• Structural Engineering and Mechanics
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• 제75권4호
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• pp.507-518
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• 2020

With the rapid development of rail transit, rail transit noise needs to be paid more and more attention. In order to accurately and effectively analyze the characteristics of low-frequency noise, a prediction model of vibration of box girder was established based on the hybrid FE-SEA method. When the train speed is 140 km/h, 200 km/h and 250 km/h, the vibration and noise of the box girder induced by the vertical wheel-rail interaction in the frequency range of 20-500 Hz are analyzed. Detailed analysis of the energy level, sound pressure contribution, modal analysis and vibration loss power of each slab at the operating speed of 140 km /h. The results show that: (1) When the train runs at a speed of 140km/h, the roof contributes more to the sound pressure at the far sound field point. Analyzing the frequency range from 20 to 500 Hz: The top plate plays a very important role in controlling sound pressure, contributing up to 70% of the sound pressure at peak frequencies. (2) When the train is traveling at various speeds, the maximum amplitude of structural vibration and noise generated by the viaduct occurs at 50 Hz. The vibration acceleration of the box beam at the far field point and near field point is mainly concentrated in the frequency range of 31.5-100 Hz, which is consistent with the dominant frequency band of wheel-rail force. Therefore, the main frequency of reducing the vibration and noise of the box beam is 31.5-100 Hz. (3) The vibration energy level and sound pressure level of the box bridge at different speeds are basically the same. The laws of vibration energy and sound pressure follow the rules below: web

• 항공우주시스템공학회지
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• 제17권6호
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• pp.54-62
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• 2023

자유로운 이착륙과 뛰어난 비행능력을 가진 플랩핑 날갯짓 비행체에 관한 집중적 연구개발이 진행되고 있다. 대부분의 플랩핑 날갯짓에 관한 연구는 동기화된 운동의 다양한 운동변수에 대한 연구들로 비동기 운동을 수행하는 에어포일의 비정상 공력 특성에 미치는 영향에 대한 관심은 크지 않았다. 본 연구에서는 히브와 피치 진동운동 주파수가 서로 다른 에어포일의 비정상 공력특성을 수치적으로 연구했다. 먼저 비동기 운동에 따른 운동특성과 받음각 변화를 파악하였다. 해석 결과 진동수 비가 1.0인 경우 양력은 발생하지 않았고 추력이 크게 발생했다. r=0.5인 경우 양력이 크게 발생하였다. 에어포일 주변의와 분포와 표면에서의 압력계수를 분석하여 비동기 진동운동을 하는 에아포일의 공력특성을 분석했다. r=0.5인 경우 r=1.0인 경우 보다 더 큰 앞전 및 뒷전 와들이 관찰되었으며, 이 와들이 비동기 진동운동을 하는 에어포일의 공력특성에 큰 영향을 미친 것을 발견하였다. 향후 피치진동의 진폭이 비동기 진동운동을 하는 에어포일의 비정상 공력특성에 미치는 영향을 연구할 계획이다.

• 대한후두음성언어의학회지
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• 제9권1호
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• pp.47-52
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• 1998

Objectives : To compare the objective differences in voice quality and voice problems between clergies and normal male control group. Materials and Methods : The sustained vowel sound of 46 clergies and 40 normal persons were analyzed, using a videostroboscopy and acoustic analyzer. Together with these analyses, a questionnaire associated with current and past voice problems was handed over to the patients. Results : The most common symptom in subjective group was the voice fatigue. Stroboscopic findings in subjective group were as following 23 cases(50%) of pachydermia, 17 cases(37%) of phase difference, 12 cases(25%) of anterior-posterior contracture, 6 cases(13%) of vocal polyp and 3 cases(7%) of vocal nodule. The mean maximal phonation time in clergies was 17.8 seconds and in control group was 19 seconds. litter, pitch perturbation quotient and shimmer were significantly increased in subjective group than in control group(p<0.05), but there were no significant differences between two groups in fundamental frequency, vFo, amplitude perturbation quotient and noise to harmonic ratio. Conclusion : In the clergies using loud and forceful voice, vocal polyp and functional voice disorder findings were frequently noted in stroboscopic examination. litter and shimmer, reflecting the roughness of voice, were increased in acoustic analysis. Therefore, clergies, classified into untrained professional voice users, need professional career guidance and counseling.

