Study on Simulation of Remotely Operated Underwater Vehicle Spatial Motion

In order to analyze the spatial maneuverability of the remotely operated underwater vehicle(ROV),the 6-DOF motion mathematic model of the ROV was founded.Hydrodynamics were analyzed by using the Taylor series.The thrusters on the ROV were discussed.This paper considers three cases of motion simulation:vertical motion,rotational motion and Z-shape motion.A series of simulation experiments showed that the 6-DOF motion mathematic model was correct and reliable,and also fit with the scene simulation.

Vertical coherency function model of spatial ground motion

Many studies have focused on horizontal ground motion, resulting in many coherency functions for horizontal ground motion while neglecting related problems arising from vertical ground motion. However, seismic events have demonstrated that the vertical components of ground motion sometimes govern the ultimate failure of structures. In this paper, a vertical coherency function model of spatial ground motion is proposed based on the Hao model and SMART 1 array records, and the validity of the model is demonstrated. The vertical coherency function model of spatial ground motion is also compared with the horizontal coherency function model, indicating that neither model exhibits isotropic characteristics. The value of the vertical coherency function has little correlation with that of the horizontal coherency function. However, the coherence of the vertical ground motion between a pair of stations decreases with their projection distance and the frequency of the ground motion. When the projection distance in the wave direction is greater than 800 meters, the coherency between the two points can be neglected.

Running safety assessment of a train traversing a three-tower cable-stayed bridge under spatially varying ground motion

To explore the influence of spatially varying ground motion on the dynamic behavior of a train passing through a three-tower cable-stayed bridge,a 3D train–track–bridge coupled model is established for accurately simulating the train–bridge interaction under earthquake excitation,which is made up of a vehicle model built by multi-body dynamics,a track–bridge finite element model,and a 3D rolling wheel–rail contact model.A conditional simulation method,which takes into consideration the wave passage effect,incoherence effect,and site-response effect,is adopted to simulate the spatially varying ground motion under different soil conditions.The multi-time-step method previously proposed by the authors is also adopted to improve computational efficiency.The dynamic responses of the train running on a three-tower cablestayed bridge are calculated with differing earthquake excitations and train speeds.The results indicate that(1)the earthquake excitation significantly increases the responses of the train–bridge system,but at a design speed,all the running safety indices meet the code requirements;(2)the incoherence and site-response effects should also be considered in the seismic analysis for long-span bridges though there is no fixed pattern for determining their influences;(3)different train speeds that vary the vibration characteristics of the train–bridge system affect the vibration frequencies of the car body and bridge.

Approximation approach to the SRM based on root decomposition in the simulation of spatially varying ground motions

The spectral representation method （SRM） is widely used to simulate spatially varying ground motions. This study focuses on the approximation approach to the SRM based on root decomposition, which can improve the efficiency of the simulation. The accuracy of the approximation approach may be affected by three factors： matrix for decomposition, distribution of frequency interpolation nodes and elements for interpolation. The influence of these factors on the accuracy of this approach is examined and the following conclusions are drawn. The SRM based on the root decomposition of the lagged coherency matrix exhibits greater accuracy than the SRM based on the root decomposition of the cross spectral matrix. The equal energy distribution of frequency interpolation nodes proposed in this study is more effective than the counter pith with an equal spacing. Elements for interpolation do not have much of an effect on the accuracy, so interpolation of the elements of the decomposed matrix is recommended because it is less complicated from a computational efficiency perspective.

The limit properties of spatial coherence of seismic ground motion

The limit properties of spatial coherence of seismic ground motion are studied based on the differential relation between rotation and translation in elastic theory, the results show that the empirical mathematical model of spatial coherence must satisfy some functional characteristics. It is also indicated that the key problem to estimate rotational power spectrum densities is to obtain precisely the two order derivative of spatial coherence.

Robot motion control in mobile environment

With the problem of robot motion control in dynamic environment represented by mobile obstacles,working pieces and external mechanisms considered, a relevant control actions design procedure has been pro-posed to provide coordination of robot motions with respect to the moving external objects so that an extension ofrobot spatial motion techniques and active robotic strategies based on approaches of nonlinear control theory canbe achieved.

