scholarly journals High-Speed Ice Friction Experiments under Lab Conditions: On the Influence of Speed and Normal Force

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
Matthias Scherge ◽  
Roman Böttcher ◽  
Mike Richter ◽  
Udo Gurgel
Keyword(s):  
Coefficient Of Friction ◽  
High Speed ◽  
Aerodynamic Drag ◽  
Limiting Factors ◽  
Maximum Speed ◽  
Cross Sectional ◽  
Sliding Speed ◽  
Ice Friction ◽  
Wide Range ◽  
The Cross

Using a high-speed tribometer, coefficients of friction for bobsled runners were measured over a wide range of loads and speeds. Between 2.8 m/s and 28 m/s (equal to 10 km/h and 100 km/h), the measured coefficients of friction showed a linear decrease with increasing speed. The experiments revealed ultra-low friction coefficients of less than 0.01 after exceeding a sliding speed of about 20 m/s. At maximum speed of 28 m/s, the average coefficient of friction was 0.007. The experiments help to bridge the gap between numerous low-speed friction tests by other groups and tests performed with bobsleds on real tracks. It was shown that the friction data obtained by other groups and our measurements can be approximated by a single master curve. This curve exhibits the largest decrease in friction up to a sliding speed of about 3 m/s. The further increase in speed generates only a small decrease in friction. In addition, friction decreases with increasing load. The decrease stops when ice wear becomes effective. The load point of constant friction depends on the cross-sectional radius of the runner. The larger the radius is, the higher the load is, before the ice shows signs of fracture. It turned out that besides aerodynamic drag (not considered in this work), ice friction is one of the main speed-limiting factors. In terms of runner geometry, a flat contact of runner and ice ensures the lowest friction. The rocker radius of the runner is of greater importance for a low coefficient of friction than the cross-sectional radius.

scholarly journals Observation and analysis of diving beetle movements while swimming

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Debo Qi ◽  
Chengchun Zhang ◽  
Jingwei He ◽  
Yongli Yue ◽  
Jing Wang ◽  
...  
Keyword(s):  
Swimming Speed ◽  
High Speed ◽  
Kinematic Model ◽  
Movement Pattern ◽  
Unmanned Vehicles ◽  
Power Stroke ◽  
Cross Sectional ◽  
Motion Data ◽  
The Cross ◽  
Diving Beetle

AbstractThe fast swimming speed, flexible cornering, and high propulsion efficiency of diving beetles are primarily achieved by their two powerful hind legs. Unlike other aquatic organisms, such as turtle, jellyfish, fish and frog et al., the diving beetle could complete retreating motion without turning around, and the turning radius is small for this kind of propulsion mode. However, most bionic vehicles have not contained these advantages, the study about this propulsion method is useful for the design of bionic robots. In this paper, the swimming videos of the diving beetle, including forwarding, turning and retreating, were captured by two synchronized high-speed cameras, and were analyzed via SIMI Motion. The analysis results revealed that the swimming speed initially increased quickly to a maximum at 60% of the power stroke, and then decreased. During the power stroke, the diving beetle stretched its tibias and tarsi, the bristles on both sides of which were shaped like paddles, to maximize the cross-sectional areas against the water to achieve the maximum thrust. During the recovery stroke, the diving beetle rotated its tarsi and folded the bristles to minimize the cross-sectional areas to reduce the drag force. For one turning motion (turn right about 90 degrees), it takes only one motion cycle for the diving beetle to complete it. During the retreating motion, the average acceleration was close to 9.8 m/s2 in the first 25 ms. Finally, based on the diving beetle's hind-leg movement pattern, a kinematic model was constructed, and according to this model and the motion data of the joint angles, the motion trajectories of the hind legs were obtained by using MATLAB. Since the advantages of this propulsion method, it may become a new bionic propulsion method, and the motion data and kinematic model of the hind legs will be helpful in the design of bionic underwater unmanned vehicles.

