深水导管架平台结构动力推覆分析方法

针对动力放大效应明显的深水导管架平台,将非线性动力分析与传统Pushover相结合,提出动力推覆分析(DPA)方法,用于研究平台结构极限承载能力及倒塌力学行为。提出安定状态的概念,作为平台动力倒塌的临界判据,引入动强度储备比和动载比等指标,建立了完善的DPA评估体系。以某深水导管架平台为例,分别从平台极限承载能力、位移响应以及失效模式3个方面对DPA和传统Pushover方法进行对比分析。结果表明:考虑动力放大效应后,基于DPA评估的平台极限位移增大,强度储备有所降低,相比Pushover方法,评估精度更高;DPA与Pushover方法所得到的塑性分布基本相同,载荷动态效应不会改变平台结构的失效模式;DPA能够更好地反映环境载荷动态历程,有效追踪平台结构的倒塌失效过程。

近地小行星动力推离在轨处置策略与效能分析

针对近地小行星频繁的撞击威胁,论证了小行星动力推离偏转处置任务。该处置方式通过侵彻锚固小行星表面并采用电力推进对小行星多次推离。通过建立近地小行星动力推离动力学模型,研究了不同自转状态小行星在动力推离处置策略下,其轨道偏移变化的情况。以2019VL5偏转小行星为例,通过数值仿真模拟动力推离处置效能及工程可实施性。仿真结果表明,在约4年的预警时间中,在特定轨道位置施加0.4N小推力,小行星能够获得的最大偏转距离2.91万km,在处置结束2500d后小行星能够获得9万km的最大偏转。小行星动力推离处置可使对具有威胁的小行星实现有效偏转,可用于未来小行星防御偏转和抵御其它太空物体攻击的轨道转移任务。

基于太阳能电推进的小行星动力推离方案设想及处置策略

近地小行星对地球构成了潜在的撞击威胁,如何有效可控地实施防御方案成为近年来的热点问题.采用电推进的动力推离在轨处置方法能够以持续作用的方式改变小行星的轨道,使小行星的可控偏转成为可能.面向未来小行星防御偏转需求,本文提出了一种以太阳能电推进为基础的分布式小行星动力推离处置方案设想.通过能源与推进系统的分布式部署,实现能源供应与偏转变轨的综合效能优化.在此方案基础上,针对不同自转特性的小行星,提出了三种附着部署与偏转处置策略,对比分析了电推开机阈值角度、推力矢量调节等参数对偏转效果的影响.研究发现,基于太阳能电推进的动力推离处置策略能够使百米级尺寸的近地小行星产生偏转,该研究可为近地小行星防御提供方案参考.

基于动力推覆方法的储液罐抗震分析

为有效评估储液罐在弹塑性阶段的抗震性能,经凝聚流体域压力自由度,建立流固耦合系统的等效动力方程,然后合并同频振型并基于广义逆理论导出谱加速度-谱位移性能曲线的投影方程,并通过控制谐波参数实现流固耦合系统的单向动力推覆,以此确定性能曲线并作为储液罐的单自由度广义本构模型。时程分析表明:上述广义本构模型的滞回曲线及时程结果与流固耦合系统吻合良好,罐体刚度均呈渐近退化。该文方法与静力推覆分析的计算耗时大致相仿,消除了特征节点对性能曲线的影响,并可考虑弹塑性阶段内罐体抗力分布的改变。

论区域体育赛事合作的动力机制——基于“推拉理论”的分析

体育赛事生产要素的高投入使得区域间的合作发展成为一个不可回避的话题。区域体育赛事产业合作也将是优化区域资源配置、提升区域竞争力的必然选择。推力(体育赛事资源的地区禀赋差)以及拉力(资源主体对利益最大化的追求),这两股力量的共同作用形成了区域体育赛事合作的动力机制。基于上述动力,区域间还需着力从构筑资源流动平台、建立利益协调机制等方式实现合作。

