Study on transient aerodynamic characteristics of parachute opening process

In the research of parachute, canopy inflation process modeling is one of the most complicated tasks. As canopy often experiences the largest deformations and loa-dings during a very short time, it is of great difficulty for theoretical analysis and experimental measurements. In this paper, aerodynamic equations and structural dynamics equations were developed for describing parachute opening process, and an iterative coupling solving strategy incorpo- rating the above equations was proposed for a small-scale, flexible and flat-circular parachute. Then, analyses were carried out for canopy geometry, time-dependent pressure difference between the inside and outside of the canopy, transient vortex around the canopy and the flow field in the radial plane as a sequence in opening process. The mechanism of the canopy shape development was explained from perspective of transient flow fields during the inflation process. Experiments of the parachute opening process were conducted in a wind tunnel, in which instantaneous shape of the canopy was measured by high velocity camera and the opening loading was measured by dynamometer balance. The theoretical predictions were found in good agreement with the experimental results, validating the proposed approach. This numerical method can improve the situation of strong dependence of parachute research on wind tunnel tests, and is of significance to the understanding of the mechanics of parachute inflation process.

The Structural Characteristics of Side-Opening Costumes during the Republic Period of China

The structural characteristics of Chinese side-opening costumes during the Republic Period of China were investigated.By measuring and recovering the physical structures of side-opening costume objects from the Folk Costumes Biography Museum of Jiangnan University,three structural characteristics were analyzed.These structural characteristics show that most of the side-opening costumes during the Republic Period of China remain traditional Chinese costume structures.The general structural characteristics of side-opening costumes are concluded and the structural cutting methods can inspire current designs as well as provide useful references for contemporary fashion designers.

Taking the Path of Poverty Reduction with Chinese Characteristics to Promote New Progress in China's Human Rights——A Keynote Speech at the Opening Ceremony of 2018 Beijing Forum on Human Rights

The 2018 Beijing Forum on Human Rights opens on this wonderful autumn day.On behalf of the China Society for Human Rights Studies, I wish to express warm congratulations on the opening of the forum and a sincere welcome to all guests from home and abroad.

Study on the Availability Opening Size of Throttle and Affection to the Velocity Characteristic of Shock Absorber

Based on the solution of the governing differential equation for deformation of throttle slice while satisfying required boundary conditions, the coefficient （Gr） and an analytical formula for computing the deformation of throttle slice is presented through equivalency transformation, which is a concise, accurate and practical method for throttle slice design and characteristic analysis. Researched the deformation at any radius, compared with ANSYS FEA software by the simulation analysis, the availability opening size of throttle that was defined by the deformation at the valve mouth radius is studied. The affection of valve mouth radius to the damper characteristic is analyzed. Tests are made for the damper characteristic, compared with simulation results, it is shown that Gr method is an accurate computation method for computing the deformation of throttle slice at valve mouth radius, suitihle to use in the damper design, analysis, and verification. The deformation at mouth radius could not be replaced with the outside radius.

Impact of depth ratio on flow structure and turbulence characteristics of compound open channel flows

Compound open channel flows appear in most natural rivers are of great importance in river management and flood control.In this study,large eddy simulations were carried out to simulate the compound open channel flows with four different depth ratios(hr=0.10,0.25,0.50,and 0.75).The main flow velocity,secondary flow,Reynolds stress,and bed shear stress were obtained from numerical simulations.The depth-averaged stream wise momentum equation was used to quantify the lateral momentum exchange between the main channel and floodplain.The instantaneous coherent structures were presented by the Q criterion method.The impact of hr on flow structure and turbulence charac-teristics was analyzed.The results showed that with the increase of hr,the high velocity area in the main channel shifted to the floodplain,and the dip phenomenon became more obvious;the Reynolds stress largely contributed to the lateral momentum exchange within the flows near the side walls of floodplain;and the vortex structures were found to significantly increase in the floodplain region.

