For the convenience of the cargo oil offloading process, the high-viscosity crude oil in oil tankers needs to be heated and insulated to keep the cargo oil temperature above the freezing point. The thermodynamics associated with the oil heating/insulation process needs to be well understood for optimization, especially when the oil tanker is subjected to a global motion, exciting oil sloshing inside the cargo tank. This paper presents an experimental study characterizing the heat transfer of the sloshing oil. In the experiment, a side tank of a VLCC (very large crude carrier) is considered as a prototype, and a 1/40 model is built following the Froude and Grashof similarity. The model is placed in a 6 DoF sloshing platform, which exciting periodic roll motion to simplified the wave-excited motion in the real scenario. The time histories of temperature at various monitoring points are measured. The results show that the conduction and convection are the dominated factors including the heat transfer when the oil is subjected to a sloshing condition. The characteristics of the temperature variation show different features at different locations and during different stage of the process; within the range of the consideration, larger motion angle and shorter exciting period results in more violent oil sloshing in the tank and, consequently, more significant effects on the heat transfer; as the sloshing becomes more significant, compared with the lower sloshing intensity, there is stronger forced convection above the heating coil. Forced convection makes the variation of oil temperature in the area above the heating coil more severe. Overall, the sloshing significantly influences the temperature distribution and causes a regional difference in the temperature characteristics. The experiment expects to provide a useful reference for guiding the oil heating/insulation process. INTRODUCTION Due to the high freezing point of crude oil, when oil tankers transport cargo oil in a low-temperature environment, once the cargo oil has solidified, it is not easy to unload. So, the cargo oil needs to be heated and insulated to ensure fluidity. At present, to prevent this from happening on ships, cargo oil is often overheated, which increase the transportation cost of cargo oil. In the current research on the heating process of cargo oil, cargo oil is mostly under a static environment. However, due to the influence of external wind and waves, cargo oil is always sloshing. Still, few related papers have been published on the effects of oil sloshing on the characteristics of temperature during the cargo oil heating process.

ABSTRACT The heating process of the crude oil in a polar tanker is simulated in this paper with the heating and thermal insulation of the cargo considered. A 3-D numerical model is established and the accuracy of the numerical methods is verified by the experimental data. After that, the temperature field and velocity of the cargo oil under the normal and low temperature environment are simulated, in which the outside low temperature of the arctic zone was set as the thermal boundary of the oil tank. The heat flux properties at different bulkheads are obtained, which can provide a theoretical basis for the heating and energy saving of the polar oil tankers in the engineering application. INTRODUCTION The heat preservation of the crude oil in the oil tanks becomes more and more important in the polar tanker because of the low temperature of the arctic environment. However, the study results of the special environment of the polar region on the cargo oil heating have not been published yet. With the unimpeded of the arctic routes, the number of oil tankers will increase significantly, and the economy of oil tankers operation and pollution of the polar environment will be more and more emphasized. The liquidity of the oil is affected by the external low temperature environment, which increases the heat dissipation of the oil and leads to the increase of the energy consumption. The influence of external temperature on the heating or cooling process of cargo oil has been studied numerically. The transient cooling by natural convection of a warm crude oil contained in a storage tank located in a cold environment was investigated numerically (Cotter and Charles, 1992,1993). A simplified heat loss model was developed to predict the mean tank temperature over time. A temperature-dependent apparent viscosity was employed to model the change in non-Newtonian fluid rheology that occurs with cooling. The increase in fluid viscosity concomitant with cooling was found to significantly slow down the rate of heat loss from the tank compared to the constant viscosity case. The temperature changing rule of the crude oil in the storage tank was obtained through a 2-D numerical model (Zhao, 2012), and the temperature distribution rule of the crude oil in the storage tank under different conditions was obtained.

ABSTRACT This paper represents the heat transfer mechanism of a double-hull tanker under static and sloshing conditions. The objective is to investigate the heat transfer mechanism and the effect of forced convection induced by sloshing on cargo oil heating process. In the experimental study, a large oil tanker side cabin is selected as the prototype, and the physical model is established on the basis of similar criteria. Then the heat transfer mechanism is analyzed and the effect of forced convection on heat transfer under the sloshing condition is explored through the analysis of the temperature curve and the derivation of the temperature. The experimental results show that, the oil temperature has obvious regional difference, the oil temperature in the upper part of the coil is obviously increased, but the oil temperature in the lower part of the coil has not changed obviously under the two environments. At the initial phase of heating, although the temperature of the monitoring point has not been significantly increased, there has been a natural convection. In the middle stage of heating, natural convection is most intense, especially in the upper part of the coil under static environment. The forced convection caused by sloshing reduces the regional difference of the oil temperature on the upper part of the coil and makes the heat transfer more balanced. The results suggest that a strictly theoretical optimization of the heating schemes in sloshing tanks can be used in future studies. INTRODUCTION During the transportation of cargo oil tanker, it is required to heat the oil due to its characteristics of high viscosity. However, excessive heating will increase energy consumption. Most of the scholars have studied the natural convection heat transfer process of crude oil in storage tanks or oil tankers, but few studies on forced convection heat transfer process of crude oil have been carried out, especially the forced convection produced by sloshing of oil tankers. The studies on the law of heat transfer of cargo oil in oil tank under static environment has been explored for many years, the results obtained are improved. Chen, et al,(2002) calculated the heating process of cargo oil in the tank numerically. The temperature distribution of crude oil in tank was calculated. Due to the limitation of conditions, the paper only considered the heat conduction process. The circs of flow field during the course of cargo oil heating and heat preservation were studied by Jin, et al (2006), and heat transfer mechanisms in the process of oil tanker transportation was discussed. It is concluded that natural convection plays the decisive role in the process of heat transmitted by the steam to cargo oil. A three-dimensional numerical analysis of unsteady flow was conducted and heat transfer to grasp the influence of heat loss from cargo-oil tank on natural heat convection was discussed by Shimizu, et al (2013). From the numerical analysis, typical flow pattern and distribution of oil temperature in oil tank were obtained.

