Point mass filter based matching algorithm in gravity aided underwater navigation

Gravity-aided inertial navigation is a hot issue in the applications of underwater autonomous vehicle(UAV). Since the matching process is conducted with a gravity anomaly database tabulated in the form of a digital model and the resolution is 2’ × 2’,a filter model based on vehicle position is derived and the particularity of inertial navigation system(INS) output is employed to estimate a parameter in the system model. Meanwhile, the matching algorithm based on point mass filter(PMF) is applied and several optimal selection strategies are discussed. It is obtained that the point mass filter algorithm based on the deterministic resampling method has better practicability. The reliability and the accuracy of the algorithm are verified via simulation tests.

Numerical solutions for point masses sliding over analytical surfaces: Part 1

In this study, we introduce a system of differential equations describing the motion of a single point mass or of two interacting point masses on a surface, that is solved by a fourth-order explicit Runge–Kutta(RK4) scheme. The forces acting on the masses are gravity, the reaction force of the surface, friction, and, in case of two masses, their mutual interaction force. This latter is introduced by imposing that the geometrical distance between the coupled masses is constant. The solution is computed under the assumption that the point masses strictly slide on the surface, without leaping or rolling. To avoid complications stemming from numerical errors related to real topographies that are only known over discrete grids, we restrict our attention to simulations on analytical continuous surfaces. This study sets the basis for a generalization to more complex systems of masses, such as chains or matrices of blocks that are often used to model complex processes such as landslides and rockfalls. The results shown in this paper provide a background for a companion paper in which the system of equations is generalized, and different geometries are presented.

An Identity and Its Applications Concerning Two Mass-points Systems

In this paper, we first give and prove a geometric identity for distance between any point and mass-points of two mass-points systems in n-dimensional Euclidean space Rn.As its application, we obtain an equality for two mass-points systems and its radius of the circumscribed sphere and an inequality for distance between mass-points of two mass-points systems and its k-dimensional volume.

Libration Points in the R3BP with a Triaxial Rigid Body as the Smaller Primary and a Variable Mass Infinitesimal Bod

The paper deals with the existence of the coplanar libration points in the restricted three-body problem when the smaller primary is a triaxial rigid body and the infinitesimal body is of variable mass. Following small parameter method, the coordinates of collinear libration points are established whereas the coordinates of triangular libration points are established by classical method. It is found that the mass reduction factor has small effect but triaxiality parameters of the smaller primary have great effects on the coordinates of the libration points.

Dynamics of Structural-Inhomogeneous Laminate and Shell Mechanical Systems with Point Constraints and Focused Masses. Part 2. Statement of the Problem of Forced Oscillations, Methods of Solution, Computational Algorithm and Numerical Results

A vibrational formulation, a technique, and an algorithm are proposed for assessing the resonance state of a package of rectangular plates and shells having point bonds and concentrated masses with different rheological properties of deformable elements under the influence of harmonic influences. The viscoelastic properties of elements are described using the linear Boltzmann-Volterra theory. An algebraic system of equations with complex coefficients is obtained, which is solved by the Gauss method. Various problems on steady-state forced vibrations for structurally inhomogeneous mechanical systems consisting of a package of plate and shell systems with concentrated masses and shock absorbers installed in it were solved. A number of new mechanical effects have been discovered associated with a decrease in the maximum resonance amplitudes of the mechanical system as a whole. The concept of “global resonance amplitude” is introduced to study the behavior of the resonance amplitudes of a mechanical system. An analysis of the numerical results showed that the interaction of resonant amplitudes is observed only in structurally inhomogeneous systems (in this case, with elastic and viscoelastic elements) and with a noticeable approximation of the natural frequencies.

On Simplified Models for Dynamics of Pointlike Objects

Motivation: We study the asymptotic-type dynamics of various real pointlike objects that one models by a variety of differential equations. Their response to an external force one defines solely by the trajectory of a single point. Its velocity eventually stops changing after cessation of the external force. The response of their acceleration to the long-term external force is slow and possibly nonlinear. Objective: Our objective is to present technique for making simplified models for the long-term dynamics of pointlike objects whose motion interacts with the surroundings. In the asymptotic-type long-term dynamics, the time variable t ∈ (tm, +∞) and tm > 0 is large, say ! Method: We apply Taylor series expansion to differential equations to model the acceleration of pointlike object whose response to the long-term external force is not instantaneous and possibly nonlinear. Results: We make simplified models for the long-term dynamics of pointlike objects by Taylor polynomials in time derivatives of the external force. Application: We interpret the relativistic Lorentz-Abraham-Dirac equation as an equation for modeling the long-term dynamics, where t ≥ tm ≫ 0. This interpretation resolves the conceptual and usage controversy surrounding its troublesome application to determine the trajectory of a radiating charged particle, thus contributing to the development of more adequate modeling of physical phenomena.

