• Title/Summary/Keyword: Mechanical Motion Capture

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A mechanical response of functionally graded nanoscale beam: an assessment of a refined nonlocal shear deformation theory beam theory

  • Zemri, Amine;Houari, Mohammed Sid Ahmed;Bousahla, Abdelmoumen Anis;Tounsi, Abdelouahed
    • Structural Engineering and Mechanics
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    • v.54 no.4
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    • pp.693-710
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    • 2015
  • This paper presents a nonlocal shear deformation beam theory for bending, buckling, and vibration of functionally graded (FG) nanobeams using the nonlocal differential constitutive relations of Eringen. The developed theory account for higher-order variation of transverse shear strain through the depth of the nanobeam, and satisfy the stress-free boundary conditions on the top and bottom surfaces of the nanobeam. A shear correction factor, therefore, is not required. In addition, this nonlocal nanobeam model incorporates the length scale parameter which can capture the small scale effect and it has strong similarities with Euler-Bernoulli beam model in some aspects such as equations of motion, boundary conditions, and stress resultant expressions. The material properties of the FG nanobeam are assumed to vary in the thickness direction. The equations of motion are derived from Hamilton's principle. Analytical solutions are presented for a simply supported FG nanobeam, and the obtained results compare well with those predicted by the nonlocal Timoshenko beam theory.

A unified formulation for modeling of inhomogeneous nonlocal beams

  • Ebrahimi, Farzad;Barati, Mohammad Reza
    • Structural Engineering and Mechanics
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    • v.66 no.3
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    • pp.369-377
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    • 2018
  • In this article, buckling and free vibration of functionally graded (FG) nanobeams resting on elastic foundation are investigated by developing various higher order beam theories which capture shear deformation influences through the thickness of the beam without the need for shear correction factors. The elastic foundation is modeled as linear Winkler springs as well as Pasternak shear layer. The material properties of FG nanobeam are supposed to change gradually along the thickness through the Mori-Tanaka model. The small scale effect is taken into consideration based on nonlocal elasticity theory of Eringen. From Hamilton's principle, the nonlocal governing equations of motion are derived and then solved applying analytical solution. To verify the validity of the developed theories, the results of the present work are compared with those available in literature. The effects of shear deformation, elastic foundation, gradient index, nonlocal parameter and slenderness ratio on the buckling and free vibration behavior of FG nanobeams are studied.

A refined nonlocal hyperbolic shear deformation beam model for bending and dynamic analysis of nanoscale beams

  • Bensaid, Ismail
    • Advances in nano research
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    • v.5 no.2
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    • pp.113-126
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    • 2017
  • This paper proposes a new nonlocal higher-order hyperbolic shear deformation beam theory (HSBT) for the static bending and vibration of nanoscale-beams. Eringen's nonlocal elasticity theory is incorporated, in order to capture small size effects. In the present model, the transverse shear stresses account for a hyperbolic distribution and satisfy the free-traction boundary conditions on the upper and bottom surfaces of the nanobeams without using shear correction factor. Employing Hamilton's principle, the nonlocal equations of motion are derived. The governing equations are solved analytically for the edges of the beam are simply supported, and the obtained results are compared, as possible, with the available solutions found in the literature. Furthermore, the influences of nonlocal coefficient, slenderness ratio on the static bending and dynamic responses of the nanobeam are examined.

Motion Analysis of Head and Neck of Human Volunteers in Low-Speed Rear Impact (저속 후방 추돌 자원자 실험을 통한 두부와 경부의 동작분석)

