APPROACH FOR LAYOUT OPTIMIZATION OF TRUSS STRUCTURES WITH DISCRETE VARIABLES UNDER DYNAMIC STRESS, DISPLACEMENT AND STABILITY CONSTRAINTS

A mathematical model was developed for layout optimization of truss structures with discrete variables subjected to dynamic stress, dynamic displacement and dynamic stability constraints. By using the quasi-static method, the mathematical model of structure optimization under dynamic stress, dynamic displacement and dynamic stability constraints were transformed into one subjected to static stress, displacement and stability constraints. The optimization procedures include two levels, i.e., the topology optimization and the shape optimization. In each level, the comprehensive algorithm was used and the relative difference quotients of two kinds of variables were used to search the optimum solution. A comparison between the optimum results of model with stability constraints and the optimum results of model without stability constraint was given. And that shows the stability constraints have a great effect on the optimum solutions.

External blast load factors for dome structures based on reliability

Dome structures have been used extensively for industrial,residential,and military infrastructure.Therefore,it is necessary to understand the damage risk potential for such structures for blast-resistant design considerations.This paper investigates the effect of blast load variability on the design value and the structural dynamic response.Therefore,the sources of uncertainty in the external blast load on dome structures were discussed firstly.Then based on the probabilistic blast load model for the dome,the rationality of a deterministic mass-increase safety method was assessed.It was found that previous deterministic design method cannot provide a consistent and sound assurance factor or reliability index on the entire dome roof.In addition,it was also proved that the assurance-based load method fails to ensure compliance with structural safety design standards on the dome roof when compared with the reliability-based blast method.A sensitivity analysis on the probabilistic blast load was conducted,and the results indicate that stand-off distance and explosive mass both act as dominant sources to influence the mean and variability of blast load.Therefore,based on the Latin hypercube sampling method,a reliability-based external blast load factor technique was proposed.This technique was further used to estimate structural damage levels of a single-layer reticulated dome under different reliability requirements,associated with a low,medium,and high level of protection grades for a specific explosion scenario,and it indicated that this technique can be useful in the building design to achieve a higher structural anti-explosion capacity.This study herein can serve as a reference for the calculation method of designed blast load.

Paralleled DC-DC Power Converters Sliding Mode Control with Dual Stages Design

This paper proposes the new cascaded series parallel design for improved dynamic performance of DC-DC buck boost converters by a new Sliding Mode Control (SMC) method. The converter is controlled using Sliding Mode Control method that utilizes the converter’s duty ratio to determine the skidding surface. System modeling and simulation results are presented. The results also showed an improved overall performance over typical PID controller, and there was no overshoot or settling time, tracking the desired output nicely. Improved converter performance and robustness were expected.

Spatially variable soils affecting geotechnical strip foundation design

Natural soil variability is a well-known issue in geotechnical design,although not frequently managed in practice.When subsoil must be characterized in terms of mechanical properties for infrastructure design,random finite element method(RFEM)can be effectively adopted for shallow foundation design to gain a twofold purpose:(1)understanding how much the bearing capacity is affected by the spatial variability structure of soils,and(2)optimisation of the foundation dimension(i.e.width B).The present study focuses on calculating the bearing capacity of shallow foundations by RFEM in terms of undrained and drained conditions.The spatial variability structure of soil is characterized by the autocorrelation function and the scale of fluctuation(δ).The latter has been derived by geostatistical tools such as the ordinary Kriging(OK)approach based on 182 cone penetration tests(CPTs)performed in the alluvial plain in Bologna Province,Italy.Results show that the increase of the B/δratio not only reduces the bearing capacity uncertainty but also increases its mean value under drained conditions.Conversely,under the undrained condition,the autocorrelation function strongly affects the mean values of bearing capacity.Therefore,the authors advise caution when selecting the autocorrelation function model for describing the soil spatial variability structure and point out that undrained conditions are more affected by soil variability compared to the drained ones.

Design and application of a multi - function combined hydraulic oil cylinder

Hydraulic equipment in engineering, in different working stages, different speed, load, variable load and variable speed is one of the most frequently encountered problems, to solve this problem is usually used to continuously adjustable pressure, adjustable flow control to achieve. In this paper, the structure design of a combination of oil tanks, combined with oil circuit examples in the case of no need to adjust the pressure, adjust the flow rate, to achieve the high speed, light load of the typical operating requirements and hydraulic servo feedback.

