• 한국음향학회지
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• 제41권2호
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• pp.159-165
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• 2022

본 논문에서는 수중 음향통신에서 Binary Phase Shift Keying(BPSK) 변조방식에 대한 프레임 동기 구조를 제안하였다. 제안된 프레임 동기 구조는 크게 두 가지로 나뉜다. 우선, 비동기 방식 상관과 Sliding 고속 푸리에 변환 방식으로 프레임의 대략적인 위치와 주파수 옵셋을 획득한다. 두번째는 주파수 오차를 신호에 보상한 후, 동기 방식 상관으로 정확한 프레임의 위치를 확인한다. 프레임 동기 구조의 성능 확인을 위해 해상실험을 수행하였다. 수신신호는 채널 특성으로 인해 전력이 크게 감소함을 확인하였으며, 이를 통해 비동기 방식 상관과 Sliding 고속 푸리에 변환 방식의 한계를 확인하였다. 결과적으로, 주파수 오차를 보상한 후 동기 방식 상관방식을 사용함으로써 안정적인 프레임 동기를 획득할 수 있었다.

• Advances in nano research
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• 제15권5호
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• pp.401-410
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• 2023

Vibration investigation of fluid-filled three layered cylindrical shells is studied here. A cylindrical shell is immersed in a fluid which is a non-viscous one. Shell motion equations are framed first order shell theory due to Love. These equations are partial differential equations which are usually solved by approximate technique. Robust and efficient techniques are favored to get precise results. Employment of the wave propagation approach procedure gives birth to the shell frequency equation. Use of acoustic wave equation is done to incorporate the sound pressure produced in a fluid. Hankel's functions of second kind designate the fluid influence. Mathematically the integral form of the Lagrange energy functional is converted into a set of three partial differential equations. It is also exhibited that the effect of frequencies is investigated by varying the different layers with constituent material. The coupled frequencies changes with these layers according to the material formation of fluid-filled FG-CSs. Throughout the computation, it is observed that the frequency behavior for the boundary conditions follow as; clamped-clamped (C-C), simply supported-simply supported (SS-SS) frequency curves are higher than that of clamped-simply (C-S) curves. Expressions for modal displacement functions, the three unknown functions are supposed in such way that the axial, circumferential and time variables are separated by the product method. Computer software MATLAB codes are used to solve the frequency equation for extracting vibrations of fluid-filled.

• 한국안전학회지
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• 제35권1호
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• pp.97-106
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• 2020

The objective of this paper is to suggest a new quantification method for multi-unit probabilistic safety assessment (PSA) that removes the overestimation error caused by the existing delete-term approximation (DTA) based quantification method. So far, for the actual plant PSA model quantification, a fault tree with negates have been solved by the DTA method. It is well known that the DTA method induces overestimated core damage frequency (CDF) of nuclear power plant (NPP). If a PSA fault tree has negates and non-rare events, the overestimation in CDF drastically increases. Since multi-unit seismic PSA model has plant level negates and many non-rare events in the fault tree, it should be very carefully quantified in order to avoid CDF overestimation. Multi-unit PSA fault tree has normal gates and negates that represent each NPP status. The NPP status means core damage or non-core damage state of individual NPPs. The non-core damage state of a NPP is modeled in the fault tree by using a negate (a NOT gate). Authors reviewed and compared (1) quantification methods that generate exact or approximate Boolean solutions from a fault tree, (2) DTA method generating approximate Boolean solution by solving negates in a fault tree, and (3) probability calculation methods from the Boolean solutions generated by exact quantification methods or DTA method. Based on the review and comparison, a new intersection removal by probability (IRBP) method is suggested in this study for the multi-unit PSA. If the IRBP method is adopted, multi-unit PSA fault tree can be quantified without the overestimation error that is caused by the direct application of DTA method. That is, the extremely overestimated CDF can be avoided and accurate CDF can be calculated by using the IRBP method. The accuracy of the IRBP method was validated by simple multi-unit PSA models. The necessity of the IRBP method was demonstrated by the actual plant multi-unit seismic PSA models.

