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Variational Principles for the Trajectory Tracking Control of Underactuated Mechanical Systems 欠驱动机械系统轨迹跟踪控制的变分原理
IF 2 4区 工程技术 Q3 ENGINEERING, MECHANICAL Pub Date : 2023-01-03 DOI: 10.1115/1.4056593
Bálint Bodor, L. Bencsik
Robotics is undergoing dynamic progression with the spread of soft robots and compliant mechanisms. The mechanical models describing these systems are underactuated, having more degrees of freedom than inputs. The trajectory tracking control of underactuated systems is not straightforward. The solution of the inverse dynamics is not stable in all cases, as it only considers the actual state of the system. Therefore employing the advances of optimal control theory is a reasonable choice. However, the real-time application of these is challenging as the solution to the discretized optimization problems is numerically expensive. This paper presents a novel iterative approach to solving nonlinear optimal control problems. The authors first define the iteration formula after which the obtained equations are discretized to prepare the numerical solution, contrarily to the accessible works in the literature having reverse order. The main idea is to approximate the cost functional with a second-order expansion in each iteration step, which is then extremized to get the subsequent approximation of the optimum. In the case of nonlinear optimal control problems, the process leads to a sequence of time-variant LQR problems. The proposed technique was effectively applied to the trajectory tracking control of a flexible RR manipulator. The case study showed that the initialization of the iteration is simple, and the convergence is rapid.
随着软机器人和柔性机构的普及,机器人技术正经历着动态的发展。描述这些系统的力学模型是欠驱动的,具有比输入更多的自由度。欠驱动系统的轨迹跟踪控制并不简单。逆动力学的解在所有情况下都是不稳定的,因为它只考虑系统的实际状态。因此,采用最优控制理论是一个合理的选择。然而,这些方法的实时应用具有挑战性,因为离散优化问题的求解在数值上是昂贵的。本文提出了一种求解非线性最优控制问题的迭代方法。作者首先定义迭代公式,然后对得到的方程进行离散,得到数值解,这与文献中可获得的逆顺序相反。主要思想是在每个迭代步骤中用二阶展开来近似代价函数,然后对其极值以得到后续的最优逼近。对于非线性最优控制问题,该过程会导致一系列时变LQR问题。将该方法有效地应用于柔性RR机械臂的轨迹跟踪控制。实例分析表明,该方法初始化简单,收敛速度快。
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引用次数: 0
Stability Analysis of Nonlinear Rotating Systems Using Lyapunov Characteristic Exponents Estimated From Multibody Dynamics 基于多体动力学估计的Lyapunov特征指数的非线性旋转系统稳定性分析
IF 2 4区 工程技术 Q3 ENGINEERING, MECHANICAL Pub Date : 2023-01-03 DOI: 10.1115/1.4056591
G. Cassoni, A. Zanoni, A. Tamer, P. Masarati
The use of Lyapunov Characteristic Exponents to assess the stability of nonlinear, time-dependent mechanical systems is discussed. Specific attention is dedicated to methods capable of estimating the largest exponent without requiring the Jacobian matrix of the problem, which can be applied to time histories resulting from simulations performed with existing multibody solvers. Helicopter ground resonance is analyzed as the reference application. Improvements over the available literature are: the problem is formulated in physical coordinates, without eliminating periodicity through multiblade coordinates; the rotation of the blades is not linearized; the problem is modeled considering absolute positions and orientations of parts. The dynamic instability that arises at some angular velocities when the isotropy of the rotor is broken (e.g., caused by the failure of one lead-lag damper, a design test condition) is observed to evolve into a large amplitude limit cycle, where the usual Floquet-Lyapunov analysis of the linearized time-periodic simply predicts instability.
