Variations In Load Distribution Research Articles

On the wake deflection of vertical axis wind turbines by pitched blades

AbstractWake losses are a critical consideration in wind farm design. The ability to steer and deform wakes can result in increased wind farm power density and reduced energy costs and can be used to optimize wind farm designs. This study investigates the wake deflection of a vertical axis wind turbine (VAWT) experimentally, emphasizing the effect of different load distributions on the wake convection and mixing. A trailing vortex system responsible for the wake topology is hypothesized based on a simplified vorticity equation that describes the relationship between load distribution and its vortex generation; the proposed vorticity system and the resulting wake topology are experimentally validated in the wind tunnel via stereoscopic particle image velocimetry measurements of the flow field at several wake cross‐sections. Variations in load distribution are accomplished by a set of fixed blade pitches. The experimental results not only validate the predicted vorticity system but also highlight the critical role of the streamwise vorticity component in the deflection and deformation of the wake, thus affecting the momentum and energy recoveries. The evaluation of the various loading cases demonstrates the significant effect of the wake deflection on the wind power available to a downwind turbine, even when the distance between the two turbines is only three diameters.

The Axial Impact Response and Plantar Load Distribution of the Hybrid III and Military Lower Extremity Under Altered Ankle Postures.

Foot injuries as a result of automotive collisions are frequent and impactful. Anthropomorphic test devices (ATDs), used to assess injury risk during impact scenarios such as motor vehicle collisions, typically assess risk of foot/ankle injuries by analyzing data in tibia load cells. The peak axial force and the tibia index are metrics commonly used to evaluate risk of injury to the lower extremity but do not directly account for injury risk to the foot, or the risk of injury associated with out-of-position loading. Two ATDs, the Hybrid III lower leg and the Military Lower Extremity, were exposed to axial impacts at seven different ankle postures. An array of piezoresistive sensors located on the insole of a boot was employed during these tests to assess the load distribution variations among postures and between ATD models on the plantar surface of the foot. Both posture and ATD model affected the load distribution on the foot, highlighting the need for regional injury risk assessments in this vulnerable anatomical region. The increase in forefoot loading during plantarflexion was not reflected in the standard industry metrics of peak axial force or tibia index, suggesting that increased fracture risk to the forefoot would not be detected. The variations in load distribution between the models could also alter injury risk assessment in frontal collisions based on differences in attenuation. These data could be used for regional foot injury assessment and to inform the design of an improved ATD foot.

Reliability modeling methods for load-sharing k-out-of-n system subject to discrete external load

Most reliability modeling methods for the load-sharing k-out-of-n system are based on the assumed lifetime distribution and the relation function between the component failure rate and component load. However, the relation function is difficult to determine since the failure rate data have to be acquired. Therefore, this paper aims to develop a more direct reliability model for the load-sharing system based on the generalized load-strength model. In the presence of discrete external load, the proposed method utilizes the load distribution variation and strength damage after component failures to directly reflect the load-sharing effect, which can avoid measuring the failure rate. Further, the existing failure-rate-based reliability modeling method is also improved since the direct relation function between the component failure rate and component load is deduced. Two methods are both illustrated through the reliability analysis of a load-sharing redundant micro-engine system.

Friday, September 28, 2018 10:30 AM–12:00 PM abstracts: innovation, surface technology and biomechanics: 180. Effects of added compression on sagittal plane lumbosacral junction rod strain and sacral screw bending moment during in vitro loading

BACKGROUND CONTEXT Variations in load distribution based on surface strain on instrumentation spanning the lumbosacral junction during in vitro loading are often used to evaluate biomechanical effects of different PSR configurations. The gold standard for biomechanical comparisons of spinal instrumentation involves the application of pure moment loads to induce bending of the instrumented spine. However spinal constructs in vivo are subjected to substantial vertical compressive forces due to gravitational loading of upper body mass. The effects of added compressive loads during in vitro bending of the PSR instrumented lumbar spine, as determined by surface strains at the lumbosacral level, are not well understood. PURPOSE The purpose of this study was to analyze the biomechanical differences in lumbosacral rod strain, and sacral screw bending moments during sagittal plane bending, with and without a compressive preload. STUDY DESIGN/SETTING In vitro biomechanical study using human cadaveric specimens. PATIENT SAMPLE A total of 14 (L1-Pelvis) cadaveric spines (5F/9M, 51.6±7.4 years, DEXA 0.837g/cm2). OUTCOME MEASURES L5-S rod strains and resultant sacral screw bending loads. METHODS A total of 14 cadaveric specimens were tested in a 6DOF robot under continuous loading in two PSR configurations (L2-S and L2-IL) using five types of loads: 7.5Nm flexion (FL), extension (EX), 400 N compression (C), combined C+FL and combined C+EX. Strain gauges were used to measure rod strains (RS) at L5-S and net sacral screw bending moments (SS). Data were analyzed using One-way RM-ANOVA followed by Holms-Sidak paired analysis (p RESULTS RS significantly increased with L2IL versus L2S (FL: +77%; EX: +65%; C+FL: +46%; C: +40%; p .2]). CONCLUSIONS The relative effects of L2IL versus L2S (increased RS and reduced SS) were consistent among all types of loads. However, the additive effects of compression on RS and SS varied with type of instrumentation (L2S vs. L2IL) and direction of bending (FL vs. EX). Compression loading significantly influences instrumentation performance and can help provide improved understanding of lumbosacral junction load distributions with PSR constructs.