新时代高校农业科技推广动力与模式分析

新形势下高校开展农技推广工作的主要驱动力,除了来自农科成果示范应用需要及新农科建设要求的内部“推力”之外,还有来自政策、农业科技与农技推广体系需要的外部“拉力”。各高校依托其建立的新农村发展研究院,不断探索形成了与公益性农技推广机构相结合的衔接型或嵌入式等高校农技推广模式。为保障持续性,建议各高校探索符合实际需求和自身特点的农技推广模式;同时,相关管理部门对高校具有推广应用价值的技术研发与攻关应予以关注和稳定支持。通过借助政府农技推广机构等推广力量和资源,合力形成农技推广协同格局,促进先进适用的农业科技成果推广应用。

旅华英国游客O→D旅游客流动力机制研究

文章在分析目前客源地→目的地旅游客流动力机制相关研究理论现状与不足的基础上,提出了"推—拉—阻"旅游动力机制。然后,在10个热点旅游城市采用100分制6点等距量表,以537份旅华英国游客有效问卷数据为依据,对旅华英国游客来我国城市旅游的旅游动力中的推力因子、拉力因子、阻力因子及其权重进行了研究。研究结果表明,旅华英国客流旅游动力中主要有8大推力因子、9大拉力因子和7大阻力因子,推力在促动力中占44%,拉力在促动力中占56%,阻力相当于促动力的39%。

农技推广协同机制分析与涉农高校实践探索

为进一步强化我国“一主多元”农技推广体系促进多元力量的协同推广,针对当前多元主体协同推广的体系不完备、机制不健全、服务效能不高等问题,借鉴系统学、协同学等相关理论,分析并提出资源整合的协同推广形成机制(机会识别、沟通、决策)和资源互动的协同推广运行机制(动力、利益、管理),即“两类六大”协同机制;并分析涉农高校作为重要“一元”开展的衔接型和嵌入式实践探索和创新做法,明晰互动式的沟通机制、“推-拉”驱动力的均衡是高校参与农技推广的重要保障。

钢制储液罐的幂次失效模型及地震力折减

为了反映钢制储液罐的渐进失效趋势并合理地量化弹塑性地震力,采用流固耦合系统的单向动力推覆分析,建立反应谱层次的幂次失效模型.根据该模型构建等向强化的广义本构关系,在特定延性下迭代求解地震力折减系数Ry.结果表明,幂次失效模型下的地震力折减系数变异性较小,双线性滞回模型下的地震力折减系数会导致过于保守或偏于危险的地震力折减.选取40条最不利地震动并按场地分类,幂次失效模型下的地震力折减系数的均值略低于目标延性值,更符合长周期结构的等位移准则.GB50341与SH/T3026规定的地震力折减系数高于API650与EN1998-4,建议将地震力折减系数调整至2.0,应进一步细化边界条件的影响.

统筹城乡视域下农户土地利用意识多尺度认知研究

农户作为农村经济发展的微观行为主体,其土地行为决策受制于农户对环境与政策的认知,而这一响应程度不仅关系到农户土地利用行为的合理性与有效性,还直接影响着相关惠农政策的落实程度与实施绩效。农户土地利用意识源于土地意识但不同于土地意识,是农户在特定时空条件下,不断认知、熟知到适应政策、协调传统继承和现实模仿冲突,开展土地利用时的心理思考;农户土地利用意识调整与改变是一个渐进而非突变过程,是农户自身条件变化、内在利益驱动、外在环境刺激间相互博弈,农户对土地产品和服务需求的自我更新与累积;基于田块、农户、村尺度构建多尺度融合推拉动力模型能实现对农户土地利用意识调整与改变的内外诱因识别,为政策绩效评价和土地利用变化(LUC)研究提供了新的视角。

Experimental Investigation on Basic Prototype of Solid Propellant Impulsive Microthrusters

A new type of impulsive microthruster and its measurement system were designed for the aim of testing the performance of a basic prototype of solid propellant impulsive microthruster. Two sets of tests were conducted. The tests show that the ignitor and the main charge of the microthruster match well, the dynamic and static capability of the test and measurement meets the test requirement and the result is creditable. The measured technical characteristics of the microthruster are that the ignition delay time is shorter than 0 3?ms, the total impulse is over 3?N·s, the operational time is shorter than 16?ms and the mass ratio of the thruster is 0 216.

