Stiffener Design to Maintain Line Heating Efficiency during the Lifting Process Considering Phase Transformation

In the shipbuilding industry, welding is the main technique used to join steel structures. There is a lifting process, post-welding, that can eliminate the correction effect of line heating. Line heating is reperformed after the lifting process. This can significantly delay the ship assembly process. Herein, we present a design method for installing a permanent stiffener to avoid the disappearance of the line heating effect during the lifting process. The change in physical properties due to heating and cooling of the line heating is calculated. The limiting stress, at which the effect of the line heating completely disappears, based on the inherent strain theory, is obtained. The phase fraction by the cooling rate is calculated using the continuous cooling transformation diagram and the Kiustinen–Marburgerm equation. Physical properties affected by the phase transformation are calculated, considering the physical properties and fraction of each phase. The square plate theory and superposition principle are used to construct a local model, with a stiffener, of the ship block. The stress caused by the shape of the stiffener and the distance between the stiffeners were calculated for the local model. The calculated stress and the limiting stress were compared to determine, for the expected line heating efficiency, the most acceptable stiffener design. Finally, to confirm the elimination of the problem, the designed stiffener is analyzed using the finite element method.

CHARACTERIZATION AND ANALYSES ON RESIDUAL STRESS AND DEFORMATION DISTRIBUTION IN LINE HEAT PROCESS

Line heating is an important plate bending process that has been adopted in shipyards for more than 60 years. This paper presents the results of a numerical and experimental study on the residual deformation and stress distribution in the plate forming process using the line heating method. In this paper, a finite element model was used to simulate the heating process, and the model was validated using experimental results. The model was then used to analyze the deformation and stress distributions in the heating and non-heating region. The impact of line heating and sequence of heating on both sides of a steel plate was discussed. The findings of the study show that the compression stress generated help to increase the shrinkage of line heating process. This study presents a valuable reference for similar thermal process.

NUMERICAL AND EXPERIMENTAL STUDY ON PLATE FORMING USING THE TECHNIQUE OF LINE HEATING

Nowadays manual and experiential technique patterns of line heating process could not meet the requirement of modern shipbuilding. Therefore, the automatic forming method is being an active research topic in manufacturing. An accurate and practical predicting method is an essential part of the automatic plate forming system. In the present work a numerical elasto-plastic thermo-mechanical model has been developed for predicting the thermal history and resulting deformation and residual stress field of line heating process. A moving Gaussian distributed heat source was used in the modelling to create a realistic simulation of the process. The transient temperature distributions were predicted using temperature-dependent material properties. The deformation and residual stress field were predicted based on the transient temperature distributions of line heating. Experiments were conducted to prove the validity of the numerical thermo-mechanical model. The final numerical results of temperature, deformation and residual stresses are in good agreement with experiment results. The proposed method presents a valuable reference for the study of similar thermal process.

The impact of Lyα emission line heating and cooling on the cosmic dawn 21-cm signal

ABSTRACT Allowing for enhanced Lyα photon line emission from Population III dominated stellar systems in the first forming galaxies, we show the 21-cm cosmic dawn signal at 10 < $z$ < 30 may substantially differ from standard scenarios. Energy transfer by Lyα photons emerging from galaxies may heat intergalactic gas if H ii regions within galaxies are recombination bound, or cool the gas faster than by adiabatic expansion if reddened by winds internal to the haloes. In some extreme cases, differential 21-cm antenna temperatures near −500 mK may be achieved at 15 < $z$ < 25, similar to the signature detected by the EDGES 21-cm cosmic dawn experiment.