Simulation verification techniques study: Simulation performance validation techniques document

Techniques and support software for the efficient performance of simulation validation are discussed. Overall validation software structure, the performance of validation at various levels of simulation integration, guidelines for check case formulation, methods for real time acquisition and formatting of data from an all up operational simulator, and methods and criteria for comparison and evaluation of simulation data are included. Vehicle subsystems modules, module integration, special test requirements, and reference data formats are also described

Cold water aquifer storage

A working prototype system is described in which water is pumped from an aquifer at 70 F in the winter time, chilled to a temperature of less than 50 F, injected into a ground-water aquifer, stored for a period of several months, pumped back to the surface in the summer time. A total of 8.1 million gallons of chilled water at an average temperature of 48 F were injected. This was followed by a storage period of 100 days. The recovery cycle was completed a year later with a total of 8.1 million gallons recovered. Approximately 20 percent of the chill energy was recovered

Simulation verification techniques study. Subsystem simulation validation techniques

Techniques for validation of software modules which simulate spacecraft onboard systems are discussed. An overview of the simulation software hierarchy for a shuttle mission simulator is provided. A set of guidelines for the identification of subsystem/module performance parameters and critical performance parameters are presented. Various sources of reference data to serve as standards of performance for simulation validation are identified. Environment, crew station, vehicle configuration, and vehicle dynamics simulation software are briefly discussed from the point of view of their interfaces with subsystem simulation modules. A detailed presentation of results in the area of vehicle subsystems simulation modules is included. A list of references, conclusions and recommendations are also given

Simulation of Pollutant Movement in Groundwater Aquifers

A three-dimensional model describing the two-phase (air-water) fluid flow equations in an integrated saturated-unsaturated porous medium was developed. Also, a three-dimensional convective-dispersion equation describing the movement of a conservative, noninteracting tracer in a nonhomogeneous, anisotropic porous medium was developed.! Finite difference forms of these two equations were derived. The two models were linked by the pore water-velocity term. The computer simulator was developed to handle a variety of boundary conditions, such as, constant pressure, constant head, a no-flow boundary, a constant flux, and a time-dependent flux based on rainfall rate. The two-phase fluid flow equations were solved using van implicit scheme to solve for water or air pressures and an explicit scheme to solve for water and air saturations. The tensorial nature of the dispersion coefficient in a Cartesian coordinate system was recognized and the method of characteristics with a numerical tensor transformation was used to solve the convective-dispersion equations. The numerical simulator was tested on problems for which analytical solutions, numerical solutions, and experimental data-are available. The two-phase infiltration model yielded excellent results upon comparison with analytical solutions, numerical simulations, and experimental data. The inclusion of air as a second phase in infiltration problems led to interesting results. The infiltration rate decreased rapidly to a value well below the saturated hydraulic conductivity. As the compressed air was released, the infiltration rate increased for a short period of time, then decreased slightly and remained below the saturated hydraulic conductivity until the end of simulation. This is in contrast to one-phase flow problems in which the saturated hydraulic conductivity is considered to be the lower bound of infiltration rate. The longitudinal and lateral concentration distributions obtained with and without tensor transformation in a homogeneous, isotropic medium and a uniform flow field were compared with known analytical solutions. Excellent agreement was obtained between the numerical solution with tensor transformation and the analytical solution. The solution without the tensor transformation resulted in a steeper concentration distribution than the analytical solution. A typical two-dimensional drainage problem in agriculture was solved in a nonhomogeneous, integrated saturated-unsaturated medium using the total simulator of fluid flow and convective-dispersion equations. A variety of outputs, such as an equipotential map or a moving points' concentration map showing isochlors were obtained at selected time steps. The limitations of the assumptions of a homogeneous and isotropic medium are illustrated by the accumulation of moving points at a transition from a higher to lower permeability. A field-size problem describing the migration of septic-tank wastes around the perimeter of a lake was also considered and solved using the total simulator. This study was an initial thrust at developing a total numerical simulator for miscible displacement in the entire flow domain of saturated and unsaturated regions. The simulator can be applied to environmental problems concerning groundwater contamination from waste disposal sites, provided the values of the input parameters, such as the field dispersivities, are known under field conditions. The uniqueness of the model developed in this study are (1) infiltration was treated as a two-phase (air-water) process, (2) the complete subsurface regime was considered as a unified whole because the flow in the saturated region was integrated with that in the unsaturated region, (3) the model allows consideration of nonhomogeneous porous media and a combination of a variety of realistic boundary conditions, and (4) the tensorial nature of the dispersion coefficients was recognized

Single Location Doublet Well to Reduce Salt-Water Encroachment: Phase I-Numerical Simulation

C. E. Jacob received patents in 1965 for a single location well doublet that would produce fresh water overlying salt-water without upconing of the heavier salt-water and pollution of the fresh water zone. No known evaluation of the concept or development of design criteria has been accomplished. In this study, a finite difference radial flow model was developed to determine groundwater velocities and salt concentration as a function of time and space. This model was verified and is available for evaluating design criteria for Jacob's single location well doublet. Initial runs with the model indicate that the concept has potential, particularly in aquifers with clay lenses in the salt-water zone. Additional runs with the model will be needed to fully establish the design criteria necessary for Jacob's single location well doublet

Solid Waste Management for Cattle Feedlots.