讨论了利用李雅普诺夫特征指数来评价非线性、时变机械系统的稳定性。特别关注能够在不需要问题的雅可比矩阵的情况下估计最大指数的方法,这种方法可以应用于由现有多体解算器模拟产生的时间历史。分析了直升机地面共振的参考应用。对现有文献的改进是:问题是在物理坐标中表述的,没有通过多叶片坐标消除周期性;叶片的旋转不是线性化的;该问题的建模考虑了零件的绝对位置和绝对方向。当转子的各向同性被破坏时,在某些角速度下产生的动态不稳定性(例如,由一个超前-滞后阻尼器的失效引起,设计测试条件)被观察到演变成一个大振幅极限环,其中通常的线性化时间周期的Floquet-Lyapunov分析只是预测不稳定性。
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引用次数: 0
Beams with A Varying Cross Section in the Generalized Strain Formulation for Flexure Modelling 变截面梁挠曲模型的广义应变公式
IF 2 4区 工程技术 Q3 ENGINEERING, MECHANICAL Pub Date : 2022-12-16 DOI: 10.1115/1.4056482
K. Dwarshuis, R. Aarts, M. Ellenbroek, D. Brouwer
Flexure joints are rapidly gaining ground in precision engineering because of their predictable behavior. However their range of motion is limited due to a stress limitation and a loss of support stiffness in deformed configurations. The support stiffness can be significantly increased by using leafsprings of which the width and thickness vary over the length of the leafspring. This paper presents formulations for two beam elements with a varying cross section that can be used for the efficient modelling of these types of leafsprings. One of these beam-formulations includes the modelling of the warping due to torsion, which is shown to be essential for accurate modelling. The 90% accuracy in stiffness results and 80% accuracy in stress results, in comparison with results of finite element analyses, are sufficient for the evaluation of concept-designs. Optimizations shows that the support stiffness of two typical flexure joints can be increased by a factor of up to 4.0 keeping the same range of motion, by allowing the cross section to vary over the length of the leafspring. In these two flexure joints, 98% of this improvement can already be obtained by only varying the thickness, keeping a constant width.
柔性关节由于其可预测的性能,在精密工程中迅速占有一席之地。然而,由于应力限制和变形结构中支撑刚度的损失,它们的运动范围受到限制。采用宽度和厚度随叶弹簧长度变化的叶弹簧,可以显著提高支撑刚度。本文提出了具有不同截面的两个梁单元的公式,可用于这些类型的叶弹簧的有效建模。其中一种梁公式包括由于扭转引起的翘曲的建模,这被证明是准确建模所必需的。与有限元分析结果相比,刚度结果的90%精度和应力结果的80%精度足以对概念设计进行评估。优化表明,通过允许横截面随叶弹簧长度变化,两个典型弯曲关节的支撑刚度可以增加高达4.0倍,以保持相同的运动范围。在这两个柔性节点中,仅通过改变厚度,保持宽度不变,就可以获得98%的改进。
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引用次数: 0
Nonlinear Agent-Based Dynamics: Which Metric Mitigates Polarization? 非线性智能体动力学:哪个度量可以减轻极化?
IF 2 4区 工程技术 Q3 ENGINEERING, MECHANICAL Pub Date : 2022-12-16 DOI: 10.1115/1.4056481
Bodo Herzog
This article provides a stochastic agent-based model to exhibit the role of aggregation metrics in order to mitigate polarization in a complex society. Our sociophysics model is based on interacting and nonlinear Brownian agents, which allow us to study the emergence of collective opinions. The opinion of an agent, xi(t) is a continuous positive value in an interval [0,1]. We find (i) most agent-metrics display similar outcomes. (ii) The middle-metric and noisy-metric obtain new opinion dynamics either towards assimilation or fragmentation. (iii) We show that a developed 2-stage metric provide new insights about convergence and equilibria. In summary, our simulation demonstrates the power of institutions, which affect the emergence of collective behavior. Consequently, opinion formation in a decentralized complex society is reliant to the individual information processing and rules of collective behavior.
