Transactions of the Canadian Society for Mechanical Engineering

Volume 32 (2008), Issue 3-4

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This paper represents the development of a dynamic model for the rotary-screw dispensing process, by taking into accounts for both fluid compressibility and non-Newtonian flow behavior. In particular, the flow behavior of the fluid being dispensed is characterized by using the power law equation; and then based on the fundamentals of flow in the screw channel and needle, a model is developed to represent the dynamics of the flow rate in the rotary-screw dispensing process. Simulations are carried out to investigate the process performance, with an emphasis on identifying the influence of the key process parameters.

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From a geometric viewpoint, a mathematical model of a single screw compressor with a conjugate pair of meshing conical teeth gate rotor is a conjugate problem. Coordinate transformation and envelope theory are applied to determine the sets of spatial points of the contacting surfaces that define the main rotor of a single screw compressor. Envelope theory and analytical procedure are used to derive mathematical models of a gate rotor and a main rotor. Stress analysis for the single screw compressor mechanism is performed. PowerMILL software package is used to simulate the manufacture of a main rotor. A numerical example with a compressor ratio of 11:6 is presented to demonstrate the application of the mathematical models developed in this paper.

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A new method of filtering strategy, referred to as the Smooth Variable Structure Filter (SVSF) is applied to the problem of state estimation on a class of nonlinear system. The SVSF is revised to reach the better estimation resolution. A comparative study is presented in which the Extended Kalman Filter (EKF) is applied to the same nonlinear system model. The estimation convergence and accuracy of the SVSF and EKF are comparable. The robustness of the SVSF to parameter variations is established through simulation results. This study is important because it allows the new SVSF to be critically compared to a standard technique such as the EKF.

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Trabecular bone's capability to adapt its architecture to the surrounding environment has been a subject of research for more than a century. The purpose of the present work is to simulate and improve a semi-mechanistic bone remodeling theory. In doing so, a computer code was developed using finite element method, also a cellular accommodation effect was incorporated in the model. Using this novel approach, trabecular-like structures for different loading conditions and directionalities similar to actual human bone have resulted for a square plate. Furthermore, it was shown that the model is sensitive loading time history. In summary, results of our research showed that a semi-mechanistic model including cellular accommodation effect is scientifically valid, and is able to predict more realistic morphologies in time-dependent simulations.

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In this paper, we describe a new method for improved performance of inertial sensors, with applications in strap-down inertial systems. A new empirical model is proposed for the bias temperature dependence compensation of accelerometers using their input and output data. Experimental testing of the accelerometer is first realized, as data for 2 inputs and 1 output are collected. Based on this data, an empirical model is built using a neuro-fuzzy network, which learns the process behavior and uses a Fuzzy Inference System (FIS) for model realization. The improvement in the reproduction quality of the experimental surface by the neuro-fuzzy model is achieved through the FIS training using a Sugeno learning algorithm with two inputs and one output. Generation and training of the FIS are performed with Matlab functions, the training of which is realized on a high number of epochs, for example, on a number of 10⁵ training epochs. It is noticed that the proposed algorithm leads to a 35.5 times reduction in the error due to temperature dependence of the bias.

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In motion generation, the objective is to calculate the mechanism parameters required to achieve or approximate a set of prescribed rigid-body positions. This work introduces a new design constraint that considers driving link static torque for a given rigid-body load. By incorporating this new constraint into a conventional spherical four-bar motion generation model [1], spherical four-bar mechanisms are synthesized to achieve-not only prescribed rigid-body positions-but also satisfy a maximum driver static torque for a given rigid-body load.

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This work formulates and demonstrates a motion generation method for the synthesis of a particular type of planar six-bar mechanism-the Watt I mechanism. The Watt I mechanism is essentially a "stacked" four-bar mechanism (having two closed loops and a single degree of freedom). Extending the planar motion generation method of Suh and Radcliffe [11] to incorporate relative motion between moving pivots, Watt I mechanisms are synthesized to simultaneously approximate two groups of prescribed rigidbody poses for simultaneous dual motion generation capability. The example included demonstrates the synthesis of a finger mechanism to achieve a prescribed grasping pose sequence.

