Reliability design optimization of composite structures based on PSO together with FEA

The present work aims to develop a method for reliability-based optimum design of composite structures. A procedure combining particle swarm optimization (PSO) and finite element analysis (FEA) has been proposed. Numerical examples for the reliability design optimization (RDO) of a laminate and a composite cylindrical shell are worked out to demonstrate the effectiveness of the method. Then a design for composite pressure vessels is studied. The advantages and necessity of RDO over the conventional equi-strength design are addressed. Examples show that the proposed method has good stability and is efficient in dealing with the probabilistic optimal design of composite structures. It may serve as an effective tool to optimize other complicated structures with uncertainties.     

Independent modal variable structure fuzzy active vibration control of thin plates laminated with photostrictive actuators

Photostrictive actuators can produce photodeformation strains under illumination of ultraviolet lights. They can realize non-contact micro-actuation and vibration control for elastic plate structures. Considering the switching actuation and nonlinear dynamic characteristics of photostrictive actuators, a variable structure fuzzy active control scheme is presented to control the light intensity applied to the actuators. Firstly, independent modal vibration control equations of photoelectric laminated plates are established based on modal analysis techniques. Then, the optimal light switching function is derived to increase the range of sliding modal area, and the light intensity self-adjusting fuzzy active controller is designed. Meanwhile, a continuous function is applied to replace a sign function to reduce the variable structure control (VSC) chattering. Finally, numerical simulation is carried out, and simulation results indicate that the proposed control strategy provides better performance and control effect to plate actuation and control than velocity feedback control, and suppresses vibration effectively.     

Analysis and improvement of ionospheric thin shell model used in SBAS for China region

The most frequently used mapping function for converting slant total electron content (STEC) to vertical total electron content (VTEC) uses a simplified ionospheric single layer model in satellite based augmentation system (SBAS). Aiming at ionospheric single layer model altitude variation, we analyzed the statistical characteristic of mapping function in systemic approach particular for the region of China, and then experimental mapping function was proposed. The experimental mapping function is used in SBAS ionospheric correction and the precision of vertical correction is compared with standard mapping function. The results show that conversion factor errors depend on latitude, time and elevation, experimental mapping function is helpful to the vertical TEC estimation and may improve the precision of SBAS ionospheric refraction correction especially for the low latitude region of China.     

Robotic Instrument for Grinding Rocks Into Thin Sections (GRITS)

We have developed a rock grinding and polishing mechanism for in situ planetary exploration based on abrasive disks, called Grinding Rocks Into Thin Sections (GRITS). Performance characteristics and design considerations of GRITS are presented. GRITS was developed as part of a broader effort to develop an in situ automated rock thin section (ISARTS) instrument. The objective of IS-ARTS was to develop an instrument capable of producing petrographic rock thin sections on a planetary science spacecraft. GRITS may also be useful to other planetary science missions with in situ instruments in which rock surface preparation are necessary.     

空间薄壁式伸展臂的展开仿真与卷曲方式研究

针对一种完全依靠自身弹性展开的空间柔性薄壁式伸展臂的展开动力学问题,基于Kirchhoff Love基本假设和广义胡克定律推导了伸展臂各部分壳体在展开前的应力计算公式,使用该公式对伸展臂的有限元模型进行预应力初始化,并采用显式时间积分方法对正向卷曲、反向卷曲和不紧密卷曲的空间薄壁式伸展臂的展开过程进行了动力学仿真,通过实验对仿真结果进行了验证。研究结果表明：应力计算公式可以正确地计算薄壁式伸展臂在展开前的应力状态,基于预应力初始化方法的显式动力学仿真可以较为准确地模拟空间薄壁式伸展臂的展开过程;反向卷曲的伸展臂在展开过程中出现了向固定段展开的现象,并且具有较高的初始应变能,不利于薄壁式伸展臂的空间应用,在设计中应选择正向卷曲的方式;不紧密卷曲的影响主要表现为卷曲段内层壳体易于从卷曲段侧边缘滑出,使伸展臂在展开过程中产生较大幅度扭转,而增大壳体材料的摩擦系数则可以有效避免这种现象。     

