Optimizing Lossy Compression Rate-Distortion from Automatic Online Selection between SZ and ZFP

With ever-increasing volumes of scientific data produced by HPC applications, significantly reducing data size is critical because of limited capacity of storage space and potential bottlenecks on I/O or networks in writing/reading or transferring data. SZ and ZFP are the two leading lossy compressors available to compress scientific data sets. However, their performance is not consistent across different data sets and across different fields of some data sets: for some fields SZ provides better compression performance, while other fields are better compressed with ZFP. This situation raises the need for an automatic online (during compression) selection between SZ and ZFP, with a minimal overhead. In this paper, the automatic selection optimizes the rate-distortion, an important statistical quality metric based on the signal-to-noise ratio. To optimize for rate-distortion, we investigate the principles of SZ and ZFP. We then propose an efficient online, low-overhead selection algorithm that predicts the compression quality accurately for two compressors in early processing stages and selects the best-fit compressor for each data field. We implement the selection algorithm into an open-source library, and we evaluate the effectiveness of our proposed solution against plain SZ and ZFP in a parallel environment with 1,024 cores. Evaluation results on three data sets representing about 100 fields show that our selection algorithm improves the compression ratio up to 70% with the same level of data distortion because of very accurate selection (around 99%) of the best-fit compressor, with little overhead (less than 7% in the experiments).Comment: 14 pages, 9 figures, first revisio

Technology evaluation of heating, ventilation, and air conditioning for MIUS application

Potential ways of providing heating, ventilation, and air conditioning for a building complex serviced by a modular integrated utility system (MIUS) are examined. Literature surveys were conducted to investigate both conventional and unusual systems to serve this purpose. The advantages and disadvantages of the systems most compatible with MIUS are discussed

Space station gas compressor technology study program, phase 1

The objectives were to identify the space station waste gases and their characteristics, and to investigate compressor and dryer types, as well as transport and storage requirements with tradeoffs leading to a preliminary system definition

Modeling A Reciprocating Compressor Using A Two-Way Coupled Fluid And Solid Solver With Automatic Grid Generation And Adaptive Mesh Refinement

Computational fluid dynamics has been increasingly used in the design and analysis of reciprocating compressors over the last several years. One of the major challenges in the use of such tools is the creation of the numerical grid on which the modeled equations are solved. Since these compressors typically consist of many interconnected and moving parts, manual creation of the grid can be labor-intensive. Furthermore, it is necessary that the choice of grid yields a sufficiently resolved solution, so that the numerical error is significantly less than the modeling error. In this work, a small displacement refrigeration compressor is modeled using a numerical grid created with an automatic meshing approach. The grid is then automatically adapted to the flow based on the local flow field variables at each time step. This cut-cell based grid matches the supplied fluid volume exactly and permits general motion of all bounding surfaces. An explicit two-way coupled approach is used to account for the fluid-structure interaction between the deforming reed valves and the flow. The fluid is solved using a finite-volume approach, whereas the solid is solved using a finite-element model. The model is validated in comparison to measured mass flow rate, pressure, temperature, and valve lift for two different operation conditions and two different working fluids, namely R-404a and R-449a. The numerical accuracy of the calculations is demonstrated through an automated grid convergence study, and the effect of the grid and time-step resolution on the pressure pulsations and valve lift is shown. While computations on a relatively coarse grid yield power, mass flow rate, and pressure oscillation frequency comparable to measurements, a finer mesh is required inside the cylinder and in the discharge muffler to predict adequately the amplitude of the pressure fluctuations

Impact reactivity of materials at very high oxygen pressure

The requirements for impact testing of materials in an oxygen atmosphere at pressures from 82.7 MPa (12,000 psi) to 172 MPa (25,000 psi) were evaluated. The impact tester system was evaluated for potential pressure increases from 69 MPa (10,000 psi) to 82.7 MPa (12,000 psi). The low pressure oxygen and nitrogen systems, the impact tower, the impact test cell, and the high pressure oxygen system were evaluated individually. Although the structural integrity of the impact test cell and the compressor were sufficient for operation at 82.7 MPa (12,000 psi), studies revealed possible material incompatibility at that pressure and above. It was recommended that if a component should be replaced for 82.7 MPa (12,000 psi) operation the replacement should meet the final objectives of 172 MPa (25,000 psi). Recommended changes in the system include; use of Monel 400 for pressures above 82.7 MPa (12,000 psi), use of bellows to replace the seal in the impact tester, use of a sapphire window attached to a fiber optic for event sensing, and use of a three diaphragm compressor

Online compression of cache-filtered address traces

International audienceTrace-driven simulation is potentially much faster than cycle-accurate simulation. However, one drawback is the large amount of storage that may be necessary to store traces. Trace compression techniques are useful for decreasing the storage space requirement. But the compression ratio of existing trace compressors is limited because they implement lossless compression. We propose two new methods for compressing cachefiltered address traces. The first method, bytesort, is a lossless compression method that achieves high compression ratios on cache-filtered address traces. The second method is a lossy one, based on the concept of phase. We have combined these two methods in a trace compressor called ATC. Our experimental results show that ATC gives high compression ratio while keeping the memory-locality characteristics of the original trace

Aeronautical Engineering: A special bibliography with indexes, supplement 54

This bibliography lists 316 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1975

GAS TURBINE PERFORMANCE DETERIORATION AND COMPRESSOR WASHING

TutorialThe privatization of utilities, intense competition in the petrochemical and gas distribution industries, coupled with increasing fuel costs, have created a strong incentive for gas turbine operators to minimize and control performance deterioration. The most significant deterioration problem faced by gas turbine operators is compressor fouling which is the focus of this paper. The effect of compressor fouling is a drop in airflow, pressure ratio and compressor efficiency, resulting in a rematching of the gas turbine and compressor and a drop in power output and thermal efficiency. This paper provides a comprehensive practical treatment of the causes, effects and control of fouling. Gas turbine inlet filtration, fouling mechanisms and compressor washing are also covered in detail. The major emphasis will be on the causes, effects detection and control of compressor fouling. The complexities and challenges of on-line washing of large output new gas turbines will also be covered. The treatment also applies to axial air compressors used in the hydrocarbon processing industry