Development of large fish farm numerical modeling techniques with in situ mooring tension comparisons

Author Posting. © Elsevier B.V., 2006. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Aquacultural Engineering 36 (2007): 137-148, doi:10.1016/j.aquaeng.2006.10.001.A study is conducted to validate a numerical model for calculating mooring system tensions of a large fish farm containing 20 net pens in the absence of waves. The model is forced using measured current velocity values obtained outside of the farm. Mooring line tensions calculated with the numerical model are compared with load cell field data sets. The approach considers current velocity reduction and load characteristics that occur through the net pen system for both clean and fouled net conditions. Without accounting for the reduction, the numerical model produces excessively conservative results. With reduction, a substantial improvement occurs. Understanding these differences will help to establish appropriate safety factors when designing large marine fish farms using the model. Additional validation studies should be conducted with wave and current forcing to investigate the modeling large fish farms for exposed or open ocean sites.The authors would also like to express sincere thanks the National Oceanic and Atmospheric Administration for funding this project through the Saltonstall-Kennedy program under Grant NAO3NMF4270183

Elastic properties of pyrolytic carbon with axisymmetric textures

In this paper, the first-order bounds, the geometric mean, the singular approximation and the self-consistent estimate of the linear elastic properties of pyrolytic carbon (PyC) are determined numerically. The texture, i.e. the orientation distribution of the normal direction of the graphene planes, is modeled by a Fisher distribution on the unit sphere. Fisher distributions depend only on one scalar concentration parameter. It is shown in detail how the effective elasticities of PyC can be estimated based on the one concentration parameter which describes the scatter width of the orientation distribution. The numerical predictions of the different bounds and estimates are compared

Evaluation of an experimental kelp farm\u27s structural behavior using regression modelling and response amplitude operators derived from in situ measurements

An experimental kelp farming system for exposed ocean conditions was designed, deployed, planted with kelp and instrumented for evaluation of its dynamic response to ocean waves, tides, and currents. The farm featured a novel lattice mooring design and anchor lines and cultivation lines (horizontal lines used as kelp growth substrate) made of fiberglass rods. The farm was deployed at a site in Saco Bay, Maine with 13 m (MLLW) water depth. There the farm was exposed to waves with heights up to 5.9 m. Anchor line tension, tide and wave height time series were gathered and processed into response amplitude operators (RAOs) and least squared error linear regression models enabling recognition of meaningful patterns between the forcing factors and the mooring response. Mean mooring line tensions were shown to increase nonlinearly with tide. Anchor line tension response amplitudes were shown to exhibit high sensitivity to both low and high frequency wave forcing. Numerical free-release test simulations suggested natural frequencies in heave of 0.91 Hz, indicating that tension response sensitivities at high frequency could be the result of resonance. Low frequency tension response disproportionate to the low frequency wave forcing could be explained by wave forcing on kelp cultivation arrays modulated by wave group envelopes. Instances of high magnitude, potentially damaging peak tensions, deemed shock loads, were prevalent in most load cases. Anchor line tension dynamics including RAO and shock load magnitudes were shown to be sensitive to mooring stiffness (ratio of tension to resulting elongation) and, in some cases, significant wave amplitude. Patterns of anchor line response indicated that additional mooring elasticity or geometric compliance and use of floatation with less sensitivity to high frequency waves could help avoid the cause of and costly consequences of amplified high frequency loading and high amplitude shock loading. RAOs and regression model results also indicated a subdued response in frequencies associated with ocean swell waves, suggesting desirable performance in waves most dominant in extreme storm events. With the proposed improvements, the farm system design suggests merit as a robust and durable macroalgae biomass production platform

On Numerical Modeling of Equal Channel Angular Extrusion of Ultra High Molecular Weight Polyethylene

