节理岩质边坡破坏过程的PFC2D数值模拟分析

边坡破坏后的运动过程及运动距离预测可以为灾害危险性区划、风险评估等提供定量分析依据,可以为灾后重建规划以及地震区工程建设提供指导.节理岩质边坡的破坏和其后的运动过程非常复杂,没有理论方法可以对这一过程进行合理的描述,而数值模拟方法是研究这一问题的有效途径.采用颗粒流程序PFC2D对节理岩质边坡的破坏和运动过程进行了研究,分析了关键参数对结果的影响,得出了破坏后的堆积形状和最终的运动距离.研究结果表明,颗粒流程序不但可以描述岩石等连续介质,而且可以描述节理岩体以及碎屑等不连续介质,是研究岩质边坡破坏运动的有效方法.     

Sculpture surface machining: a generalized model of ball-end milling force system

A new mechanistic model is presented for the prediction of a cutting force system in ball-end milling of sculpture surfaces. The model has the ability to calculate the workpiece/cutter intersection domain automatically for a given cutter location (CL) file, cutter and workpiece geometries. Furthermore, an analytical approach is used to determine the instantaneous chip load (with and without runout) and cutting forces. In addition to predicting the cutting forces, the model also employs a Boolean approach for a given cutter, workpiece geometries, and CL file to determine the surface topography and scallop height variations along the workpiece surface which can be visualized in 3-D. The results of model validation experiments on machining Ti-6A1-4V are also reported. Comparisons of the predicted and measured forces as well as surface topography show good agreement.     

Can we learn more from the data underlying the statistical α-β model with respect to the dynamical behavior of avalanches?

Hazard and risk assessment in avalanche-prone areas involves estimation of runout distances of potential avalanches. Methods for determination of the runout may be divided into two categories: 1) methods based on statistical approaches such as the well known α-β model or 2) methods based on numerical avalanche models such as the PCM-model or VS-type models (just to name the more traditional ones). Methods in the second group have the advantage that besides the runout distance, velocity and impact pressure distributions along the avalanche track can also be obtained, this being a requisite for meaningful risk assessments. However, the predictive power of dynamical models depends on the use of appropriate rheological models and their parameters.In the statistical α-β model, the maximum runout distance is solely a function of topography. The runout distance equations were found by regression analysis, correlating the longest registered runout distance of several hundred avalanche paths with a selection of topographic parameters.In this paper, we re-evaluate Norwegian and Austrian avalanche data, which served as basis for the α-β model in the respective countries, and additional avalanche data with respect to dynamical measures. As most of those avalanche data originate more or less from extreme events (i.e. avalanches with return periods of the order of 100 years), the dynamical measures may give hints about an appropriate rheology for dynamical models suitable for extreme avalanche events.The analysis raises reasonable doubt whether the classical ansatz for the retarding acceleration of snow avalanches with additive terms involving Coulomb-friction and a velocity-squared dependency, which is used in many avalanche models, is adequate for a physically-based model. Back-calculations of runout distances using a simple block model show a discrepancy between commonly proposed parameter values (and of the underlying rheological models) and the observations.     

An Improved Method for the Determination of 3D Cutting Force Coefficients and Runout Parameters in End Milling

A simple improved method is suggested for determining constant cutting force coefficients, irrespective of the cutting condition and cutter rotation angle. This can be achieved through the combination of experimentally deternimed cutting forces with those from simulation, performed by a mechanistic cutting force model and a geometric uncut chip thickness model. Additionally, this study presents an approach that estimates runout-related parameters, and the runout offset and its location angle, using only one measurement of cutting force. This method of estimating 3D end milling force coefficients was experimentally verified for a wide range of cutting conditions, and gave significantly better predictions of cutting forces than any other methods. The estimated value of the runout offset also agreed well with the measured value.     

Influence of manufacturing errors on the dynamic characteristics of planetary gear systems

A dynamic analysis using a hybrid finite element method was performed to characterize the effects of a number of manufacturing errors on bearing forces and critical tooth stress in the elements of a planetary gear system. Some tolerance control guidelines for managing bearing forces and critical stress are deduced from the results. The carrier indexing error for the planet assembly and planet runout error are the most critical factors in reducing the planet bearing force and maximizing load sharing, as well as in reducing the critical stress.     

