Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993pasj...45..377o&link_type=abstract
Publications of the Astronomical Society of Japan, v.45, p.377-392.
Astronomy and Astrophysics
Astronomy
Hydrodynamics, Image Processing, Instruments, Numerical Methods
Scientific paper
Based on the concept of DREAM (Disk REsource Array Machine), we have developed a special-purpose computer for computational fluid dynamics, i.e., the first model of DREAM, DREAM-1. In computer simulations of fluid dynamics, the number of grid points determines both the resolution and accuracy. On conventional computers, the number of grid points is limited by the size of the main memory. The essence of the DREAM concept is to use magnetic disk units as the main memory instead of silicon chips. Thus, we are able to use a main memory that is 100-times larger than that of silicon chips for the same cost. DREAM solves two difficulties of using magnetic disk units as the main memory. First, the data-transfer speed of a disk unit is slower than that of the silicon memory chips. We solve this difficulty by accessing many disk units in parallel and using a small cache. Second is the long access time of the disk unit. In finite-difference calculations, we access the data only in long vectors. The access time therefore becomes negligible. DREAM-1 has one vector processing unit (VPU) and one hard-disk unit. The peak speed of VPU is 12 Mflops. The capacity and the data-transfer rate of the hard-disk unit are 400 Mbyte and 2 Mbyte s(-1) , respectively. We implemented one- and two-dimensional fluid dynamics codes on DREAM-1. The sustained computing speed was 4 Mflops for 1-D and 2.7 Mflops for 2-D. The speed of 4 Mflops is the naked VPU speed while the slow down to 2.7 Mflops of the 2-D simulations is due mainly to the overhead of disk access. We plan to increase the peak speed of the VPU to 20 Mflops and to build 4 units. These units are connected in a one-dimensional ring network. This parallel DREAM system will have a peak speed of 80 Mflops and will be able to perform a (300)(3) 3-D fluid calculation in 4--12 d. We also discuss the potential ability of DREAM: for example, the DREAM system can solve an I/O neck of such observational instruments as a CCD-camera or a VLBI.
Chikada Yoshihiro
Ebisuzaki Toshikazu
Hachisu Izumi
Makino Junichiro
Ohno Yousuke
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