基于动态特性补偿的冲击波测试数据处理方法

利用激波管对传感器进行动态标定,采用特殊白化滤波器广义最小二乘迭代法建立冲击波测试传感器的数学模型并对其动态特性进行分析,提出采用基于零极点相消原理补偿法来对传感器动态特性进行补偿。实际试验的测试数据处理应用表明,基于动态特性补偿的数据处理方法能够提高传感器动态特性和冲击波测试数据的准确度。

     

非线性弹性介质中冲击波斜反射的研究

本文讨论了各向同性非线性超弹性介质在平面小应变下的冲击波斜反射问题。给出了本构关系、简单波解和冲击波解,并作为例子求解了入射冲击波在自由面的斜反射问题。     

水下爆炸冲击波壁压理论及数值计算方法改进研究

水下爆炸冲击波是舰船抗冲击评估中重要的载荷成分,也是水中结构物毁伤程度快速预报的关键和依据。通过小当量实验发现,由于传统 Taylor 平板理论公式忽略了冲击波波速的非线性变化 ,导致其在预报近距离水下爆炸冲击波壁压脉宽时出现偏差。为此,给出了比例爆距R/W1/3为0.11～5.30 m/kg1/3 (R为爆距,W为炸药质量)下的冲击波速度拟合公式,对传统Taylor理论公式进行修正。修正后,在R/W1/3=0.11 m/kg1/3下,壁压脉宽及冲量偏差大幅减小;在R/W1/3≥0.21 m/kg1/3下,两者偏差均小于12%。此外,在处理水下近场和中远场爆炸问题时,发现数值耗散会导致壁压峰值被明显削弱,于是提出了一种可行的数值策略消除计算中数值耗散导致的削弱效应,结果与修正的Taylor平板理论公式吻合良好,峰值偏差均小于9%。改进后的冲击波壁压理论公式及数值计算方法可为舰船抗爆抗冲击领域提供理论和技术支撑。     

爆炸冲击波反射流场的理论计算方法

爆炸冲击波遇到固壁,依次发生正规和非正规反射。本文中基于镜像方法,将爆炸冲击波在固壁反射等效为真实和虚拟爆炸流场的相互作用,建立了波后流场的理论计算方法。首先,假定反射波是以虚拟爆源为中心的圆弧,马赫杆是以爆心在固壁投影点为中心的圆弧。然后,根据爆炸自由场传播规律,利用基于几何近似的方法,建立流场中冲击波结构随时间演化的计算方法,确定任意时刻波后流场区域。最后,利用新发展的叠加模型LAMBR (LAMB revisied),将真实和虚拟爆炸流场进行叠加,给出波后流场中的压力、密度和速度等物理量。通过与数值模拟结果和已有数据进行对比,发现该方法得到的流场物理量分布、峰值等能够反映流场发展的主要规律,从而验证了该理论方法的合理性。而且,该理论方法所需的时间相较于数值模拟大大缩短。     

基于动态校准数据的压杆测试系统动态特性校正技术

针对应变式压杆测试系统在冲击波的超压测量中存在动态响应不足的问题,建立了激波管校准平台.采用系统辨识建模和动态补偿的方法,将时域分析和频域估计相结合,设计了一种动态补偿滤波器,改善了压杆测试系统的动态特性,使频带展宽,响应时间减少.     

冲击波测试系统低频特性与补偿方法研究

为提高冲击波超压峰值的测量精度,多数学者把重点集中在系统高频特性研究上,以拓宽带宽的方式提高峰值测试的准确性。冲击波另外两个主要参数正压作用时间、比冲量却和测试系统的低频特性息息相关。针对实爆中出现的不同传感器正压作用时间差异较大的问题,对冲击波信号进行了边际谱分析,获得了信号的低频特性。建立了一阶参数模型来表征低频特性,通过激波管试验数据获取了7种系统的低频模型参数。采用零极点配置法设计了低频补偿模型。结果表明:冲击波测试系统低频特性严重影响冲击波信号正压作用时间测试准确性,基于低频特性补偿的数据处理方法可以有效的提高冲击波信号正压作用时间、比冲量地测试精度。     

