Prediction of welding deformation of hull panel blocks using an advanced inherent strain analysis method considering the heat equivalent layer effect

When a large-scale structure is fabricated via a complex welding process, deformation and residual stress are challenges that must be resolved. In a thermo-elasto-plastic analysis, calculations are carried out from room temperature through the heating and cooling of the welded joint section where the base metal is melted by the welding heat. It is difficult to apply this type of analysis to large, complex structures due to the prolonged computational time and huge processing volume required. Inherent strain analysis is a more effective approach to analyzing welding strain, and enables the use of an elastic analysis instead of a thermo-elastoplastic analysis to predict the strain residual stress that occurs in the welded part. This study compares an existing method that analyzes the strain in the welded part by using the correlation between the zone affected by the heat and the adjacent zone constraining the heat-affected zone, and an advanced analysis method that is intended to enhance the accuracy of the results by considering the heat equilibrium zone that exists between the adjacent regions constraining the heat-affected zone. The advanced inherent strain analysis method is applied to obtain more accurate results for a hull panel block model, which is one of the most complex welding structures, by considering a restraint diagram organized according to the welding and fabrication sequence of the members.     

A study on the development of equivalent beam analysis model on pedestrian protection bumper impact

This paper presents a dynamically equivalent beam analysis model on pedestrian protection bumper impact instead of a non-linear finite element impact analysis method. Equivalent beam analysis model was developed by substituting the femur and tibia for dynamically equivalent Euler beam. Dynamically equivalent forces of bumper beam, upper stiffener and lower stiffener are found by a finite element analysis results and applied to the Euler beam model of lower legform impactor. This equivalent beam analysis model was used to obtain a bending angle of lower legform impactor by using finite element beam theory. Peak acceleration of the tibia was obtained by developing an approximate acceleration equation. A linear interpolation of non-linear finite element analysis results considering the dimension variation of bumper beam factors affecting the acceleration was used to get an approximate acceleration equation. The accuracy of this simple analysis model was tested by comparing its results with those of the non-linear finite element analysis. Tested bumper beam types were press type beam and roll forming beam used widely in the current car bumpers. The differences of maximum acceleration of the tibia between the two models did not exceed 10% and the bending angle did not exceed 20%. This accuracy is enough to be used in the early stage of bumper beam design to check the bumper pedestrian performance quickly. Use of equivalent beam analysis model is expected to reduce the analysis time with respect to the non-linear finite element analysis significantly.     

Multi-Range approach of stereo vision for mobile robot navigation in uncertain environments

The detection of free spaces between obstacles in a scene is a prerequisite for navigation of a mobile robot. Especially for stereo vision-based navigation, the problem of correspondence between two images is well known to be of crucial importance. This paper describes multi-range approach of area-based stereo matching for grid mapping and visual navigation in uncertain environment. Camera calibration parameters are optimized by evolutionary algorithm for successful stereo matching. To obtain reliable disparity information from both images, stereo images are to be decomposed into three pairs of images with different resolution based on measurement of disparities. The advantage of multi-range approach is that we can get more reliable disparity in each defined range because disparities from high resolution image are used for farther object a while disparities from low resolution images are used for close objects. The reliable disparity map is combined through post-processing for rejecting incorrect disparity information from each disparity map. The real distance from a disparity image is converted into an occupancy grid representation of a mobile robot. We have investigated the possibility of multi-range approach for the detection of obstacles and visual mapping through various experiments.