• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.8 s.179
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• pp.2074-2082
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• 2000

In this study, to investigate and to predict the crack growth behavior under variable amplitude loading, crack growth tests are conducted on 7075-T6 aluminum alloy. The loading wave forms are generated by normal random number generator. All wave forms have same average and RMS(root mean square) value, but different standard deviation, which is to vary the maximum load in each wave. The modified Forman's equation is used as crack growth equation. Using the retardation coefficient D defined in previous study, the load interaction effect is considered. The variability in crack growth process is described by the random variable Z which was obtained from crack growth tests under constant amplitude loading in previous work. From these, a statistical model is developed. The curves predicted by the proposed model well describe the crack growth behavior under variable amplitude loading and agree with experimental data. In addition, this model well predicts the variability in crack growth process under variable amplitude loading.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.1225-1227
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• 1992

This paper presents a study on the variable structure PI(proportional and integrate) control which is insensible to the variation of parameters or external disturbance for driving DC motor. In the presented variable structure PI control (VSPIC), the sliding mode control was used at the below of 4000 rpm and PI control also used at the above of 4000 rpm with no load. In other way, the PI control was used at the below of 4000 rpm and the sliding mode control at the above of 4000 rpm with some loading, and then the output waveform following the variation of load was measured. intel 8031 microcomputer unit and IBM PC was combined to form the full system and the speed control was performed with it. The experimental result of the fast response to speed was more improve than it was open loop state. For load varing, the sliding mode insensible to external disturbance was applied and the improved response was obtained.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.1
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• pp.47-55
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• 2005

An experimental study has been peformed to develop a scheme for fault detection and diagnosis(FDD) in a vapor compression refrigeration system. This study is to analyze fault effect on the system performance and to find efficient diagnosis rules for easy determination of abnormal system operation. The refrigeration system was operated with a variable speed compressor to modulate cooling capacity. The FDD system was designed to consider transient load conditions. Four major faults were considered, and each fault was detected over wide operating load range by separating the system response to the load change. Rule-based method was used to diagnose and classify the system faults. From the experimental results, COP degradation due to the faults in a variable speed system is severer than that in a constant speed system. The method developed in this study can be used in the fault detection of refrigeration systems with a variable speed compressor.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.1
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• pp.63-69
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• 2015

The primary aim of this paper is to evaluate the probabilistic fatigue crack propagation models using the residual of a random variable and to present the probabilistic model fit for the probabilistic fatigue crack growth behavior in Mg-Al-Zn alloys under maximum load conditions. The models used in this study were prepared by applying a random variable to empirical fatigue crack propagation models such as the Paris-Erdogan model, Walker model, Forman model, and modified Forman model. It was verified that the good models for describing the stochastic variation of the fatigue crack propagation behavior in Mg-Al-Zn alloys under maximum load conditions were the 'probabilistic Paris-Erdogan model' and 'probabilistic Walker model'. The influence of the maximum load conditions on the stochastic variation of fatigue crack growth is also considered.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.2
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• pp.158-165
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• 2012

In this paper, the test bed using three-phase PWM converter connected with single phase inverter in series is set up to configure an active AC electric load. Since the two topologies, three-phase PWM converter and single-phase inverter, can be operated bidirectionally, the system not only re-generates surplus power to grid but also prevents power dissipation. However, the construction of system has a drawback. That is, ripple components two times of inverter operation frequency occur at DC-Link due to cascade connection, it can be cause of three phase unbalance Since the operational characteristic of the active AC electric load, the power frequency entered into the electric load can be varied, and the ripple of DC-Link is changed as well. In this paper, the three-phase PWM converter using a variable notch filter is proposed, and the reduction of three-phase current unbalance is presented. the validity of the proposed PWM converter using a variable notch filter is verified by the simulation and experimental results.

• Proceedings of the KIPE Conference
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• 2007.11a
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• pp.15-17
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• 2007

The variable speed engine generator set is interested for an isolated power system due to reduced fuel consumption and less emission. However, because of sluggish dynamic behavior of the internal combustion engine the power quality would be degraded during the sudden load power surge, where the power required by the load is not available by the engine due to the reduced engine speed. An isolated power system based on variable speed engine with a super-capacitor bank improves dynamic characteristics under sudden load change, and power quality, fuel consumption, and pollutants can be reduced remarkably. Also, it is verified by the computer simulation that the inverter of 3phase-4leg is compatible to the isolated power system with unbalanced load. In this paper, the feasibility of the system has been verified based on a 26kw commercial diesel engine system.

• Journal of the Korean Society for Advanced Composite Structures
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• v.6 no.3
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• pp.77-85
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• 2015

In this paper, we present the result of investigations pertaining to the elastic buckling of simply supported columns with various cross-sectional dimensions but the same length and volume. In the investigations the accuracy of the analysis methods is studied and it was found that the result obtained by the successive approximations technique is the most accurate. In addition, the elastic buckling loads of columns with variable cross-section dimensions are obtained by the theoretical and numerical methods. From the results, it was found that the buckling loads obtained by the numerical methods are close to the buckling loads obtained by the successive approximations technique for the practical standpoints. Moreover, the buckling load of column with convexity in its middle is the highest while the buckling load of the tapered column is the lowest as expected.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.5
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• pp.7-15
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• 2009

This paper introduces a new variable valve actuation mechanism with movable second cam center. Valve lift and open duration can be continuously varied according to engine speed and load conditions. A new method to analyze the kinematic relations between the first and second cam profiles and valve motion are also introduced. Because of rocker motion of the second cam, conventional motion conversion program could not be used in this problem. An example shows continuous variations of valve motion and adequate ramp incorporation throughout all valve lift modes. Valve acceleration profile at the high lift mode is similar to that of conventional valvetrains. Contact geometry analysis of the mechanism gives basic information on the load conditions between the components.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.3
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• pp.218-226
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• 2002

This study was carried out to develop continuously variable-speed transmission(CVT) fur an agricultural tractor. The full-toroidal variator mechanism with flour discs and six rollers was utilized as a device fur changing speed ratio continuously. In system layout design, the sizes of the roller cylinders and the end-load cylinder, which were critical factors for controlling the variator, were designed. The planetary gear unit and six pairs of the gear assemblies were designed to establish the maximum speed of the vehicle at 30 ㎞/hr. In addition, the hydraulic clutch, the silent chain, the hydraulic manifold and the electronic controller were designed. Based on the design, a prototype CVT was developed and tested. Test results show that the CVT developed in this study could successfully provide variable speed of the tractor.

• Tribology and Lubricants
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• v.17 no.6
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• pp.426-434
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• 2001

The hermetic reciprocating compressor driven by the BLDC motor rotating with variable speeds, is modelled and analyzed for dynamic characteristics. The governing equations of piston, connecting rod and crank-shaft of the reciprocating compression mechanism and characteristics of driving torque of the motor are obtained. Dynamic behavior of the crankshaft supported on 2 journal bearings is analyzed considering compression load and eccentric unbalance for the 4 rotating speeds of crankshaft. And. reaction forces generated from oil film in the journal bearings are analyzed under transient condition using Reynolds' equation. To take into account the dynamic characteristics depending on the variable rotating speeds, comparison on the dynamic behavior of crank-shaft is made for the 4 operating modes of the compressor. Results show that the magnitude of crankshaft locioperating on the lower rotating speeds is more larger than the higher ones due to reduction of inertia force of the reciprocating piston.