• Title/Summary/Keyword: harmonic-analysis

Search Result 1,736, Processing Time 0.024 seconds

Extraction of Geomagnetic Field from KOMSAT-1 Three-Axis Magnetometer Data

  • Hwang, Jong-Sun;Lee, Sun-Ho;Min, Kyung-Duck;Kim, Jeong-Woo
    • Proceedings of the KSRS Conference
    • /
    • 2002.10a
    • /
    • pp.242-242
    • /
    • 2002
  • The Earth's magnetic field acquired from KOMPSAT-1's TAM (Three-Axis Magnetometer) between June 19th and 21st 2000 was analyzed. The TAM, one of the KOMPSAT-1's Attitude and Orbit Control Subsystems, plays an important role in determining and controlling the satellite's attitude. This also can provide new insight on the Earth's magnetic field. By transforming the satellite coordinate from ECI to ECEF, spherical coordinate of total magnetic field was achieved. These data were grouped into dusk (ascending) and dawn (descending) data sets, based on their local magnetic times. This partitioning is essential for performing 1-D WCA (Wavenumber Correlation Analysis). Also, this enhances the perception of external fields in the Kompsat-1's TAM magnetic maps that were compiled according to different local. The dusk and dawn data are processed independently and then merged to produce a total field magnetic anomaly map. To extract static and dynamic components, the 1-D and 2-D WCAs were applied to the sub-parallel neighboring tracks and dawn-dusk data sets. The static components were compared with the IGRF, the global spherical harmonic magnetic field model. The static and dynamic components were analyzed in terms of corefield, external, and crustal signals based on their origins.

  • PDF

Topology Optimization of an Acoustic Diffuser Considering Reflected Sound Field (반사 음장을 고려한 음향 확산 구조의 위상 최적 설계)

  • Yang, Jieun;Lee, Joong Seok;Kim, Yoon Young
    • Transactions of the Korean Society for Noise and Vibration Engineering
    • /
    • v.23 no.11
    • /
    • pp.973-981
    • /
    • 2013
  • The main role of an acoustic diffuser is to diffuse reflected sound field spatially. Since the pioneering work of Schroeder, there have been investigations to improve its performance by using shape/sizing optimization methods. In this paper, a gradient-based topology optimization algorithm is newly presented to find the optimal distribution of reflecting materials for maximizing diffuser performance. Time-harmonic acoustic analysis in a two-dimensional acoustic domain is carried out where the domain is discretized by finite elements. Perfectly matched layers are placed to surround the domain to simulate non-reflecting boundary conditions. Design variables are assigned to each element of which material properties are interpolated between those of air and those of a rigid body. An approach to extract the reflected field from the total acoustic field is employed. To validate the effectiveness of the proposed method, design problems are solved at different frequencies. The performance of the optimized diffusers obtained by the proposed method is compared against that of the conventional Schroeder diffusers.

Comparison of vibration and Noise Characteristics for Reciprocating Air Compressor through the Change of Crankshaft Parameters (크랭크샤프트의 형상 변경을 통한 소형 왕복동 공기압축기의 진동 및 소음 특성 비교)

  • Park, Sang-Gil;Lee, Hae-Jin;Aminudin, Bin Abu;Lee, Jung-Youn;Oh, Jae-Eung
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
    • /
    • 2005.11a
    • /
    • pp.530-533
    • /
    • 2005
  • Recently, modern reciprocating air compressors tend to be smaller and lighter. But, as the development of performance, they have many problems for noise and vibration. For this reason, many researches are processing for the reduction of noise and vibration by arranging cylinders with V/W type. Especially, noise and vibration problems of reciprocating air compressor cause a rotating unbalance of crankshaft, so it needs a change of crankshaft parameters appropriately. Hence in this study, we changed crankshaft parameters to solve the rotating unbalance and compared results in order to verify the noise and vibration reduction between new and original air compressor. According to modify a crankshaft parameter, the improvements of noise and vibration were showed results of spectrum measured at selected points of the air compressor crankshaft housing and sound intensity contours measured at a belt left side, table that figure out characteristics of noise. Furthermore, we analyzed objective sound quality metrics with recording data of systems. The results showed that, the new design has improved the level of the first harmonic of vibration displacement, noise and objective sound quality metrics.

