During the foaming process of polyurethane, the surfactant plays a significant role in stabilizing and setting the foam. Simulation this role helps in better predicting the final performance and optimum foam formulation. The relation between the amount of surfactant added to the formulation and the surface tension was studied experimentally by using the capillary rise method to develop a simulation model. This model was aimed to study the critical role of the mechanism that surfactants have in the initial stages of gel formation and through the point where viscosity is high enough to create resistance to support the foams. Bubble sizes were calculated based on the number of nucleation sites, gas generation rate, surface tension, and inner bubble pressure. Since important properties of polyurethane foam, such as compressive strength, closed-cell content, and thermal conductivity can be related to the bubble sizes, this model can be used to predict foam performance and to develop new foam formulations.

In this study, the rupture criterion of bubbles wall in Aluminum metal foam liquid was investigated at the first stage, using Lattice Boltzmann. The two phases modeling were accomplished by using a modified Shan-Chen model. This model was run for several bubbles in A356+3wt.%SiC melt system. Then, bubbles morphologies (virtual metallographic) for A356+3wt.%SiC foams were simulated. Results showed that simulation data and the virtual metallographic have a good agreement with the metallographic empirical results after solidification. In the second stage, several cubic A356+3wt.%SiC foams were compressed under uni-axial compression load based on ASTM E9 standard. Stress-strain curves of foams were determined by a data acquisition system gaining 10 samples per second. Foams plastic deformation behavior then was simulated based on a new asymptotic function using ABAQUS software. Discretized digital solid-model of the solid bubbles was prepared with virtual metallographic images which obtained from the present code. The load-displacement curves were then plotted for simulation and experimental results. Results show that both curves which were obtained from experimental and simulation have a good agreement with approximately 1.8% error. Therefore, the present software could be a useful tool for predicting the metal foams plastic deformation behavior without any experimental try and error.

The lattice Boltzmann models, especially the pseudopotential models, have been developed to investigate multicomponent multiphase fluids in presence of phase change process. However, the interparticle force between different components causes compressibility error in the non-phase-change component. This restricts the model capability in quantitative analysis of the physical foaming process, such as expansion rate and decay time. In the present study, a multicomponent multiphase pseudopotential phase change model (the MMPPCM) is improved by introducing an effective mass form of high-pressure-difference multicomponent model in the non-phase-change component. The improved model is compared with the MMPPCM based on simulations of the phase change process of static and moving fluids, as well as the physical foaming process. Density variation of non-phase-change component and its effect on flow field characteristics are analyzed during the phase change process. Simulation results of physical foaming process lead to about 10% ~ 20% reduction of the compressibility error for the improved model as compared with the results of MMPPCM. The improved model also enhances the computational stability of phase change simulation of the static droplets.

Background and Objectives: The Hemispherical Resonator Gyroscope (HRG) is an inertial sensor that is a good choice for space missions and inertial navigation due to their low noise, low energy consumption, long life, and excellent accuracy and sensitivity. It consists of three main parts: the shell, the excitation and detection system, and the control circuits. In recent years, with using MEMS technology in the construction of HRG, vibrating shells with low volume and low price are made.Methods: The hemispherical shell is the main part and the beating heart of hemispherical resonator gyroscopes and is responsible for sensing. An optimized shell is required to implement the excitation and detection system and operate the gyroscope properly. In this research, the structure of a spherical shell with an environmental base that does not need to release the shell from its environment for its excitation and detection system is selected and the relationships governing this type of shell to improve the parameters of the glass blowing method will be investigated. Also, all sub-processes of this type method of fabrication to optimize the glass-blown spherical shell are implemented.Results: The process of making spherical shell by glass blowing using the chemical foaming process is used to obtain shells with height to radius ratio greater than 1, and finally, a glass shell with an etched cavity with a radius of 562 μm and depth of 524 μm created by the CNC process, with height to radius ratio of approximately 1.8 Has been achieved. In this method, using direct transfer of calcium carbonate to the etched cavity, before anodic bonding, the glass shell volume has been increased from 0.602 nL to 1.04 nL.Conclusion: The result is that to achieve a glass shell with a height to radius ratio of more than 1, in addition to improving the fabrication process, it is necessary to transfer the solid foaming agent to the etched cavity. Finally, in the fabrication of the glass-blown spherical shell, we have used the chemical foaming process (CFP) to obtain shells with a height to radius ratio greater than 1.