Sequential Refinement Solver using Space-Time Domain Decomposition for Non-linear Multiphase Flow Problems

Convergence failure and slow convergence rate are among the biggest challenges with solving the system of non-linear equations numerically. While using strictly small time steps sizes and unconditionally stable fully implicit scheme mitigate the problem, the computational load becomes enormous. We introduce a sequential local refinement scheme in space-time domain that improves convergence rate and prevents convergence failure while not restricting to small time step, thus boosting computational efficiency. We rely on the non-linear two-phase flow model. The algorithm starts by solving the coarsest mesh. Then regions with certain features such as saturation front is refined to the finest resolution sequentially. Such process prevents convergence failure. After each refinement, the solution from the previous mesh is used to estimate initial guess of the current mesh for faster convergence. Numerical results are presented to confirm accuracy of our algorithm as compared to the traditional fine time step approach. We also observe 5 times speedup in the runtime by using our algorithm

Benefits of in situ propellant utilization for a Mars sample return mission

Previous Mars rover sample return mission studies have shown a requirement for Titan 4 or STS Space Shuttle launch vehicles to complete a sample return from a single Mars site. These studies have either used terrestrial propellants or considered in situ production of methane and oxygen for the return portion of the mission. Using in situ propellants for the return vehicles reduces the Earth launch mass and allows for a smaller Earth launch vehicle, since the return propellant is not carried from Earth. Carbon monoxide and oxygen (CO/O2) and methane and oxygen (CH4/O2) were investigated as in situ propellants for a Mars sample return mission and the results were compared to a baseline study performed by the Jet Propulsion Laboratory using terrestrial propellants. Capability for increased sample return mass, use of an alternate launch vehicle, and an additional mini-rover as payload were included. CO/O2 and CH4/O2 were found to decrease the baseline Earth launch mass by 13.6 and 9.2 percent, respectively. This resulted in higher payload mass margins for the baseline Atlas 2AS launch vehicle. CO/O2 had the highest mass margin. And because of this, it was not only possible to increase the sample return mass and carry an additional mini-rover, but was also possible to use the smaller Atlas 2A launch vehicle

The Persistence of Earnings and Corporate Governance in IPO Firms

In this study, we investigate the earnings persistence in IPO firms by examining the two components of earnings: accruals and cash flows. We also analyze the impact of corporate governance on earnings and the two earnings components. In our comparison of the top and bottom quartiles based on the firms\u27 earnings at the IPO year, we find that although the top quartile firms have a significantly positive accrual component in the IPO year, they eventually have the same negative accrual component of earnings as the bottom quartile firms in the second year after the IPO. In contrast, we find that the significant difference in the cash flow component between the top and bottom quartiles persists during the two years after the IPO. This finding supports the existing literature that the cash flow component contributes to the persistence of earnings while the accrual component does not. We also find that the corporate governance structure has a significant impact on earnings and the components of earnings for the top quartile firms, but not for the bottom quartile firms. This is particularly evident since the top quartile firms have the opportunity to manage their earnings, while firms in the lowest quartile are unable to manage their earnings