional distance units. All images for the feed buoy tests were recorded at 30-frames/second.
The free release experiments were done with the buoy model only. For heave tests, the model was raised slightly from its equilibrium position and released from rest. The model oscillated vertically with decaying amplitude as indicated on the typical free release time series shown in Figure 12. Pitch testing was similar except the model was tipped (without changing its vertical position) and released from rest. At least three replicates were done for each type of test.
Heave damped natural period was found to be 2.35 seconds. Since this is somewhat shorter than the period range of the normal wave environment (3 10 seconds), wave contouring behavior could be expected for vertical motion. The pitch damped natural period was 6.46 seconds putting the pitch resonance condition (buoy only) in the middle of the wave energy range during storms. No attempt was made to adjust frequencies by re-ballasting since the reserve buoyancy and reserve righting moment attributes already achieved were regarded as the highest priority.
Due to tank width and depth limitations, the full grid could not be modeled in the wave response experiments. Instead, the grid corner points were fixed using four fixtures at the tank walls. Figure 13 illustrates tank wave test set-up. Essentially, it was assumed that the feed buoy dynamics would be most influenced by directly connected, compliant members, while remote components such as anchor lines would play a diminished role. The central spar cage model was anchored by its pendant weight so that the cage was in its submerged mode, and cage bridle lines were rigged to the grid points. The buoy was moored to replicate the Figure 9 configuration with tethers to the grid points and the hose to the top of the cage. Elastic lines were used for the tether and hose members, and the compliance characteristics of these members were also Froude-scaled. A light, Styrofoam float sliding on a taut, vertical fishline was used to record wave elevation using OPIE. The motion of targets on the float and the feed buoy were recorded by OPIE through the side window of the tank. The regular wave, single frequency experiments were done at periods ranging from 1.9 11.7 seconds thereby spanning the range of expected wave energy and bracketing the heave and pitch damped natural periods.
The results for heave and pitch, normalized by dividing by wave amplitude, are shown in Figure 14 and Figure 15. The heave response shows the resonance at the heave natural frequency with a drop-off in response at high frequencies and wave contouring behavior at low frequencies. The pitch response, on the other hand, did not show a pronounced resonance. Visual observations and inspection of the individual time series suggested that wave drag and wave inertial forces on the bucket, as well as mooring restraining moments on the bottom of the bucket, are playing an important role. During the wave cycle, periodic hose slackness followed by snap was observed for all by the highest frequencies.
Field Trials: The feed buoy was deployed as designed at the OOA site on January 8, 2003. After final installation and start-up of the internal components, the system performed as intended. Use of the feed buoy reduced the number of trips to the site, and regular nourishment was beneficial to fish growth rate. Within a month, however, a winter ice storm coated the buoy with a thick, heavy layer of ice. The reserve buoyancy and righting moment were instrumental in the buoy’s survival, but internal flooding damaged the electrical system. This was repaired, and the buoy resumed its remote feeding function. Later, termination splices on the tethers leading northeast (storm direction) were found to be overstretched, while those for the southwest tether were unaltered. Other difficulties included a persistent problem in the charging circuit that took some time to diagnose properly. Once identified and fixed, the buoy has been an asset in providing regular, metered feeding with less time and effort on the part of the operations staff.
Discussion: Finite element modeling and tank testing resulted in a compliant mooring system that is able to position the buoy for feeding yet can accommodate large changes in surface elevation due to tide and large waves. The buoy/mooring system has functioned without failure during a period of time that included winter weather despite an ice storm that caused a large increase in weight distributed over the buoy’s upper surfaces. The finite element analysis allowed extreme, as well as typical conditions to be analyzed, and the ability to quickly change design parameters enabled an optimal mooring system to be identified. The complementary physical model experiments resulted in reliable measurement of buoy dynamic characteristics such as natural frequencies. The wave tank tests also yielded seakeeping response over the spectrum of wave excitation and, in addition, provided a visual assessment of potential problem areas such as snap and chafe.
