Variable-stoke swash plate mechanisms are widely used for compressors in automotive air-conditioning systems, but the dynamics of the system has not been investigated sufficiently. In the present study, we derived a dynamic equation based on the Lagrangian mechanics for the mechanism and solved it numerically. The solutions were compared with the ones obtained from the commercial multibody dynamics software, DAFUL. We proposed a static function that can be conveniently used to predict the steady-state behavior of the system without conducting a full dynamic analysis of the variable-stoke swash mechanism. Using the static function, for example, we showed why the stroke of the variable-stoke swash tends to increase with the driving speed and showed a simple way to reverse the tendency. Especially, we observed that the system can have multiple steady-state solutions depending on initial conditions. Based on this observation, we theoretically showed that a hysteresis phenomenon can occur in the variable-stoke swash mechanism so that the behavior of the system can depend on the operation history of the system.

a concrete slab track system with various thicknesses, ranging from 0.11 to 0.13 m. Recently, some newly constructed sleepers have exhibited both surface-opening and latent cracks, as shown in Figure 1. A total of 332 sleepers with surface-opening cracks were discovered among the 306,000 sleepers installed for the second-stage construction of the KTX railway from Taegu to Gyeongju, South Korea. A team of investigators organized by the South Korean government concluded that conical cracks had developed in the sleepers because of volume expansion of the freezing water entrapped in the embedded fastening assemblies during the winter. Among the 306,000 sleepers, 18,177 were identified to be suspicious or damaged by freezing. The problem was then to identify sleepers with internal damage for repair. Sleepers with surface-opening cracks are easily detected by visual inspection. However, sleepers with hairline cracks or latent cracks are hard to detect. To make matters worse, the KTX railway construction schedule required the inspections to be finished in a couple of months.The goal of the research described here was to design an optimal nondestructive testing (NDT) method for the identification of sleepers with hairline cracks or latent cracks. The impact-echo method (1, 2), the spectral analysis of surface waves (SASW) method (3), and the flexural rigidity assessment of concrete tracks by antisymmetric Lamb waves (FRACTAL) method (4) were used to investigate three typical sleepers: an undamaged sleeper, a sleeper with surface-opening cracks, and a sleeper with hairline cracks and possible latent cracks. The proposed optimal procedure involves two stages of testing: FRACTAL tests for preliminary scanning and SASW tests for in-depth investigation. The procedure was applied to all 18,177 of the suspicious sleepers, and some typical results are presented in this paper.In the impact-echo test, stress waves from an impulse source are applied to the top surface of a platelike structure and are then reflected back from the bottom of the surface or from internal anomalies within the structure. The multiple reflections between the two plate boundaries are analyzed to determine the thickness of the structure or the The construction of a high-speed railway in South Korea was recently impeded by the unexpected problem of cracks in sleepers. These were presumably induced by the volume expansion of freezing water entrapped in the fastening assemblies during the winter. A total of 306,000 sleepers had to be investigated on an urgent basis for hairline cracks and possible latent cracks. These findings suggested that an appropriate nondestructive testing (NDT) technique for the inspection of concrete sleepers should be designed to meet two requirements: speed and reliability in testing. Research was performed to identify an optimal NDT technique by using sleepers with three different crack conditions: without any cracks, with a surface-opening crack, and with a hairline crack and possible latent cracks. Flexural rigidity rather than ma...

Technologies for rapid concrete curing using elevated temperature are important for saving cost and time when constricting concrete structures. Recently, a microwave heating form was developed. In this study the early strength of concrete cured by the developed form was experimentally investigated. Large scale mock up tests were conducted six times, and the results were analyzed based on the maturity theory. Logarithmic correlation curves were generated based on the measured strength and estimated maturity. It was confirmed that the strength development of the concrete cured by microwave heating form can be estimated by the equivalent age theory usually applied to steam-curing technology. By using the microwave heating form, one day at most is enough to get the required strength for the safe removal of forms, even in cold weather.

In this study, displacement estimation algorithm, which is not requiring an absolute reference point unlike the conventional displacement measurement method, is developed using the geophone. To estimate displacement of the bridge, measured velocity time signal is integrated in the frequency domain. And, the estimated displacement is compared with the measured result using a conventional method. Based on the dynamic field test results, it was found that the estimated displacement by the present algorithm is similar to that of a conventional method. The displacement estimation algorithm proposed in this paper can be effectively applied to measure the displacement of a structure, which is difficult to install a displacement transducer at the fixed point.

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