Dynamic Response Analysis of the Equivalent Water Depth Truncated Point of the Catenary Mooring Line

The real-time computer-controlled actuators are used to connect the truncated parts of moorings and risers in the active hybrid model testing system. This must be able to work in model-scale real time, based on feedback input from the floater motions. Thus, mooring line dynamics and damping effects are artificially simulated in real time, based on a computer-based model of the problem. In consideration of the nonlinear characteristics of the sea platform catenary mooring line, the equations of the mooring line motion are formulated by using the lumped-mass method and the dynamic response of several points on the mooring line is investigated by the time and frequency domain analysis method. The dynamic response of the representative point on the mooring line is analyzed under the condition of two different corresponding upper endpoint movements namely sine wave excitation and random wave excitation. The corresponding laws of the dynamic response between the equivalent water depth truncated points at different locations and the upper endpoint are obtained, which can provide technical support for further study of the active hybrid model test.

Ultrasound diagnosis of fractures in mass casualty incidents

The role of point-of-care ultrasound in mass casualty incidents(MCIs)is still evolving.Occasionally,hospitals can be destroyed by disasters resulting in large number of trauma patients.CAVEAT and FASTER ultrasound protocols,which are used in MCIs,included extremity ultrasound examination as part of them.The literature supports the use of ultrasound in diagnosing extremity fractures both in hospitals and MCIs.The most recent systematic review which was reported by Douma-den Hamer et al in 2016 showed that the pooled ultrasound sensitivity and specificity for detecting distal forearm fractures was 97% and 95% respectively.Nevertheless,majority of these studies were in children and they had very high heterogeneity.The portability,safety,repeatability,and cost-effectiveness of ultrasound are great advantages when treating multiply injured patients in MCIs.Its potential in managing fractures in MCIs needs to be further defined.The operator should master the technique,understand its limitations,and most importantly correlate the sonographic findings with the clinical ones to be useful.This editorial critically reviews the literature on this topic,describes its principles and techniques,and includes the author’s personal learned lessons so that trauma surgeons will be encouraged to use ultrasound to diagnose fractures in their own clinical practice.

The Libration Points in Photogravitational Restricted Three-Body Problem

The phologravilational restricled three-body problem in which the mass reduclionfactors of two primaries q_1 q_2( -∞, 1] are siudied and an analytic meihod toesli,;iale the number of libralion points ana io calculate lheir hoalion is given in thispaper. The results show lhal in phologravilalional reslricled three-body problem, thenumber of librafion poinis is .from one to seven for different q_1 and q_2. As application,the motion of dust grain like comet tail in the solar syslern is also discussed.

Wavelet analysis of stagnation point flow of non-Newtonian nanofluid

The wavelet approach is introduced to study the influence of the natural convection stagnation point flow of the Williamson fluid in the presence of thermophysical and Brownian motion effects. The thermal radiation effects are considered along a permeable stretching surface. The nonlinear problem is simulated numerically by using a novel algorithm based upon the Chebyshev wavelets. It is noticed that the velocity of the Williamson fluid increases for assisting flow cases while decreases for opposing flow cases when the unsteadiness and suction parameters increase, and the magnetic effect on the velocity increases for opposing flow cases while decreases for assisting flow cases. When the thermal radiation parameter, the Dufour number, and Williamson’s fluid parameter increase, the temperature increases for both assisting and opposing flow cases. Meanwhile, the temperature decreases when the Prandtl number increases. The concentration decreases when the Soret parameter increases, while increases when the Schmidt number increases. It is perceived that the assisting force decreases more than the opposing force. The findings endorse the credibility of the proposed algorithm, and could be extended to other nonlinear problems with complex nature.

