Aerospace Engineering and Mechanics

A quick reference guide to CubeSats, the standardized approach to miniaturized satellites that has revolutionized access to space. This document is for those who are new to CubeSats or just need a concise reference.

Keywords: CubeSat, engineering design, licensing, online reference links, spacecraft, subsystems, systems

Density-based and pressure-based approaches in solving the Navier-Stokes equations for computational field simulations for compressible and incompressible flows have been presented. For the density-based flow solver, a generalized grid based framework has been developed and employed to simulate the complex-geometry problems with ease. The integral form of the standard and artificial compressibility form of Navier-Stokes equations has been taken as the governing form for the density-based method. For the pressure-based flow solver, the differential form of the conservation equations in the curvilinear coordinates was solved with a non-staggered structure-grid topology. A predictor plus multi-corrector algorithm (which can handle the flow with a wide range of Mach numbers without using the artificial compressibility and the preconditioning method) is utilized in the pressure-based method. Also, the capability has been developed to model the gas-particle (liquid and/or solid) multi-phase flows in the Eulerian-LaGrangian particle-tracking framework. Though the strengths and weaknesses of these two methods have been well documented, there is yet an extensive study to compare these two methods in terms of their numerical accuracies, computational efficiencies, and limitations. In this paper, these two models are validated separately, and the results are presented. Comparisons of these two methods with various benchmark test cases will be assessed and addressed in the future.

The characteristics of propellant mixing near the injector have a profound effect on liquid rocket engine performance. Injector element geometry and propellant momentum are the only parameters available to control such mixing. A multiphase flow combustion model utilizing propellant real-fluid properties was developed to predict the mixing and thermal environment created by element configurations. The multiphase model was incorporated into a mature computational fluid dynamics code that can be used to simulate the flowfield near the injector and to analyze the combustion chamber and nozzle wall heating. The validity of the present model and code was investigated by comparing predictions to test data for two liquid oxygen/gaseous hydrogen unielement shear coaxial injector and two cryogenic nitrogen jet injection experiments. These simulations and those of several other investigators were critically compared at the 2nd International Workshop on Rocket Combustion Modeling. Based on these comparisons, it appears that the present model is a good, computationally efficient approximation of liquid rocket injector flows for both subcritical and supercritical spray combustion. Nomenclature a = speed of sound of a multicomponent mixture B ij = coefficients of the thermal property polynomial for a given species Cp = constant-pressure specific heat D = diameter of the center tube in an injector element D p = inverse of the matrix of the coefficients of the convective terms in the finite-difference form of the momentum equations H = real-fluid enthalpy of a given species H 0 = ideal-gas enthalpy of a given species O=F = oxidizer-fuel ratio in mass p = static pressure p 0 = pressure correction p n = pressure at the previous time step p n1 = pressure at the current time step p c = critical pressure of a given species p r = reduced pressure of a given species R = gas constant r = radial distance T = temperature T c = critical temperature of a given species T r = reduced temperature t = time V = velocity at the immediate time step V 0 = velocity correction X = axial distance Z c = compressibility of a given species at the critical point p = partial derivative of density with respect to pressure at constant temperature = specific heat of a multicomponent mixture = density of a given species or mean density of a mixture n = density at the previous time step = density at the immediate time step 0 = density correction c = density of a given species at the critical point r = reduced density of a given species

The simulation of flow past bodies in relative motion is a challenging task due to the presence of complex flow features, moving grids, and rigid body movements under the action of external forces and moments. A generalized grid-based overset framework is presented for the simulation of this class of problems. The equations that govern the fluid flows are cast in an integral form and are solved using a cell-centered finite volume upwind scheme. The rigid body dynamics equations are formulated using quaternion and are solved using fourth-order Runge-Kutta (RK) time integration. The overset framework and the six degree of freedom (6-DOF) rigid body dynamics simulators are developed in a library form for easy incorporation into existing flow solvers. The details of the flow solver, the 6-DOF library, and the overset framework are presented in this paper along with the validation results of the developed system.

In this paper, we report an extension of the Space-time Conservation Element-Solution Element (CE/SE) framework based viscous flow solver. The formulation of the Courant Number Insensitive Scheme (CNIS) is explained. The developed solver is validated through simulation of 2-D problems, such as, driven cavity, and external flow over a circular cylinder. Verifications are also conducted to study the numerical accuracy and sensitivity of grid spacing. The numerical results and their comparison with analytical and experimental results are presented. Possible future work is also discussed.

This paper describes the development and the validation of two computational fluid dynamics (CFD) frameworks for multidisciplinary and multi-scale simulations. The first framework is an overset grid topology with a six-degree of freedom rigid body dynamics library for both structured-grid and unstructured-grid approaches. This framework will enable the CFD flow solver to simulate the problems involving relative motions between multiple bodies such as the stage/store separation process, etc. The second framework is a hybrid scheme that integrates a direct simulation Monte-Carlo (DSMC) method for rarefied gas flows and a Navier-Stokes (NS) solver for continuum flows. The hybrid DSMC-NS numerical framework can greatly improve the computational efficiency for simulation of problems with disparate length scales or a wide range of Knudsen numbers. A density-based Navier-Stokes flow solver, HYB3D, and a pressure-based Navier-Stokes flow solver, FDNS, were employed in this study to demonstrate the capability, strength, and accuracy of these two frameworks. Numerical simulations of benchmark test cases were conducted as the preliminary evaluation for these two frameworks, and the numerical results are presented.

BACKGROUND: Of great interest in cancer prevention is how nutrient components affect gene pathways associated with the physiological events of puberty. Nutrient-gene interactions may cause changes in breast or prostate cells and, therefore, may result in cancer risk later in life. Analysis of gene pathways can lead to insights about nutrient-gene interactions and the development of more effective prevention approaches to reduce cancer risk. To date, researchers have relied heavily upon experimental assays (such as microarray analysis, etc.) to identify genes and their associated pathways that are affected by nutrient and diets. However, the vast number of genes and combinations of gene pathways, coupled with the expense of the experimental analyses, has delayed the progress of gene-pathway research. The development of an analytical approach based on available test data could greatly benefit the evaluation of gene pathways, and thus advance the study of nutrient-gene interactions in ...