Haw Long Lee

A Nonlinear Inverse Problem in Estimating the Heat Generation in Rotary Friction Welding

In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to estimate the unknown time-dependent heat generation at the interface of cylindrical bars during rotary friction welding process from the knowledge of temperature measurements taken within the stationary bar. In the direct problem, the heat capacity and thermal conductivity are functions of temperature; hence, this is a nonlinear inverse problem. The temperature data obtained from the direct problem are used to simulate the temperature measurements, and the effect of the errors in these measurements upon the precision of the estimated results is also considered. Results show that an excellent estimation on the time-dependent heat generation can be obtained for the test cases considered in this study. The current methodology can be applied to the prediction of heat generation in rotary friction welding.

Three-Dimensional Pipe Fouling Layer Estimation by Using Conjugate Gradient Inverse Method

In this study, a conjugate gradient method based inverse algorithm is applied to estimate the unknown three-dimensional fouling-layer profiles on the inner wall of a piping system using simulated temperature measurements taken on the pipe wall. The temperature data obtained from the direct problem are used to simulate the exact temperature measurements. Results show that an excellent estimation on the fouling-layer profiles can be obtained for the two cases investigated in this study. The technique presented here can be used as an alternative to ultrasonic waves fouling detection techniques to provide crucial information for the optimization of cleaning schedule for piping systems.

Estimation of surface heat flux and temperature distributions in a multilayer tissue based on the hyperbolic model of heat conduction

In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to solve the inverse hyperbolic heat conduction problem in estimating the unknown time-dependent surface heat flux in a skin tissue, which is stratified into epidermis, dermis, and subcutaneous layers, from the temperature measurements taken within the medium. Subsequently, the temperature distributions in the tissue can be calculated as well. The concept of finite heat propagation velocity is applied to the modeling of the bioheat transfer problem. The inverse solutions will be justified based on the numerical experiments in which two different heat flux distributions are to be determined. The temperature data obtained from the direct problem are used to simulate the temperature measurements. The influence of measurement errors on the precision of the estimated results is also investigated. Results show that an excellent estimation on the time-dependent surface heat flux can be obtained for the test cases considered in this study.

Damping vibration of scanning near-field optical microscope probe using the Timoshenko beam model

The effect of interactive damping on the flexural vibration frequency for the scanning near-field optical microscope (SNOM) fiber probe based on the Timoshenko beam theory, including the effects of shear deformation and rotary inertia, has been analyzed. In the analysis, the effects of the transverse contact stiffness, damping factor and the ratio of different probe dimensions on the damping vibration frequency were studied. The results show that increasing the ratio of probe length to radius increases the damping vibration frequency of mode 1. Besides, the damping vibration frequencies, based on the Bernoulli-Euler beam theory and the Timoshenko beam theory, are compared. When the contact stiffness is very large for the higher modes, the effects of shear deformation and rotary inertia on the frequency becomes significant. Furthermore, increasing the damping factor increases the vibration frequency. The trend is more obvious, especially dimensionless damping factor @hf>0.4.

An inverse problem in estimating the laser irradiance and thermal damage in laser-irradiated biological tissue with a dual-phase-lag model

Abstract The aim of this study is to solve an inverse heat conduction problem to estimate the unknown time-dependent laser irradiance and thermal damage in laser-irradiated biological tissue from the temperature measurements taken within the tissue. The dual-phase-lag model is considered in the formulation of heat conduction equation. The inverse algorithm used in the study is based on the conjugate gradient method and the discrepancy principle. The effect of measurement errors and measurement locations on the estimation accuracy is also investigated. Two different examples of laser irradiance are discussed. Results show that the unknown laser irradiance and thermal damage can be predicted precisely by using the present approach for the test cases considered in this study.

Mechanical Behaviors of Nanoimprinted Cu-Ni Alloys Using Molecular Dynamics Simulation

Molecular dynamics (MD) simulation with a tight-binding potential is used to studied the mechanical behaviors of nanoimprinted Cu-Ni alloys before and after annealing. The annealing process consists of three different stages. Initially, there is a gradual heating from the original temperature of 300 K to the specified annealing temperature of 823 K and then it is followed by a period of constant heating at that temperature, after which the specimen temperature is allowed to cool gradually to the original temperature. The results showed that when the punch is advancing, the punching force obtained from the simulation with a tight-binding potential is lower than with the Morse potential. The internal energy of Cu-Ni alloys decreased with increasing the temperature and the component of Cu during the annealing process. In addition, comparing the residual stress in the Cu-Ni alloys with and without annealing treatment, the stress is significantly released after annealing.

Damping vibration Studies of scanning near-field optical microscope

Scanning near-field optical microscopy (SNOM) is one of the major proximal probe technologies for obtaining high-resolution images beyond the diffraction limit of light and to fabricate nanometer-scale structures. The effect of interactive damping on the flexural vibration frequency for the scanning near-field optical microscope (SNOM) fiber probe based on the Timoshenko beam (including the effects of shear deformation and rotary inertia) theory, has been analyzed. The effects of the transverse contact stiffness, damping factor and the ratio of different probe dimensions on the damping vibration frequency were studied. The results show that increasing the ratio of probe length to radius increases the damping vibration frequency of mode 1. The damping vibration frequencies, based on the Bernoulli-Euler beam theory and the Timoshenko beam theory, are compared. When the contact stiffness is very large for the higher modes, the effects of shear deformation and rotary inertia on the frequency becomes significant. Furthermore, increasing the damping factor increases the vibration frequency, especially for dimensionless damping factor &egr;f >0.4

On the Use of Different Wavelengths to Digitally Determine the Isochromatic Fringe Order

Four approaches, a novel, two modified and a previous developed approaches, are compared for the determination of the total fringe orders using different wavelengths. The results show that an error of 0.05 fringes can be achieved by all methods. The MIN-MAX method gives the best result for fringe orders greater than 0.6, a better result can be given by the rest methods for fringe orders less than 0.5. The three-wavelength criterion could yield better result than that of the two-wavelength for determination of the total fringe order. Owing to various noises, both criteria cannot assure to obtain correct fringe order. Therefore two-wavelength method would be sufficient to determine the total fringe orders with a correctly determined total fringe order.