Topological Design via a Rule Based Genetic Optimization Algorithm

A topological structural design approach is presented which is based upon the implementation of a two phase evolutionary optimization algorithm in conjunction with a finite element analysis code. The first phase utilizes a conventional genetic approach which performs a global search for the optimal design topology. Dual level material properties are specified within the genetic encoding and are applied to each individual element in the design mesh to represent either design material or a void. The second phase introduces a rule based refinement which allows for user design intent to accelerate the solution process and eliminate obvious design discrepancies resulting from the phase one search. A series of plate design problems are presented where the objective is to minimize the overall volume of the structure under predefined loading and constraint conditions. The constraints include both stress and deflection considerations where stress is calculated through the use of a commercial finite element package. The initial plate example incorporates a coarse mesh, but a gradual decrease in element size was employed for the remaining cases examined. Replacement of the phase one search with a set of randomly generated designs is demonstrated in order to form a greatly reduced design space which drastically increases the efficiency of the solution process. Comparison results are drawn between the conventional genetic algorithm and the two phase procedure.

A low-frequency pure metal metamaterial absorber with continuously tunable stiffness

To address the incompatibility between high environmental adaptability and deep subwavelength characteristics in conventional local resonance metamaterials,and overcome the deficiencies in the stability of existing active control techniques for band gaps,this paper proposes a design method of pure metal vibration damping metamaterial with continuously tunable stiffness for wideband elastic wave absorption.We design a dual-helix narrow-slit pure metal metamaterial unit,which possesses the triple advantage of high spatial compactness,low stiffness characteristics,and high structural stability,enabling the opening of elastic flexural band gaps in the low-frequency range.Similar to the principle of a sliding rheostat,the introduction of continuously sliding plug-ins into the helical slits enables the continuous variation of the stiffness of the metamaterial unit,achieving a continuously tunable band gap effect.This successfully extends the effective band gap by more than ten times.The experimental results indicate that this metamaterial unit can be used as an additional vibration absorber to absorb the low-frequency vibration energy effectively.Furthermore,it advances the metamaterial absorbers from a purely passive narrowband design to a wideband tunable one.The pure metal double-helix metamaterials retain the subwavelength properties of metamaterials and are suitable for deployment in harsh environments.Simultaneously,by adjusting its stiffness,it substantially broadens the effective band gap range,presenting promising potential applications in various mechanical equipment operating under adverse conditions.

基于视觉检测的智能桥梁检查车设计与分析

针对公路变截面梁的特点,提出了一种基于视觉检测的智能检查车。该智能检查车由车体平台和视觉检测平台组成,既能无人智能快速检测,又能人工定点维修,有效地提高了桥梁养护效率及检查工作的安全性。介绍了车体平台的具体结构设计和视觉检测平台的具体组成,并对智能检测和人工检查做了对比试验分析,结果表明智能检测比人工检查具有更好的病害检测完整性和更高的检测效率。

面向壁厚均匀的液压成形三通管的坯料设计方法与参数优化

目的研究连续变厚度管液压成形过程中三通管的壁厚均匀性问题。方法首先,利用有限元软件分析得到了等厚管液压成形三通管过程中的成形规律,根据其成形规律,反向设计了用于液压成形三通管的连续变厚度管坯;其次,采用正交试验方法,研究了连续变厚度管厚区壁厚、过渡区长度对液压成形三通管成形质量的影响;最后,采用多岛遗传算法,对连续变厚度管的结构参数进行了优化验证,提高了液压成形三通管的成形质量。结果在等厚管液压成形三通管成形过程中,支管顶部壁厚值持续减小、轴向过渡圆角及直管底部中间位置处壁厚值持续增大;环向过渡圆角处等效应力最大,其他位置连续变化;轴向压应力使得三通管壁厚增大,拉应力使得壁厚减小;正交试验结果表明,当连续变厚度管厚区厚度、环向过渡区长度达到某一值时将出现较好的壁厚均匀性;在4种过渡区曲线线型中,直线型的壁厚均匀性最好;通过多目标优化得到最佳连续变厚度管结构参数,并通过有限元仿真进行验证,相对误差均在2%以内,使用优化后的连续变厚度管液压成形三通管相对于等厚管,壁厚均匀值减小了0.423 mm。结论可以采用厚度补偿或减薄的方式来提高成形三通管的壁厚均匀性;连续变厚度管坯相比于等厚管,显著提高了液压成形三通管的壁厚均匀性。

考虑土性参数空间变异性的珠三角软土地区土钉支护结构可靠度分析

如何定量定性描述软土土性参数空间变异性对准确确定软土土性参数和合理评价软土地区土钉支护结构稳定性至关重要。采用既有统计分析方法定量描述空间变异性通常需要大量数据,难以满足。本文基于随机场理论模拟软土土性参数空间变异性,建立了一套考虑土性空间变异性的软土地区土钉支护结构可靠度设计方法,最后以MATLAB软件包为平台进行计算程序的开发与工程实例研究。分析结果表明,本文采用随机场方法模拟软土土体固有空间变异性及其在土钉支护结构可靠度分析中的应用具有合理性与普适性。

