Vertical ice forces on long straight walls

Uplifting ice forces in frozen-in vertical walls can result from a water level rise. The governing differential equation and its solutions have been presented by Löfquist, who considered both the case of an elastic ice sheet as well as the case of a plastic ice sheet. The ultimate force has since then been calculated as the force immediately prior to formation of a crack close to the wall and parallel to it. If the ice sheet stays interlocked at this crack an even larger ultimate force may be induced. This larger ultimate force is evaluated on basis of the theory of elasticity.The situation in question has only been sparsely considered in the literature. Consequently, it was found worthwhile to include all the associated formulae, i.e. also some of the already well-known ones.     

Laminated anisotropic gently sloping shells and plates subjected to nonsteady forces and various temperature effects

We constructed a new and more accurate model of the state of stress and strain of laminated anisotropic shells and plates that takes into account the influence of dynamic factors on transverse shear strains, thermal strains in the transverse direction, and the non-steady nature of the deformation process. By the variational approach we obtained a system of equations of force-induced motion and the boundary conditions. After representation in the form of the slope deflection method the total order of the system is equal to 20 and does not depend on the number of layers. For rectangular laminated orthotropic pin-supported shells on analytical solution of the nonsteady-state problem of dynamics was obtained by expansion in modes. The results are compared with known three-dimensional solutions, and also with solutions based on other applied theories. The article shows that the introduction of additional desired functions of shear yields a more accurate state of stress and strain of a double-layered plate than the known models.Translated from Problemy Prochnosti, No. 1, pp. 91–101, January, 1996.     

海底倾斜度对声传播的影响

1引言南海海底环境复杂,存在着许多海深及底质水平变化的区域。由于海底变化对水声物理规律有着非常大的影响[1],因此,在此类海域进行声传播预报和海底反演时的参数选取和模型构建时必须给予足够的重视。国际上关于海底大起伏的实验和理论研     

Model tests of ice forces on fixed and oscillating cones

A series of model tests has been carried out on downward breaking conical structures using low salinity model ice. Comparison with information in the literature showed that a downward breaking cone experiences lower ice forces than an upward breaking cone. Fixed cones of angles of 15, 30, 45 and 60 deg were tested in 50-mm-thick ice of 60 kPa flexural strength at velocities ranging from 0.01 to 0.5 m/s. The effects of thickness and flexural strength variations were also investigated. Horizontal forces were observed to increase with increasing velocity. Ice thickness variation was observed to have a stronger influence on the vertical forces than on the horizontal forces. Vertical and horizontal forces showed a decrease with decreasing flexural strength.Two test series were run with the 45 deg conical structure arranged so that it oscillated. Horizontal force reductions of up to two thirds were observed.     

Textile protection of snow and ice: Measured and simulated effects on the energy and mass balance

Measurements and simulations of the energy fluxes and mass changes of an artificially covered snow and ice surface (geotextile material) and an unaltered control plot in an Austrian glacier ski resort are presented and compared. A modified version of the snow cover model SNOWPACK is used to successfully reproduce the artificially compacted and the additionally covered snow cover in a physically based way. Supplementary measurements of crucial material properties of the 4.5 mm thin geotextile serve as model input as well. Results indicate that the shortwave reflectivity of the covers is responsible for 46% of the performance. Thermal insulation of the material (14%) and a negative latent heat flux due to evaporation of precipitation from the cover surface (10%) have almost the same contribution. A layer of air between the cover and the snow and ice surface (thickness 7.5 cm to 12 cm) adds the rest, which is at the upper limit of observations and may therefore also compensate for model errors. This generally explains the high performance of the method in glacier ski resorts and, most importantly, an altitude dependent application limit of the method: the method becomes less effective at lower altitudes, where sensible heat fluxes become more important compared to shortwave radiation.     

