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Formation adaptation in obstacle-cluttered environments via MPC-based trajectory planning

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Science China(Information Sciences) 2024年第7期67卷 321-323页

作者： Yuda CHEN Zhongkui LI department of mechanics and engineering Science College of Engineering Peking University

Formation is a typical collective behavior in multiagent systems utilized in areas such as inspection, surveillance, and transportation. Commonly-used approaches to achieve formation include virtual structure [1], con...

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Analysis of piezoelectric semiconductor fibers under gradient temperature changes

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Applied Mathematics and mechanics(English Edition) 2024年第2期45卷 311-320页

作者： Shuangpeng LI Ruoran CHENG Nannan MA Chunli ZHANG department of engineering mechanics Zhejiang UniversityHangzhou 310027China

Piezoelectric semiconductors(PSs)possess both semiconducting properties and piezoelectric coupling effects,making them optimal building blocks for semiconductor devices.PS fiber-like structures have wide applications in multi-functional semiconductor devices.In this paper,a one-dimensional(1D)theoretical model is established to describe the piezotronic responses of a PS fiber under gradient temperature changes.The theoretical model aims to explain the mechanism behind the resistance change caused by such gradient temperature changes.Numerical results demonstrate that a gradient temperature change significantly affects the physical fields within the PS fiber,and can induce changes in its surface resistance.It provides important theoretical guidance on the development of piezotronic devices that are sensitive to temperature effects.

关键词： piezoelectric semiconductor(PS)fiber one-dimensional(1D)model piezotronic effect gradient temperature change

Theoretical and experimental study of a bi-stable piezoelectric energy harvester under hybrid galloping and band-limited random excitations

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Applied Mathematics and mechanics(English Edition) 2024年第3期45卷 461-478页

作者： Haitao LI Tianyu ZHENG Weiyang QIN Ruilan TIAN Hu DING J.C.JI Liqun CHEN department of engineering mechanics North University of ChinaTaiyuan 030051China department of engineering mechanics Northwestern Polytechnical UniversityXi'an 710072China department of engineering mechanics Shijiazhuang Tiedao UniversityShijiazhuang 050043China Shanghai Key Laboratory of mechanics in Energy engineering Shanghai Frontier Science Center of MechnoinformaticsShanghai Institute of Applied Mathematics and MechanicsSchool of Mechanics and Engineering ScienceShanghai UniversityShanghai 200072China School of Mechanical and Mechatronic engineering University of Technology SydneyNew South Wales 2007Australia

In the practical environment,it is very common for the simultaneous occurrence of base excitation and crosswind.Scavenging the combined energy of vibration and wind with a single energy harvesting structure is fascinating.For this purpose,the effects of the wind speed and random excitation level are investigated with the stochastic averaging method(SAM)based on the energy envelope.The results of the analytical prediction are verified with the Monte-Carlo method(MCM).The numerical simulation shows that the introduction of wind can reduce the critical excitation level for triggering an inter-well jump and make a bi-stable energy harvester(BEH)realize the performance enhancement for a weak base excitation.However,as the strength of the wind increases to a particular level,the influence of the random base excitation on the dynamic responses is weakened,and the system exhibits a periodic galloping response.A comparison between a BEH and a linear energy harvester(LEH)indicates that the BEH demonstrates inferior performance for high-speed wind.Relevant experiments are conducted to investigate the validity of the theoretical prediction and numerical simulation.The experimental findings also show that strong random excitation is favorable for the BEH in the range of low wind speeds.However,as the speed of the incoming wind is up to a particular level,the disadvantage of the BEH becomes clear and evident.

关键词： bi-stability inter-well response galloping band-limited random

A design and manufacturing methodology for encoded soft-textile robots

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Science China(Physics,mechanics & Astronomy) 2024年第5期67卷 212-213页

作者： Yihui Zhang Applied mechanics Laboratory Department of Engineering MechanicsTsinghua UniversityBeijing 100084China

The development of programmable soft robots with bioinspired morphing capabilities has attracted considerable interest.The mode and complexity of morphing capabilities are essential to the manipulation and movement ab... 详细信息

关键词： environments robots manipulation

Direct-to-indirect mapping for optimal low-thrust trajectories

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Astrodynamics 2024年第1期8卷 27-46页

作者： David Ottesen Ryan P.Russell department of Aerospace engineering and engineering mechanics The University of Texas at AustinAustinTexas78712USA

Optimal,many-revolution spacecraft trajectories are challenging to solve.A connection is made for a class of models between optimal direct and indirect solutions.For transfers that minimize thrust-acceleration-squared,primer vector theory maps direct,many-impulsive-maneuver trajectories to the indirect,continuous-thrust-acceleration equivalent.The mapping algorithm is independent of how the direct solution is obtained and requires only a solver for a boundary value problem and its partial derivatives.A Lambert solver is used for the two-body problem in this work.The mapping is simple because the impulsive maneuvers and co-states share the same linear space around an optimal trajectory.For numerical results,the direct coast-impulse solutions are demonstrated to converge to the indirect continuous solutions as the number of impulses and segments increases.The two-body design space is explored with a set of three many-revolution,many-segment examples changing semimajor axis,eccentricity,and inclination.The first two examples involve a small change to either semimajor axis or eccentricity,and the third example is a transfer to geosynchronous orbit.Using a single processor,the optimization runtime is seconds to minutes for revolution counts of 10 to 100,and on the order of one hour for examples with up to 500 revolutions.Any of these thrust-acceleration-squared solutions are good candidates to start a homotopy to a higher-fidelity minimization problem with practical constraints.