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Noise control is important and essential in a manufacturing factory, where the noise level is restricted by the Occupational Safety and Health Act. Several researches on new techniques of single noise control have been well addressed and developed; however, the study of noise depression on the whole plant noise by using optimum allocation planning is hardly found. An improper machine allocation will not only result in the tremendous cost on noise control task, but also cause the harmful environment for the neighborhood; therefore, the approach of optimum and economic allocation of noise sources within a constrained plant area becomes crucial and obligatory. In this paper, a novel technique of simulated annealing (SA) is applied in the numerical optimization, and the multi-noise plant with various sound monitoring systems is also introduced. Before optimization, the single noise is tested and compared with the simulated data from SoundPlan, a commercial sound simulation package, for the accuracy check of the mathematical model. The result reveals to be within good agreements. The proposed SA optimization on the allocation of multi-noise plant surely provides an economic and effective methodology in reducing the sound accumulation around the plant boundary.

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This work uses validated 2D and 3D finite element models of the creep-feed grinding operation to study the effects of face cooling on the workpiece temperatures. The results show that as the intensity of the face cooling is increased the maximum contact temperature decreases and the location of the maximum contact temperature shifts away from the finished workpiece material and towards the uncut workpiece surface. The finite element models are also used to study the maximum temperatures along the workpiece during a complete grinding pass. The temperature profiles show that there are four important temperature features on the workpiece, which are the cut-in, steady-state, temperature spike, and cut-out zones. Cut-in occurs when the grinding wheel initially engages the workpiece, steady-state occurs in the middle of the workpiece, the temperature spike occurs at the beginning of cut-out, and cut-out occurs as the grinding wheel disengages from the workpiece. Finally, the results show that face cooling need only be applied to the area immediately adjacent to the contact zone to be effective and that there is very little benefit to applying coolant to the entire front and back workpiece faces.

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An adjustable six-bar mechanism mechanical press, in which one of its link length can be adjusted and its driving crank also can be varied according to different forming processes, is proved to be feasible in this paper. By properly designing the speed trajectory of the driving crank and the adjusting magnitudes of the adjustable link in length, the desired kinamatic characteristics of the ram can be obtained. The examples are given to verify its feasibility and effectiveness in practical applications.

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The paper presents the fundamentals of the squeeze-flow of the thermal interface material (TIM) that takes place during the pressing of a heat sink to the back side of a flip-chip is studied. A two-dimensional string model is developed for predicting the time-varying plate separation and squeeze-rate in terms of the squeeze force. The predictions are compared to a one-dimensional string model and to a squeeze-drop flow model. Results indicate that the flow resulting from the squeezing of a string of TIM between two rigid plates is truly two-dimensional. The effect of surface tension and of the heat transfer is found to be negligible under the assembly conditions. The flow behaviour of the TIM with suspensions of high thermal conductivity particles is also investigated. It is shown that the fluid remains Newtonian for particle volume fractions smaller than 30%. For volume fractions larger than 30%, the fluid becomes Non-Newtonian during the early stages of the squeezing process, i.e. for t ≤ 1s. In the later stages however (t > 10s), the fluid may be considered Newtonian.

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The paper presents a graphical-analytical technique for the synthesis of non-circular gears in pathgenerating geared five-bar mechanisms. In such mechanisms, a two degree-of-freedom (dof) five-bar linkage is integrated by a pair of non-circular gears to precisely guide a coupler point along a prescribed planar trajectory. The synthesis method proposed here considers the most general case, where the prescribed trajectory consists of a series of open curves. Each segment of the prescribed path identifies a phase of the mechanism motion that is referred to as requested motion branch. In each of these phases, for any prescribed position of the coupler point, the inverse kinematic analysis of the linkage and the Aronhold-Kennedy theorem are used to identify the actual configuration of the system and locate the instantaneous centre of the relative motion between the two cranks of the linkage. The regions of the gear's centrodes, corresponding to the requested motion branches, are thus synthesized. These regions are connected to each other by using proper polynomial functions, as to guarantee a continuous and cyclic motion of the mechanism. An example is illustrated where the requested coupler point trajectory consists of a series of straight line segments.

