小天体着陆动力学参数不确定性影响分析

针对小天体不规则程度高、引力场复杂,且物理参数存在较高不确定性的问题,基于小天体着陆动力学方程线性化近似解析解,对各动力学参数不确定性的影响进行了分析。考虑动力学方程线性化带来的误差,引入线性化误差补偿校正方法,建立了探测器轨迹对动力学参数不确定性的敏感度方程。以小行星Eros 433为例,重点分析了目标小天体质量、自转角速度、引力势函数系数,以及探测器初始状态、推力加速度等动力学参数不确定性对探测器着陆轨迹的影响。数学仿真分析表明,针对本文选取的目标小天体,推力加速度扰动为主要影响因素,探测器初始状态的不确定性为次要影响因素,其他参数扰动的影响较小。     

短距离起飞加速度对飞行员操作影响的分析

短距离起飞产生的过载加速度可能对飞行员的安全操作造成极大隐患。本文建立飞行员-座舱系统的多刚体模型,仿真分析了胸-背方向的加速度载荷（Gx）对飞行员驾驶状态下的人机动力学响应。首先,根据第3百分位的男性人体测量学数据,通过三维CAD软件建立了飞行员的虚拟假人模型;并根据设计参数的要求建立了包括座椅和操作杆（油门杆与驾驶杆）在内的飞机座舱模型。然后,以标准的短距离起飞的加速度模拟曲线为载荷条件,利用多刚体动力学软件ADAMS模拟了飞行员在短距离加速起飞过程中的动力学响应及飞行员与操作系统之间的力学相互关系。仿真结果表明,过载加速度会经飞行员身体传递给操作杆,5G加速度载荷产生的传递力作用在驾驶杆和油门杆上的值分别为128 N和211 N,两者均已超过了通常操作杆所设计的有效阈值,因此存在误操作的可能。另外,本文结合仿真结果和国外现有战机设计,提出了短距离起飞下飞行员避免误操作的可行方式,结果显示该方式可以有效地转移加速度传递所带来的影响。本文方法将为在短距离起飞作用下避免误操作的分析提供技术途径,得到的结果将为驾驶部位的人机设计提供参考。      

代偿服加压条件下的血液动力学仿真

利用仿真方法研究飞行员穿着高空代偿服加压条件下生理参数的变化情况,探索加压对人体血液循环功能的影响及其变化规律,为飞行员高空防护提供理论支持.在Heldt立位应激模型的基础上,针对代偿服加压特性进行修正,建立人体加压条件下的血液动力学模型,同时通过地面加压试验验证模型的正确性.模型模拟得到全身侧管式代偿服不同加压条件下的血液动力学参数平均动脉压、每搏量和每分量,并与试验值进行对比,模型结果与试验值吻合较好,验证了模型的有效性.模型可有效地模拟代偿服加压条件下的血液动力学变化情况.     

基于刚柔耦合模型的月球着陆器动力学分析

基于刚柔耦合多体动力学理论,提出了一种基于三维实体造型、有限元分析与多体动力学分析的刚柔耦合动力学仿真分析方法;利用该方法建立了月球着陆器着陆动力学模型,分别在地球重力环境和月球重力环境(1/6地球重力环境)下,对某典型着陆工况下的着陆动力学进行了仿真分析,得到了着陆器着陆的缓冲性能分析结果,包括主支柱最大缓冲行程、左右辅助支柱最大缓冲行程、最大质心加速度响应;将仿真结果与试验结果相比较,验证了着陆器动力学模型的正确性以及仿真分析方法的有效性,为今后的着陆器缓冲试验提供了动力学模型和仿真分析方法.从能量角度对月球着陆器的着陆过程进行分析,弥补了缓冲试验难以进行能量分析的不足.     

带翼潜航器动力学建模及动稳定性

带翼潜航器具有面积较大的升力面,滚转运动是带翼潜航器的基本机动方式之一.利用计算流体力学(CFD,Computational Fluid Dynamics)方法研究了带翼潜航器的动导数,计算结果表明:粘性力以及主翼对机体和尾翼的干扰对加速度导数影响较大,不能将加速度导数简化为附加质量系数.带翼潜航器水动力模型直接采用加速度导数,动力学和运动学方程组考虑滚转运动参数的影响.利用小扰动假设将动力学和运动学方程组线性化,并将方程组分为纵向和横航向两组.通过计算扰动运动方程组的模态研究了带翼潜航器的动稳定性.提出的动力学模型及动稳定性分析方法可用于带翼潜航器的稳定性分析以及运动控制系统的设计.     