不同慢性病中老年女性骨折风险及低骨量切点预测分析

背景:中老年女性是骨质疏松的高发人群,慢性病增加骨质疏松罹患风险。低骨量是骨质疏松发病前的危险阶段,目前缺少常见慢性病人群的骨折风险差异及诊断指标切点值的相关报道。目的:通过对不同慢性病中老年女性骨折风险的分析,探讨肥胖、高血压、高血脂、糖尿病、动脉硬化与骨密度的相关性,找到可预测低骨量指标的切点值,为防治骨质疏松提供参考。方法:将45-70岁203名女性受试者分为正常组和慢性病组,采用超声骨密度测量仪进行跟骨骨密度测试,采用动脉硬化仪测试肱-踝脉搏波传导速度,采用全自动生化分析仪测试血糖、血脂,采用身体成分分析仪测试体质量指数、脂肪质量及肌肉质量。结果与结论:①61-70岁女性骨密度和骨折风险系数及51-60岁、61-70岁骨强度与<50岁比较,差异有显著性意义(P<0.05);②糖尿病组骨折风险明显高于其余各组,动脉硬化组则高于正常组和肥胖组(P<0.05);③骨密度与年龄、左侧血管弹性程度、右侧血管弹性程度、三酰甘油呈负相关,与体质量指数呈正相关(P<0.05);上述指标与骨密度受试者工作特征(ROC)曲线下面积介于0.5-0.7之间,低骨量对应切点分别为55.5岁(年龄)、756.0 cm/s(左侧血管弹性)、789.0 cm/s(右侧血管弹性)、1.115 mmol/L(三酰甘油)、22.35 kg/m^(2)(体质量指数);④结论:糖尿病和动脉硬化增加中老年女性骨折风险,测定体质量指数、血管弹性和三酰甘油对女性低骨量预测具有一定早期诊断价值。

The Gravitational Radiation Emitted by a System Consisting of a Point Particle in Close Orbit around a Schwarzschild Black Hole

We analytically model a relativistic problem consisting of a point-particle with mass m in close orbit around a stationary Schwarzschild black hole with mass M = 1 using the null-cone formalism when l = 2. We use the -function to model the matter density of the particle. To model the whole problem, we apply the second order differential equation obtained elsewhere for a dynamic thin matter shell around a Schwarzschild black hole. The only thing that changes on the equation is the quasi-normal mode parameter which now represent the orbital frequency of the particle. We compare our results with that of the standard 5.5 PN formalism and found that there is a direct proportionality factor that relates the two results, i.e. the two formalisms.

基于等效分布质点的发动机悬置系统试验建模

为获得发动机悬置系统的相关参数,将非刚性、小柔性弹性体的发动机近似为含有n个质点的分布质点系。首先,根据拉格朗日方程建立了发动机悬置系统6自由度(6 degrees of freedom,简称6DOF)振动微分方程,包括质量阵、刚度阵和阻尼阵;其次,基于等效分布质点系统,构建发动机悬置3n DOF系统;然后,针对3点支撑的发动机台架系统,利用地磅测得每一个悬置处支撑的静态质量,通过发动机悬置测试试验系统测得发动机的激励输入信号及响应信号;最后,利用递推最小二乘法辨识得到分布质点系统的阻尼矩阵和刚度矩阵,在Matlab/Simulink中建立发动机悬置系统的仿真模型,并通过测试值与仿真值的对比,证明了辨识的准确性。给出的发动机悬置等效分布质点3n DOF系统在工程实际中,为悬置系统设计悬置支撑参数反解、悬置参数系统辨识提供了理论基础与实现途径。

利用点云处理的实时的类别级位姿估计

针对传统的视觉算法无法准确地测量物体3D质心和尺寸、无法检测数据集中未出现过的物体等问题,提出一种基于点云的类别级物体质心与位姿估计算法.首先通过2D分割算法对物体待检测区域进行分割,并通过BlendMask提高实时性;然后将分割区域生成点云,并结合先验形状输入到神经网络中重建物体模型;最后输出一个变形场以及对应矩阵,并通过Umeyama算法对物体进行位姿估计.实验结果表明,所提算法达到了较高的精度;在质心估计方面也优于包络盒中心作为质心的算法;实时速率达到了13帧/s.在GPUNVIDIA2060上进行仿真实验,证明了所提算法计算的质心优于对比算法,以及该算法的准确性及可靠性.

多源点云优化的城市三维模型构建

简易模型与传统复杂的单体模型相比,对存储、可视化、传输和后续应用技术要求低,敏感信息承载量少,且能满足大部分应用需求,具有更高的应用价值。考虑应用需求与技术现状,自然资源部将城市三维模型(L0D1.3级)纳入实景三维中国建设任务中。目前相关生产以半自动化采集为主,工程化应用存在技术流程烦琐、效率较低且对数据量限制较大等问题。本文立足山东实际,提出了一种基于多源点云优化的城市三维模型快速构建技术,在充分利用现有数据基础上有效提升了数据处理效率,大幅减少了生产成本,并在实景三维山东建设过程中得到了有效验证,具有较好的社会经济效益与推广价值。