Simulation of multi-support depth-varying earthquake ground motions within heterogeneous onshore and offshore sites

This paper presents a novel approach to model and simulate the multi-support depth-varying seismic motions（MDSMs） within heterogeneous offshore and onshore sites.Based on 1 D wave propagation theory,the three-dimensional ground motion transfer functions on the surface or within an offshore or onshore site are derived by considering the effects of seawater and porous soils on the propagation of seismic P waves.Moreover,the depth-varying and spatial variation properties of seismic ground motions are considered in the ground motion simulation.Using the obtained transfer functions at any locations within a site,the offshore or onshore depth-varying seismic motions are stochastically simulated based on the spectral representation method（SRM）.The traditional approaches for simulating spatially varying ground motions are improved and extended to generate MDSMs within multiple offshore and onshore sites.The simulation results show that the PSD functions and coherency losses of the generated MDSMs are compatible with respective target values,which fully validates the effectiveness of the proposed simulation method.The synthesized MDSMs can provide strong support for the precise seismic response prediction and performance-based design of both offshore and onshore large-span engineering structures.

A coherency function model of ground motion at base rock corresponding to strike-slip fault

At present, the method to study spatial variation of ground motions is statistic analysis based on dense array re-cords such as SMART-1 array, etc. For lacking of information of ground motions, there is no coherency function model of base rock and different style site. Spatial variation of ground motions in elastic media is analyzed by deterministic method in this paper. Taking elastic half-space model with dislocation source of fault, near-field ground motions are simulated. This model takes strike-slip fault and earth media into account. A coherency func-tion is proposed for base rock site.

Over-Constraints and a Unified Mobility Method for General Spatial Mechanisms Part 2:Application of the Principle

The pre-research on mobility analysis presented a unified-mobility formula and a methodology based on reciprocal screw theory by HUANG, which focused on classical and modem parallel mechanisms. However its range of application needs to further extend to general multi-loop spatial mechanism. This kind of mechanism is not only more complex in structure but also with strong motion coupling among loops, making the mobility analysis even more complicated, and the relevant research has long been ignored. It is focused on how to apply the new principle for general spatial mechanism to those various multi-loop spatial mechanisms, and some new meaningful knowledge is further found. Several typical examples of the genera/multi-loop spatial mechanisms with motion couple even strong motion couple are considered. These spatial mechanisms include different closing way： over-constraint appearing in rigid closure, in movable closure, and in dynamic closure as well; these examples also include two different new methods to solve this kind of issue： the way to recognize over-constraints by analyzing relative movement between two connected links and by constructing a virtual loop to recognize over-constraints. In addition, over-constraint determination tabulation is brought to analyze the motion couple. The researches above are all based upon the screw theory. All these multi-loop spatial mechanisms with different kinds of structures can completely be solved by following the directions and examples, and the new mobility theory based on the screw theory is also proved to be valid. This study not only enriches and develops the theory and makes the theory more universal, but also has a special meaning for innovation in mechanical engineering.

Improved spatio-SNR FGS video coding scheme using motion compensation on enhancement-layer

MPEG-4 fine-granularity-scalable （FGS） technology is an effective solution to resolve the network bandwidth varying because FGS provides very fine granular SNR scalability. However, this scalability is obtained with sacrifice of coding efficiency. An one-loop FGS structure is presented based on motion compensation （MC ＋ FGS） to improve the coding efficiency of base FGS. Then it describes and discusses the hybrid spatial-SNR FGS （FGSS） structure that extends SNR scalability of FGS to spatial scalability （spatio-SNR scalability）. FGSS structure inherent the low coding efficiency of FGS structure. Combining MC ＋ FGS structure with FGSS structure, a structure of MC ＋ FGSS structure is obtained which acquires both structures＇ advantages and counteracts both structures＇ defects. Experimental results prove the MC＋ FGSS structure not only obtains fine granular spatio-SNR scalability, but also achieves high coding efficiency.

Effects of near-fault ground motions on the nonlinear behaviour of reinforced concrete framed buildings

The design provisions of current seismic codes are generally not very accurate for assessing effects of near-fault ground motions on reinforced concrete （r.c.） spatial frames, because only far-fault ground motions are considered in the seismic codes. Strong near-fault earth- quakes are characterized by long-duration （horizontal） pulses and high values of the ratio ~PGA of the peak value of the vertical acceleration, PGAv, to the analogous value of the horizontal acceleration, PGAH, which can become critical for girders and columns. In this work, six- and twelve-storey r.c. spatial frames are designed according to the provisions of the Italian seismic code, considering the horizontal seismic loads acting （besides the gravity loads） alone or in combination with the vertical ones. The non- linear seismic analysis of the test structures is performed using a step-by-step procedure based on a two-parameter implicit integration scheme and an initial stress-like itera- tive procedure. A lumped plasticity model based on the Haar-K^n~m principle is adopted to model the inelastic behaviour of the frame members. For the numerical investigation, five near-fault ground motions with high values of the acceleration ratio C^p6A are considered. Moreover, following recent seismological studies, which allow the extraction of the largest （horizontal） pulse from a near-fault ground motion, five pulse-type （horizontal） ground motions are selected by comparing the original ground motion with the residual motion after the pulse has been extracted. The results of the nonlinear dynamic analysis carried out on the test structures highlighted thathorizontal and vertical components of near-fault ground motions may require additional consideration in the seis- mic codes.

