In this work, the rising of a single bubble in a quiescent liquid under microgravity condition was simulated. In addition to general studies of microgravity effects, the initiation of hydrodynamic convection, solely due to the variations of interface curvature (surface tension force) and thus the generation of shearing forces at the interfaces was also studied. Then, the variation of surface tension due to the temperature gradient (Marangoni convection), which can initiate the onset of convection even in the absence of buoyancy, was studied. The related unsteady incompressible full Navier-Stokes equations were solved using a finite difference method with a structured staggered grid. The interface was tracked explicitly by connected marker points via a hybrid front capturing and tracking method. A one field approximation was used where one set of governing equations is only solved in the entire domain and different phases are treated as one fluid with variable physical properties, while the interfacial effects are accounted for by adding appropriate source terms to the governing equations. Also, a Multi-grid technique, in the context of the projection method, improved convergences and Computational stiffness. The results show that the bubble moves in a straight path under microgravity condition, compared to the zigzag motion of bubbles in the presence of gravity. Also, in the absence of gravity, the variation of surface tension force due to interface curvature or temperature gradient can still cause the upward motion of the bubble. This phenomenon was explicitly shown in the results of this paper.

A one-dimensional, transient and thermal degradation model for predicting responses of composite materials when are exposed to the fire is presented. The presented model simulates ablation of composites with different layers of materials and considers material properties as functions of temperature. The reactions are modeled by using Arrhenius-type parameters and density-temperature diagrams which are obtained by specific experimental techniques such as thermogravimetric analysis. This transient thermal model has been implemented in form of a computer code by means of new numerical methods in order to predict the temperature distribution in the liner, the amount of char and erosion, and the liner thickness variations with time. By using implemented computer code, ablation phenomena in a glass-filled phenolic composite has been simulated with the same parameters of a similar experiment. The results are in a good agreement with the experimental data and the model can successfully be used in the design of thermal protection shields as an aid of material and thickness selection.

In the present study, the Large Eddy simulation (LES) turbulence closure is applied for the fi rst time, to the best of our knowledge, to investigate the viability of air conditioning systems in a large space. The results of LESs were validated against experimental measurements and the model was used to study the effect of different design variables including Air Changes per Hour (ACH), supply temperature, and return air vent height on design objectives such as local and global thermal comfort indexes and energysaving parameter by using a systematic multi-objective optimization approach. Sensitivity analysis showed that global and local thermal comfort indexes were highly sensitive to the air supply temperature, while energy saving was sensitive to ACH and the supply temperature to the same extent. In addition, it was found that height of the return air vent affected energy saving more than other factors. Finally, an energy saving rate of 22. 9% along with thermal comfort indexes within the allowable range is achievable by using the best design through the multi-objective optimization.

Background: Accurate voxel phantom is needed for dosimetric simulation in radiation therapy for malignant tumors in female pelvic region. However, most of the existing voxel phantoms are constructed on the basis of Caucasian or non-Chinese population. Materials and Methods: A Computational framework for constructing female pelvic voxel phantom for radiation dosimetry was performed based on Chinese Visible Human (CVH) datasets. First, several organs within pelvic region were segmented from CVH datasets. Then, polygonization and voxelization were performed based on the segmented organs and a 3D Computational phantom is built in the form of a set of voxel arrays. Results: The generated phantom can be converted and loaded into treatment planning system for radiation dosimetry calculation. From the observed dosimetric results of those organs and structures, we can evaluate their absorbed dose and implement some simulation studies. Conclusion: A voxel female pelvic phantom was developed from CVH datasets. It can be utilized for dosimetry evaluation and planning simulation, which would be very helpful to improve the clinical performance and reduce the radiation toxicity on organ at risk (OAR).