Heat Transfer during Multiple Jet Impingement on the Top Surface of Hot Rolled Steel Strip

Using a unique pilot facility a series of tests were conducted using three top jets to simulate the heat transfer that occurs during run‐out table (ROT) cooling. Steel samples instrumented with internal thermocouples were tested on this facility and the effect of top jet configuration (nozzle spacing of 40 to 115mm), and water flow rate (15 and 30 1/min) were quantified using moving plate samples. The multiple top jet work indicated that heat transfer across the plate width varies significantly and is high directly under the nozzle but decreases rapidly away from the nozzle in the interaction region. As cooling progresses a much larger wetted region occurs and more uniform cooling is experienced across the plate. Multiple jet cooling experiments have also confirmed that nozzle spacing does have an effect on heat transfer. This effect is predominate in the interaction region where closer nozzle spacing leads to enhanced and more uniform heat transfer in the lateral direction across the plate width away from the nozzle. As expected higher water flow rates led to higher heat transfer both under the nozzle and in the interaction region.     

加工中心缸盖阀座导管的加工技术分析

结合本公司生产的发动机缸盖所用刀具,介绍了目前缸盖阀座导管孔系的加工技术,分析了刀具的结构及设计风险,并通过大量工艺试验及批量生产进行了验证。     

Landslide disasters in Ehime Prefecture resulting from the July 2018 heavy rain event in Japan

In early July 2018, record heavy rainfalls caused enormous damage from western Japan to the Tokai region. In particular, Hiroshima, Okayama, and Ehime Prefectures suffered extensive human casualties and tremendous damage to housing units and the infrastructure due to landslides and river flooding. The authors conducted a series of reconnaissance operations and analyzed various kinds of data, including rainfall records, aerial photographs, official statistics of the disasters, and topographical and geological maps of Ehime Prefecture. In this report, the authors focus on the rainfall characteristics, geological background, and landslide statistics and distributions associated with the July 2018 events, and present examples of typical damage by geological belt. Based on this, they discuss several characteristics of the landslides, including the rainfall thresholds by geological belt, the characteristics of the runout distance of the debris flows, and the rainfall thresholds for landslide initiation in terms of the Soil Water Index (SWI). Based on an official database of a total of 413 landslides occurring in Ehime Prefecture and the authors’ newly developed database of 883 landslides in the southern part of the prefecture, several findings were obtained, for example, that slopes in the Shimanto Belt had a lower rainfall threshold for landslide initiation than slopes in the other two geological belts, namely, Sambagawa and Chichibu Belts.     

磁悬浮刚性转子系统振动机理分析与动力学建模

磁悬浮惯性执行机构采用磁轴承支承,可通过主动控制实现极微振动,但磁悬浮惯性执行机构仍存在频谱分量丰富的振动.首先在转子动静不平衡和Sensor Runout振动机理分析的基础上,重点分析了Magnet Runout产生振动机理;然后,建立包含多振动源的系统动力学建模,并将整个动力学模型分解为平动和转动子系统,分析表明转子动静不平衡、Sensor Runout和Magnet Runout是通过不同的途径产生振动,不仅产生同频振动还包含倍频振动;最后,提出磁悬浮刚性转子系统主动振动控制的要求,为以后的主动振动控制研究奠定基础.     

Real time monitoring and diagnosis system development in turning through measuring a roundness error based on three-point method

A real time monitoring and diagnosis system to measure spindle center displacement (roundness error) during turning operation is introduced in this paper. The system was developed based on the three-point method. The error generated during cutting process was monitored and diagnosed by using a system equipped with a designed DSP (Digital Signal Processor) board and FFT (Fast Fourier Transform) algorithm. The system could estimate cutting force and predict other cutting characteristics such as chattering and tool wear. Using the spindle center fluctuation, i.e. a roundness error movement from the center, the relationship between the cutting force and the roundness error could also be investigated. The roundness error that eliminated geometric shape error and eccentric error from the measured signals in the frequency domain proved to be a dominating factor in determining cutting characteristics.