Computational Fluid Dynamics
Quantum Chromo-dynamics (QCD)
Global Climate Change
A possible layout of the computer cabinets for a 5-teraflops massively parallel computer. Such a machine will be able to perform 5 trillion arithmetic calculations per second. By comparison, the Intel Paragon XP/S 150 at ORNL can perform 150 billion arithmetic calculations per second.
The confluence of ever-accelerating scientific expectations and technical innovation is dramatically extending the limits of computational power. Indeed, limit may be an inappropriate word here. Machines now running exceed a teraflops (1 trillion FLoating point OPerations per Second, or 1 TF), 10-TF machines are being planned, and the path to petaflops (1000 TF) is being defined. So, given the remarkable rate of change in the computing realm, we must talk in terms of current technological capabilities, as well as near-term design objectives with a well-defined time horizon in describing computational capabilities. It is clear, though, that planning for machines in the range of 5 to 10 TF in the 19981999 time frame is an appropriate target; this is the target for which we are aiming.
The Center for Computational Sciences (CCS) at ORNL has been one of the world's leaders in computational power over the last several years. However, contracts in place for systems at DOE Defense Programs (DP) laboratories (Los Alamos National Laboratory and Lawrence Livermore National Laboratory) provide for systems extending to 3 TF, or well beyond the roughly 200 gigaflops (GF, or billion flops) in the CCS. The applications emphasis for these DP machines is assurance of the reliability of the U.S. nuclear stockpile in an era of no weapons testing, which basically defines DOE's Accelerated Strategic Computing Initiative (ASCI).
Computation, modeling, and simulation requirements for the DOE Energy Research (ER) community also extend into the multiple-TF realm. Providing a substantial component of this computational capability and establishing routine TF-level distributed computing are the foci of this ORNL initiative. Given the striking accomplishments of the CCS in bringing its Intel Paragons to very high levels of productivity by
connecting the two largest CCS Paragons over high-speed asynchronous transfer mode (ATM) OC-12 networks to provide a machine with peak performance near 200 GF and
taking the distributed computing lead with Sandia National Laboratories (SNL) by solving huge problems through linking the Paragons at the two sites over ATM networks,
the CCS clearly represents the development environment required to bring a multiple-TF machine to optimal effectiveness for an extensive range of ER applications. This last point is of prime importance because the ER requirements extend across a very wide spectrum.
A striking array of challenges awaits TF-level machines. Meaningful modeling of mechanical behavior becomes possible, including static and dynamic properties of dislocations and dislocation arrays, radiation effects, and complex phenomena such as stress-corrosion cracking. Further, proper modeling of mechanical behavior can lead to structural integrity and an understanding of aging far surpassing current levels. Multiple-component-alloy design studies with the objective of maximizing strength-to-weight ratios will be key to achieving fuel efficiency goals for automobiles. Investigations of the performance of these alloys in simulated harsh environments will lead to alloys providing improved longevity and safety when operating in such environments and will also extend the range of operating conditions for many systems. Modeling of computer processor and memory chips with ever-decreasing feature sizes will require highly sophisticated semiconductor models incorporating accurate thermodynamic capabilities to deal properly with heat generation and dissipation strategies.
A multi-TF system will greatly aid computational chemists in meeting the challenge of accurately describing structure and interactions in nucleic acids (DNA and RNA) and in understanding the interactions between these molecules and proteins. Successes here will have very significant implications for biology and medicine. It is likely that an understanding of the complexities of protein folding can emerge from computational studies with adequate power. We anticipate dramatic advances in characterizing catalytic mechanisms in problems such as the photoinduced transformation in bacteriorhodopson and key electron and proton transfer steps in photosynthesis. Detailed models for catalysis in complex structures such as zeolites will be computationally manageable. Very powerful systems will make it possible to investigate in detail the subtle chemistry that occurs in our atmosphere and in the earth's ozone shield.
Computational Fluid Dynamics
Computational fluid dynamics simulations usually involve flow coupled to processes such as chemical reactions. Frequently there are great disparities in temporal and spatial scales that demand powerful computational resources for simulations of high accuracy. Compressible fluid flow is of fundamental importance in a wide variety of contextswakes and boundary layers of aircraft, missiles, and projectiles in flight; mixing regions of air and combustible material in reactive flows; environmental fluid dynamics of atmospheric storms; and mixing in rivers and estuaries. More accurate models requiring TF computing are needed here as they are for the design of superior spark-ignition and compression-ignition (diesel) engines.