Ultra high molecular weight polyethylene (UHMWPE) is widely used in biomedical applications, e.g. as a bearing surface in total joint arthroplasty. Recently, equal channel angular extrusion (ECAE) was proposed as a processing method to achieve higher molecular entanglement and superior mechanical properties of this material. Numerical modeling can be utilized to evaluate the influence of such important manufacturing parameters as the extrusion rate, temperature, geometry of the die, back pressure and friction effects in the ECAE of polyethylenes. In this paper we focus on the development of efficient FE models of ECAE for UHMWPE. We study the applicability of the available constitutive models traditionally used in polymer mechanics for UHMWPE, evaluate the importance of the proper choice of the friction parameters between the billet and the die, and compare the accuracy of predictions between 2D (plane strain) and 3D models. Our studies demonstrate that the choice of the constitutive model is extremely important for the accuracy of numerical modeling predictions. It is also shown that the friction coefficient significantly influences the punch force and that 2D plane strain assumption can become inaccurate in the presence of friction between the billet and the extrusion channel

Design, deployment, and operation of an experimental offshore seaweed cultivation structure

Seaweed cultivation systems suitable for offshore and exposed locations have the potential to enable expansion of global seaweed production to levels capable of substantially supplementing or offsetting terrestrial agriculture. A demonstration scale, experimental seaweed cultivation system (farm) intended to withstand exposed ocean environments was designed, deployed, planted with kelp (a type of seaweed), monitored and decommissioned. Objectives for the field program included: [1] observation of the farm\u27s behavior and survivability in exposed ocean conditions, [2] demonstration of novel farm system design features and component technologies, and [3] evaluation of farm operability. Novel design features included a lattice mooring system geometry, multi-shaft helical anchors, and the use of fiberglass rod as a replacement for rope anchor lines and kelp growth substrate in order to mitigate the risk of marine animal entanglement. New hardware was developed for transmitting tension loads to and from fiberglass rods, enabling their use in the farm. A numerical model was used in the design stage to simulate the farm in ocean conditions. Analysis results were used to specify farm components, evaluate sensitivities to installation precision, identify potential issues with component interaction, consider operational constraints and investigate the implications of single point failures. The farm was installed at a Gulf of Maine, USA site and planted with Saccharina latissima (sugar kelp) in November 2021 through January 2022 and monitored for one growth season. Kelp was sampled 3 times and met-ocean conditions were measured throughout the season. Kelp was harvested in May 2022 and the structure was removed June 2022. Recovered components were inspected for wear. The farm survived a series of storm events with significant wave heights greater than 2 m and at least one storm with a maximum wave height of 5.9 m. The farm system experienced only minor corrosion, wear and damage. Farm operations revealed the need for improved accessibility, tension control and anchor placement accuracy. Observations and tests revealed relatively poor kelp holdfast attachment to the fiberglass rope replacement. Nonetheless, demonstration results suggest that the experimental farming system design was suitable for use in exposed settings

Development of Realistic Simulation Techniques to Predict Cure-Induced Microcracking

Abstract: Three-dimensiona

Quantitative computed tomography of humpback whale (Megaptera novaeangliae) mandibles : mechanical implications for rorqual lunge-feeding

Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology 293 (2010): 1240-1247, doi:10.1002/ar.21165Rorqual whales (Balaenopteridae) lunge at high speed with mouth open to nearly 90 degrees in order to engulf large volumes of prey-laden water. This feeding process is enabled by extremely large skulls and mandibles that increase mouth area, thereby facilitating the flux of water into the mouth. When these mandibles are lowered during lunge-feeding, they are exposed to high drag and therefore may be subject to significant bending forces. We hypothesized that these mandibles exhibited a mechanical design (shape and density distribution) that enables these bones to accommodate high loads during lunge-feeding without exceeding their breaking strength. We used quantitative computed tomography (QCT) to determine the three-dimensional geometry and density distribution of a pair of sub-adult humpback whale (Megaptera novaeangliae) mandibles (length = 2.10 m). QCT data indicated highest bone density and crosssectional area, and therefore high resistance to bending and deflection, from the coronoid process to the middle of the dentary, which then decreased towards the anterior end of the mandible. These results differ from the caudorostral trends of increasing mandibular bone density in mammals such as humans and the right whale, Eubalaena glacialis, indicating that adaptive bone remodeling is a significant contributing factor in establishing mandibular bone density distributions in rorquals.This work was funded by an NSERC undergraduate summer research award to Daniel J. Field, and by an NSERC discovery grant to Robert E. Shadwick