Journal of Mechanical Science and Technology

Yoon, Soon; Kim, Moon; Lee, Dae

doi: 10.1007/BF02945086pmid: N/A

Turbulent flow and heat transfer characteristics of a two-dimensional oblique plate impinging jet (OPIJ) were experimentally investigated. The local heat transfer coefficients were measured using thermochromic liquid crystals. The jet mean velocity and turbulent intensity profiles were also measured along the plate. The jet Reynolds number (Re, based on the nozzle width) ranged from 10, 000 to 35,000, the nozzle-to-plate distance ( H/B ) from 2 to 16, and the oblique angle (α) from 60 to 90 degree. It has been found that the stagnation point shifted toward the minor flow region as the oblique angle decreased and the position of the stagnation point nearly coincided with that of the maximum turbulent intensity. It has also been observed that the local Nusselt numbers in the minor flow region were larger than those in the major flow region for the same distance along the plate mainly due to the higher levels in turbulent intensity caused by more active mixing of the jet flow.

Park, Sang Il; Hartley, J. G.

doi: 10.1007/bf02945082pmid: N/A

The effective thermal conductivities of bonded molding sands vary with the dry density, binder content, initial moisture content, temperature as well as the types of sand and binder clay. In this study, a theoretical model for predicting the effective thermal conductivities of bentonitebonded molding sands was developed. The results of measurement of the effective thermal conductivities of molding sands at temperatures up to 750°C were used. The binder thermal conductivities of both western bentonite and southern bentonite were suggested as a function of dry density, binder content and initial moisture content and were assumed not to vary with temperature. The radiation model proposed by Vortmeyer was also incorporated. The model developed in this study was proved to predict well the effects of binder content, initial moisture content, dry density and temperature.

Yun, Byong-Jo; Sim, Suk-K.; Hwang, Su-Hyun; Park, Goon Cherl

doi: 10.1007/bf02945083pmid: N/A

Local two-phase flow parameters were measured to investigate the internal flow structures of steam-water boiling flow in an annulus channel. Two kinds of measuring methods for the local two-phase flow parameters were investigated. A two-conductivity probe was used for local vapor parameters and a Pitot tube for local liquid parameters. Using these probes, the distributions of phasic velocities, interfacial area concentration (IAC) and void fraction are measured in a steam-water boiling flow. In this study, it is observed that the local void fraction is smoothly decayed out from the surface of a heating rod to the channel center in subcooled boiling without any wall void peaking, which were observed in air-water experiments. The distributions of the local IAC and bubble frequency coincide with those of the local void fraction for a given area-averaged void fraction.

Jang, Jin-Hee; Han, Chang-Soo

doi: 10.1007/bf02945075pmid: N/A

In this paper, sensitivity analysis of side slip angle for a front wheel steering vehicle is performed in the frequency domain. For the derivation of the transfer function, a simple vehicle model with two degrees of freedom is used in the initial modeling stage. This model exhibits the simplest lateral dynamic effect, and is useful for understanding the dynamic characteristics and control aspects of the target system. Vehicle mass, inertia, cornering stiffness, and wheel base are taken to be the design variables. Sensitivity functions of the transfer function with respect to the design variables are derived. From this study, we see that a transition speed exists in the frequency response of side slip angle. This implies that the characteristics are changed from minimum phase to non-minimum phase as the vehicle speed increases. The objective of this study is to propose a basis for design and re-design of the vehicle by checking the side slip angle variations with respect to design variable changes in the frequency domain. Finally, dominant design variables are suggested based on the sensitivity analysis.

Cho, Yun-Ho; Chang, Ho-Myung

doi: 10.1007/BF02945081pmid: N/A

A chemical kinetic model is developed for the non-catalytic reduction of nitric oxide (NO) by hydrazine (N 2 H 4 ). Since the reduction of NO was observed in an experimental reaction with N 2 H 4 , the hydrazine has been suggested as a new reductant of NO in addition to the conventional ammonia, urea and isocyanic acid. In the proposed kinetic model, a set of fifty one chemical reactions that includes the various branching reactions of N 2 H 4 to NH 2 and the wellknown reaction NO+NH 2 →N 2 +H 2 O is simultaneously considered with the usual partial equilibrium assumptions. The NO reduction is estimated to occur at a temperature range between 700K and 1400 K, which is wider and lower than in the conventional Thermal DeNOx process. The maximum amount of the reduced NO is slightly less than that in the Thermal DeNOx. The effects of the other input parameter on the NO reduction rate also discussed.

