Application of Meshless Methods for Thermal Analysis

Many numerical and analytical schemes exist for solving heat transfer problems. The meshless method is a particularly attractive method that is receiving attention in the engineering and scientific modeling communities. The meshless method is simple, accurate, and requires no polygonalisation. In this study, we focus on the application of meshless methods using radial basis functions (RBFs) — which are simple to implement — for thermal problems. Radial basis functions are the natural generalization of univariate polynomial splines to a multivariate setting that work for arbitrary geometry with high dimensions. RBF functions depend only on the distance from some center point. Using distance functions, RBFs can be easily implemented to model heat transfer in arbitrary dimension or symmetry

A multidimensional finite element method for CFD

A finite element method is used to solve the equations of motion for 2- and 3-D fluid flow. The time-dependent equations are solved explicitly using quadrilateral (2-D) and hexahedral (3-D) elements, mass lumping, and reduced integration. A Petrov-Galerkin technique is applied to the advection terms. The method requires a minimum of computational storage, executes quickly, and is scalable for execution on computer systems ranging from PCs to supercomputers

Turbulent structure in the wake of sphere

The study of turbulent wakes is considered necessary to understand the droplet behavior associated with the collision coalescence phenomena in atmospheric clouds. The Vertical Atmospheric Wind Tunnel enables experiments dealing with this droplet behavior to be analyzed. The experiments conducted in the UMR Vertical Atmospheric Wind Tunnel consist of two parts: one is the investigation of the flow field characteristics in the test section of the wind tunnel; the other is the measurement of the turbulent structure in the wake of a sphere. The test section is rectangular in design and has a cross-sectional area of 36 square inches (6 inches X 6 inches). Mean velocity profiles show the flow to be uniform but increasing in magnitude throughout the downstream portion of the test section. Boundary layer thickness becomes noticeable during the latter portion of the test section. Turbulence intensity, measured in the longitudinal direction of the test section at 10 different downstream positions by a DISA 55D01 hot-wire anemometer, show the background turbulence generated by the wind tunnel to be very small. Mean velocity profiles in the wake of a sphere indicate rapid wake dissipation and show wake interaction with the wall boundary layer of the test section. Axisymmetric turbulence intensities are measured using an X-probe and two DISA 55D01 CTA units in both the Near and Far wakes of the sphere. Reynolds shear stresses are likewise measured and the wake development analyzed through the turbulent energy equation --Abstract, pages ii-iii

Numerical simulation of heat, mass, and momentum transfer in an atmospheric boundary layer

Considerable interest has developed in recent years to understand transport phenomena in thermally stratified boundary layers. More complete knowledge in this field is needed to improve the prediction of the diffusion of air pollutants in the lower atmosphere as well as in forecasting air-water circulation for weather conditions. The atmospheric boundary layer is modeled using the equations of continuity, momentum, energy, and concentration. Closure of this set of partial differential equations is hindered by the turbulence terms. Using turbulence kinetic energy, the system of equations is closed by internally determining the exchange coefficients of heat, mass, and momentum along with other atmospheric parameters. This approach makes it possible for the history of turbulent motion to be taken into account. Verification of this model is made by systematically comparing the numerical results with available wind tunnel data for neutral, stable, and unstable conditions. Application of the model is made to study the formation of advection fogs occurring over cold sea surfaces. However, the predicted results of liquid water and water vapor contents have yet to be verified with actual data obtained from field measurements --Abstract, page ii

Application of an HP-Adaptive Finite Element Method for Thermal Flow Problems

Numerical results are presented for a set of convective thermal flow problems using an hp-adaptive finite element technique. The hp-adaptive model is based on mesh refinement and spectral order incensement to produce enhanced accuracy while attempting to minimize computational requirements. An a-posteriori error estimator based on the L2 norm is employed to guide the adaptation procedure. Example test cases consisting of natural convection in a differentially heated enclosure, flow with forced convection heat transfer over a backward facing step and natural convection within an enclosed partition are presented. Numerical results are compared with published data in the literature

An H-Adaptive Finite-Element Technique for Constructing 3D Wind Fields

An h-adaptive, mass-consistent finite-element model (FEM) has been developed for constructing 3D wind fields over irregular terrain utilizing sparse meteorological tower data. The element size in the computational domain is dynamically controlled by an a posteriori error estimator based on the L2 norm. In the h-adaptive FEM algorithm, large element sizes are typically associated with smooth flow regions and small errors; small element sizes are attributed to fast-changing flow regions and large errors. The adaptive procedure employed in this model uses mesh refinement–unrefinement to satisfy error criteria. Results are presented for wind fields using sparse data obtained from two regions within Nevada: 1) the Nevada Test Site, located approximately 65 mi (1 mi ~ 1.6 km) northwest of Las Vegas, and 2) the central region of Nevada, about 100 mi southeast of Reno

