다산 정약용의 <주역사전>, 기호학으로 읽다

방인 교수의 책 , 기호학으로 읽다>>는 그 규모나 상세함 모두에서 독자를 압도한다. 서술 태도의 진지함만이 아니라 다루고 있는 영역도 전면적이어서 주역 학계에 미칠 영향도 상당할 것이다. 특히 다양한 기호학적 접근 방식을 통해 크게는 주역, 작게는 다산역의 이해도를 높이는 계기를 마련했다고 본다. 그는 이미 다산의 , 2007, 소명출판) 이 책이 갖는 다산역에 대한 학문적 성취도도 설득력을 충분히 갖추고 있다. 저자는 책 전편을 통해서 다산이 갖는 역학사적 위치와 의의를 모괘지모괘(某卦之某卦)라는 추이와 괘효의 변화의 성격에 집중하고 있다. 짐작컨대 그가 기호학적 접근의 필요성을 느낀 것도 이러한 다산의 괘효의 상수적 변화에 대한 이해를 높이려는 데 있지 않았을까 생각한다. 다산이 제시한 의 해석규칙을 기호학이라는 도움 없이 이해하고자 했을 때의 허전함과 부족함이 기호학에 대한 관심으로 옮겨가지 않았을까 하는 것이다

소형 로켓엔진에서 전기펌프 사이클 적용에 대한 실험 및 수치적 타당성 연구

학위논문(석사) -- 서울대학교대학원 : 공과대학 항공우주공학과, 2022.2. 윤영빈.As the miniaturization of satellites and the use of satellite constellation increase, the demand for small launch vehicles is also increasing. Accordingly, numerous private companies are developing and operating small launch vehicles, and in particular, the number of small launch vehicles which applying the electric pump cycle, is increasing. The electric pump cycle is a propellant feed system that drives a pump using an electric motor, unlike a gas generator cycle that drives the pump with a gas turbine. Many studies have been conducted to evaluate the performance of the electric pump cycle compared to other propellant feed systems based on the mass modeling. However, no study has been conducted to validate the application of the electric pump cycle in small rocket engines with thrust level of 10 kN or less. In this study, the validity of the application of the electric pump cycle was dealt with in an experimental and numerical method. First, a cryogenic performance test using liquid nitrogen as simulants was conducted using a cryogenic electric pump system for a 5.4 kN class pintle rocket engine. From the numerical analysis and cryogenic performance test results, the successful operation of the electric pump under the cryogenic environment was validated. Second, based on mass modeling, the performance of electric pump cycle, gas generator cycle and pressure-fed cycle was compared and analyzed. Small rocket engines with thrust level of 10 kN or less are characterized by very low specific speed of the pump due to small thrust level. In this study, mass modeling was performed in consideration of the hydraulic efficiency of the pump according to the specific speed. The performance of the propellant feed system according to the combustion pressure, thrust, and rotational speed conditions of the pump was compared for a small rocket engine. Under the conditions of combustion pressure of 10 bar, thrust level of 5.4 kN, and pump rotational speed of 28,000 RPM used in the experimental feasibility study, the performance of the electric pump cycle was higher than that of the other two propellant feed systems. Finally, this study numerically verified the feasibility of applying an electric pump cycle to a small rocket engine of 10 kN or less and experimentally verified that it would be possible to apply an electric pump cycle to a small rocket engine of 5.4 kN.인공위성의 소형화 및 군집 시스템의 활용이 증가함에 따라 소형 발사체에 대한 수요도 늘어나고 있다. 이에 따라, 수많은 민간 기업에서 소형 발사체를 개발 및 운용하고 있으며, 특히 전기펌프 사이클을 적용한 소형 발사체들이 증가하고 있는 추세이다. 전기펌프 사이클은 가스터빈으로 펌프를 구동하는 가스 발생기 사이클과는 달리, 전기모터를 사용하여 펌프를 구동하는 연료 공급 시스템이다. 질량 모델링을 통해 전기펌프 사이클과 다른 연료 공급 시스템과 비교하여 전기펌프 사이클의 성능을 평가하는 연구가 많이 이루어져 왔다. 하지만10 kN급 이하의 소형 로켓엔진에서 전기펌프 사이클 적용에 대한 타당성을 검토한 연구는 이루어지지 않았다. 본 연구에서는 실험 및 수치적인 방법으로 전기펌프 사이클 적용에 대한 타당성을 다루었다. 첫째, 5.4 kN급 극저온 전기펌프 시스템을 설계하여 액체질소를 매질로 한 극저온 성능 시험을 수행했다. 수치 해석과 극저온 성능 시험 결과로부터 극저온 환경에서 전기펌프의 정상적인 작동을 확인했다. 둘째, 질량 모델링을 기반으로 전기펌프 사이클, 가스발생기 사이클, 가압식 사이클의 성능을 비교 및 분석했다. 10 kN급 이하의 소형 로켓엔진은 작은 추력으로 인해 펌프의 비속도가 매우 낮다는 특징이 있다. 본 연구에서는 비속도에 따른 펌프의 수력학적 효율을 고려하여 질량 모델링을 수행했으며, 소형 로켓엔진에서 연소압, 추력, 펌프의 회전속도 조건에 따른 연료 공급 시스템의 성능을 비교했다. 실험적 타당성 연구에서 사용한 10 bar의 연소압, 5.4 kN의 추력, 28,000 RPM의 펌프 회전속도 조건에서, 전기펌프 사이클의 성능이 다른 두 연료 공급시스템보다 높았다. 최종적으로 본 연구에서는 10 kN 급 이하의 소형 로켓엔진에서 전기펌프 사이클 적용의 타당성을 수치적으로 검증하였으며, 5.4 kN급 소형 로켓엔진에서 전기펌프 사이클 적용이 가능함을 실험적으로 검증하였다.Chapter 1. INTRODUCTION 1 1.1 Study background 1 1.2 Previous studies 6 1.3 Purpose of research 10 Chapter 2. EXPIERMNETAL VALIDATION 11 2.1 Electirc pump design 11 2.1.1 Mechanical components 13 2.1.2 Electrical components 19 2.2 Numerical method 21 2.3 Experimental method 25 2.3.1 Test facility 25 2.3.2 Test condition 27 2.4 Results and discussion 29 Chapter 3. PERFORMANCE EVALUATION 31 3.1 Gas generator cycle 31 3.2 Electric pump cycle 33 3.3 Pressure-fed cycle 35 3.4 Results and discussion 37 Chapter 4 CONCLUSION 44 Bibliography 46 Abstract in Korean 47석

