Non-dimensional analysis on blast wave propagation in foam concrete:Minimum thickness to avoid stress enhancement

Foam concrete is a prospective material in defense engineering to protect structures due to its high energy absorption capability resulted from the long plateau stage.However,stress enhancement rather than stress mitigation may happen when foam concrete is used as sacrificial claddings placed in the path of an incoming blast load.To investigate this interesting phenomenon,a one-dimensional difference model for blast wave propagation in foam concrete is firstly proposed and numerically solved by improving the second-order Godunov method.The difference model and numerical algorithm are validated against experimental results including both the stress mitigation and the stress enhancement.The difference model is then used to numerically analyze the blast wave propagation and deformation of material in which the effects of blast loads,stress-strain relation and length of foam concrete are considered.In particular,the concept of minimum thickness of foam concrete to avoid stress enhancement is proposed.Finally,non-dimensional analysis on the minimum thickness is conducted and an empirical formula is proposed by curve-fitting the numerical data,which can provide a reference for the application of foam concrete in defense engineering.

Non-Dimensional Analysis of Thermal Effect on Skin Exposure to an Electromagnetic Beam

We consider the problem of inducing withdrawal reflex on a test subject by exposing the subject’s skin to an electromagnetic beam. Heat-sensitive nociceptors in the skin are activated wherever the temperature is above the activation temperature. Withdrawal reflex occurs when the activated volume reaches a threshold. We non-dimensionalize the problem to write the temperature as the product of a parameter-free function of non-dimensional variables and a function of beam parameters. This formulation allows studying beam parameters without knowing skin material parameters. We examine the effects of spot size, total power and distribution type of the electromagnetic beam on 3 quantities at reflex: 1) the time to reflex, 2) the maximum temperature increase, and 3) the total energy consumption. We find that the flat-top beam is the best, with the lowest energy consumption and the smallest maximum temperature increase. The Super-Gaussian beam is only slightly inferior to the flat-top. The Gaussian beam has by far the worst performance among these three.

Local Similarity Relationships of Non-Dimensional Wind and Temperature Gradient in the Tower-Layer Atmosphere over Beijing City

Micrometeorological data for wind and temperature from a 325 m high tower in Beijing City are analyzed by use of local similarity theory. Non-dimensional wind and temperature gradients, Phi(m) and Phi(h), are determined by three techniques called, respectively, eddy-correlation, mean profiles and inertia-subrange cospectra (ISC) method for a wide range of atmospheric stratification from unstable to stable conditions. Average dissipation rate Phi(e) of turbulent kinetic energy (TKE) is evaluated from u-spectrum, as a quantity required in the last technique. Ratio of the eddy transfer coefficients, alpha(= K-h / K-m), is calculated from Phi(m) and Phi(h) estimations. The results from various techniques are compared with each other and with some available empirical results in the tower-layer, It is shown that the empirical relationships determined by mean profiles and ISC methods in the lower-layer turbulence ore in agreement with each other and with some other results.

Hydrodynamic Lubrication of Elastic Foil Gas Bearing Using Over Relaxation Iteration Method and Non-Dimensional Equation

The purpose is to accurately predict the performance of foil bearing and achieve accurate results in the design of foil bearing structure.A new type of foil bearing with surface microstructure is used as experimental material.First,the lubrication mechanism of elastic foil gas bearing is analyzed.Then,the numerical solution process of the static bearing capacity and friction torque is analyzed,including the discretization of the governing equation of rarefied gas pressure based on the non-dimensional modified Reynolds equation and the over relaxation iteration method,the grid planning within the calculation range,the static solution of boundary parameters and static solution of the numerical process.Finally,the solution program is analyzed.The experimental data in National Aeronautics and Space Administration(NASA)public literature are compared with the simulation results of this exploration,so as to judge the accuracy of the calculation process.The results show that under the same static load,the difference between the minimum film thickness calculated and the test results is not obvious;when the rotor speed of the bearing is 60000 r/min,the influence of the boundary slip effect increases with the increase of the micro groove depth on the flat foil surface;when the eccentricity or the micro groove depth of the bearing increases,the bearing capacity will be strengthened.When the eccentricity is 6µm and 14µm,the viscous friction torque of the new foil bearing increases significantly with the increase of the depth of the foil micro groove,but when the eccentricity is 22µm,the viscous friction torque does not change with the change of the depth of the foil micro groove.It shows that the bearing capacity and performance of foil bearing are improved.