Experimental study of a honeycomb energy-absorbing device for high-speed trains

2019 ◽  
Vol 234 (10) ◽  
pp. 1170-1183
Author(s):  
Benhuai Li ◽  
Zhaijun Lu ◽  
Kaibo Yan ◽  
Sisi Lu ◽  
Lingxiang Kong ◽  
...  
Keyword(s):  
Energy Absorption ◽  
High Speed ◽  
Aerodynamic Drag ◽  
Weight Ratio ◽  
Large Mass ◽  
High Speed Train ◽  
Cross Sectional ◽  
High Speed Trains ◽  
Thin Walled ◽  
Energy Absorbing

Aluminium honeycomb is a light weight, thin-walled material with a typical multi-cellular construction and a good strength-to-weight ratio. Therefore, aluminium honeycomb can be used as an energy-absorbing device for high-speed trains. Due to its large mass and high operating speed, a high-speed train can generate large impact energy. Thus, an energy-absorbing device with a greater energy absorption capability must be designed for high-speed trains. To reduce the aerodynamic drag, the cross-sectional area of a high-speed train is limited. Therefore, a honeycomb energy-absorbing device should be designed in such a way that it is longer than the traditional energy-absorbing devices; however, this may lead to bending, destruction and uncontrollable deformation of the honeycomb; these factors are not conducive for energy absorption. In this paper, a sleeve structure was designed for high-speed trains, and a crash experiment of the energy-absorbing structure showed that the bending and destruction of the honeycomb energy-absorbing device are effectively suppressed compared with the ordinary honeycomb energy-absorbing structure. Moreover, the fluctuation of the crash force was smaller and the crash force is more stable than the traditional thin-walled energy-absorbing structure. Therefore, the deformation instability problem of the ordinary honeycomb energy-absorbing structure and the crash force fluctuation problem of the traditional thin-walled energy-absorbing structure can be solved. Then, a crash experiment and simulation involving a high-speed train with improved honeycomb energy-absorbing device was carried out, and the results showed that the deformation of the end of the train body was stable and controllable, and the train body deceleration satisfied the collision standard EN15227.

Inclusion of Whisker Spray Drag in Performance Prediction Method for High-Speed Planing Hulls

2007 ◽  
Vol 44 (01) ◽  
pp. 35-56
Author(s):  
Daniel Savitsky ◽  
Michael F. DeLorme ◽  
Raju Datla
Keyword(s):  
Performance Prediction ◽  
High Speed ◽  
Aerodynamic Drag ◽  
Prediction Method ◽  
Viscous Drag ◽  
Cross Sectional ◽  
Stagnation Line ◽  
Prediction Program ◽  
Pressure Drag ◽  
Hull Forms

The planing hull performance prediction method published by Savitsky in the October 1964 issue of SNAME's Marine Technology included only the viscous drag and pressure drag components in the bottom area aft of the stagnation line. While discussing the existence of an additional component of viscous drag in the whisker spray region forward of the stagnation line, a method to quantify this drag component was not developed in Savitsky (1964). Earlier studies by Savitsky and Ross (1952) and Savitsky and Neidinger (1954) discuss the potential whisker spray drag component but do not present a complete analytical derivation of its magnitude nor verification of the results by comparison with experimental data. The present study fills this void by developing a method for quantifying the whisker spray contribution to total hull resistance as a function of deadrise angle, trim angle, and speed, and incorporating the results into the SNAME published hull performance prediction method. The analytical results are compared with data from model tests conducted at three separate towing tank facilities and show fairly good agreement with these data. It is shown that for high-speed planing hulls, the whisker spray drag component can be as much as 15% of the total drag. In addition, (1) procedures are provided for the proper location, size, and geometry of spray strips to deflect the whisker spray away from the hull bottom; (2) the aerodynamic drag of the hull cross-sectional area above the waterline is also quantified and included in the final performance prediction method; and (3) the equilibrium trim angle identified in the prediction program (for prismatic hull forms) is, for nonprismatic hulls, related to the trim angle of the v4 buttock line (relative to the level water surface) when measured at the forward edge of the mean wetted length.

Friction of a Rubber Wedge Sliding on Glass

1991 ◽  
Vol 64 (1) ◽  
pp. 108-117 ◽  
Author(s):  
C. W. Extrand ◽  
A. N. Gent ◽  
S. Y. Kaang
Keyword(s):  
Coefficient Of Friction ◽  
Applied Load ◽  
Unit Length ◽  
Sliding Speed ◽  
Normal Loading ◽  
Contact Width ◽  
Wide Range ◽  
The Coefficient Of Friction ◽  
Apparent Coefficient Of Friction ◽  
Pressure Independent

