Papers by Author: Je Ee Ho

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Authors: Je Ee Ho
Abstract: The ferrohydrostatic pressure is an important magnetization characteristic for the ferro-fluid used as the working medium of shock absorber or as a leak-proof dynamics seal of rotating shaft. To generalize and analyze the experimental results, an analytic formulation of magnetic pressure derived from the Ferrohydrodynamics (FHD) Bernoulli theory is constituted. Meantime, an auxiliary testing mechanism on the magnetic levitation, features as an easy, economical and efficient utility, is then set up in this study and which is quit different from the expensive cost required in precise VSM measurement system. While compared with above results, a good agreement will be accessed within the working interval of magnetic flux 0 ~ 60 mT.
1652
Authors: Je Ee Ho, Da Chih Chen
Abstract: For most of previous study on electron beam drilling (E.B) or laser beam drilling (L.B), the evaporating phenomena was assumed to be a minor parameter and could be neglected. In fact, the assumption usually leads to the overestimation of drilling efficiency and causes a significant deviation from experiment result. To improve this defect, a critical flow theory, based on the reacting pressure downward into the melting layer, is first introduced in this study; which not only successfully separates the evaporating model to convective model, but the critical transition of drilling characteristic will be also accessed. Examine the melting cavity of copper drilling conducted in E.B process, the evaporating phenomena responsible for drilled cavity had been verified to be as a prior parameter as the incident energy density is below 6×1010 w/m2. When compared with the experiment data made by Allmen [1], proposed theory shows an excellent agreement for copper drilling and their relative errors are no more than 30%.
3949
Authors: Je Ee Ho, Hong Tsu Young
Abstract: For optical micro- machinery processing, nanosecond laser possess a special advantage in using it as a fabrication method of smaller hole subjected to the minimum thermal distortion. Thus it has become an effective and powerful tool widely used in drilling, cutting and welding process for micro-manufacturing field. To estimate the working performance of pulsed laser, an auxiliary method in numerical skill or semi-empirical technology is usually utilized, where the important parameters including energy intensity, duration and wavelength of laser beam will be taken into account. Nevertheless, several troubles, the unstable numerical iteration for phase change and precise calibration of sensor required in the measuring process, seem to be still inevitable, and which easily makes the numerical calculation become more complicated, even the global ablating behavior will be lost. To compensate the inadequacy mentioned above, an analytic model of optical ablation for pulsed laser, based on the evaporation effect responsible for penetration mechanism, is then derived in this study. Here the penetrating behavior, during the micro-machining process, can be clearly examined with the consideration of plasma absorption. After compared with experimental results made by Chen and Schmidt for copper drilling and steel ablation for Tim, a better agreement of analytic results identifies the accessibility of proposed model which also contributes to the future investigation on pico-or femto- laser material processing.
861
Authors: Je Ee Ho, Chen Lung Yen, Jian Xun Lin
Abstract: In this study, apparent ferro-viscosity on applied directional field, through the evaluation of mean piping flow velocity, is examined. Here viscosity in magnetized ferro-flow is found to be closely dependent on the field intensity as well as direction, which is quite different from the constant thermal property usually used in traditional fluid dynamics problem. To predict ferro-magnetization and ferro-viscosity induced under horizontal and vertical field imposed , an auxiliary electromagnetic mechanism is then designed and set up ,As a result, the apparent viscosity ,for ferro-concentration ψ0.4 and 0.04 exposed to field in different direction, will initiate a faster growth within field strength of 6~12 mT where the quick magnetization of ferro-particles starts working, and magnetic field along with flow direction is found to have more potential to induce viscous drag. While compared with theoretic results on Brownian relaxation theory in Langevin function, experimental vortex viscosity behave a good agreement within the working magnetic intensity 0~36 mT and their maximum relative errors will be less than 10% and 50% for ferro-concentration ψ0.4 and 0.04 at working temperature at 25 o c.
115
Authors: Je Ee Ho, Ching Yen Ho
Abstract: The incident energy flux impinged on the free surface of liquid layer was considered to be balanced with the latent heat in evaporation and the heat in directional conduction but neglecting convective heat transfer due to a small Peclet number at the cavity base. The quasi-steady state model was developed in this study to analyze the effect of the energy density during the penetration process and an exponential expression for penetration velocity as a function of liquid-thickness and temperature was also derived. The penetration velocity versus energy density calculated by the present model showed good agreements with the experimental data for drilling copper, which the relative errors between the calculated and the experimental data are less than 15%. By the setup of non-uniform grids distribution in numerical method, this work had successfully predicted the variation of the penetration velocity with energy density distribution. The effects of the energy density on flow rate, thickness of liquid layer, base temperature of fusion zone had also been discussed in this study.