水下爆破冲击波作用下典型鱼类临界安全波压模型研究

为了探究水下爆破冲击波对鱼类损伤的影响,首先通过理论分析探讨了水下冲击波在鱼体的传播过程和对鱼鳔的损伤机理,构建了典型有鳔鱼类临界安全波压模型,并结合实测数据、参考相关文献,确定了模型参数。结果表明,典型有鳔鱼类临界安全波压与鱼体长呈线性关系。其中,水介质和鱼鳔壁介质的波阻抗比、鱼鳔宽度因数、鱼鳔壁厚因数、鱼鳔径向临界拉应力因数和鱼鳔形状因数分别为0.3～2.0、0.04～0.09、0.002、60和0.6～1.1。然后,根据典型有鳔鱼类临界安全波压模型参数,得到最大和最小鱼类临界安全波压模型分别为p_ic,max=30L和p_ic,min=3L(p_ic,max的单位为kPa,L的单位为cm)。最后,通过鱼类损伤情况的实测数据和文献数据,验证了鱼类临界安全波压模型。结果表明,不同体长的鱼类在不同冲击波压力时的受损状况分布,基本与鱼类所能承受的最大和最小的临界安全波压范围符合。并根据鱼类临界安全波压与体长的关系,划分了死亡区、存活有影响区和存活无影响区。     

孔压静力触探(CPTU)测试成果影响因素及原始数据修正方法探讨

孔压静力触探(CPTU)是20世纪80年代在国际上兴起的新型原位测试技术,因其诸多优点,目前在欧美诸国已得到广泛应用。由于探头规格、技术标准和操作程序的差异,影响CPTU测试成果的因素很多,而且其影响程度也各不相同。根据前人的研究成果,对CPTU测试成果的影响因素进行了分析总结,以期在CPTU资料整理和应用中引起重视。最后,简要论述了考虑诸多影响因素的原始数据修正方法。     

冲击波作用下乳化炸药压力减敏的表征方法

引入一个新的物理量压力减敏程度,来更合理地表征乳化炸药发生压力减敏的难易程度,为研究其作用机理提供量化的分析工具。分别利用乳化炸药发生压力减敏前后的爆炸冲击波峰压及其对数、冲击波能量和总能量计算压力减敏程度,比较并分析计算结果的优劣。结果表明,几个参数计算的结果都能达到相近的效果,用冲击波峰压计算起来简单方便,冲击波能量计算效果较好。用冲击波参数计算的压力减敏程度能够反映乳化炸药压力减敏的本质,建议采用冲击波峰压计算压力减敏程度,在数值差别不明显时采用冲击波能量来计算。     

有限元模型阻尼特性的复参数修正方法研究

阻尼对于结构动力学响应具有重要的影响,但有限元模型一般很难对阻尼特性进行精确建模.基于实测频响函数,研究了一种有限元模型阻尼特性的复参数修正方法.以待修正区域各单元质量、刚度矩阵的比例修正系数为复修正参数,建立了单元矩阵比例修正的灵敏度方程直接算法,并对比分析了复修正参数与不同阻尼特性之间的数学关系.以六自由度集中参数模型和25杆平面桁架模型为例,验证了复参数修正方法在阻尼特性修正中的有效性.     

Acceleration of the pressure correction method for a rotating Navier-Stokes problem

The behaviour of the pressure correction method is studied for the solution of the incompressible steady-state Navier-Stokes and continuity equations in a rotating cylindrical-polar co-ordinate system, the specific problem being that of laminar source-sink flow between two corotating discs. Modifications to improve the linearization and the handling of the rotation terms are introduced, and we compare three extended pressure correction schemes and also the use of a multigrid algorithm in part of the calculation procedure as a linear solver.     

气体泄爆压力分步计算模型及其湍流修正

通过将密闭空间内爆燃泄放过程进行微分,假设各微分时段内爆燃泄放过程均按照先燃烧、再泄放、最后压力平衡的过程独立分步进行,最终得到泄爆压力分步计算模型。同时,在尺寸为2 m×1.2 m×0.6 m的爆炸腔体一端安装击穿压力相同、泄放面积不同的泄爆构件进行泄爆实验,对分步压力计算模型进行验证。对比发现:大面积泄放条件下,2个传感器测得的压力曲线基本重合,均为单峰值曲线,此时模型计算值与实验结果吻合较好;小面积泄放条件下,腔体内压力曲线均为双峰值曲线,由于泄放截面改变加剧口部湍流扰动,使得腔体内部产生压力梯度,近泄爆口处传感器测得的第2个压力峰值要大于腔体内部传感器相应的测量值,经湍流速度修正后的压力计算模型可以较好地描述近泄爆口处的压力变化情况。     

A comparative study of pressure correction and block-implicit finite volume algorithms on parallel computers