As far as internal systems are concerned, the feed metering and delivery system worked well mechanically. The dispensing valves functioned as intended, and the pump was able to transmit the feed slurry through the feed hose without clogging or back-up. The electrical, control and telemetry systems were subject to minor breakdowns in the severe marine environment. The iterative process of deploying systems, encountering problems and responding with improvements has led to increased understanding and the capability of more robust design.
Lessons learned at the quarter-ton scale are being incorporated into the next, larger, feed buoys under development in the UNH research program. Meanwhile, the quarter-ton feed buoy is being utilized at the OOA site and will be subject to long-term observation and evaluation.
One-Ton Feed Buoy
Background: Another prototype feed buoy was developed this past year to specifically feed 32,000 young cod in SeaStation SS3000 deployed at the site. This system is similar in design and operation as the quarter-ton buoy described in the previous section, however, the new buoy has a one-ton feed capacity. The one-ton feed system consists of a surface buoy, moorings attached to the 4-cage grid, a feed transfer hose, industrial feed dispensing machinery and a telemetry/control system. The buoy is taut-moored in the empty bay diagonal to the submerged SS3000 cage. The one- and quarter-ton feed buoys were developed because reliable methods of supplying regulated feed to submerged cages in the open ocean environment are not yet commercially available in the United States.
Design Configuration: The external appearance and major dimensions of the feed buoy are shown in left side of Figure 16, while the arrangement of the hopper, dispensing machinery, generator, pumps and other internal systems are illustrated on the right side. The main body of the buoy consists of a 2.5 m diameter cylinder that is 5.0 m tall. The section is split into two parts; the lower section is made of steel, while the upper section is aluminum (it is important to note that the dissimilar metals are electrically isolated). The aluminum upper portion was used to reduce the weight so that the center of gravity is significantly lower than the center of buoyancy, offering a substantial righting moment.
Feed Storage and Distribution: Feed is loaded into the buoy through the top hatch and stored in the hopper as shown in Figure 16. The hopper container can hold a maximum of 11 kN of feed. Beneath the hopper is a stainless steel rotary airlock, which dispenses the food and seals the hopper from getting wet, since any moisture on the feed pellets can turn the food into a soggy paste clogging hopper. The airlock consists of a _ hp motor which drives an 8-vane rotary unit within a sealed housing. The vanes can rotate at 10 rpm dosing approximately 18 kg/min (the dosing rate can be adjusted by changing the rpm). The feed drops into a mixing chamber below the airlock valve where it mixes with water and becomes a slurry mixture. The feed slurry is then pumped out of the buoy and through a 100 m long transfer hose to the cage.
Power Supply, Control and Telemetry System: The one-ton feed buoy also incorporates its own power supply, control and telemetry systems that were designed in the past year. The systems built for the one-ton buoy were substantially different than those designed for the quarter-ton buoy. With increase feed capacity, the power requirements were also increased and therefore required a 5 kW diesel generator as the major power source. The control system was also different. In the previous feeder, the control system was designed to be passive (i.e. conditional testing was not necessary for operation). The control system in the one-ton buoy, however, was designed to check if certain components (like the diesel generator) were running before the feed process could be started. Working this type of control into the system has been one of the greatest hurdles with this design because more diagnostic data has to be acquired and analyzed from the subsystems within the buoy. In addition, since the generator is capable of producing hazardous voltages in excess of 240 VAC, more safety precautions were incorporated maintain a safe situation. Emergency stop systems, accurate current limiting circuits, wiring that complies with the 2003 National Electric Code, interior lighting, and a fire extinguishing system are all part of the existing safety precautions. If any safety problem does occur (i.e. circuit breaker tripped, emergency stop system activated, etc.) this information is logged by the internal computer and transmitted to shore. The control system is shown being tested in the left side of Figure 17, while the pressure where the system is housed is shown on the right side.
