Aerodynamic shape and drag scaling law of a flexible fibre in a flowing medium

The study of a flexible body immersed in a flowing medium is one of the best way to find its aerodynamic shape.This Letter revisited the problem that was first studied by Alben et al.(Nature 420,479–481,2002).To determine the aerodynamic shape of the fibre,a simpler approach is proposed.A universal drag scaling law is obtained and the universality of the Alben-Shelley-Zhang scaling law is confirmed by using dimensional analysis.A complete Maple code is provided for finding aerodynamic shape of the fibre in the flowing medium.

High loading carbon nanotubes deposited onto porous nickel yarns by solution imbibition as flexible wire-shaped supercapacitor electrodes

The deposition of active materials directly onto metal wires is a general strategy to prepare wire-shaped electrodes for flexible and wearable energy storage devices. However, it is still a critical challenge to coat active materials onto the aimed metal wires because of their smooth surface and small specific surface area. In this work, high porous nickel yarns（PNYs） was fabricated using commercial nylon yarns as templates through step-wise electroless plating, electroplating and calcination processes. The PNYs are composed of multiplied fibers with hollow tubular structure of 5–10 μm in diameter, allowing the imbibition of carbon nanotubes（CNTs） solution by a facile capillary action process. The prepared CNTs/PNY electrodes showed a typical electrochemical double layer capacitive performance and the constructed allsolid flexible wire-shaped symmetric supercapacitors provided a specific capacitance of 4.67 F/cm3 with good cycling stability at a current density of 0.6 A/cm3.

Influences of the Helical Strake Cross-Section Shape on Vortex-Induced Vibrations Suppression for A Long Flexible Cylinder

An experimental study on a bare flexible cylinder as well as cylinders fitted with two types of cross-sectioned helical strakes was carried out in a towing tank. The main purpose of this paper is to investigate the effects of strakes’ cross-section on the vortex-induced vibrations （VIV） suppression of a flexible cylinder. The square-sectioned and round-sectioned helical strakes were selected in the experimental tests. The uniform current was generated by towing the cylinder models along the tank using a towing carriage. The Reynolds number was in the range of 800–16000. The strain responses were measured by the strain gages in cross-flow （CF） and in-line （IL） directions. A modal analysis method was adopted to obtain the displacement responses using the strain signals in different measurement positions. The comparison of the experimental results among the bare cylinder, square-sectioned straked cylinder and round-sectioned straked cylinder was performed. The helical strakes can effectively reduce the strain amplitude, displacement amplitude, response frequencies and dominant modes of a flexible cylinder excited by VIV. And the mean drag coefficients of straked cylinders were approximately consistent with each other. In addition, the square-sectioned and round-sectioned strakes nearly share the similar VIV reduction behaviors. Sometimes, the strakes with round-section represent more excellent effects on the VIV suppression of response frequency than those with square-section.

Experimental Study on Mechanism and Shape Characteristics of Suspended Flexible Dam

Hydraulic structures such as groin, longitudinal dike and seawall are common in water conservancy and water transportation engineering projects at home and abroad, which have long been dominated by solid mass structural form. With brush and stone as building materials, this kind of structure has an obvious engineering effect. However, it not only requires huge capital investments, but also has negative impacts on the ecological environment. The suspended flexible dam is an innovative engineering measure, and few theoretical and experimental researches of this type dam can be found at present. This paper studies the mechanism and shape characteristics of this dam and obtains the dynamic equilibrium equation of flexible dam, the float buoyancy expression, and the condition for transformation among three forms of the underwater shape of the dam. The results are valuable in engineering application and can be used as the reference for the future work due to the distinctive design philosophy, the small negative effects on environment and the consistency for sustainable development.

A Flexible Hingeless Control Surface Inspired by Aquatic Animals

A flexible hingeless control surface model was proposed for motion control of Underwater Vehicles (UVs),which is inspiredby the flexible bending control surfaces of underwater creatures,such as fish and squid.Computational Fluid Dynamics(CFD) simulation demonstrates that,in comparison with the hinged or rigid control surface,the proposed flexible bendingcontrol surface can suppress the flow separation so as to improve the turning performance.A prototype of the flexible controlsurface was fabricated,in which Shape Memory Alloy (SMA) wires were selected as the actuators.The elastic energy storageand exchange mechanism was incorporated into the actuation of the control surface to improve the efficiency.Thermal analysisof SMA wires was performed to find proper actuating condition.Open-loop bending experiments were carried out.The resultsshow that the proposed control surface can achieve the maximum bending angle of 104°.Moreover,the power and energyconsumption under different pulse conditions were compared.

