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1.
Since the jets and detonation gaseous products are separated by sharp interfaces,the traditional smoothed particle hydrodynamics (SPH) method is difficult to avoid the computational instability at interfaces.The multi-phase SPH (MSPH) method was applied to improving the stability,which smoothes the particle density and makes pressure continuous at interfaces.Numerical examples of jet forming process were used to test capability of the MSPH method.The results show that the method remains algorithm stability for large density gradient between the jets and gaseous products and has potential application to both the explosion and the jet problems.The effect of initiation ways of the shaped charge was discussed as well. 相似文献
2.
Since the jets and detonation gaseous products are separated by sharp interfaces, the traditional smoothed particle hydrodynamics (SPH) method is difficult to avoid the computational instability at interfaces. The multi-phase SPH (MSPH) method was applied to improving the stabil-ity, which smoothes the particle density and makes pressure continuous at interfaces. Numericalexamples of jet forming process were used to test capability of the MSPH method. The results show that the method remains algorithm stability for large density gradient between the jets and gaseous products and has potential application to both the explosion and the jet problems. The effect of initiation ways of the shaped charge was discussed as well. 相似文献
3.
Rocks are heterogeneous from the point of microstructure which is of significance to their dynamic failure behavior. Both the compressive and tensile strength of rock-like materials is regarded different from the static strength. The present study adopts smoothed particle hydrodynamics (SPH) which is a virtual particle based meshfree method to investigate strain rate effect for heterogeneous brittle materials. The SPH method is capable of simulating rock fracture, free of the mesh constraint of the traditional FEM and FDM models. A pressure dependent J-H constitutive model involving heterogeneity is employed in the numerical modeling. The results show the compressive strength increases with the increase of strain rate as well as the tensile strength, which is important to the engineering design. 相似文献
4.
The water mitigation effect on the propagation of shock wave was investigated numerically. The traditional smoothed particle hydrodynamics (SPH) method was modified based on Riemann solution. The comparison of numerical results with the analytical solution indicated that the modified SPH method has more advantages than the traditional SPH method. Using the modified SPH algorithm, a series of one-dimensional planar wave propagation problems were investigated, focusing on the influence of the air-gap between the high-pressure air and water and the thickness of water. The numerical results showed that water mitigation effect is significant. Up to 60% shock wave pressure reduction could be achieved with the existence of water, and the shape of shock wave was also changed greatly. It is seemly that the small air-gap between the high-pressure air and water has more influence on water mitigation effect. 相似文献
5.
A droplet undergoes spreading,rebounding or splashing when it impacts solid boundary,which is a typical phenomenon of free surface flow that exists widely in modern industry.Smoothed particle hydrodynamics（SPH）method is applied to numerically study the dynamical behaviors of the droplet impacting solid boundary,and both the spreading and rebounding phenomena of the droplet are reproduced in the simulation.The droplet deformation,flow fields and pressure fields inside the droplet at different moments are analyzed.Two important factors,the initial velocity and diameter,are discussed in determining the maximum spreading factor,revealing that the maximum spreading factor increases with the increase of the impact velocity and droplet diameter respectively. 相似文献
6.
Developing a Scale of Attitudes Toward Seeking Psychological Help: Validity and Reliability Analyses
Ayse Sibel Türküm 《International journal for the advancement of counseling》2004,26(3):321-329
The present study was conducted to develop the scale for Attitudes Toward Seeking Psychological Help (ASPH). Four dimensions of ASPH were determined by using factor analysis, which was conducted with 356 participants. The dimensions were named as confidence for getting psychological help; beliefs about the functions of psychological help; endurance against labelling, and self-disclosure. Reliability coefficient was found as satisfactory in the scale (.88) and subscales (.76, .77, .76, and .68). Test-retest reliability was .99. Validity of the scale was examined by using discriminant validity analysis and it was observed as sufficient. The results of the study showed that ASPH has an identifiable factor structure and it is a reliable and valid scale. 相似文献
7.
本文展示球体数目大大增加的堆集物建模,采用数字平滑法对球状堆积物进行模拟研究,研究结果显示出前所未有的大粒子系统模型面貌,由于模型扩大,增加了堆集面上的增平均应力分布的变差,其结果与发表的实验应力分布非常吻合。 相似文献
8.
