• Title/Summary/Keyword: Coefficient estimate

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Estimation of the Maximum Friction Coefficient of the Rough Terrain to Control the Mobile Robots (주행로봇 제어를 위한 험지의 최대마찰계수 추정)

  • Kang, Hyun-Suk;Kwak, Yoon-Keun;Choi, Hyun-Do;Jeong, Hae-Kwan;Kim, Soo-Hyun
    • Journal of Institute of Control, Robotics and Systems
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    • v.14 no.10
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    • pp.1062-1072
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    • 2008
  • When mobile robots perform the mission in the rough terrain, the traversability depended on the terrain characteristic is useful information. In the traversabilities, wheel-terrain maximum friction coefficient can indicate the index to control wheel-terrain traction force or whether mobile robots to go or not. This paper proposes estimating wheel-terrain maximum friction coefficient. The existing method to estimate the maximum friction coefficient is limited in flat terrain or relatively easy driving knowing wheel absolute velocity. But this algorithm is applicable in rough terrain where a lot of slip occurred not knowing wheel absolute velocity. This algorithm applies the tire-friction model to each wheel to express the behavior of wheel friction and classifies slip-friction characteristic into 3 major cases. In each case, the specific algorithm to estimate the maximum friction coefficient is applied. To test the proposed algorithm's feasibility, test bed(ROBHAZ-6WHEEL) simulations are performed. And then the experiment to estimate the maximum friction coefficient of the test bed is performed. To compare the estimated value with the real, we measure the real maximum friction coefficient. As a result of the experiment, the proposed algorithm has high accuracy in estimating the maximum friction coefficient.

Evaluation of Diffusion Property of Latex Modified Concrete (LMC(Latex Modified Concrete)의 염소이온 확산 특성)

  • Park, Sung-Ki;Won, Jong-Pil;Park, Chan-Gi
    • Journal of The Korean Society of Agricultural Engineers
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    • v.50 no.4
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    • pp.27-37
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    • 2008
  • It is most serious problem which is various occurs from the agricultural concrete structure and off shore concrete structure the problem which it comes to think is deterioration of the concrete which is caused with the corrosion of the reinforcing steel which is caused by with permeation of the water and the sea water. Specially the off shore concrete structure has been deteriorated by the steel reinforcement corrosion. The latex modified concrete(LMC) was adds latex in the plain concrete as the latex has increase the durability of concrete. This study were accomplished to the estimate the diffusion coefficient of LMC, and the time dependent constants of diffusion. The average chloride diffusion coefficient was estimated. Also, the average chloride diffusion coefficient was compared with diffusion coefficient test results of 28 curing days. The test results indicated that the average chloride diffusion coefficient could closely estimate the test results of the diffusion coefficient test results of 28 curing days.

Estimation of Ultrasound Attenuation Coefficient by Homomorphic Deconvolution Method (Homomorphic Deconvolution 법에 의한 초음파 감쇄정수 추정)

  • Hong, Seung-Hong;Huh, Woong
    • Journal of Biomedical Engineering Research
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    • v.5 no.1
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    • pp.39-46
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    • 1984
  • In order to improve the performance of ultrasonic diagnostic equipment, it is important to development the signal processing considering the ultrasonic properties of biological medium and propagation mechanism in tissue. Attenuation coefficient is not only important factor to analyze propagation properties, but also it is significant to estimate it in view of tissue characterization, so we show one of the method to estimate attenuation coefficient of biological tissue and the results of estimation.

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Estimation of Bed Form Friction Coefficients using ADCP Data

  • Lee, Minjae;Park, Yong Sung
    • Proceedings of the Korea Water Resources Association Conference
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    • 2021.06a
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    • pp.63-63
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    • 2021
  • Bed shear stress is important variable in river flow analysis. The bed shear stress has an effects on bed erosion, sediment transport, and mean flow characteristics. Quadratic formula to estimate bed shear stress is widely used, 𝜏=𝜌cfu|u| in which friction coefficient, cf, needs to be assigned to numerical models. The aim of this study is to estimate Chezy coefficient using bathymetry data measured by ADCP. Bed form geometry variables will be estimated form bed profile, then Chezy coefficient will be determined using estimated bed form geometry variables in order to set friction coefficient to numerical model. From the probability density function obtained from the bathymetry data, Chezy coefficient will be randomly generated since Chezy coefficient is not uniform over the space and it does not depend on spatial variables such as water depth and distance from river bank. Numerical test will be performed to find to demonstrate randomly extracted Chezy coefficient is appropriate. The result of this study is valuable in that the friction coefficient is estimated in consideration of the bed profile, and as a result, uncertainty of the friction coefficient can be reduced.

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A Study on the Estimation of Frictiom Coefficient between Tire and Road Surface Using Running Car data (실차 데이터를 이용한 차륜과 노면간의 마찰계수 예측에 관한 연구)

  • 우관제;산기준일
    • Transactions of the Korean Society of Automotive Engineers
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    • v.7 no.6
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    • pp.207-213
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    • 1999
  • In this study, the possibility of estimation of friction coefficient between tire and road surface using running car data are checked. To get necessary data, such as tire and car velocities and braking force, a test car is driven with certain magnitude of decelerations from pre-set initial velocities to stop . The data are used to estimate friction coefficient with property chosen parameters , e.g,, driving stiffness, pressure distribution functions, etc. Experimental results show that running data car be used with properly chosen parameters to estimate friction coefficient.

