Mechanical Response of Four-Bar Linkage Microgrippers with Bidirectional Electrostatic Actuation

This paper presents both an experimental and a numerical study concerning the mechanical response of a silicon microgripper with bidirectional electrostatic actuation to externally applied excitations. The experimental set-up is composed of a probe station equipped with mobile probes that apply contact forces. This part of the investigation aims to test the device’s mechanical resistance, its mobility capability and possible internal contacts during the system deformation. The second part of the paper is dedicated to the study of the free undamped vibrations of the microsystem. Finite Element Analysis (FEA) is carried out to evaluate the system vibration modes. The analysis of the modes are useful to predict possible mechanical interference among floating and anchored fingers of the actuating comb drives.

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Study on Train Wheel Out-of-Roundness Monitoring Method by PVDF Sensing Technology

The Open Mechanical Engineering Journal ◽

10.2174/1874155x01408010077 ◽

2014 ◽

Vol 8 (1) ◽

pp. 77-80

Author(s):

Ying Song ◽

Zhichen Wang ◽

Yanliang Du

Keyword(s):

Visual Inspection ◽

Strain Sensor ◽

Condition Index ◽

Contact Forces ◽

Strain Response ◽

Element Analysis ◽

Monitoring Method ◽

Sensing Technology ◽

Train Speed ◽

Set Up

Wheel out-of-roundness (OOR) inevitably jeopardizes the safety of railway operations. Regular visual inspection and checking by experienced workers are the commonly adopted practices to identify wheel defects. However, the defects may not be spotted timely. The paper puts forward a new method of real-time monitor wheel OOR based on PVDF strain sensor. In this method, the track strain response upon wheel-rail interaction is measured and processed to generate a condition index which directly reflects the wheel condition. Firstly, theoretical model of relationship between PVDF sensor output and wheel/rail loads was set up, and the principle for measuring vertical wheel/rail contact forces was proposed. Secondly, the effects of horizontal wheel/rail force and train speed on the output results have been discussed. Finally, this approach was verified by finite element analysis, and the preliminary results showed that this electromagnetic-immune system provides an effective alternative for wheel defects’ detection.

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Development of a Luminal Esophageal Temperature Monitoring Device for Use During Treatment for Atrial Fibrillation

ASME-JSME 2018 Joint International Conference on Information Storage and Processing Systems and Micromechatronics for Information and Precision Equipment ◽

10.1115/isps-mipe2018-8578 ◽

2018 ◽

Author(s):

Scott Garner ◽

Karcher Morris ◽

Raul Pegan ◽

Thomas Savides ◽

Frank E. Talke

Keyword(s):

Finite Element ◽

Ex Vivo ◽

Numerical Study ◽

Temperature Monitoring ◽

Esophageal Wall ◽

Esophageal Temperature ◽

Element Analysis ◽

Flow Through ◽

Set Up ◽

Potential Use

Luminal esophageal temperature monitoring is of high importance during catheter ablation surgeries of the left atrium. A device is currently under development to accurately measure temperature of the inner esophageal wall. Ex vivo tests using porcine esophageal and left atrial tissue have been set up and performed to better understand heat flow through the biomaterials in contact. To compliment ex vivo experiments, a numerical analysis using thermal finite element analysis has been implemented to compliment ex vivo experiments with a numerical study of the temperature distribution across tissue layers as a function of tissue thickness, as well as heat source contact size and time. Both the ex vivo experiments and finite element simulations aid in development of a practical prototyped device for potential use during catheter ablations.

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Numerical Analysis to Predict Dynamic Response of Mini Cantilever Beam Submerged in Viscous Fluids

Volume 11: Nano and Micro Materials, Devices and Systems; Microsystems Integration ◽

10.1115/imece2011-62188 ◽

2011 ◽

Cited By ~ 1

Author(s):

A. Hossain ◽

A. Mian

Keyword(s):

Dynamic Response ◽

Resonant Frequency ◽

Cantilever Beam ◽

Numerical Study ◽

Numerical Analyses ◽

Fluid Viscosity ◽

Q Factor ◽

Element Analysis ◽

Viscous Media ◽

Set Up

This research employed the finite element analysis (FEA) method to predict the dynamic response of a mini cantilever beam partially submerged in viscous media. First, the FEA method was validated by comparing the numerical results with corresponding experiments. Then, extensive numerical analyses were performed to investigate the variation of modal response in terms of resonant frequency and Q-factor with changing fluid viscosity and density. The resonant frequency of the beam was found to be reduced with increasing the fluid viscosity and density. The Q-factor was also reduced with increasing fluid viscosity. However, it did not changed significantly by changing fluid density. Numerical analyses were also repeated with varying the depth of beam (one-third, two-third and full) submerged in viscous media. The beam was found to be the most sensitive to respond in resonant frequency and Q-factor when submerged by one-third in viscous media. Results obtained from this numerical study can be used to design the optimized MEMS based test set up for measuring the rheological properties of viscous fluid.