The selection of bandwidth in kernel equating is important because it has a direct impact on the equated test scores. The aim of this article is to examine the use of double smoothing when selecting bandwidths in kernel equating and to compare double smoothing with the commonly used penalty method. This comparison was made using both an equivalent groups design and a nonequivalent group with anchor test design. The performance of the methods was evaluated through simulation studies using both symmetric and skewed score distributions. In addition, the bandwidth selection methods were applied to real data from a college admissions test. The results show that the traditional penalty method works well although double smoothing is a viable alternative because it performs reasonably well compared to the traditional method. 相似文献
9.
The core of smoothed particle hydrodynamics (SPH) is the nearest neighbor search subroutine. In this paper, a nearest neighbor
search algorithm which is based on multiple background grids and support variable smooth length is introduced. Through tested
on lid driven cavity flow, it is clear that this method can provide high accuracy. Analysis and experiments have been made
on its parallelism, and the results show that this method has better parallelism and with adding processors its accuracy become
higher, thus it achieves that efficiency grows in pace with accuracy. 相似文献
10.
Usama Umer Jaber Abu Qudeiri Mohammad Ashfaq Abdulrahman AL-Ahmari 《浙江大学学报(A卷英文版)》2016,17(11):873-885
Chip morphology predictions in metal cutting have always been challenging because of the complexity of the various multiphysical phenomena that occur across the tool-chip interface. An accurate prediction of chip morphology is a key factor in the assessment of a particular machining operation with regard to both tool performance and workpiece quality. Although finite element (FE) models are being developed over the last two decades, their capabilities in modeling correct material flow around the tool tip with shear localization are very limited. FE models with an arbitrary Lagrangian Eulerian (ALE) approach are able to simulate correct material flow around the tool tip. However, these models are unable to predict any shear localization based on material flow criteria. On the other hand, FE models with a Lagrangian formulation can simulate shear localization in the chip segments; they need to make use of a mesh-based chip separation criterion that significantly affects material flow around the tool tip. In this study a mesh-free method viz. smoothed particles hydrodynamics (SPH) is implemented to simulate shear localization in the chip while machining hardened steel. Unlike other SPH models developed by some researchers, this model is based on a renormalized formulation that can consider frictional stresses along the tool-chip interface giving a realistic chip shape and material flow. SPH models with different cutting parameters are compared with the traditional FE models and it has been found that the SPH models are good for predicting shear localized chips and do not need any geometric or mesh-based chip separation criteria. 相似文献
11.
Gaining a thorough understanding of the theoretical principles of rock breaking with a disc cutter is a critical issue in tunnel boring machine (TBM) technology. To fully consider the complexity and importance of the basic principles of rock breaking during tunnel excavation, in this paper we use a new method, the smooth particle hydrodynamics (SPH), to study the rock-breaking mechanism and verify its accuracy and feasibility. Using the SPH method, we induce the rock fragmentation process with two cutters in synchronous and sequential orders. The results show that when the cutters act on rock sequentially, the second indentation influences the crack evolution of the first indentation. With increased cutter spacing, the second crack gradually becomes independent of the first crack. Under synchronous action of the two cutters, a bursiform nucleus is generated beneath the cutters and the area of the nucleus increases with increased cutter spacing. Whether the cutters act on the rock sequentially or synchronously, we found the optimum cutter spacing of our chosen rock type to be 60 mm. Our analyses results show that the efficiency of sequential rock cutting is superior to synchronous cutting, both with respect to crack evolution and cutter force. 相似文献
12.
Time series prediction has been successfully used in several application areas, such as meteorological forecasting, market
prediction, network traffic forecasting, etc., and a number of techniques have been developed for modeling and predicting
time series. In the traditional exponential smoothing method, a fixed weight is assigned to data history, and the trend changes
of time series are ignored. In this paper, an uncertainty reasoning method, based on cloud model, is employed in time series
prediction, which uses cloud logic controller to adjust the smoothing coefficient of the simple exponential smoothing method
dynamically to fit the current trend of the time series. The validity of this solution was proved by experiments on various
data sets.
Project (No. 2001AA112030) supported by the National Hi-Tech Development Program (863) of China 相似文献
13.
城市地铁变形预测的三次指数平滑法 总被引：2，自引：0，他引：2
详细介绍了指数平滑法及三次指数平滑法的预测过程,应用此方法对实测资料进行了预计和比较.结果表明,其平均相对误差都小于1%.由此可见,该方法对城市地铁变形预测具有一定的应用价值.同时,文中指出了应用指数平滑法的一些优点及应注意的一些问题. 相似文献
14.
