• Journal of the Society of Naval Architects of Korea
• /
• v.28 no.2
• /
• pp.174-186
• /
• 1991

There exist many frame structural systems which may be regarded as a combined structural system composed of beam/bar elements and attachments reducible to damped spring-mass systems. In this paper, analytical methods based on the receptance for the vibration analysis of such a system are presented. For the free vibration analysis and response calculations to point excitations, receptances of a uniform Timoshenko beam and a bar are derived in closed and spectral forms, and the method to obtain the system receptance by synthesizing the receptances of the elements and other subsystems is presented. The system damping property is also obtainable by sysnthesizing the components' damping properties. For calculations of the system responses to support motion, the Support Displacement Transfer Ratio(SDTR) of a uniform Timoshenko beam and a bar conceptually similar to the receptance is defined, and the method of synthesizing them with other subsystems' receptances is also presented. Such a method is very convenient especially in dynamic reanalysis subject to changes of some design variables.

• ETRI Journal
• /
• v.42 no.1
• /
• pp.17-25
• /
• 2020

Multiple-input multiple-output systems can achieve a full sum rate (SR) via full duplex (FD). However, its performance is degraded by self-interference (SI) that occurs between the transmitter and receiver at the same node and thus is constrained by error floors. Conversely, half duplex (HD) can avoid the SI albeit at lower spectral efficiency, and the slope of its error curve is determined by the diversity order. In this study, a link selection scheme based on switching between FD and HD is examined as a simple method to improve the bit error rate (BER) performance of FD systems. In the proposed link selection algorithm, either FD or HD is selected based on the received minimum distance and signal-to-interference plus noise ratio. Simulation results indicate that the proposed hybrid FD/HD switching system offers significant BER performance improvement when compared with that of the conventional FD and FD based on only the received minimum distance under the same fixed SR. Under relatively sufficient SI cancellation, it is demonstrated to outperform the HD with a diversity advantage in low and medium signal-to-noise ratio region.

• ETRI Journal
• /
• v.37 no.1
• /
• pp.32-42
• /
• 2015

Orthogonal frequency-division multiplexing (OFDM) suffers from spectral nulls of frequency-selective fading channels. Linear precoded (LP-) OFDM is an effective method that guarantees symbol detectability by spreading the frequency-domain symbols over the whole spectrum. This paper proposes a computationally efficient and low-cost implementation for discrete Hartley transform (DHT) precoded OFDM systems. Compared to conventional DHT-OFDM systems, at the transmitter, both the DHT and the inverse discrete Fourier transform are replaced by a one-level butterfly structure that involves only one addition per symbol to generate the time-domain DHT-OFDM signal. At the receiver, only the DHT is required to recover the distorted signal with a single-tap equalizer in contrast to both the DHT and the DFT in the conventional DHT-OFDM. Theoretical analysis of DHT-OFDM with linear equalizers is presented and confirmed by numerical simulation. It is shown that the proposed DHT-OFDM system achieves similar performance when compared to other LP-OFDMs but exhibits a lower implementation complexity and peak-to-average power ratio.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.13 no.5
• /
• pp.1023-1031
• /
• 1989

An experimental study is conducted to investigate the turbulent wake flow around tubes in vertical single row tube banks. All measurements are performed at Reynolds number(Re$_{max}$) 4.2*10$_{3}$ - 2.5*10$_{4}$ with varying tube spacings from the wide pitch ratio(H/D=3.07) to the very narrow one(H/D=1.23). Flow patterns are visualized using the smoke-wire method. Mean static pressures, velocity components, and various statistical quantities of turbulence are obtained by the computer on-line technique. In the case of wide tube spacings, the near wakes of tube show similar trends to those of a single tube, and their flow indicats an anisotropic turbulence. However, as the pitch ratio decreases, wide and narrow wakes appear alternately behind adjacent tubes due to the deflected flow. Also, in the case of H/D .leq. 1.54, Karman vortex is not formed at the side of relatively wide wake.e.

