• Title/Summary/Keyword: velocity gradient

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Influence of electro-magneto-thermal environment on the wave propagation analysis of sandwich nano-beam based on nonlocal strain gradient theory and shear deformation theories

  • Arani, Ali Ghorbanpour;Pourjamshidian, Mahmoud;Arefi, Mohammad
    • Smart Structures and Systems
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    • v.20 no.3
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    • pp.329-342
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    • 2017
  • In this paper, the dispersion characteristics of elastic waves propagation in sandwich nano-beams with functionally graded (FG) face-sheets reinforced with carbon nanotubes (CNTs) is investigated based on various high order shear deformation beam theories (HOSDBTs) as well as nonlocal strain gradient theory (NSGT). In order to align CNTs as symmetric and asymmetric in top and bottom face-sheets with respect to neutral geometric axis of the sandwich nano-beam, various patterns are employed in this analysis. The sandwich nano-beam resting on Pasternak foundation is subjected to thermal, magnetic and electrical fields. In order to involve small scale parameter in governing equations, the NSGT is employed for this analysis. The governing equations of motion are derived using Hamilton's principle based on various HSDBTs. Then the governing equations are solved using analytical method. A detailed parametric study is conducted to study the effects of length scale parameter, different HSDBTs, the nonlocal parameter, various aligning of CNTs in thickness direction of face-sheets, different volume fraction of CNTs, foundation stiffness, applied voltage, magnetic intensity field and temperature change on the wave propagation characteristics of sandwich nano-beam. Also cut-off frequency and phase velocity are investigated in detail. According to results obtained, UU and VA patterns have the same cut-off frequency value but AV pattern has the lower value with respect to them.

Comparative Study on k-ε and k-ω Closures under the Condition of Turbulent Oscillatory Boundary Layer Flow at High Reynolds Number (높은 레이놀즈수를 가진 난류 진동 경계층에서의 k-ε과 k-ω 난류모형의 비교)

  • Son, Min-Woo;Lee, Guan-Hong;Lee, Kil-Seong;Lee, Du-Han
    • Journal of Korea Water Resources Association
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    • v.44 no.3
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    • pp.189-198
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    • 2011
  • The aim of this study is to compare k-$\varepsilon$ and k-$\omega$ closures under the condition of oscillatory layer flow at high Reynolds number. A one dimensional vertical model incorporated with flow momentum equations and turbulence models (k-$\varepsilon$ and k-$\omega$) is applied to the laboratory measurements in the turbulent oscillatory boundary layer. The numerical simulation reveals that both turbulence models calculate similar velocity profiles and turbulent kinetic energy (TKE). In addition, both deliver high accuracy under the condition of negligible spanwise pressure gradient. Therefore, it is recommended in this study to use k-$\varepsilon$ closure, of which numerical coefficients have been calibrated from many studies, for the cases of straight channel, estuary, and coastal environment where the spanwise pressure gradient is not significant.

Joint Inversion of DC Resistivity and Travel Time Tomography Data: Preliminary Results (전기비저항 주시 토모그래피 탐사자료 복합역산 기초 연구)

  • Kim, Jung-Ho;Yi, Myeong-Jong;Cho, Chang-Soo;Suh, Jung-Hee
    • Geophysics and Geophysical Exploration
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    • v.10 no.4
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    • pp.314-321
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    • 2007
  • Recently, multi-dimensional joint inversion of geophysical data based on fundamentally different physical properties is being actively studied. Joint inversion can provide a way to obtaining much more accurate image of the subsurface structure. Through the joint inversion, furthermore, it is possible to directly estimate non-geophysical material properties from geophysical measurements. In this study, we developed a new algorithm for jointly inverting dc resistivity and seismic traveltime data based on the multiple constraints: (1) structural similarity based on cross-gradient, (2) correlation between two different material properties, and (3) a priori information on the material property distribution. Through the numerical experiments of surface dc resistivity and seismic refraction surveys, the performance of the proposed algorithm was demonstrated and the effects of different regularizations were analyzed. In particular, we showed that the hidden layer problem in the seismic refraction method due to an inter-bedded low velocity layer can be solved by the joint inversion when appropriate constraints are applied.

A Study On IoT Data Consistency in IoT Environment (사물인터넷 환경에서 IoT 데이터 정합성 연구)

  • Choi, Changwon
    • Journal of Internet of Things and Convergence
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    • v.8 no.5
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    • pp.127-132
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    • 2022
  • As the IoT technology is more developed, it is more important for the accuracy of IoT data. Since the IoT data supports a different formats and protocols, it is often happened that the IoT system is failed or the incorrect data is generated with the unreliable IoT devices(sensor, actuator). Because the abnormality of IoT device or the user situation is not detected correctly, this problem makes the user to be unsatisfied with the IoT system. This study proposes the decision methodology of IoT data consistency whether the IoT data is generated in normal range or not by using the mathematical functions('gradient descent function' and 'linear regression function'). It may be concluded that the gradient function method is suitable for the IoT data which the 'increasing velocity' is related with the next generated pattern(eg. sensor devices), the linear regression function method is suitable for the IoT data which the 'the difference from linear regression function' is related with the next generated pattern in case the data has a linear pattern(eg. water meter, electric meter).

