DynDE : a differential evolution for dynamic optimization problems

This paper presents an approach of using Differential Evolution (DE) to solve dynamic optimization problems. Careful setting of parameters is necessary for DE algorithms to successfully solve optimization problems. This paper describes DynDE, a multi-population DE algorithm developed specifically to solve dynamic optimization problems that doesn't need any parameter control strategy for the F or CR parameters. Experimental evidence has been gathered to show that this new algorithm is capable of efficiently solving the moving peaks benchmark

Permeability correction factor for fractures with permeable walls

Enhanced Geothermal Systems (EGS) are based on the premise that heat can be extracted from hot dry rocks located at significant depths by circulating fluid through fracture networks in the system. Heated fluid is recovered through production wells and the energy is extracted in a heat exchange chamber. There is much published research on flow through fractures, and many models have been developed to describe an effective permeability of a fracture or a fracture network. In these cases however, the walls of the fracture were modelled as being impermeable. In this paper, we have extended our previous work on fractures with permeable walls, and we introduce a correction factor to the equation that governs fracture permeability. The solution shows that the effective fracture permeability for fractures with permeable walls depends not only on the height of the channel, but also on the wall permeability and the wall Reynolds number of the fluid. We show that our solution reduces to the established solution when the fracture walls become impermeable. We also extend the discussion to cover the effective permeability of a system of fractures with permeable walls.R. Mohais, C. Xu, P. A. Dowd, and M. Han

On the effect of permeable magmatic foam on heat transfer in channelized lava flow

Rosemarie Mohais, Balswaroop Bhat

Heat transfer of permeable discs rotating in a magnetic field

Print OnlyAn electrically conducting Newtonian fluid is squeezed between two parallel infinite axisymmetric discs placed in an orthogonal magnetic field. Both discs are permeable. The upper disc is allowed to rotate in its own plane while moving freely along the z-axis. The lower disc is fixed with respect to the z-axis, but is allowed to rotate within its own plane. This paper addresses two cases, the first where each disc is set at a constant uniform temperature, the temperature of the upper disc being higher than the temperature of the lower disc. Using a similarity solation for small Reynolds numbers, analytical and numerical solutions are derived through which the effects of the permeability on the temperature and heat transfer profiles of the fluid film are studied. In the first case, the heat transfer profile is affected by the disc permeability up to the limiting where the discs rotate at the same speed. The temperature profile however is unaffected. In the second case considered, the lower disc is subjected to a heat flux whilst keeping the upper disc at a uniform constant temperature. In the second case, analytical and numerical solutions show that although the temperature and heat transfer profiles are influenced by the temperature ratio of the disc, they however remain unaffected by disc rotation and disc permeability.Rosemarie Mohais and Balswaroop Bhat

Earthquake classifying neural networks trained with random dynamic neighborhood PSOs

This paper investigates the use of Random Dynamic Neighborhoods in Particle Swarm Optimization (PSO) for the purpose of training fixed-architecture neural networks to classify a real-world data set of seismological data. Instead of the ring or fully-connected neighborhoods that are typically used with PSOs, or even more complex graph structures, this work uses directed graphs that are randomly generated using size and uniform out-degree as parameters. Furthermore, the graphs are subjected to dynamism during the course of a run, thereby allowing for varying information exchange patterns. Neighborhood re-structuring is applied with a linearly decreasing probability at each iteration. Several experimental configurations are tested on a training portion of the data set, and are ranked according to their abilities to generalize over the entire set. Comparisons are performed with standard PSOs as well as several static non-random neighborhoods.Arvind S. Mohais, Rosemarie Mohais, Christopher Ward and Christian Posthof

Fluid flow through branched channels in a fracture plane in an enhanced geothermal system

Fluid flow in Enhanced Geothermal Systems (EGS) occurs primarily through fractures which are embedded in an almost impermeable granite rock matrix. Experimental and numerical studies have shown that flow in fractures exhibits channeling effects; this means that flow occurs along preferred pathways, most likely the paths of least resistance. There has been evidence to date of dendritic and star-like patterns in granite and as a result, authors have used fractal theory in order to address flow phenomena in these patterns. The application of Bejan’s Constructal theory to this problem however has never been attempted. We base our model on dendritic patterns of flow paths in heterogeneous rock fractures. Flow enters into a main channel which bifurcates into daughter channels of unique dimensions of length and height. We study these parameters for consecutive channels in the flow path and show that for minimization of resistance to flow within a plane using area and volume constraints for a T-shaped channel, a simple relationship holds for the ratios of lengths and heights which will enable maximum flow for this configuration.R. Mohais, C. Xu, P. A. Dowdhttp://www.asmeconferences.org/congress2012

Temperature and heat transfer profiles of a fluid film squeezed between two permeable isothermal discs rotating within a magnetic field

We consider the case of an electrically conducting fluid squeezed between two permeable, parallel discs placed within a magnetic field. Each disc is maintained at a distinct isothermal temperature and is allowed to rotate independently. The upper disc is then set in motion towards the lower one. Using a similarity solution, analytical and numerical solutions are derived from which the effects of various flow parameters on the temperature and heat transfer profiles are studied. The Hartmann number has an effect on the temperature profiles when the discs are allowed to rotate in the same direction, but the effects are negligible during rotation in the opposite direction. The Prandtl number also affects the temperature and heat transfer profiles for small values of the Squeeze Reynolds number. The effect of permeability on the heat transfer profile varies depending on the speed of rotation of the discs relative to each other.B. Bhatt and R. Mohai

Comparing predicted and observed ground motions from subduction earthquakes in the Lesser Antilles

This brief article presents a quantitative analysis of the ability of eight published empirical ground-motion prediction equations (GMPEs) for subduction earthquakes (interface and intraslab) to estimate observed earthquake ground motions on the islands of the Lesser Antilles (specifically Guadeloupe, Martinique, Trinidad, and Dominica). In total, over 300 records from 22 earthquakes from various seismic networks are used within the analysis. It is found that most of the GMPEs tested perform poorly, which is mainly due to a larger variability in the observed ground motions than predicted by the GMPEs, although two recent GMPEs derived using Japanese strong-motion data provide reasonably good predictions. Analyzing separately the interface and intraslab events does not significant modify the results. Therefore, it is concluded that seismic hazard assessments for this region should use a variety of GMPEs in order to capture this large epistemic uncertainty in earthquake ground-motion prediction for the Lesser Antilles.