超静空间科学卫星分离式主动隔振技术

针对量子科学实验、时频传递实验等项目研发的先进载荷对微振动频谱积分的特殊指标需求，研究一种分离式主动隔振技术。分离式隔振技术将卫星划分为载荷模块和服务模块，考虑两模块之间柔性连接线缆和限位弹簧，首先建立两模块的动力学模型。随后，设计基于加速度反馈的六自由度隔振控制器，考虑执行机构控制和驱动电路的电气噪音，在时域和频域仿真分析载荷模块对服务模块的振动隔离性能。仿真结果表明，主动隔振后载荷模块三轴加速度功率谱密度在05~200Hz内积分值小于2 μgn。最后，分析主动隔振控制器参数对载荷模块加速度功率谱积分指标的影响。分离式主动隔振可为我国超静科学卫星的振动隔离提供一种技术途径。     

折叠翼无人机冷气发射装置动态特性分析及优化

针对冷气投放装置工作过程中存在的机械系统和气压系统耦合非线性动力学问题,提出了一种满足折叠翼无人机（UAV）结构形式和空中发射技术要求的冷气发射动态特性分析方法及优化设计方法。以某型折叠翼无人机为研究对象,基于联合仿真建立了无人机气动发射系统动力学模型,搭建了冷气发射系统试验样机,并完成压缩气体空中发射试验,验证了仿真模型的准确性。在此基础上,分析了无人机与冷气发射装置主要系统参数对无人机发射动态性能的影响,针对该系统进行了参数优化设计。结果表明:储气瓶体积和充气压力是影响无人机冷气发射动态特性的关键参数,随着储气瓶体积和充气压力增大,最大发射速度和加速度明显增大,储气瓶体积从15 L增加至30 L,最大发射速度增加了52.7%,最大发射加速度增长了60.9%呈正相关影响;充气压力从0.4 MPa增加至0.7 MPa,最大发射速度增长了50.5%,最大发射加速度增长了69.9%;发射角度对无人机发射性能影响较小,可忽略不计。      

高速无人机地面变速滑跑转弯方向稳定性研究

高速起降无人机地面滑跑过程中受到轮胎力、气动力、舵面力等多个非线性因素的影响，容易发生转弯失控，在地面打转甚至冲出跑道等严重事故。目前利用分岔理论分析飞机地面滑跑非线性转弯系统稳定性时，都是基于匀速滑跑的平衡态系统，无法分析加减速对非线性非自治飞机地面滑跑系统稳定性的影响。对此，提出利用达朗贝尔原理将非线性动态系统转化为等效非线性平衡态系统进行分岔特性研究。在MATLAB/Simulink中建立无人机非线性地面变速滑跑动力学模型，并基于达朗贝尔原理在系统模型中引入惯性力，将系统转化为等效平衡态系统，进而利用数值延拓法对系统全局稳定性及分岔特性进行求解，分析了无人机变速滑跑过程中加速度对无人机转弯方向稳定性的影响，并对系统出现的鞍结分岔现象、Hopf分岔现象进行分析。通过对3种典型工况下无人机的运动状态和受力进行分析，揭示了无人机地面变速滑跑转弯时发生方向失稳的本质与机理。同时，在加速度单参数分岔分析的基础上，采用开折方法，将前轮转角作为附加参数引入无人机地面滑跑动力学模型，进行双参数分岔分析，讨论了双参数组合对无人机地面滑跑方向稳定性的影响规律，并就双参数分岔过程中新出现的BT分岔、G...     

舰载机弹射起飞安全性的影响因素分析

为了全面考察舰载机（CBA）弹射起飞系统的安全性能,在绝对坐标系下,利用自然坐标法,建立了弹射起飞过程的多体耦合动力学模型,结合舰载机弹射仿真曲线,从舰载机加速度和飞行轨迹两方面研究了不同参数对弹射安全的影响规律。仿真结果表明:在弹射滑跑阶段,弹射力对水平加速度影响较大,在自由飞行阶段,发动机推力对水平加速度影响较大,而起飞重量在整个弹射过程对加速度均有明显影响;定力栓临界值的增大对加速度、飞行轨迹影响不大,但需要考虑其带来的结构振动和时延效应;较长的剩余甲板可以增加离舰升力,从而有效减小离舰下沉量;舰船纵摇可引起飞行轨迹大幅下沉,应避免舰船纵摇位移最大的时刻离舰起飞,其中舰船运动引起牵制杆的提前释放也应是控制弹射时间的考虑因素之一;弹射起飞安全性设计是一个多变量寻优过程,单一要素的优化难以得到满意结果,需综合分析各要素的影响。      

Growth restoration in azuki bean and maize seedlings by removal of hypergravity stimuli.