Improved prediction of soil liquefaction susceptibility using ensemble learning algorithms

  • Satyam Tiwari;Sarat K. Das;Madhumita Mohanty;Prakhar
    • Geomechanics and Engineering
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    • v.37 no.5
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    • pp.475-498
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    • 2024
  • The prediction of the susceptibility of soil to liquefaction using a limited set of parameters, particularly when dealing with highly unbalanced databases is a challenging problem. The current study focuses on different ensemble learning classification algorithms using highly unbalanced databases of results from in-situ tests; standard penetration test (SPT), shear wave velocity (Vs) test, and cone penetration test (CPT). The input parameters for these datasets consist of earthquake intensity parameters, strong ground motion parameters, and in-situ soil testing parameters. liquefaction index serving as the binary output parameter. After a rigorous comparison with existing literature, extreme gradient boosting (XGBoost), bagging, and random forest (RF) emerge as the most efficient models for liquefaction instance classification across different datasets. Notably, for SPT and Vs-based models, XGBoost exhibits superior performance, followed by Light gradient boosting machine (LightGBM) and Bagging, while for CPT-based models, Bagging ranks highest, followed by Gradient boosting and random forest, with CPT-based models demonstrating lower Gmean(error), rendering them preferable for soil liquefaction susceptibility prediction. Key parameters influencing model performance include internal friction angle of soil (ϕ) and percentage of fines less than 75 µ (F75) for SPT and Vs data and normalized average cone tip resistance (qc) and peak horizontal ground acceleration (amax) for CPT data. It was also observed that the addition of Vs measurement to SPT data increased the efficiency of the prediction in comparison to only SPT data. Furthermore, to enhance usability, a graphical user interface (GUI) for seamless classification operations based on provided input parameters was proposed.

Comparison between Human Follicular Fluid and SpermGrad for Sperm Preparation in Asthenozoospermia (무력정자증 환자에서 인간 난포액과 SpermGrad를 이용한 정자처리법의 비교)

  • Chung, Youn Kyung;Lee, Jung Ryeol;Moon, Jeong-Hee;Kim, Hyun-Jun;Han, Sang-Hoon;Jee, Byung-Chul;Ku, Seung-Yup;Suh, Chang-Suk;Kim, Seok-Hyun;Choi, Young-Min;Kim, Jung-Gu;Moon, Shin-Yong
    • Clinical and Experimental Reproductive Medicine
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    • v.33 no.1
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    • pp.53-60
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    • 2006
  • Objective: We tested the usefulness of swim-down technique using human follicular fluid (hFF) in sperm preparation. Methods: Semen samples were obtained from twelve male partners showing asthenozoospermia (sperm motility < 50%) at the time of routine andrologic evaluation in Seoul National University Bundang Hospital. After dividing into two aliquots, each samples were processed either by swim-down using 100% hFF or density gradient using SpermGrad. Sperm quality was assessed by computer-assisted semen analyzer (CASA). Results: Motility, Rapid motility, VCL (curvilinear velocity), ALH (amplitude of lateral head displacement), and hyperactivated sperms were significantly increased, and LIN (mean linearity) was decreased significantly after sperm preparation in both groups. Motility was significantly higher after swim-down using 100% hFF when compared with density gradient using SpermGrad ($81.2{\pm}4.7$ vs. $67.6{\pm}2.3$, p=0.02) The other parameters assessed by CASA were not different between the two methods. Conclusion: Swim-down method with 100% hFF may be a useful method in preparation of sperm from asthenozoospermia.

Transcatheter Intravascular Stent Placement in a Shih Tzu Dog with Refractory Pulmonic Stenosis (카테터를 통한 혈관스텐트 장착을 통한 심한 폐동맥협착증 치료 1례)

  • Kim, Hyun-Wook;Kim, Sung-Soo;Lee, Joon-Soek;Nam, So-Jeong;Choi, Ran;Hyun, Chang-Baig
    • Journal of Veterinary Clinics
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    • v.26 no.1
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    • pp.48-53
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    • 2009
  • A 4-year-old intact male Shih Tzu dog (5.4 kg of body weight) was referred with primary complaints of heart murmur and exercise intolerance. Diagnostic studies found severe valvular pulmonic stenosis (peak velocity of 6.4 m/s, pressure gradient 165 mmHg). The dog was treated with 3 cm (length) ${\times}$ 1.5 cm (diameter) of Palmaz biliary stent. The outcome of stent placement was favorable and remarkably reduced the severity of PS (6.4 m/s to 3.0 m/s of peak velocity). Clinical condition was remarkably improved with the absence of cardiac murmur, although mild pulmonic regurgitation existed from the day of stent placement. To our best knowledge, this case is the first clinical trial for treating PS with intravascular stent in Korea.