• 한국정밀공학회지
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• 제13권10호
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• pp.139-145
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• 1996

The machining accuracy and performance is largely influenced by the static, dynamic and thermal characteristics of spindle systems in machine tools, because the spindle system is a intermedium for cutting force from tool and machine powef from motor. Large cutting force and power are transmitted by bearing with a point or line contact. So, the spindle system is the static and dynamic weakest point in machine structure. For improvement of static stiffness of spindle system can be changed design parameters, such as diameter of spindle, stiffness of bearing and bearing span. But for dynamic stiffness, the change of the design parameters are not useful. In this paper, the combined bearing arrangement is suggested for high damping spindle system. The combined bearing arrangement is composed of tandem double back to back arrangement type ball bearins and a high damping hydrostatic bearing. The variation of static deflection and amplitude in first natural frequency is evaluated with the location of hydrostatic bearing between front and rear ball bearing. The optimized location of hydrostatic bearing for high static and dynamic stiffness is determined rapidly and exactly using the mode shape and transfer function of spindle. The calculation of damping effect on vibration by unbalance of grinding wheel and pulley in optimized spindle system is carried out to verify the validity of the combined bearing arrangement. Finally, the simulation of grinding process show that the surface roughness of workpiece with high damping spindle system is 60% better than with ball bearing spindle system.

• 한국생산제조학회지
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• 제24권5호
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• pp.502-507
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• 2015

In this study, a microscale drilling process was conducted to evaluate the cutting characteristics of functionally graded materials. A mixture of M2 and Cu powders were formed and sintered to produce disk specimens of various compositions. Subsequently, a microscale hole was created in the specimen by using a desktop-size micro-machining system. By using design of experiments and analysis of variance, it was found that the M2-Cu composition, spindle speed, and the interactions between these two factors had significant effects on the magnitude of cutting forces. However, the influence of feed rate on the cutting force was negligible. A mathematical model was established to predict the cutting force under a wide range of process conditions, and the reliability of the model was confirmed experimentally. In addition, it was observed that increasing the wt% of Cu in an M2-Cu specimen increased the high-frequency amplitude of cutting forces.

• 전자공학회논문지SC
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• 제43권4호
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• pp.45-52
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• 2006

본 연구에서는 위상잡음과 지터(jitter) 특성을 개선한 $5mm{\times}7mm$ 크기의 적층 세라믹 SMD(surface mounted device)형 VCXO를 개발한다. PECL(positive emitter coupled logic) 칩패키지를 발진수정자에 결선한 VCXO는 그 길이 및 패키지 내부의 패턴 등에 의하여 부유인덕턴스 및 기생 커패시턴스가 발생하고, 전원의 반사 및 잡음 발생으로 출력신호의 진폭 감소 및 신호 손실이 발생하여 발진기 성능을 정상적으로 평가할 수 없다. 이러한 신호 손실 및 진폭감소를 방지하기 위해 지그(Jig) 시스템을 개발하고, 이를 통하여 발진기의 정확한 스펙트럼 분석 및 성능을 평가한다. 동작전원은 3.3 V, 주파수 범위 120-180 MHz 및 Q인수는 5K이다.

• Journal of Advanced Marine Engineering and Technology
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• 제32권2호
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• pp.241-249
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• 2008

In this study, lateral vibration analysis has been conducted on a propulsion and lift shafting system for an air cushion vehicle using ANSYS code. The shafting system is totally flexible multi-elements system including air propeller, aluminum alloy of lift fan and thin walled shaft with flexible coupling. The analysis included the lateral natural frequencies, mode shapes and harmonic analysis of the shafting system taking into account three-dimensional models for propulsion and lifting shaft system. In case of ACV the yawing and pitching rate of craft will be quite high. During yawing and pitching of craft significant gyroscopic moment will be applied to the shafting and will generate high amplitude of lateral vibration. So, such a shafting system has very intricate lateral vibrating characteristics and natural frequencies of shafting must be avoided in the range of operating revolution. The control of lateral vibration is included in this study.