Hypergravity stimuli, gravitational acceleration of more than 1 x g, decrease the growth rate of azuki bean epicotyls and maize coleoptiles and mesocotyls by decreasing the cell wall extensibility via an increase in the molecular mass of matrix polysaccharides. An increase in the pH in the apoplastic fluid is hypothesized to be involved in the processes of the increase in the molecular mass of matrix polysaccharides due to hypergravity. However, whether such physiological changes by hypergravity are induced by normal physiological responses or caused by physiological damages have not been elucidated. In the present study, we examined the effects of the removal of hypergravity stimuli on growth and the cell wall properties of azuki bean and maize seedlings to clarify whether the effects of hypergravity stimuli on growth and the cell wall properties are reversible or irreversible. When the seedlings grown under hypergravity conditions at 300 x g for several hours were transferred to 1 x g conditions, the growth rate of azuki bean epicotyls and maize coleoptiles and mesocotyls greatly increased within a few hours. The recovery of growth rate of these organs was accompanied by an immediate increase in the cell wall extensibility, a decrease in the molecular mass of matrix polysaccharides, and an increase in matrix polysaccharide-degrading activities. The apoplastic pH also decreased promptly upon the removal of hypergravity stimuli. These results suggest that plants regulate the growth rate of shoots reversibly in response to hypergravity stimuli by changing the cell wall properties, by which they adapt themselves to different gravity conditions. This study also revealed that changes in growth and the cell wall properties under hypergravity conditions could be recognized as normal physiological responses of plants. In addition, the results suggest that the effects of microgravity on plant growth and cell wall properties should be reversible and could disappear promptly when plants are transferred from microgravity to 1 x g. Therefore, plant materials should be fixed or frozen on orbit for detecting microgravity-induced changes in physiological parameters after recovering the materials to earth in space experiments.     

人体对三级起飞加速度的反应

航天员在飞船起飞时,常会遇到二级或三级加速度作用.为了解这种类型加速度对人体的影响,在人体离心机上,在背角为15°情况下,十名健康的青年被试者承受了峰值分别为+4Gx、+6Gx和+5Gx、每级作用时间为150秒的三级加速度作用.实验中记录了被试者的心电、血压、心振动图、脑阻抗图和呼吸情况,分析和讨论了某些重要的生理指标的变化.结果表明,被试者的主观感觉是良好的,生理指标变化处于正常代偿范围之内,较好地耐受了上述三级起飞加速度的作用.      

Sailing with solar and planetary radiation pressure

Literature on solar sailing has thus far mostly considered solar radiation pressure (SRP) as the only contribution to sail force. However, considering a sail in a planetary mission scenario, a new contribution can be added. Since the planet itself emits radiation, this generates a radial planetary radiation pressure (PRP) that is also exerted on the sail. Hence, this work studies the combined effects of both SRP and PRP on a sail for two case studies, i.e. Earth and Venus. In proximity of the Earth, the effect of PRP can be significant under specific conditions. Around Venus, instead, PRP is by far the dominating contribution. These combined effects have been studied for single- and double-sided reflective coating and including eclipse. Results show potential increase in the net acceleration and a change in the optimal attitude to maximise the acceleration in a given direction. Moreover, an increasing semi-major axis manoeuvre is shown with and without PRP, to quantify the difference on a real-case scenario.     

长期贮存平台惯导系统壳体效应变化行为模型

长期贮存条件下平台惯导系统壳体效应具有与使用状态不同的漂移特性,其漂移规律与各性能参数退化及其相互耦合特性相关,在工程应用中往往难以分析贮存条件下壳体效应稳定性水平和合理配置标定维护资源。本文通过全面分析伺服电路零位和框架轴上干扰力矩引起壳体效应漂移的原理及其漂移表达式,在此基础上深入挖掘了表达式中漂移参数的变化特性,综合给出了伺服电路零位和框架轴上干扰力矩引起壳体效应漂移的变化行为模型,并结合实际贮存环境剖面对其进行了长期漂移特性、加速特性和稳定性分析,分析表明在现有贮存条件下,伺服电路零位和框架轴上干扰力矩引起的壳体效应在X、Y和Z轴的长期漂移特性相近,与实际使用状态的响应特性不同,且无加速特性,具有较好的稳定性水平,从而为合理安排标定维护资源提供了依据。      

Possible influence of solar extreme events and related geomagnetic disturbances on human cardio-vascular state: Results of collaborative Bulgarian–Azerbaijani studies