ON THE DYNAMIC MODELING AND CONTROL OF 2-DOF PLANAR PARALLEL MECHANISM WITH FLEXIBLE LINKS

The object of study is about dynamic modeling and control for a 2degree-of-freedom (DOF) planar parallel mechanism (PM) with flexible links. The kinematic anddynamic equations are established according to the characteristics of mixed rigid and flexiblestructure. By using the singular perturbation approach (SPA), the model of the mechanism can beseparated into slow and fast subsystems. Based on the feedback linearization theory and inputshaping technique, the large scale rigid motion controller and the flexible link vibrationcontroller can be designed separately to achieve fast and accurate positioning of the PM.

GENERAL SOLUTION FOR U-SHAPED BELLOWS OVERALL-BENDING PROBLEMS

The formulae for stresses and angular displacements of U-shaped bellows overall bending in a meridian plane under pure bending moments are presented based on the general solution for slender ring shells proposed by Zhu Weiping, et al. and the solution for ring plates. The results evaluated in this paper are compared with those on EJMA (standards of the expansion joint manufacturers association) and of the experiment given by Li Tingxilz, et al.

A Shape-Memory Deployable Subsystem with a Large Folding Ratio in China’s Tianwen-1 Mars Exploration Mission

Once China’s Tianwen-1 Mars probe arrived in a Mars orbit after a seven-month flight in the deep cold space environment,it would be urgently necessary to monitor its state and the surrounding environment.To address this issue,we developed a flexible deployable subsystem based on shape memory polymer composites(SMPC-FDS)with a large folding ratio,which incorporates a camera and two temperature telemetry points for monitoring the local state of the Mars orbiter and the deep space environment.Here,we report on the development,testing,and successful application of the SMPC-FDS.Before reaching its Mars remote-sensing orbit,the SMPC-FDS is designed to be in a folded state with high stiffness;after reaching orbit,it is in a deployed state with a large envelope.The transition from the folded state to the deployed state is achieved by electrically heating the shape memory polymer composites(SMPCs);during this process,the camera on the SMPC-FDS can capture the local state of the orbiter from multiple angles.Moreover,temperature telemetry points on the SMPC-FDS provide feedback on the environment temperature and the temperature change of the SMPCs during the energization process.By simulating a Mars on-orbit space environment,the engineering reliability of the SMPC-FDS was comprehensively verified in terms of the material properties,structural dynamic performance,and thermal vacuum deployment feasibility.Since the launch of Tianwen-1 on 23 July 2020,scientific data on the temperature environment around Tianwen-1 has been successfully acquired from the telemetry points on the SMPCFDS,and the local state of the orbiter has been photographed in orbit,showing the national flag of China fixed on the orbiter.

Wire-Shaped 3D-Hybrid Supercapacitors as Substitutes for Batteries

We report a wire-shaped three-dimensional(3D)-hybrid supercapacitor with high volumetric capacitance and high energy density due to an interconnected 3D-configuration of the electrode allowing for large number of electrochemical active sites,easy access of electrolyte ions,and facile charge transport for flexible wearable applications.The interconnected and compact electrode delivers a high volumetric capacitance(gravimetric capacitance)of 73 F cm−3(2446 F g−1),excellent rate capability,and cycle stability.The 3D-nickel cobalt-layered double hydroxide onto 3D-nickel wire(NiCo LDH/3D-Ni)//the 3D-manganese oxide onto 3D-nickel wire(Mn3O4/3D-Ni)hybrid supercapacitor exhibits energy density of 153.3 Wh kg−1 and power density of 8810 W kg−1.The red lightemitting diode powered by the as-prepared hybrid supercapacitor can operate for 80 min after being charged for tens of seconds and exhibit excellent electrochemical stability under various deformation conditions.The results verify that such wire-shaped 3D-hybrid supercapacitors are promising alternatives for batteries with long charge–discharge times,for smart wearable and implantable devices.