航天器异种金属钎焊接头静态裂纹行为分析

采用高频感应钎焊方法连接了航天推进系统的异种金属(钛合金与不锈钢)薄壁小直径导管结构,结构的质量和性能远远优于螺栓连接的导管结构.钎焊接头静态拉伸试验发现,银基钎料钎焊的接头承载能力要优于铜基钎料.对静态拉伸断裂接头的微观组织进行了分析,结果发现,银基钎料钎焊的接头区域出现的裂纹仅在钎缝区域萌生和扩展,当裂纹扩展到钎缝与母材的界面位置时停止扩展.铜基钎料钎焊的接头区域的裂纹从3个位置萌生:钎缝2种组织的交界处,钎缝与钛合金、不锈钢的界面.裂纹驱动力主要是由静态拉伸载荷和异种金属钎焊接头失配行为构成的,而裂纹扩展抗力主要与钎焊接头的微观组织有关.     

空间充气薄膜衍射成像结构的热力耦合分析

随着空间光学技术的发展,衍射成像系统成为空间光学领域的研究热点。提出了一种充气薄膜衍射成像结构设计方案,针对其在空间热载荷作用下的热力耦合效应开展研究。建立了充气薄膜衍射成像结构的热力耦合顺序分析框架,基于I DEAS和ANSYS软件二次开发技术,实现了热力耦合数值分析,得到了结构在轨运行时的瞬态温度场、热应力、热变形等。分析结果表明,充气支撑结构产生了较大热变形,但最大热应力远小于聚酰亚胺薄膜材料的抗拉强度,而镜面中心处没有出现较大的热变形响应,为充气薄膜衍射成像结构的防热设计提供了技术支持。     

δ0.05mm薄钢带力学性能测试方法研究

研究了拉伸速率、试样类型、试样表面状态对δ0.05mm薄钢带力学性能测试的影响,通过数据对比,结果表明：拉伸速率对薄钢带的力学性能测试结果影响并不大,而试样的类型和试样的表面状态对力学性能测试结果有很大的影响;表面无缺陷的哑铃型试样可以满足检测要求,提高钢带检验一次合格率。     

并列双方柱的疏水涂层防冰效果结冰风洞实验评估

采用结冰风洞实验研究的方法,利用0.3m×0.2m结冰风洞主实验段,在不同结冰气象条件下对涂覆在并列双方柱实验模型表面的不同纳米疏水涂层结冰特性进行了实验研究,对左右并排的方柱实验模型表面的结冰外形进行了测量和比较,建立了基于9个结冰外形几何特征量的防冰效果量化评估方法,对有、无纳米疏水涂层表面的结冰外形几何特征量无量纲化偏差进行了计算和分析。研究表明:基于结冰外形几何特征量的防冰效果量化评估方法可以较好地评估纳米疏水涂层的防冰效果。与未涂覆防冰涂层的铝合金材料相比,硅橡胶及其添加颗粒的纳米涂层均具有一定的防冰性能,与硅橡胶涂层相比,有的添加颗粒的纳米涂层防冰效果略好一点,而有的略差一点,没有明显提高。在硅橡胶基底材料中添加纳米疏水颗粒,可以在涂层表面构筑一些微纳结构,从而起到防冰作用。因此,在硅橡胶涂层中添加纳米疏水颗粒是一种值得探索的防冰涂层制备研究方向,但如果仅采用物理混合搅拌的方法,纳米颗粒难以在硅橡胶涂层表面形成稳定疏水性能的微纳乳突结构。纳米疏水涂层只能降低结冰速率,无法完全杜绝材料表面的结冰现象。      

Reduction of vibration by periodically stitched sandwich panel

This work reveals that the addition of periodically distributed stitches to sandwich structure enables a significant reduction of vibration in stop-band and this new functionality is systematically investigated. Firstly, a finite element model which is capable of taking into consideration the three layers of the sandwich as well as the stitches is developed. The diagram of dispersion is calculated by applying Floquet-Bloch theorem to the boundaries of unit cell. With properly chosen properties of stitches, a stop-band for flexural wave is observed. This stop-band is further confirmed by the forced response of a large stitched sandwich panel under point excitation. The level of vibration in the stop-band is significantly reduced. The influence of the stitch rigidity and density on upper and lower limits of stop-band is also examined, which confirms that stitched sandwich can be tuned to mitigate vibration in a certain frequency band with appropriate stitch properties. These investigations have demonstrated the potential application of stitched sandwich in the area of vibration reduction.