• 터널과지하공간
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• 제12권1호
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• pp.31-36
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• 2002

터널화재시 화원의 크기에 따른 연기기동을 파악하기 위하여 모현실험 및 수치해석이 수행되었다. 모형실험의 결과를 실제 터널에 대해 적용하기 위하여 Frode상사법을 이용하였다. 터널공간내의 화재 해석에 대한 수치해석의 타간성을 입증하기 위하여 모형실험과 수치해석에서 얻어진 연층의 온도분포를 비교하였다. 터널내 온도분포를 해석함으로써 배기장치가 없는 짧은 터널에 대하여 연층은 전체 터널 높이의 절반 이하로 하강하지 않는다는 사실을 파악하였다. 또한 실험에서 얻어진 연층선단의 전파속도는 화재 발생부의 1/3 풍에 비례한다는 사실을 파악하였으며 이는 기존의 경험식 및 수치해석결과와도 잘 일치하였다. 따라서 짧은 터널에서 화재시 피난대책을 수립하는데 있어서 연층의 수평전파가 수직전파에 비해 중요한 설계변수임을 본 연구를 통하여 제시하였다.

• 오토저널
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• 제2권1호
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• pp.21-31
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• 1980

Two phase boundary layer equations of laminar filmwise condensation are solved by an approximate integral method under the following condition; saturated vapour flows vertically downward over a cooled surface of uniform temperature, the condensate film is so thin that the inertia and convection terms are neglected. The following conclusions are drawn under the above assumptions. 1. free convection In case of the linear temperature profile in a liquid film, numerical results for the average coefficients of heat transfer may be expressed as N $u_{m}$=4/3,(G $r_{l}$ /4.H)$^{1}$4/ and in case of the quadratic profile, numerical results may be expressed as N $u_{m}$=2/1.682,(G $r_{l}$ /H)$^{1}$4/. 2. Forced convection When the temperature profile is assumed to be linear in a liquid film, numerical results fir the average heat transfer coefficients may be expressed as N $u_{m}$=(A, R $e_{l}$ /H)$^{1}$2/. This expression is compared with the experimental results hitherto reported; For theoretical Nusselt number (N $u_{m}$)$_{th}$<2*10$^{4}$, the experimental Nusselt number (N $u_{m}$)$_{exp}$ is on the average larger than theoretical Nusselt number (N $u_{m}$)$_{th}$ by 30%. For (N $u_{m}$)$_{th}$>2*10$^{4}$, experimental Nusselt number (N $u_{m}$)$_{exp}$ is about 1.6 times as large as theoretical Nusselt number (N $u_{m}$)$_{th}$. These large deviation may be caused by the presence of turbulence in the liquid film. In case of the quadratic temperature profile in a liquid film, numerical results for the average coefficients of heat transfer may be expressed as N $u_{m}$'=(2,A,Re/H)$^{1}$2/. This formular shows that theoretical Nusselt number (N $u_{m}$)$_{th}$ is larger than experimental Nusselt number (N $u_{m}$)$_{exp}$ by 60%. It is speculated that when the temperature difference between cooled surface and saturated vapour is small, temperature profile in a liquid film is quadratic.quadratic.. quadratic.quadratic..atic..

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권8호
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• pp.2607-2625
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• 2014

Previous studies on multiuser multiple-input multiple-output (MIMO) mostly assume a homogeneous signal-to-noise ratio (SNR), where each user has the same average SNR. However, real networks are more likely to feature heterogeneous SNRs (a random-valued average SNR). Motivated by this fact, we analyze a multiuser MIMO downlink with a zero-forcing (ZF) receiver in a heterogeneous SNR environment. A transmitter with Mantennas constructs M orthonormal beams and performs the SNR-based proportional fairness (S-PF) scheduling where data are transmitted to users each with the highest ratio of the SNR to the average SNR per beam. We develop a new analytical expression for the sum throughput of the multiuser MIMO system. Furthermore, simply modifying the expression provides the sum throughput for important special cases such as homogeneous SNR, max-rate scheduling, or high SNR. From the analysis, we obtain new insights (lemmas): i) S-PF scheduling maximizes the sum throughput in the homogeneous SNR and ii) under high SNR and a large number of users, S-PF scheduling yields the same multiuser diversity for both heterogeneous SNRs and homogeneous SNRs. Numerical simulation shows the interesting result that the sum throughput is not always proportional to M for a small number of users.

• Structural Engineering and Mechanics
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• 제53권3호
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• pp.443-453
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• 2015

Cable-beam structures characterized by variable stiffness nonlinearities are widely found in various structural engineering applications, for example in space deployable structures. Space deployable structures in orbit experience both high temperature caused by sun's radiation and low temperature by Earth's umbral shadow. The space temperature difference is above 300K at the moment of exiting or entering Earth's umbral shadow, which results in structural thermally induced vibration. To understand the thermally induced oscillations, the analytical expression of Boley parameter of cable-beam structures is firstly deduced. Then, the thermally induced vibration of cable-beam structures is analyzed using finite element method to verify the effectiveness of Boley parameter. Finally, by analyzing the obtained numerical results and the corresponding Boley parameters, it can be concluded that the derived expression of Boley parameter is valid to evaluate the occurrence conditions of thermally induced vibration of cable-beam structures and the key parameters influencing structural thermal flutter are the cable stiffness and thickness of beams.