得到了计算各向异性非均匀介质电场的有限差分方程,验证了所得差分方程的正确性;得到了各向异性三棱体内外电场与电势的分布,研究了该目标的Rayleigh散射特性;仿真结果表明：外电场极化方向的介电常数明显的影响散射,垂直方向的介电常数影响不大;算法不受目标形状、电磁参数等因素的影响,简单明了,具有良好的通用性。 相似文献
15.
In equating, smoothing techniques are frequently used to diminish sampling error. There are typically two types of smoothing: presmoothing and postsmoothing. For polynomial log-linear presmoothing, an optimum smoothing degree can be determined statistically based on the Akaike information criterion or Chi-square difference criterion. For cubic-spline postsmoothing, visual inspection has been an important tool in choosing such optimum degrees in operational settings. This study introduces a new statistic for assessing the fitness of the cubic-spline postsmoothing method, which accommodates three conditions: (1) one standard error band, (2) deviation from unsmoothed equivalents, and (3) smoothness. A principal advantage of the new statistic proposed in this study is that an optimum degree of smoothing can be selected automatically by giving consistent amount of attention to deviation and smoothness across multiple equatings, whereas visual inspection may not be consistent. 相似文献
16.
Initial fabric anisotropy can greatly affect the shear behavior of particulate materials during shear. The bedding plane effect induced by particle orientation is one of the main fabric anisotropic factors that may affect other factors. It is hard to experimentally examine the effect of bedding direction of particles on the shear behavior of particulate materials, such as sand. A 2D discrete element method (DEM) is employed in this paper to study the influence of different orientations of oval particles on the behavior of dense assemblies under simple shear. As well as the macroscopic shear behavior, the evolution of particle orientation, contact normal, and inter-particle contact forces within the samples with different initial bedding angles during shear have been extensively examined. It was found that the initial bedding direction of the particles has great influence on the non-coaxiality between the directions of principal stress and principal strain increment. The bedding direction also affects the strength and dilatancy responses of DEM samples subjected to simple shear, and the samples with larger bedding angles exhibit higher shear strength and larger volume dilation. A modified stress-force-fabric relationship is proposed to describe the effect of particle bedding direction on the shear strength of samples, and the new equation can better describe the stress-force-fabric relationship of assemblies with initial anisotropic fabrics compared with the existing model. 相似文献
17.
聚能射流形成的数值模拟,涉及到大变形、高应变率以及材料的破坏,传统的拉格朗日或欧拉方法在解决该问题均有很大的局限性,先后发展了网格重分、ALE、SPH等方法,以及界面处理技术,各有所长,但尚未完全解决,而在实际工作中,切合实际的药型罩介质本构关系则是聚能射流数值模拟的关键,高效并行计算与可视化则是聚能射流数值模拟的必由之路,并阐述了聚能射流数值模拟的发展趋势． 相似文献
18.
INTRODUCTIONTimeseriespredictionhasbeensuccessfullyusedinseveralapplicationareas,suchasmeteo rologicalforecasting (Andrei,1972 ) ,loadpre dictioninpowersystem (OuandLi,1999) ,marketprediction (Gilesetal.,1997) ,net worktrafficprediction (Edwardsetal.,1997… 相似文献
19.
MAO Zhi-hong MA Li-zhuang ZHAO Ming-xi LI Zhong 《浙江大学学报(A卷英文版)》2006,7(9):1603-1608
INTRODUCTION With the proliferation of 3D scanning tools, in- terest in removing noise from meshes has increased. An important problem is how to suppress noise while preserving desirable geometric features of the model. In general, smoothing algorithms are roughly classi- fied into two categories: linear and nonlinear smoothing (Gonzalez and Woods, 2002). For linear smoothing, each mesh point is moved to the bary- center of its neighbors. Linear smoothing treats fea- ture (large variatio… 相似文献
20.
Gautam Puhan 《Journal of Educational Measurement》2011,48(3):274-292
The impact of log‐linear presmoothing on the accuracy of small sample chained equipercentile equating was evaluated under two conditions . In the first condition the small samples differed randomly in ability from the target population. In the second condition the small samples were systematically different from the target population. Results showed that equating with small samples (e.g., N < 25 or 50) using either raw or smoothed score distributions led to considerable large random equating error (although smoothing reduced random equating error). Moreover, when the small samples were not representative of the target population, the amount of equating bias also was quite large. It is concluded that although presmoothing can reduce random equating error, it is not likely to reduce equating bias caused by using an unrepresentative sample. Other alternatives to the small sample equating problem (e.g., the SiGNET design) which focus more on improving data collection are discussed. 相似文献