NON-DIMENSIONAL DESIGN PARAMETERS FOR FOD TOLERANT FAN BLADES

Non-dimensional design concept for FOD tolerant fan blades is introduced based on the analyses of simplified impact models. The fan blades arc idealized as either beams or plates of elastic or rigid-plastic materials. The case of constant force impact as well as that of mass impact is analyzed. The centrifugal force effects are also considered in the beam models. The critical fracture conditions arc shown in simple npn-dimensional formulae or diagrams for each case.

Non-dimensional analysis of static bifurcation in a natural circulation loop

The steady-state characteristics of a two-phase natural circulation loop were investigated based on the homogenous model. Transcendental equations of non-dimensional loop mass flow rate under various conditions were also derived. The static bifurcation diagram of a two-phase natural circulation described with non-dimensional vari-ables Npch-m + was obtained. In addition, various steady-state characteristics of a natural circulation loop were ana-lyzed and discussed. These characteristics include the existence of multiple solutions under certain conditions, and the maximum mass flow rate. The authors also examined the effects of important parameters such as sub-cooling number, riser-to-heated-region length ratio, and riser-to-heated-region diameter ratio.

THE OPTIMIZATION OF CONTROL SYSTEM WITH NON-DIMENSION TIME BY LIAPUNOV'S SECOND METHOD AND THE OPTIMAL DAMPING CONTROL

In this note Liapunov’s second method with non-dimension time by Felilajam is developed from the method of parameter optimization in the second-order systemt to parameter optimization in any arbitrary order systems, and the problem of optimization in the control system becomes one of multidimensional geometric programming with constraint.

十字滑台式多维不倒杆自主纠偏实验装置设计

为了让学生理解海洋风力发机不倒杆结构,该文设计了基于十字滑台的多维不倒杆自主纠偏实验装置,上位机测量并绘制不倒杆在三维空间中的角度、角速度和角加速度的变化,探究抵御外部干扰的相关物理量。通过研究不同受风力面积、不同材料的杆的平衡性,得出选用密度较大、迎风面积小的杆可较好抵御外界干扰。该装置的灵敏度较高,能够作为应用物理和新能源等专业的实验教学装备,有助于深入理解新能源领域的控制理论,提高学生动手能力。

非结构化高维大数据异常流量时间点挖掘算法

非结构化数据的维度较高,每个样本数据包含的特征非常多,导致了维度灾难问题,使得降低维度并保持有效特征提取难度较大,影响大数据流量异常时间点挖掘的精度。为此,提出新的基于空间映射的非结构化高维大数据流量异常时间点挖掘方法。通过近似解集的几何特征建立稀疏回归模型,求解高维目标空间映射到低维目标子空间的稀疏投影矩阵。根据密度分布选择出一个高密度集合作为聚类中心的候选集,确定聚类的初始聚类中心。同时对聚类形成的各个簇采用剪枝算法,选择时间点候选集,对候选集展开二次判断,挖掘高维大数据流量异常时间点。实验结果表明,数据的降维能有效提高流量异常挖掘精度。相比之下,所提方法的高维大数据流量异常时间点挖掘更加精准,耗时更短。

