• 한국자동차공학회논문집
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• 제12권2호
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• pp.123-130
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• 2004

The automobile suspension system is composed of parts that affect performances of a vehicle such as ride quality, handling characteristics, straight performance and steering effort, etc. Moreover, by using the finite element analysis the cost for the initial design step can be decreased. In the design of a suspension system, usually system vibration and structural rigidity must be considered simultaneously to satisfy dynamic and static requirements simultaneously. In this paper, we consider the weight reduction and the increase of the first eigen-frequency of a suspension part, the upper control arm, especially using topology optimization and size optimization. Firstly, we obtain the initial design to maximize the first eigen-frequency using topology optimization. Then, we apply the multi-objective parameter optimization method to satisfy both the weight reduction and the increase of the first eigen-frequency. The design variables are varying during the optimization process for the multi-objective. Therefore, we can obtain the deterministic values of the design variables not only to satisfy the terms of variation limits but also to optimize the two design objectives at the same time. Finally, we have executed reliability based optimal design on the upper control arm using the Monte-Carlo method with importance sampling method for the optimal design result with 98％ reliability.

• 한국화재소방학회논문지
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• 제18권4호
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• pp.35-41
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• 2004

스프링클러 헤드의 살수 특성은 화재의 초기 진화 성능을 결정짓는 매우 중요한 요소이며, 이는 헤드노즐의 형상에 크게 좌우된다. 본 연구에서는 국내 시장점유율이 가장 높은 4개 제조사의 헤드 제품군에 대하여 방수계수 값과 방향성 살수 분포 특성을 규명하였다. 방수계수는 모두 기준 값을 상회하였지만, 헤드 종류별로 동일한 설계 값을 가짐에도 불구하고 큰 차이를 보이는 것으로 나타나 제품 간 품질차이가 큰 것으로 나타났다. 다만, 방수계수는 압력변화에 관계없이 비교적 일정하게 나타났다. 방향별 살수 분포 특성은 일부 헤드 샘플의 경우 매우 심각한 편향 분포를 나타냄으로써 성능개선 연구가 시급한 것으로 판단되었다

• 한국자동차공학회논문집
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• 제22권2호
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• pp.107-114
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• 2014

This paper applies a compensated low pass filter (LPF) to current measurements for permanent magnet synchronous motor (PMSM) drives. The noise limits the bandwidth of current controllers and has more adverse influences on control performances under the light load condition because of the low signal-to-noise ratio. In order to eliminate the noise sensitivity, this paper proposes a digital LPF with a compensator of gain attenuation and phase delay which are unacceptable in current information for PMSM drives. Characteristics of the proposed LPF are analyzed in comparison with the general LPFs. The compensated LPF is basically designed by the orthogonal property of the measured currents in the ${\alpha}{\beta}$ stationary reference frame. In addition, an implementation issue of the proposed method is discussed. Experimental results using the proposed method show improvements of the current control performance from two perspectives, rapid step responses and reductions of harmonic distortion.

• 한국산업보건학회지
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• 제9권2호
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• pp.1-18
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• 1999

The purpose of this study was to compare performances of two analytical methods, the OSHA 42 and the NIOSH 5522, of quantifying total isocyanates in air. These methods were compared in terms of accuracy and precision and the detection limits using four(4) spiked samples in each of four(4) concentration levels which ranged from 0.25 to 2.0 times of the ACGIH TLV-TWA. In addition, two methods were used to as sess airborne concentrations of total isocyanates at the following processes including autobody spray painting, furniture spray painting, polyurethane foaming, urethane adhesion, UV coating, and pigment mixing. The results of this study showed that the NIOSH 5522 method was better than the OSHA 42 method in terms of accuracy, precis ion, and detection limit for quantifying airborne total isocyanates. It was also clear that the NIOSH method was capable of detecting not only monomeric but also non-monomeric isocyanates. The results of air concentrations of total isocyanates among processes studied indicate that some processes may exceed the recommended level of isocyanates. In addition, to evaluate toxicological effects of total isocyanates, it is recommended to consider additive effects of isocyanates present in mixtures.

• 한국항공우주학회지
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• 제40권5호
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• pp.431-438
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• 2012

고기동 무인항공기용 터보제트엔진의 고성능 운용을 위한 비선형 제어기를 설계하였다. 제트엔진의 비선형특성을 제어기 설계에 반영하기 위해 당해엔진의 동적해석코드를 개발하였고 이를 이용한 선형모델로부터 선형해석의 한계성을 검증함으로써 비선형 제어기 설계의 당위성을 보였다. PI형 퍼지제어기를 일반 미분제어기와 결합하여 효율적인 퍼지제어기를 설계하였으며, 일반 PID제어기와 비교하여 압축기서지 및 연소정지영역, 터빈온도의 제한 등 안전운전 범위 내 운전을 보장하면서도 월등한 제어성능을 보임으로써 설계된 퍼지제어기의 유용성을 입증하였다.

