Normal stress differences, a phenomenon which is exhibited by many non-Newtonian fluids or non-linear elastic materials, also arises in the Couette flow of granular materials. This problem is studied using a continuum model proposed by Rajagopal and Massoudi (1990). For a steady, fully developed condition, the governing equations were reduced to a system of coupled non-linear ordinary differential equations, and the resulting boundary value problem was solved numerically (Kumar et al., 2003). The expression for one of the normal stress differences is derived in this paper and from the values of volume fraction obtained in (Kumar et al., 2003), the normal stress difference is calculated. The effect of material parameters, i.e., dimensionless numbers on the normal stress difference is studied. It is observed that the distribution parameter, "B₂" and the density parameter "P" affect the normal stress differences most.

    In this paper, a problem of the two-dimensional wave generation due to an initial disturbance at the free surface in an ocean of finite depth in the presence of surface tension and a uniform running stream is investigated. Using linear theory, the problem is formulated as an initial value problem for the velocity potential describing the ensuing motion in the fluid. In the mathematical analysis the Laplace and Hankel transform techniques have been utilized to obtain the elevation of the free surface in the form of an infinite integral. This is then evaluated asymptotically for large time and distance by applying the method of stationary phase. The form of the free surface is depicted graphically for two types of initial disturbances. The effect of the surface tension and the presence of the running stream on the wave motion are discussed.

    A new technique of modelling nonlinear viscoelastic behavior of low-density flexible foams including cellular plastics used in advanced implants, namely, artificial analogs of periodont of the dental system and trabecular bones of the skeletal system has been developed. The material microstructure is modeled by a rod structure with chaotically oriented cubic cells. Young's modulus and critical strain (i.e., the case of stability loosing) dependence on the solid state phase fraction of flexible cellular plastics has been investigated. The dependences of tangential stress on shear strain, hydrostatic pressure on volume strain and axial stress on longitudinal deformation with taking into account solid phase viscosity at a given strain rate have been obtained for the simulated materials. The numerical results led to the conclusion that at a certain compression rate the transversal strain factor of a material becomes negative.

    The Hall effects on unsteady MHD plasma behaviour of a rotating environment with oscillating pressure gradient in the presence of a transverse magnetic field have been studied. The solution in a dimensionless form contains five pertinent flow parameters, viz., 'alpha'_m, E, P, 'omega' and m are, respectively, the magnetic interaction parameter, the Ekman number, the magnetic Prandtl number, the inertial frequency and the Hall current parameter. A new approach is based on the plasma behaviour in the electromagnetic field in a rotating environment which corresponds to inertial frequency over the oscillating pressure gradient. Eventually, the dominance of inertial frequency is experienced by the mechanism; the whole system stops due to the absence of inertial frequency of a rotating environment.

    To design a high speed spindle with enhanced qualitative performances - high accuracy and service life together with a stable dynamic and thermal regime - two main conditions have to be secured: an optimum internal load distribution on the bearings and an efficient and safe lubrication regime. The preload force, by the significant changes produced on the bearings functioning parameters, i.e., kinematics, both load internal distribution and amount, appears as one of the most important factors affecting the main reliability parameters of high speed spindles. A theoretical research assisted by an experimental validation on grinding machine spindles was developed to determine the bearings preload influence on the spindles main reliability parameters, i.e., service life, dynamic and thermal stability. From the analysis of the results obtained, the optimum bearings preloads able to secure, in given operating conditions, the imposed reliability parameters for the high speed spindles were determined.

    Employing complex variables and complex functions the exact solutions to equations governing the motion of an incompressible second-grade fluid are determined.

    In this paper, some characteristic features of a dynamical system proposed by Rikitake (1958), as a model for the self-generation of the Earth's magnetic field by large current carrying eddies in the core are examined. First, a linear stability analysis of a fixed point of the Rikitake system of three dynamical equations is made. Next, utilizing the conjecture that an integral of motion must assume constant value when evaluated at a singularity, a few integrals of motion of the Rikitake system are worked out. Finally, the effects of a linear feedback control on the linearized versions of the Rikitake system in terms of state perturbation variables, are investigated. The dynamical equations are solved numerically by the fourth order Runge-Kutta method. The results are presented graphically and discussed.

    This paper presents an analytical and computer aided procedure for the multicriteria design optimisation of planetary gear trains. Geometric and operating constraints for internal and external gears and whole planetary gear trains are defined. For the defined multicriteria optimisation model of the planetary gear train, a computer program based on an interactive dialogue is developed. The results of the program are presented on an appropriate tables with Pareto-optimal solutions. A graphical illustration of the above problem is presented in terms of objective functions.

    The flow of a power-law lubricant in a squeeze film bearing with one porous wall is considered. The bearing is modelled by two curvilinear surfaces and the porous wall is adhered to the curved non-porous surface. The flow in the bearing clearance is considered with inertia and the Navier-Stokes and Poisson equations are uncoupled by using the Morgan-Cameron approximation. Using the averaged inertia method the closed-form solution is obtained. A step bearing is discussed as an example.

    In this paper, the application of an active tuned mass damper (ATMD) is studied for controlling the earthquake induced vibration of buildings using a sliding mode control (SMC). Since the structural system may have uncertainties and/or parameter changes, the sliding mode control has been preferred because of its robust character. Additionally, this control method can easily be applied to non-linear systems. The time history of the base and top floor displacements, control force input and frequency responses of both the uncontrolled and sliding mode of a realistic 9-storey building model controlled by the ATMD are presented at the end of the study. The earthquake ground motion used is obtained using the seismic data of the Marmara Earthquake (M_w = 7.4) in Turkey in August 17th, 1999.

    The effects of thermal radiation on flow past an impulsively started infinite vertical plate in the presence of variable temperature is considered. The temperature near the plate is made to rise linearly with time. The fluid considered is a gray, absorbing-emitting radiation but a non-scattering medium. The dimensionless governing equations are solved using the Laplace-transform technique. The velocity and temperature are studied for different parameters like the Prandtl number, time and radiation parameter. It is observed that the velocity slightly decreases with increasing the value of the radiation parameter.

    In this paper, we study the effects of thermal radiation on the unsteady free convection and mass transfer boundary layer over a vertical moving plate of an optically thin gray gas.

    The King Mongkut's Institute of Technology North Bangkok (KMITNB), founded in 1959 with the support of the government of the Federal Republic of Germany, is one of the premier higher education institutions in Thailand with a strong base in applied sciences, technology and engineering. The faculty of engineering, the largest of the four faculties of the institute, was founded with an aim to provide a range of professional engineering education service to meet the community and industry at the early phase of industrialization in Thailand. The degrees were established to fill a need for better-educated engineers in the practice of engineering as well as in research and development.
    The Machinery Health Monitoring and Tribology Laboratory (MHM and Tribo. Lab.) forms part of the Production Engineering Department, Faculty of Engineering. Currently, machinery health monitoring research is combined with tribology studies. In general terms, the current activities of the condition monitoring and tribology research group include: