Diagonally split Runge–Kutta (DSRK) time discretization methods are a class of implicit time-step... more Diagonally split Runge–Kutta (DSRK) time discretization methods are a class of implicit time-stepping schemes which offer both high-order convergence and a form of nonlinear stability known as unconditional contractivity. This combination is not possible within the classes of Runge–Kutta or linear multistep methods and therefore appears promising for the strong stability preserving (SSP) time-stepping community which is generally concerned with computing oscillation-free numerical solutions of PDEs. Using a variety of numerical test problems, we show that although second- and third-order unconditionally contractive DSRK methods do preserve the strong stability property for all time step-sizes, they suffer from order reduction at large step-sizes. Indeed, for time-steps larger than those typically chosen for explicit methods, these DSRK methods behave like first-order implicit methods. This is unfortunate, because it is precisely to allow a large time-step that we choose to use implicit methods. These results suggest that unconditionally contractive DSRK methods are limited in usefulness as they are unable to compete with either the first-order backward Euler method for large step-sizes or with Crank–Nicolson or high-order explicit SSP Runge–Kutta methods for smaller step-sizes. We also present stage order conditions for DSRK methods and show that the observed order reduction is associated with the necessarily low stage order of the unconditionally contractive DSRK methods.
Page 1. On ionospheric pre-storm phenomena Victor U. Chukwuma Department of Physics, Olabisi Onab... more Page 1. On ionospheric pre-storm phenomena Victor U. Chukwuma Department of Physics, Olabisi Onabanjo University, P. O Box 351, Ago-Iwoye, Nigeria Tel : +2348055075270, Email: victorchukwuma@yahoo.com Abstract ...
A numerical model and computational procedure for static recrystallization are developed using a ... more A numerical model and computational procedure for static recrystallization are developed using a phase-field method coupled with crystal-plasticity theory. In this model, first, the microstructure and dislocation density during the deformation process of a polycrystalline metal are simulated using a finite element method based on strain-gradient crystal-plasticity theory. Second, the calculated data are mapped onto the regular grids used in the phase-field simulation. The stored energy is calculated from the dislocation density and is smoothed to avoid computational difficulty. Furthermore, the misorientation required for nucleation criteria is calculated at all grid points. Finally, phase-field simulation of the nucleation and growth of recrystallization is performed using the mapped data. By performing a series of numerical simulations based on the proposed numerical procedure, it has been confirmed that the recrystallization microstructure can be reproduced from the deformation microstructure.
Triathlons (races involving consecutive swimming, bicycling, and running) have become commonplace... more Triathlons (races involving consecutive swimming, bicycling, and running) have become commonplace in the United States. These races may involve from 30 minutes to 36 hours of continuous exercise, usually in warm or hot environments. Little has been published regarding the medical and physiological aspects of these events. This paper represents the first large study to date on the subject, including both an analysis of medical complications at six triathlons as well as a prospective electrolyte study conducted at two of these races. Medical records were kept and examined for all athletes requiring treatment during a typical United States Triathlon Series (USTS) race in 1986 (1,000 starters; finish times, 2 to 4 hours), a typical Ironman Qualifier (IQ) race in 1986 (622 starters; finish times, 4 to 8 hours), and the 1982 through 1985 Hawaii Ironman World Championships (4,583 starters; finish times, 9 to 17 hours). At the USTS race, fewer than 2% (17/1,000) of the starters required aid, at the IQ, approximately 10% (61/622) of the starters were treated, and at the Ironman, an average of 17% (794/4,583) received medical attention. The most common diagnoses at the USTS and IQ were dehydration and heat exhaustion. At the Ironman, dehydration and heat problems were complicated by hyponatremia. Because hyponatremia has been reported as a complication of ultraendurance events, a prospective study was performed on 36 athletes during a USTS race and 64 athletes at the 1984 Ironman race. Prerace and postrace blood samples showed that no athletes were hyponatremic following the shorter USTS race, but 27% (17/64) of the athletes studied were hyponatremic following the Ironman race.(ABSTRACT TRUNCATED AT 250 WORDS)
The paper presents the results of an investigation into the effect of acid immersion on the aging... more The paper presents the results of an investigation into the effect of acid immersion on the aging of room temperature vulcanized (RTV) silicone rubber coatings in inclined plane tests (IPT). Two commercial coatings, RTV-A filled with ATH (aluminum tri-hydrate) and RTV-B filled with silica, are compared before and after acid immersion. Acid aging consists of immersing the samples in 3.9 pH nitric acid at a temperature of 90°C for 2 weeks. The relative comparison between the two samples is based on the development of the fundamental and third harmonic of the leakage current during IPT tests, eroded area, the time to failure and SEM microphotographs. All of these observations show that acid rain damages RTV-A more severely than RTV-B. However virgin ATH filled sample showed a better performance compared to the silica filled material.