1987
Authors: Je Ee Ho, Ling Tzu Lien
Abstract: Under non-uniform magnetic field distribution, the humping ferro-damp used to reduce the oscillation of ferro-wave is investigated. Through experimental observation and analytic analysis, the dynamical stability at the so called “humping pool”, enclosed by both centers of permanent magnetisms, is found to be closely dependent on the oscillating frequency, field intensity & the separated distance of magnetisms. Though nodal shift of pool 0.07~0.11 cm, recorded from video-camera suited on self-designed oscillating system, begins to occur as in the deployment of higher ferro-level or lower field strength 0~ 30 mT, however such the stable response of humping pool, without remarkable change of vibrating amplitude 0.03 ~0.06 cm, might be under control while oscillating frequency of 0.5~2 Hz is subjected. That could be attributed to the concentrated ferro-viscosity as well as the strongest ferro-magnetization, induced at the humps, initiates a recovering constrain for oscillating pool. Unlike above humping damp accessed, an irregular and random ferro-profile will be generated outside pool region. Such humping deployment, as a manner of shockproof, might be utilized to reduce the seismic damage and that makes damping analysis of seismic study become more practical and approach to the intended demand.
383
Authors: Je Ee Ho
Abstract: A ferro-hydrodynamic ( FHD ) model, based on modified Bernoulli theory, to estimate the average ferro-flow velocity is developed in this study. In which, the effective viscosity, strongly dependent on the magnetic intensity and volumetric concentration of ferro-particle, is considered. Referred to the Langevin function, the induced magnetic pressure together with hydraulic head as well as frictional head successfully formulates the modified ferro-Bernoulli model .To correct the analytic results, a self-designed experimental mechanism, equipped with light gate and current-carry solenoid, is set up as well ,which is used to measure the average velocity of piping flow via the duration recorded for ferro-fluid passing through both light gates While compared with experimental results, a good agreement of analytic solutions will be delivered within the working magnetic intensity ,0~36 mT, and the flow velocity is found to be significantly reduced during initial magnetization 0~12 mT as the working condition, subjected to ferro-concentration 0.04~0.4 at temperature 25 oc~45 oc, is specified in this study.
23
Authors: Je Ee Ho, Da Chih Chen
Abstract: Surface tension of ferrofluid, an important parameter enclosing the boundary condition of ferro-hydrodynamic ( FHD ) problem, is investigated in this study. Referred to modified Langevin function and apparent weight loss theory, an auxiliary experimental mechanism of ring-pull method is then designed and set up, which will be used to determine the surface tension of testing sample through various magnetization degree induced by field intensity. While compared with the results predicted from Rayleigh theory using commercial product of Matsumoto Co., an excellent agreement is delivered within the working magnetic intensity 0~40 mT. Here dimensionless parameter α is found to dorminate the prompt increase of surface tension coefficient as the ferro-magnetization ratio reaches at 70 % saturation magnetization. .
101
Authors: Je Ee Ho, Hong Tsu Young
Abstract: In Laser Beam (L.B.) and Electron Beam (E.B.) drilling, the energy distribution significantly affects both the penetrating efficiency and working performance, both of which are usually estimated by numerical skill or experimental measure. Through the application of a stimulation model, an unstable solution with the finite difference method will result near the solidliquid interface unless much finer grid sizes are set up. To improve on the above defect, nonuniform grids are therefore utilized; this will complicate the built-up of the program and also easily causes the simulated energy distribution to be divergent in the iteration process. In this study, an estimated small Peclet number and observed narrow-deep cavity made the convective and radial diffusion terms small enough to be neglected in the governing equation. From these assumptions, the model was then used to investigate the drilling efficiency where two-phase flow convection could be simplified further into one dimension and thus the analytical solution becomes possible by transferring the penetration velocity into the logarithmic form. When compared with the experiment made by Allmen [1] , the present model shows good agreement in higher energy density and relative errors are no more than 10%.
308
Authors: Je Ee Ho, Chen Lung Yen
Abstract: In this study, a 2-D model with dimensionless analysis was proposed by discussing the roles of the active material properties in high energy beam drilling. With the assumption of small Pelect number, quasi-steady transformation and scalar analysis in this model, several dimensionless parameters had been generalized. Among these parameters, the dimensionless material property , defined as evaporation latent heat to internal energy at melting point, was proven to be the key member; which not only significantly influenced the nonlinear variation inside the work piece, but also directly determined the penetration results whose behavior showed a resemblance to the distribution of exponential function in . Further more, the maximum efficiency had been successfully estimated, and the dramatic change of drilling characteristic during the transitional energy region was also reasonably simulated. When compared with the experimental results from Allmen [1], the present model with given copper properties showed an excellent agreement on material removal rate (their relative errors were not more than 15 %.)
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