Transactions of the Canadian Society for Mechanical Engineering

Volume 32 (2008), Issue 2

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In this paper, the nonlinear friction characteristic of a custom made symmetrical linear hydraulic actuator is investigated using the Extended Kalman Filter (EKF). A new and very accurate characterization of friction is made by using a quadratic function of the piston velocity. Further to this proposed empirical friction model, the EKF is used to estimate the function coefficients. In this paper, an iterative approach is used to maintain system observability and render the estimation process more reliable. The study is conducted in simulation and by using measured experimental data. The estimated states and parameters by the EKF are found to be convergent to their known values in simulation and, further to experimental results, unique and repeatable. In addition, changes in the friction characteristics, which can occur in the physical system due to wear in the piston seals or degradation in the oil properties, are detected and accurately estimated by the EKF in simulation. This study presents an accurate nonlinear model for the representation of friction in a hydraulic actuator. It paves the way for the implementation of strategies for early fault detection in hydraulic systems.

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The classic Burmester problem aims at finding the geometric parameters of a planar four-bar linkage whose coupler link attains a prescribed set of finitely separated poses. The solution proposed is claimed to be comprehensive because it (a) includes all four types of dyads - RR (revolute-revolute), PR (prismatic-revolute), RP and PP - and (b) gives due consideration to the numerics behind the solution. A PR dyad is treated as a RR dyad with its fixed joint centre at infinity, similar interpretations applying to RP and PP dyads. The paper includes the synthesis of planar four-bar linkages in its full generality, that of dyads with P joints being given the utmost attention. Finally, the underlying numerics receives the attention seldom found in the literature on the subject, our main concern being numerical robustness.

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This paper investigates the hydraulic behaviour of unconventional radial pump stages observed utilizing the CFD analyses. The main emphasis was put on the influence of radial pump stage (RPS) geometry on the basic flow direction in the pump regime. In order to preclude defining the flow direction as a boundary condition, a closed hydraulic system was modelled to investigate the hydraulic behaviour of the RPS and its energy characteristics. It was confirmed that centripetal flow through the RPS is possible in the pump regime, but not without the installation of an appropriate stator on the inner rotor radius. The influence of the inner rotor radius stator geometry on the basic flow direction in the pump regime is discussed. The manner of the operation type switching between centripetal and centrifugal pumping achieved with the variation of the hydraulic losses within the closed hydraulic system is explained. In addition to the closed hydraulic system calculations used for investigation of the RPS operation in the pump regime, the open hydraulic system was modelled to determine the energy characteristics of the analysed radial pump stages in other operating regimes. All operating regimes of the important RPS cases are presented by means of four-quadrant charts.

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To acquire the fatigue characteristics of viscoelastic suspensions mounted in newly-developed construction vehicles, an experimental study of fatigue characteristics should be carried out on the vibration damping rubber suspension components. However, due to the lack of corresponding fatigue failure criteria for the damping rubber components, how to determine the parameters for the accelerated fatigue experiments becomes a new research subject. Based on the accelerated fatigue experiments on the viscoelastic suspensions, the parameters on fatigue failure characteristics such as the cycle index (n_e), the slope (k) of S-N logarithm curve and the allowable temperature rise, and so on, were investigated. To develop a new viscoelastic suspension for the crawler bulldozer, three types of rubber made from different formulas for the viscoelastic suspensions were studied and their experimental loads were divided into 8 levels in terms of the practical working conditions of the bulldozer. The accelerated fatigue experiments of viscoelastic suspensions were performed and the obtained parameters were applied to the fatigue experiments for the suspensions of a newly-designed 386 kW crawler bulldozer. Under the industrial application over 4,000 hours, the results were shown to be consistent with the predicted experimental values.

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It is well known that the presence of large heterogeneous textured regions in forged near alpha titanium alloys could lead to large variations of mechanical properties when fatigue and creep cycles are applied at room tem perature. On the other hand, experimental studies and microtexture investigations are complex to setup, lengthy and costly, and one cannot expect to understand the alloy behavior by relying only on empirical approaches. Hence, numerical methods are excellent alternatives for analyzing the influence of microscopic and macroscopic heterogeneities on mechanical properties in shorter times and with minimum need for experimentation. In the present investigation, a cellular automata (CA) method was used to simulate the effect of texture heterogeneities, on both local and global mechanical properties. A 2D array of cells was used and the stresses and strains developed in various heterogeneous regions were evaluated using the Eshelby theory. Using the CA method, various types of microstructures were modeled and compared with each other to quantify the influence of processing parameters on mechanical properties. The results predict, and are used to explain, the experimentally phenomena observed in creep responses during cold fatigue/creep tests of near alpha titanium samples.

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Steady, laminar, mixed convection flow was considered in an inclined lid-driven rectangular enclosure heated from one side moving with a constant speed and cooled from the stationary adjacent side while the other sides are kept stationary and adiabatic. The governing equations were solved numerically for the stream function, vorticiry, and temperature ratio using the differential quadrature method for various Reynolds, Grashof, and Richardson numbers as well as different aspect ratios and inclination angles for the enclosure. The results show that the motion of the side wall, the aspect ratio, and the inclination angle of the enclosure had significant effects on the flow and temperature fields.