Premixture Composition Optimization for the Ram Accelerator Performance Enhancement (램 가속기 성능 향상을 위한 예 혼합기 조성비 최적화에 관한 연구)

  • 전용희;이재우;변영환
    • Journal of the Korean Society of Propulsion Engineers
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    • v.4 no.2
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    • pp.21-30
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    • 2000
  • Numerical design optimization techniques are implemented for the improvement of the ram accelerator performance. The design object is to find the minimum ram tube length required to accelerate projectile from initial velocity $V_o$ to target velocity $V_e$. The premixture is composed of $H_2$, $O_2$, $N_2$ and the mole numbers of these species are selected as design variables. The objective function and the constraints are linearized during the optimization process and gradient-based Simplex method and SLP(Sequential Linear Programming) have been employed. With the assumption of two dimensional inviscid flow for internal flow field, the analyses of the nonequilibrium chemical reactions for 8 steps 7 species have been performed. To determined the tube length, ram tube internal flow field is assumed to be in a quasi-steady state and the flow velocity is divided into several subregions with equal interval. Hence the thrust coefficients and accelerations for corresponding subregions are obtained and integrated for the whole velocity region. With the proposed design optimization techniques, the total ram tube length had been reduced 19% within 7 design iterations. This optimization procedure can be directly applied to the multi-stage, multi-premixture ram accelerator design optimization problems.

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Measurement of the Laminar Boundary Layer in a Streamwise Corner by using PIV Technique (PIV 기법을 이용한 Streamwise Corner 층류 경계층 측정 연구)

  • Park, Dong-Hun;Park, Seung-O;Kwon, Ki-Jung;Shim, Ho-Joon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.37 no.12
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    • pp.1165-1172
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    • 2009
  • The laminar boundary layer along a streamwise corner formed by two flat plates intersecting at right angle is measured by using Particle Image Velocimetry(PIV) technique. The free stream velocity ranges from 2.96m/s to 3.0m/s. The angle of incidence of the corner is set to 1.2 degree providing slightly favourable pressure gradient to ensure a laminar flow in the corner region. A round shape leading edge is used and the length of the model is about 1000mm. In the bisector plane, the measurement data show separation type velocity profiles having an inflection point which is a typical characteristic of laminar corner boundary layers. As the distance away from the bisector plane increases, velocity profiles are found to change into the Blasius profile. The change completes around half length of the boundary layer thickness in the bisector plane away from the bisector plane along the plate. In the bisector plane, the growth characteristic of the boundary layer thickness and the approximate similarity of velocity profiles are confirmed from the measurement data.

A STUDY OF LYNDS 1299 DARK CLOUD

  • RYU OK-KYUNGI;LEE YOUNGUNG
    • Journal of The Korean Astronomical Society
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    • v.31 no.2
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    • pp.161-171
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    • 1998
  • We have mapped about 1.5 square degree regions of Lynds 1299, a well isolated dark cloud in the Outer Galaxy (l = $122^{\circ}$, b = $-7^{\circ}$), in the J = 1- 0 transition of $^{12}CO$ and $^{13}CO$ with the 13.7 m radio telescope at Taeduk Radio Astronomy Observatory (TRAO). We found that there are two velocity components in the molecular emission, at $V_{LSR} = -52 km S^{-1}$ (Cloud A) and -8.8 km $s^{-1}$ (Cloud B), respectively. We have derived physical parameters of two molecular clouds and discussed three different mass estimate techniques. We found that there are large discrepancies between the virial and LTE mass estimates for both clouds. The large virial mass estimate reflects the fact that both are not gravitationally bound. We adopt the mass of $5.6 {\times}10^3 \;M{\bigodot}$ for Cloud A and $1.2{\times}10^3 \;M{\bigodot}$) for Cloud B using conversion factor. Cloud A is found to be associated with a localized star forming site, and its morphology is well matching with that of far-infrared (FIR) dust emission. It shows a clear ring structure with an obvious velocity gradient. We suggest that it may be a remnant cloud from a past episode of massive star formation. Cloud B is found to be unrelated to Cloud A (d = 800 pc) and has no specific velocity structure. The average dust color temperature of the uncontaminated portion of Cloud A is estimated to be 24$\~$27.4 K. The low dust temperature may imply that there is no additional internal heating source within the cloud. The heating of the cloud is probably dominated by the interstellar radiation field except the region directly associated with the new-born B5 star. Overall, the dust properties of Cloud A are similar to those of normal dark cloud even though it does have star forming activity.

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