INVESTIGATION OF FLIGHT DYNAMICS OF THRUST VECTORING AIRCRAFT USING EXTENDED CONTINUATION METHODS

This paper presents the flight dynamical behavior of the thrust vectoring aircraft with extended bifurcation and continuation methods. In contrast to the standard bifurcation and continuation methods, the extended methods are capable of calculating the continuation curves of the equilibrium points for the particular type of trimming flight. Therefore, these methods can not only give the performance measures of aircraft, but also determine the stability of trimming points. In this paper, the methods are used to verify the effectiveness of the thrust vectoring control law, to define the flight envelope boundary, to analyze the stability and controllability of trimming flight, and to predict the departures of the instable flight. The result shows that the extended methods provide more flight dynamic information and are useful in preliminary design of the thrust vectoring aircraft.

HYBRID APPROACH FOR ESTIMATING COUPLING EFFECT BETWEEN PROPELLANT SLOSHING DYNAMIC AND SPACECRAFT GNC

An approach based on equivalent mechanics theory and computational fluid dynamics （CFD） technology is proposed to estimate dynamical influence of propellant sloshing on the spacecraft. A mechanical model is estab- lished by using CFD technique and packed as a ＂sloshing＂ block used in spacecraft guidance navigation and control （GNC） simulation loop. The block takes motion characteristics of the spacecraft as inputs and outputs of pertur- bative force and torques induced by propellant sloshing, thus it is more convenient for analyzing coupling effect between propellant sloshing dynamic and spacecraft GNC than using CFD packages. An example demonstrates the accuracy and the superiority of the approach. Then, the deducing process is applied to practical cases, and simulation results validate that the proposed approach is efficient for identifying the problems induced by sloshing and evaluating effectiveness of several typical designs of sloshing suppression.

Simulation of Airblast Load and Its Effect on RC Structures

In the analysis of a structure subjected to an explosion event, the determination of the blast load constitutes a crucial step. The effect of the blast load on the structure depends not only on the peak shock overpressure, but also the impulse (hence the duration). For structures with a regular geometry, the blast load may be fairly well estimated using appropriate empirical formulae; however, for more complex situations, a direct simulation using appropriate computational techniques is necessary. This paper presents a numerical simulation study on the prediction of the blast load in free air using a hydrocode, with focus on the sensitivity of the simulated blast load to the mesh grid size. The simulation results are compared with empirical predictions. It is found that the simulated blast load is sensitive to the mesh size, especially in the close-in range, and with a practically affordable mesh grid density, the blast load tends to be systematically underestimated. The study is extended to internal blast cases. An example concrete slab under internal explosion is analyzed using a coupled analysis scheme. The internal blast load from the simulation is examined and the response of the RC slab is commented.

IMPROVEMENT OF AERODYNAMIC PERFORMANCE OF SUPERSONIC AIRCRAFT USING CANARD SURFACE WITH TVFC

The purpose of increasing the aerodynamic efficiency and enhancing the supermaneuverability for the selected supersonic aircraft is presented. Aerodynamic characteristics, the surface pressure distribution and the maximum lift are estimated for the baseline configuration for different Mach numbers and attack angles in subson- ic and supersonic potential flows, using a low-order three-dimensional panel method supported with the semi-empirical formulas of the data compendium （DATCOM）. Total nose-up and nose-down pitching moments about the center of gravity of the complete aircraft in the subsonic region depending on flight conditions and aircraft performance limitations are estimated. A software package is developed to implement the two-dimensional thrust vectoring flight control technique （pitch vectoring up and down） controlled by the advanced aerodynamic and control surface （the foreplane or the canard）. Results show that the canard with the thrust vectoring produces enough nose-down moment and can support the stabilizer at high maneuvers. The suggested surface can increase the aerodynamic efficiency （lift-to-drag ratio） of the baseline configuration by 5%-6% in subsonic and supersonic flight regimes.