本文提供了一个基于随机主体的模型来展示聚合指标在缓解复杂社会中的两极分化中的作用。我们的社会物理学模型是基于相互作用和非线性布朗代理的,这使我们能够研究集体意见的出现。agent的意见xi(t)在区间[0,1]内是一个连续的正值。我们发现(i)大多数代理指标显示相似的结果。中间度量法和噪声度量法获得新的趋向同化或分裂的意见动态。(iii)我们表明,开发的2阶段度量提供了关于收敛和均衡的新见解。总之,我们的模拟证明了制度的力量,它影响集体行为的出现。因此,在一个分散的复杂社会中,意见的形成依赖于个人信息处理和集体行为规则。
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引用次数: 1
Finite-time Synchronization of Fractional-order Energy Resources Demand-Supply Hyperchaotic Systems via Fractional-order Prediction-based Feedback Control Strategy with Bio-inspired Multiobjective Optimization 基于生物多目标优化的分数阶预测反馈控制策略的分数阶能源供需超混沌系统有限时间同步
IF 2 4区 工程技术 Q3 ENGINEERING, MECHANICAL Pub Date : 2022-12-13 DOI: 10.1115/1.4056462
A. Soukkou, Y. Soukkou, S. Haddad, M. Benghanem, A. Rabhi
The concept of fractional-order control (F-oC) is exploited in this paper to synchronize fractional-order dynamical systems. The addressed systems in this paper reflect the real physical phenomena characterized by the complicated relationship between supply and demand for energy resources in the Shanghai area. Thus, we provide the developed fractional energy resource attractor and the simulation results regarding synchronization under the proposed control law of the same fractional energy resource attractor. Note that most of the synchronization methods achieved excellent performance when dealing with complex continuous systems; however, no method addressed the synchronization problem of fractional-order energy resource systems based on the F-oC and modern optimization techniques, to the best of our knowledge. By designing the finite-time control theory, the finite-time full synchronization of two identical fractional-order energy resources demand-supply hyperchaotic systems (F-oERDSHSs) is investigated due to its performance. The advanced prediction-based fractional-order control law (Pb-FoCL) is established for finite-time synchronization of F-oERDSHSs. The design procedure becomes a multiobjective optimization problem of the knowledge base of the developed controller while satisfying the desired performance requirements. The Finite-Time Stability (F-TS) of the control-loop system is proved by using the finite-time Lyapunov stability theory. Furthermore, the Improved Artificial Hummingbird Algorithm (I-AHA) is used to find an optimal knowledge base of Pb-FoCL while achieving the design constraints. Simulation results are provided to verify the efficiency of the proposed control strategy.
本文利用分数阶控制(F-oC)的概念实现分数阶动力系统的同步。本文研究的系统反映了上海地区能源供需关系复杂的真实物理现象。在此基础上,给出了所开发的分数阶能量吸引子,以及在相同分数阶能量吸引子控制律下的同步仿真结果。请注意,大多数同步方法在处理复杂连续系统时都取得了优异的性能;然而,就我们所知,没有一种方法能解决基于F-oC和现代优化技术的分数阶能源系统的同步问题。通过设计有限时间控制理论,研究了两个相同分数阶能源供需超混沌系统的有限时间全同步问题。建立了基于超前预测的分数阶控制律(Pb-FoCL),用于f - overerdshss的有限时间同步。在满足预期性能要求的情况下,设计过程成为对所开发控制器知识库进行多目标优化的问题。利用有限时间李雅普诺夫稳定性理论证明了控制环系统的有限时间稳定性。在此基础上,利用改进的人工蜂鸟算法(I-AHA),在满足设计约束条件的同时,找到了最优的pcb - focl知识库。仿真结果验证了所提控制策略的有效性。
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引用次数: 2
Constrained Large-Displacement Thermal Analysis 约束大位移热分析
IF 2 4区 工程技术 Q3 ENGINEERING, MECHANICAL Pub Date : 2022-12-12 DOI: 10.1115/1.4056182
A. Shabana, Mahmoud Elbakly, Dayu Zhang
Two different cases are encountered in the thermal analysis of solids. In the first case, continua are not subject to boundary and motion constraints and all material points experience same displacement-gradient changes as the result of application of thermal loads. In this case, referred to as unconstrained thermal expansion, the thermal load produces uniform stress-free motion within the continuum. In the second case, point displacements due to boundary and motion constraints are restricted, and therefore, continuum points do not move freely when thermal loads are applied. This second case, referred to as constrained thermal expansion, leads to thermal stresses and its study requires proper identification of the independent coordinates which represent expansion degrees-of-freedom. To have objective evaluation and comparison between the two cases of constrained and unconstrained thermal expansion, the reference-configuration geometry is accurately described using the absolute nodal coordinate formulation (ANCF) finite elements. ANCF position-gradient vectors have unique geometric meanings as tangent to coordinate lines, allowing systematic description of the two different cases of unconstrained and constrained thermal expansions using multiplicative decomposition of the matrix of position-gradient vectors. Furthermore, generality of the approach for large-displacement thermal analysis requires using the Lagrange–D'Alembert principle for proper treatment of algebraic constraint equations. Numerical results are presented to compare two different expansion cases, demonstrate use of the new approach, and verify its results by comparing with conventional finite element (FE) approaches.
