International Journal of Engineering
Volume:14 Issue: 3, Aug 2001

Among the many force s to which hydraulic structures are exposed to, the forces induced by cavitation incident are of typical hydrodynamic unknown forces. The aim of this study is to define these forces as coupled fluid-structure interaction under two dynamic effects. The first dynamic effect which incorporates facilities for dealing with cavitation fluid is based on the appearance and bursting of vapor bubbles. The second hydrodynamic effect is dynamic excitation mechanism of the structure. In fluid-structure interaction, both the structure behavior and fluid are considered linear. Fluids can take some tension the extent of which depends on concentration and size of micro bubbles present; nevertheless, if the absolute pressure drops to a value close to the vapor pressure of the fluid, bubbles are formed and cavitation phenomena occurs. In this paper a fixed-wheel gate under the head pressure of a reservoir is considered to be affected by under flow cavitation. Normally, partially opened gates induce energy dissipation resulting in high turbulence, causing negative pressure and cavitation at the back and this excites the gate vibration. Moreover, there are several mechanisms which may cause heavy, self-excited vibration. According to the proposed method, a time function presenting the oscillation and pressure fluctuation in t he vicinity of gate lip is estimated. This estimation is based on the parameters obtained from a two dimensional solution of flow under the gate lip. Accordingly, periodic time variable nodal forces are calculated and applied to gate lip element nodes. A transient dynamic solution of the gate, while its lip is sustaining nodal forces is estimated as time function. The results for the most sever modal deformation of the structure time history of some critical elements and variation of equivalent force versus time are presented.

The permanent deformation pavement of roads and streets at tropical zones Abstract (if layers are sufficiently compacted) is due to increase of asphalt layers temperature and consequential decrease of modulus of elasticity. Therefore, the asphalt mixture moves aside of the wheels of heavy vehicles and cause permanent deformations without volume variation. On the other hand, if the asphalt layer modulus of elasticity is not appropriate, additional stresses will be moved to the soil subgrade and thus causes permanent deformation. The materials used for the asphalt layers can be controlled by the proposed method so that additional stresses can be avoided. This study includes three types of pavements (thin, intermediate and thick) on three kinds of subgrades (weak, intermediate and strong) at tropical zones of Iran. Modulus of elasticity and Poisson ratio of layers are selected based on the earlier studies. The heavy axles of vehicles in Iran which cause the most damages are considered in this study (13 tons with two axle trucks). Then the modulus of elasticity of the asphalt mixtures is changed and stress-strain analysis is performed by the Elsym5 computer software to produce the maximum normal strain at the subgrade for all above mentioned types. The number of passing axles used in the analysis is obtained by the formula proposed by the Asphalt Institute (N=1.6×10-9(ε)-4.477). Nomographs showing number of passing axles versus modulus of elasticity for all cases based on the computer analysis are drawn. The designed pavement can be compared to the corresponding nomograph mentioned above to control the modulus of elasticity of asphalt mixtures which prevent the subgrade from additional stresses by using the predicted passing axles.

Shaft position sensing is an essential part of switched reluctance (SR) motor drive In order to synchronize the pulses of phase current with the period of rising inductance of the proper motor phase. Direct sensors such as, Hall effect and optical encoder are commonly used in SR motors. The purpose of this paper is to present an indirect shaft positioning sensing known as "sensorless " control for switched reluctance motor. It uses stator inductance measurement technique by multiplexing each phase inductance to predict the rotor position and also using a micro controller to produce proper gate pulses for the motor phases. This circuit has the ability of controlling the proper advancement of firing time for each power transistor (adjusting the dwell angle) in the drive circuit either manually or automatically for different speeds. It has also the option of selecting the direction of rotation for the motor and uses a PWM scheme for variable speed as well as, a full stop braking system. This control circuit in conjunction with a two switch per phase configuration converter drive has been tested on a 35W, 12V; 3-phase switched reluctance motor and the test results are presented.

The capability of multilevel input ring-TCM coding scheme for generating high-rate codes with improved symbol Hamming and squared Euclidean distances is demonstrated. The existence of uniform codes and the decoder complexity are also considered.

A New Static Var Generator (SVG), using cascaded full-bridge inverters (FBI) with binary output levels and the parallel connections of two cascaded inverters by means of current sharing reactor in each phases is introduced. The new M-level inverter, where M is 2n+2 - 3, consists of only 2n single-phase full bridges for each phases. The proposed technique not only increases the current capacity of proposed SVG but also decreases the output harmonic contents. Also, it can be connected directly to the distribution system without a transformer. Simulation results, based on the PSCAD/EMTDC, a high performance electromagnetic transient simulation program, are used to illustrate the flexibility of control action and also the performance of the proposed SVG in a power system environment.

