检索结果-南通市图书馆

共底贮箱内液体晃动动力学特性研究及实验验证

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2023年第12期39卷 115-125页

作者：马伯乐岳宝增刘峰卢煜柳翠翠关晓东 School of Aerospace engineering Beijing Institute of Technology Beijing China Beijing Institute of Spacecraft System Engineering Beijing China

本文通过数值方法、实验方法和等效力学模型方法研究了共底贮箱内液体晃动的动力学特性.研究结果表明,一阶晃动频率随着充液比的增加而增大.然而,二阶晃动频率随着充液比的增加而减小.通过两个算例来验证改进的移动脉动球模型,其结果与... 详细信息

本文通过数值方法、实验方法和等效力学模型方法研究了共底贮箱内液体晃动的动力学特性.研究结果表明,一阶晃动频率随着充液比的增加而增大.然而,二阶晃动频率随着充液比的增加而减小.通过两个算例来验证改进的移动脉动球模型,其结果与数值和实验结果非常吻合.此外,通过CFD研究了CBH槽内非线性液体晃动的复杂多模态或高阶模态特征,结果表明,在强迫激励下能明显观察到高阶晃动模态.最后,通过实验揭示了共底贮箱内的旋转晃动和对称旋转晃动现象.发现由于激励振幅和激励频率的数值变化,旋转晃动会变得不稳定,并发展为对称旋转晃动.对称旋转晃动将以特定的节奏间歇性地开始,这取决于激励的频率.

关键词：晃动频率液体晃动等效力学模型充液比球模型高阶模态多模态激励频率

Orbit Design Elements of Chang’e 5 Mission

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Space(Science & Technology) 2021年第1期2021卷 28-49页

作者： Zhong-Sheng Wang Zhanfeng Meng Shan Gao Jing Peng Beijing Institute of Spacecraft System Engineering Beijing 100094China

The three key orbit design technologies employed in the Chang’e 5 mission are identified and discussed in this paper:orbit design for lunar orbit rendezvous and docking,orbit design for precision lunar landing and inclination optimization,and orbit design for Moon-to-Earth transfer.First,an overview of the Chang’e 5 mission profile is presented,which is followed by detailed discussions of the three key orbit design technologies,including an introduction of the tracking-based orbit design methodology.Flight data are provided to demonstrate the correctness of the designs.

关键词： discussions orbit Earth

An Optimal Bit-Rate Allocation Algorithm to Improve Transmission Efficiency of Images in Deep Space Exploration

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

China Communications 2020年第7期17卷 94-100页

作者： Yong Xu Jionghui Li Xiangyu Lin Fan Bai Beijing Institute of Spacecraft System Engineering Beijing100094

As fixed compression ratio is used in traditional deep space exploration image transmission application,the same compression code rate is allocated to each image.However,since the information of each image in a space observation mission is nonuniform,the image with more information will inevitably lead to more compression distortion than the image with less information.Obviously,it’s not an efficient way to transmit information in terms of data importance or overall distortion.Therefore,we proposed a combinatorial optimal bit rate allocation algorithm to improve the efficiency of image transmission in space application.Different from traditional method,the rate-distortion model of wavelet coefficients for each image in a transmission task was built,and under the overall maximum transmission rate constraint,an bit-rate optimal allocation was applied for each image to minimize the overall distortion of a batch of images.The proposed algorithm can be widely used in image compression algorithm with embedded code stream characteristics,such as JPEG2000 and SPIHT.Experimental results shows that in the range of 2.6 to 10 compression ratio,the algorithm can reduce image distortion MSB by 40%~64%at the same overall transmission code rate,which equivalent to improvement of PSNR 3 dB to 5.4 dB.

关键词： JPEG2000 Efficiency distortion

Adaptive ANCF method and its application in planar flexible cables

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2018年第1期34卷 199-213页

作者： Yue Zhang Cheng Wei Yang Zhao Chunlin Tan Yongjian Liu Department of Aerospace engineering Harbin Institute of Technology Institute of Spacecraft System Engineering CAST