Numerical Analysis for Temperature Characteristics of Open Boundary Crushed-rock Embankment on Qinghai-Tibet Railway

At present, in order to protect the stability of permafrost beneath emban kment, the crushed-rock emban kment, as a new type of emban kment structure, has widely been used in the construction of Qinghai-Tibet Railway. Its crushed-rock layer is almost open in tow bilateral boundaries and closed at top and bottom, and air can flow into/out of the ballast layer and crushed-rock layer. Therefore, the convection and transfer heat patterns are very complicated in the ballast layer and crushed-rock layer of the emban kment, which are regarded as porous media. In this paper, based on the wind, temperature and geology conditions of Qinghai-Tibet Plateau, a numerical approach of the unsteady two-dimensional continuity, momentum (non-Darcy flow) and energy equations of heat convection for incompressible fluid in porous media is provide to analyse the velocity and temperature characteristics of the crushed-rock emban kment with different emban kment heights under open boundary condition for the coming 50 years. The calculated results indicate that, due to the influence of the external wind, the convective heat transfer mainly relies on the forced convection in the open crushed-rock emban kment. Even if the air temperature will be warmed up by 2.6℃ in the coming 50 years, it still has a better cooling effect on the underlying soils and a low temperature frozen-soil core is formed in the permafrost below it if the emban kment is constructed in the regions whose present mean annual air temperature is -4.0℃. Furthermore, the cooling effect of high crushed-rock emban kment is better than that of low emban kment. This results from the fact that the wider bottom of high emban kment has a more influence dimension on the underlying frozen soil. However, cardinal winds on Qinghai-Tibet Plateau disturb its convection pattern, so that an asymmetric temperature distribution occurs under high emban kment and it is possible to induce a transverse uneven deformation of emban kment, but no similar situation occurs under low emban kment. This asymmetric temperature field problem should be considered when crushed-rock emban kment is designed and constructed.

XI JINPING THOUGHT ON SOCIALISM WITH CHINESE CHARACTERISTICS FOR A NEW ERA OPENS NEW HORIZON FOR INTERNATIONAL COMMUNIST MOVEMENT

The 19^(th) National Congress of the Communist Party of China(CPC)established Xi Jinping Thought on Socialism with Chinese Characteristics for a New Era as the guiding ideology of the CPC,marking a new leap forward in synthesizing basic principles of Marxism with China’s concrete conditions.This Thought enriches and develops scientific socialism,the guiding ideology of the International

甘肃积石山 M_(s)6.2级地震的震害特征与启示

2023年12月18日,甘肃省临夏回族自治州积石山保安族东乡族撒拉族自治县(35.70°N,102.79°E)发生了6.2级地震,震中烈度为VIII度。地震发生后,通过实地烈度评估与科学考察,对震区VI~VIII度区不同建(构)筑物与生命线工程的震害特点进行了统计分析;从抗震设计与施工管理、场地放大效应与地震次生灾害对建筑结构抗震性能的影响等角度,提出了此次地震的震害启示。结果表明:1)严重破坏和毁坏的建筑结构主要集中在老旧的土木结构、砖木结构和无设防或设防不规范的砖混结构。2)造成建筑结构破坏的主要原因是少量自建房抗震设计和施工的不规范、场地放大效应和地震次生灾害。3)优化和改良生土砌筑材料,改进纵横墙间的拉结措施,强化结构整体性是提高土木结构抗震的有效方法;普及“上下圈梁与构造柱”等基本抗震设防措施,规范水泥砂浆强度,提升农村工匠的施工水平,可有效提高砌体结构的整体性,避免房屋出现整体性垮塌;室内洗手间的墙体应该与房顶、纵横墙间建立有效联接,提高结构的抗震性能。4)孤突斜坡、河流高阶地与岸边为抗震不利地带。当建造用地极为匮乏,不得不选址在这些场地之上时,应该综合考虑场地的地形地貌特征、岩土体物理力学特性、水文地质条件、抗震设防目标、建筑结构类型等影响因素,做好地震灾害风险评估,根据评估结果进行科学设防。灾后重建过程中,应由政府统一规划选址、统一设计,规范施工。