  • Hong, Seong Woo;Park, Won-Pil;Park, Sung-Ji;You, Jae-Ho;Kong, Sejin;Kim, Hansung
    • Journal of Auto-vehicle Safety Association
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    • v.4 no.2
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    • pp.37-43
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    • 2012
  • The purpose of this research is to obtain and analyze dynamic responses from human volunteers for the development of the human-like mechanical or mathematical model for Korean males in automotive rear collisions. This paper focused on the introduction to a low-speed rear impact sled test involving Korean male subjects, and the accumulation of the motion of head and neck. A total of 50 dynamic rear impact sled tests were performed with 50 human volunteers, who are 30-50 year-old males. Each subject can be involved in only one case to prevent any injury in which he was exposed to the impulse that was equivalent to a low-speed rear-end collision of cars at 5-8 km/h for change of velocity, so called, ${\Delta}V$. All subjects were examined by an orthopedist to qualify for the test through the medical check-up of their necks and low backs prior to the test. The impact device is the pendulum type, tuned to simulate the crash pulse of a real vehicle. All motions and impulses were captured and measured by motion capture systems and pressure sensors on the seat. Dynamic responses of head and T1 were analyzed in two cases(5 km/h, 8 km/h) to compare with the results in the previous studies. After the experiments, human subjects were examined to check up any change in the post medical analysis. As a result, there was no change in MRI and no injury reported. Six subjects experienced a minor stiffness on their back for no more than 2 days and got back to normal without any medical treatment.

A Study on the Side Collision Accident Reconstruction Using Database of Crush Test of Model Cars (모형자동차 충돌시험의 데이터베이스를 이용한 측면 충돌사고 재구성)

  • Sohn, Jeong-Hyun;Park, Seok-Cheon;Kim, Kwang-Suk
    • Transactions of the Korean Society of Automotive Engineers
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    • v.17 no.2
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    • pp.49-56
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    • 2009
  • In this study, a side collision accident reconstruction using database based on the deformed shape information from the collision test using model cars is suggested. A deformation index and angle index related to the deformed shape is developed to set the database for the collision accident reconstruction algorithm. Two small size RC cars are developed to carry out the side collision test. Several side collision tests according to the velocity and collision angles are performed for establishing the side collision database. A high speed camera with 1000fps is used to capture the motion of the car. A side collision accident reconstruction algorithm is developed and applied to find the collision conditions before the accident occurs. Two collision cases are tested to validate the database and the algorithm. The results obtained by the reconstruction algorithm show good match with original conditions with regard to the velocity and angle.

Study of Spring Modeling Techniques for Kinematic and Dynamic Analysis of a Spring Operating Mechanism for the Circuit Breaker (회로차단기용 스프링조작기의 기구동역학 해석을 위한 스프링모델링 기법 연구)

  • Sohn, Jeong-Hyun;Lee, Seung-Kyu;Kim, Seung-Oh;Yoo, Wan-Suk
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.31 no.7 s.262
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    • pp.777-783
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    • 2007
  • Since the performance of the circuit breaker mainly depends on the spring operating mechanism, the analysis of the spring operating mechanism is required. The spring, especially closing spring, stores the deformation energy due to the compression and then accelerates the big loads rapidly in the circuit breaker. To accurately carry out the kinematic and dynamic analysis of the circuit breaker, the precise modeling of the spring behavior is necessary. In this paper, the static stiffness of the spring is captured by using the tester. A simple mechanism similar to the spring operating mechanism was designed to generate the release motion of the spring. A high speed camera was used to capture the behavior of the spring. Three types of spring models such as a linear spring model, modal spring model, and nodal spring model are suggested and compared with the experimental results.

Deformation characteristics of spherical bubble collapse in Newtonian fluids near the wall using the Finite Element Method with ALE formulation

  • Kim See-Jo;Lim Kyung-Hun;Kim Chong-Youp
    • Korea-Australia Rheology Journal
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    • v.18 no.2
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    • pp.109-118
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    • 2006
  • A finite-element method was employed to analyze axisymmetric unsteady motion of a deformable bubble near the wall. In the present study a deformable bubble in a Newtonian medium near the wall was considered. In solving the governing equations a structured mesh generator was used to describe the collapse of highly deformed bubbles with the Arbitrary Lagrangian Eulerian (ALE) method being employed in order to capture the transient bubble boundary effectively. In order to check the accuracy of the present FE analysis we compared the results of our FE solutions with the result of the collapse of spherical bubbles in a large body of fluid in which solutions can be obtained using a 1D FE analysis. It has been found that 1D and 2D bubble deformations are in good agreement for spherically symmetric problems confirming the validity of the numerical code. Non-spherically symmetric problems were also solved for the collapse of bubble located near a plane solid wall. We have shown that a microjet develops at the bubble boundary away from the wall as already observed experimentally. We have discussed the effect of Reynolds number and distance of the bubble center from the wall on the transient collapse pattern of bubble.