A comparison of a new parallel block-implicit method and the parallel pressure correction procedure for the solution of the incompressible Navier–Stokes equations is presented. The block-implicit algorithm is based on a pressure equation. The system of non-linear equation s is solved by Newton's method. For the solution of the linear algebraic systems the Bi-CGSTAB algorithm with incomplete lower–upper (ILU) decomposition of the matrix is applied. Domain decomposition serves as a strategy for the parallelization of the algorithms. Different algorithms for the parallel solution of the linear system of algebraic equations in conjunction with the pressure correction procedure are proposed. Three different flows are predicted with the parallel algorithms. Results and efficiency data of the block-implicit method are compared with the parallel version of the pressure correction algorithm. The block-implicit method is characterized by stable convergence behaviour, high numerical efficiency, insensitivity to relaxation parameters and high spatial accuracy. © 1997 John Wiley & Sons, Ltd.     

A pressure correction method for fluid–particle interaction flow: Direct‐forcing method and sedimentation flow

A direct‐forcing pressure correction method is developed to simulate fluid–particle interaction problems. In this paper, the sedimentation flow is investigated. This method uses a pressure correction method to solve incompressible flow fields. A direct‐forcing method is introduced to capture the particle motions. It is found that the direct‐forcing method can also be served as a wall‐boundary condition. By applying Gauss's divergence theorem, the formulas for computing the hydrodynamic force and torque acting on the particle from flows are derived from the volume integral of the particle instead of the particle surface. The order of accuracy of the present method is demonstrated by the errors of velocity, pressure, and wall stress. To demonstrate the efficiency and capability of the present method, sedimentations of many spherical particles in an enclosure are simulated. Copyright © 2010 John Wiley & Sons, Ltd.     

Validation of the GeoWATCH soil moisture model and proposed bias correction method

The US Army is required to be a good steward of the land per US Army regulation AR 200-1. Based on this regulation, Army installations need to manage lands, to reduce potential damage and impacts to water quality and habitat that may occur from training. Maneuver training does impact the vegetation and soil and this damage is directly related to soil moisture. Soil moisture is an important factor for understanding the potential for soil surface disturbance due to vehicle impacts and predicting soil resilience to vehicle traffic, however, producing accurate estimates of the spatial and temporal variation of soil moisture has historically been elusive. GeoWATCH, which stands for Geospatial Weather-Affected Terrain Conditions and Hazards (formerly DASSP), simulates soil moisture world-wide, at relatively small spatial and temporal scales. GeoWATCH uses a physics-based downscaling approach that uses weather-scale land surface model estimates of soil moisture and land surface water and energy fluxes, with high resolution geospatial data. GeoWATCH soil moisture outputs coupled with vehicle impact models, are anticipated to be useful for near-real-time estimation of ground disturbance, but will require ground validation. To validate GeoWATCH soil moisture estimates, we utilized Soil Climate Analysis Network (SCAN) gauge network soil moisture data from 127 sites across 34 states. Statistical analysis of the raw GeoWATCH output indicated the model performs statistically better in certain soil textures. Model bias is largest for sandy soils, whereas clayey soils were least biased. As a result, bias correction models were applied to the raw GeoWATCH simulated values using linear regression to predict correction factor (CF) values based on physical site characteristics. The bias correction models significantly improved the performance of the GeoWATCH soil moisture model in terms of average performance statistics and number of statistically cally unbiased sites. This process could easily be incorporated into GeoWATCH, allowing for a capability to rapidly estimate vehicle impacts and determine rehabilitation requirements by installation land managers.     

Nanometric positioning accuracy in the presence of presliding and sliding friction: Modelling,identification and compensation

Presliding and sliding frictional effects, limiting the performances of ultrahigh precision mechatronics devices, are studied in this work. The state-of-the-art related to frictional behavior in both motion regimes is, hence, considered, and the generalized Maxwell-slip (GMS) friction model is adopted to characterize frictional disturbances present in a micromanipulation device. All the parameters of the model are identified via experimental set-ups and included in the overall MATLAB/SIMULINK model. With the aim of compensating frictional effects, the modelled response of the system is thus compared to experimental results when using proportional-integral-derivative (PID) control, feed-forward model-based compensation and a self-tuning adaptive regulator. The adaptive regulator proves to be the most efficient and is, hence, used in the final repetitive point-to-point positioning tests allowing to achieve nanometric precision and accuracy.     