在固体的热分析中遇到两种不同的情况。在第一种情况下,连续体不受边界和运动约束,所有材料点由于热载荷的作用而经历相同的位移梯度变化。在这种情况下,称为无约束热膨胀,热载荷在连续体内产生均匀的无应力运动。在第二种情况下,由于边界和运动约束的点位移受到限制,因此,连续点在施加热载荷时不能自由移动。第二种情况,称为约束热膨胀,会导致热应力,研究它需要适当地确定代表膨胀自由度的独立坐标。为了对有约束和无约束热膨胀两种情况进行客观的评价和比较,采用绝对节点坐标法(ANCF)有限元精确地描述了参考构型几何。ANCF位置梯度向量作为坐标线的切线具有独特的几何意义,允许使用位置梯度向量矩阵的乘法分解系统地描述两种不同的无约束和约束热膨胀情况。此外,大位移热分析方法的通用性要求使用拉格朗日-达朗贝尔原理对代数约束方程进行适当处理。数值结果比较了两种不同的展开情况,说明了新方法的应用,并通过与传统有限元方法的比较验证了其结果。
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引用次数: 3
The Homotopy Analysis Method for Solving Differential Equations with Generalized Caputo-Type Fractional Derivatives 广义caputo型分数阶导数微分方程的同伦分析方法
IF 2 4区 工程技术 Q3 ENGINEERING, MECHANICAL Pub Date : 2022-12-04 DOI: 10.1115/1.4056392
Wafia Fafa, Z. Odibat, N. Shawagfeh
This study expands and modifies the homotopy analysis method to handle differential equations with generalized Caputo-type fractional derivatives. Analytical approximate solutions for such models were successfully provided using the proposed modification. The determination of the valid region of convergence for the proposed method, with respect to the auxiliary control parameter, was discussed when using fractional operators. Then, mainly, the accuracy and effectiveness of the proposed method was verified through illustrative examples and comparisons with the predictor corrector method and RK4 method. Finally, it is expected that the studied generalized operators and the suggested method can be widely applied in the field of fractional calculus.
本文对同伦分析方法进行了扩展和修正,以处理具有广义caputo型分数阶导数的微分方程。利用所提出的修正,成功地给出了这类模型的解析近似解。讨论了在使用分数阶算子时,该方法相对于辅助控制参数的有效收敛区域的确定。然后,主要通过举例验证了该方法的准确性和有效性,并与预测校正方法和RK4方法进行了比较。最后,期望所研究的广义算子及其方法能在分数阶微积分领域得到广泛应用。
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引用次数: 1
Effective Optimized Decomposition Algorithms for Solving Nonlinear Fractional Differential Equations 求解非线性分数阶微分方程的有效优化分解算法
IF 2 4区 工程技术 Q3 ENGINEERING, MECHANICAL Pub Date : 2022-11-23 DOI: 10.1115/1.4056254
Marwa Laoubi, Z. Odibat, B. Maayah
In this paper, the optimized decomposition method, which was developed to solve integer-order differential equations, will be modified and extended to handle nonlinear fractional differential equations. Fractional derivatives will be considered in terms of Caputo sense. The suggested modifications design new optimized decompositions for the series solutions depending on linear approximations of the nonlinear equations. Two optimized decomposition algorithms have been introduced to obtain approximate solutions of broad classes of IVPs consisting of nonlinear fractional ODEs and PDEs. A comparative study was conducted between the proposed algorithms and the Adomian decomposition method by means of some test illustration problems. The implemented numerical simulation results showed that the proposed algorithms give better accuracy and convergence, and reduce the complexity of computational work compared to the Adomian's approach. This confirms the belief that the optimized decomposition method will be used effectively and widely as a powerful tool in solving various fractional differential equations.