斜坡海底对声场水平纵向相关性的影响

利用数值仿真分析和总结了不同斜坡海底条件下声场水平相关性随水平间隔和传播距离的变化规律,并利用楔形简正波理论对海底倾斜引起的声场水平纵向相关变化机理进行了解释.研究结果表明,上坡和下坡地形的声场水平纵向相关性具有很大的差别.与水平海底相比,下坡海底会增加声场水平纵向相关性,上坡海底会减小声场水平纵向相关性.有效简正波之...     

基于遗传模拟退火算法的空袭兵力分配及优化

对遗传模拟退火算法中的交叉、变异操作进行了改进，并实施了最优保留策略，形成了改进遗传模拟退火算法．以突击效果最大化和兵力损失最小化为目标函数，以空袭兵力总量的限制、空袭兵器挂载类型的限制等为约束条件，建立了空袭兵力分配及优化模型．在考虑兵力分配模型特点的基础上，利用改进遗传模拟退火算法求解．通过与多目标数学规划和标准遗传算法优化进行的比较表明，该方法能够有效地解决带约束的多目标优化问题．     

The critical velocities of a load moving on a floating ice plate that is subjected to in-plane forces

The critical velocities of moving loads over floating ice plates were determined by several authors. In all of these analyses it was assumed that the in-plane force field in the ice cover is zero. However, due to constrained thermal strains, in-plane forces do occur in the field. The purpose of the present paper is to determine its effect upon the critical velocities of the moving loads. It is shown that a uniform compression force field reduces the critical velocity whereas a tension force field has the opposite effect. Graphs are presented to show these findings.     

Partial structure factors of a simulated polymer melt

Fully atomistic molecular dynamic simulations were carried out by using the Insight (Insight II 4.0.0 P version) and the Discover-3 programs from MSI with the polymer consortium force field. The model system used in these simulations was built using the Amorphous Cell module. The polymer system simulated was glassy polyisoprene (PI) as used in previous neutron scattering (NS) measurements. A first molecular dynamics at 363 K was run for 1 ns using the Discover-3 program collecting data every 0.01 ps and a subsequent one (taking the previous output sample as an input for the following dynamics) was run for 2 ns collecting data every 0.5 ps. The results of the second run agreed to those of the first run, indicating that the sample was well equilibrated at this high temperature. Starting from the obtained atomic trajectories we have calculated the partial static structure factors for NS corresponding to different PI samples with different levels of deuteration (PId3, i.e., methyl group deuterated and main chain protonated; PId5, i.e., methyl group protonated and main chain deuterated; PId8, i.e., fully deuterated and PIh8, i.e., fully protonated). The results obtained are compared to the coherent NS cross-sections measured on real samples by means of D7 spectrometer with polarization analysis (ILL, Grenoble). A good agreement is obtained between experimental and simulated data validating the simulated sample. Moreover, the dynamic evolution of these correlations has also been calculated from the simulations. With these time dependent functions, the magnitude measured in a neutron spin echo (NSE) experiment can be constructed. Here we present two examples dealing with the fully deuterated sample PId8 and a partially deuterated sample, PId5, that show how computer simulation constitutes an invaluable tool for interpreting NSE results.     

Quantum effects on phase transitions in high-pressure ice

The H₂O ice phases VIII, VII, and X as well as their phase transformations are studied theoretically at 100 K as a function of pressure up to about 100 GPa. A combination of ab initio electronic structure calculations within the framework of density functional theory and the path integral representation of the nuclei is used. This allows the effects of thermal and quantum mechanical fluctuations on the properties of ice at high compression to be assessed separately and also in conjunction. Pronounced quantum effects are uncovered and different mechanisms are found to be at work at the antiferroelectric to paraelectric transition and the symmetrization transition.     

Effect of a water film on the structure of ice growing beneath it

It is demonstrated that ice growing beneath a water film may take on either a transparent or an opaque form, depending on the thickness of the water film.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 2, pp. 323–328, August, 1977.     