K-S变换及其电网超谐波时频分析应用

依据FFT→优化窗→IFFT思路,突破线性时频变换的窗函数积分性能桎梏,实现高性能优化窗函数的线性时频变换应用,建立新型时频变换算法——K-S变换.对信号x(t)的FFT频谱向量进行频移处理后,与该频移点下Kaiser优化窗的频谱向量进行Hadamard乘积,再将乘积结果进行FFT逆变换(IFFT),构造出K-S变换复时频矩阵,由此获得x(t)的时间-频率-幅值、时间-频率-相位三维信息;给出逆变换的数学推导与局部性质、线性性质和变分辨率特性;0~150 kHz电网的稳态与时变超谐波信号仿真实验表明,K-S变换的时域、频域分辨能力均优于流行的短时傅里叶变换、S变换,具有优良的变分辨率性能;0~40 kHz超谐波信号的实测证明,基于K-S变换的超谐波电压幅值测量绝对误差均小于0.032 3 V.

改变导叶翼型对水泵水轮机“S”特性的影响

针对水泵水轮机“S”特性区域的不稳定性问题,提出使用改型活动导叶翼型进行性能提升.以某水泵水轮机模型为研究对象,采用SST k-ω湍流模型对水泵水轮机全流道进行三维数值计算,通过对活动导叶翼型的改型设计,得出流量-转速模拟曲线,分析水泵水轮机组“S”特性改善情况.将计算与试验结果进行对比,并对改型活动导叶翼型前后机组的无叶区进行压力脉动分析.结果表明:在保证整体效率依然保持在92%附近的前提下,新的活动导叶翼型对机组的“S”特性依旧具有改善效果;无叶区压力脉动主要是受到活动导叶叶栅区域的分流在此重新聚集影响,并且与转轮叶片的动静相互扰动引起的;改型后的活动导叶降低了无叶区的压力脉动幅值,提升了水泵水轮机运行中的并网稳定性.

基于哨兵函数和S变换的风力机叶片材料损伤特性研究

利用声发射检测技术研究玻璃纤维增强环氧树脂复合材料的损伤特性,在此过程中,采用哨兵函数来表征该材料的损伤程度,并通过S变换和模糊C均值(FCM)聚类来分析声发射信号,从而获得材料的损伤特征。三点弯曲实验结束后对试件断口进行扫描电子显微镜(SEM)拍照来验证,可得:通过对SEM照片的分析得到基体开裂、纤维脱粘、分层破坏、纤维断裂4种损伤模式;对整个声发射事件进行哨兵函数分析,观察到试件在弯曲过程中哨兵函数曲线呈明显下降趋势;对依据哨兵函数划分的不同阶段的信号进行VMD降噪处理,然后采用S变换进行时频分析得到不同损伤的特征频率,最后采用FCM聚类进行验证。结果表明:哨兵函数值的突变可作为材料断裂的预警信号,材料损伤类型的识别可依据S变换的频率分布结果进行确定。

电液3-UPS/S并联稳定平台参数振动特性分析

针对电液3-UPS/S并联稳定平台驱动液压缸的压力脉动所产生的参数振动,建立了稳定平台的参数振动方程并利用多尺度法求解了主共振响应与组合共振响应的一次近似解;分析了主共振与组合共振响应特性以及振动幅值在初始工作空间内的变化规律,最后采用四阶龙格库塔法与模态试验对参数振动模型进行验证。结果表明:数值解与理论解之间的最大误差为4.20%,固有频率理论值与试验值之间的最大误差为4.66%,可验证参数振动模型的正确性。