The first Italian blast-induced liquefaction test (Mirabello, Emilia-Romagna, Italy): description of the experiment and preliminary results

Soil liquefaction can result in significant settlement and reduction of load-bearing capacity. Moreover, the increase and the accumulation of pore pressure during an earthquake and its post-seismic dissipation can generate permanent deformations and settlements. The quantitative evaluation of post-liquefaction settlements is of extreme importance for engineering purposes, i.e. for earthquake-resistant design of new buildings and safety evaluation of existing ones. Quantifying the extent of these phenomena is, however, rather difficult. Uncertainties arise from the stochastic nature of the earthquake loading, from the simplifications of soil models, and from the difficulty in establishing correlations between the pre-earthquake soil state and the post-seismic deformations. Field scale liquefaction tests, under controlled conditions, are therefore important for a correct quantification of these phenomena. Recent experiences (e.g. New Zealand, United States) show that liquefaction can be induced and monitored with field scale blast tests to study the related effects on soil geotechnical properties. Within this framework this paper introduces the preliminary results obtained from a research project on blast-induced liquefaction at the field scale; tests were performed at a trial site located in Mirabello (Ferrara, Italy), a village strongly affected by liquefaction phenomena during the 2012 Emilia Romagna earthquake. Invasive tests, such as piezocone, seismic dilatometer and down-hole tests, and non-invasive tests were carried out before and after the execution of two blast test sequences to study the variation in physical properties of the soils. Pore pressure transducers, settlement profilometers, accelerometers and an instrumented micropile were installed with the objective of measuring, during and after the detonations, the generation and subsequent dissipation of the pore pressure, the vertical deformations, and the blast-induced ground motions respectively. Variations in load distribution on deep foundations due to soil liquefaction were also evaluated on a test micropile instrumented with a strain gauge chain. Topographical surveys were carried out to measure ground surface settlements. Laboratory tests and trenches also provided increase understanding of the site characteristics.

Study on Dynamic Reconfiguration of Distribution Network Considering Distribution Generation

A new dynamic reconfiguration method considering distribution generation (DG) was presented. The dynamic reconfiguration problem was solved from three aspects: firstly, the time interval partition of the entire scheduling period was optimized by load distribution variation index; secondly, a plurality of time intervals were optimized and reconfigured by using the multi-objective particle swarm optimization model of multi-period encoding; finally, the optimal time interval numbers was determined by gradually approaching the falling threshold of net loss. If the system contained DG, DG’s output curve was determined by the analysis of its dynamic characteristics. The results of the test showed that the proposed method was effective to solve the dynamic reconfiguration with DG.

Comparative Prospective Study of Load Distribution Projection Among Patients with Vertebral Fractures Treated with Percutaneous Vertebroplasty and a Control Group of Healthy Volunteers

Through a prospective comparison of patients with vertebral fractures and normal population, we illustrate effect of percutaneous vertebroplasty (PV) upon projection of load distribution changes. Vertebroplasty group (36 symptomatic patients with osteoporotic vertebral fractures) was evaluated on an electronic baropodometer registering projection of weight bearing areas on feet. Load distribution between right and left foot (including rear-front of the same foot) during standing and walking was recorded and compared before (group V1) and the day after (group V2) PV. Control group (30 healthy asymptomatic volunteers-no surgery record) were evaluated on the same baropodometer. Mean value of load distribution difference between rear-front of the same foot was 9.45 ± 6.79 % (54.72-45.28 %) upon standing and 14.76 ± 7.09 % (57.38-42.62 %) upon walking in the control group. Respective load distribution values before PV were 16.52 ± 11.23 and 30.91 ± 19.26 % and after PV were 10.08 ± 6.26 and 14.25 ± 7.68 % upon standing and walking respectively. Mean value of load distribution variation between the two feet was 6.36 and 14.6 % before and 4.62 and 10.4 % after PV upon standing and walking respectively. Comparison of load distribution variation (group V1-V2, group V1-control group) is statistically significant. Comparison of load distribution variation (group V2-control group) is not statistically significant. Comparison of load distribution variation among the two feet is statistically significant during walking but not statistically significant during standing. There is a statistically significant difference when comparing load distribution variation prior vertebroplasty and that of normal population. After vertebroplasty, this difference normalizes in a statistically significant way. PV is efficient on equilibrium-load distribution improvement as well.

