Analysis of internal ablation for the thermal control of aerospace vehicles

A new method of thermal protection for transatmospheric vehicles is introduced. The method involves the combination of radiation, ablation and transpiration cooling. By placing an ablating material behind a fixed-shape, porous outer shield, the effectiveness of transpiration cooling is made possible while retaining the simplicity of a passive mechanism. A simplified one-dimensional approach is used to derive the governing equations. Reduction of these equations to non-dimensional form yields two parameters which characterize the thermal protection effectiveness of the shield and ablator combination for a given trajectory. The non-dimensional equations are solved numerically for a sample trajectory corresponding to glide re-entry. Four typical ablators are tested and compared with results obtained by using the thermal properties of water. For the present level of analysis, the numerical computations adequately support the analytical model

Continuum Breakdown Parameter Based on Entropy Generation Rates

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76968/1/AIAA-2003-157-250.pd

Epistemic Modeling Uncertainty of Rapid Neural Network Ensembles for Adaptive Learning

Emulator embedded neural networks, which are a type of physics informed neural network, leverage multi-fidelity data sources for efficient design exploration of aerospace engineering systems. Multiple realizations of the neural network models are trained with different random initializations. The ensemble of model realizations is used to assess epistemic modeling uncertainty caused due to lack of training samples. This uncertainty estimation is crucial information for successful goal-oriented adaptive learning in an aerospace system design exploration. However, the costs of training the ensemble models often become prohibitive and pose a computational challenge, especially when the models are not trained in parallel during adaptive learning. In this work, a new type of emulator embedded neural network is presented using the rapid neural network paradigm. Unlike the conventional neural network training that optimizes the weights and biases of all the network layers by using gradient-based backpropagation, rapid neural network training adjusts only the last layer connection weights by applying a linear regression technique. It is found that the proposed emulator embedded neural network trains near-instantaneously, typically without loss of prediction accuracy. The proposed method is demonstrated on multiple analytical examples, as well as an aerospace flight parameter study of a generic hypersonic vehicle

Numerical integration techniques for discontinuous manufactured solutions

When applying the method of manufactured solutions (MMS) on computational fluid dynamic software, determining the exact solutions and source terms for finite volume codes where the stored value is an integrated average over the control volume is non-trivial and not frequently discussed. MMS with discontinuities further complicates the problem of determining these values. In an effort to adapt the standard MMS procedure to solutions that contain discontinuities we show that Newton–Cotes and Gauss quadrature numerical integration methods exhibit high error, first order limitations. We propose a new method for determining the exact solutions and source terms on a uniform structured grid containing shock discontinuities by performing linearly and quadratically exact transformations on split cells. Transformations are performed on triangular and quadrilateral elements of a systematically divided discontinuous cell. Using a quadratic transformation in conjunction with a nine point Gauss quadrature method, a minimum of 4th order accuracy is achieved for fully general solutions and shock shapes. A linear approximation of curved shocks is also experimentally shown to be 2nd order accurate. The numerical integration method is then applied to a CFD code using simple discontinuous manufactured solutions which return consistent 1st order convergence values. The result is an important step towards being able to use MMS to verify solutions with discontinuities. This work also highlights the use of higher order numerical integration techniques for continuous and discontinuous solutions that are required for MMS on higher order finite volume codes

Assessment of Entropy Generation Rate as a Predictor of Continuum Breakdown

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77391/1/AIAA-2003-3783-821.pd

Hypocholesterolemic Effect and In Vitro Pancreatic Lipase Inhibitory Activity of an Opuntia ficus-indica Extract

Cholesterol control is fundamental for prevention of cardiovascular disorders. In this work, the hypocholesterolemic activity of an aqueous Opuntia ficus-indica extract (AOE) was tested in triton-induced mice. The inhibitory activity on pancreatic lipase enzyme was evaluated in vitro by the same extract. Furthermore, polyphenol content of the extract was evaluated. Hypercholesterolemia was induced in three groups of mice by intraperitoneal administration of Triton WR-1339. After induction of hypercholesterolemia, the groups were treated with an AOE (500 mg/kg) and saline solution and the positive control group with orlistat, respectively. Cholesterol levels were measured 24 h later in peripheral blood. The levels of blood cholesterol after administration of AOE significantly decreased compared to negative control. The inhibitory activity of AOE on pancreatic lipase enzyme was evaluated at concentrations from 60 to 1000 g/mL. The AOE inhibited the pancreatic lipase with an IC 50 = 588.5 g/mL. The AOE had a high content of polyphenolic compounds. These results show that AOE is able to prevent hypercholesterolemia by pancreatic lipase inhibition, in part due to its polyphenolic compounds

Drag and Heat Transfer Effects on Hypersonic Vehicles in Close-Proximity Flight

A computational investigation of the drag and heat transfer experienced by multiple trailing (following) vehicles in hypersonic flight is presented. Linear arrays of vehicles in flight at Mach 10 are modeled. Results are presented for both parametric two-dimensional cases and for a three-dimensional case. Drag and heat transfer on trailing vehicles in two-dimensional (five vehicle) arrays, for both powered and unpowered configurations, are shown to reduce progressively from leading vehicle to trailing vehicle such that trailing vehicles can experience less than 30% of the drag and heat transfer experienced by the lead vehicle. The three-dimensional study examines pressure drag effects for generic lifting body/wave-rider configurations in a three vehicle array. Drag due to pressure on the trailing vehicle in such an array falls to approximately 20% of that experienced by the lead vehicle for an unpowered case and to less than 20% for the powered case. The drag and heat transfer reductions are due to the developing slip stream resulting from the successive vehicles, with attendant and progressively increasing reductions in local approach Mach numbers, local approach velocities, and surface pressures experienced by trailing vehicles

Drag and Heat Transfer Effects on Hypersonic Vehicles in Close-Proximity Flight

A computational investigation of the drag and heat transfer experienced by multiple trailing (following) vehicles in hypersonic flight is presented. Linear arrays of vehicles in flight at Mach 10 are modeled. Results are presented for both parametric two dimensional cases and for a three dimensional case. Drag and heat transfer on trailing vehicles in 2-D (five vehicle) arrays, for both powered and unpowered configurations, are shown to reduce progressively from leading vehicle to trailing vehicle such that trailing vehicles can experience less than 30% of the drag and heat transfer experienced by the lead vehicle. The 3-D study examines pressure drag effects for generic lifting body/wave-rider configurations in a three vehicle array. Pressure drag on the trailing vehicle in such an array falls to approximately 20% of that experienced by the lead vehicle for an unpowered case and to less than 20% for the powered case. The drag and heat transfer reductions are due to the developing slipstream resulting from the successive vehicles, with attendant and progressively increasing reductions in local approach velocities, local approach Mach numbers, and local approach pressures experienced by trailing vehicles

Parallel unstructured grid generation

A parallel unstructured grid generation algorithm is presented and implemented on the INTEL hypercube. Different processor hierarchies are discussed, and the appropriate hierarchies for mesh generation and mesh smoothing are selected. A domain-splitting algorithm for unstructured grids, which tries to minimize the surface-to-volume ratio of each subdomain, is described. This splitting algorithm is employed both for grid generation and grid smoothing. Results obtained on the INTEL hypercube demonstrate the effectiveness of the algorithms developed