  • PDF

Proposition to Natural Frequency of Liquid Column Vibration Absorber with Vertical-horizontal Area Ratio (수직-수평부 단면적비에 따른 동조액체기둥형 감쇠장치의 고유진동수 산정식 제안)

  • Woo, Sung-Sik;Chung, Lan;Lee, Joung-Woo
    • Transactions of the Korean Society for Noise and Vibration Engineering
    • /
    • v.19 no.2
    • /
    • pp.119-126
    • /
    • 2009
  • LCVA has an advantage that its natural frequency can be easily controlled by changing the area ratio of the vertical column and horizontal part. The previous studies investigated the dynamic characteristics of the LCVA under harmonic load. This study experimentally obtained the first and second mode natural frequencies of the LCVA from shaking table tests using white noise and compared the values with the ones by previous study. Test results show that the measured first mode natural frequency of the LCVA has a different value compared with calculated one. The effective length($L_e$) was revised using by power equation. In the case01 to 19, the standard deviation($S_r$) is 4.7292 and the coefficient of correlation(r) is 0.9856. In the case21 to 61, the standard deviation($S_r$) is 14.2143 and the coefficient of correlation(r) is 0.9935. The second mode frequency increases with the increasing area ratio, which is due to the sloshing motion effect resulting from the large area of the vertical column.

Investigation on Seismic-Response Characteristics and Optimal Design Parameters of Tuned Mass Damper Considering Site Effects (지반특성에 따른 동조질량감쇠기의 지진응답특성 및 최적설계변수)

  • Kang, Kyung-Soo
    • Journal of the Korea Academia-Industrial cooperation Society
    • /
    • v.12 no.11
    • /
    • pp.5306-5313
    • /
    • 2011
  • Most previous studies for finding optimal design parameters of a tuned mass damper(TMD) have been focused on the harmonic excited single-degree-of freedom system. In this study, optimal values of damping ratio and tuning frequency ratio of a TMD applied to control a seismically excited structure are investigated through numerical analyses. Considering that the structural responses due to earthquake loads are strongly dependent on the soil condition, the site effects on the optimal parameters of the TMD are studied and compared to those presented by previous studies. Numerical analyses results indicate that better control performance can be obtained by using the parameters proposed by this study in the seismic application of the TMD.

Three-phase Three-level Boost-type Front-end PFC Rectifier for Improving Power Quality at Input AC Mains of Telecom Loads

  • Saravana, Prakash P.;Kalpana, R.;Singh, Bhim
    • Journal of Power Electronics
    • /
    • v.18 no.6
    • /
    • pp.1819-1829
    • /
    • 2018
  • A three-phase, three-switch, and three-level boost-type PWM rectifier (Vienna rectifier) is proposed as an active front-end power factor correction (PFC) rectifier for telecom loads. The proposed active front-end PFC rectifier system is modeled by the switching cycle average model. The relation between duty ratios and DC link capacitor voltages is derived in terms of the system input currents. Furthermore, the feasible switching states are identified and applied to the proposed system to reduce the switching stress and DC ripples. A detailed equivalent circuit analysis of the proposed front-end PFC rectifier is conducted, and its performance is verified through simulations in MATLAB. Simulation results are verified using an experimental setup of an active front-end PFC rectifier that was developed in the laboratory. Simulation and experimental results demonstrate the improved power quality parameters that are in accordance with the IEEE and IEC standards.

Deposition of Ferroelectric PB(Zr0.52Ti0.48)O3 Films on Platinized Silicon Using Nd:YAG Laser

  • Im, Hoong-Sun;Kim, Sang-Hyeob;Choi, Young-Ku;Lee, Kee-Hag;Jung, Kwang-Woo
    • Bulletin of the Korean Chemical Society
    • /
    • v.18 no.1
    • /
    • pp.56-61
    • /
    • 1997
  • Lead zirconate titanate (PZT) thin fills were deposited onto the Pt/Ti/SiO2/Si substrate by the pulsed laser deposition with the second harmonic wavelength (532 nm) of Nd:YAG laser. In order to determine the optimum conditions for the film deposition, the phase of the films were investigated as functions of ambient oxygen pressure, substrate temperature, and laser fluence. Also the chemical composition analysis was conducted for the PZT films deposited under various ambient oxygen pressure. When the distance between substrate and bulk PZT target is set to 20 mm, the optimum conditions have been determined to be 3 torr of oxygen pressure, 1.5 J/cm2 of laser fluence, and 823-848(±10) K range of substrate temperature. At these conditions, perovskite phase PZT films were obtained on platinized silicon. The chemical composition of the films is very similar to that of PZT bulk target. The physical structure of the deposited films analyzed by scanning electron microscopy shows a columnar morphology perpendicular to the substrate surface. Capacitance-Voltage hysteresis loop measurements show also a typical characteristics of ferroelectric thin film. The dielectric constant is found to be 528 for the 0.48 μm thickness of PZT thin film.