The control system was designed to be modular since the buoy hatches are limited in size. The major components consist of the five electrical panels, one electronic pressure cylinder that contains a Persistor CF-2 microcontroller to control and acquires data from all subsystems and 900 MHz RS-232 spread spectrum telemetry system that is interfaced to the microcontroller. The five electrical panels consist of:
- A data acquisition/control panel for acquiring and multiplexing all data and control information back to the pressure cylinder,
- A DC distribution panel for control and distribution of all 12 volt power along with diagnostic interfacing to relay information back to the data acquisition panel
- An AC distribution panel for control and distribution of all high voltage AC power again containing more diagnostic interfacing,
- A generator control and data acquisition panel to control and acquire detailed information about the status of the generator; and
- A battery charging panel to keep the 12 volt battery banks charged. The system also contains three isolated battery banks to keep its subsystems functioning independently if one should fail. Additionally, the system has been pre-wired for the addition of cage lighting and a host of biological monitoring equipment.
Finite Element Analysis: Various mooring designs were analyzed using the UNH developed, numerical model Aqua-FE. A two-point mooring consisting of two compliant rubber hoses was analyzed. The mooring tethers were attached to the grid corners of the SS3000 grid as shown in schematic on the left side of Figure 18. One of the UNH design conditions consisting of wave with a height of 9 m, a period of 8.8 sec and a 1 m/sec to 0.25 m/sec current decreasing linearly with depth was used as input to the numerical model. An example one time step of the dynamic simulation is shown on the right side of Figure 18. Under this loading condition, the forces on the mooring remained below the breaking loads of the mooring components. The results were acceptable considering the conservativeness of the parameters and frequency of such a severe storm.
One-Ton Feed Buoy Physical Modeling: Early in the one-ton feed buoy design development, a 1:24 scale physical model, shown in Figure 19 (left), was fabricated for free release and wave excitation experiments. The initial free release tests were done using the same optical positioning system (OPIE) employed in the quarter-ton feed buoy experiments and used similar procedures. The heave damped natural period was measured at 3.5 seconds (all values full scale), while the pitch damped natural period was 8.9 seconds when the “bucket” contained 13.4 kN of lead ballast. The heave result was favorable since the heave resonance would occur during low amplitude, fair weather conditions, while wave contouring behavior would be expected for storm waves. The pitch tests, on the other hand, indicated a resonant situation for expected storm wave periods. Re-ballasting with 22.2 kN in the bucket reduced pitch natural period to 6.2 seconds, though the heave natural period increased only slightly to 3.7 seconds. Adding a drag inducing baffle between the lower legs increased the pitch period by about _ second. Thus feasible adjustments were not sufficient for moving the pitch natural frequency out of the high energy wave regime. Independently, it was decided to increase the length of the legs by 1.2 meters. The model was modified to reflect this change and used for further tank testing with waves. The primary objective was to observe designed mooring configurations to check for snap and chafe situations (see Figure 19 - right).
Temporary Mooring System: Designs using rubber hoses for taut-moored tethers were optimized to reduce feed hose contact with one of the grid lines at the same time that snap of all mooring members was minimized. When delivery of the desired compliant components before the planned installation date became doubtful, tank testing was used to observe a temporary mooring system employing low-stretch bridle lines having mid-span submerged weights. The schematic on Figure 20 shows the temporary mooring design configuration.
Deployment: The feed buoy was transported from Jere Chase Ocean Engineering building to the New Hampshire Port Authority on November 5, 2003. The buoy is shown being unloaded on Figure 21 (left). While at the barge dock, the buoy was lowered into the water and the steel and aluminum buoy pieces were assembled as shown on Figure 21 (right). The generator, the cooling system, feed components and all electronics/sensors were either piped or wired in the buoy. All of the mechanical and electrical components onshore were tested before being towed to the OOA site.
On December 10, 2003 the buoy was towed from the NH Port Authority to the aquaculture site using the vessel, R/V Gulf Challenger (Figure 22). The entire tow took approximately six hours split over two days, since a tow speed of less than 3 knots was maintained. Once at the fish cage site, the buoy was attached to the mooring lines and the mid-span weights to the center of the moorings were added. The buoy is shown deployed adjacent to the quarter-ton buoy on Figure 23.