In this paper a fuzzy expert system for predicting the performance of a switched reluctance motor has been developed. The design vector consists of design parameters, and output performance variables are efficiency and torque ripple. An accurate analysis program based on Improved Magnetic Equivalent Circuit (IMEC) method has been used to generate the input-output data. These input-output data is used to produce the initial fuzzy rules for predicting the performance of Switched Reluctance Motor (SRM). The initial set of fuzzy rules with triangular membership functions has been devised using a table look-up scheme. The initial fuzzy rules have been optimized to a set of fuzzy rules with Gaussian membership functions using gradient descent training scheme. The performance prediction results for a 6/8, 4kw, SR motor shows good agreement with the results obtained from IMEC method or Finite Element (FE) analysis. The developed fuzzy expert system can be used for fast prediction of motor performance in the optimal design process or on-line control schemes of SR motor.

The forward position kinematics (FPK) of a parallel manipulator with new architecture supposed to be used as a moving mechanism in a flight simulator project is discussed in this paper. The closed form solution for the FPK problem of the manipulator is first determined. It has, then, been shown that there are at most 24 solutions for FPK problem. This result has been verified by using other techniques such as geometric approach and a numerical method known as polynomial continuation. Numerical examples are performed to display all possible solutions available for the devised manipulator.

This paper deals with kinematics and dynamics of the human shoulder in order to obtain the workspace related to the reachability of the wrist and applications to determine load for the wheelchair. The model contains six revolute degrees of freedom (D.O.F), two in costoclavicular and three in the shoulder joint and one in the elbow joint, while a six D.O.F model was developed according to given information of this study. A general computational procedure for the human shoulder given arbitrary trajectory is laid out in detail. Kinematics and dynamic behavior of the model were then considered. Finally, a numerical example involving a six-degree of freedom manipulator using the method is presented and the results are discussed for a specified trajectory.

In this study the interaction between self-excited and paramet rically excited oscillations in two-degree-of-freedom systems with quadratic nonlinearities is investigated. The fundamental parametric resonance of the first mode and 3:1 internal resonance is considered, followed by 1:2 internal and parametric resonances of the second mode. The method of multiple time scales is applied to derive four first-order non-linear ordinary differential equations that describe the modulation of the amplitudes and phases of both modes caused by resonance. These equations are used to determine steady state amplitudes. To determine stability of the steady state solutions, small disturbances in the amplitudes and phases are superposed on the steady state solutions and the resulting equations are linearized. The eigenvalues of the corresponding system of first-order differential equations determine the stability of the steady state solutions. The instability modes are discussed and the amplitude and frequency response curves are presented by varying parameters of the system.

Exhaust Gas Recirculation (EGR) concept is the most simple and Abstract more economical method for NO pollutant reduction in spark ignition engines. However, when the higher amount of the EGR gas enters into the engine, the power, torque and fuel economy of the engine decrease. One effective solution for reduction of undesirable effect of this method is to use cooled EGR, that results in more reduction of NO pollutant, in the meantime imposing lesser reduction on engine performance. For this purpose a mathematical model has been developed for simulation this method by using two zone combustion model. Results indicate that, when the cooled EGR is use d, be ca use o f the higher he a ting specific values of two principle species existed in exhaust gases, namely CO2 and H2O, reduction of combust ion chamber temperature is higher, hence, the amount of NO emission decreases further. In turn, because of higher specific mass of cooled EGR gas in comparison with hot EGR, the mass of the mixture in cylinder will increase, thus increasing the peak pressure of the combust ion chamber accordingly, and so the power output of the engine will not decrease notably in comparison with non EGR case. The comparison shows that there exist good agreement between the experimental and predicted results.

A linear vortex panel method is extended to include the effect Abstract of ground proximity on the aerodynamic properties of two dimensional airfoils. The image method is used to model the ground effect. According to the results, lift coefficient of an airfoil may increase or decrease in ground effect based on a combinative effect of its camber, thickness, angle of attack and ground clearance. Airfoils with different section parameters are analysed and their relative effectiveness are compared.

In this paper, the results of the Spherical Oil Agglomeration of Abstract. 45 micrometer superpits low grade co al pa rticles (Bagworth Colliery, U.K.) within a su spension are prese nte d.Demineralized agglomerates were recovered directly by sieving on a 106 micrometer sieve. Verygood reductions in the ash content of the feed coal samples were achieved. In order to reducethe high levels of the crude oil dosage comparatively, small quantities of surfactants were added t o the su spension. Of the va rious su rfactant s screened, Tr iton x.405 (non.ionic) proved to bevery efficient and a crude oil reduction of over 60 wt% was achieved for concentrates containing8 wt% ash.