This collaborative study is based on the analysis and comparison of results of coordinated experimental investigations conducted in Bulgaria and Azerbaijan for revealing a possible influence of solar activity changes and related geomagnetic activity variations on the human cardio-vascular state. Arterial blood pressure and heart rate of 86 healthy volunteers were measured on working days during a period of comparatively high solar and geomagnetic activity (2799 measurements in autumn 2001 and spring 2002) in Sofia. Daily experimental investigations of parameters of cardio-vascular health state were performed in Azerbaijan with a permanent group of examined persons. Heart rate and electrocardiograms were digitally registered (in total 1532 records) for seven functionally healthy persons on working days and Saturdays, in the Laboratory of Heliobiology at the Medical Center INAM in Baku, from 15.07.2006 to 13.11.2007. Obtained digital recordings were subjected to medical, statistical and spectral analyses. Special attention was paid to effects of solar extreme events, particularly those of November 2001 and December 2006. The statistical method of the analysis of variance (ANOVA) and post hoc analysis were applied to check the significance of the influence of geomagnetic activity on the cardio-vascular parameters under consideration. Results revealed statistically significant increments for the mean systolic and diastolic blood pressure values of the group with geomagnetic activity increase. Arterial blood pressure values started increasing two days prior to geomagnetic storms and kept their high values up to two days after the storms. Heart rate reaction was ambiguous and not significant for healthy persons examined (for both groups) under conditions with geomagnetic activity changes. It is concluded that heart rate for healthy persons at middle latitudes can be considered as a more stable physiological parameter which is not so sensitive to environmental changes while the dynamics of arterial blood pressure reveals a compensatory reaction of the human organism for adaptation.     

Effects of altered gravity on plant cell processes: results of recent space and clinostatic experiments.

Space and clinostatic experiments revealed that plant cell structure and metabolism rearrangements depend on taxonomical position and physiological state of objects, growth phase and real or simulated microgravity influence duration. It was shown that clinostat conditions reproduce only a part of microgravity biological effects. It is established that various responses occur in microgravity: 1) rearrangements of cytoplasmic organelles ultrastructure and calcium balance; 2) physical-chemical properties of the plasmalemma are changed; 3) enzymes activity is often enhanced. These events provoke the acceleration of growth and differentiation of cells and their aging as a result; at the same time some responses can be considered as cell adaptation to microgravity.     

Prediction of horizontal gas–solid flows under different gravitational fields

In this paper the performance of horizontal pneumatic conveying under different gravity environments is evaluated. An Euler–Lagrange approach validated versus ground experiments is employed to predict the relevant particle variables such as particle mass flux, mean conveying and fluctuating velocities in terrestrial, lunar and micro-gravity conditions. Gravity reduced computations predict a reduction in the global particle–wall collision frequency. Also, in the case of low wall roughness and small particle mass loading, reduction of gravity acceleration implies an increase of particle–wall collision frequency with the upper wall of the channel affecting greatly the particle mass flux profile. In the case of high wall roughness and/or high particle-to-fluid mass loading (i.e., around 1.0) particle conveying characteristics are similar in the three gravity conditions evaluated. This is due to the fact that both, wall roughness and inter-particle collisions reduce gravitational settling. However, the influence of gravity on the additional pressure loss along the channel due to the conveying of the particles is much reduced.     

曲率对旋转态气膜冷却效率影响的数值模拟

通过对旋转状态下曲率叶片模型上气膜冷却现象的流动和换热进行数值模拟,得到了不同主流雷诺数、吹风比和旋转数情况下吸力面和压力面上的冷却效率分布.计算选用κ-ω和SST(Shear-Stress Transport)湍流模型,主流雷诺数Re=3 198.4~6 716.6,吹风比M=0.2~1.2,旋转数Rt=0~0.015 9.结果表明:旋转数的增大导致气膜孔下游中心区域的冷却效率下降,但使压力面整场的冷却效果略有提高;吹风比的增大使得吸力面和压力面上的冷却效率逐渐降低,主流雷诺数的变化对壁面整体冷却效果则影响不大.此外,相同工况下吸力面上的冷却效率要高于压力面上的对应值.     

A torus-shaped solar sail accelerated via thermal desorption of coating

A torus-shaped sail consists of a reflective membrane attached to an inflatable torus-shaped rim. The sail’s deployment from its stowed configuration is initiated by introducing inflation pressure into the toroidal rim with an attached circular flat membrane coated by heat-sensitive materials that undergo thermal desorption (TD) from a solid to a gas phase. Our study of the deployment and acceleration of the sail is split into three steps: at a particular heliocentric distance a torus-shaped sail is deployed by a gas inflated into the toroidal rim and the membrane is kept flat by the pressure of the gas; under heating by solar radiation, the membrane coat undergoes TD and the sail is accelerated via TD of coating and solar radiation pressure (SRP); when TD ends, the sail utilizes thrust only from SRP. We study the stability of the torus-shaped sail and deflection and vibration of the flat membrane due to the acceleration by TD and SRP.