不同体质量虫纹鳕鲈对耗氧率、窒息点及排氨率的影响

开展了不同体质量虫纹鳕鲈对耗氧率、窒息点及排氨率的影响试验。采用密闭流水式呼吸试验法,测定了4种不同体质量[A组(100.3±5.8)g、B组(205.1±12.1)g、C组(298.5±17.2)g、D组(405.9±15.6)g]虫纹鳕鲈的耗氧率、窒息点及排氨率。结果表明,虫纹鳕鲈的耗氧率及排氨率,随其体质量的增加而降低;耗氧率日波动较大,每日的06:00—08:00与16:00—18:00处于高水平;窒息点随体质量的增加升高,且A组与D组之间差异显著(P<0.05)。提出,在实际生产中,可根据虫纹鳕鲈不同养殖阶段耗氧率、养殖密度及生物滤池总体耗氧率,测算液氧加入量,提高液氧利用率和循环水的养殖容量,增加养殖效益。

基于列车运行多模型的能耗仿真计算

针对目前城市轨道交通系统能耗剧增导致能耗计算量大、计算不够精准的问题,通过考虑电机动态效率,精确计算实际列车侧能耗,并构建基于列车运行单质点和多质点模型的能耗仿真计算模型。首先分析列车牵引传动系统的能量流动过程,建立各部件效率与列车运行状态的关系。然后,结合各部件效率转换,依据两表法推导基于电功率的实际列车能耗计算公式,综合分析影响能耗的因素,进一步提出考虑单质点和多质点列车模型的能耗仿真计算方法。最后,以国内某市域线路的四站三区间为例,验证本文所提能耗模型的准确性。研究结果表明:无论是单质点还是多质点列车运行模型下的运行能耗,与实际运行能耗相比,均能实现5%以内的偏差;在单质点模型的基础上,多质点模型的运行能耗进一步减小了1.66%的偏差。本文所提模型可以为列车节能优化提供理论支撑,助力我国绿色经济发展。

基于Workbench的导管架吊装分析

为对导管架整体吊装安全性进行数值模拟分析,采用有限元法。利用ANSYS Workbench对导管架进行整体建模。模型中全部采用壳单元进行模拟。有限元网格划分过程中对不同的板厚和位置设置不同的偏移方向。利用力质量单元向导管架模型赋值,利用重力加速度施加场力。导管架起吊的吊点采用远程点的方式进行模拟,远程点与吊点之间的控制方程简化钢丝绳的建模。对吊点等关键部位进行细化网格处理。在导管架吊装受力后处理时,检查结构的整体应力情况,并重点检查吊点的应力情况。检查远程点反力并与导管架重量进行比对。检查导管架整体位移避免发生翻转。

物理化学实验教学细节探讨——凝固点降低法测定物质摩尔质量

“凝固点降低法测定物质摩尔质量”是物理化学实验中的经典实验之一。鉴于现有的物理化学实验教材和文献对凝固点测定部分内容描述不够细致,如过冷现象产生的原因解释不够全面、深入;纯溶剂近似凝固点测定需要观察“当有固体析出时”,析出的固体优先在玻璃管的何处出现?析出的固体呈现什么形貌?这些问题的存在,会使学生操作实验时产生困扰。本文针对上述问题,通过实验创新对溶剂凝固过程进行全程拍摄,分析固体析出的具体位置、形貌,得出学生实验操作时,应观察固体从玻璃管底部优先析出絮状物为宜;通过凝固点降低法,观察溶剂固体析出的细节,计算、分析溶质的分子量,得到了可靠的实验结果。本文对凝固点降低法操作细节深入研究与探讨,可以有效地避免或消除实验操作中出现的问题,大大提高学生实验效果。

考虑舰船激励和系留点偏移的系留无人机运动响应研究

为了研究舰船运动和系留点位置偏移对系留无人机系统运动响应的影响,采用集中质量法建立了系留无人机系统的数学模型,采用四阶龙格库塔法对方程进行数值求解。讨论了舰船运动幅值、频率以及系留点偏移量对系统运动响应以及系缆对无人机拉力的影响。构建了系留无人机系统的实验模型,分析了舰船运动对无人机系统的动力学影响。结果表明:端点激励幅值越大无人机和系缆的运动幅度越大,系缆对无人机的拉力幅值也变大;不同激励频率会激起系缆不同的运动形式;系留点垂向偏移距离越大无人机的滚转角运动范围也越大;通过与实验结果进行对照,定性验证了理论计算的正确性。