Shin, Bum-sik; Chun, Kwang; Lee, Hang-kyung

doi: 10.1007/BF02945085pmid: N/A

Fuel injection pipe pressures are measured and simulated to study the effect of fuel injection system characteristies on the heat release in a direct injection diesel engine. The fuel injection simulation is based on a linear model. The governing equations are solved by the finite difference method. The measured fuel pipe pressures and the simulated fuel pipe pressures matched well to each other except for the interval when the nozzle is closing. The effects of the fuel pipe length and the nozzle opening pressure are tested. The longer fuel pipe length causes proportional retardation of the fuel injection time. The higher nozzle opening pressure results in increase of the maximum fuel pipe pressure and shorter combustion duration.

Jang, Jin-Hee; Han, Chang-Soo

doi: 10.1007/BF02945075pmid: N/A

In this paper, sensitivity analysis of side slip angle for a front wheel steering vehicle is performed in the frequency domain. For the derivation of the transfer function, a simple vehicle model with two degrees of freedom is used in the initial modeling stage. This model exhibits the simplest lateral dynamic effect, and is useful for understanding the dynamic characteristics and control aspects of the target system. Vehicle mass, inertia, cornering stiffness, and wheel base are taken to be the design variables. Sensitivity functions of the transfer function with respect to the design variables are derived. From this study, we see that a transition speed exists in the frequency response of side slip angle. This implies that the characteristics are changed from minimum phase to non-minimum phase as the vehicle speed increases. The objective of this study is to propose a basis for design and re-design of the vehicle by checking the side slip angle variations with respect to design variable changes in the frequency domain. Finally, dominant design variables are suggested based on the sensitivity analysis.

Ryu, Jeha; Kim, Ho-Soo; Yim, Hong Jae

doi: 10.1007/bf02945077pmid: N/A

This paper presents an efficient and accurate method for dynamic stress computation based on reanalysis in flexible multibody dynamic system simulation. The mode acceleration concept that is widely used in linear strucural dynamics was utilized for accuracy improvement. A mode-acceleration equation for each flexible body is defined and the load term in the right hand side of the equation is represented as a combination of space-dependent and time-dependent terms so that efficient computations of dynamic stresses can be achieved. The load term is obtained from dynamic simulation of a flexible multibody system and a finite element method is used to compute stresses by quasi-static analyses. A numerical example of a flexible four-bar mechanism shows effectiveness of the proposed method for flexible multibody dynamic systems such as linkages and vehicle systems.

Bae, Yoon Y.; Emanuel, George

doi: 10.1007/bf02945084pmid: N/A

Similarity solution of the compressible, laminar boundary-layer equation depends on pressure gradient parameter β and wall to inviscid stagnation temperature ratiogw. However, the derived quantities, such as various thicknesses, also depend on speed parameter S, thereby requiring three dimensional tables for the tabulated results. A new formulation is provided that enables all quantities of interest to be determined by the two-dimensional tables in which β andgw are the input parameters. With such a set, accurate values can be found for the skin-friction coefficient, Stanton number, and the five most common viscous and thermal boundary-layer thicknesses for arbitrary values of the speed parameter. A comprehensive set of tables is provided in which β ranges from its separation value to 100 andgw ranges 0 to 5. Quasi-linearization method is applied to the governing equations and generalized Newton-Raphson method is used to obtain successive initial condition. As a result computation time is reduced significantly.

Yoon, Soon Hyun; Kim, Moon Kyung; Lee, Dae Hee

doi: 10.1007/bf02945086pmid: N/A

Turbulent flow and heat transfer characteristics of a two-dimensional oblique plate impinging jet (OPIJ) were experimentally investigated. The local heat transfer coefficients were measured using thermochromic liquid crystals. The jet mean velocity and turbulent intensity profiles were also measured along the plate. The jet Reynolds number (Re, based on the nozzle width) ranged from 10, 000 to 35,000, the nozzle-to-plate distance (H/B) from 2 to 16, and the oblique angle (α) from 60 to 90 degree. It has been found that the stagnation point shifted toward the minor flow region as the oblique angle decreased and the position of the stagnation point nearly coincided with that of the maximum turbulent intensity. It has also been observed that the local Nusselt numbers in the minor flow region were larger than those in the major flow region for the same distance along the plate mainly due to the higher levels in turbulent intensity caused by more active mixing of the jet flow.