scholarly journals A Review of Grooved Dynamic Gas Bearings

2019 ◽  
Vol 72 (1) ◽  
Author(s):  
Lili Gu ◽  
Eliott Guenat ◽  
Jürg Schiffmann
Keyword(s):  
High Speed ◽  
State Of The Art ◽  
Integrated Design ◽  
The State ◽  
Small Scale ◽  
Second Phase ◽  
Foil Bearings ◽  
Turbulence Effects ◽  
Physical Phenomena ◽  
Gas Bearing

Abstract This paper offers an extensive review of publications dealing with the modeling, the design, and the experimental investigation of grooved dynamic gas-lubricated bearings. Recent years have witnessed a rise in small-scale and high-speed turbomachinery applications. Besides the well-known gas foil bearings, grooved bearings offer attractive advantages, which unveil their potential in particular at small scale due to the structural simplicity as well as satisfying predictability. This paper starts with a general background of the application of gas-lubricated bearings and introduces and compares the different gas bearing topologies. Further, the state-of-the-art modeling of grooved gas-lubricated bearings is introduced, systematically assessing the advantages and inconveniences of two major approaches, i.e., the narrow groove theory (NGT) and direct discretization method. Since the NGT method is an elegant and efficient approach to model the complex effects of periodic grooves, a critical section is dedicated to the NGT. In a second phase, different models to include additional physical phenomena such as real gas lubrication, rarefaction, or turbulence effects are reviewed. The paper concludes with a critical assessment of the state-of-the-art and indicates potential fields of research that would allow to shed more light into the understanding of these bearings, as well as with some thoughts on the integrated design methodologies of gas bearing supported rotors.

Tribological Characterization of Machining at Very Small Contact Areas

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Michael R. Lovell ◽  
P. Cohen ◽  
Pradeep L. Menezes ◽  
R. Shankar
Keyword(s):  
High Speed ◽  
Friction Mechanisms ◽  
High Speed Steel ◽  
Small Scale ◽  
Machining Processes ◽  
Macroscopic Theory ◽  
Contact Areas ◽  
Tribological Characterization ◽  
Physical Phenomena

When machining miniaturized components, the contact conditions between the tool and the workpiece exhibit very small contact areas that are on the order of 10−5 mm2. Under these conditions, extremely high contact stresses are generated, and it is not clear whether macroscopic theories for the chip formation, cutting forces, and friction mechanisms are applicable. For this reason, the present investigation has focused on creating a basic understanding of the frictional behavior in very small scale machining processes so that evaluations of standard macroscale models could be performed. Specialized machining experiments were conducted on 70/30 brass materials using high-speed steel tools over a range of speeds, feeds, depths of cut, and tool rake angles. At each operating condition studied, the friction coefficient and the shear factor τk were obtained. Based on the experimental results, it was determined that the standard macroscopic theory for analyzing detailed friction mechanisms was insufficient in very small scale machining processes. An approach that utilized the shear factor, in contrast, was found to be better for decoupling the physical phenomena involved. Utilizing the shear factor as an analysis parameter, the parameters that significantly influence the friction in microscale machining processes were ascertained and discussed.

Accelerating Mobile-Cloud Computing

2015 ◽  
pp. 1933-1955
Author(s):  
Tolga Soyata ◽  
He Ba ◽  
Wendi Heinzelman ◽  
Minseok Kwon ◽  
Jiye Shi
Keyword(s):  
Cloud Computing ◽  
Mobile Devices ◽  
High Speed ◽  
Mobile Cloud Computing ◽  
Response Times ◽  
State Of The Art ◽  
The State ◽  
Mobile Cloud ◽  
Computational Resources ◽  
Traditional Approaches

With the recent advances in cloud computing and the capabilities of mobile devices, the state-of-the-art of mobile computing is at an inflection point, where compute-intensive applications can now run on today's mobile devices with limited computational capabilities. This is achieved by using the communications capabilities of mobile devices to establish high-speed connections to vast computational resources located in the cloud. While the execution scheme based on this mobile-cloud collaboration opens the door to many applications that can tolerate response times on the order of seconds and minutes, it proves to be an inadequate platform for running applications demanding real-time response within a fraction of a second. In this chapter, the authors describe the state-of-the-art in mobile-cloud computing as well as the challenges faced by traditional approaches in terms of their latency and energy efficiency. They also introduce the use of cloudlets as an approach for extending the utility of mobile-cloud computing by providing compute and storage resources accessible at the edge of the network, both for end processing of applications as well as for managing the distribution of applications to other distributed compute resources.