In the conventional absolute nodal coordinate formulation(ANCF), the model is pre-meshed, the number,distribution and type of elements are unchangeable during the simulation. In addition, the deformations of a flexible body are space-varying and time-varying, one cannot predict when, where, and how the deformations will occur. Therefore, in order to obtain a satisfactory accuracy during the whole simulation, the model is usually densely meshed, but it will result in a loss of computational efficiency. In this study,an adaptive absolute nodal coordinate formulation(AANCF)is proposed to optimize the accuracy and efficiency of flexible dynamics. The movement features of flexible bodies are analyzed, and the conventional and adaptive ANCF methods are compared. Then the adaptive computation strategy is presented. The discretization errors come from the inability of interpolation functions of individual elements to capture the complexity of the exact solution, so the mesh can be adaptively optimized by changing the element sizes or the orders of interpolation functions during dynamic computation. Important issues of AANCF, including error estimation,mesh updating, and performance of the AANCF model, are analyzed and discussed in detail. A theoretical model of a planar AANCF cable is presented, where the strategies of dividing and merging elements are discussed. Moreover, the continuity of dynamic variables is deduced, and the mean factors that affect the continuity are obtained, which is very important for the subsequent continuity optimization. Thesimulation results indicate that the distribution of elements varies with time and space, and the elements are denser in large-deformed domains. The AANCF model improved the computational accuracy and efficiency, but the system energy is discontinuous when the elements are merged. Therefore,a continuity-optimized AANCF model is given based on the previous continuity analysis, the results show that the accuracy and continuity of energy are further improved by the continuity-o

关键词： Absolute nodal coordinate formulation Adaptive computation Continuity Accuracy Efficiency

Precipitate Characteristics and Mechanical Performance of Cast Mg–6RE–1Zn–xCa–0.3Zr(x=0 and 0.4 wt%) Alloys

在线全文

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English Letters) 2022年第4期35卷 596-608页

作者： Zijian Yu Xi Xu Baotian Du Kang Shi Ke Liu Shubo Li Xiuzhu Han Tao Xiao Wenbo Du College of Materials Science and engineering Beijing University of TechnologyBeijing 100124China Beijing Institute of Spacecraft System Engineering Beijing 100094China

In this study,the Mg–4Y–1Gd–1Nd–xCa–1Zn–0.3Zr(x=0 and 0.4 wt%)cast alloys with low rare earth concentration were prepared in different routes of heat treatments,and their microstructures and mechanical properties were investigated.The Mg–4Y–1Gd–1Nd–1Zn–0.4Ca–0.3Zr cast alloy with ultimate tensile strength(UTS)of 264±7.8 MPa,tensile yield strength(TYS)of 153±1.2 MPa and elongation to failure(EL)of 17.2±1.2% was successfully developed by appropriate heat treatment.The improved mechanical performance was attributed to the combined strengthening effects of fine grains,Mg24RE5,β′,β_(1),γ′and LPSO phases.In the heat treatment process,cooling method of T4 treatment affected the microstructure,which consequently determined the mechanical properties air cooling,rather than water cooling,gave rise to the formation of γ′phase in the alloy without Ca addition.However,Ca addition facilitated the formation of γ′phase,and the γ′phase precipitated in the alloy after T4 treatment either by water cooling or by air cooling,but the air cooling increased the number density of γ′phase in comparison to the water cooling.Although the γ′phase strengthened the studied alloys,the formation of γ′phase inhibited the precipitatition of β′and β_(1) phases in the following T6 treatment,and consequently reduced the strengthening effect ofβ′andβ_(1) phases.The results showed that the mechanical performance of the studied alloys was largely determined by the precipitation of γ′phase,which was regulated by the Ca addition and the cooling method of T4 treatment.

关键词： Magnesium alloy Microstructure Mechanical properties Rare earth Heat treatment

Task-Oriented Topology system Synthesis of Reconfigurable Legged Mobile Lander Integrating Active and Passive Metamorphoses

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Mechanical engineering 2023年第3期36卷 89-109页

作者： Youcheng Han Ziyue Li Gaohan Zhu Weizhong Guo Jianzhong Yang Wei Liu State Key Lab of Mechanical system and Vibration School of Mechanical EngineeringShanghai Jiao Tong UniversityShanghai 200240China Beijing Institute of Spacecraft System Engineering Beijing 100094China

To explore hostile extraterrestrial landforms and construct an engineering prototype,this paper presents the task-oriented topology system synthesis of reconfigurable legged mobile lander(ReLML)with three operation modes from adjusting,landing,to roving.Compared with our preceding works,the adjusting mode with three rotations(3R)provides a totally novel exploration approach to geometrically matching and securely arriving at complex terrains dangerous to visit currently;the landing mode is redefined by two rotations one translation(2R1T),identical with the tried-and-tested Apollo and Chang'E landers to enhance survivability via reasonable touchdown buffering motion;roving mode also utilizes 2R1T motion for good motion and force properties.The reconfigurable mechanism theory is first brought into synthesizing legged mobile lander integrating active and passive metamorphoses,composed of two types of metamorphic joints and metamorphic execution and transmission mechanisms.To reveal metamorphic principles with multiple finite motions,the finite screw theory is developed to present the procedure from unified mathematical representation,modes and source phase derivations,metamorphic joint and limb design,to final structure assembly.To identify the prototype topology,the 3D optimal selection matrix method is proposed considering three operation modes,five evaluation criteria,and two topological subsystems.Finally,simulation verifies the whole task implementation process to ensure the reasonability of design.

