This article introduces a computer program for computer-aided education about Mohr's circle and its practical use. The instructional tool has been implemented as part of a finite element analysis program, VisualFEA. The proposed approach to teaching and learning Mohr's circle is distinguished from previous work by its association with practical analysis models. The Mohr's circle is displayed and operated on the basis of stress data obtained from finite element analysis whereas arbitrarily assumed numerical values are used in other programs. The analysis can be extended to elasto-plastic models with various yield criteria. Thus, the program can be regarded not only as an instructional module for studying Mohr's circle itself, but also as a training tool for exercising its practical application. This article describes the characteristics of the program's educational features and suggests important points for teaching and learning Mohr's circle and related subjects using VisualFEA.

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This study was conducted to investigate the effect of ventilation at high temperature on the control of powdery mildew, silverleaf whitefly two-spotted spider mite occurred at Korean melon cultivation greenhouse, and on leaf rolling and flowering of the plant in summer season. 'Alchanggul' grafted onto 'Hidden Power' rootstock was planted on soil bed with the distance of 40 cm. Three ventilation temperatures of 45°C, 40°C, and 35°C as set points were compared. Ventilation treatment was done by control of side window operation from 18th June to 13th July when silverleaf whitefly, mite, and powdery mildew were occurred in all greenhouses. The temperature inside greenhouse was increased up to the set temperature point on sunny days and maintained for about 9 hours with high relative humidity at 45°C condition. The differences of day maximum air temperature and day minimum RH were the highest at 45°C treatment. After 11 days of treatments, the damage by powdery mildew and two-spotted spider mite was almost recovered at 45°C treatment but not at 40 and 35°C. The population of silverleaf whitefly and two-spotted spider mite were significantly decreased at 45°C treatment at 14 days after treatment, while powdery mildew symptom was not significantly decreased. Leaf rolling was observed at high temperature but not severe at 45°C treatment. After 26 days of treatments, female flowers did not bloom at all at 45°C treatment, and the number of male flowers was 1.2 among 15 nodes of newly grown shoots. As the result, it indicates that ventilation at the high temperature of 45°C for about 2 to 3 weeks can be an applicable method to control above mentioned pests and disease, and to recover the vegetative growth of Korean melon by reducing flowering of the plant.

This study was carried out to develop rain shelter which can make an appropriate size and environment for Chinese cabbage rainproof cultivation. Fifty three farms with chinese cabbage rainproof cultivation system have been investigated to set up width and height of rain shelter. Mostly the width of 6m was desired for rain shelter and the height of 1.6m for their eaves, so these values were chosen as the dimensions for rain shelter. After an analysis of their structural safety and installation costs by the specifications of the rafter pipe, Ø25.4×1.5t and 90cm have been set as the size of rafter that such size costs the least. This size is stable with 27m•s −1 of wind velocity and 17cm of snow depth. Therefore it is difficult to apply this dimension to area with higher climate load. In order to sort out such problem, the rain shelter has been designed to avoid damage on frame by opening plastic film to the ridge. Once greenhouse band is loosen by turning the manual switch at the both sides of rain shelter and open button of controller is pushed then switch motor rises up along the guide pipe and plastic film is opened to the ridge. Chinese cabbage can be damaged by insects if rain shelter is opened completely as revealed a field. To prevent this, farmers can install an insect-proof net. Further, the greenhouse can be damaged by typhoon while growing Chinese cabbage therefore the effect of an insect-proof net on structural safety has been analyzed. And then structural safety has been analyzed through using flow-structure interaction method at the wind condition of 40m•s −1 . And it assumed that wind applied perpendicular to side of the rain shelter which was covered by insect-proof net. The results indicated that plastic film was directly affected by wind therefore high pressure occurred on the surface. But wind load on insectproof net was smaller than on plastic film and pressure distribution was also uniform. The results of structural analysis by applying pressure data extracted from flow analysis indicated that the maximum stress occurred at the end of pipe which is the ground part and the value has been 54.6MPa. The allowable stress of pipe in the standard of structural safety must be 215 MPa or more therefore structural safety of this rain shelter is satisfied.

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