Transactions of the Canadian Society for Mechanical Engineering
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Volume 38 (2014), Issue 1
Finite element based elasto-plastic analysis of classical and first order beams with Armstrong–Frederick kinematic hardening model
Ehsan Hashemi, Behrooz Farshi
This investigation is focused on the elasto-plastic behavior of classical and first order Timoshenko beams by a finite element formulation under two major kinematic hardening models. The approach consists of proposing a finite element formulation with variable stiffness matrix and optimized solution for the Armstrong–Frederick theory together with the Ziegler–Prager model under cyclic flexural and deformation controlled loading conditions. In symmetrical cyclic deformation and flexural controlled states of the first order beams, it was concluded that after several cycles, the total stress-strain curves tend to be coincident. It also corroborates that the anisotropic characteristic cases with symmetric loading exhibit a ratcheting response for both beam models.
Design, simulation and bifurcation analayis of a novel micromachined tunable capacitor with extended tunability
Hamed Mobki, Kaveh Rashvand, Saeid Afrang, Morteza H. Sadegh, Ghader Rezazadeh
In this paper, a novel RF MEMS variable capacitor has been presented. The applied techniques for increasing the tunability of the capacitor are the increasing of the maximum capacitance and decreasing of the minimum capacitance. The proposed structure is a simple cantilever Euler–Bernoulli micro-beam suspended between two conductive plates, in which the lower plate is considered as stationary reference electrode. In this structure, two pedestals are located in both tips of the cantilever beam. In the capacitive micro-structures, increasing the applied voltage decreases the equivalent stiffness of the structure and leads the system to an unstable condition (pull-in phenomenon). By deflecting the beam toward the upper (lower) plate the minimum (maximum) capacitance decreases (increases) and tunability increases consequently. The located pedestals increase and decrease the maximum and minimum capacitance respectively. The results show that the proposed structure increases the tunability of cantilever beam significantly. Furthermore, bifurcation behavior of movable electrode has been investigated.
Geometric approach to solving the inverse displacement problem of calibrated decoupled 6R serial robots
Albert Nubiola, Ilian A. Bonev
This paper presents a simple but efficient way to numerically calculate the inverse displacement problem of calibrated decoupled 6R serial robots. The method is iterative and works with any type of calibrated robot model, such as level-3 models, since it requires no algebraic computation and no resolution of high-order polynomials, only the computation of the forward displacement problem of the calibrated robot model and the inverse kinematics of the nominal robot model. The method proposed can find up to eight possible solutions for a given end-effector pose. A numerical example is presented, with one million arbitrary endeffector poses of a level-3 calibrated ABB IRB 120 robot. The computation time for solving the inverse problem is analyzed, and in most cases is found to be only four times the time needed to calculate the nominal inverse kinematics and the calibrated direct kinematics. Furthermore, the method is fast enough to be implemented directly into the robot controller using the RAPID programming language.
Application of a polygeneration optimization technique for a hospital in northern Ontario
Alberto Romero, Monica Carvalho, Dean L. Millar
An optimization technique based on Mixed Integer Linear Programming (MILP) was applied to a hospital located in Sudbury, Ontario, Canada. The energy services included electricity, heat, steam, and coolth. Different options for the system’s operation were also considered in the optimization procedure. The optimization model determines the optimal configuration of the polygeneration system and the best operational strategy. The primary objective for optimization is to minimize the hospital’s annual energy costs. This objective can be achieved by consuming low-priced natural gas, operating the gas engines at full load to generate electricity, and selling all of this electricity into the provincial grid, which ensures the hospital’s eligibility to receive government payments for cogeneration.
Effect of internal power-angle on turbo-generator rotor vibration characteristics under eccentricity faults
Shuting Wan, Yuling He, Changgeng Zhan
This paper investigates the effect of the turbo-generator internal power-angle on the rotor radial vibration characteristics under air gap eccentricity faults. Firstly the air gap magnetomotive force, the magnetic permeance and the magnetic flux density of the eccentricity faults is deduced, and the formula of the magnetic pull per unit area is obtained. Then the restrictive factors of the magnetomotive force and the internal powerangle are analyzed. The unbalanced magnetic pull (UMP) that acts on the rotor is further deduced, and the rotor vibration characteristics are given. Finally the experiments are taken on a SDF-9 non-salient fault simulating generator to verify the theoretical results. The investigation results of this paper will be beneficial to air gap eccentricity faults diagnosis of turbo-generator.
Analytical approach for estimating the pressure drop potential in convective vortex heat engines
This paper presents a new analytical approach for estimating the pressure drop potential in proposed technical concepts in which convective vortices are to be used as heat engines. The main novelty is analytical connection of the well-known CAPE value with the magnitude of the pressure potential. The proposed analytical approach is important and useful for research in energy concepts where convective vortices are to be used as sources of mechanical work for electricity production. Furthermore, it is the first approach developed by which the pressure drop potential can be calculated for concepts utilising convective vortex heat engines, and it is an important step forward for the theoretical research of alternative energy concepts with convective vortices.
A numerical and experimental investigation of coalescence between cylindrical holes
Joel S. Griffin, Clifford J. Butcher, Zengtao Chen
A sequential digital image technique was employed to detect the onset of coalescence between pairs of holes in tensile specimens. The coalescence event was induced between cylindrical holes that were positioned with various spacing and ligament orientations. Using finite-element analysis as a framework, the coalescence predictions of a classic micromechanical model were compared with the experimental coalescence results. It was found that the predicted strains at coalescence could be significantly improved by accounting for local work-hardening in the ligament region between the two holes. Digital image correlation was used to extract strain values from the digital image record, for both the far-field and the intervoid ligament.
Elastic beam with nonlinear suspension and a dynamic vibration absorber at the free end
Yi-Ren Wang, Chia-Man Chang
This study considered a slender hinged-free beam with suspension cables simulated using nonlinear springs. We added a time-dependent boundary dynamic vibration absorber (DVA) that was suspended at the free end of the beam to reduce vibration and prevent internal resonance. DVA with various spring constants were considered and the optimal mass range for the DVA to reduce vibration in the main structure was also proposed.
Dynamics of a sorting process with a stream of discrete impact loads
Tomasz Piatkowski, Janusz Sempruch, Tomasz Tomaszewski
The sorting process applied to a stream of unit loads (cubiform objects, parcels) transported on conveyors is investigated. The sorting process is performed by means of an active fence (flexible arm) that makes a 1dof rotary motion. The manipulated loads are treated as bodies with nonlinear elastic-damping properties described by modified nonlinear Kelvin model. The equations of motion of the flexible fence, and those of the interacting object, are derived using the finite element method. The assessment of influence of constructional and operating parameters of the fence on the course of the sorting process and dynamic forces exerted on the loads handled is studied.
Three-phase-lag heat conduction in a functionally graded hollow cylinder
Abdolhamid Akbarzadeh, Jiawei Fu, Zengtao Chen
Heat conduction in a functionally graded, infinitely-long hollow cylinder is studied based on the three-phaselag model. Material properties except the phase-lags vary according to a power-law within the cylinder. The phase-lag heat conduction equation is written in a form in which various models of heat conduction theories can be generated. The governing differential equations in the Laplace domain are solved exactly and a numerical Laplace inversion technique is employed for restoring results in the time domain. The effects of different heat conduction theories, phase-lags, geometries, and non-homogeneity indices are studied on the spatial distribution and time-history of temperature.
Full journal title: Transactions of the Canadian Society for Mechanical Engineering
Abreviated journal title: Trans. Can. Soc. Mech. Eng.
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