Discussion: Lessons learned from the previous quarter-ton buoy made the construction and outfitting of the larger one-ton feed buoy simpler, however, the one-ton buoy had its own new level of complexity with controlling the generator and the overall buoy size. The feed transfer hose to the cage has not been attached at the current time, however, once a day of decent marine weather comes, the feed buoy will be fully operational and able to feed. Until then the 32,000 cod are being fed manually, when weather permits through a hose at the surface.
PROGRESS ON TASK #4: Web-based Control
The web-based monitoring and control center is still in the process of being developed. Simple, online text-based web pages were quickly developed to allow viewing information about the status of the quarter-ton feed buoy along with site conditions provided by the monitoring buoy. Additionally, another web-based system was established to send out daily emails to inform operators of the site conditions from the wave measuring monitoring buoy over the previous 24-hour period (see Irish and Fredriksson, 2003 and OOA Monitoring progress report for more details). An example of the automated email sent to operations and engineering personnel with the wave buoy data is shown on Figure 24. The buoys are being developed with the capability to allow for full control through the web-based system. An example of the web-based diagnostic information acquired from the quarter- ton feed buoy is shown on Figure 25. Work performed to date, however, focused on the development of the hardware components. Pending successful deployment and operations of the one-ton feed buoy, attention will be shifted to allow for development of the web-based control. Interactive web-pages have been conceived and laid out that will allow site operators to view graphical interpretations of streaming data and secure pages for control of the site operations.
PROGRESS ON TASK #5: Finite Element Modeling Improvements
Wave and Current Forcing modifications: The in-situ observations showed that velocity and direction of current significantly vary with depth. Typical example of measured current profile is presented in Figure 26. A simple model of wave interaction with non-uniform current was proposed. The current was assumed to be uniform in horizontal direction. Current profile was implemented in the finite element program Aqua-FE to analyze the dynamic performance of various structures subjected to mechanical and current/wave-related environmental loading. The non-uniform current was approximated as a piece-wise linear vector field. The wave dispersion relation was modified to take into account wave-current interaction. A new wave frequency is given by , where is a wave frequency without current, is a wave number, and is a average current in the direction of wave propagation. This expression is valid for linear current profiles (Biesel 1950). For non-linear profiles additional investigations are necessary. The possibility to add user-defined wave-current interaction without altering code was added.
The hydrodynamic loading due the wave and current was modified as follows. For each structural element the current profile was vectorially superimposed over the wave velocity field. The drag force was calculated using Morison equation based on superimposed velocity (see Sarpkaya and Isaacson, 1981).
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.
Baldwin, K.C, Celikkol, B., Chambers, M., Fredriksson, D.W., Irish, J.D., and M.R. Swift. (2003) Open Ocean Aquaculture Engineering. Proceedings of the Oceans 2003 Conference. San Diego, Californis.
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. (2001) “Open Ocean Fish Cage and Mooring System Dynamics”, PhD Dissertation, Engineering Systems Design, University of New Hampshire, Durham, NH, 296 p.
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, No. 2, pp. 117-270.
Fredriksson, D.W., M.R. Swift, J.D. Irish and B. Celikkol. (2003c). The Heave Response of a Central Spar Fish Cage Transactions of the ASME, J. of Off. Mech. and Arct. Eng. Vol 25, pp 242- 248.
Fredriksson, D.W., J. DeCew, M.R. Swift, I. Tsukrov, M.D. Chambers, and B. Celikkol. (2004). The Design and Analysis of a Four-Cage, Grid Mooring for Open Ocean Aquaculture. Aqua. Eng. (submitted).
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. (submitted)
Decew, J. (2002). Numerical and Physical Modeling of the SADCO-Shelf Submersible Fish Cage. Master’s Degree Thesis submitted in partial requirement for the Ocean Engineering degree program. University of New Hampshire, Durham, NH. 267 p.
DeCew, J., D.W. Fredriksson, L. Bougrov, M.R. Swift, O. Eroshkin and B. Celikkol. (2004). Numerical and Physical Modeling of a Modified Gravity Type Cage and Mooring System. IEEE J. of Ocean. Eng. (submitted).