Abstract The contact width, and hence contact area, for an elastic wedge pressed against a rigid flat surface appears to be proportional to the applied load per unit length. For a particular rubber sample, the reciprocal of the constant of proportionality, i.e., the mean normal pressure, was 130 kPa, i.e., about 7% of the tensile modulus E of the material. It was also independent of sliding speed over the range examined. Thus, a sharp wedge gave a relatively high loading pressure, independent of the applied load. As a result, the coefficient of friction was also independent of applied load over a wide range. The coefficient of friction was measured for a wedge of an unfilled natural rubber vulcanizate over wide ranges of sliding speed (50 µm/s to 100 mm/s) and test temperature (3°C to 63°C). It was found to increase with sliding speed and decrease with temperature over these ranges. The results at different temperatures were superposable using the WLF rate-temperature equivalence to create a master curve of friction vs. reduced sliding speed, rising from a value of about 1.5 at high temperatures and low speeds to about 5 at low temperatures and high speeds. Chlorination of a thin surface region reduced the coefficient of friction and its dependence on speed and temperature. It then became similar to that typically found for thermoplastics, 0.4 to 0.7. The geometry of sliding a flexible strip against a rigid curved surface caused high values of the apparent coefficient of friction to be obtained at relatively small departures from normal loading. In an extreme case, frictional seizure was observed when a high-friction sample contacted the glass surface at an angle of about 15° to the direction of loading. The apparent coefficient of friction then became indefinitely large. This same phenomenon of abnormally large frictional effects would be expected to occur in the case of conventional windshield-wiper blades, sliding over curved glass windshields.

scholarly journals Vehicle-Bridge Coupling Vibration Analysis for Simply Supported Girders of High-Speed Railway Bridges Based on the Cross-Sectional Decentralized Centre of Mass and Shear

2021 ◽  
Vol 2021 ◽  
pp. 1-18
Author(s):  
Chen Daihai ◽  
Zhou Shuai ◽  
Xu Shizhan ◽  
Li Zheng ◽  
Fang Yilin
Keyword(s):  
Dynamic Response ◽  
High Speed ◽  
Influence Factors ◽  
Centre Of Mass ◽  
Cross Sectional ◽  
High Speed Railway ◽  
Coupling Vibration ◽  
Offset Distance ◽  
Spatial Beam ◽  
The Cross

Taking the simply supported box girder bridge of high-speed railway as an example, the effect of cross-sectional decentralized centre of mass and shear on the spatial beam element stiffness matrix was theoretically derived. Based on the vehicle-bridge coupling vibration analysis method of the railway bridge, an analysis program of vehicle-bridge coupling vibration for the high-speed railway was compiled, and its reliability was verified through an example analysis. On this basis, considering the cross-sectional decentralized centre of mass and shear, the influence factors of vehicle-bridge coupling vibration response were studied, which included the offset distance of the beam section’s mass and shear centre, offset distance of track centreline, vehicle weight, and vehicle speed. The results show that the additional items of the spatial beam element stiffness matrix are generated by the torsion effect when the cross-sectional decentralized centre of mass and shear is considered, and it will affect the lateral and vertical stiffness of the element. The cross-sectional decentralized centre of mass and shear has a significant effect on the lateral dynamic response of the bridge’s mid-span, but the influence on the vertical response of the bridge and the dynamic response of the car body is small. The main influence factors of the lateral dynamic response of the bridge are the vertical offset distance of the beam section’s centre of mass and shear, the lateral offset distance of the track centreline, and the vehicle weight.

Structural innovation in state variables and expected stock returns

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Prodosh E. Simlai
Keyword(s):  
Risk Factors ◽  
Stock Returns ◽  
Systematic Risk ◽  
Expected Returns ◽  
State Variables ◽  
Cross Sectional ◽  
Content Type ◽  
Wide Range ◽  
The Cross ◽  
Structural Innovation