Abstract No. 187: Percutaneous vertebroplasty and baropodometry: comparative prospective study of load distribution variation between osteoporotic patients and normal population

Abstract No. 187: Percutaneous vertebroplasty and baropodometry: comparative prospective study of load distribution variation between osteoporotic patients and normal population

Muscle forces and spinal loads at C4/5 level during isometric voluntary efforts.

The goal of this study was to determine neck muscle forces and spinal loads that result from isometric muscle contractions. Electromyographic (EMG) activity of the neck musculature and a three-dimensional biomechanical model of the neck were used. The model was EMG-based and estimated muscle forces and spinal loads at the C4/5 level. EMG signals were collected from eight sites at the C4/5 level of the neck using Ag-AgCl surface electrodes from 10 adult male subjects. The subjects performed isometric contractions gradually developing to maximum efforts in flexion, extension, left lateral bending, and right lateral bending. During maximum voluntary contraction (MVC) trials most muscles generated high levels of EMG signal during cervical rotation. The posterior surface of the neck (trapezius) was the only electrode site at which maximum activity EMG consistently occurred by the same method (rotation) in all subjects. Variations in the EMG patterns were observed in different experiments that produced overall neck moments of equal magnitudes. With these data the model computed variations in load distribution among the agonist muscles. Consistent also with EMG distributions, the model also computed co-contractions of antagonist muscles. The average (+/- SD) magnitudes of peak moments were 28.3 (+/- 3.3) Nm in extension, 17.7 (+/- 3.1) Nm in flexion, 16.9 (+/- 2.8) Nm in left lateral bending, and 17.0 (+/- 2.9) Nm in right lateral bending. The model predicted C4/5 joint compressive forces during peak moments were 1372 (+/- 140) N in extension, 1654 (+/- 308) N in flexion, 956 (+/- 169) N in left lateral bending, and 1065 (+/- 207) N in right lateral bending. Results suggest that higher C4/5 joint loads than previously reported are possible during maximum isometric muscle contractions.

Analysis of human neck loads during isometric voluntary ramp efforts: EMG-Assisted optimization modeling approach

Neck muscle forces and spinal loads at the C4/5 level were estimated that result from isometric voluntary ramp efforts gradually developing to maximums in flexion, extension, left lateral bending and right lateral bending. Electromyographic (EMG) activities, a three-dimensional anatomic data of the neck and a hybrid model, EMG-assisted optimization (EMGAO) model, were used. The model computed the cervical loads at 25%, 50%, 75%, and 100% of peak moments. The highest model-predicted C4/5 joint compressive forces occured during flexion; 361 (±164) N, 811 (±288), N, 1207 (±491) N and 1674 (±319) N in 25%, 50%, 75% and 100% of peak moment respectively. Variations in load distribution among the agonistic muscles and co-contractions of antagonistic muscles were estimated during ramp effors. Results suggest that higher C4/5 joint loads than previously reported are possible during isometric, voluntary muscle contractions. These higher physiological loads at C4/5 level must be considered possible during orthopedic reconstruction at this level.

The trout tail fin: A self-cambering hydrofoil

The trout's tail fin is flexible, yet it propels the trout. It can do so because the flexibility is of a special, limited kind. The tail fin is not simply a sheet of compliant material. Instead it is supported by bony rays, each of which is a flexible girder. These girders can bend in agreement with the hydrodynamic load, but when they do so their structure requires that they steer the fin as a whole in opposition to the load. The fin automatically adjusts its camber so that the shape of the distribution of hydrodynamic load upon it is the same whatever the speed of the fish and whatever the path of the tail fin through the water — unless, as may be the case, parts of the swimming cycle demand a bend sharper than the fin can accomodate. If the latter occurs, cyclic variations in load distribution will result. These may be needed if the tail is to generate the forces required to match the body mechanically at every part of the cycle.