MAESTRO, CASTRO, and SEDONA -- Petascale Codes for Astrophysical Applications

Performing high-resolution, high-fidelity, three-dimensional simulations of Type Ia supernovae (SNe Ia) requires not only algorithms that accurately represent the correct physics, but also codes that effectively harness the resources of the most powerful supercomputers. We are developing a suite of codes that provide the capability to perform end-to-end simulations of SNe Ia, from the early convective phase leading up to ignition to the explosion phase in which deflagration/detonation waves explode the star to the computation of the light curves resulting from the explosion. In this paper we discuss these codes with an emphasis on the techniques needed to scale them to petascale architectures. We also demonstrate our ability to map data from a low Mach number formulation to a compressible solver.Comment: submitted to the Proceedings of the SciDAC 2010 meetin

MAESTRO: An Adaptive Low Mach Number Hydrodynamics Algorithm for Stellar Flows

Many astrophysical phenomena are highly subsonic, requiring specialized numerical methods suitable for long-time integration. In a series of earlier papers we described the development of MAESTRO, a low Mach number stellar hydrodynamics code that can be used to simulate long-time, low-speed flows that would be prohibitively expensive to model using traditional compressible codes. MAESTRO is based on an equation set derived using low Mach number asymptotics; this equation set does not explicitly track acoustic waves and thus allows a significant increase in the time step. MAESTRO is suitable for two- and three-dimensional local atmospheric flows as well as three-dimensional full-star flows. Here, we continue the development of MAESTRO by incorporating adaptive mesh refinement (AMR). The primary difference between MAESTRO and other structured grid AMR approaches for incompressible and low Mach number flows is the presence of the time-dependent base state, whose evolution is coupled to the evolution of the full solution. We also describe how to incorporate the expansion of the base state for full-star flows, which involves a novel mapping technique between the one-dimensional base state and the Cartesian grid, as well as a number of overall improvements to the algorithm. We examine the efficiency and accuracy of our adaptive code, and demonstrate that it is suitable for further study of our initial scientific application, the convective phase of Type Ia supernovae.Comment: Accepted to Astrophysical Journal Suppliment (http://iop.org). 56 pages, 15 figures

Corrosion resistance of new biocompatible composite materials for biomedical applications, obtained by spark plasma sintering

Inżynieria biomateriałów oraz technologie związane z medycyną należą do jednej z najbardziej dynamicznie rozwijających się dziedzin naukowych w ostatnich latach. Tytan i jego stopy wraz ze stopami na osnowie żelaza, kobaltu oraz stopami z pamięcią kształtu tworzą grupę biomateriałów metalicznych. Tytan i jego stopy w porównaniu z innymi materiałami metalicznymi charakteryzuje się dobrą biozgodnością, niskim w porównaniu z innymi biomateriałami metalicznymi, ale porównując do metali w ogóle do np. aluminium ma niższy moduł Younga, wysoką wytrzymałością względną i niskim ciężarem właściwym. Istotnym elementem tego materiału jest odporność korozyjna, której analiza i badania są przedmiotem niniejszej pracy. W pracy przedstawiono analizę odporności korozyjnej nowych stopów tytanu otrzymanych metodą metalurgii proszków, konsolidowanych technologią SPS z różnymi parametrami procesu. Technologia SPS jest procesem konsolidacji materiałów z proszków w określonej temperaturze i pod określonym ciśnieniem (prasowanie), które powodują odkształcenie plastyczne ziaren scalanego proszku. Tak przygotowane próbki porównano z materiałem komercyjnym – lity stop Ti6Al4V ELI w postaci pręta. Przedmiotem analizy były krzywe potencjodynamiczne wykonane na podstawie danych uzyskanych z urządzenia SP-150 marki Bio-Logic Science Instruments z przystawką niskoprądową w komorze pomiarowej o pojemności 1 litra. Porównano charakterystyki korozyjne nowych stopów tytanowych i litego stopu handlowego. Wyznaczono także porowatość, gęstość oraz twardość. Stwierdzono przesuniecie potencjału korozyjnego badanych spieków w stronę wyż- szych potencjałów względem stopu handlowego. Zaobserwowano korelację pomiędzy właściwościami korozyjnymi, a właściwościami mechanicznymi materiałów uzyskanych dla różnych parametrów spiekania.Biomaterials engineering and technologies related to medicine belong to one of the most dynamically developing scientific fields in recent years. Titanium and its alloys with iron-based cobalt alloys, as well as alloys with shape memory, form the group of metallic biomaterials. Titanium and its alloys compared with other metallic materials is characterized by good biocompatibility, a low Young’s modulus in comparison with other metallic biomaterials as well as compared to metals in general for example aluminum, high strength and low relative specific gravity. An important element of this material is corrosion resistance, whose analysis and testing are the subject of this work. The paper presents an analysis of the corrosion resistance of new titanium alloys obtained by powder metallurgy, consolidated using SPS technology with different process parameters. SPS technology is the process of consolidating material from powders at a predetermined temperature and under a certain pressure (compaction) that causes plastic deformation of the grains of the merged powders. The thus prepared samples were compared with a commercial material - Ti6Al4V ELI solid alloy in the form of a rod. The subject of analysis was potentiodynamic curves made on the basis of data obtained from the Bio-Logic Science Instruments SP-150 device with a low current attachment in a measuring chamber with a capacity of 1 liter. We compared the corrosion characteristics of the new titanium alloys and the commercial solid alloy. The porosity, density and hardness were also determined. A shift in the corrosion potential of the investigated sinters to higher potentials in relation to the commercial alloy was found. A correlation between the corrosive properties and the mechanical properties of the materials obtained employing the various sintering parameters was observed