安百拓液压凿岩机活塞受力面积分析与三段法述评

搜集了11个安百拓双控式凿岩机和4个后控式凿岩机冲击活塞的直径数据,计算得到在凿岩机冲击运动周期中,回程与冲程活塞受力面积的比值范围。根据比值数据的分析,指出基于三段法理论的设计变量作为凿岩机性能评价指标的普适性较差。据此,本文强调了数据分析在凿岩机研究中的重要作用。文中还介绍了改进的三段法理论及其计算实例,论述了改进的三段法的优点与缺点。

风电叶片内窥机器人结构设计与运动仿真

针对风电叶片前缘空间不规则、直径变化范围大的特点,文中制订了内窥机器人设计要求,提出以履带式行走机构和剪叉式变径机构为基础的设计方案,分别建立两种不同的内窥机器人三维模型,详细介绍了两种内窥机器人结构及各部件功能。机器人主要由行走模块、变径模块和支撑模块构成,具有大范围变径、小范围随形支撑和差速转向能力。机器人本体配有可移动电源并可进行无线控制,搭载检测设备可以对前缘空间进行检测。最终对机器人变径机构进行运动仿真,结果表明:机器人工作直径为395~1492 mm,满足设计要求。

微细线控变路径穿刺针设计与验证

目的提出一种协作机器人基体+线控微细变路径机器人末端执行系统耦合的精准微细微创机器人系统,设计了包含外针的刚性体、内针的非均匀柔性体、力控线、像纤内部成像等部件的穿刺进针结构,验证此系统的可行性。方法通过搭建穿刺机器人穿刺进针结构实物,对影响变路径精准穿刺针关键部件进行结构优化设计分析,基于正交实验设计方法设计主要影响穿刺针精准性的孔中心距边缘起始距离、开孔直径、两孔之间距离3因素3水平实验,并结合实物进行实验验证与仿真。结果记忆合金变路径穿刺针尖端位移量与孔中心距边缘的起始距离关系较大,影响的主次因素为孔中心距边缘起始距离>孔开口>孔距。当孔中心距边缘起始距离为1 mm、开孔直径为0.2 mm、两孔之间距离为2.6 mm时,穿刺针尖端位移量取最大值。结论实验验证了设计系统的功能适用性和变路径穿刺的线弹性滞后特性,为进一步活体实验和系统优化提供借鉴。

变跨变幅钢栈桥结构设计及受力性能分析

【目的】为了研究变跨变幅钢栈桥在多荷载工况下的承载性能。【方法】以向莆联络线向莆左线特大桥施工中的一座钢栈桥为研究对象,通过桥梁有限元软件Midas civil建立数值模型,分析其在5种不同工况下各个构件的受力状态。【结果】研究结果表明:钢栈桥贝雷梁在各种工况作用下,结构强度及刚度均有较大安全富余;桩顶分配梁在工况1及工况2作用下,其折算应力的安全富余系数较小,仅为1.23和1.20,工况5作用下其刚度的安全富余系数为1.20,施工过程中需要避免过重的临时荷载堆放;钢管立柱在工况5作用下的正应力安全富余系数仅为1.50,施工过程中应采取措施确保施工的安全性;转角处三角区设计符合结构性能要求。【结论】研究成果可为同类栈桥设计提供借鉴。

一种等离子体溯源测量装置设计及性能测试

文章设计了一套等离子体溯源测量装置为验证感应耦合等离子体(ICP)源作为校准源的性能,找出满足朗缪尔探针溯源校准的最佳等离子体测试条件,提升测试准确性,采用控制变量法对不同工况下ICP源等离子体电子密度和电子温度的稳定性和均匀性,以及电子密度的重复性进行测试。结果表明:在放电开始5~20 min内,等离子体电子密度和电子温度的稳定性分别优于99.4%和98.9%;在探针伸入真空腔体内440~480 mm的范围内,等离子体电子密度和电子温度的均匀性分别优于97.2%和93.6%;在等离子体源放电功率100~900 W范围时,等离子体电子密度的重复性优于86.6%,并且多数在92%以上。本研究可为后续等离子体诊断手段的优化提供参考。