Proposal and Implementation of Minutiae-based Fingerprint Identification and Authentication Algorithm using Confidence Concept

Maste

Wigner-Ville Distribution Applying the Rotating Window and Its Characteristics

Wigner-Ville distribution which is a time-frequency analysis has a fatal drawback, when the signal has multiple components. This is the cross-talk and often causes a neagative value in the distribution. Wingner-Ville distriution is an expression of power, therefore the cross-talk must be avoided. Smoothing the Wigner-Ville distribution by convoluting it with a window, is most commonly used to reduce the cross-talk. There can be infinite number of distributions depending on the windows. But, the smoothing reduces resolution in time-frequency plane; this motives to design a more effective window in reducing cross-talk while remaining resolution. The domain in which the cross-talk and legitimate components can be easily distinguished, is the ambiguity function. In the ambiguity function domain, the legitimate components appear as linear lines passing through the orgine. But, the cross-talk is widely distributes in the ambiguity function plane. Based on the relative distributions of cross-talk and legitimate components, rotating window can be designed to minimize cross-talk. Applying the rotating window to the ambiguity function corresponds to smoothing the Wigner-Ville distribution. Therefore, the effects of rotating window is estimated in terms of the bias error due to smooting the Wigner-Ville distribution. By applying the rotating window, not only the Wigner-Ville distribution but also its properties are changed. The properties of the new distribution are checked, in order to complete analyzing the rotating window

