Study on the Propagation of Dimensional Deviation in the Hull Block Building Process

Dimensional accuracy of hull block plays a critical role in guaranteeing the whole ship accuracy and reducing the hull butt-joint cost. The current industry practice of dimensional control in shipbuilding mainly focuses on the prediction of cutting and welding deformation based on engineering experience. Its main limitation is that the propagation and accumulation of deviations in the whole building process are neglected. In this article, cutting errors, assembly deviations, welding shrinkages, turnover distortions, and thermal expansions generated at different stages are analyzed. The propagation and accumulation of deviations and variations in the double-bottom block building process are studied based on the measured data in the whole process. Finally, the correlations of deviations between the adjacent stage are concluded. The conclusions can be used to guide the accuracy control in the hull block building process and reduce dimension trimming.

A Cattaneo-Mindlin problem for a rigid punch with tangential load applied above the interface line

We study the contact between a rigid flat punch and an elastic half-space using Coulomb friction for a normal load followed by a tangential load applied at a certain height above the interface line. The study is inspired by recent experiments by the group of Jay Fineberg in Israel. Three regimes are found in the evolution of slip at the interface depending on a dimensionless parameter [Formula: see text] , the ratio between the halfwidth of the contact and the product of twice friction coefficient and height of the loading point. Normal pressure and shear tractions are plotted for each case. It is shown that the effect of height does not collapse the data, contrary to the experimental data of Fineberg’s setup. However, this is not surprising given the many deviations from the ideal configuration we have studied, namely the finite thickness of the bottom block, the presence of vertical surfaces on the upper block (both not permitting the assumption of halfspace elasticity) and finally local effects due to concentrated tangential load which give rise to local and not only global induced moment.

Research on the Assembly Sequence of a Ship Block Based on the Disassembly Interference Matrix

Reasonable optimized block assembly sequence has vital practical significance for ship construction, and the research has been done in this article at the aim of obtaining optimal assembly sequence. First, taking a double-bottom block as the object of study, by analyzing the connection relationship between each part, a disassembly network diagram and disassembly interference matrix can be generated by applying the demolition method. Based on the disassembly interference matrix, disassembly sequence can be generated according to certain rules, then the assembly sequence is the invert of disassembly sequence; next, considering comprehensively the part's physical attribute affecting the assembly sequence, the final assembly sequence can be obtained for two assembly ways using the analytic hierarchy process; lastly, DELMIA software is applied to implement the virtual simulation of the assembly process in accordance with the assembly sequence. The work of the article is of certain guidance significance to parts assembly in ship production and can lay a good foundation for realizing the ship block's digital assembly.

The Improved AVS Intra Prediction Algorithm

AVS introduces intra-prediction coding technique to improve the intra-coding efficiency. There are 5 candidate modes for luminance intra-prediction and 4 candidate modes for chrominance. The method of intra prediction for the current video coding standard mainly uses the pixels of the left, the top, the upper right neighboring blocks, and doesnt use the pixels of the right and bottom blocks. It is not because there is low correlation between the current block and the right and bottom blocks, but the right and bottom blocks need to refer to the data of current block to decode the display. If the mode of the right block is the vertical mode, it can use the data of right block to predict the current block and a new prediction mode of mean-left-right is presented, and if the mode of the bottom block is the horizontal mode, it can use the data of bottom block to predict the current block and a new prediction mode of mean-top-bottom is presented. The corresponding adjustment is implemented for AVS encoder and decoder. Experimental results show that the PSNR increases about 0.03db and the coding bit rate decreases by about0.73% with small complexity increasing.

Study on the Underwater Rotating Apparatus with Changeable Rotating Angle

We proposed the underwater rotating apparatus with changeable rotating angle for the FDSO bottom construction, which includes a pair of arc-shaped base, the hydraulic support, the arc-shaped hydraulic rail, the driving motor, power supply units and the computer. The underwater rotating angle mathematical model was built with the known bottom block division. The apparatus has the features of changeable underwater rotating angle, nondestructive to the FDSO bottom and the semi-submersible barge, low labor intensity when compared with the original apparatus. Finally, the underwater rotating apparatus was successfully applied to build the Sevan Driller FDSO bottom, and the results show the model is correct and valid, which provides an important reference for the FDSO construction.

Determination of the Effects of the Pre-Outfitting and Pre-Piping Assembly Operations on Shipyard Productivity

The process improvement operations are very significant in shipbuilding industry as the other industries. In recent years, the shipyards attempt to improve their processes by examining their current production system and to reduce the cycle time of the interim product so that they can keep their competitive power. If the cycle time of the interim products is decrease, that may cause to increase the annual production capacity and market share of the shipyard. In order to do this, the shipyards have to analyse their own production system and carry out some improvements on it. In this study, the effects of carrying out the outfitting and piping assembly operations in earlier work stations were investigated by using a methodology presented here. The steps in the methodology were applied to a double bottom block of a container ship. It was shown that if the outfitting and the piping assembly operations are carried out in earlier stations instead of the block assembly station, this may increase the throughput by 33%. The results of the study were discussed in the final section.