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In this study, the effects of three different types of materials of post-cooling pipes on thermal stress and temperature gradients in mass concrete were investigated numerically. It was found that, of the three types of cooling pipe materials observed in this study, steel pipes caused the fastest cooling and the lowest concrete temperature, followed by polyethylene (PEX) and polyvinyl chloride (PVC) pipes. The temperature difference only occurs at locations less than 100 m from the cooling water inlet. The concrete temperatures obtained using a steel cooling pipe can reach temperatures 70% and 36% lower than those obtained using PVC and PEX cooling pipes, respectively. Compare to PEX and PVC cooling pipes, the steel cooling pipe can reduce the risk of cracking associated with the expansion of the core region and the shrinkage of the surface of the concrete. However, the steel cooling pipe increases the risk of cracking near the cooling pipe, where the tensile stress that occurs due to the use of steel pipes can reach values 25.3% and 12.7% higher than those occurring due to the use of PVC and PEX pipes, respectively. In high temperature regions, expansion of PEX and PVC pipes causes an increase in thermal stress, especially in the area near the cooling pipes.

This study considers the accuracy of cell-to-face centre interpolation of convected quantities in unstructured finite volume meshes with cell-centred storage of variables. The accuracy of the interpolation algorithms were tested in isolation using ideal data to determine their numerical accuracy on both standard and artificially distorted meshes. It was found that the formally second- and third-order accurate interpolations based on one-dimensional interpolation along the line connecting the cells to the right and left of the face under consideration only have first-order accuracy in standard unstructured mesh, and less than first-order accuracy in distorted unstructured mesh. L1 interpolation errors in the distorted unstructured mesh are greater than in standard unstructured mesh. The order of accuracy and L1 errors can be improved by applying spatial corrections. The formally second-order accurate multi-dimensional interpolations tested in this study that are not based on one-dimensional interpolation along lines connecting the neighbour cells have first-order accuracy in both standard and distorted unstructured mesh. Linear interpolation between end vertices produces greatest L1 error in standard mesh; polynomial interpolation, linear interpolation between cell centres and standard QUICK produce the greatest L1 error in distorted mesh. Spatially correct QUICK, spatially correct linear interpolation between cell centres, Laplacian interpolation to face centres, and Taylor series expansion about an upstream cell produce the smallest L1 error in both standard and distorted mesh. Based on accuracy and the simplicity of implementation, Taylor series expansion about an upstream cell is the best choice for use in unstructured mesh., Finite volume; Interpolation algorithm; Unstructured mesh; Accuracy comparison.

In the past two decades, the consumption of fossil fuels worldwide has significantly increased, resulting in shortages of energy sources, increasing energy prices and increasing amounts of pollutant releases to the environment. For these reasons, developing alternative energy sources is critical to mitigating future energy crises and reducing the negative effects of pollutants to the environment. One popular class of alternative energy sources is renewable energy sources. Specifically, in Indonesia, renewable energy is available in the form of solar, hydro-power, geothermal, wind energy and biomass. Each type of renewable energy source has its advantages and disadvantages, so that selecting the most appropriate source among them is very important to gain the optimal benefit. The purpose of this work is to develop a selection methodology and to determine the most appropriate renewable energy sources for electricity generation for Indonesia. A selection methodology was proposed, based on fuzzy AHP, which involved a new procedure for the aggregation of expert opinions. Some selection criteria appropriate for Indonesia were also introduced. Hydro power was found to be the best renewable energy source, followed by geothermal, solar, wind energy and biomass.

Hydration heat trapped in concrete can cause cracks due to thermal stress caused by temperature gradient inside the concrete. The trapped heat can be removed by using a post-cooling system, where the concrete is cooled by running water through pipes embedded in it. However, post cooling may cause thermal stresses owing to the temperature gradient in the region adjacent to the cooling pipe. In this study, the thermal stress and temperature gradient caused by the space between the cooling pipes and cooling water temperatures of the post-cooling system are investigated numerically. Based on the concrete type, thermal properties and dimension of post cooling components used in this study, it was found that, compared to cooling water temperature, the space between the cooling pipes had a stronger effect on the distribution of temperature and thermal stress in the concrete. The increase in cooling water temperature tend to increase concrete temperature and decrease thermal stress especially in region next to cooling pipe, while the increase in distance between cooling pipe tend to increase both of concrete temperature and thermals thermal stress near the cooling pipes. To reduce the risk of concrete cracking due to post cooling, it is not enough just to adjust the temperature of the cooling water and space between cooling pipes. The cooling water temperature, space between cooling pipe and convection coefficient from surface of cooling pipes to cooling water need to be set to obtain a temperature distribution which result a thermal stress which lower than tensile ultimate strength of the concrete.