关键词： Legged mobile lander Topology synthesis Active and passive metamorphoses Finite screw Metamorphic joint Reconfigurable mechanism

Microstructure,Texture Evolution,and Strain Hardening Behaviour of As-extruded Mg-Zn and Mg-Y Alloys under Compression

在线全文

学校读者我要写书评

暂无评论

Journal of Wuhan University of Technology(Materials Science) 2023年第2期38卷 430-439页

作者： HAN Xiuzhu XIAO Tao YU Zijian Beijing Institute of Spacecraft System Engineering Beijing100094China Faculty of Materials and Manufacturing Beijing University of TechnologyBeijing100124China

Microstructure,texture evolution and strain hardening behaviour of the Mg-1Y and Mg-1Zn(wt%)alloys were investigated under room temperature compression.Microstructural characterization was performed by optical microscopy,scanning electron microscopy,electron back scattered diffraction and transmission electron microscopy.The experimental results show that Mg-1Zn alloy exhibits conventional three-stage strain hardening curves,while Mg-1Y alloy exhibits novel six-stage strain hardening curves.For Mg-1Y alloy,rare earth texture leads to weak tensile twinning activity in compression and consequently results in a moderate evolution totexture.Moreover,inefficient tensile twinning activity and weak slip-twinning interaction give rise to excellent ductility and high hardening capacity but low strain hardening rate.For Mg-1Zn alloy,basal texture leads to pronounced tensile twinning activity in compression and consequently results in rapid evolution totexture.The intense tensile twinning activity and strong slip-twinning interaction lead to high strain hardening rate but poor ductility and low hardening capacity.

关键词： magnesium alloy texture rare earth twinning strain hardening behavior

Establishment and Optimization of Ablation Surrogate Model for Thermal Protection Material

在线全文

学校读者我要写书评

暂无评论

Journal of Beijing institute of Technology 2023年第4期32卷 477-493页

作者： Weizhen Pan Bo Gao Beijing Institute of Spacecraft System Engineering Beijing 100094China School of Astronautics Harbin Institute of TechnologyHarbin 150001China

The temperature response calculation of thermal protection materials,especially ablative thermal protection materials,usually adopts the ablation model,which is complicated in process and requires a large amount of calculation.Especially in the process of optimization calculation and parameter identification,the ablation model needs to be called many times,so it is necessary to construct an ablation surrogate model to improve the computational efficiency under the premise of ensuring the accuracy.In this paper,the Gaussian process model method is used to construct a thermal protection material ablation surrogate model,and the prediction accuracy of the surrogate model is improved through optimization.

关键词： ablation surrogate model thermal protection material

Preload relaxation analysis and reliable life prediction of space connection and separation device based on accelerated degradation tests

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2023年第3期36卷 202-211页

作者： Gen LIU Qiong WU Zhihua WANG Yixin LUO Yufeng QI School of Aeronautic Science and engineering Beihang UniversityBeijing 100191China Institute of Spacecraft System Engineering China Academy of Space TechnologyBeijing 100081China

The safety and reliability of space connection and separation device has become a key issue due to the increasing service span of deep space exploration mission.The long-term preload relaxation(a key failure mode)of connection and separation devices is focused in this paper.A series of tests have been designed and implemented to investigate the preload relaxation regulation and a comprehensive method has been constructed to analyze and predict the reliable lifetime of the device.The two-stage preload relaxation law of the device is found and reasonably considered.Due to the different relaxation mechanism,the first-stage preload relaxation is assessed based on the working-condition test results,and the second-stage preload relaxation is characterized by accelerated test results.Finally,the service reliability and reliable life are evaluated.The experiment and assessment results demonstrate the reasonability and effectiveness of the proposed method which can achieve long-service reliability analysis for space connection and separation device within limited time.

关键词： Accelerated degradation tests Life prediction Preload relaxation Reliability-analysis Space connection and separation device