Vertical Limb Stiffness Increased with Gait Speed in the Elderly (노인군 보행 속도 증가에 따른 하지 강성 증가)

  • Hong, Hyun-Hwa;Park, Su-Kyung
    • Journal of the Korean Society for Precision Engineering
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    • v.28 no.6
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    • pp.687-693
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    • 2011
  • Spring-mass models have been widely accepted to explain the basic dynamics of human gait. Researchers found that the leg stiffness increased with gait speed to increase energy efficiency. However, the difference of leg stiffness change with gait speed between the young and the elderly has not been verified yet. In this study, we calculated the lower limb stiffness of the elderly using walking model with an axial spring. Vertical stiffness was defined as the ratio of the vertical force change to the vertical displacement change. Seven young and eight elderly subjects participated to the test. The subjects walked on a 12 meter long, 1 meter wide walkway at four different gait speeds, ranging from their self-selected speed to maximum speed randomly. Kinetic and kinematic data were collected using three force plates and motion capture cameras, respectively. The vertical stiffness of the two groups increased as a function of walking speed. Maximum walking speed of the elderly was slower than that of the young, yet the walking speed correlated well with the optimal stiffness that maximizes propulsion energy in both groups. The results may imply that human may use apparent limb stiffness to optimize energy based on spring-like leg mechanics.

Work Posture Analysis Using Digital Ergonomic Simulation (디지털 인간공학 시뮬레이션 기법을 이용한 작업자세 분석)

  • Kim, Nam-Du;Yim, Hyun-June;Park, Hee-Sok;Cha, Tae-In
    • Journal of the Ergonomics Society of Korea
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    • v.26 no.2
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    • pp.81-88
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    • 2007
  • The objective of this study was to investigate the validity of the digital ergonomic simulation (DES) method as a prospective alternative to the ergonomic analyses conducted by experts. The DES method utilizes commercial digital manufacturing software, and can compute the RULA scores continuously throughout the simulated work cycle. It was shown in a case study that the accuracy and objectivity of the DES method are superior to those obtained by experts. Also, it was demonstrated that the DES method has a distinct capability to simulate and validate a proposed work plan. Major limitations of the current DES method lie in the extensive time and efforts required for accurate digital simulation, which may be overcome through an automatic module for RULA data acquisition and a motion capture system.

A semi-analytical study on the nonlinear pull-in instability of FGM nanoactuators

  • Attia, Mohamed A.;Abo-Bakr, Rasha M.
    • Structural Engineering and Mechanics
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    • v.76 no.4
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    • pp.451-463
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    • 2020
  • In this paper, a new semi-analytical solution for estimating the pull-in parameters of electrically actuated functionally graded (FG) nanobeams is proposed. All the bulk and surface material properties of the FG nanoactuator vary continuously in thickness direction according to power law distribution. Here, the modified couple stress theory (MCST) and Gurtin-Murdoch surface elasticity theory (SET) are jointly employed to capture the size effects of the nanoscale beam in the context of Euler-Bernoulli beam theory. According to the MCST and SET and accounting for the mid-plane stretching, axial residual stress, electrostatic actuation, fringing field, and dispersion (Casimir or/and van der Waals) forces, the nonlinear nonclassical equation of motion and boundary conditions are obtained derived using Hamilton principle. The proposed semi-analytical solution is derived by employing Galerkin method in conjunction with the Particle Swarm Optimization (PSO) method. The proposed solution approach is validated with the available literature. The freestanding behavior of nanoactuators is also investigated. A parametric study is conducted to illustrate the effects of different material and geometrical parameters on the pull-in response of cantilever and doubly-clamped FG nanoactuators. This model and proposed solution are helpful especially in mechanical design of micro/nanoactuators made of FGMs.