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Development of a programming logic to estimate the wall friction coefficient in vehicle tunnels with piston effects (교통환기력이 작용하는 터널 내 벽면마찰계수 추정을 위한 프로그램 로직 개발)

  • Kim, Hyo-Gyu;Choi, Pan-Gyu;Ryu, Ji-Oh;Lee, Young-Hoon
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.20 no.1
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    • pp.39-53
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    • 2018
  • Generally, the total ventilation resistance coefficient in a tunnel consists of inlet/outlet loss coefficient, wall friction coefficient, and other loss coefficient caused by sudden expansion and contraction of cross-section, etc. For the tunnel before opening, when the running ventilation fan is stopped, the wind speed in the tunnel is reduced by the total ventilation resistance drag. The velocity decay method is comparatively stable and easy to estimate the wall friction coefficient in the pre-opening tunnel. However, the existing study reported that when the converging wind speed is a negative value after the ventilation fan stops, it is difficult to estimate the wall friction coefficient according to the velocity decay method. On the other hand, for the operating tunnel in which the piston effect acts, a more complex process is performed; however, a reasonable wall friction coefficient can be estimated. This paper aims at suggesting a method to minimize the measurement variables of the piston effect and reviewing a method that can be applied to the operating tunnel. Also, in this study, a new method has been developed, which enables to calculate an variation of the piston effect if the piston effect is constant with a sudden change of external natural wind occurring while the wind speed in the tunnel decreases after the ventilation fan stops, and a programming logic has been also developed, which enables dynamic simulation analysis in order to estimate the wall friction coefficient in a tunnel.

Worst-Case Estimate of Envelope Correlation Coefficient for Small MIMO Mobile Antennas Below 1 GHz

  • Zhao, Xing;Tak, Jinpil;Choi, Jaehoon
    • Journal of electromagnetic engineering and science
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    • v.15 no.1
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    • pp.44-52
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    • 2015
  • A worst-case estimate of an envelope correlation coefficient (ECC) is obtained for small multiple-input multiple-output (MIMO) mobile antennas operating below 1 GHz. The worst-case estimate is numerically derived in this paper using spherical and exponential wave functions. The derived result confirms that the worst-case ECC can be easily obtained from the rotation angle between the radiation patterns of two MIMO elements, which are attained directly from the amplitude of 2D electric field patterns without any additional phase and polarization information. As a practical example, MIMO mobile antennas with different antenna element arrangements are compared to verify the validity of the proposed worst-case estimate. Moreover, based on these analyses, we also suggest an effective approach to reduce the ECC of a small MIMO mobile antenna operating below 1 GHz by properly locating the antenna elements to make the radiation patterns perpendicular to each other.

A Study on Correlations for Void Ratio, Coefficient of Uniformity and Coefficient of Curvature for Determination of Relative Density for Sands

  • Im, Soyeong;Jin, Yongguo;Chun, Byungsik
    • Journal of the Korean GEO-environmental Society
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    • v.14 no.3
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    • pp.13-17
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    • 2013
  • Determination of geotechnical characteristics of soil is either to use the field samples to measure the characteristics of soil through laboratory test or measuring the characteristics directly in the field. Field test can be derived similar value by considering characteristics of site and laboratory test can be confirmed the characteristic of soil by testing with field samples. This article describes relative density as the measure of compaction for cohesionless soils and presents several simple and mathematical relationships to help engineers estimate needed parameters for relative density calculations. The main purpose of this research is to investigate possible correlations between coefficient of uniformity, coefficient of curvature, maximum and minimum void ratio, mean grain size. Results show a linear relationship between the minimum and maximum void ratios and a power function relationship between coefficient of uniformity and the limiting void ratios. Void ratio range, which is the difference between the maximum and minimum void ratios, appeared to be log normally distributed but showed no simple mathematical fit to the data. these results were shown to help engineers estimate needed parameters for relative density calculations.

Estimation of Random Coefficient AR(1) Model for Panel Data

  • Son, Young-Sook
    • Journal of the Korean Statistical Society
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    • v.25 no.4
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    • pp.529-544
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    • 1996
  • This paper deals with the problem of estimating the autoregressive random coefficient of a first-order random coefficient autoregressive time series model applied to panel data of time series. The autoregressive random coefficients across individual units are assumed to be a random sample from a truncated normal distribution with the space (-1, 1) for stationarity. The estimates of random coefficients are obtained by an empirical Bayes procedure using the estimates of model parameters. Also, a Monte Carlo study is conducted to support the estimation procedure proposed in this paper. Finally, we apply our results to the economic panel data in Liu and Tiao(1980).

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HOPF'S BOUNDARY TYPE BEHAVIOR FOR AN INTERFACE PROBLEM

  • Beygmohammadi, Maryam;Sweers, Guido
    • Journal of the Korean Mathematical Society
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    • v.54 no.1
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    • pp.249-265
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    • 2017
  • Interface problem here refers to a second order elliptic problem with a discontinuous coefficient for the second order derivatives. For the corresponding boundary value problem, the maximum principle still holds but Hopf's boundary point lemma may fail. We will give an optimal power type estimate that replaces Hopf's lemma at those boundary points, where this coefficient jumps.