Abstract A new technology, utilizing electromagnetic force to promote deformation of ship hull plate during line heating process, is called electromagnetic force assisted line heating (EFALH), which can improve efficiency and accuracy of plate deformation. Some key issues are solved in the numerical simulation of EFALH to study this technology and design processing parameters. These issues include implementing multi-physics coupling, establishing three-dimensional finite element model, and analyzing thermal boundary conditions. Optimization analysis of relation between the auxiliary effect of electromagnetic force and the temperature of steel plate is introduced, and main technological parameters for EFALH are designed, providing guidance for the experiment.

ABSTRACT In case of actual line heating process in the shipyard, the various weaving motions of gas torch moving along the target heating line have been adopted. By adopting weaving motions, it is possible to keep the maximum temperature under melting point and also to maintain the constant heating velocity through rhythmical motion of workers. In this study, an approach to determine the optimal heating conditions of line heating with weaving motions was presented, and some examples were introduced. The maximum angular distortion per unit hour was adopted as an objective function. SUMT algorithm is applied as an optimization tool. To get the optimal heating conditions, equivalent load method based on inherent strain was used. This study also deals with the process of deriving the optimal heating conditions for the specified thickness, heat flux with various torch speeds and weaving breadths as variables. The results of calculated optimal weaving heating conditions were well corresponded to the manufacturing standard. INTRODUCTION The inherent strain method has been used as one of the most efficient analysis method to predict the plate forming deformation by line-heating (Jang, Ko and Seo, 1997). Inherent strain method is an approach to calculate the deformation by elastic equivalent forces which is obtained by integration of inherent (irrecoverable) strain in the HAZ region. Due to its accuracy and efficiency, the inherent strain method will be able to substitute thermal elasto-plastic 3-D FEM analysis which requires much more computing time. It is very important to properly assume the inherent strain region for the precise prediction of plate deformation by line heating. There have been several methods to assume the inherent strain region. Recently, an improved method considering phase transformation effect of steel has been developed (Jang, Ha and Ko, 2003).

ABSTRACT The operating procedure of frame twisting process is investigated. The distributions of the heat input parameters are identified by performing spot heating test. The temperature histories in a T-shape ship longitudinal frame during face and web heating processes are estimated using the identified heat input parameters. The relationship between the residual and constrained deformation is calculated by elastic-plastic FE analysis using the estimated plate temperature as thermal body force. The calculated deformation agrees approximately with the measured one. This shows the accuracy and validity of the employed techniques for plate temperature and frame deformation estimation. It is also shown that substantial reductions in computing costs can be achieved without loss of accuracy by performing shell-based FE analysis. INTRODUCTION Gas heating process, which is one of the most characteristic works in the shipbuilding industry, is applied to the formation of curved hull plates and twisted longitudinal frames. This work has not been carried out by automatic operation, but by skilled workers. Recently the automatic operation has been strongly desired because of the decrease in skilled workers. Development of an accurate deformation estimation method is the prerequisite for the automation of this process. Repetitive circular heating with high power gas torch is performed in the frame twisting process. It had been considered difficult to simulate this process because there had been no accurate method to estimate the heat transition during repetitive heating. The estimation technique of heat transition during gas heating process had been studied by many researchers. Moshaiov and Latorre (1985) studied the temperature distribution of a plate using a distributed heat source moving along the plate surface. Tsuji and Okumura (1988) found that the heat flux distribution could be expressed approximately by superposition of two gaussian distributions.

ABSTRACT During fabrication of deck house block in passenger ships, the problem of unexpected large deformation and distortion frequently occurs. Hence, amending of these deformation become more important in thin plate welding. The spot heating and line heating methods were very widely employed to amend deformation of thin plate structures. Few papers are available on the working conditions of spot heating method but only little information on deformation control. In this study, evaluation was carried out on the temperature distribution of spot and line heating methods using FEA and practical experiments for various heating time. In FEA, heat input model was established using Tsuji's double Gaussian heat input mode (Tsuji, I., 1988). This model was verified by comparing with experimental data. Also radial shrinkage and angular distortion due to spot heating were determined and compared with experimental results. Thermo elasto-plastic analysis was performed using commercial FE code, MSC/MARC. Radial shrinkage and angular distortion were measured using 3D measuring apparatus. Based on these results, criteria for amending thin plate fairing was established in our fabrication yard. INTRODUCTION In recent years of ship building technology, thin plate welding and control of its deformation is considered as a serious problem. During the fabrication of thin plate structures, welding distortions are inevitable and serious problem of whole ship structure in strength. Because of the need to reduce total weight of ships, deck plate thickness has been gradually reduced resulting in use of 5mm thickness plate associated with buckling distortion during deck block fabrication. The best way to control buckling distortion is to optimize welding parameters and structural parameters. But this requires lot of trial and error experiments. In many cases, line heating or triangular heating is not in much correct to control thin plate deformation.