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In this paper, performance evaluation of wet cooling tower is done. To achieve this aim, first, thermal behavior of counter-flow wet cooling tower is studied through a simulation model. The influence of the environmental conditions on the thermal efficiency of the cooling tower is investigated. The cooling tower performance is simulated in terms of varying air and water temperatures, and of the ambient conditions. This model allows the use of a variety of packing materials. Second, the exergetic analysis is applied to study the cooling tower potential of performance improvement. The model is validated against the experimental data.

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High speed end milling of hardened steel offers several advantages over EDM in die/molds applications especially due to recent development in machine tools, spindles and controllers. However successful implementation of this technology is limited mainly due to faster tool wear and undesirable surface properties. Finite element modeling and simulation techniques are capable of optimizing the cutting conditions and tool geometry by predicting the temperature and stresses distributions. In this study a finite element model has been developed to predict cutting forces, temperature and stresses distributions in flat end milling processes of hardened steel using PCBN at high cutting speeds. High speed end milling experiments were conducted using flat bottom end mills with single insert having straight cutting edge. Comparison of simulated and experimental cutting forces data shows reasonable agreement at high speed regime using the developed model.

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The quality, productivity and safety of machining can be significantly improved through the optimization of cutting conditions. The first step in achieving such an objective is the development of accurate and reliable models for predicting the critical process parameters. In this paper, an innovative Artificial Neural Network (ANN) model that predicts both cutting force and surface roughness in end milling is developed and validated. A set of five input variables is selected to represent the machining conditions while twelve quantities representing two key process parameters, namely, cutting force and surface roughness, form the variables of the network output. Full factorial design of experiments is used to generate data for both training and validation. Successful training of the neural network is demonstrated through comparison of simulated and experimental results for four different output variables, namely cutting force, surface roughness, feed marks, and tooth passing frequency. The predictive ability of the model is verified experimentally by comparing simulated output variables with their experimental counterparts. A good agreement is observed.

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A mathematical model for determining the optimum towing velocity of tabular icebergs is presented. The optimization problem is formulated in terms of a benefit function that takes into account the ice mass delivered and the total fuel consumption for the tow. Results indicate that the optimum towing velocity is mainly affected by the water-to-fuel cost ratio. It is shown that towing icebergs from Antarctica to South Africa is a profitable way of supplying fresh-water provided that the towing velocity is optimized with the proposed method.

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A two-dimensional convection-diffusion-reaction equation is discretized by the finite volume element method on triangular meshes. Time-dependent convection-diffusion-reaction equation is developed along the characteristic path using the characteristic-based scheme, while the finite volume method is employed for deriving the discretized equations. The concept of the finite element technique is applied to estimate the gradient quantities at the cell faces of the finite volume. Numerical test cases have shown that the method does not require any artificial diffusion to improve the solution stability. The robustness and the accuracy of the method have been evaluated by using available analytical and numerical solutions of the pure-convection, convection-diffusion and convection-diffusion-reaction problems.

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All components of the track suffer from a variation in the performance during their lifetime to a different degree. These variations include replacement of timber sleepers with concrete sleepers and changes in the ballast conditions due to tamping or track accumulative loadings. These changes sometimes cause a large discrepancy between results obtained form theoretical evaluations and those obtained from field measurements, making the reliability of the current understanding of the long term behavior of the railway track questionable. There is a need to investigate the impact of the changes in conditions of the track support system on the track design parameters. This research is an attempt to response to this need. In this paper, the influences of the changes in rail support conditions on the magnitude of the rail bending moments (as the main rail design criterion) are investigated. This is achieved through parametric analyses of railway track by developing a theoretical model using dynamic deflection method. The model developed here, considers the main track components and offers the possibility of parametric analyses. The reliability of the model was evaluated by comparing the results obtained from the model with those obtained from measurements in a track field. After calibrating the model, it is used to conduct parametric analyses. The sensitivity of the rail bending moment to the changes in sleeper type and arrangements, and to the ballast mechanical conditions is investigated. The results are discussed aiming at to improve the current understanding of the long term behavior of railways.