Phase I: Design and Analysis of a Process for Melt Casting Metallic Fuel Pins Incorporating Volatile Actinides

The proposed research would be conducted in 3 phases. Each of the phases would be carried out over a one-year period. Phase I includes model development, analysis, and the selection of a new casting furnace design. The work discussed in this report was completed as Phase I. Phase II of the program will lead to more modeling and validation to evaluate the proposed furnace concept. Phase III would be a joint effort between UNLV and Argonne National Laboratory (ANL) to demonstrate the acceptable use of the new furnace in a simulated remote environment. The Phase III work would include the design and modification/fabrication of a small test furnace for remote operation. Some of the casting furnace techniques that will be evaluated include an induction skull melter, continuous casting, and the modification of the present process to operate at higher pressures. The groundwork laid this past year developed a set of modeling tools to assist in the design of a realistic fabrication technique. The primary technical hurdle to overcome in the fabrication of a 21 metallic alloy fuel is that of efficiently including the highly volatile actinide elements (i.e., americium). A comprehensive model for the mass transport has been developed and will be implanted in year two of the project

Development of a Systems Engineering Model of the Chemical Separations Process

Two activities are proposed: the development of a systems engineering model and the refinement of the Argonne code AMUSE (Argonne Model for Universal Solvent Extraction). The detailed systems engineering model will be the start of an integrated approach to the analysis of the materials separations associated with the AAA Program. A second portion of the project will streamline and improve an integral part of the overall systems model, which is the software package AMUSE. AMUSE analyzes the UREX process and other related solvent extraction processes and defines many of the process streams that are integral to the systems engineering model. Combining these two tasks is important in ensuring that calculations made in AMUSE are accurately transferred to the overall systems model. Additional modules will be developed to model pyrochemical process operations not treated by AMUSE. These modules will be refined as experiments are conducted and as more knowledge is gained in process steps. Integrating all aspects of the proposed separations processes will allow for detailed process analyses, trade-off studies or the evaluation of proposed process steps, complete material balances that include all potential waste streams, the impact of changes in feed streams, studies detailing the importance of process control and instrumentation, and the ultimate optimization of the process

Ascent and Decompression of Viscous Vesicular Magma in a Volcanic Conduit

During eruption, lava domes and flows may become unstable and generate dangerous explosions. Fossil lava-filled eruption conduits and ancient lava flows are often characterized by complex internal variations of gas content. These observations indicate a need for accurate predictions of the distribution of gas content and bubble pressure in an eruption conduit. Bubbly magma behaves as a compressible viscous liquid involving three different pressures: those of the gas and magma phases, and that of the exterior. To solve for these three different pressures, one must account for expansion in all directions and hence for both horizontal and vertical velocity components. We present a new two-dimensional finite element numerical code to solve for the flow of bubbly magma. Even with small dissolved water concentrations, gas overpressures may reach values larger than 1 MPa at a volcanic vent. For constant viscosity the magnitude of gas overpressure does not depend on magma viscosity and increases with the conduit radius and magma chamber pressure. In the conduit and at the vent, there are large horizontal variations of gas pressure and hence of exsolved water content. Such variations depend on decompression rate and are sensitive to the exit boundary conditions for the flow. For zero horizontal shear stress at the vent, relevant to lava flows spreading horizontally at the surface, the largest gas overpressures, and hence the smallest exsolved gas contents, are achieved at the conduit walls. For zero horizontal velocity at the vent, corresponding to a plug-like eruption through a preexisting lava dome or to spine growth, gas overpressures are largest at the center of the vent. The magnitude of gas overpressure is sensitive to changes of magma viscosity induced by degassing and to shallow expansion conditions in conduits with depth-dependent radii

Assessing wind energy potential for Nevada

This inaugural event is dedicated to showcasing the renewable/sustainable energy projects of UNLV faculty, staff, students, and collaborators, as well as other external projects underway statewide and nationally. The development and utilization of new technologies to protect the environment, achieve energy independence, and strengthen the economy will be explored. Speakers and poster-session presenters will provide further insight to many ongoing projects and innovative research ideas. Organized by UNLV’s Office of Strategic Energy Programs, the event offers participants the opportunity to learn about energy projects and will encourage networking and collaboration. This symposium is intended for researchers, educators, students, policy makers, public and private-sector energy and environmental professionals, and citizen