基于红外辐射的爆炸火焰温度补偿测算技术

应用辐射测温法进行爆炸火焰温度测试时,火焰发射率取经验定值的方法与火焰燃烧机理存在较大的偏差,同时测点距离与环境温湿度也会导致不同程度的热辐射衰减,从而影响爆炸火焰温度的测量精度。本文针对上述两个问题,基于大气辐射理论与光学传播规律,提出了辐射路径衰减补偿模型,结合由红外热像仪和比色测温仪测量的爆炸火焰动态发射率,对爆炸场火焰真温进行联合反演,并将测算结果与比色测温仪测得的火焰表面温度进行对比,得到了反演温度误差范围。试验结果表明,利用本文所提出的补偿模型测算得到的爆炸火焰温度,误差由补偿前的55.699%～89.847%降低到11.292%～59.077%,有效提高了外场爆炸瞬态火焰温度的测算精度。     

Sensitivity analysis of the Bagley correction to shear and extensional rheology

The excess pressure losses due to end effects in the capillary flow of two linear low-density polyethylene resins (LLDPE) were studied. These losses were first determined experimentally by using two methods: 1) by extrapolating experimental data of pressure drop versus length-to-radius ratios (L/R) to zero capillary length and 2) by means of using orifice dies (L/R≅0). Both methods resulted in practically the same end corrections. Numerical simulation was also used to model this important aspect of experimental rheology. The constitutive equations used in the simulations are a multimode K-BKZ equation, a multimode Phan-Thien/Tanner, and finally a purely viscous Carreau equation. It was found that the numerical predictions agreed qualitatively but underestimated the experimental data for the various geometries used to determine the end effects. Furthermore, it is demonstrated that the entrance pressure loss is also insensitive to extensional rheology, while it depends more strongly on the shear rheology. This finding raises doubts as to the usefulness of end pressure (known also as Bagley correction) as a method of determining the extensional viscosity of polymer melts at high rates. Received: 18 December 1997 Accepted: 21 May 1998     

A comparison of coarse and fine grain parallelization strategies for the simple pressure correction algorithm

The primary aim of this work was to determine the simplest and most effective parallelization strategy for control-volume-based codes solving industrial problems. It has been found that for certain classes of problems, the coarse-grain functional decomposition strategy, largely ignored due to its limited scaling capability, offers the potential for significant execution speed-ups while maintaining the inherent structure of traditional serial algorithms. Functional decomposition requires only minor modification of the existing serial code to implement and, hence, code portability across both concurrent and serial computers is maintained. Fine-grain parallelization strategies at the ‘DO loop’ level are also easy to implement and largely preserve code portability. Both coarse-grain functional decomposition and fine-grain loop-level parallelization strategies for the SIMPLE pressure correction algorithm are demonstrated on a Silicon Graphics 4D280S eight CPU shared memory computer system for a highly coupled, transient two-dimensional simulation involving melting of a metal in the presence of thermal-buoyancy-driven laminar convection. Problems requiring the solution of a larger number of transport equations were simulated by including further scalar variables in the calculation. While resulting in slight degradation of the convergence rate, the functional decomposition strategy exhibited higher parallel efficiencies and yielded greater speed-ups relative to the original serial code. Initially, this strategy showed a significant degradation in convergence rate due to an inconsistency in the parallel solution of the pressure correction equation. After correcting for this inconsistency, the maximum speed-up for 16 dependent variables was a factor of 5·28 with eight processors, representing a parallel efficiency of 67%. Peak efficiency of 76% was achieved using five processors to solve for 10 dependent variables.     

Using tangential method to detect the singular points and to discriminate the stability condition of a movable mass point on any guide curve rotating about a vertical axis without friction

The state plane method has been used to search the singular pointand to determine their equilibrium state for a mass point sliding on aguide rail rotating about a vertical axis with friction disregarded.For the same purpose,this paper presents another method which mightbe briefly named“The Tangential Force method”.In contrast with thestate plane method.the new method is much simpler both in argumenta-tion and calculation,especially when one resorts to the five criteriain section XIII.throughout the paper the function for defining the guide rail wasintroduced,with great endeavor,in the equations newly set up,in or-der to avoid deducing them each time.i.e.,the useful equations areset up somewhat once for ever.Moreover,the condition of letting the tangential force vanishyields two solutions,the parabolic and the exponential curves of theshape of the guide rails;they are two additional orthogonal curvefamilies although not conjugate harmonics.In the last part of the paper,we present nine examples to showt