机织角联锁变密度复合材料的面外压缩力学特性

为研究变密度结构设计对三维机织角联锁复合材料面外力学性能的影响,设计制备了三维机织角联锁不变密度复合材料、三维机织角联锁经纱变密度复合材料和三维机织角联锁纬纱变密度复合材料。结合扫描电子显微镜、数字图像相关技术和X射线计算机断层扫描等检测技术,对角联锁变密度复合材料的面外压缩力学行为、内部损伤量化和渐进损伤等进行了测试与表征。研究结果表明:上疏下密角联锁纬纱变密度复合材料展现出优异的压缩性能,其压缩比强度比不变密度复合材料高3.40%;同时,上疏下密角联锁纬纱变密度复合材料损伤体积仅为11.64 mm 3,远低于不变密度复合材料的26.90 mm 3。进一步分析得到,不变密度复合材料压缩破坏以剪切失效为主,而上疏下密角联锁纬纱变密度复合材料则为基体开裂。

一种具有变结构的轻量化陆空两栖平台技术研究

结合无人机空中飞行与无人车陆地行驶的功能特点,通过流体仿真、气动力学分析,设计了一种具有变结构功能的陆空两栖平台。采用隐藏式旋翼设计,有效降低了平台宽度,提高了地面行驶模态下的通过性。在此基础上,针对陆空两栖平台的飞行控制问题,对平台模型进行简化,并对平台参数进行优化和模型校核,验证了平台模型的有效性和可信度。设计了自抗扰控制(active disturbance rejection control, ADRC)方案,并进行了simulink仿真和原理样机测试。试验表明,所设计的陆空两栖平台兼具良好的路面行驶能力与空中飞行能力,具备一定的越障功能,为未来军事应用中飞行器长航时、大载重、强稳定性等功能的实现提供了技术参考。

类贯流式水轮机水力设计与数值模拟

针对某工程实例水头变化大,生态流量小的问题,应用流体机械设计理论和计算流体动力学(CFD)数值模拟计算方法,设计了一种适用于低水头的变速类贯流式水轮机,基于RNGκ-ε湍流模型,对该水轮机全流道进行三维定常数值模拟,得到了各部件流场的压力、速度和速度矢量变化规律,发现内部流态良好,水力损失均较小,机组效率高达94.71%,符合设计要求。采用变转速运行,能够适应较宽的水头变化,在偏离设计工况运行时,效率依然能维持在94%以上,具有很高的工程应用价值。

Genetic Optimization via Diverse Crossover Intelligence

An intelligent crossover methodology within the genetic algorithm (GA) is explored within both mathematical and finite element arenas improving both design and solution convergence time. This improved intelligent crossover outperforms the traditional genetic algorithm combined with a rule-based approach utilizing domain specific knowledge developed by Webb, et al. [1]. The encoding of the improved crossover consists of two chromosome strings within the genetic algorithm where the first string represents the design or solution string, and the second string represents chromosome crossover string intelligence. This improved crossover methodology saves the best population members or designs evaluated from each generation and applies crossover chromosome intelligence to the best saved population members paired with globally selected parents. Enhanced features of this crossover methodology employ the random selection of the best designs from the prior generation as a potential parent coupled with alternating intelligence pairing methods. In addition to this approach, two globally selected parents possess the ability to mate utilizing crossover chromosome string intelligence maintaining the integrity of a global GA search. Overall, the final population following crossover employs both global and best generation design chromosome strings to maximize creativity while enhancing the solution search. This is a modification to a conventional GA that can be translated into GA encoding. This technique is explored initially through a Base 10 mathematical application followed by the examination of plate structural optimization considering stress and displacement constraints. Results from crossover intelligence are compared with the conventional genetic algorithm and from Webb, et al. [1] which illustrates the outcome of a two phase genetic optimization algorithm.

基于离散变量的多材料结构拓扑优化设计

多材料结构拓扑优化相比于单材料结构优化具有更大的设计空间,展现出巨大的设计潜力和应用前景。本文基于离散设计变量研究多材料结构拓扑优化,通过建立有效的设计优化方法,获得轻质高效的结构设计。首先,根据离散变量的特点,建立多材料结构拓扑优化模型,由离散变量下约束函数和目标函数的灵敏度信息构造序列近似整数规划子问题,采用运动极限策略限制设计变量的改变量以保证整数规划子问题的近似精度。为了解决离散变量的组合复杂性,采用具有多项式复杂度的正则松弛算法来高效求解(和经典的连续变量算法效率相当)。本文利用多材料结构最小柔顺性优化问题以及最大传热效率优化问题研究离散变量方法的有效性。数值算例表明,离散变量优化方法可以获得稳定迭代收敛的多材料拓扑设计,优化构型中的材料界面清晰分明,有效避免了出现模糊区域。