Yoshihiro Mochimaru

Voltage required to detach an adhered particle by Coulomb interaction for micromanipulation

An adhered particle can be detached by Coulomb interaction. The voltage required for detachment for micromanipulation is theoretically analyzed by employment of a boundary element method. The system consists of a manipulating probe, a spherical particle, and a substrate plate, all of these objects being conductive. The manipulator and the substrate are cylindrical, and axial symmetry is assumed. Although a numerical method is used to solve the equations, all parameters are normalized. The effect of the shape parameters on the Coulomb force is systematically calculated. The force is independent of system size and depends on the relative shape of the system. The force is proportional to the applied voltage raised to the second power. The force generated by the Coulomb interaction is compared with the adhesion force deduced from the Johnson–Kendall–Roberts theory, and the voltage required for detachment is clearly expressed. The possibilities and limitations of micromanipulation using both the adhesion pheno...

Unsteady-state development of plane couette flow for viscoelastic fluids

Abstract Unsteady-state development of plane Couette flow for viscoelastic fluids is analyzed using a constitutive equation that can be obtained from molecular theory, in which the molecules are regarded as finitely extensible dumbbells. Typical features of the flow situation are as follows: (i) For a fluid with moderate elasticity, not only stress overshoot but also velocity overshoot are predicted. (ii) For suitable combinations of elasticity and gap width, and for some time intervals stress propagation and reflection phenomena are predicted. (iii) After a sufficient time has elapsed, the stress state behaves similarly to that corresponding to the start-up of a steady simple shear flow.

LDA measurement and a theoretical analysis of the in-cylinder air motion in a DI diesel engine

The swirl velocity in the combustion bowl of a DI diesel engine was measured by means of laser doppler anemometry, varying the swirl intensity and engine speed. At the same time an axisymmetrical two dimensional laminar model for simulating the in-cylinder air motion was presented. The boundary condition of the flow near the wall was investigated by a comparison of predicted and measured swirl velocity, and as a result the free slip condition was found to be suitable for the present model.

A Study on Natural Convection from Two Cylinders in a Cavity

Steady-state natural convection heat transfer characteristics from cylinders in a multiply-connected bounded region are clarified. A spectral finite difference scheme (spectral decomposition of the system of partial differential equations, semi-implicit time integration) is applied in numerical analysis, with a boundary-fitted conformai coordinate system through a Jacobian elliptic function with a successive transformation to formulate a system of governing equations in terms of a stream function, vorticity and temperature. Multiplicity of the domain is expressed explicitly.

Normal stress measurement of dilute polymer solutions

Abstract Viscoelastic fluids such as dilute polymer solutions show anomalous drag reduction phenomena, for example, in a turbulent pipe flow. In order to investigate such phenomena quantitatively it is necessary to clarify the characteristic flow behaviour, especially the relationship between normal stress difference and shear rate. In this report, the method of measuring the total force acting on the outlet section of a pipe is adopted for obtaining a normal difference, and several problems affecting the relationship between normal stress differences and shear rate, such as flow disturbance, surface tension, and geometry of the exit, are discussed. From the results of measurements it is suggested that this method is applicable below certain values of the flow Reynolds number for very dilute polymer solutions of the order of 10 ppm concentration.

Fast multipole boundary element method using the binary tree structure with tight bounds: application to a calculation of an electrostatic force for the manipulation of a metal micro particle☆

Abstract Boundary element method is one of the most powerful tools to solve partial differential equations. However, it takes a lot of computational time when applied to an actual problem with a large number of unknowns. In this research, the binary tree structure with tight bounds and the downward pass for this structure are adopted for the fast multipole method to reduce the number of M2L translations, thereby further reducing the computational time. Furthermore, the recurrence formulae to calculate the multipole moments of a triangular element are derived. The fast multipole boundary element method using the binary tree structure with tight bounds is developed and the analyses of an electrostatic force acting on a metal micro particle above a complex structure are performed to confirm the effectiveness of this method.

Extension of spectral finite difference schemes for computational fluid dynamics

Abstract Extending schemes of a spectral finite difference method for treating a mixture of different types of boundary conditions along a single boundary is proposed to give heat and fluid flow fields for the mixture of Neumann and Dirichlet conditions with or without a free surface in an elliptic cavity under various circumstances.

Numerical simulation of flow past a circular cylinder under a magnetic field

Abstract Steady-state laminar flow fields around a circular cylinder placed normally to a uniform flow under a uniform magnetic field are analyzed. The fluid is assumed to be incompressible and to have moderate magnetic diffusivity. A hydrodynamic assumption regarding the magnetic field is introduced. A Fourier spectral method is used to decompose the vorticity transport equation. Using a semi-implicit method, the resulting differential equations can be integrated easily by a time marching method to obtain a steady-state solution. It is found that the flow characteristics vary remarkably according to the Hartmann number, the Reynolds number and the direction of an applied magnetic flux density vector, although the dependence on the magnetic Prandtl number is small as long as it is

Coherent structure in the turbulent wake behind a circular cylinder

A wake behind a circular cylinder at Reynolds number 850–1700 was visualized by the smoke-wire method. The observations of the How together with the results of quantitative measurements, such as various velocity correlation coefficients, illustrated the formation process of spoon-shaped large eddies in the region 90 ≤ x/d ≤ 230 attained through the deformation and rearrangement of the regular Karman vortices. A spoon vortex was likely to pair with the counterpart on the opposite side of the wake. The large-scale bulges of the turbulent and non-turbulent interface of the wake were shown to correspond to these spoon vortices. These results indicate that some coherent structures are organized by rearrangement and deformation of initially regular vortices in turbulent flow.

NUMERICAL SIMULATION OF FORCED CONVECTION HEAT TRANSFER FROM A CIRCULAR CYLINDER UNDER A MAGNETIC FIELD

Steady-state laminar forced convection heat transfer from a circular cylinder located normally to a uniform flow under a uniform magnetic field is analyzed numerically. Through the introduction of Fourier series expression into the stream function and temperature, the energy equation can be divided into Fourier components, supplemented with the thermal wake behaviour and uniform heat flux along the cylinder surface being assumed. Thus truncating the series up to a certain order and discretizing the equations in space gives rise to a system of substantially linear simultaneous equations, from which the temperature distribution and the mean Nusselt numer are obtained. As a result, for a fixed Reynolds number and a fixed Hartmann number, the mean Nusselt number decreases as an Eckert number increases if the temperature of the cylinder surface is higher than that in the free stream, whereas it increases as the absolute value of the Eckert number increases if the surface temperature is lower.