• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.5
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• pp.709-717
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• 2000

Cyclic variability has long been recognized as limiting the range of operating conditions of spark ignition engines, in particular, under lean and highly diluted operation conditions. The cyclic combustion variations can be characterized by the pressure parameters, combustion parameters, and flame front parameters. The coefficient of variation in indicated mean effective pressure ($COV_{IMEP}$) defines the cyclic variability in indicated work per cycle, and it has been found that vehicle driveability problems usually result when $COV_{IMEP}$ exceeds about 10%. For analysis of the cyclic variability in SI engines at idling, the results show that cyclic variability by the $COV_{IMEP}$ or the coefficient of variation in maximum pressure can be explained and may be consequently reduced by the help of the optimum spark timings.

• Journal of The Korean Society of Agricultural Engineers
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• v.60 no.2
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• pp.95-101
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• 2018

The objective of this study is to evaluate the liquefaction cyclic shear stress ratio considering the soil uncertainty. In this study, the probabilistic ground response analysis and the cyclic shear stress ratio analysis for the liquefaction potential evaluation are performed considering the soil variability. The statistical properties of input ground parameters were analyzed to investigate the parameters affecting the seismic response analysis. The Probabilistic analysis was carried out by Monte Carlo Simulation method. The ground response analysis was performed considering the soil variability and the probability distribution characteristics of the ground acceleration. The probability distribution of the peak ground acceleration by seismic characteristics was presented. The differences of liquefaction shear stress ratio results according to soil variability were compared and analyzed. The maximum acceleration of the ground by the deterministic method was analyzed to be overestimation of the ground amplification phenomenon. Also, the shear stress ratio was overestimated.

• Journal of Mechanical Science and Technology
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• v.15 no.1
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• pp.81-87
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• 2001

Cyclic variability limits the range of operating conditions of spark ignition engines, especially under lean and highly diluted operation conditions. The cyclic combustion variations can be characterized by pressure parameters, combustion related parameters, and flame-front related parameters. The coefficient of variation (COV) in indicated mean effective pressure (IMEP) defines the cyclic variability in indicated work per cycle.

• Journal of the korean Society of Automotive Engineers
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• v.14 no.3
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• pp.90-101
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• 1992

An experimental study was carried out to investigate the characteristics of cyclic variability of combustion in a single cylinder spark ignition engine. Cylinder pressure of 240 consecutive cycles were measured for various engine operating conditions. From these data, a thermody-n amic analysis was performed for the typical cases in order to identify the cause and effect re -lation of the cyclic variation. In determining the number of cycles required for estimating the coefficient of variation of IMEP and so on, the oprating conditions must be cosidered to fit the objective of the analysis. It is thought that the variation in early flame stage is amplified through the flame propagation and results in the phase change between pressure and volume, which can be the major reason of cyclic variation of IMEP in case of lean operation.

• Journal of Energy Engineering
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• v.22 no.2
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• pp.197-204
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• 2013

A cyclic variability has long been recognized as limiting the range of operating conditions of spark ignition engines, in particular, under idling conditions. The coefficient of variation (COV) in indicated mean effective pressure (IMEP) defines the cyclic variability in indicated work per cycle, and it has been found that vehicle drivability problems usually result. For analysis of the cyclic variations in spark ignition engines at idling, the results show that cyclic variability by the COV, COV of IMEP, the lowest normalized value (LNV), and burn angles can help to design the spark ignition engine.

• Journal of Biosystems Engineering
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• v.33 no.5
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• pp.355-361
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• 2008

As agricultural machinery has become larger and tillage practices have changed in recent decades, compaction as a result of wheel traffic and tillage has caused increasing concern. If strategies to manage compaction, such as deep tillage, could be applied only where needed, economic and environmental benefits would result. For such site-specific compaction management to occur, compacted areas within fields must be efficiently sensed and mapped. We previously developed an on-the-go soil strength profile sensor (SSPS) for this purpose. The SSPS measures within-field variability in soil strength at five soil depths up to 50 cm. Determining the variability structure of SSPS data is needed for site-specific field management since the variability structure determines the required intensity of data collection and is related to the delineation of compaction management zones. In this paper, soil bin data were analyzed by a spectral analysis technique to determine the variability structure of the SSPS data, and to investigate causes and implications of this variability. In the soil bin, we observed a repeating pattern due to soil fracture with an approximate 12- to 19-cm period, especially at the 10-cm depth, possibly due to cyclic development of soil fracture on this interval. These findings will facilitate interpretation of soil strength data and enhance application of the SSPS.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.2
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• pp.221-229
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• 1996