基于刚柔耦合模型的多轴车辆平顺性仿真分析

针对采用一体化设计、整体式车身结构的多轴车辆,建立刚柔耦合虚拟样机模型,对多轴车辆的平顺性进行研究。基于驾驶室连接方式、驾驶室结构形式和驾驶室顶部连通形式3个设计要素,分析整车在不同载重和不同工况下的平顺性。分析表明,带有斜支撑桁架结构的驾驶室能够有效降低车辆行驶时驾驶室的加权加速度均方根值;顶部不连通的结构形式驾驶室舒适性更好;通过优化驾驶室结构形式和顶部连通形式,车辆在空载和满载情况下的平顺性得到了较大的改善,能够更好地满足使用要求。

细长桁架臂卸载反弹动应力分布规律及试验

为研究细长桁架臂在卸载冲击下的动态响应变化规律,提出了基于等效梁振型函数的桁架臂动应力分布计算模型。根据等效梁振型函数,探讨了卸载后桁架臂动应力分布假设,分析了影响桁架臂卸载反弹动响应的相关参数。以装备细长桁架臂的动臂塔机为对象,建立了桁架臂精细化有限元模型和起重机刚柔耦合模型,通过仿真辨识了应力分布模型的关键参数。实施了动臂塔机系列载荷卸载冲击试验,桁架臂上主弦杆的动应力试验值与理论计算结果误差小于7%,表明动应力分布理论模型与实际相符。通过理论模型预测了极限工况下桁架臂上主弦杆动应力分布状态,发现在最大载荷卸载条件下起重臂动应力峰值超过结构承载极限,为卸载条件下起重机关键结构的优化设计提供依据。

双膛石灰竖窑粉尘排放特性及控制技术研究

分析了石灰双膛竖窑在泄压过程中的粉尘排放特性,初始冲击波压力过高导致烟气无法直连布袋除尘器,这是造成粉尘污染的主要原因。弄清了初始冲击波的形成、传播与演化行为特征,比对了延长直管长度、增加弯管数量、增加变径结构与泄压腔体三种方式对冲击波压力的衰减效果,提出了一种基于压块泄压阀的柔性泄压直联布袋技术,将放散烟气初始冲击波压力由8 kPa降至1 kPa,达到烟气直连布袋、环境粉尘污染得到大幅改善的效果。同时,针对粉尘在阀体和管道中易沉降的难题,提出了一种基于3通内旋阀的扇形旋塞防沉降技术,解决了粉尘在阀体与管道系统内的沉降难题。

中心刚体-形状记忆合金层合功能梯度梁的动力学特性研究

文章对中心刚体-形状记忆合金层合功能梯度梁系统在平面内作大范围运动进行动力学特性研究。SMA层采用多项式的形状记忆合金的本构模型和假设的层合部分的功能梯度分布,在考虑横向变形引起纵向变形的非线性耦合量。采用假设模态法对SMA层合FGM梁系统进行离散,运用第二类Lagrange方程推导得到系统高次刚柔耦合模型,编写软件程序进行动力学仿真。研究了形状记忆合金层的在不同功能梯度下温度对动力学特性的影响以及不同温度下增加SMA层厚度对动力学特性的影响。研究结果表明温度和SMA层厚度对系统的动力学特性影响较大。

基于形状记忆合金丝的柔性康复手套设计

针对康复手套穿戴舒适度低、整体结构复杂等问题,研究一种基于形状记忆合金丝驱动的柔性可穿戴康复手套.根据人手生物结构和运动范围分析,设计贴合人手的可穿戴康复手套,并对形状记忆合金驱动器的收缩性能进行动力学和热力学分析.搭建康复手套试验平台,进行连续被动和镜像康复训练试验,结果表明基于形状记忆合金的柔性康复手套可实现手部伸展拉伸等康复训练,验证了该康复手套设计的有效性.