PurposeThe purpose of this study is to investigate whether the surprise components of systematic risk, which are useful in forecasting future investment opportunities, help explain the cross-section of average returns associated with portfolios sorted on size, book-to-market and accruals. This study also aims to examine the mispricing attributes of the size, value and accrual effects by investigating the relative economic relevance of aggregate risk factors, which are related to exogenous shocks in state variables, in the cross-sectional returns of triple-sorted portfolios.Design/methodology/approachThis study uses innovations of systematic risk, which affect the cash flows and risk-adjusted discount rates of all firms in an economy and determines the expected returns of portfolios based on firm characteristics. This study uses independent sorts based on size, book-to-market and total accruals – all of which are measured at the firm level – and construct three-dimensional test portfolios. For unobserved innovations, this study estimates a triangular structural vector autoregressive system and obtain the exogenous innovations in state variables. The author uses Fama-MacBeth two-pass cross-sectional regressions and examines whether the structural innovations explain a significant part of the cross-sectional variation in the average returns of the test portfolios.FindingsThis study finds that variations in expected returns of testing assets are determined by differences in the underlying assets’ exposure to systematic risk innovation. The empirical evidence also shows that exogenous innovation in Fama-French (FF) risk factors leaves out important cross-sectional information about expected returns, and additionally, the FF-factor betas have lower cross-sectional power than the proxy for innovation betas. The cross-sectional differences in the test portfolios’ sensitivity to instruments such as the short-term Treasury bill rate and term spread survive the presence of FF-factor betas.Originality/valueIn contrast to the existing literature, this study uses structural innovations that are uncorrelated and thus exogenous in nature. The author creates test portfolios that display a wide range of average returns and are unlikely to show spurious variability in risk exposures. Unlike the existing research, where size, value and accrual anomalies have been analyzed in isolation, this study examine these pricing patterns jointly, focusing on the possible contributing role of structural innovation in economy-wide predictor variables. To the best of the author’s knowledge, this paper is the first attempt to link the sensitivity of portfolios sorted on size, book-to-market and accruals to exogenous structural innovation.

Nonlinear In-Plane Stability of Deep Parabolic Arches Using Geometrically Exact Beam Theory

2018 ◽  
Vol 18 (01) ◽  
pp. 1850006 ◽  
Author(s):  
Aditya Sabale ◽  
K. V. Nagendra Gopal
Keyword(s):  
Continuation Method ◽  
Constitutive Law ◽  
Exponential Map ◽  
Cross Sectional ◽  
Concentrated Load ◽  
Wide Range ◽  
Geometrically Exact Beam ◽  
Rod Model ◽  
Post Buckling ◽  
The Cross

In this paper, we investigate the in-plane stability and post-buckling response of deep parabolic arches with high slenderness ratios subjected to a concentrated load on the apex, using the finite element implementation of a geometrically exact rod model and the cylindrical version of the arc-length continuation method enabled with pivot-monitored branch-switching. The rod model used here includes geometrically exact kinematics of the cross-section, exact kinetics, and a linear elastic constitutive law; and advantageously employs quaternion parameters to treat the cross-sectional rotations and to compute the exponential map in the configurational update of rotations. The evolution of the Frenet frame along the centroidal curve is used to determine the initial curvature of the rod. Three sets of boundary conditions, i.e. fixed–fixed (FF), fixed–pinned (FP) and pinned–pinned (PP), are considered, and arches with a wide range of rise-to-span ratios are analyzed for each set. Complete post-buckling response has been derived for all cases. The results reveal that although all the PP arches and all the FF arches (with the exception of FF arches with rise-to-span ratio less than 0.3) considered in this study buckle via bifurcation, the nature of stability of the different solution branches in the post-buckling regime differs from case to case. All FP slender parabolic arches exhibit limit-point buckling, again with several markedly different post-buckling behaviors. Also, some arches in the FF and PP case are shown to exhibit a clear bistable behavior in the post-buckled state.

Vibrations of Tapered Timoshenko Beams in Terms of Static Timoshenko Beam Functions

2000 ◽  
Vol 68 (4) ◽  
pp. 596-602 ◽  
Author(s):  
D. Zhou ◽  
Y. K. Cheung
Keyword(s):  
Timoshenko Beam ◽  
Ritz Method ◽  
Free Vibrations ◽  
Basis Functions ◽  
Timoshenko Beams ◽  
Cross Sectional ◽  
Wide Range ◽  
Convergence Study ◽  
The Cross ◽  
Angle Of Rotation

In this paper, the free vibrations of a wide range of tapered Timoshenko beams are investigated. The cross section of the beam varies continuously and the variation is described by a power function of the coordinate along the neutral axis of the beam. The static Timoshenko beam functions, which are the complete solutions of a tapered Timoshenko beam under a Taylor series of static load, are developed, respectively, as the basis functions of the flexural displacement and the angle of rotation due to bending. The Rayleigh-Ritz method is applied to derive the eigenfrequency equation of the tapered Timoshenko beam. Unlike conventional basis functions which are independent of the cross-sectional variation of the beam, these static Timoshenko beam functions vary in accordance with the cross-sectional variation of the beam so that higher accuracy and more rapid convergence have been obtained. Some numerical results are presented for both truncated and sharp-ended Timoshenko beams. On the basis of convergence study and comparison with available results in the literature it is shown that the first few eigenfrequencies can be given with quite good accuracy by using a small number of terms of the static Timoshenko beam functions. Finally, some valuable results are presented systematically.