江南园林空间节奏量化分析研究——以留园为例

节奏虽作为音乐领域的惯用名词,但常被用于描述园林中的空间体验。旨在突破传统空间于文学层面的“节奏”评价,客观、理性地分析江南园林空间节奏的发展规律。借节奏在音乐领域的概念,对园林的空间节奏进行深入的解读和量化分析,以留园为空间样本,基于统计学和空间句法对游览状态的变化时间与造景密度进行图示分析。发现园林空间节奏的快慢感受与游观速度无关,而与运动状态的变化速率有关。最终根据所得数据结论提取留园中的空间节奏序列模式及空间原型,为空间节奏的设计方法提出实践的可能性方案。

跨断层工程输入地震动模拟及地震响应

为解决跨断层结构输入地震动的问题,揭示其地震响应规律,基于断层物理模型并引入等效脉冲函数,构建考虑地震动空间变化特征的转换矩阵,提出一种高、低频叠加的混合模拟方法,实现断层两侧输入地震动的模拟。首先,依据建立的桥址场地断层模型,采用随机有限断层方法生成目标点位的高频地震动;再由走滑断层两侧地震动的脉冲效应和永久位移的特征,采用不同的等效脉冲模型分别模拟断层平行向和法向的低频脉冲分量,两者在截止频率处采用Butterworth滤波器进行高通和低通滤波,依据场地模型以及走滑断层两侧地震动的空间相干性,建立转换矩阵以模拟其空间变异性,最终将匹配滤波后的高、低频分量在时域叠加得到断层两侧的输入地震动。从时程、频谱以及结构响应三方面验证了模拟结果的合理性。以实际的跨断层悬索桥为研究对象,基于OpenSees建立全桥的三维有限元模型,采用模拟的断层两侧地震动进行动力时程分析。研究结果表明:桥梁跨断层的角度和位置,以及永久位移幅值对跨断层桥梁地震响应有显著影响,较大的残余内力和残余位移是造成跨断层桥梁破坏的重要原因。

月球车驾驶运动感知特性研究

航天员月球车驾驶技能地面训练需要模拟逼真的运动感知特性,其关键在于掌握地面与月面驾驶运动感知的差异。笔者建立了高度逼真的月球车驾驶运动仿真场景,模拟月球车驾驶运动的地月差异;开发了以空间定向模型为框架的人体运动感知软件,仿真比较了月球车驾驶前向运动感知的地月差异。结果表明,月面环境下月球车加速度变化范围减小、加减速缓慢且易发生侧滑;视觉信息受限时动态俯仰角感知显著大于地面,而静态俯仰角感知则大大降低;这种地月差异在加入视觉信息后大幅度减少。揭示了月面与地面驾驶运动感知特性的差异,为月球车驾驶运动模拟策略的优化提供了依据。

考虑润滑间隙效应的空间并联机构动力学优化

为了改善润滑间隙效应引起的空间并联机构动态性能的渐变劣化问题,以3-RRPaR冗余并联机构为研究对象,提出一种考虑润滑间隙效应的空间并联机构动力学优化方法。建立了考虑润滑转动副间隙的3-RRPaR冗余并联机构动力学模型;以优化末端执行器的动力学响应误差和优化间隙关节处的约束反力为目的设置目标函数,通过优化末端执行器质量以及转动惯量的方式来缓解运动副间隙导致的劣化效应,建立了考虑润滑间隙效应3-RRPaR冗余并联机构动力学优化模型;试验验证了所建动力学模型的有效性,对比分析两种目标函数对优化效果的影响以选择最佳优化方式,并分析优化前后考虑润滑间隙效应的空间并联机构动力学特性,结果表明动力学优化使润滑间隙转动副处约束反力峰值降低16.16%,为改善间隙效应提高空间并联机构动态性能提供了理论支撑。

抽象性位移事件及其汉语编码的认知阐释

作为认知主体的人不仅有能力识解出抽象性位移事件,而且有能力将其编码为特定的语言结构并用于交际。作为一种特殊的位移事件,抽象性位移事件的形成是有认知理据的,这一认知理据就是抽象实体的可动化机制。该机制有其自身的认知特性,其使用会受到一定的条件限制。编码抽象性位移事件的语言表达式可以叫作抽象性空间位移关系构式。汉语抽象性空间位移关系构式的构成既要受到整体性限制条件的制约,又要受到局部性限制条件的制约。