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An air bearing materials handling system supports its load on two compliant runners having the form of oval cylinders moving along shallow concave rails. Air is supplied by manifolds integral with the rails through nozzles spaced at intervals in the rail surface. Loads up to 3 tonnes can be moved with an effective coefficient of sliding friction of about 1%. Developed by trial-and-error, the system has incompletely understood features. Two are: die role of the system geometry in providing load support; and the construction of the runners, which consist of layers of cellulose fibre tissue wound onto a core, and enclosed in a plastic cover. Exploratory research aimed at establishing the effect of these features on the load fraction supported by air pressure is reviewed. Flat surface equivalents instrumented for pressure surveys are developed to assess the role of the tissue, and to suggest alternatives. The load fraction is determined, and the response to asymmetric loading is investigated. The minimum number of tissue layers necessary for bearing action is identified, and the performance of compliant alternatives is explored. The review concludes with a discussion of the elements required of a mathematical model suitable for guiding design improvement.

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This paper proposes a planetary gear train with ring-involute tooth profile. Inherent in a planetary gear train is the conjugate problem among the sun, the planet gears and the ring gear. The sun gear and the planet gear can be obtained by applying the envelope method to a one-parameter family of a conical tooth surface. The conical tooth rack cutter was presented in a previous paper [5]. The obtained planet gear then becomes the generating surface. The double envelope method can be used to obtain the envelope to the family of generating surfaces. Subsequently the profile of a ring gear of the planetary gear trains can be easily obtained, and using the generated planet gear and applying the gear theory, the ring gear is generated. To illustrate, the planetary gear train with a gear ratio of 24:10:7 is presented. Using rapid prototyping and manufacturing technology, a sun gear, four planet gears, and a ring gear are designed. The RP primitives provide an actual full-size physical model that can be analyzed and used for further development. Results from these mathematical models are applicable to the design of a planetary gear train.

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A geometric model and mathematical model of planetary gear mechanism with double circular-arc teeth is determined using the imaginary rack cutters and double envelope concept. The mathematical model of a ring gear with double circular-arc teeth in a second envelope has been developed. In this paper, the conditions of the gear meshing and contact load of the gears are simulated by assembly errors. The goal of the stress analysis is to determine the contact stress on the planet gear and ring gear, and planet gear and sun gear. Given the assembly errors of the planetary gear mechanism including center distance error and mis-aligmment error, the maximum von-Mises stress in the planetary gear mechanism with double circular-arc teeth is analyzed using visualNastran desktop package. It is found that the center distance error is more critical to mis-alignment error.

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The paper describes recent progress on numerical simulation of soft body impact onto a fibre reinforced composite wing leading edge structure. The work is based on the application of non-linear explicit finite element analysis to simulate the response of composite wing structures under soft body impact loads. Soft body impactors such as gelatine (substitute bird) or ice (hailstones) are highly deformable on impact and flow over the structure spreading the impact load. Therefore, first benchmark simulations were carried out for soft body impact onto a rigid target. Soft body impactor was modeled using the Arbitrary Lagrangian-Eulerian (ALE) method. The results obtained using this impact model for different velocity were compared to the experimental test results in terms of local pressure, including Hugoniot and stagnation pressures, and global load to validate the accuracy of the model. Then, the impact of soft body onto a composite wing structures was described. A composite failure model which includes ply damage and interplay delamination model has been used to predict impact damage in the structure modeled using shell elements. The simulation tool predicts the impact damage in leading edge structure.

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This paper presents a comparative study of three optimization algorithms, namely Genetic Algorithms (GAs), Pattern Search Algorithm (PSA) and Sequential Quadratic Program (SQP), for the design optimization of vehicle suspensions based on a quarter-vehicle model. In the optimization, the three design criteria are vertical vehicle body acceleration, suspension working space, and dynamic tire load. To implement the design optimization, five parameters (sprung mass, un-sprung mass, suspension spring stiffness, suspension damping coefficient and tire stiffness) are selected as the design variables. The comparative study shows that the global search algorithm (GA) and the direct search algorithm (PSA) are more reliable than the gradient based local search algorithm (SQP). The numerical simulation results indicate that the design criteria are significantly improved through optimizing the selected design variables. The effect of vehicle speed and road irregularity on design variables for improving vehicle ride quality has been investigated. A potential design optimization approach to the vehicle speed and road irregularity dependent suspension design problem is recommended.

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This paper examines the effects of geometrical parameters of pillar post rotors on the thermal performance of automotive vehicle brakes. The thermal performance of vented disc brakes strongly depends on the aerodynamic characteristics of the air flow through the rotor passages. These air flow passages are determined by the geometrical parameters of the brake rotors. In this study, different pillar post rotor models are considered and the corresponding numerical simulations are performed, in order to investigate the effects of various geometrical parameters on the thermal performance. These geometrical parameters include the shape, size, and distribution of a pillar post. The new insight from these parametric studies provides useful guidelines to optimize the geometry of pillar post rotors of automotive vehicles.