Abstract:The design strength of a greenhouse structure is generally determined by analyzing strength after applying wind load using the wind pressure coefficient according to a design guide. Until now, the stability analysis for wind load has been performed through static structural analysis. However, a greenhouse is subjected to dynamic wind loads of various amplitudes, and it is reasonable to judge stability through fatigue analysis. For fatigue analysis, a stress-normalized model was constructed based on the square of wind speed, and the value obtained by squaring wind speed was used as dynamic load time data. Life cycle was calculated under stress generated by self-weight by compensating fatigue estimation stress. Furthermore, the effect of self-weight was examined and errors of up to 21% were obtained depending on the configuration of the stress-normalized model. When self-weight and wind speed were applied simultaneously, the effect of self-weight reduced when the stress-normalized model was used at high wind speed. Therefore, it is appropriate that the fatigue analysis is based on the fatigue stress model normalized by the square of wind speed, fatigue estimation stress is corrected to the static stress due to self-weight, and the square of wind speed is used as the dynamic load.

We describe a two-dimensional piezoelectric laser scanner designed and tested to obtain a large steering angle of 1° and fast response characteristics of 200 Hz. To overcome the relatively small expansion capability of piezoelectric actuators, the displacement amplification mechanisms with two levers in series are employed to magnify the end tip of the lever which is connected to a 0.5-in. glass mirror. For fast response characteristics, the natural frequencies of the hinge mechanisms were calculated by using the finite element analysis technique. In order to evaluate the performance of the proposed scanner, the hinge mechanism has been manufactured of titanium alloy and the natural frequencies of the hinge mechanism have been measured by sine sweep test. Also, the actual machining test on the burning paper has been done by using a high power laser, and it is shown that the proposed laser scanner is capable of steering the laser beam 1° with a frequency of 200 Hz.

In order to improve energy efficiency by increasing heat dissipation performance of bus-bar which distributes the current in high-power switchboard, the heat dissipation effects of the shape modification and surface treatment of Cu bus-bar were studied. The surface temperatures of the conventional plate-type bus-bar, and the improved tunnel-type bus-bar were compared by using electromagnetic and thermal analyses. The optimum thickness of tunnel-type bus-bar and the spacing and array among three bus-bars were calculated; and the surface temperature of tunnel-type bus-bar showed 7.9 °C lower than that of plate-type bus-bar in a 3-phase array condition. In addition, the surface and internal temperatures of the uncoated, CNT (Carbon nanotube)-coated, and BN (Boron nitride)-coated Cu bus-bars were measured with thermal imaging camera and the experiment using a hot plate. It was confirmed that the difference in the internal temperature between uncoated and BN-coated Cu was 19.4 °C. The application of the bus-bar improved from this study might contribute to the increase in power energy efficiency.

No abstract

Herein, the behavior of a rolling type seismic isolation system with a position restoring device (PRD) is investigated, for alleviating problems such as rapid convergence and position restoration. The equation of motion is derived by modeling the behavior of the seismic isolation system, and the seismic characteristics according to the design variables of the PRD are investigated through numerical analysis. The vibration characteristics of the equation of motion show nonlinearity and depend on different variables. Numerical analysis was performed by using the fourth and fifth order Runge–Kutta method, and the vibration characteristics were analyzed with respect to the design parameters in the rolling type seismic isolation system with PRD, and compared to a model without PRD. In the model with PRD, numerical results show that the vibration suppression capability of the earthquake and the position restoration after disturbance are improved compared to those of the model without PRD. In addition, the rolling type seismic isolation system had nonlinear characteristics at specific frequencies, where the response increases suddenly and harmonics occur. This phenomenon can be controlled by the ratio of mass to stiffness and the damping coefficient, showing that the mount system can be designed to avoid resonance through optimal design.