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Technical Brief: Finite Element Modeling of Tight Elastic Knots

Journal of Applied Mechanics ◽

10.1115/1.4049023 ◽

2020 ◽

pp. 1-7

Author(s):

Changyeob Baek ◽

Paul Johanns ◽

Tomohiko G. Sano ◽

Paul Grandgeorge ◽

Pedro M. Reis

Keyword(s):

Finite Element ◽

Mechanical Behavior ◽

Mechanical Response ◽

Three Dimensional ◽

Test Cases ◽

Element Analysis ◽

3D Deformation ◽

Predictive Understanding ◽

Set Up ◽

3D Solid

Abstract We present a methodology to simulate the mechanics of knots in elastic rods using geometrically nonlinear, full three-dimensional (3D) finite element analysis. We focus on the mechanical behavior of knots in tight configurations, for which the full 3D deformation must be taken into account. To set up the topology of our knotted structures, we apply a sequence of prescribed displacement steps to the centerline of an initially straight rod that is meshed with 3D solid elements. Self-contact is enforced with a normal penalty force combined with Coulomb friction. As test cases, we investigate both overhand and figure-of-eight knots. Our simulations are validated with precision model experiments, combining rod fabrication and X-ray tomography. Even if the focus is given to the methods, our results reveal that 3D deformation of tight elastic knots is central to their mechanical response. These findings contrast to a previous analysis of loose knots, for which 1D centerline-based rod theories sufficed for a predictive understanding. Our method serves as a robust framework to access complex mechanical behavior of tightly knotted structures that are not readily available through experiments nor existing reduced-order theories.

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Discrete element analysis of the punching behaviour of a secured drapery system: from laboratory characterization to idealized in situ conditions

Acta Geotechnica ◽

10.1007/s11440-020-01119-z ◽

2021 ◽

Author(s):

Antonio Pol ◽

Fabio Gabrieli ◽

Lorenzo Brezzi

Keyword(s):

Mechanical Response ◽

Steel Wire ◽

Discrete Element ◽

Wire Mesh ◽

Steel Plates ◽

Loading Conditions ◽

Element Analysis ◽

In Situ Conditions ◽

Wire Meshes

AbstractIn this work, the mechanical response of a steel wire mesh panel against a punching load is studied starting from laboratory test conditions and extending the results to field applications. Wire meshes anchored with bolts and steel plates are extensively used in rockfall protection and slope stabilization. Their performances are evaluated through laboratory tests, but the mechanical constraints, the geometry and the loading conditions may strongly differ from the in situ conditions leading to incorrect estimations of the strength of the mesh. In this work, the discrete element method is used to simulate a wire mesh. After validation of the numerical mesh model against experimental data, the punching behaviour of an anchored mesh panel is investigated in order to obtain a more realistic characterization of the mesh mechanical response in field conditions. The dimension of the punching element, its position, the anchor plate size and the anchor spacing are varied, providing analytical relationships able to predict the panel response in different loading conditions. Furthermore, the mesh panel aspect ratio is analysed showing the existence of an optimal value. The results of this study can provide useful information to practitioners for designing secured drapery systems, as well as for the assessment of their safety conditions.

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Design and analysis of concrete-filled tubular flange girders under combined loading

Advances in Structural Engineering ◽

10.1177/13694332211001520 ◽

2021 ◽

pp. 136943322110015

Author(s):

Rana Al-Dujele ◽

Katherine Ann Cashell

Keyword(s):

Finite Element ◽

Axial Force ◽

Failure Modes ◽

Numerical Study ◽

Combined Loading ◽

Torsional Stiffness ◽

Fe Model ◽

Combined Effects ◽

Element Analysis ◽

Hollow Section

This paper is concerned with the behaviour of concrete-filled tubular flange girders (CFTFGs) under the combination of bending and tensile axial force. CFTFG is a relatively new structural solution comprising a steel beam in which the compression flange plate is replaced with a concrete-filled hollow section to create an efficient and effective load-carrying solution. These members have very high torsional stiffness and lateral torsional buckling strength in comparison with conventional steel I-girders of similar depth, width and steel weight and are there-fore capable of carrying very heavy loads over long spans. Current design codes do not explicitly include guidance for the design of these members, which are asymmetric in nature under the combined effects of tension and bending. The current paper presents a numerical study into the behaviour of CFTFGs under the combined effects of positive bending and axial tension. The study includes different loading combinations and the associated failure modes are identified and discussed. To facilitate this study, a finite element (FE) model is developed using the ABAQUS software which is capable of capturing both the geometric and material nonlinearities of the behaviour. Based on the results of finite element analysis, the moment–axial force interaction relationship is presented and a simplified equation is proposed for the design of CFTFGs under combined bending and tensile axial force.