A modified method for simulating non-stationary multi-point earthquake ground motion

A spectral-representation-based algorithm is proposed to simulate non-stationary and stochastic processes with evolutionary power,according to a prescribed non-stationary cross-spectral density matrix. Non-stationary multi-point seismic ground motions at different locations on the ground surface are generated for use in engineering applications. First,a modified iterative procedure is used to generate uniformly modulated non-stationary ground motion time histories which are compatible with the prescribed power spectrum. Then,ground motion time histories are modeled as a non-stationary stochastic process with amplitude and frequency modulation. The characteristic frequency and damping ratio of the Clough-Penzien acceleration spectrum are considered as a function of time in order to study the frequency time variation. Finally,two numerical examples are presented to validate the efficiency of the proposed method,and the results show that this method can be effectively applied to the dynamic seismic analysis of long and large scale structures.

基于绝对位移法的曲线梁桥多维多点弹塑性随机响应分析

针对当前地震动空间效应下曲线梁桥地震反应分析多采用确定性激励输入且忽略桥梁非线性的情况,采用了多维多点非平稳随机激励对曲线连续梁桥进行弹塑性响应分析。建立非线性有限元模型并降维解耦非平稳地震动非平稳演化功率谱(energy power spectral density,EPSD)矩阵,采用绝对位移法对桥梁进行非线性时程分析。考虑不同视波速、场地条件、相干性以及平稳与非平稳地震激励,综合分析了曲线连续梁桥的随机响应及其频域特性和时域特性。结果表明,地震动空间效应和地震动的非平稳性对曲线梁桥随机响应影响很大,其中地震动空间效应对桥梁随机响应大小及其频域分布有显著影响,而非平稳性会对随机响应大小及其时变响应趋势产生重要影响。因此,在曲线连续梁桥抗震分析中需充分考虑地震动空间效应和地震动非平稳性,以避免错误估计桥梁抗震性能。提供了全面的分析结果,对加强曲线连续梁桥的抗震设计和评估,从而提高其抗震性能和可靠性具有重要意义。

融合时频空间特征的土石坝地震易损性分析改进MLP模型研究

针对现有地震易损性分析中采用的峰值加速度、峰值速度等地震动指标未能充分反映地震动复杂的时频空间特征,且现有基于对数空间线性函数关系假设的地震需求模型难以揭示地震动指标与地震响应间复杂非线性关系的问题,提出一种融合时频空间特征的土石坝地震易损性改进多层感知机(Multi Layer Perceptron,MLP)模型。该模型利用胶囊网络(Capsule Network,CapsNet)能够充分捕捉和表征目标特征空间位置分布的优势,从地震动小波时频图中提取反映地震动时频空间分布的深层特征,并以特征拼接的方式与既有特征进行融合,构建地震动融合指标;进一步地,采用树形Parzen优化算法(Tree structured Parzen Estimator,TPE)对MLP的神经元数量、学习率等超参数进行优化,提出基于TPE-MLP的土石坝地震需求模型,以反映地震动融合指标与地震响应间的复杂非线性关系,进而实现土石坝地震易损性的可靠分析。案例分析表明,相比于既有地震动指标,基于地震动时频空间特征融合指标的土石坝地震需求模型的MAE降低了40.5%,表明了所提模型的可靠性和优越性。

考虑地震动空间变化的区域公路网连通可靠性研究

区域公路网是社会交通大动脉和地震灾害救援生命线,连通可靠性反映了地震灾害发生后公路网的通行能力,地震动受震源位置及震中距的影响而具有显著的空间变化,对公路网的震后破坏状态具有重要影响。以邯郸地区公路网为研究对象,通过设定震源位置与震级,研究地震动空间变化影响下的区域公路网连通可靠性。首先,设定邯郸市1830年磁县大地震及一个虚拟地震为地震情景,分别设置震级为M6.0、6.5、7.0和7.5,基于地震动衰减关系表达地震动空间变化,得到公路单元对应的PGA。然后,结合地震易损性模型分析公路单元震后通行概率。最后,针对区域公路网空间范围大的典型特征,优化城市道路所用的最大可能状态算法,对邯郸地区公路网进行连通可靠性评估。结果表明,区域尺度下公路网络单元和节点数量多、空间展布复杂,其抗震连通可靠性与既有公路分布、区域城市位置等因素密切相关,地震动空间变化显著影响公路单元的震后破坏状态和通行概率,研究成果可为区域尺度公路网地震灾害评估及抗震韧性研究提供参考。