• 한국전자파학회논문지
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• 제26권2호
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• pp.196-203
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• 2015

곡면 위상 배열 안테나나 곡면 주파수 선택 구조 등의 전파 특성을 해석하기 위해서는 원통형 배열 구조의 효율적인 해석방법에 대한 연구가 필요하다. 원통형 배열 구조가 실제 적용되는 구조는 유한 배열 구조지만, 대부분 전자기 해석은 무한 배열 구조라 가정하므로 실제 구조의 특성과 근사화한 구조의 특성 간의 오차가 발생하게 된다. 따라서 원통형 무한 배열 구조와 유한 배열 구조의 전파 특성의 비교와 분석이 필요하다. 본 논문에서는 원통형 무한 배열 구조를 해석하기 위해 원통형 Floquet harmonics 해석 방법을 적용하였으며, 원통형 유한 배열 구조를 해석하기 위해서는 너비가 좁은 스트립(strip)이 배열된 배열 구조를 가정하여 thin wire approximation을 적용한 method of moments(MoM)를 이용하였다. 본 논문에서는 원통형 유한 배열 구조와 무한 배열 구조의 전파 특성을 비교하기 위하여 투과 특성과 전류 분포를 계산하였다.

• Tribology and Lubricants
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• 제36권5호
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• pp.279-289
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• 2020

In this paper, a method is proposed for establishing an approximate prediction model of rotor-dynamics through modal testing. In particular, the proposed method is applicable to systems that cannot be established according to conventional methods owing to the absence of information regarding the dimensions and material of the rotor-bearing system. The proposed method is demonstrated by employing a motor dynamometer driven by a 1 MW class induction motor without dimension and material information. The proposed method comprises a total of seven steps, wherein an initial model is established by incorporating approximate dimensions and material information, and the model is improved on the basis of the natural frequency characteristics of the system. During model improvement, the modification factor is introduced for adjusting the elastic modulus and shear modulus of the system. Analysis of critical speed and imbalance response indicates that the separation margin is 67% and the maximum vibration amplitude is less than the amplitude limit of 0.032 mm under the API 611 standard, which means that the motor dynamometer can stably operate at a rated speed of 1800 rpm. Hence, the obtained results validate the feasibility of the proposed method. Furthermore, for broad usage, it is necessary to accordingly apply and validate the proposed method for various rotor-bearing systems.

• 한국전자파학회논문지
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• 제22권2호
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• pp.191-198
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• 2011

본 논문에서는 1차원 모드 방정식의 FDTD 해석 결과와 분수 함수 근사법을 이용하여 다층 구조의 Green 함수를 근사화 하는 방법을 제안한다. 파수 값에 따른 FDTD 해석 결과를 Fourier 변환 과정을 거쳐 spectral domain 상에서 Green 함수를 계산한다. FDTD 수치 해석 결과로 얻은 Green 함수에 분수 함수 근사법을 적용하여 pole과 residue를 계산하여 Green 함수를 분수 함수로 근사화 한다. 제안된 방법은 path-loss 계산 방법 중 하나인 정상 모드(normal mode)에 사용할 수 있다. 단일 주파수 해석에 유효한 기존의 정상 모드 방법과는 달리 본 논문에서 제안하는 FDTD 기반 방법은 광대역 해석을 할 수 있다. 제안된 방법의 유용성을 입증하기 위해 정상 모드 해석기반의 Kraken 시뮬레이터 결과와 공진 모드의 pole 값을 비교한다. 또 알려진 해석해를 갖는 문제에 제안된방법을 적용하여 정확도를 검증하였다.