Parameter uncertainty effects on variance-based sensitivity analysis

In the past several years there has been considerable commercial and academic interest in methods for variance-based sensitivity analysis. The industrial focus is motivated by the importance of attributing variance contributions to input factors. A more complete understanding of these relationships enables companies to achieve goals related to quality, safety and asset utilization. In a number of applications, it is possible to distinguish between two types of input variables—regressive variables and model parameters. Regressive variables are those that can be influenced by process design or by a control strategy. With model parameters, there are typically no opportunities to directly influence their variability. In this paper, we propose a new method to perform sensitivity analysis through a partitioning of the input variables into these two groupings: regressive variables and model parameters. A sequential analysis is proposed, where first an sensitivity analysis is performed with respect to the regressive variables. In the second step, the uncertainty effects arising from the model parameters are included. This strategy can be quite useful in understanding process variability and in developing strategies to reduce overall variability. When this method is used for nonlinear models which are linear in the parameters, analytical solutions can be utilized. In the more general case of models that are nonlinear in both the regressive variables and the parameters, either first order approximations can be used, or numerically intensive methods must be used.     

Experimental hypervelocity impact effects on simulated planetesimal materials

Experimental results are presented from a series of hypervelocity impact tests on simulated comet and asteroid materials for the purpose of characterizing their response to hypervelocity kinetic energy impacts. Nine tests were conducted at the Air Force Arnold Engineering Development Center (AEDC) S1 Range Facility on ice, rock, and iron target samples using a spherical 2.39 mm diameter aluminum impactor at impact velocities of from 7.6 to 8.4 km/sec. The test objectives were to collect target response phenomenology data on cratering, momentum deposition and enhancement, target fragmentation, and material response under hypervelocity impact loading conditions. A carefully designed ballistic pendulum was used to measure momentum deposition into the targets. Observations and measurements of the impacted samples provide important insights into the response of these materials to kinetic energy impacts, especially in regards to unexpectedly large measured values of momentum enhancement to some of the targets. Such information is required to allow us to successfully deflect or fragment comets or asteroids which might someday be detected on collision trajectories with Earth.     

Comparing headphone and speaker effects on simulated driving

Twelve persons drove for three hours in an automobile simulator while listening to music at sound level 63dB over stereo headphones during one session and from a dashboard speaker during another session. They were required to steer a mountain highway, maintain a certain indicated speed, shift gears, and respond to occasional hazards. Steering and speed control were dependent on visual cues. The need to shift and the hazards were indicated by sound and vibration effects. With the headphones, the driver's average reaction time for the most complex task presented—shifting gears—was about one-third second longer than with the speaker. The use of headphones did not delay the development of subjective fatigue.     

模糊聚类算法稳定图应用于桥梁结构参数识别

将模糊聚类算法应用于稳定图理论,并将该稳定图与协方差驱动的随机子空间法相结合,进行桥梁结构模态参数识别&;#61472;。提出不考虑阻尼的影响,以频率为横坐标,以模态保证准则MAC中任一列数据为纵坐标的模糊聚类算法稳定图。通过比较稳定图中各聚类圆大小的方法进行稳定图真假模态的判别,从而使模态判别不再需要人的主观参与而变得更加智能和准确。通过简支梁和连续梁仿真分析验证了模糊聚类算法稳定图用于桥梁结构参数识别的准确性和较强的抗干扰性。     

Balanced gait generations of a two-legged robot on sloping surface

In this paper, dynamically balanced gait generation problem of a 7-DOF two-legged robot moving up and down through the sloping surface is presented. The gait of the lower links during locomotion is obtained after assuming suitable trajectories for the swing leg and hip joint. The trunk motion is initially generated based on the concept of static balance, which is different from the well-known semi-inverse method and then checked for its dynamic balance calculated using the concept of Zero-Moment Point (ZMP). Lagrange–Euler formulation is attempted for the determination of joint torques. Average power consumption at each joint is then determined based on the computed torques. Moreover, the variations of dynamic balance margin and average power consumption are studied for both ascending and descending through the sloping surface. Both of them are found to be more for the ascending gait generation compared to those for the descending case. The effects of variations of the slope have also been studied on the average dynamic balance margin and power consumption for both the cases.     