Gosz, M., Kestler, K., Swift, M.R. and Celikkol, B., (1996). Finite Element Modeling of Submerged Aquaculture Net-pen Systems. In: Open Ocean Aquaculture. Proceedings of an International Conference. May 8 10, 1996, Portland, Maine, Marie Polk, Ed. New Hampshire/Maine Sea Grant College Program Rpt. #UNHMP-CP-SG-96-9, 523-554.
Irish, J.D. and D.W. Fredriksson, (2003) Compliant Mooring Technology to Separate Buoy Motion from In-line Current Meter Observations, Proceedings of the IEEE Seventh Working Conference on Current Measurement Technology, San Diego.
Kurgan, C. (2003). Fish Cage and Multiple Mooring Systems Finite Element Modeling. Master’s Degree Thesis submitted in partial requirement for the Mechanical Engineering degree program. University of New Hampshire, Durham, NH.
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.
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
No major difficulties encountered, other challenges are described above.
E. Anticipated Success in Meeting Project Objectives on Schedule
See below.
F. Reports, manuscripts, and presentations resulting from the project
Reports and manuscripts are included in the body of the report as reference material. Several presentations were made as described after the reference section below.
World Aquaculture Conference 2003: Small Scale Feed Buoy for Open Ocean Aquaculture presented by G. Rice on May 21 in Salvador, Brazil. Contributing authors: Brett Fullerton, James Irish, Walter Paul, Michael Chambers and Barbaros Celikkol.
World Aquaculture Conference 2003: Moored Fish Cage Dynamics in Waves and Currents by D.W. Fredriksson on May 21 in Salvador, Brazil. Contributing authors: Rob Swift, James Irish, Igor Tsukrov and Barbaros Celikkol.
World Aquaculture Conference 2003: Open-Ocean Aquaculture: Finite Element Modeling Applications presented by D.W. Fredriksson for Igor Tsukrov on May 21 in Salvador, Brazil. Contributing authors: Oleg Eroshkin Judson DeCew, Can Kurgan, Rob Swift and Barbaros Celikkol.
IEEE/OCEANS 2003 Conference: Open Ocean Aquaculture Engineering presentation by K. Baldwin on September 23 in San Diego, California. Contributing authors: Barbaros Celikkol, Rob Swift, Igor Tsukrov and D.W. Fredriksson.
Fisheries Dynamics 2003: Open Ocean Fish Cage and Mooring System Modeling presented by D.W. Fredriksson at the National Fisheries Research and Development Center in Busan, South Korea on September 24. Contributing authors: Igor Tsukrov, Ken Baldwin, Rob Swift and Barbaros Celikkol.
Pukong National University: Open Ocean Fish Cage and Mooring System Modeling presented by D.W. Fredriksson at the National Fisheries Research and Development Center in Busan, South Korea on September 25. Contributing authors: Igor Tsukrov, Ken Baldwin, Rob Swift and Barbaros Celikkol.
Aquaculture Canada 2003 Conference: An Open Ocean Aquaculture System for Submerged Operations in New England presented by D.W. Fredriksson on October 31 in Victoria, BC Canada. Contributing authors: Judson DeCew, Brett Fullerton, Rob Swift, Michael Chambers, Glen Rice and Barbaros Celikkol.
Aquacultural Engineering Issues Forum 2003: The Design and Analysis of a Four-Cage Grid Mooring for Open Aquaculture presented by D.W. Fredriksson on November 4 in Seattle WA. Contributing authors: Judson DeCew, Rob Swift, Igor Tsukrov, Michael Chambers and Barbaros Celikkol.
Aquacultural Engineering Issues Forum 2003: Design and Analysis of an Automated Feed Buoy presented by D.W. Fredriksson for Brett Fullerton on November 4 in Seattle WA. Contributing authors: Rob Swift, Glen Rice, Oleg Eroshkin and Stan Boduch.
II. Tasks and Activities for Next Reporting period
A. Tasks for the next reporting period