scholarly journals Lossless Image Compression Techniques: A State-of-the-Art Survey

Symmetry ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 1274 ◽  
Author(s):  
Md. Atiqur Rahman ◽  
Mohamed Hamada
Keyword(s):  
Image Compression ◽  
High Speed ◽  
Communication Theory ◽  
State Of The Art ◽  
Signal To Noise Ratio ◽  
Daily Basis ◽  
The State ◽  
Huge Amount ◽  
Lossless Image Compression ◽  
Art Techniques

Modern daily life activities result in a huge amount of data, which creates a big challenge for storing and communicating them. As an example, hospitals produce a huge amount of data on a daily basis, which makes a big challenge to store it in a limited storage or to communicate them through the restricted bandwidth over the Internet. Therefore, there is an increasing demand for more research in data compression and communication theory to deal with such challenges. Such research responds to the requirements of data transmission at high speed over networks. In this paper, we focus on deep analysis of the most common techniques in image compression. We present a detailed analysis of run-length, entropy and dictionary based lossless image compression algorithms with a common numeric example for a clear comparison. Following that, the state-of-the-art techniques are discussed based on some bench-marked images. Finally, we use standard metrics such as average code length (ACL), compression ratio (CR), pick signal-to-noise ratio (PSNR), efficiency, encoding time (ET) and decoding time (DT) in order to measure the performance of the state-of-the-art techniques.

High-Speed and Area-Efficient Reconfigurable Multiplexer Bank for RAM-Based Finite State Machine Implementations

2015 ◽  
Vol 24 (07) ◽  
pp. 1550101 ◽  
Author(s):  
Raouf Senhadji-Navaro ◽  
Ignacio Garcia-Vargas
Keyword(s):  
High Speed ◽  
Finite State Machine ◽  
State Of The Art ◽  
Behavioral Model ◽  
State Machine ◽  
The State ◽  
Experimental Results ◽  
State Machines ◽  
Finite State ◽  
Area Efficient

This work is focused on the problem of designing efficient reconfigurable multiplexer banks for RAM-based implementations of reconfigurable state machines. We propose a new architecture (called combination-based reconfigurable multiplexer bank, CRMUX) that use multiplexers simpler than that of the state-of-the-art architecture (called variation-based reconfigurable multiplexer bank, VRMUX). The performance (in terms of speed, area and reconfiguration cost) of both architectures is compared. Experimental results from MCNC finite state machine (FSM) benchmarks show that CRMUX is faster and more area-efficient than VRMUX. The reconfiguration cost of both multiplexer banks is studied using a behavioral model of a reconfigurable state machine. The results show that the reconfiguration cost of CRMUX is lower than that of VRMUX in most cases.

Flashing of Pressurized Slurry in Metallurgical Processing: A Review of the State of the Art, Operational Experiences, and Recommendations for Future Research

2014 ◽  
Author(s):  
Adam Blackmore ◽  
Umesh Shah ◽  
Murray Pearson ◽  
Atanasis Plikas ◽  
Bonnie Sim
Keyword(s):  
High Pressure ◽  
State Of The Art ◽  
The State ◽  
Future Research ◽  
Operational Experience ◽  
Equipment Failure ◽  
Hydrometallurgical Processing ◽  
Metallurgical Processing ◽  
Physical Phenomena ◽  
Shed Light

Flashing of high temperature, pressurized slurry within hydrometallurgical processing circuits is a commonly encountered multiphase flow scenario, which can lead to catastrophic equipment failure and serious operational problems if not designed correctly. The current work aims to shed light on the state of the art modelling and experimentation, important physical phenomena, and recent operational experience surrounding this problem. In addition, recommendations will be provided for future modelling and experimental efforts in order to direct research into avenues that provide valuable information for engineers designing piping and vessels where the flashing of high pressure slurry occurs.

