Effect Of Body Geometry Research Articles

Effects of Body Geometry and Propulsion Type on Unmanned Underwater Vehicle Interactions With Marine Vegetation

Abstract Interactions with marine vegetation can disrupt unmanned underwater vehicle missions. Very little information is publicly available about the mechanisms causing these interactions or the consequences of them. This article compares the interactions between three different style underwater vehicles and two different types of marine vegetation. Similar test setups and procedures were used to allow for the direct comparison between REMUS-100, BlueROV2, and GhostSwimmer vehicles. Experimental test runs were conducted at different vegetation densities using either synthetic eelgrass or synthetic giant kelp. The resulting interactions depended on the vegetation type, vegetation density, propulsion mechanism of the vehicle, and vehicle geometry. Synthetic giant kelp caused a multitude of interactions with the dominant ones being interference, blockage, and entanglement with the vehicle body. Collectively, these three interactions occurred 84% of the time on giant kelp runs where an interaction was observed. Eelgrass caused propeller entanglement and even body blockage depending on the unmanned underwater vehicle geometry. In high density eelgrass, we observed that a spinning propulsion mechanism experiences entanglement 100% of the time when at low speed. The use of an oscillating tail for propulsion coupled with a completely streamlined body appears to successfully mitigate adverse marine vegetation interactions.

Effects of body geometry, body composition, cardio-pulmonary capacity, and fitness on young men's thermal preference.

This paper investigated principal parameters affecting individual differences of thermal preference. 36male college students were selected from three thermal preference groups by a questionnaire, including 10 of cool preference (Gcp), 17 of neutral preference (Gnp), and 9 of warm preference (Gwp). Subsequently, their thermal preferences were further examined by a human trial in a climate chamber. Once significant differences were found between groups, subjects' 57 parameters, including body geometry, body composition, cardio-pulmonary capacity, and physical fitness, were measured. Compared to Gwp, Gcp had higher weight (80.0 vs. 64.2kg), body mass index (BMI) (26 vs. 20.8kg·m-2 ), body surface area (BSA) (1.94 vs. 1.78m2 ), waist-to-hip ratio (WHR) (87.29% vs. 80.23%), body circumferences (except for forearm circumference), skinfold thickness of all the local parts, volume of expired air (VE) (50.97 vs. 40.81L/min), and body fat rate (BFR) (24.44% vs. 14.07%), but had a lower specific surface area (SSA) (0.02477 vs. 0.02791m2 /kg), resting metabolic rate (RMR) per kilogram (1.21 vs. 1.47W/kg), diastolic blood pressure (DBP) (65.30 vs. 74.69mmHg), and percentages of muscle (71.17% vs. 80.95%), total water (55.35% vs. 63.14%), skeletal muscle (42.47% vs. 47.94%), protein (14.90% vs. 16.94%), inorganic salt (5.29% vs. 5.86%), and bone mineral (0.044% vs. 0.048%). Among these parameters, body fat and SSA played a dominant role (accounting for 85.76%) in explaining individual differences in thermal preference.

Resistance Prediction on Submerged Axisymmetric Bodies Fitted with Turbulent Spot Inducers

A method to predict bare hull ship resistance is presented in this article. Hull resistance is assumed to consist of friction drag and residual drag. The friction drag coefficient is represented by an equivalent flat plate coefficient multiplied by a form factor to incorporate effects of body geometry and boundary layer (BL) characteristics on drag. Theories of form factors including the effect of BL transition locations have been successfully derived. Form factors are shown to have a noticeable effect on body drag at high Reynolds numbers (Re) and a significant effect at model Re. Residual drag coefficient is obtained from model tests with application of scaling formulae to relate model scale residual drag coefficient to full scale drag coefficient. To address the issue of laminar flow on models in residual drag measurements, a new device termed a "turbulent spot inducer" is introduced in model tests. Finally, a new scaling formula to relate model scale residual drag coefficient to full scale residual drag coefficient with the flow on body surface partly laminar and partly turbulent is derived. It is shown that a traditional 1þK scaling method used in the marine industry is a special case of the newly derived residual drag scaling formula.

