976 research outputs found

    Design and Analysis of Bio-inspired Nacelle for Current Energy Turbine

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    he world’s oceans contain a substantial amount of energy, stored in ocean currents and waves. Ocean current energy can be extracted using similar principles to existing wind energy platforms. A problem with such extraction methods is that the velocity of the fluid in ocean currents is too low for efficient energy generation. A potential solution to this problem is the use of a concentrator or diffuser to increase fluid velocity to the blades, but this carries with it extra costs. A more cost effective solution to this problem is presented by the use of a down flow current turbine in which the body geometry can be changed to increase velocity across the turbine blades. A scale of a commercial down flow turbine is tested in a wind tunnel in order to validate CFD simulations. A biologically inspired nacelle based on the Box fish (Ostracion cubicus) is presented and CFD simulations performed using the validated model. It is shown that by changing the body geometry of this down flow turbine, the velocity incident on the turbine blades can be increased for a given free stream velocity and such a design can cost less than a commercially available turbine

    An Archaeological Survey of the North Carolina Zoological Park

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    A miscellaneous report by the Research Laboratories of Archaeology, University of North Carolina at Chapel Hill. These reports discuss the findings of archaeological survey, testing, and excavations undertaken by the RLA between 1973 and 1985

    A Model for Data Collection and Reporting for Cow/Calf and Feedlot Operations

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    This fact sheet evaluates identification tags used at the Utah State cow/calf ranch operation, includng the identification devices, the hardware used to record individual data, and the data collection software

    A Redshift Survey of the Strong Lensing Cluster Abell 383

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    Abell 383 is a famous rich cluster (z = 0.1887) imaged extensively as a basis for intensive strong and weak lensing studies. Nonetheless there are few spectroscopic observations. We enable dynamical analyses by measuring 2360 new redshifts for galaxies with rpetro20.5_{petro} \leq 20.5 and within 50^\prime of the BCG (Brightest Cluster Galaxy: R.A.2000=42.014125_{2000} = 42.014125^\circ, Decl2000=03.529228_{2000} = -03.529228^\circ). We apply the caustic technique to identify 275 cluster members within 7h1h^{-1} Mpc of the hierarchical cluster center. The BCG lies within 11±110-11 \pm 110 km s1^{-1} and 21 ±56h1\pm 56 h^{-1} kpc of the hierarchical cluster center; the velocity dispersion profile of the BCG appears to be an extension of the velocity dispersion profile based on cluster members. The distribution of cluster members on the sky corresponds impressively with the weak lensing contours of Okabe et al. (2010) especially when the impact of foreground and background structure is included. The values of R200_{200} = 1.22±0.01h11.22\pm 0.01 h^{-1} Mpc and M200_{200} = (5.07±0.09)×1014h1(5.07 \pm 0.09)\times 10^{14} h^{-1} M_\odot obtained by application of the caustic technique agree well with recent completely independent lensing measures. The caustic estimate extends direct measurement of the cluster mass profile to a radius of 5h1\sim 5 h^{-1} Mpc.Comment: 29 pages, 9 figures, ApJ accepte

    The Case of the Frequent Flyer Fraudster

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    This case, based on a real fraud, engages students in a fraud investigation learning activity with a focus on interrogation. Students analyze an interrogation, identify and discuss verbal and nonverbal cues to deception, discuss legal ramifications of conducting fraud examinations, and develop recommendations to improve internal controls. The intended audience is a fraud examination course

    Intersection between natural and artificial swimmers: a scaling approach to underwater vehicle design.