The engine speed fluctuation at idle operation mainly comes from cyclic variation of combustion in SI engine. In the present study, engineering model that is representing the cyclic variation of combustion was proposed for the sub-model of the engine cycle simulation. From the observed behaviors of the mass burn rates, probability density functions for the parameters of Wiebe function were defined. The mass burn rate of each cycle is obtained by Monte Cralo perturbation method with the probability function. The simulation results shows that trends of cylinder pressure variation and imep distribution follow up with those of experimental results at idle condition.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1249-1252
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• 2003

To analyse the cyclic variations in a test engine, the burn parameters are determined on a cycle-to-cycle basis through the analysis of the engine pressure data. Combustion analysis based on cylinder-pressure provides a mechanism through which a combustion researcher can understand the combustion process. The objective of this paper is to identify the most significant sources of cycle-to-cycle combustion variability in a spark ignition engine at idle. The burn rate analysis program was used and the burn parameters were used to determine the variations in the input parameter. In this study, the author investigated the relationship of indicated mean effective pressure, coefficient of variation of indicated mean effective pressure and burn angles, and lowest normalized value in a spark ignition engine for the cyclic variations.

• International Journal of Ocean System Engineering
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• v.2 no.3
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• pp.160-169
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• 2012

Flux Cored Arc Welding (FCAW) is a common practice to join thick plates such as the structural members of large scale offshore structures and very large container ships. The objective of this study was to investigate the mechanical properties and variability of the fatigue crack initiation life in the flux cored arc welded API 2W Gr.50 steel joints typically applied to offshore structures with a focus on the effect of the materials in fatigue crack growth life from the notch root of a compact tension specimen. Offshore structural steel (API 2W Gr.50) plates (60-mm thick) were used to fabricate multi-path flux core arc welded butt welded joints to clearly consider fatigue fractures at the weld zone from the notch. Fatigue tests were performed under a constant amplitude cyclic loading of R = 0.4. The mean fatigue crack initiation life of the HAZ specimen was the highest among the base metal (BM), weld metal (WM), and heat affected zone (HAZ). In addition, the coefficient of variation was the highest in the WMl specimen. The variability of the short fatigue crack growth rates from the notch tips in the WM and HAZ specimens was higher than in BM.

• Restorative Dentistry and Endodontics
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• v.45 no.2
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• pp.25.1-25.12
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• 2020

Objectives: This systematic review evaluated the influence of autoclave sterilization procedures on the cyclic fatigue resistance of heat-treated nickel-titanium (NiTi) instruments. Materials and Methods: A systematic search without restrictions was conducted in the following electronic databases: PubMed, Scopus, Web of Science, ScienceDirect, Cochrane, and Open Grey. The hand search was also performed in the main endodontic journals. The eligible studies were submitted to the methodological assessment and data extraction. Results: From 203 abstracts, a total of 10 articles matched the eligible criteria. After reading the full articles, 2 were excluded because of the absence of the heat-treated instruments in the experimental design and 3 due to the lack of a control group using heat-treated instruments without autoclave sterilization. From the 5 included studies, 1 presented a low risk of bias, 3 presented moderate and 1 high risk. It was observed heterogeneous findings in the included studies, with autoclave sterilization cycles increasing, decreasing or not affecting the cyclic fatigue life of heat-treated NiTi instruments. However, the retrieved studies evaluating the cyclic fatigue resistance of endodontic instruments presented different protocols and assessing outcomes, this variability makes the findings less comparable within and also between groups and preclude the establishment of an unbiased scientific evidence base. Conclusions: Considering the little scientific evidence and considerable risk of bias, it is still possible to conclude that autoclave sterilization procedures appear to influence the cyclic fatigue resistance of heat-treated NiTi instruments.