Diagonally split Runge–Kutta (DSRK) time discretization methods are a class of implicit time-step... more Diagonally split Runge–Kutta (DSRK) time discretization methods are a class of implicit time-stepping schemes which offer both high-order convergence and a form of nonlinear stability known as unconditional contractivity. This combination is not possible within the classes of Runge–Kutta or linear multistep methods and therefore appears promising for the strong stability preserving (SSP) time-stepping community which is generally concerned with computing oscillation-free numerical solutions of PDEs. Using a variety of numerical test problems, we show that although second- and third-order unconditionally contractive DSRK methods do preserve the strong stability property for all time step-sizes, they suffer from order reduction at large step-sizes. Indeed, for time-steps larger than those typically chosen for explicit methods, these DSRK methods behave like first-order implicit methods. This is unfortunate, because it is precisely to allow a large time-step that we choose to use implicit methods. These results suggest that unconditionally contractive DSRK methods are limited in usefulness as they are unable to compete with either the first-order backward Euler method for large step-sizes or with Crank–Nicolson or high-order explicit SSP Runge–Kutta methods for smaller step-sizes. We also present stage order conditions for DSRK methods and show that the observed order reduction is associated with the necessarily low stage order of the unconditionally contractive DSRK methods.
Page 1. On ionospheric pre-storm phenomena Victor U. Chukwuma Department of Physics, Olabisi Onab... more Page 1. On ionospheric pre-storm phenomena Victor U. Chukwuma Department of Physics, Olabisi Onabanjo University, P. O Box 351, Ago-Iwoye, Nigeria Tel : +2348055075270, Email: victorchukwuma@yahoo.com Abstract ...
A numerical model and computational procedure for static recrystallization are developed using a ... more A numerical model and computational procedure for static recrystallization are developed using a phase-field method coupled with crystal-plasticity theory. In this model, first, the microstructure and dislocation density during the deformation process of a polycrystalline metal are simulated using a finite element method based on strain-gradient crystal-plasticity theory. Second, the calculated data are mapped onto the regular grids used in the phase-field simulation. The stored energy is calculated from the dislocation density and is smoothed to avoid computational difficulty. Furthermore, the misorientation required for nucleation criteria is calculated at all grid points. Finally, phase-field simulation of the nucleation and growth of recrystallization is performed using the mapped data. By performing a series of numerical simulations based on the proposed numerical procedure, it has been confirmed that the recrystallization microstructure can be reproduced from the deformation microstructure.
Triathlons (races involving consecutive swimming, bicycling, and running) have become commonplace... more Triathlons (races involving consecutive swimming, bicycling, and running) have become commonplace in the United States. These races may involve from 30 minutes to 36 hours of continuous exercise, usually in warm or hot environments. Little has been published regarding the medical and physiological aspects of these events. This paper represents the first large study to date on the subject, including both an analysis of medical complications at six triathlons as well as a prospective electrolyte study conducted at two of these races. Medical records were kept and examined for all athletes requiring treatment during a typical United States Triathlon Series (USTS) race in 1986 (1,000 starters; finish times, 2 to 4 hours), a typical Ironman Qualifier (IQ) race in 1986 (622 starters; finish times, 4 to 8 hours), and the 1982 through 1985 Hawaii Ironman World Championships (4,583 starters; finish times, 9 to 17 hours). At the USTS race, fewer than 2% (17/1,000) of the starters required aid, at the IQ, approximately 10% (61/622) of the starters were treated, and at the Ironman, an average of 17% (794/4,583) received medical attention. The most common diagnoses at the USTS and IQ were dehydration and heat exhaustion. At the Ironman, dehydration and heat problems were complicated by hyponatremia. Because hyponatremia has been reported as a complication of ultraendurance events, a prospective study was performed on 36 athletes during a USTS race and 64 athletes at the 1984 Ironman race. Prerace and postrace blood samples showed that no athletes were hyponatremic following the shorter USTS race, but 27% (17/64) of the athletes studied were hyponatremic following the Ironman race.(ABSTRACT TRUNCATED AT 250 WORDS)
The paper presents the results of an investigation into the effect of acid immersion on the aging... more The paper presents the results of an investigation into the effect of acid immersion on the aging of room temperature vulcanized (RTV) silicone rubber coatings in inclined plane tests (IPT). Two commercial coatings, RTV-A filled with ATH (aluminum tri-hydrate) and RTV-B filled with silica, are compared before and after acid immersion. Acid aging consists of immersing the samples in 3.9 pH nitric acid at a temperature of 90°C for 2 weeks. The relative comparison between the two samples is based on the development of the fundamental and third harmonic of the leakage current during IPT tests, eroded area, the time to failure and SEM microphotographs. All of these observations show that acid rain damages RTV-A more severely than RTV-B. However virgin ATH filled sample showed a better performance compared to the silica filled material.
Uploads
Papers by ATH UTS