Isolation and algae-lysing characteristics of the algicidal bacterium B5

Water blooms have become a worldwide environmental problem. Recently, algicidal bacteria have attracted wide attention as possible agents for inhibiting algal water blooms. In this study, one strain of algicidal bacterium B5 was isolated from activated sludge. On the basis of analysis of its physiological characteristics and 16S rDNA gene sequence, it was identified as Bacillusfusiformis. Its algaelysing characteristics on Microcystis aeruginosa, Chlorella and Scenedesmus were tested. The results showed that： （1） the algicidal bacterium B5 is a Gram-negative bacterium. The 16S rDNA nucleotide sequence homology of strain B5 with 2 strains of B. fusiformis reached 99.86%, so B5 was identified as B. fusiformis; （2） the algal-lysing effects of the algicidal bacterium B5 on M. aeruginosa, Chlorella and Scenedesrnus were pronounced. The initial bacterial and algal cell densities strongly influence the removal rates of chlorophyll-a. The greater the initial bacterial cell density, the faster the degradation of chlorophyll-a. The greater the initial algal cell density, the slower the degradation of chlorophyll-a. When the bacterial cell density was 3.6 × 10^7 cells/ml, nearly 90% of chlorophyll-a was removed. When the chlorophyll-a concentration was less than 550 μg/L, about 70% was removed; （3） the strain B5 lysed algae by secreting metabolites and these metabolites could bear heat treatment.

Kinematic and Dynamic Characteristics Analysis of Bennett's Linkage

Bennett's linkage is a spatial fourlink linkage,and has an extensive application prospect in the deployable linkages.Its kinematic and dynamic characteristics analysis has a great significance in its synthesis and application. According to the geometrical conditions of Bennett 's linkage,the motion equations are established,and the expressions of angular displacement,angular velocity and angular acceleration of the followers and the displacement,velocity and acceleration of mass center of link are shown. Based on Lagrange's equation,the multi-rigid-body dynamic model of Bennett's linkage is established. In order to solve the reaction forces and moments of joint,screw theory and reciprocal screw method are combined to establish the computing method.The number of equations and unknown reaction forces and moments of joint are equal through adding link deformation equations. The influence of the included angle of adjacent axes on Bennett 's linkage 's kinematic characteristics,the dynamic characteristics and the reaction forces and moments of joint are analyzed.Results show that the included angle of adjacent axes has a great effect on velocity,acceleration,the reaction forces and moments of Bennett's linkage. The change of reaction forces and moments of joint are apparent near the singularity configuration.

Interaction of Oblique Waves and A Rectangular Structure with An Opening Near A Vertical Wall

With the method of separation of variables and the eigenfunction expansion employed, an analytical solution is presented for the radiation and diffraction of a rectangular structure with an opening near a vertical wall in oblique seas, in which the unknown coefficients are determined by the boundary conditions and matching requirement on the interface. The effects of the width of the opening and the angle of incidence on the hydrodynamic characteristics of a rectangular structure with an opening near a vertical wall are mainly studied. The comparisons of the calculation results with wall-present and with wall-absent are also made. The results indicate that the variation trends of the heave added mass and excitation force with wall-present are almost the same as those with wall-absent, and that the peak values in the former case are obviously larger than those in the latter due to the reflection of the vertical wall.