• 산업경영시스템학회지
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• 제21권47호
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• pp.57-68
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• 1998

Work environments have been changed with the advent of new technologies, such as computer technology. However, human cognitive limits can't pace up with the change of work environment. Designing human-computer system requires knowledge and evaluation of the human cognitive processes which control information flow workload. Futhermore, under limited reaction time and/or urgent situation, human operator may the work stress, work error and resultant deleterious work environment. This paper evaluate the visual factors of major information processing factors(information density, amount of information, operational speed of speed)on operator performance of supervisory control under urgent(limited reaction time)environments which require deleterious work condition. To describe the work performance int the urgent work situations with time stress and dynamic event occurrence, a new concept of information density was introduced. For a series of experiments performed for this study, three independent variables(information amount, system proceeding speed, information density) were evaluated using five dependent variables. The result of statistical analyses indicate that the amount of information affected on all of five dependent measure. Number of failure and number of secondary task score were influenced by both amount of information and operational speed of system. However reaction time of secondary task were affected by both amount of information and information density. As a result, the deleterious factors for the performances seemed to be a scanning time to supervise each control panel. Consequently, a new display panel was suggest to reduce operator work load for scanning task showing better operator performance.

• Journal of Information Processing Systems
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• 제6권4호
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• pp.553-562
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• 2010

The core services in cloud computing environment are SaaS (Software as a Service), Paas (Platform as a Service) and IaaS (Infrastructure as a Service). Among these three core services server virtualization belongs to IaaS and is a service technology to reduce the server maintenance expenses. Normally, the primary purpose of sever virtualization is building and maintaining a new well functioning server rather than using several existing servers, and in improving the various system performances. Often times this presents an issue in that there might be a need to increase expenses in order to build a new server. This study intends to use grid service architecture for a form of server virtualization which utilizes the existing servers rather than introducing a new server. More specifically, the proposed system is to enhance system performance and to reduce the corresponding expenses, by adopting a scheduling algorithm among the distributed servers and the constituents for grid computing thereby supporting the server virtualization service. Furthermore, the proposed server virtualization system will minimize power management by adopting the sleep severs, the subsidized servers and the grid infrastructure. The power maintenance expenses for the sleep servers will be lowered by utilizing the ACPI (Advanced Configuration & Power Interface) standards with the purpose of overcoming the limits of server performance.

• 품질경영학회지
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• 제49권4호
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• pp.539-550
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• 2021

Purpose: The purpose of this study is to propose a multivariate CUSUM control chart that can detect the out-of-control state fast while monitoring the cross- and auto- correlated multivariate time series data. Methods: We first build models to estimate the observation data and calculate the corresponding residuals. After then, a multivariate CUSUM chart is applied to monitor the residuals instead of the original raw observation data. Vector Autoregression and Artificial Neural Net are selected for the modelling, and Separated-MCUSUM chart is selected for the monitoring. The suggested methods are tested under a number of experimental settings and the performances are compared with those of other existing methods. Results: We find that Artificial Neural Net is more appropriate than Vector Autoregression for the modelling and show the combination of Separated-MCUSUM with Artificial Neural Net outperforms the other alternatives considered in this paper. Conclusion: The suggested chart has many advantages. It can monitor the complicated multivariate data with cross- and auto- correlation, and detects the out-of-control state fast. Unlike other CUSUM charts finding their control limits by trial and error simulation, the suggested chart saves lots of time and effort by approximating its control limit mathematically. We expect that the suggested chart performs not only effectively but also efficiently for monitoring the process with complicated correlations and frequently-changed parameters.

• 통합자연과학논문집
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• 제14권3호
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• pp.123-129
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• 2021

This research examines the effect of positively skewed population distribution on the two sample t-test through simulation. For simulation work, two independent samples were selected from the same chi-square distributions with 3, 5, 10, 15, 20, 30 degrees of freedom and sample sizes 3, 5, 10, 15, 20, 30, respectively. Chi-square distribution is largely skewed to the right at small degrees of freedom and getting symmetric as the degrees of freedom increase. Simulation results show that the sampled populations are distributed positively skewed like chi-square distribution with small degrees of freedom, the F-test for the equality of variances shows poor performances even at the relatively large degrees of freedom and sample sizes like 30 for both, and so it is recommended to avoid using F-test. When two population variances are equal, the skewness of population distribution does not affect on the t-test in terms of the confidence level. However even though for the highly positively skewed distribution and small sample sizes like three or five the t-test achieved the nominal confidence level, the error limits are very large at small sample size. Therefore, if the sampled population is expected to be highly skewed to the right, it will be recommended to use relatively large sample size, at least 20.

• Journal of Power Electronics
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• 제19권6호
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• pp.1527-1535
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• 2019

Because of the shortcomings of the PID controllers and traditional drive systems of permanent magnet synchronous motors (PMSMs), a PMSM passivity-based control (PBC) drive system based on a quasi-Z source matrix converter (QZMC) is proposed in this paper. The traditional matrix converter is a buck converter with a maximum voltage transmission ratio of only 0.866, which limits the performance of the driven motor. Therefore, in this paper a quasi-Z source circuit is added to the input side of the two-stage matrix converter (TSMC) and its working principle has also been verified. In addition, the controller of the speed loop and current loop in the conventional vector control of a PMSM is a PID controller. The PID controller has the problem since its parameters are difficult to adjust and its anti-interference capability is limited. As a result, a port controlled dissipative Hamiltonian model (PCHD) of a PMSM is established. Thereafter a passivity-based controller based on the interconnection and damping assignment (IDA) of a QZMC-PMSM is designed, and the stability of the equilibrium point is theoretically verified. Simulation and experimental results show that the designed PBC control system of a PMSM based on a QZMC can make the PMSM run stably at the rated speed. In addition, the system has strong robustness, as well as good dynamic and static performances.