Comparative study: Flow-induced noise on underwater acoustic pressure, particle velocity, and intensity sensors

A neutrally buoyant underwater acoustic p-u intensity probe contains discrete sensors for direct measurement of acoustic pressure and particle velocity [J. A. McConnell and G. C. Lauchle, J. Acoust. Soc. Am. 103, 2755(A) (1998)]. Intensity is calculated from the cross spectrum between these two quantities. Thus a single probe can be categorized as a compound sensor capable of independently measuring acoustic pressure, particle velocity, and intensity. Using this probe, a comparative study concerning the measurement of all three quantities in the presence of mean flow and an independent sound source was performed. Bias errors, which result from the flow-induced noise generated by towing the sensor (e.g., a cylindrical body) in cross flow at low speeds through a channel of water, are presented. Other parameters of interest include analysis of experimental pressure–pressure and pressure–velocity correlation functions. The effect of body geometry (e.g., variation in aspect ratio) on the measured bias errors and correlation functions is also presented. [Work supported by the Office of Naval Research, the Naval Submarine League, and the Acoustics Technology Branch of the Naval Air Warfare Center—Aircraft Division, via the DoD Small Business Innovation Research Program.]

Time Resolved Torque of Three-Dimensional Rotating Bluff Bodies in a Cylindrical Tank

Torque measurements have been made on rotating three-dimensional bluff bodies in a cylindrical container from start-up to mean flow steady state. The flow is observed to pass through three distinct temporal regimes in the transient process. These regimes include a build-up period where the torque remains approximately constant, a decay period where the torque decreases, and a mean steady state where the mean torque remains at a constant level. Effects of body geometry, rotation rate, acceleration rate, and fluid height in the tank are quantified. The torque coefficient during the build-up and mean steady-state regimes is shown to be a function of Reynolds number and body geometry. A time scale marking the beginning of the decay period is presented in terms of the problem parameters. Over the range of parameters studied, the build-up, decay, and mean steady-state regimes are completely specified by the Reynolds number, geometric parameters, and decay time scale.

Multi-legged walking machine body design

The effects of body geometry on walking machine performance have been investigated, and a body design procedure proposed. The relationships between static workspace, body-geometry and installed joint torques have been derived. A body design procedure that uses this data is then described, and two design examples discussed. The procedure results in a body geometry which minimises the installed joint torques, and hence the machine weight, for the desired workspace area.

The effect of body geometry and incident flow characteristics on the distortion of turbulence

An experimental study of the characteristics of a turbulent field upstream from a cylinder normal to the mean flow is presented for various geometries of the cylinder section. Four configurations were tested: a flat plate of 0.05 × 0.01 m section, a square bar of 0.05 × 0.05 m, a rectangular bar of 0.05 × 0.1 m and a circular cylinder, 0.05 m diameter. Tests were carried out for grid and shear incident flows to study the effects of the turbulence characteristics of the incoming flow. A method to deduce the pressure spectrum at the stagnation point by extrapolating the longitudinal velocity spectra measured along the stagnation streamline was used. Theoretical analysis was done to establish formulae to approximate both velocity and pressure spectra.

The effect of body geometry on the flow noise of cylinders in cross flow

The effect of body geometry on the flow noise of cylinders in cross flow

Transition and Strouhal Number for the Incompressible Wake of Various Bodies

Incompressible wakes behind three-dimensional bluff bodies have been studied in order to gain information about the effects of body geometry. The results of Magarvey and Bishop achieved by dropping liquid droplets through another liquid were duplicated using solid spheres, and observations were made of the wakes of bodies of various shapes, particularly cones. It was found that wake transition, defined as the first occurrence of finite unsteadiness, could be approximately correlated for a range of spheres and cones by a Reynolds number based on the total wake momentum thickness, θ2 = CDA/2π, Reθt ≈ 95. The cases of the teardrop and the disc deviate from this correlation, and explanations are discussed. It was also found that for regular vortex shedding the data for spheres and cones could be correlated with the Rayleigh-Strouhal formula based on θ; Sθ=0.305 [1−(95/Reθ)].Constraining the body to travel along a wire, thus reducing body-fluid interactions, produced an aperiodicity in the shedding phenomenon but left the value of the Strouhal number effectively unchanged.

Impact Theory Calculations of the Lift and Drag of Ducted Bodies

SummaryNewtonian impact theory has been used to estimate the external pressure forces on ducted bodies of rectangular, circular and semi-circular cross section. With an allowance for skin friction (or other incidence-independent drag) it is shown that maximum lift/drag ratios of about three to four are possible with little effect of body geometry provided that short and very divergent, or tall and narrow rectangular ducts are avoided.Large changes occur in the separate lift and drag at maximum lift/drag ratio and these have to be made compatible with the weight and thrust capacity of the configurations. The maximum lift/drag ratio of a duct can be improved by the addition of wings, especially for a duct with poor lift/drag ratio, but the best overall performance is with a duct of good lift/drag ratio and low drag.It is anticipated that impact theory underestimates the pressure forces, and hence the lift/drag ratios, which would obtain at finite Mach numbers but the trends with geometrical changes should be reasonably reliable.