Wen-Fang Wu

Proximity effect of superconductivity and magnetism in the Nd0.7Ca0.3MnO3∕YBa2Cu3O7 bilayer

Temperature and current dependent resistivity are investigated in the single YBa2Cu3O7 layer and the YBa2Cu3O7∕Nd0.7Ca0.3MnO3 (YBCO∕NCMO) bilayer with the thickness of each layer being 200nm. Our results show that the onset temperature (Tcon) of the superconducting transition in YBCO layer is linearly suppressed by current with a rate of 0.1K∕mA. However, Tcon of the NCMO∕YBCO bilayer is reduced effectively from 54to30K with increasing the applied current from 1to40mA, which indicates an enhanced effect of pair breaking by the polarized quasiparticles.

Stability analysis of railway vehicles and its verification through field test data

Abstract Dynamic stability is one of the important performance indices of railway vehicles. In the present paper, a twenty‐eight‐degree‐of‐freedom dynamic model is proposed to study the response and stability of railway vehicles. Nonlinear quantities existing in the railway vehicle system such as conicity, track irregularity and contact force between the wheel and rail are considered. Numerical simulation is performed based on a type of vehicle currently operated by Taipei Rapid Transit Corporation along with different kinds of track irregularity as random inputs. The stability of the vehicle is discussed in detail and compared with other full‐scale test data available. It is found that the simulation result is in good agreement with the test data. Both of them indicate the transverse acceleration of the bogie meets the required stability criteria set by authorities for mass rapid transit vehicle systems. With regard to the car‐body, when the vehicle is operated below the speed of 148 km/h, the lateral throw of the car‐body is found to be below the required level. To avoid flange contact, the lateral excursion of the wheel‐set is examined as well. It is found that flange‐rail contact will not occur very frequently for the studied vehicle when operated at its regular service speeds. It is concluded that the dynamic model is appropriate for the stability study of a railway vehicle, and the dynamic performance of the studied transit vehicle is quite good.

A study of risk-based non-destructive in-service inspection

Based on the concept of probabilistic fracture mechanics, non-destructive inspection policies are studied in this paper. Special attention is paid to the reduction of structural failure probability through the employment of in-service inspection (ISI). Analytical formulation is derived and numerical examples are presented. In addition to the conclusions drawn from numerical experience, the present study indicates how appropriate ISI schedule can be planned by considering the risk of structural failure in situ.

Random Outcome and Stochastic Analysis of Some Fatigue Crack Growth Data

Fatigue crack propagation data of a batch of AISI 4340 steel specimens are released in the present paper. The statistical nature of the data is specially emphasized, and a probabilistic fracture mechanics model is introduced to analyze the data. The stochastic differential equation associated with the model is then solved. The solution gives us the crack exceedance probability as well as the probability distribution of the random time to reach a specified crack size. These quantities are useful in the reliability assessment of structures made of the tested material. Comparing the analytical result with the experimental result, it is found that the proposed probabilistic fracture mechanics model can reasonably explain the experimental data. For those data that cannot be fitted well by the proposed model, methods of improvement are proposed in the present paper as well.

Dynamic Analysis and Ride Quality Evaluation of Railway Vehicles – Numerical Simulation and Field Test Verification

A rather complete dynamic model with special emphases on nonlinear conicity and creep force and in consideration of random irregularity of rail profile is proposed to simulate the response and investigate the ride quality of railway vehicles. The CP341 vehicle that will soon be used in Taipei Rapid Transit System is considered in particular as the studied role model. Some of the field test data carried out for this type of vehicle are revealed as well and used for the verification of the proposed model. Both simulation and test results show that the resonant frequency of the studied vehicle is in the range of 0.6∼1 Hz, and the one-third octave root-mean-square acceleration curves of the vehicle in all studied cases meet the ride quality criteria set for the mass rapid transit vehicle systems. It is observed that the secondary suspension of the vehicle has the low frequency filtering property and the primary suspension has high frequency characteristics. A poorer ride quality in vertical direction rather than in lateral direction is also confirmed in the study. It is concluded that the proposed model can be used to simulate the dynamic response and evaluate the ride quality of any railway vehicle.