A Method to Reduce the Cross-Talk of Wigner-Ville Distribution;Rotating Window

Wigner-Ville distribution has been recognized as a useful tool and applied to various types of mechanical noise and vibration signals, but its limitation which mainly comes from the cross-talk has not been well addressed. The cross-talk takes place for a signal with multiple components, simply because the Wigner-Ville distribution is a bilinear transform. The cross-talk often causes a negative value in the distribution. This cannot be accepted for the Wigner- Ville distribution, because it is an expression of power. Smoothing the Wigner-Ville distribution by convoluting it wih a window, is most commonly used to reduce the cross-talk. There can be infinite number of distributions depending on the windows. In this paper, we attempted to develop a distribution which is the best or the optimal in reducing the cross-talk. This could be possible by employing the ambiguity function. For a general signal, however it is difficult to express the ambiguity function as a mathematically closed form. This requires an appropriate modeling to make such expression possible. We approximated the Wigner-Ville distribution as a sum of linear segments. In the ambiguity function domain, the legitimate components are reflected as linear lines passing through the origin. Every lines has its own length and slope. But, the cross-talk is widely distributed in the ambiguity function plane. Based on this realization, we proposed a two-dimensional window which is in fact rotating window, that can eliminate cross-talk component. The rotating window is examined numerically and is found to have a better performance in reducing the cross-talk than conventional windows, the Gaussian window

Comparisons of Estimation Methods of Instantaneous Frequency and Examples of its Application to Beam, Engine Block, and Car Door Vibration

Although a frequency analysis by FFT algorithm has been widely used in the vibration community, this approach has somewhat limited features when an analysist want to see the details of frequency trends because FFT shows only energy contents along frequencies. So the concept of instantaneous frequency that represents the dominant frequency component at each time needs to be introduced. In this paper, to get the instantaneous frequency, two methods are used. Methods using Hilbert transform and evolutionary spectrum are those. One of the problems of estimating instantaneous frequency using Hilbert transform is that it is normally very sensitive to signal to noise ratio(SNR) because of the differentiation. Moving window is applied on the estimation of instantaneous frequency, and instantaneous frequency histogram are used to handle this problem and proved to be very effective. Computer simulations for various signals have been done to understand the characteristics of instantaneous frequency. The usefulness of signal analysis using instantaneous frequency was tested by three simple experiments, which were engine experiment, beam experiment, and car door experiment. The instantaneous frequency analysis is found to be a useful technique to analyze the signals that have time varying frequencies

A measurement of flow noise spectrum of an axisymmetric body

The pressure fluctuation on the surface of a submerged body has been recognized as a dominant noise source. There have been many studies concerning the flow induced noise on a flat plate. However, the noise over an axisymmetric body has not been well reported. This paper addresses the way in which we have investigated the mechanism of noise generation due to an axisymmetric body. The associated experiments and signal processing methods are introduced. A 3-dimensional axisymmetric body whose length and diameter were 2 m and 10.4 cm, was prepared as a test specimen. The wall pressure on the surface of the body was measured in a large scale low noise wind tunnel at KIMM(Korea Institute of Machinery and Metals). To measure the wall pressure, we used two microphone arrays which were tangential and normal to the flow. Based on the measured signal, frequency-wavenumber spectrum which explains the structure of turbulence noise, was estimated. Tangential to the flow, there exists convective ridge at a relatively higher wavenumber region; this can cause spatial aliasing. To circumvent this problem, the cross spectrum was interpolated. The interpolation has been performed by unwrapping the phase and smoothing the cross spectrum. The phase unwrapping was done based on the Corcos model; the phase of cross spectrum decreases linearly with the distance between microphones. Aforementioned signal processings are possible by employing the experimental results that the estimated wavenumber spectrum quite resembles the Corcos model. We try to modify the Corcos model which is applicable to the flat plate, by altering the magnitude of cross spectrum to fit the experimental data more accurately. We proposed that this wavenumber spectrum model is suitable for the 3-dimensional axisymmetric body. Normal to the flow, there exists a little correlation between signals of different microphones. The circumferential wavenumber spectrum contains uniform power along the wavenumbers

A study on the analysis of vibration signal using instantaneous frequency

학위논문(석사) - 한국과학기술원 : 기계공학과, 1993.2, [ viii, 69 p. ]한국과학기술원 : 기계공학과