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    Approximately 72% of the Earth’s surface is covered by water, yet only 20% has been mapped [1]. Autonomous Underwater Vehicles (AUVs) are one of the main tools for ocean exploration. The demand for AUVs is expected to increase rapidly in the coming years [2], so there is a need for faster and more energy efficient AUVs. A drawback to using this type of vehicle is the finite amount of energy that is stored onboard in the form of batteries. Science and roboticists have been studying nature for ways to move more efficiently. Phillips et al. [3] presents data that contradicts the idea that fish are better swimmers than conventional AUVs when comparing the energetic cost of swimming in the form of the Cost of Transport (COT). The data presented by Phillips et al. only applies to AUVs at higher length and naval displacement (mass) scales, so the question arises of whether an AUV built at different displacements and length scales is more efficient than biological animals and if current bio-inspired platforms are better than conventional AUVs. Besides power requirements, it is also useful to compare the kinematic parameters of natural and artificial swimmers. In this case, kinematic parameters indicate how fast the swimmer travels through the water. Also, they describe how fast the propulsion mechanism must act to reach a certain swimming speed. This research adopts the approach of Gazzola et al. [4] where the Reynolds number is associated with a dimensionless number, Swim number (Sw) in this case, that has all the kinematic information. A newly developed number that extends the swim number to conventional AUVs is the Propulsion number (Jw), which demonstrates excellent agreement with the kinematics of conventional AUVs. Despite being functionally similar, Sw and Jw do not have a one-to-one relationship. Sw, Jw, COT represent key performance metrics for an AUV, herein called performance criteria, which can be used to compare existing platforms with each other and estimate the performance of non-existent designs. The scaling laws are derived by evaluating the performance of 229 biological animals, 163 bioinspire platforms, and 109 conventional AUVs. AUVs and bio-inspired platforms have scarce data compared with biological swimmers. Only 5% of conventional and 38% of bio-inspired AUVs have kinematic data while 30% of conventional and 18% of bio-inspired AUVs have energetic data. The low amount of performance criteria data is due to the nature of most conventional AUVs as commercial products. Only recently has the COT metric been included in the performance criteria for bio-inspired AUVs. For this reason, the research here formulates everything in terms of allometric scaling laws. This type of formulation is used extensively when referring to biological systems and is defined by an exponential relationship f (x) = axb, where x is a physical parameter of the fish or vehicle, like length or displacement. Scaling laws have the added benefit of allowing comparisons with limited data, as is the case for AUVs. The length and displacement scale (physical scale) must be established before estimating the performance criteria. Scale is primarily determined by the payload needed for a particular application. For instance, surveying the water column in deep water will require different scientific tools than taking images of an oyster bed in an estuary. There is no way to identify the size of an AUV until it is designed for that application, since these scientific instruments each have their own volume, length, and weight. A methodology for estimating physical parameters using computer vision is presented to help determine the scale for the vehicle. It allows accurate scaling of physical parameters of biological and bio-inspired swimmers with only a side and top view of the platform. A physical scale can also be determined based on the vehicle’s overall volume, which is useful when determining how much payload is needed for a particular application. Further, this can be used in conjunction with 3D modeling software to scale nonexistent platforms. Following the establishment of a physical scale, which locomotion mode would be most appropriate? Unlike conventional AUVs that use propeller or glider locomotion, bio-inspired platforms use a variety of modes. Kinematics and energy expenditures are different for each of these modes. For bio-inspired vehicles, the focus will be on the body-caudal fin (BCF) locomotion, of which four types exist: anguilliform, carangiform, thunniform, and ostraciiform. There is ample research on anguilliform and carangiform locomotion modes, but little research on thunniform and ostraciiform modes. In order to determine which locomotion mode scales best for a bio-inspired AUV, this research examines the power output and kinematic parameters for all four BCF modes. In order to achieve this, computational fluid dynamics simulations are performed on a 2D swimmer for all four modes. Overset meshes are used in lieu of body-fitted meshes to increase stability and decrease computational time. These simulations were used to scale output power over several decades of Reynolds numbers for each locomotion mode. Carangiform locomotion was found to be the most energy efficient, followed by anguilliform, thunniform, and ostraciiform. In order to utilize the above scaling laws in designing a novel platform, or comparing an existing one, there must be a unifying framework. The framework for choosing a suitable platform is presented with a case study of two bio-inspired vehicles and a conventional one. The framework begins by determining how the platform can be physically scaled depending on the payload. Based on the physical scale and derived scaling laws, it then determines performance criteria. It also describes a method for relative cost scaling for each vehicle, which is not covered in the literature. The cost scaling is based on the assumption that all payloads and materials are the same. The case study shows that a conventional AUV performs better on all performance criteria and would cost less to build

    Bending strength model for internal spur gear teeth

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    Internal spur gear teeth are normally stronger than pinion teeth of the same pitch and face width since external teeth are smaller at the base. However, ring gears which are narrower have an unequal addendum or are made of a material with a lower strength than that of the meshing pinion may be loaded more critically in bending. In this study, a model for the bending strength of an internal gear tooth as a function of the applied load pressure angle is presented which is based on the inscribed Lewis constant strength parabolic beam. The bending model includes a stress concentration factor and an axial compression term which are extensions of the model for an external gear tooth. The geometry of the Lewis factor determination is presented, the iteration to determine the factor is described, and the bending strength J factor is compared to that of an external gear tooth. This strength model will assist optimal design efforts for unequal addendum gears and gears of mixed materials

    Spur, helical, and spiral bevel transmission life modeling

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    A computer program, TLIFE, which estimates the life, dynamic capacity, and reliability of aircraft transmissions, is presented. The program enables comparisons of transmission service life at the design stage for optimization. A variety of transmissions may be analyzed including: spur, helical, and spiral bevel reductions as well as series combinations of these reductions. The basic spur and helical reductions include: single mesh, compound, and parallel path plus revert star and planetary gear trains. A variety of straddle and overhung bearing configurations on the gear shafts are possible as is the use of a ring gear for the output. The spiral bevel reductions include single and dual input drives with arbitrary shaft angles. The program is written in FORTRAN 77 and has been executed both in the personal computer DOS environment and on UNIX workstations. The analysis may be performed in either the SI metric or the English inch system of units. The reliability and life analysis is based on the two-parameter Weibull distribution lives of the component gears and bearings. The program output file describes the overall transmission and each constituent transmission, its components, and their locations, capacities, and loads. Primary output is the dynamic capacity and 90-percent reliability and mean lives of the unit transmissions and the overall system which can be used to estimate service overhaul frequency requirements. Two examples are presented to illustrate the information available for single element and series transmissions
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