Thickness dependent spin-injection effects in Nd0.7Ca0.3MnO3∕YBa2Cu3O7 bilayers

Two Nd0.7Ca0.3MnO3∕YBa2Cu3O7 (NCMO/YBCO) bilayers with different thickness ratios are fabricated and the spin-injection effects are investigated. The NCMO/YBCO samples have thicknesses of 100nm∕200nm and 200nm∕200nm, which are denoted as N/Y(1) and N/Y(2), respectively. It is shown that the current-induced suppression rate of superconducting transition temperature (dTc∕dI) in YBCO is enhanced by four to six times of magnitude in N/Y(1) and N/Y(2) compared with that in pure YBCO. Furthermore, dTc∕dI in N/Y(2) is larger than that in N/Y(1), which suggests that the thickness of NCMO has influence on the pair breaking in YBCO.

Performance and Bearing Load Analysis of a Twin Screw Air Compressor

To study the performance and estimate the oscillating bearing loads of a twin screw air compressor, a theoretical model is proposed in this paper. Based on the model, a computer simulation program is developed and effects of different design parameters such as rotor profile, geometric clearance, oil injected position, oil temperature, oil flow rate and other operational conditions are investigated. Output variables such as bearing loads, specific power, compression efficiency, volumetric efficiency, discharge temperature are obtained. Some of the results are then compared with experimentally measured data, and good agreements are found between the simulation results and the measured data.

Stability Analysis and Derailment Evaluation of Rail Vehicles

A 28-degree-of-freedom dynamic model is proposed to study the stability of rail vehicles and examine the impact load caused by wheel-flat. Different kinds of track irregularity are considered as random inputs. The stability of the vehicle is discussed in detail and compared with available full-scale test data. It is found that numerical simulation results are in good agreement with test data for a certain type of vehicle. Both of them indicate the transverse acceleration of the bogie meets the required stability criteria. It is also found that derailment will not occur when the vehicle runs at its regular service speeds.

Probabilistic analysis of core shroud cracks

Abstract Traditional limit load analysis and fracture mechanics analysis have been applied to evaluate the integrity of the degraded nuclear power plant components. Although these methodologies are generally accepted by the regulatory authorities in the nuclear industry, conservatism introduced by the uncertainties of inspection, material property, crack geometry, applied loading, neutron environment, etc. is recognized to have great impact on the evaluation accuracy. A probabilistic analysis may overcome this shortcoming and reveal some additional insight to the problem. The purpose of the present study is to apply probabilistic methods to analyze the degraded core shroud, and to predict the quantitative risk of the cracked shroud. In the analysis, the loading condition, crack growth rate, material properties and existing defects are all considered random. A sample analytical result shows that, based on some previously observed data and under certain assumptions, the crack-through probability of the studied core shroud is in the order of 10 −7 after 13 cycles of operation. The probability will increase considerably through operation cycles or operation years if no repair action is taken.

Effect of Lubrication on the Performance and Dynamic Loads of Scroll Compressors

To study the effect of lubrication on the performance and dynamic loads of scroll compressors, a theoretical model is proposed in this paper. The model includes both thermal and dynamic analyses in which the lubrication theory is emphasized in particular. A computer simulation program is written accordingly, and the effects of different design parameters including oil flow rate, injection position, injection temperature and rotating speed are investigated. The output variables such as gas force, contact force, contact moment and thermal performance of the compressor are obtained. Some of the results are compared with experimentally measured data, and good agreements are found between the simulation results and the measured data. The applicability of the simulation program is thus verified.Analytical results from running this program can provide us valuable information on the design improvement of a scroll compressor.