基于吉布斯采样的方位自聚焦阵形校正方法

阵列形态作为阵列信号处理的基础参数,其准确度严重影响阵列信号处理算法的增益和性能。针对柔性声基阵的阵形畸变问题,提出一种基于吉布斯采样的方位自聚焦阵形校正方法。该方法建立噪声源目标的阵列接收模型,以阵列互相关函数、阵列协方差函数为基础的联合似然,通过吉布斯采样循环迭代方式,实现对阵列形态的实时估计。最后结合非声传感器提供的阵列航向信息,对阵列形态进行旋转匹配,获得阵列校正后的各阵元相对位置输出。仿真结果证明,通过该方法阵形校正后能够获得相对准确的阵元相对位置,具有较好的研究和参考意义。

基于电磁力的机翼非接触式加载试验平台特性研究

目的研究分析基于电磁力的非接触式翼面加载的可行性与适用特点。方法利用多匝铜线绕制的驱动线圈,通入大电流产生强磁场,柔性线圈贴附于机翼表面,柔性线圈中的电流与强磁场相互作用产生较大的电磁力,实现对翼面的稳定加载。建立电磁力加载仿真计算模型,基于该模型分析不同线圈结构时电磁力特性,并设计力学加载平台,开展试验测试。结果对比了柔性线圈和薄铁片2种电磁力加载方式的不同,柔性线圈产生的电磁力比薄铁片小,但具有更好的线性度和可控性。上下布置2个驱动线圈能产生更大电磁力,但需要使2个驱动线圈电流方向相反,电流方向相反时产生的电磁力比方向相同时增强了16倍。减小驱动线圈间距,使柔性线圈靠近驱动线圈,也能显著提高电磁力。开展了力学加载平台试验,柔性线圈产生的电磁力达到57 N,并可持续加载320 s。结论通过试验验证了提出的基于电磁场非接触式翼面加载的可行性,柔性线圈易贴附于机翼表面,可为复合材料、复杂翼形的力学加载测试提供一定参考。

基于索力和振动特性监测的多跨空间异型刚梁柔拱组合桥梁安全韧性分析

对多跨空间异型刚梁柔拱组合体系无推力拱桥进行有限元建模分析,基于振动法对吊杆索力进行检测,通过理论索力与实测索力的对比,分析该类复杂结构桥梁索力的受力规律。同时,基于历年桥梁索力检测结果,研究索力随外部荷载改变时的变化特征,对桥梁索力在长期运营状态下的健康状态进行安全韧性分析。通过测试桥梁的自振特性,分析桥梁结构整体性能,为评价桥梁工作状况提供依据。

柔性尾鳍的形状对仿生机器鱼水动力学特性的影响研究

研究了仿生机器鱼不同形状柔性尾鳍的水动力学特性。根据仿生学观测结果,研制了4种形状的仿生机器鱼尾鳍,通过开展水动力学实验,对比分析了尾鳍外形、结构、材料和运动参数对水动力学参数的影响。结果表明,增大尾鳍的摆角幅度和摆动频率有利于提高推进力,但会引起游动的不稳定性;柔性强的新月形尾鳍具有较好的推进性能;展弦比越小的无鳍条尾鳍,高频游动性能越好,鳍条会降低尾鳍的高频游动性能。

基于高分辨率模态柔度矩阵桥梁损伤识别的少量传感器方法

为了降低监测系统成本和提高桥梁损伤识别精度,本文利用少量传感器获得高分辨率模态振型.在考虑路面粗糙度的情况下,基于柔度变化率进行损伤识别.在不同路面粗糙度水平下,对移动车辆荷载作用下桥梁上所测位移响应进行特征正交分解,再将得到的主成分矩阵中高频动力分量信息过滤,获得高分辨率的模态振型.利用少量传感器方法得到的高分辨率模态振型计算柔度变化率,将其作为桥梁损伤定位的指标.为了验证该方法的有效性,对一简支梁进行模拟和试验.结果显示,该方法在考虑不同粗糙度水平情况下,利用少量传感器得到高分辨率模态振型的柔度变化率能准确定位损伤.

异形采光顶及临空侧邦精装修施工技术研究

现代建筑对于节能和环保的要求越来越高,而采光顶作为建筑物重要的采光结构,其设计和施工需要考虑节能和环保因素,因此,对其精装修施工技术进行研究可以推动建筑行业朝着更加节能环保的方向发展。文章探讨了异形采光顶及临空侧邦精装修施工技术,通过对施工要点及相关技术进行分析,如可移动桁架车和索网立柱柔性平台,提出了相应的解决方案和策略。研究发现,在进行异形采光顶和临空侧邦精装修时,需要充分考虑结构特点、材料选用、施工工艺等因素,确保施工质量和安全。