一种古籍修复用纸伸缩性检测方法的探讨

补纸选配是古籍修复中的重要环节,但其伸缩性尚未引起足够重视。古籍修复补纸均为传统手工抄制,浸水后强度较低。按现行国家标准浸湿法检测补纸伸缩性时易产生撕裂、变形等问题,适用性较差。本研究探讨了一种古籍修复补纸的伸缩性检测方法——喷润法。利用水分检测仪对补纸相对含水量进行测定,从测量时间和可操作性的角度验证了该方法的可行性。通过十余种常用补纸的伸缩性检测结果发现,喷润法与浸湿法所得结果具有较好的一致性。随后探讨了古籍书叶伸缩性检测的适用性,并结合具体案例,建议在修复前分析古籍书叶与补纸的伸缩性匹配度。喷润法有效避免了补纸浸湿后的拉伸变形或破裂,既适用于古籍修复补纸,也适用于古籍书叶的无损检测,可为古籍修复策略的制定提供科学依据和参考。

大盾构管片最不利上浮状态下三维形变特征模型试验方案设计

隧道施工期管片所受浆液浮力并非恒定,壁后浆液压力的不均匀分布会导致管片变形和隧道环的位错损伤。为减弱或避免因管片上浮造成的结构病害,通过自主设计研发一种考虑千斤顶水平推力、围岩压力以及同步注浆上浮力作用的管片三维加载模型试验系统,对大直径管片最不利上浮状态下的瞬时变形进行分析。试验装置由围压加载装置和非均布上浮力加载装置组成,可实现单点或多点同步加卸载;模型试验采用不同刚度弹簧模拟上浮期隧道与地层之间的相互作用;根据相似理论对管片模型和连接螺栓进行精细化设计和加工;根据实际工程中试验段的围压对模型围压初始值进行换算,并将动、静态上浮力相结合,提出更符合工程实际的盾构隧道横、纵向上浮力分析模型。结果表明:在拱底非均布上浮力的作用下,拱底竖向位移和收敛变形沿纵向均近似呈对数正态分布,其最大值均出现在脱出盾尾后第3环;各环管片的收敛变形与拱底竖向位移近似呈线性关系,斜率介于0.63~1.49之间;模型试验结果与实测数据相吻合。研究成果可为盾构隧道管片抗浮设计和施工提供一定的技术支持。

基于SolidWorks的快速造型非标准螺纹的几种方法

分析了SolidWorks中造型非标螺纹的多种方法,详细介绍了各种方法造型过程,阐述了各种方法可能出现的问题和解决技巧,并从操作难易程度、可编辑性、运行速度、生成工程图是否符合国标、能否3D打印等多方面对几种方法进行了比较,指明了几种方法的应用场合,设计者可以根据需要灵活选择。

浅海孤立子内波作用下的三维声场空间特性

针对浅海环境下孤立子内波对声场空间特性的影响,以三维抛物方程理论及高精度根式算子近似方法为基础,建立了适应孤立子内波环境的三维声场计算方法。充分考虑孤立子内波传播特点与浅海中点源柱扩散形式的声场结构特征,形成以直角坐标系−柱坐标系的联合环境处理的声场计算形式,通过改变环境参数输入形式,提升了计算效率,并研究了孤立子内波影响下的三维声场分布特性。结果表明,平坦海底情况下,内波影响下的三维声场垂直和水平分布结构均发生变化,且随频率增加而增大,尤其是声源深度在跃层附近时变化更为明显;非平坦海底环境下,三维声场受到非水平海底和内波的双重调制作用,导致孤立子内波影响下的声场水平分布变化进一步加剧,从而在一定程度上反映出海底地形这一大尺度非均匀性对声场产生的水平折射效应以及对声传播特性的影响。

基于分裂阳极的非柱对称电弧电流密度分布测量方法

电弧是弧焊过程中熔池金属熔化的能量来源,分裂阳极法是电弧阳极能量密度直接测量的有效方法之一.常规分裂阳极法是建立在电弧为柱对称结构的基础上,不适用于非柱对称电弧的阳极电流密度测量.试验提出在两条相互垂直的路径上依次进行分裂阳极电流数据采集的新方法,引入表征电弧不对称度的特征参量,进行椭圆环分割,以计算电弧阳极电流密度分布,修正分裂阳极法.通过预设的二维高斯分布的电流密度模型,检验了修正的分裂阳极法的可行性.结果表明,采用修正的分裂阳极法可以有效计算出电弧阳极电流密度分布.利用修正后的分裂阳极法实现了非柱对称侧向压缩等离子弧阳极电流密度的测量,与x方向相比,侧向压缩的等离子弧在y方向压缩明显,呈现典型的非柱对称特性.