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Evolution of Meniscal Biomechanical Properties with Growth: An Experimental and Numerical Study

Bioengineering ◽

10.3390/bioengineering8050070 ◽

2021 ◽

Vol 8 (5) ◽

pp. 70

Author(s):

Marco Ferroni ◽

Beatrice Belgio ◽

Giuseppe M. Peretti ◽

Alessia Di Giancamillo ◽

Federica Boschetti

Keyword(s):

Mechanical Properties ◽

Stress Relaxation ◽

Developmental Stage ◽

Mechanical Response ◽

Numerical Study ◽

Numerical Models ◽

Mechanical Stimulus ◽

Specific Response ◽

Mechanical Parameters ◽

Biochemical Analyses

The menisci of the knee are complex fibro-cartilaginous tissues that play important roles in load bearing, shock absorption, joint lubrication, and stabilization. The objective of this study was to evaluate the interaction between the different meniscal tissue components (i.e., the solid matrix constituents and the fluid phase) and the mechanical response according to the developmental stage of the tissue. Menisci derived from partially and fully developed pigs were analyzed. We carried out biochemical analyses to quantify glycosaminoglycan (GAG) and DNA content according to the developmental stage. These values were related to tissue mechanical properties that were measured in vitro by performing compression and tension tests on meniscal specimens. Both compression and tension protocols consisted of multi-ramp stress–relaxation tests comprised of increasing strains followed by stress–relaxation to equilibrium. To better understand the mechanical response to different directions of mechanical stimulus and to relate it to the tissue structural composition and development, we performed numerical simulations that implemented different constitutive models (poro-elasticity, viscoelasticity, transversal isotropy, or combinations of the above) using the commercial software COMSOL Multiphysics. The numerical models also allowed us to determine several mechanical parameters that cannot be directly measured by experimental tests. The results of our investigation showed that the meniscus is a non-linear, anisotropic, non-homogeneous material: mechanical parameters increase with strain, depend on the direction of load, and vary among regions (anterior, central, and posterior). Preliminary numerical results showed the predominant role of the different tissue components depending on the mechanical stimulus. The outcomes of biochemical analyses related to mechanical properties confirmed the findings of the numerical models, suggesting a specific response of meniscal cells to the regional mechanical stimuli in the knee joint. During maturation, the increase in compressive moduli could be explained by cell differentiation from fibroblasts to metabolically active chondrocytes, as indicated by the found increase in GAG/DNA ratio. The changes of tensile mechanical response during development could be related to collagen II accumulation during growth. This study provides new information on the changes of tissue structural components during maturation and the relationship between tissue composition and mechanical response.

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On Hydromechanical Interaction during Propagation of Localized Damage in Rocks

Minerals ◽

10.3390/min11020162 ◽

2021 ◽

Vol 11 (2) ◽

pp. 162

Author(s):

A.A. Jameei ◽

S. Pietruszczak

Keyword(s):

Numerical Study ◽

Fluid Pressure ◽

Implicit Time ◽

Integration Scheme ◽

Internal Length ◽

Element Analysis ◽

Equivalent Permeability ◽

Mechanical Coupling ◽

Splitting Test ◽

Localized Damage

This paper provides a mathematical description of hydromechanical coupling associated with propagation of localized damage. The framework incorporates an embedded discontinuity approach and addresses the assessment of both hydraulic and mechanical properties in the region intercepted by a fracture. Within this approach, an internal length scale parameter is explicitly employed in the definition of equivalent permeability as well as the tangential stiffness operators. The effect of the progressive evolution of damage on the hydro-mechanical coupling is examined and an evolution law is derived governing the variation of equivalent permeability with the continuing deformation. The framework is verified by a numerical study involving 3D simulation of an axial splitting test carried out on a saturated sample under displacement and fluid pressure-controlled conditions. The finite element analysis incorporates the Polynomial-Pressure-Projection (PPP) stabilization technique and a fully implicit time integration scheme.

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Fast Two-Stage Computation of an Index Policy for Multi-Armed Bandits with Setup Delays

Mathematics ◽

10.3390/math9010052 ◽

2020 ◽

Vol 9 (1) ◽

pp. 52

Author(s):

José Niño-Mora

Keyword(s):

Numerical Study ◽

Arithmetic Operation ◽

Bandit Problem ◽

Index Policy ◽

Two Stage ◽

Second Stage ◽

Whittle Index ◽

Set Up ◽

Computing Method ◽

Special Case

We consider the multi-armed bandit problem with penalties for switching that include setup delays and costs, extending the former results of the author for the special case with no switching delays. A priority index for projects with setup delays that characterizes, in part, optimal policies was introduced by Asawa and Teneketzis in 1996, yet without giving a means of computing it. We present a fast two-stage index computing method, which computes the continuation index (which applies when the project has been set up) in a first stage and certain extra quantities with cubic (arithmetic-operation) complexity in the number of project states and then computes the switching index (which applies when the project is not set up), in a second stage, with quadratic complexity. The approach is based on new methodological advances on restless bandit indexation, which are introduced and deployed herein, being motivated by the limitations of previous results, exploiting the fact that the aforementioned index is the Whittle index of the project in its restless reformulation. A numerical study demonstrates substantial runtime speed-ups of the new two-stage index algorithm versus a general one-stage Whittle index algorithm. The study further gives evidence that, in a multi-project setting, the index policy is consistently nearly optimal.

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