• Wind and Structures
• /
• v.38 no.2
• /
• pp.119-128
• /
• 2024

The aerodynamic damping is an essential factor that can considerably affect the dynamic response of the cable-stayed bridge induced by crosswind load. However, developing an accurate and efficient aerodynamic damping model is crucial for evaluating the crosswind load-induced response on cable-stayed bridges. Therefore, this study proposes a new method for identifying aerodynamic damping of the bridge structures under crosswind load using an extended Kalman filter (EKF) and the particle filter (PF) algorithm. The EKF algorithm is introduced to capture the aerodynamic damping ratio. PF technique is used to select the optimal spectral representation of the noise. The effectiveness and accuracy of the proposed solution were investigated through full-scale vibration measurement data of the crosswind-induced on the bridge's girder. The results show that the proposed solution can generate an efficient and robust estimation. The errors between the target and extracted values are around 0.01mm and 0.003^o, respectively, for the vertical and torsional motion. The relationship between the amplitude and the aerodynamic damping ratio is linear for small reduced wind velocity and nonlinear with the increasing value of the reduced wind velocity. Finally, the results show the influence of the level of noise.

• The Journal of the Acoustical Society of Korea
• /
• v.26 no.3E
• /
• pp.87-96
• /
• 2007

In this paper we propose a new noise reduction algorithm for stationary and nonstationary noisy environments. Our algorithm classifies the speech and noise signal contributions in time-frequency bins, and is not based on a spectral algorithm or a minimum statistics approach. It relies on calculating the ratio of the standard deviation of the noisy power spectrum in time-frequency bins to its normalized time-frequency average. We show that good quality can be achieved for enhancement speech signal by choosing appropriate values for ${\delta}_t\;and\;{\delta}_f$. The proposed method greatly reduces the noise while providing enhanced speech with lower residual noise and somewhat higher mean opinion score (MOS), background intrusiveness (BAK) and signal distortion (SIG) scores than conventional methods.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
• /
• v.2 no.1
• /
• pp.13-21
• /
• 2003

This paper presents the analysis of the mode characteristics of an annular ring microstrip patch antenna for circular polarization with attachment mode using method of moments in the spectral domain. For a probe excitation, the input impedance are obtained by using the single mode approximation for both the $TM_{11}$ and $TM_{12}$ modes and compared with those by Vector Hankel Transform. While the $TM_{11}$ mode has a high Q, it is a poor radiating mode; the $TM_{12}$ mode is more suitable for antenna applications. It is also shown that the bandwidth of the $TM_{12}$ mode is wider than that of the $TM_{11}$ mode in terms of axial ratio for circular polarizatio

• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2011.07a
• /
• pp.85-88
• /
• 2011

This paper describes a single channel speech enhancement as the pre-processor of automatic speech recognition system. The improvements are based on using optimally modified log-spectra (OM-LSA) gain function with a non-causal a priori signal-to-noise ratio (SNR) estimation. Experimental results show that the proposed method gives better perceptual evaluation of speech quality score (PESQ) and lower log-spectral distance, and also better word accuracy. In the enhancement system, parameters was turned for automatic speech recognition.

• Bulletin of the Korean Chemical Society
• /
• v.24 no.7
• /
• pp.971-974
• /
• 2003

By utilizing singular value decomposition (SVD) and shift averaged Harr wavelet transform (WT) with a set of Daubechies wavelet coefficients (1/2, -1/2), a method that can simultaneously eliminate an unwanted large solvent peak and noise peaks from NMR data has been developed. Noise elimination was accomplished by shift-averaging the time domain NMR data after a large solvent peak was suppressed by SVD. The algorithms took advantage of the WT, giving excellent results for the noise elimination in the Gaussian type NMR spectral lines of NMR data pretreated with SVD, providing superb results in the adjustment of phase and magnitude of the spectrum. SVD and shift averaged Haar wavelet methods were quantitatively evaluated in terms of threshold values and signal to noise (S/N) ratio values.

• Proceedings of the KSRS Conference
• /
• 2003.11a
• /
• pp.334-336
• /
• 2003

Satellite and airborne hyperspectral sensor images are suitable for investigating the vegetation state in agricultural land. However, image data obtained by an optical sensor inevitably includes mixels caused by high altitude observation. Therefore, mixel analysis method, which estimates both the pure spectra and the coverage of endmembers simultaneously, is required in order to distinguish the qualitative spectral changes due to the chlorophyll quantity or crop variety, from the quantitative coverage change. In this paper, we apply our agricultural independent component analysis (ICA) model to an airborne hyperspectral sensor image, which includes noise and fluctuation of coverage, and estimate pure spectra and the mixture ratio of crop and soil in agricultural land simultaneously.