基于3DS Max的驾驶盲区内非机动车运行安全研究

驾驶盲区的存在致使驾驶员无法准确感知周边路况信息,这是导致交通事故的常见原因之一.由于车辆自身空间结构的布置及尺寸影响,产生了许多驾驶盲区,驾驶员应对车辆的各个盲区区域保持高度警觉,防止交通事故发生.分析机动车驾驶盲区内非机动车发生交通事故的原因,介绍具有代表性的盲区类型,建立典型盲区事故场景模型,分析其可能造成的交通事故,并采用3DS Max模拟驾驶盲区事故发生的全过程,通过FTA模型进一步分析驾驶盲区内发生非机动车事故的原因,进而提出有效的盲区防治对策,以减少驾驶盲区事故的发生.

基岩中入射波三维时域反演及自由场构建

基岩入射波一维和二维时域反演不能反映入射方位角和斜入射角的空间任意性,导致构建的自由场可能与实际偏离较远,因此有必要开展基岩入射波三维时域反演研究。基于波函数组合法,利用基岩中P波、SV波和SH波的入射波时程表达地表控制点自由场,建立基于设计地震动的基岩入射波三维时域反演方法,并进一步构建了多波组合斜入射下的空间非一致自由场,分析了基于一维和二维反演方法构建的自由场偏差,揭示了不同反演和自由场构建方法对于沥青混凝土心墙土石坝地震响应的影响机制。结果表明:基于地震动三维反演方法构建的自由场具有空间非一致性,能够更全面地反映场地的地震动场情况。当入射方位角在0°~60°、斜入射角在40°~90°范围内,与三维反演方法相比,一维反演方法构建的特征点x向自由场偏差较大,位移峰值最大偏差为55.8%;当入射方向与某个水平坐标轴平行时,二维反演方法构建的特征点另一个水平向自由场偏差较大,位移峰值最大偏差为100%。介质泊松比增大,一维反演下x向自由场偏差减小,二维反演下x向自由场偏差增大,特征点位移峰值最大偏差分别为46%和36%。与基于地震动三维反演方法获得的心墙拉应力最大值相比,二维和一维反演下拉应力最大值分别减小了83.3%和20.0%。

采用X射线三维重构技术检测厚皮柑橘的体积可食率

针对传统无损检测技术无法定量分析厚皮柑橘体积可食率的问题,该研究开发了一套线阵X射线图像采集和三维重构装置,包括果实旋转升降、数据采集、辐射防护及运动控制,实现厚皮柑橘果实的体积可食率检测。以“不知火”柑橘为检测对象,利用X射线投影图的信息熵为评价依据,根据果实大小对检测参数进行优化,得到X射线源的管电压为67 kV,管电流为0.92 mA,线阵探测器的积分时间为1 ms。以旋转角度2.0°为间隔,在圆周方向采集180幅X射线投影图并生成正弦图,通过滤波反向投影算法将正弦图重构为切面图,再利用图像滤波、图像增强、阈值分割对切面图进行图像分割处理,分割出背景区域、果皮区域、果肉区域和空腔区域,然后基于区域面积比定义切面图像可食率。同时,测量了柑橘基本物理参数,计算了切面图像可食率,并建立了与柑橘体积可食率之间的相关关系。结果表明,切面图像可食率与体积可食率相关性最高,相关系数为0.93。最后,选择切面图像可食率作为数学模型的输入特征,利用线性回归模型对厚皮柑橘体积可食率进行定量分析,其预测集决定系数、预测集均方根误差、相对分析误差分别为0.86、4.81%和2.71。综上,利用X射线三维重构技术对厚皮柑橘体积可食率进行无损检测可行,可为其他农产品内部品质无损检测提供参考。