• 한국통신학회논문지
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• 제30권8C호
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• pp.754-761
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• 2005

본 논문에서는 나카가미-n(라이시안) 페이딩 채널 상에서 그레이 부호화된 직사각 QAM(Rectangular-QAM) 신호를 최대비 합성(maximal ratio combining) 다이버시티로 수신하는 경우 비트노율(Bit Error Rate, BER)을 계산하는 수식을 다양한 채널에 적용할 수 있도록 일반적 형태로 유도하고 그 성능 분석을 실시한다. 유도된 BER 수식은 휘태커 함수)Whittaker function)와 초기하 함수(confluent hypergeometric)로 표현된다. 또한 M-PSK와의 성능 비교를 통하여 나카가미-n 페이딩 채널의 특성을 확인한다. BER 수식이 일반적인 형태로 유도되었기 때문에 가시 경로(line-of-sight)를 가지는 통신채널이나 위성통신 채널의 성능분석에 본 논문에서 유도한 BER 수식을 쉽게 적용할 수 있다.

• 한국전자파학회논문지
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• 제17권8호
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• pp.788-794
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• 2006

본 논문에서는 임피던스 반 평면 문제에서 나오는 Sommerfeld 적분의 closed-form을 계산한다. 우선 주어진 Sommerfeld 적분을 두 개의 급수 형태로 표현한다. 급수 중 하나는 exponential integral로 알려진 초월 함수로, 다른 것은 Lommel 함수로 표현이 된다. Lommel 함수 표현으로부터 주어진 Sommerfeld 적분의 closed-form을 incomplete Weber integral로 표현한다. incomplete Weber integral은 여러 분야에서 사용되고 있고 많은 성질들이 알려져 있다. 또 exponential integral 함수 표현으로부터 Sommerfeld 적분을 incomplete Gamma 함수로 근사화한다. 구한 모든 식들은 수칙 적분 결과와 비교하여 validation을 한다.

• Journal of Communications and Networks
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• 제11권3호
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• pp.240-247
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• 2009

The results of performance analysis by adopting the channel scenarios characterized as Weibull fading for an multicarrierdirect sequence-coded division multiple access (MC-DS-CDMA) system are proposed in this investigation. On the other hand, an approximate simple expression with the criterion of bit error rate (BER) versus signal-to-noise ratio (SNR) method is derived for an MC-DS-CDMA system combining with maximal ratio combining (MRC) diversity based on the moment generating function (MGF) formula of Weibull statistics, and it associates with an alternative expression of Gaussian Q-function. Besides, the other point of view on the BER performance evaluation of an MC-DS-CDMA system is not only the assumption of both single-user and multi-user cases applied, but the phenomena of partial band interference (PBI) is also included. Moreover, in order to validate the accuracy in the derived formulas, some of the system parameters, such as Weibull fading parameter (${\beta}$), user number (K), spreading chip number (N), branch number (L), and the PBI (JSR) values, etc., are compared with each other in the numerical results. To the best of author's knowledge, it is a brand new idea which proposes the evaluation of the system performance for an MC-DS-CDMA system over the point of view with Weibull fading channel.

• Geomechanics and Engineering
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• 제24권6호
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• pp.599-610
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• 2021

Conduits are commonly installed below the ground for utility conveyance around the world. Vertical load on a buried conduit is an important parameter that needs to be known to ensure its safe design and installation. Consideration of soil arching in load calculations helps achieve a more realistic and efficient design. In the past, considering the arching effect, the design charts have been presented for use by practicing engineers to calculate the vertical load on the conduit buried below the level ground. There are currently no design charts for calculating the vertical load on the conduit buried under a sloping ground. In this paper, an attempt has been made to present the derivation of a generalized analytical expression considering that the soil mass overlying the conduit has a sloping face and the arching phenomenon takes place. The developed generalized expression has been used to present some design charts considering specific values of slope geometry, soil properties and burial depths. Furthermore, analytical results for specific soil parameters have been compared with the results extracted from a commercial software PLAXIS 2D, for a developed numerical model and an independent study.

• Journal of Mechanical Science and Technology
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• 제20권4호
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• pp.473-481
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• 2006

Predicting fatigue life by numerical methods was almost impossible in the field of rubber materials. One of the reasons is that there is not obvious fracture criteria caused by nonstandardization of material and excessively various way of mixing process. But, tearing energy as fracture factor can be applied to a rubber-like material regardless of different types of fillers, relative to other fracture factors and the crack growth process of rubber could be considered as the whole fatigue failure process by the existence of potential defects in industrial rubber components. This characteristic of fatigue failure could make it possible to predict the fatigue life of rubber components in theoretical way. FESEM photographs of the surface of industrial rubber components were analyzed for verifying the existence and distribution of potential defects. For the prediction of fatigue life, theoretical way of evaluating tearing energy for the general shape of test-piece was proposed. Also, algebraic expression for the prediction of fatigue life was derived from the rough cut growth rate equation and verified by comparing with experimental fatigue lives of dumbbell fatigue specimen in various loading condition.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2007년도 추계학술대회 논문집
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• pp.69-71
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• 2007

Need correct analysis of thrust for control performance improvement of HB-LPM (Hybrid type Linear Pulse Motor). It is difficult to analyze HB-LPM's thrust. In this paper, HB-LPM's thrust is expressed to mathematical expression. And it is proved validity of this numerical formula by thrust measurement system. Two phase driver is composed. It is verified validity of numerical formula that measure waveform of electric current and voltage that is supplied in each phase. In this study, composed two phase drive driver, advantage of this IGBT element 6 by accumulated IPM module 1 Driver composition possible. That is, can economize 1 moule. In other words, Driver composition is available by IGBT or metal oxide semiconductor field effect transistor element 4. This is economical big gain.