Conformation of L-Ascorbic Acid in solution. 1. Neutral L-Ascorbic Acid

  • Shin, Young A.;Kang, Young-Kee
    • Bulletin of the Korean Chemical Society
    • /
    • v.12 no.1
    • /
    • pp.61-67
    • /
    • 1991
  • Conformational free energy calculations using an empirical potential function and the hydration shell model (a program CONBIO) were carried out on the neutral L-ascorbic acid (AA) in the unhydrated and hydrated states. The conformational energy was minimized from starting conformations which included possible conformations of six torsion angles in the molecule. The conformational entropy of each low energy conformation in both states was computed using a harmonic approximation. From the analysis of conformational free energies for AA in both states, intramolecular hydrogen bonds (HBs) are proved to be an essential factor in stabilizing the overall conformations, and cause the conformations in both states to be quite different from those in crystal. In the case of hydrated AA, there is a competition between HBs and hydration, and the hydration around the two hydroxyl groups attached to the acyclic side chain forces the molecule to form less stable HBs. The hydration affects strongly the conformational energy surfaces of AA. Several feasible conformations obtained in this work indicate that there exists an ensemble of several conformations in aqueous solution. The calculated probable conformations for the rotation about the C5-C6 bond of the acyclic side chain are trans and gauche +, which are in good agreement with results of NMR experiment.

Development of simulator by induced contact loss phenomenon for high-speed train operation (고속전철 주행에 따른 이선현상 모의 시뮬레이터 개발)

  • Kim, Jae-Moon;Kim, Yang-Soo;Kim, Chul-Soo;Chang, Chin-Young;Kim, Youn-Ho
    • Proceedings of the KSR Conference
    • /
    • 2009.05b
    • /
    • pp.499-503
    • /
    • 2009
  • In this study, the dynamic characteristic of a contact wire and pantograph suppling electrical power to high-speed trains are investigated from an electrical response point of view. To analysis power line disturbance by induced contact loss phenomenon for high speed operation, a hardware Simulator which considered contact loss between contact wire and the pantograph as well as contact wire deviation is developed. It is confirmed that a contact wire and pantograph model are necessary for studying the dynamic behavior of the pantograph system. One of the most important needs accompanied by increasing the speed of high-speed train is reduced that an arc phenomenon by loss of contact brings out EMI. In case of a high-speed train using electrical power, as comparison with diesel rolling stock, PLD(Power Line Disturbance) such as harmonic, transient voltage and current, EMI, dummy signal injection etc usually occurs. Throughout experiment, it is verified that an arc phenomenon is brought out for simulator operation and consequently conducted noise is flowed in electric circuit by power line disturbance.

  • PDF

Detection Copy-Move Forgery in Image Via Quaternion Polar Harmonic Transforms

  • Thajeel, Salam A.;Mahmood, Ali Shakir;Humood, Waleed Rasheed;Sulong, Ghazali
    • KSII Transactions on Internet and Information Systems (TIIS)
    • /
    • v.13 no.8
    • /
    • pp.4005-4025
    • /
    • 2019
  • Copy-move forgery (CMF) in digital images is a detrimental tampering of artefacts that requires precise detection and analysis. CMF is performed by copying and pasting a part of an image into other portions of it. Despite several efforts to detect CMF, accurate identification of noise, blur and rotated region-mediated forged image areas is still difficult. A novel algorithm is developed on the basis of quaternion polar complex exponential transform (QPCET) to detect CMF and is conducted involving a few steps. Firstly, the suspicious image is divided into overlapping blocks. Secondly, invariant features for each block are extracted using QPCET. Thirdly, the duplicated image blocks are determined using k-dimensional tree (kd-tree) block matching. Lastly, a new technique is introduced to reduce the flat region-mediated false matches. Experiments are performed on numerous images selected from the CoMoFoD database. MATLAB 2017b is used to employ the proposed method. Metrics such as correct and false detection ratios are utilised to evaluate the performance of the proposed CMF detection method. Experimental results demonstrate the precise and efficient CMF detection capacity of the proposed approach even under image distortion including rotation, scaling, additive noise, blurring, brightness, colour reduction and JPEG compression. Furthermore, our method can solve the false match problem and outperform existing ones in terms of precision and false positive rate. The proposed approach may serve as a basis for accurate digital image forensic investigations.