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

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

Mechanics of the right whale mandible : full scale testing and finite element analysis

Author Posting. © Elsevier B.V., 2009. 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 Journal of Experimental Marine Biology and Ecology 374 (2009): 93-103, doi:10.1016/j.jembe.2009.03.012.In an effort to better understand the mechanics of ship-whale collision and to reduce the associated mortality of the critically endangered North Atlantic right whale, a comprehensive biomechanical study has been conducted by the Woods Hole Oceanographic Institution and the University of New Hampshire. The goal of the study is to develop a numerical modeling tool to predict the forces and stresses during impact and thereby the resulting mortality risk to whales from ship strikes. Based on post-mortem examinations, jaw fracture was chosen as a fatal endpoint for the whales hit by a vessel. In this paper we investigate the overall mechanical behavior of a right whale mandible under transverse loading and develop a finite element analysis model of the bone. The equivalent elastic modulus of the cortical component of right whale mandible is found by comparing full-scale bending tests with the results of numerical modeling. The finite element model of the mandible can be used in conjunction with a vessel-whale collision event model to predict bone fracture for various ship strike scenarios.Funding for this work was provided by the National Science Foundation (Graduate Research Fellowship Program, Campbell-Malone), the National Oceanic and Atmospheric Administration (Right Whale Grants Program, award number NA04NMF4720402), and the Woods Hole Oceanographic Institution Ocean Life Institute

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

Ocean forests: breakthrough yields for macroalgae

The US Department of Energy Advanced Research Projects Agency - Energy (ARPA-E) MacroAlgae Research Inspiring Novel Energy Research (MARINER) program is encouraging technologies for the sustainable harvest of large funding research of macroalgae for biofuels at less than $80 per dry metric ton (DMT). The Ocean Forests team, led by the University of Southern Mississippi, is developing a complete managed ecosystem where nutrients are transformed and recycled. The team’s designs address major bottlenecks in profitability of offshore aquaculture systems including economical moored structures that can withstand storms, efficient planting, managing and harvesting systems, and sustainable nutrient supply. The work is inspired by Lapointe who reported yields of Gracilaria tikvahiae equivalent to 127 DMT per hectare per year (compared with standard aquaculture systems in the range of 20 to 40 DMT/ha/yr). This approach offers the potential for breakthrough yields for many macroalgae species. Moreover, mini-ecosystems in offshore waters create communities of macroalgae, shellfish, and penned finfish, supplemented by visiting free-range fish that can increase productivity, produce quality products, and create jobs and income for aquafarmers. Additional benefits include reduced disease in fish pens, cleaning contaminated coastal waters, and maximizing nutrient recycling. Cost projections for a successful, intensive, scaled system are competitive with current prices for fossil fuels

Elastic deformation of composite cylinders with cylindrically orthotropic layers

a b s t r a c t This paper provides explicit analytical expressions for displacement and stress fields in a multilayered composite cylinder with cylindrically orthotropic layers subjected to homogeneous boundary conditions. The solutions are derived in the assumption of perfect bonding between layers. The components of displacement, strain and stress are expressed in terms of the integration constants found from boundary conditions by utilizing the transfer matrix approach. Several examples are considered. The approach is validated by comparing with previously known solutions