• Steel and Composite Structures
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• 제31권2호
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• pp.187-199
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• 2019

This paper presents the semi-analytical development of the dynamic instability behavior and the dynamic response of functionally graded (FG) cylindrical shallow shell panel subjected to different type of periodic axial compression. First, in prebuckling analysis, the stresses distribution within the panels are determined for respective loading type and these stresses are used to study the dynamic instability behavior and the dynamic response. The prebuckling stresses within the shell panel are the same as applied in-plane edge loading for the case of uniform and linearly varying loadings. However, this is not true for the case of parabolic loadings. The parabolic edge loading produces all the stresses (${\sigma}_{xx}$, ${\sigma}_{yy}$ and ${\tau}_{xy}$) within the FG cylindrical panel. These stresses are evaluated by minimizing the membrane energy via Ritz method. Using these stresses the partial differential equations of FG cylindrical panel are formulated by applying Hamilton's principal assuming higher order shear deformation theory (HSDT) and von-$K{\acute{a}}rm{\acute{a}}n$ non-linearity. The non-linear governing partial differential equations are converted into a set of Mathieu-Hill equations via Galerkin's method. Bolotin method is adopted to trace the boundaries of instability regions. The linear and non-linear dynamic responses in stable and unstable region are plotted to know the characteristics of instability regions of FG cylindrical panel. Moreover, the non-linear frequency-amplitude responses are obtained using Incremental Harmonic Balance (IHB) method.

• 한국결정성장학회지
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• 제19권5호
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• pp.215-222
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• 2009

Many concepts of external magnetic field applications in crystal growth processes have been developed to control melt convection, impurity content and growing interface shape. Especially, travelling magnetic fields (TMF) are of certain advantages. However, strong shielding effects appear when the TMF coils are placed outside the growth vessel. To achieve a solution of industrial relevance within the framework of the $KRISTMAG^{(R)}$ project inner heater-magnet modules(HMM) for simultaneous generation of temperature and magnetic field have been developed. At the same time, as the temperature is controlled as usual, e.g. by DC, the characteristics of the magnetic field can be adjusted via frequency, phase shift of the alternating current (AC) and by changing the amplitude via the AC/DC ratio. Global modelling and dummy measurements were used to optimize and validate the HMM configuration and process parameters. GaAs and Ge single crystals with improved parameters were grown in HMM-equipped industrial liquid encapsulated Czochralski (LEC) puller and commercial vertical gradient freeze (VGF) furnace, respectively. The vapour pressure controlled Czochralski (VCz) variant without boric oxide encapsulation was used to study the movement of floating particles by the TMF-driven vortices.

• 음성과학
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• 제15권4호
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• pp.159-170
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• 2008

The purpose of this study was to find out the ability of coordination of the articulatory motor and the ability of control of the respiration and laryngeal for spastic dysarthria by acoustic analysis. The sustained of vowel /a/ and repetition of syllable /pa/ in 15 normal and 10 spastic dysarthria were measured. Multi-Speech, MDVP, and MSP were used for data recording and analysis. As a result, the mean DDK rate in the spastic group was significantly slower than in the normal. The maximum phonation time in the spastic group ($4.80{\pm}1.94$) was shorter than in the normal ($11.20{\pm}3.72$). The DDKjit in the spastic group was significantly higher than in the normal. The DDKsla was reduced in the spastic group. The mean syllable duration in the spastic group (146.2ms) was significantly longer than in the normal (75.8ms). The mean energy was reduced in the spastic group. The range of Fo was greater than in the normal. The frequency perturbation (jitter, vFo) and amplitude perturbation (shimmer, vAm) were higher than in the normal group. The NHR was higher than in the normal group. The parameters of this were significantly difference between the spastic dysarthria and the normal (p<0.05). Finally, the spastic dysarthria has short respiration, slow speech rate, and voice quality problem. The these results will help to establish a plan and the intervention of treatment.