四川盆地SZ页岩气藏气井产量变化规律及递减预测新模型

页岩气井生产特征和常规油气井相比有明显区别,研究页岩气藏产量变化规律及递减预测,对指导页岩气田开发现场措施调整、提高最终可采储量与采出程度等具有重要意义。以四川盆地SZ页岩气藏为例,基于其页岩气井在不同生产阶段日产气量、累积产气量变化特点,开展了不同类型页岩气井产量递减变化规律研究。提出了无因次产量递减率指标,来统一定量描述不同类型页岩气井产量递减率的变化规律;利用产量与递减率之间的定量变化,构建出一种新型的页岩气产量递减预测模型,进而推导出累积产量的数学表达式,考虑新模型中关键参数的取值变化,计算得到了不同初始递减率、产量递减幅度下的日产气量变化规律;结合目前已有的常用产量递减模型,对比分析新模型在不同类型井产量历史拟合及动态预测中的适应性。研究结果表明:新模型相比于已有模型,对SZ页岩气藏不同类型页岩气井产量变化的拟合程度更高、预测效果更好。本文研究可以对页岩气藏有效地进行产量预测和储量动用效果评价提供借鉴。

黄河上游茨哈峡至羊曲河段生态调度目标鱼类筛选

选择黄河上游茨哈峡至羊曲干支流河段内生态调度目标鱼类并明确其需求次序,可为生态调度方案的制订提供决策依据。采用2005-2006年、2011-2012年、2014-2017年、2022年茨哈峡至羊曲干支流河段渔获物调查结果,考虑不同鱼类繁殖活动对生态水文过程的需求以及数据可得性,选择反映鱼类生活史特征、地理分布特征、保护必要性、种质资源价值和资源量现状等信息的10个指标构建评价体系,采用聚类分析与非维度排序方法对茨哈峡至羊曲干支流河段分布的21种土著鱼类生态调度需求次序进行分组分析。结果显示,生态需求等级最高的有厚唇裸重唇鱼(Gymnodiptychus pachycheilus)、黄河高原鳅(Triplophysa pappenheimi)、黄河裸裂尻鱼(Schizopygopsis pylzovi)、拟鲇高原鳅(T. siluroides)、花斑裸鲤(Gymnocypris eckloni)、刺鮈(Acanthogobio guentheri)、骨唇黄河鱼(Chuanchia labiosa)、极边扁咽齿鱼(Platypharodon extremus)8种鱼,主要为适应缓流生境且均为砂砾产卵类型鱼类;根据评价体系综合结果分析,这8种鱼为茨哈峡至羊曲河段的主要生态调度目标鱼类,其他13种鱼作为该河段生态调度的兼顾对象。

高速飞行器热防护结构非均匀热流载荷反演方法

为准确掌握高速飞行器热防护结构服役时承担的非均匀气动热载荷,提出了一种基于共轭梯度理论的非均匀热流载荷的反演方法.以隔热瓦结构为例,开展了2类典型非均匀热流载荷下的数值仿真研究.通过引入一阶样条曲线插值表征非均匀热流的时变规律,降低了待反演参数数量.分析了反演方法的可行性以及温度测量偏差等因素对反演精度的影响.研究结果表明:非均匀热流时变规律的样条线表征方法可以将反演参数数量缩减到4个,极大地提升了反演效率;提出的反演方法可以精确反演结构非均匀热流载荷的时间和空间分布特性,对于含噪声的测量数据,该方法由于采用了插值重构的表征方法而体现出较好的抗噪性能.