关键词： direct optimization indirect optimization impulsive maneuvers Lambert's problem two-body dynamics primer vectortheory

Subpicosecond laser ablation behavior of a magnesium target and crater evolution:Molecular dynamics study and experimental validation

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Chinese Physics B 2024年第7期33卷 613-622页

作者：江国龙周霞 State Key Laboratory of Structural Analysis for Industrial Equipment Department of Engineering MechanicsFaculty of Vehicle Engineering and MechanicsDalian University of TechnologyDalian 116024China

The micro-ablation processes and morphological evolution of ablative craters on single-crystal magnesium under subpicosecond laser irradiation are investigated using molecular dynamics(MD) simulations and experiments.The simulation results exhibit that the main failure mode of single-crystal Mg film irradiated by a low fluence and long pulse width laser is the ejection of surface atoms,which has laser-induced high stress.However,under high fluence and short pulse width laser irradiation,the main damage mechanism is nucleation fracture caused by stress wave reflection and superposition at the bottom of the film.In addition,Mg[0001] has higher pressure sensitivity and is more prone to ablation than Mg[0001].The evolution equation of crater depth is established using multi-pulse laser ablation simulation and verified by experiments.The results show that,under multiple pulsed laser irradiation,not only does the crater depth increase linearly with the pulse number,but also the quadratic term and constant term of the fitted crater profile curve increase linearly.

关键词： laser-material interaction molecular dynamics(MD)simulation ablation crater morphology magnesium

Feasibility and reliability of agricultural crop height measurement using the laser sensor array

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Information Processing in Agriculture 2024年第2期11卷 228-236页

作者： Pejman Alighaleh Tarahom Mesri Gundoshmian Saeed Alighaleh Abbas Rohani department of biosystems engineering Faculty of AgricultureFerdowsi University of MashhadMashhadIran department of biosystems engineering University of Mohaghegh ArdabiliArdabilIran Auckland Bioengineering Institute University of AucklandNew Zealand

Crop height measurement is widely used to analyze and estimate the overall crop condition and the amount of biomass production.Not only is manual measurement on a large scale time-consuming but also it is not practical.Besides,advanced equipment is available but they require technical skills and are not reasonable for smallholders.This article investigates the feasibility of a simple and low-cost measurement system that can monitor crops height of paddy rice and wheat using laser technology.After designing and fabricating,this system was tested and evaluated in both laboratory and farm sections.In the laboratory,paddy rice height was measured,and in the field section,the height detection system measured wheat height.The results showed that the coefficient of determination(R3)between manual measurement and height detection system measurement for paddy rice was 0.96 and for wheat was 0.85.Besides,there was no significant difference between the two datasets at the level of 5%.Hence,this system can be a useful and accurate tool to monitor crops height in different growing steps.

关键词： Plant height Laser Rice Wheat Crop monitoring

Deciphering the controlling factors for phase transitions in zeolitic imidazolate frameworks

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National Science Review 2024年第4期11卷 151-163页

作者： Tao Du Shanwu Li Sudheer Ganisetti Mathieu Bauchy Yuanzheng Yue Morten M.Smedskjaer department of Chemistry and Bioscience Aalborg University department of Mechanical engineering-engineering mechanics Michigan Technological University Physics of Amo Rphous and Inorganic Solids Laboratory(PARISlab) Department of Civil and Environmental EngineeringUniversity of CaliforniaLos Angeles

Zeolitic imidazolate frameworks（ZIFs） feature complex phase transitions, including polymorphism,melting, vitrification, and polyamorphism. Experimentally probing their structural evolution during transitions involving amorphous phases is a significant challenge, especially at the medium-range length scale. To overcome this challenge, here we first train a deep learning-based force field to identify the structural characteristics of both crystalline and non-crystalline ZIF phases. This allows us to reproduce the structural evolution trend during the melting of crystals and formation of ZIF glasses at various length scales with an accuracy comparable to that of ab initio molecular dynamics, yet at a much lower computational cost. Based on this approach, we propose a new structural descriptor, namely, the ring orientation index, to capture the propensity for crystallization of ZIF-4(Zn（Im）2, Im = C3H3N2-) glasses, as well as for the formation of ZIF-zni(Zn（Im）2) out of the high-density amorphous phase. This crystal formation process is a result of the reorientation of imidazole rings by sacrificing the order of the structure around the zinc-centered tetrahedra. The outcomes of this work are useful for studying phase transitions in other metal-organic frameworks（MOFs） and may thus guide the development of MOF glasses.

关键词： metal-organic frameworks phase transitions melting glass formation transferable deep learning force field ring orientation

Matched Volterra reduced-order model for an airfoil undergoing periodic translation

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Chinese Journal of Aeronautics 2024年第1期37卷 19-23页

作者： Lianrui NIE Ziniu WU department of engineering mechanics Tsinghua UniversityBeijing 100084China

This paper is devoted to application of the Reduced-Order Model(ROM)based on Volterra series to prediction of lift and drag forces due to airfoil periodic translation in transonic flow region.When there is large amplitude oscillation of the relative Mach number,as appeared in helicopter rotor movement in forward flight,the conventional Volterra ROM is found to be unsatisfactory.To cover such applications,a matched Volterra ROM,inspired from previous multistep nonlinear indicial response method based on Duhamel integration,is thus considered,in which the step motions are defined inside a number of equal intervals with both positive and negative step motions to match the airfoil forward and backward movement,and the kernel functions are constructed independently at each interval.It shows that,at least for the translation movement considered,this matched Volterra ROM greatly improves the accuracy of prediction.Moreover,the matched Volterra ROM,with the total number of step motions and thus the computational cost close to those of the conventional Volterra ROM method,has the additional advantage that the same set of kernels can match various translation motions with different starting conditions so the kernels can be predesigned without knowing the specific motion of airfoil.

关键词： Airfoil periodic translation Lift and drag Reduced-order model Transonic flow Unsteady flow