4 p

Ionizing Radiation Environment on the International Space Station: Performance vs. Expectations for Avionics and Material

The role of structural shielding mass in the design, verification, and in-flight performance of International Space Station (ISS), in both the natural and induced orbital ionizing radiation (IR) environments, is reported. Detailed consideration of the effects of both the natural and induced ionizing radiation environment during ISS design, development, and flight operations has produced a safe, efficient manned space platform that is largely immune to deleterious effects of the LEO ionizing radiation environment. The assumption of a small shielding mass for purposes of design and verification has been shown to be a valid worst-case approximation approach to design for reliability, though predicted dependences of single event effect (SEE) effects on latitude, longitude, SEP events, and spacecraft structural shielding mass are not observed. The Figure of Merit (FOM) method over predicts the rate for median shielding masses of about 10g/cm(exp 2) by only a factor of 3, while the Scott Effective Flux Approach (SEFA) method overestimated by about one order of magnitude as expected. The Integral Rectangular Parallelepiped (IRPP), SEFA, and FOM methods for estimating on-orbit (Single Event Upsets) SEU rates all utilize some version of the CREME-96 treatment of energetic particle interaction with structural shielding, which has been shown to underestimate the production of secondary particles in heavily shielded manned spacecraft. The need for more work directed to development of a practical understanding of secondary particle production in massive structural shielding for SEE design and verification is indicated. In contrast, total dose estimates using CAD based shielding mass distributions functions and the Shieldose Code provided a reasonable accurate estimate of accumulated dose in Grays internal to the ISS pressurized elements, albeit as a result of using worst-on-worst case assumptions (500 km altitude x 2) that compensate for ignoring both GCR and secondary particle production in massive structural shielding

The Ionizing Radiation Environment on the International Space Station: Performance vs. Expectations for Avionics and Materials

The role of structural shielding mass in the design, verification, and in-flight performance of International Space Station (ISS), in both the natural and induced orbital ionizing radiation (IR) environments, is reported

Heat Transport in Groundwater Systems--Finite Element Model

Solar energy is a promising alternate energy source for space heating. A method of economic long term solar energy storage is needed. Researchers have proposed storing solar energy by injecting hot water heated using solar collectors into groundwater aquifers for long term energy storage. Analytical solutions are available that predict water temperatures as hot water is injected into a groundwater aquifer, but little field and laboratory data are available to verify these models. The objectives of this study were to construct a laboratory model to simulate hot water injection into a confined aquifer, to use data from the model to verify analytical solutions modeling this process, and to evaluate the effects of physical properties and design parameters on thermal recovery efficiency. Initial studies of hot water injection into underground reservoirs were done by the petroleum industry while studying secondary and tertiary oil recovery methods. These studies involved small laboratory models. Advances in computer technology made it possible to model these systems numerically. Many assumptions must be made to predict temperature distributions and thermal efficiencies using analytical models which are not required in numerical solutions. To simulate hot water injection into a confined aquifer, a laboratory model (a 1.8288 m deep, 0.2 radian sector tank, that was 7.01 m in the radial direction) was constructed. There were 39 temperature and 15 fluid pressure measuring locations through the model. Water was supplied to the model at a constant temperature and flow rate. The flow layer was composed of a fine grained Texblast blasting sand. Four runs were made. During the initial run, no heat transfer took place and the hydraulic conductivity was measured. Three runs were made where the heat transfer was monitored. Water level data from the heat transfer runs showed that as the temperature of the aquifer increased, the hydraulic conductivity increased. Temperature data indicated that the three radii closest to the well bore reached thermal equilibrium. The equilibrium temperature decreased as radius increased. From Run 1 to Run 2, the equilibrium temperature increased at each radius because a larger flow rate was used. A vertical thermal gradient existed in the flow layer with the less dense warm water floating out over the cooler more dense water initially in the model. During the pumping cycle, the temperatures gradually decreased. The temperature of the water as it was pumped out of the model was measured and the energy recovered was computed using the initial temperature as a reference. Various other temperatures were used as a base reference to calculate recovery efficiency. There were heat losses out the sides of the model. The assumption of angular symmetry made in all analytical solutions was therefore not met. For this reason, the analytical solutions showed adequate, but not great, agreement with the experimental temperature distributions. Using the analytical solutions, the effects of changing system design parameters were evaluated. Increasing thermal conductivity in the flow layer caused the temperature distribution to spread out but had no effect on thermal efficiency. Increasing the thermal conductivity in the confining layers caused the temperature profile to not move as far from the well, and decreased thermal efficiency. Injection rates are only indirectly related to thermal efficiency. The physical parameter having the greatest effect on thermal efficiency was the flow layer thickness. As thickness increased, thermal efficiency increased