Vacuum chamber suppression of gas-explosion propagation in a tunnel

To control and reduce the harm of a gas explosion, a new method is proposed for suppressing gas-explosion propagation in a tunnel by using a vacuum chamber. We studied the suppression effect on gas explosions by placing a vacuum chamber at dif-ferent positions along the tunnel. The results indicate that: 1) the vacuum chamber can absorb the explosion wave and explosion energy as much as possible at the beginning of the gas explosion, and; 2) when the vacuum chamber is used the closer it is to the ignition source the more significant the suppression effect. In addition, by using the vacuum chamber: 1) the flame propagation velocity decreases from ultrasonic to subsonic; 2) the flame propagation distance is remarkably shortened; 3) the maximum peak value of overpressure (pm) decreases from 0.34 to 0.17 MPa or less, and; 4) the impulse of the blast wave (I) decreases from 20 to 8 kPa·s or less.

Study on Unsteady Hydrodynamic Performance of Propeller in Waves

The speed of a ship sailing in waves always slows down due to the decrease in efficiency of the propeller. So it is necessary and essential to analyze the unsteady hydrodynamic performance of propeller in waves. This paper is based on the numerical simulation and experimental research of hydrodynamics performance when the propeller is under wave conditions. Open-water propeller performance in calm water is calculated by commercial codes and the results are compared to experimental values to evaluate the accuracy of the numerical simulation method. The first-order Volume of Fluid(VOF) wave method in STAR CCM+ is utilized to simulate the three-dimensional numerical wave. According to the above prerequisite, the numerical calculation of hydrodynamic performance of the propeller under wave conditions is conducted, and the results reveal that both thrust and torque of the propeller under wave conditions reveal intense unsteady behavior. With the periodic variation of waves, ventilation, and even an effluent phenomenon appears on the propeller. Calculation results indicate, when ventilation or effluent appears, the numerical calculation model can capture the dynamic characteristics of the propeller accurately, thus providing a significant theory foundation forfurther studying the hydrodynamic performance of a propeller in waves.

Influence on the hydrodynamic performance of a variable vector propeller of different rules of pitch angle change

To design a more effective blade pitch adjustment mechanism,research was done on changes to the hydrodynamic characteristics of VVPs(Variable Vector Propeller) caused by different rules for changing pitch angle. A mathematical method for predicting the hydrodynamic characteristics of a VVP under unsteady conditions is presented based on the panel method. Mathematical models for evaluation based on potential flow theory and the Green theorem are also presented. The hydrodynamic characteristics are numerically predicted. To avoid gaps between panels,hyperboloidal quadrilateral panels were used. The pressure Kutta condition on the trailing edge of the VVP blade was satisfied by the Newton-Raphson iterative procedure. The influence coefficients of the panels were calculated by Morino's analytical formulations to improve numerical calculation speed,and the method developed by Yanagizawa was used to eliminate the point singularity on derivation calculus while determining the velocities on propeller surfaces. The calculation results show that it's best for the hydrodynamic characteristics of the VVP that pitch angle changes follow the sine rule.

Hydrodynamic Efficiency Improvement of the High Skew Propeller for the Underwater Vehicle Under Surface and Submerged Conditions

An algorithm based on the Boundary Element Method(BEM)is presented for designing the High Skew Propeller(HSP)used in an Underwater Vehicle(UV).Since UVs operate under two different kinds of working conditions(i.e.surface and submerged conditions),the design of such a propeller is an unwieldy task.This is mainly due to the fact that the resistance forces as well as the vessel efficiency under these conditions are significantly different.Therefore,some factors are necessary for the design of the opti-mum propeller to utilize the power under the mentioned conditions.The design objectives of the optimum propeller are to obtain the highest possible thrust and efficiency with the minimum torque.For the current UV,the main dimensions of the propeller are pre-dicted based on the given required thrust and the defined operating conditions.These dimensions(number of blades,pitch,diameter,expanded area ratio,thickness and camber)are determined through iterative procedure.Because the propeller operates at the stern of the UV where the inflow velocity to the propeller is non-uniform,a 5-blade HSP is preferred for running the UV.Finally,the propel-ler is designed based on the numerical calculations to acquire the improved hydrodynamic efficiency.