• 한국공작기계학회논문집
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• 제17권5호
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• pp.95-100
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• 2008

An active micro-mixer, which is composed of an oscillating micro-stirrer in the micro-channel to provide effective mixing was optimized. The effects of molecular diffusion and disturbance by the stirrer were considered with regard to two types of mixer models: the simple straight micro-channel and micro-channel with an oscillating stirrer. Two types of mixer models were studied by analyzing mixing behaviors such as their interaction after the stirrer. The mixing was calculated by Lattice Boltzmann methods using the D2Q9 model. In this study, the time-averaged mixing index formula was used to estimate the mixing performance of time-dependent flow. The mixing indices of the two models were compared. From the results, it was found that the mixer with an oscillating stirrer was much more enhanced and stabilized. Therefore, an approximate optimization of an active micro-mixer with an oscillating stirrer was performed using Kriging method with OLHD(Optimal Latin Hypercube Design) in order to determine the optimal design variables. The design parameters were established as the frequency, the length and the angle of the stirrer. The optimal values were obtained as 1.0346, 0.66D and $\pm45^{\circ}$, respectively. It was found that the mixing index of the optimal design increased by 88.72% compared with that of the original design.

• 대한약침학회지
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• 제26권4호
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• pp.348-356
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• 2023

Objectives: Neuralgia-pharmacopuncture (NP) was recently developed as a water-soluble type of pharmacopuncture inspired by CS (care special pain)-pharmacopuncture. I aimed to evaluate the toxic response and approximate lethal dose of when NP when administered intramuscularly to Sprague Dawley rats. Methods: The experimental group was divided into the NP test substance group and the saline control group and administered at a dose of 1.0 mL/animal to the posterior thigh muscles on both sides using a 1 mL syringe; each group consisted of five males and five females. Each rat was monitored for clinical signs and changes in body weight for 14 days after a single intramuscular injection. After completing observation, necropsy findings and localized tolerance at the injection site were assessed via gross necropsy and histopathological examination. Results: No deaths occurred in the NP or control group, regardless of sex. During the observation period, no changes (such as general symptoms, weight change, or visual observation results at the time of autopsy) were judged to be due to the test substance. Histopathological examination showed no changes at the administration site judged to be caused by the test substance in either the male or female test substance administration groups. In addition, mononuclear cell infiltration of the outer membrane of the femoris muscle at the administration site was observed at the same frequency and extent in the control and NP groups, and was judged to be caused by physical stimulation by the injection needle; therefore, it had no toxicological significance. Conclusion: Based on the above results, the approximate lethal dose for a single intramuscular administration of the test substance NP in Sprague-Dawley rats was judged to be > 1.0 mL/animal, and there were no findings that were judged to be due to the test substance at the administration site.

• Journal of electromagnetic engineering and science
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• 제3권2호
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• pp.133-139
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• 2003

The nonuniqueness of a mathematically rigorous solution to 2-dimensional inverse scattering problems is explained in a limiting view of the numerical calculations based on the spectral-domain moment method. It is illustrated that its theoretical uniqueness cannot be assured even by performing additional measurements of the scattered fields not only along multiple lines but also with angular/frequency-diversities. In a real situation, however, computational error and measurement noise are inevitable. Those limitations render it meaningless to controvert the existence of a theoretically rigorous solution. Hence the most practical issue is how to remedy the instability of its practically approximate solution.

• Structural Engineering and Mechanics
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• 제14권3호
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• pp.345-364
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• 2002

The scaling laws for vibration response of anti-symmetrically laminated plates are derived by applying the similitude transformation to the governing differential equations directly. With this approach, a closed-form solution of the governing equations is not required. This is a significant advantage over the method employed by other researchers where similitude transformation is applied to the closed-form solution. The scaling laws are tested by comparing the similitude fundamental frequencies to the theoretical fundamental frequencies determined from the available closed-form solutions. In case of complete similitude, similitude solutions from the scaling laws exactly agree with the theoretical solutions. Sometimes, it may not be feasible to select the model which obeys the similarity requirement completely, therefore partial similitude is theoretically investigated and approximate scaling laws are recommended. The distorted models in stacking sequences and laminated material properties demonstrate reasonable accuracy. On the contrary, a model with distortion in fiber angle is not recommended. The derived scaling laws are very useful to determine the vibration response of complex prototypes by performing the experiment on a model with required similarities.