在本文中,优化分解方法是为解决整阶微分方程而发展起来的,将其改进和推广到处理非线性分数阶微分方程。分数阶导数将根据卡普托意义来考虑。所建议的修改设计了基于非线性方程的线性近似的级数解的新的优化分解。介绍了两种优化分解算法,用于求解由非线性分数阶微分方程和偏微分方程组成的一类广义微分方程的近似解。通过若干试验实例问题,将所提算法与Adomian分解方法进行了比较研究。实现的数值模拟结果表明,与Adomian方法相比,本文提出的算法具有更好的精度和收敛性,并且减少了计算量。这证实了优化分解方法将作为求解各种分数阶微分方程的有力工具得到有效和广泛的应用。
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引用次数: 2
On the Periodicity of the Rational Dynamical System Corresponding to the Vannimenus–Ising Model
IF 2 4区 工程技术 Q3 ENGINEERING, MECHANICAL Pub Date : 2022-11-17 DOI: 10.1115/1.4056133
H. Akın
The universal behaviors of a rational dynamical system associated with the Vannimenus–Ising model having two coupling constants on a Cayley tree of order three are studied. Cobweb diagrams and related map iterates for some relevant parameters are investigated. The local stability of fixed points is discussed and illustrated through cobweb diagrams. We deal with quantitative universality, such as orbit diagrams and Lyapunov exponents for a class of rational maps. We show that our model is periodic using orbit diagrams and relevant Lyapunov exponents.
研究了具有两个耦合常数的有理动力系统在三阶Cayley树上的普遍行为。研究了蛛网图和一些相关参数的相关映射迭代。讨论了不动点的局部稳定性,并用蛛网图加以说明。我们处理了一类有理图的数量通用性,如轨道图和李雅普诺夫指数。我们用轨道图和相关的李雅普诺夫指数来证明我们的模型是周期性的。
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引用次数: 4
Construction of Friction Model of the Third Body Layer and Its Effects on the Dynamic Characteristics in Brake System 第三体层摩擦模型的建立及其对制动系统动态特性的影响
IF 2 4区 工程技术 Q3 ENGINEERING, MECHANICAL Pub Date : 2022-11-17 DOI: 10.1115/1.4056181
Yuhang Zhang, Daogao Wei, Bofu Wu, Ping Jiang
The noise of disk brake pair has always been a difficult problem for enterprises and researchers. Many factors induce the noise of disk brake pair, among which the influence of the third body particle flow generated by the external gravel or its own abrasive debris has not been paid much attention. Three-body contact has different friction properties and requires a new friction model to describe it. This paper presents a friction model of disk brake pair on the basis of the predecessors. The new model further considers the influence of the third body on the nonlinear behavior of the brake system on the basis of the previous model of the brake pair. Through numerical simulation, it is concluded that the geometry size of the third body has great influence on the stability interval of the braking system. Finally, the influence of the third body particles on the motion stability of the braking system under different particle size ranges is studied. It is found that larger particle size can improve the motion stability of the system.
盘式制动器副的噪声问题一直是困扰企业和研究人员的难题。引起盘式制动副噪声的因素很多,其中外部砾石或自身磨粒屑产生的第三体颗粒流的影响一直未引起重视。三体接触具有不同的摩擦特性,需要一种新的摩擦模型来描述。本文在前人研究的基础上,建立了盘式制动器副的摩擦模型。新模型在原有制动副模型的基础上,进一步考虑了第三体对制动系统非线性行为的影响。通过数值模拟,得出了第三体几何尺寸对制动系统稳定区间影响较大的结论。最后,研究了不同粒径范围下第三体颗粒对制动系统运动稳定性的影响。研究发现,粒径越大,系统的运动稳定性越好。
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引用次数: 0
期刊
Journal of Computational and Nonlinear Dynamics
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