The effects of driver training on simulated driving performance

Given that the beneficial effects of driver training on accident risk may not be an appropriate criterion measure, this study investigates whether professionally trained and experienced drivers exhibit safer driving behaviour in a simulated driving task compared with drivers without professional driver training. A sample of 54 police trained drivers and a sample of 56 non-police trained drivers were required to complete two tasks. Firstly to overtake a slow-moving bus on a hazardous stretch of single-lane road with bends and hills and secondly to follow a lead vehicle travelling at 55mph in a built-up section with a speed limit of 30mph. Results showed that in comparison with non-police trained drivers, police drivers were significantly less likely to cross the central division of the road at unsafe locations during the overtaking task and reduced their speed on approach to pedestrians at the roadside in the following task to a greater extent. Police drivers also adopted a more central lane position compared with non-police trained drivers on urban roads and at traffic lights during the following task. Driver group differences in simulated driving performance are discussed with reference to the implications for driver training assessment and skill development.     

Modeling the dynamic effects of ice shedding on spacer dampers

Effects of ice-shedding-induced cable vibration on spacer dampers are studied by applying a dynamic model. The model is based on the authors' recent development, which is improved here by applying spacer properties obtained experimentally. The model simulates cable vibration and bundle rotation at mid-span, where the spacer is attached to the cables, as well as the spacer deformation and forces acting on the spacer during the vibration of twin, triple and quad conductor bundles. Ice accumulation on a spacer may change the latter's elastic and damping properties, whose influence on the vibration is considered in the model together with the effect of varying cable properties. Simulation results show how the risk of bundle collapse and the load on the spacer is reduced when the number of subconductors in the bundle is increased. The model also predicts that the most important property which can reduce forces acting on the spacer during vibration is spacer damping, whereas the bundle rotation is affected to the greatest extent by cable damping.     

The influence of disturbing effects on the performance of a wide field coded mask X-ray camera

The coded aperture telescope, or Dicke camera, is seen as an instrument suitable for many applications in X-ray and gamma ray imaging. In this paper the effects of a partially obscuring window mask support or collimator, a detector with limited spatial resolution, and motion of the camera during image integration are considered using a computer simulation of the performance of such a camera. Cross correlation and the Wiener filter are used to deconvolve the data. It is shown that while these effects cause a degradation in performance this is in no case catastrophic. Deterioration of the image is shown to be greatest where strong sources are present in the field of view and is quite small ( 10%) when diffuse background is the major element. A comparison between the cyclic mask camera and the single mask camera is made under various conditions and it is shown the single mask camera has a moderate advantage particularly when imaging a wide field of view.     

Calculation of the forces acting upon a rigid structure from an aircraft impact

A numerical method is presented which permits the calculation of the loads produced by an aircraft impacting upon a rigid structure at an arbitrary angle to the surface normal. This method is utilized to compute the variation of the horizontal and vertical components of the corresponding reaction with aircraft impact angle for a Boeing 707-320 Airliner and Phantom F4 Military Jet. Furthermore, three flight trajectory distributions have been studied which are relevant to the aircrash problem. Firstly, an idealised rectangular distribution; secondly, a sin 2 distribution corresponding to a undirectional horizontal beam onto a hemispherical dome or an isotropic trajectory distribution onto an upright rectangular (or cylindrical) structure. Finally, a ‘well’ distribution is considered which approximates to the trajectory distribution observed from aircrash data. For each angular distribution, the vertical and horizontal reaction histories have been calculated to 50 and 90% confidence levels for both types of aircraft. Finally, it is concluded that the application of the normal load case in a design code is conservative in nature, corresponding to a 90% confidence level for the flight trajectory distributions likely to occur.