Transactions of the Canadian Society for Mechanical Engineering

Volume 35 (2011), Issue 3

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The present paper reports the time dependent simulation of a turbulent plane synthetic jet using an unsteady Reynolds averaged Navier-Stokes approach on the basis of the first and second moment closure turbulence models. All the applied turbulence models can capture a global feature of the long time averaged flow field quite well. However, the standard k−ε model yields a disappointing prediction of the turbulence field with inaccurately high levels of turbulence kinetic energy and normal Reynolds stress distributions. The second moment closure model with quadratic nonlinear pressure strain approximation shows the most reasonable prediction of the phase averaged flow and turbulence fields.

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An adaptive finite element method is presented to determine the K_I and K_II stress intensity factors of crack plate with different inclusions. The paper starts from describing twodimensional fracture mechanics theory, an adaptive finite element formulation and the reflection photoelastic technique. An adaptive finite element method is evaluated by analyzing two examples. A single edge cracked plate made from polycarbonate. The second example is the slant edge 45° cracked plate subjected to a uniform uniaxial tensile stress. The K_I and K_II results are found to be function of the crack length per width and the inverse function of E ratio. These examples demonstrate the efficiency of the adaptive finite element method to provide accurate solutions as compared to those from the reflection photoelastic technique.

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In this paper, a nonlinear Finite Element (FE) approach based on the layerwise displacement theory is utilized to obtain the interlaminar stresses due to buckling phenomena in unsymmetric laminated smart composite morphing structure. An On/Off control strategy is designed to control the snap-through phenomena. Due to cycling nature of applied load on morphing, these structures are vulnerable to failure due to fatigue. A failure control mechanism utilizing a piezoelectric actuator is developed to control the failure.

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This study aims at measuring the characteristic parameters of form grinding wheels used for microdrill fluting, whose wheel contours are specially made up of combinations of multiple curves. With the aid of the indirect duplication of wheel contours and by using computer vision, this paper presents a systematic process for the wheel contour measurement. The measuring process includes five sequential steps: the edge detection, the straight line detection, the contour separation, the circular arc fitting, and the circular arc angle evaluation. To test the proposed measuring process, a measuring apparatus was built, and experiments measuring the characteristic parameters of diamond grinding wheels used for microdrill fluting were conducted. It showed that the proposed measuring process was feasible to measure the characteristic parameters of certain form grinding wheels used for microdrill fluting.

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The planetary gearbox is a critical mechanism in helicopter transmission systems. Tooth failures in planetary gear sets will cause great risk to helicopter operations. A gear pitting damage level estimation methodology has been devised in this paper by integrating a physical model for simulation signal generation, a three-step statistic algorithm for feature selection and damage level estimation for grey relational analysis. The proposed method was calibrated firstly with fault seeded test data and then validated with the data of other tests from a planetary gear set. The estimation results of test data coincide with the actual test records, showing the effectiveness and accuracy of the method in providing a novel way to model based methods and feature selection and weighting methods for more accurate health monitoring and condition prediction.

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This paper presents a systematic methodology for the design and analysis of an offset slidercrank mechanism with a translating roller-follower. In the proposed approach, a generic kinematic model of the offset slider-crank and roller-follower is constructed using a homogenous coordinate transformation method and the slider cam profile are then derived using conjugate surface theory. The pressure angle and principal curvatures of the designed slider cam are analyzed based on the analytical expression of the cam profile. Finally, the NC data required to machine the slider cam are produced by equating the ability matrix of the 3-axis CNC machine tool with the desired tool location matrix.

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This paper presents direct kinematic analysis of a family of 3R1T parallel manipulators, while R and T denote the rotational and translational degrees of freedom respectively. The manipulators consist of two rigid bodies, a movable platform and a fixed (base) connected to each other by four active legs and one constraining passive leg. First, the direct position kinematics of the manipulators is analyzed. For a general manipulator of this class, this analysis results in a univariate polynomial of degree 30 along with a set of other univariate polynomials of degree 16 and 4 respectively. However, for a special architecture of the manipulators, it is shown that the direct position kinematics leads to a minimal univariate polynomial of degree 12. A numerical example is also included to confirm the results. Moreover, direct velocity and direct kinematic singularities of the manipulators are analyzed using Jacobian matrices.

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One of the key factors in designing a motor built-in high speed spindle is to assemble the motor rotor and shaft by means of hot-fit. Presented in this paper is a study of the influence of a hot-fit rotor on the local stiffness of the hollow shaft. Dynamic analyses of the rotor-hollow shaft assembly using contact elements are conducted. The normal contact stress state between the rotor and the hollow shaft is obtained through the use of contact elements with friction effects included. The normal contact stress, considered as the pr-stress between the rotor and the hollow shaft, is then adopted for subsequent modal analyses. In this study, the modal analysis results are verified by a modal testing experiment. The percent errors of the first natural frequency and the second natural frequency are down to about 0.58% and 0.79%, respectively.