scholarly journals Factors that influenced access and utilisation of sexual and reproductive health services among Ugandan youths during the COVID-19 pandemic lockdown: An online cross-sectional survey

2021 ◽  
Author(s):  
Simon Binezero Mambo ◽  
Franck K. Sikakulya ◽  
Robinson Ssebuufu ◽  
Yusuf Mulumba ◽  
Henry Wasswa ◽  
...  
Keyword(s):  
Reproductive Health ◽  
Health Services ◽  
Sexually Transmitted Infections ◽  
Sexual And Reproductive Health ◽  
Limiting Factors ◽  
Reproductive Health Services ◽  
Long Distance ◽  
Cross Sectional ◽  
Sexually Transmitted ◽  
Wide Range

Abstract BackgroundThe COVID-19 pandemic has caused a wide range of disruptions in health care access in many low and middle income countries. The aim of this study was to explore factors that influenced access and utilisation of sexual and reproductive health services among Ugandan youths during the COVID-19 pandemic lockdown. MethodsThis was an online cross-sectional study carried out from April 2020 to May 2020 in Uganda. An online questionnaire was used and participants aged 18years to 30 years were recruited using the snowballing approach. The statistical analysis was done using STATA version 14.2.Results Out of 724 participants, 203 (28%) reported not having information and/or education concerning sexual and reproductive health (SRH). About a quarter of the participants (26.9%, n=195) reported not having access to testing and treatment services of sexually transmitted infections during the lockdown. Lack of transport means was the commonest (68.7%) limiting factor to accessing SRH services during the lockdown followed by the long distance from home to SRH facilities (55.2%), high cost of services (42.2%) and curfew conditions (39.1%). Sexually transmitted infections were the commonest (40.4%) problems related to SRH during the lockdown followed by unwanted pregnancy (32.4%) and sexual abuse (32.4%). Limiting factors were more prevalent among the co-habiting youths [CPR: 1.3 (1.13-1.49) and APR:1.2 (1.06-1.41)] followed by unemployed [CPR: 1.3 (1.09 - 1.53) and APR:1.2 (1 - 1.42)] and non-salaried [APR:1.2 (1- 1.42)] than other participants. The bivariate and multivariate regression analyses indicate that problems were more prevalent among the co-habiting youths [CPR: 2.7 (1.88 - 3.74) and APR: 2.3 (1.6 - 3.29)] followed by the unemployed [CPR: 2 (1.27 - 3.2) and APR: 1.6 (1.03 - 2.64)] than in other categories. ConclusionThe findings of this study show that Ugandan youths had limited access to SRH information and services during the COVID-19 lockdown. Cohabiting and unemployed youths were the most affected by problems related to SRH. Lack of transport means and high cost of services were the major limiting factors to access SRH services among the youths. The findings call for concerted efforts from the Government and other stakeholders to incorporate SRH among the priority services when designing responses to any outbreak crisis.

Microfabrication research at the National Submicron Facility

1983 ◽  
Vol 41 ◽  
pp. 86-89
Author(s):  
E.D. Wolf
Keyword(s):  
Integrated Circuits ◽  
Particle Physics ◽  
High Speed ◽  
New Technology ◽  
High Energy ◽  
High Energy Particle ◽  
New Science ◽  
Wide Range ◽  
Intermediate Domain ◽  
Circuit Function

Most microelectronics devices and circuits operate faster, consume less power, execute more functions and cost less per circuit function when the feature-sizes internal to the devices and circuits are made smaller. This is part of the stimulus for the Very High-Speed Integrated Circuits (VHSIC) program. There is also a need for smaller, more sensitive sensors in a wide range of disciplines that includes electrochemistry, neurophysiology and ultra-high pressure solid state research. There is often fundamental new science (and sometimes new technology) to be revealed (and used) when a basic parameter such as size is extended to new dimensions, as is evident at the two extremes of smallness and largeness, high energy particle physics and cosmology, respectively. However, there is also a very important intermediate domain of size that spans from the diameter of a small cluster of atoms up to near one micrometer which may also have just as profound effects on society as “big” physics.

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