Influence on the type of materials of the friction pair on the wear mechanism of spinal intervertebral disk implants

The paper discusses the purpose of a spinal disc implant. Indicated a significant effect on the material pair of friction on the frictional resistance. Tribological test results of spinal disc implants performed on the simulator. Discussed the mechanism of wear of the implants. Drew attention to the destructive role of wear products

Tribological study of implanted artificial spinal disc

W artykule omówiono metody leczenia dysfunkcji kręgosłupa za pomocą implantowania sztucznych krążków międzykręgowych. Wskazano na materiałowe i konstrukcyjne wymagania, które powinien spełniać implant. Podano wyniki badań tribologicznych prowadzonych na symulatorze kręgosłupa zaprojektowanym i wykonanym w Instytucie Obróbki Plastycznej w Poznaniu.The article discusses treatments for spinal dysfunction by the implantation of artificial intervertebral discs focusing on the material and structural requirements to be fulfilled by the implant. The final results of tribological tests were conducted on the spine simulator designed and built at the Institute for Metal Forming Institute in Poznan

Tribological investigations of materials used for spine disc implants

Ailments linked to back pain is a serious problem not only medical but also social. Not only elder people but also people in working age suffers from problems related to spine pain. The most common disorders of the spine are pain syndromes of the lumbar part where center of gravity of the human body is located and w here major forces are acting on the vertebrae and intervertebral discs. The market currently offers a variety of spinal implant solutions (FIG 1). In the Metal Forming Institute there is realized research Project entitled Investigations and spine implants functionality evaluation in material and tribological aspects. In the frame of the Project it was designed and manufactured special simulator adapted for intervetebrals pine discs implants investigations. Simulator scheme is presented on FIG. 2. Main goals of the realized Project are: • Investigation of friction-mechanical processes during implant usage. • Evaluation of wear intensity of various types of intervertebral discs and investigations of appearing wear products. • Selection of optimal material and surface machining method providing minimal wear of intervertebral disc elements wear. For experiments there was implant designed by K. Skalski and J. Skoworodko selected [1], which consists of 3 elements: upper liner, lower liner and nucleus pulpous (FIG. 3). Actually there are 3 types of friction couple materials tested: 316L steel - polyethylene UHMWPE – 316L steel, titanium alloy Ti6Al4V – polyethylene UHMWPE and nitrided Ti6Al4V titanium alloy – polyethylene UHMWPE. In fluence of number of cycles on friction coefficient, surface roughness and poliethylene linner thickness change illustrates FIG. 4. As it results from performed investigations, too high hardness level of metal elements (upper and lower clasps) provides to accelerated wear of the polyethylene part. New challenge is application of “metal-metal” friction couple

Assessment and analysis of impregnated tribological systems working at elevated temperatures

Nacisk na redukcję oporów tarcia i w efekcie zużycia tribologicznego w maszynach, staje się coraz bardziej istotny dla poprawy ich wydajności, trwałości i niezawodności. Występujące zjawisko tarcia wywołuje głównie negatywne skutki, bowiem jego bezpośrednim następstwem jest zużycie tribologiczne prowadzące do stopniowej utraty niezawodności. W niniejszej pracy przedstawiono wyniki badań tribologicznych par trących pracujących w temperaturach 300 i 500°C. Przedmiot badań stanowiły tuleje łożyskowe o gęstości 6,7 g/cm3 poddane procesowi impregnacji ciśnieniowej submikrometrycznymi cząstkami smarów stałych MoS2 i WS2. Badania tarciowo-zużyciowe przeprowadzono na testerze TWT-500N pracującym w układzie ring-on-shaf. Analiza uzyskanych wyników badań pozwoliła stwierdzić, iż zastosowanie smaru stałego MoS2 w temperaturze 300°C i WS2 w temperaturze 500°C pozwala na obniżenie wartości współczynnika tarcia do wartości poniżej 0,08 i 0,05.With emphasis on the reduction of frictional resistance and tribological wear of machine component parts, it becomes more and more important, in order to improve their efficiency, durability and reliability. Friction causes mostly negative effects, because the immediate consequence is tribological wear, leading to a gradual loss of reliability. This paper presents the results of tribological friction pairs working at temperatures of 300 and 500°C. The objects of the study were bearing sleeves with a density of 6.7 g/cm3 that had previously undergone a process of pressure impregnation by submicrometer MoS2 and WS2 solid lubricant particles. Friction and wear tests were conducted with the use of a ring-on-shaft TWT-500N testing machine. Analysis of the obtained results led to the conclusion that the application of MoS2 at 300°C and WS2 at 500°C reduces friction coefficient, respectively, to less than 0.08 and 0.05