水泵水轮机S特性区能量损失及流动特性研究

为了调节电网的稳定性,抽水蓄能电站需要频繁启停和变换工况运行,导致水泵水轮机容易进入S特性区,机组振动增加,并网失败。本文以模型水泵水轮机为研究对象,采用熵产理论详细分析了S特性区不同工况下的能量损失规律,明确了熵产率分布与内部流动结构的关系。结果表明:S特性区内近飞逸工况总熵产最大,约为设计工况的5.1倍,脉动熵产占据的比例接近80%,随着流量的减小,转轮熵产占比逐渐降低,活动导叶和尾水管的熵产占比增加。小流量工况转轮进口靠近下环位置首先出现了明显的漩涡,导致了活动导叶出口和转轮进口的高熵产区,随着流量进一步减小,漩涡逐渐向上冠转移,并且切向速度增大,在转轮进口形成挡水环,阻碍水流进入转轮,在无叶区内出现了环状分布的高熵产区。反水泵工况,水流在低压边与逆时针旋转的叶片撞击,导致水流很难进入叶片内部,形成了大尺度的回流涡结构;双列叶栅内充满大量涡结构,导致活动导叶吸力面的熵产率增大,并且向固定导叶传播。

蒲石河电站水泵水轮机转轮S特性优化研究

针对蒲石河抽水蓄能电站机组启动和甩负荷时水泵水轮机转轮S特性诱发的厂房振动问题,本文基于CFD数值仿真计算和模型试验对机组原9叶片转轮的S特性进行了分析研究,发现在S区工况运行时原转轮进口存在回流区,产成较大的水力损失,从而造成转轮的通流能力下降。基于此发现,本研究提出将9叶片转轮改为7叶片转轮的优化方案。通过对比CFD仿真结果及试验验证,新方案的转轮进口回流现象得到调整,从而有效改善了转轮“S”特性,解决了厂房振动的源头问题。实际工程的应用证明新方案起到了很好的效果,本方案思路可为同类型电站类似问题解决及老旧抽水蓄能电站改造提供参考借鉴。

Effects of Drought Stress Simulated by Polyethylene Glycol on Seed Germination, Root and Seedling Growth, and Seedling Antioxidant Characteristics in Job’s Tears

Two Job’s tears cultivars, yy18-1 (high resistance to drought stress) and yy12-7 (susceptible to drought stress) were used to investigate the responses of seed germination, root and seedling growth, and seedling antioxidant characteristics to drought stress simulated by polyethylene glycol (PEG) 6000 solutions with 0, -0.05, -0.1, -0.15, and -0.2 MPa osmotic potentials. The results showed that the germination energy, germination rate, germination index, root and seedling lengths, root and seedling diameters, root and seedling fresh masses, root and seedling dry masses, and seedling relative water content (RWC) decreased with the decrease of the osmotic potential of PEG 6000 solution. The contents of hydrogen peroxide (H2O2), malondialdehyde (MDA), and proline in seedling increased with the decrease of the osmotic potential of PEG 6000 solution. The activities of peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) in seedling increased and then decreased with the decrease of osmotic potential of PEG 6000 solution. -0.1 MPa was the optimal osmotic potential of PEG 6000 solution simulated drought stress at germination stage for Job’s tears. The proline content and activities of POD and CAT were important mechanisms for the maintenance of drought resistance in Job’s tears seedling.

基于线路阻抗特性的SOP低电压穿越控制策略

分布式新能源出力具有波动性,且接入位置不均匀,当其规模化接入配电网后将增大发生故障的概率。在配电网发生故障时,增强并网电力电子设备的低电压穿越(low voltage ride through,LVRT)性能是保障配电网稳定运行的技术关键,已成为当前研究热点之一。以柔性互联配电网中的柔性电力电子开关(soft open point,SOP)为对象,结合配电网馈线线路阻抗特性,提出一种基于线路阻抗特性的SOP LVRT控制策略。首先,分析线路阻抗对换流器接入公共耦合点(point of common coupling,PCC)电压的影响,并推导出利用换流器注入功率抬升电压的机理;其次,提出基于馈线出线侧及换流器本地量测数据的PCC点至故障点的线路等效阻抗测量方法;然后,构建基于阻抗测量法的SOP LVRT整体策略;最后,在PSCAD仿真平台上验证所提控制策略,结果表明,在不同电压跌落范围内,所提SOP LVRT控制策略能同时补偿有功功率和无功功率,较仅采用无功补偿能更明显提升PCC电压水平。