Quantum Chromo-dynamics (QCD)
QCD is widely accepted as the fundamental description of the strong interactions of elementary particle physics. Much of the experimental work carried out at DOE's high-energy and nuclear physics laboratories is aimed at probing this theory; it has seminal implications for understanding the development of our universe. In principle, this theory should allow the calculation of some of the most fundamental quantities in nature. In practice, it has proven extremely difficult to extract many of the predictions of QCD. Currently, the only promising avenue for doing so is through large-scale numerical simulations. A multi-TF system should enable definitive first-principles calculations of the mass spectrum of strongly interacting particles such as neutrons and protons and of their observable physical properties. Another computational target is an understanding of the phase transition from ordinary matter to the suggested quark-gluon plasma state of matter. This state of matter, where particles like protons disintegrate into their quark and gluon constituents, is predicted to occur under conditions of extraordinarily high energy, in other words, extraordinarily high temperatures. The Relativistic Heavy Ion Collider, a powerful accelerator soon to come on line at Brookhaven National Laboratory, will help scientists search for evidence of the quark-gluon plasma; computational modeling will be needed to complement this search.
A multi-TF system would enable highly accurate three-dimensional simulations of earthquakes in specific geographic locales. In addition to providing an expanding database and concomitant extended understanding of these phenomena, the simulations would provide ground motion information to assist architects and engineers in designing buildings capable of withstanding these motions.
The complex nature of subsurface biological, physical, and chemical processes has, in the last decade, prompted extensive development of computer models to simulate and predict the fate of environmentally toxic materials in one of the most valuable resources of this nationgroundwater. The addition of valid bio-physicochemical processes to current models of this highly heterogeneous system necessitates computational systems in the TF range. Such systems will enable the incorporation of scientifically validated subsurface flow and transport processes in multiphase fluids and fractured geological formations and promote the inclusion of phenomena such as in-situ bioremediation and molecular-level geochemical kinetics. Perhaps even more significant are the large-scale water resources management strategies that we would be able to establish given TF-level computing. Risk assessment and decision analysis could be carried out for a time scale sufficiently long to provide scientifically sound and technologically plausible solutions, thereby providing invaluable support for those making environmental and safety decisions where financial realities compel priority setting.
Global Climate Change
Substantial strides have been made in modeling the oceans and the atmosphere. However, additions of land mass details and polar ice together with improved resolution require TF capabilities. Having accurate models is extremely important for the future because the effects of pollution, greenhouse gases, and other atmosphere constituents, if improperly analyzed and interpreted, can lead to technical and political decisions that can have seriously deleterious consequences for the planet.
In all of these application areas, and more that could be included, important problems already identified require computational power in the range of 5 to 10 TF and even more for some areas. Processing power is but one factor in the specification of the requisite balanced system. For a 5-TF system, additional requirements include
Further, the CCS partnership with SNL has shown the way to solving problems of extraordinary size and complexity through linking supercomputers over high-speed networks. To extend this strategy into the multiple-TF regime, an essential expectation in our view, will require networks operating in the range of 10 gigabits/sec, roughly OC-192 requirements.
The extension of computational capabilities into the range described here does require a very high degree of sensitivity to the tenets of scalability. To illustrate the scope of the proposed system, we show a possible layout of the computer cabinets for a 5-TF machine.
Hardware does not a 5-TF computer make. Software challenges abound. Operating systems, I/O software, communications software and protocols, visualization systems, and network interfaces, together with applications software, must all work together with the hardware in solving problems. Indeed, it is here in the software realm that many of the most difficult scalability issues will emerge.
It is obvious that there are major challenges in designing, developing, and ensuring near-optimum performance from a system in the 5-TF range. However, the contributions this system would provide to the ER science/technology programs and to meeting ever-expanding expectations of these programs demand that these challenges be faced. Furthermore, the partnership between ORNL and SNL that has brought distributed computing to unprecedented levels of capability should be encouraged to extend these capabilities into the TF realm. With the Intel Teraflops machine now being assembled at SNL (the design goal is 1.8 TF) and the proposed TF-level machine at ORNL, this extension is assured.Kenneth L. Kliewer, director of the Center for Computational Sciences at ORNL