A preliminary study of the load bearing capacity of a new foil thrust gas bearing

2010 ◽  
Vol 225 (3) ◽  
pp. 673-678 ◽  
Author(s):  
R G Chen ◽  
Q Zhou ◽  
Y Liu ◽  
Y Hou
Keyword(s):  
High Speed ◽  
Thrust Bearing ◽  
Load Capacity ◽  
Rapid Development ◽  
Experimental Investigations ◽  
Simple Type ◽  
Preliminary Measurement ◽  
Foil Bearings ◽  
Compliant Structure ◽  
Gas Bearing

With the rapid development of high-speed, oil-free turbomachinery, more and more attention is concentrated on compliant aerodynamic foil bearings. However, the common corrugated bump foil forming the compliant structure is so complicated that manufacturing it is time-consuming and troublesome. In this article, a simple type of aerodynamic foil thrust gas bearing with an elastic hemispherical convex dot support configuration is first proposed. Then experimental investigations on stability and its load capacity characteristic for this foil thrust bearing were conducted on a multi-functional thrust bearing test rig. The preliminary measurement and analysis are presented through the wave and spectrum of axial displacement response in the time and frequency domain. It is demonstrated that the proposed bearing can operate well and has good stability in tests, and experimental results show that the axial load can reach 25 N when the rotational speed is about 114 200 r/min.

Development of a High Speed Gas Bearing Test Rig to Measure Rotordynamic Force Coefficients

2011 ◽  
Vol 133 (10) ◽  
Author(s):  
J. Jeffrey Moore ◽  
Andrew Lerche ◽  
Timothy Allison ◽  
David L. Ransom ◽  
Daniel Lubell
Keyword(s):  
High Speed ◽  
High Amplitude ◽  
Fluid Film ◽  
Test Rig ◽  
Force Coefficient ◽  
Gas Bearings ◽  
Foil Bearings ◽  
Fluid Film Bearings ◽  
Wide Range ◽  
Gas Bearing

The use of gas bearings has increased over the past several decades to include microturbines, air cycle machines, and hermetically sealed compressors and turbines. Gas bearings have many advantages over traditional bearings, such as rolling element or oil lubricated fluid film bearings, including longer life, ability to use the process fluid, no contamination of the process with lubricants, accommodating high shaft speeds, and operation over a wide range of temperatures. Unlike fluid film bearings that utilize oil, gas lubricated bearings generate very little damping from the gas itself. Therefore, successful bearing designs such as foil bearings utilize damping features on the bearing to improve the damping generated. Similar to oil bearings, gas bearing designers strive to develop gas bearings with good rotordynamic stability. Gas bearings are challenging to design, requiring a fully coupled thermo-elastic, hydrodynamic analysis including complex nonlinear mechanisms such as Coulomb friction. There is a surprisingly low amount of rotordynamic force coefficient measurement in the literature despite the need to verify the model predictions and the stability of the bearing. This paper describes the development and testing of a 60,000 rpm gas bearing test rig and presents measured stiffness and damping coefficients for a 57 mm foil type bearing. The design of the rig overcomes many challenges in making this measurement by developing a patented, high-frequency, high-amplitude shaker system, resulting in excitation over most of the subsynchronous range.

scholarly journals LDPC Decoder of High Speed Multi-Rate DVB-S2 Based on FPGA

2019 ◽  
Vol 37 (2) ◽  
pp. 299-307 ◽  
Author(s):  
TianJiao Xie ◽  
Bo Li ◽  
Mao Yang ◽  
Zhongjiang Yan
Keyword(s):  
High Speed ◽  
State Of The Art ◽  
Ldpc Codes ◽  
The State ◽  
Elementary Transformation ◽  
Parity Check ◽  
Ldpc Decoder ◽  
Art Works ◽  
Decoder Architecture ◽  
Lower Triangular

A multi-rate LDPC decoder architecture for DVB-S2 codes based on FPGA is proposed. Through elementary transformation on the parity check matrices of DVB-S2 LDPC codes, a new matrix whose left is a QC sub-matrix and right is Transformation of Staircase lower triangular (TST) sub-matrix is obtained. The QC and TST are designed separately, therefore the successful experience of the most popular Quasi-Cyclic (QC) LDPC decoder architecture can be drawn on. While for TST sub-matrix, the variable nodes updating only need to be considered and the check nodes updating is realized compatibility with QC sub-matrix. Based on the proposed architectures, a multi-rate LDPC decoder implemented on Xilinx XC7VX485T FPGA can achieve the maximum decoding throughput of 2.5 Gbit/s at the 20 iterations when the operating frequency is 250 MHz, which demonstrates the highest throughput compared with the state-of-the-art works.

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