• Title/Summary/Keyword: Parametric variations

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Axisymmetric vibrations of layered cylindrical shells of variable thickness using spline function approximation

  • Viswanathan, K.K.;Kim, Kyung Su;Lee, Jang Hyun;Lee, Chang Hyun;Lee, Jae Beom
    • Structural Engineering and Mechanics
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    • v.28 no.6
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    • pp.749-765
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    • 2008
  • Free axisymmetric vibrations of layered cylindrical shells of variable thickness are studied using spline function approximation techniques. Three different types of thickness variations are considered namely linear, exponential and sinusoidal. The equations of axisymmetric motion of layered cylindrical shells, on the longitudinal and transverse displacement components are obtained using Love's first approximation theory. A system of coupled differential equations on displacement functions are obtained by assuming the displacements in a separable form. Then the displacements are approximated using Bickley-spline approximation. The vibrations of two-layered cylindrical shells, made up of several types of layered materials and different boundary conditions are considered. Parametric studies have been made on the variation of frequency parameter with respect to the relative layer thickness, length ratio and type of thickness variation parameter.

Laser Welding Parameter Variations and its Application for Plastic Adhesion

  • Park, Sung-Jin;Park, Sung-Joon;Park, Hae-Young;Park, Jae-Wook;Sim, Ji-Young;Choi, Jin-Young;Kim, Hee-Je
    • Journal of Electrical Engineering and Technology
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    • v.2 no.1
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    • pp.112-117
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    • 2007
  • a parametric investigation was conducted to evaluate the effect of the laser beam for plastic adhesion. To determine the best condition for plastic adhesion, the $CO_2$(wavelength $10.6{\mu}m$) and nd:yag(wavelength $10.6{\mu}m$) laser were experimented with. From the experiment results obtained, the nd:yag laser was revealed to be the most suitable for plastic adhesion. In this study, three adhesion parameters such as input power level, working time of laser beam and pps(pulse per second) were systematically adjusted for suitable adhesion. From these experiments, it was observed that the target plastic melted and was evaporated by the nd:yag laser. Furthermore, the relationships between adhesive surface by laser beam and above three parameters were discovered.

A Robust Dynamic Decoupling Control Scheme for PMSM Current Loops Based on Improved Sliding Mode Observer

  • Shen, Hanlin;Luo, Xin;Liang, Guilin;Shen, Anwen
    • Journal of Power Electronics
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    • v.18 no.6
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    • pp.1708-1719
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    • 2018
  • A complete current loop decoupling control strategy based on a sliding mode observer (SMO) is proposed to eliminate the influence of current dynamic coupling and back electromotive force (EMF) in the vector control of permanent magnet synchronous motors. With this strategy, current dynamic decoupling and back EMF compensation can be simultaneously achieved. Unlike conventional methods, the proposed strategy can avoid the disturbances caused by the parametric variations of motor systems and maintain the advantages of proportional integral (PI) controllers, which are robust and easy to operate. An improved SMO, which uses a special PI regulator other than a linear saturation function as the equivalent control law in the boundary layer of a sliding surface, is proposed to eliminate the estimated errors caused by the quasi-sliding mode and obtain a satisfactory decoupling performance. The stability and parameter robustness of the proposed strategy are also analyzed. Physical experimental results are presented to verify the validity of the method.

Investigations on seismic response of two span cable-stayed bridges

  • Bhagwat, Madhav;Sasmal, Saptarshi;Novak, B.;Upadhyay, A.
    • Earthquakes and Structures
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    • v.2 no.4
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    • pp.337-356
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    • 2011
  • In this paper, cable-stayed bridges with single pylon and two equal side spans, with variations in geometry and span ranging from 120 m to 240 m have been studied. 3D models of the bridges considered in this study have been analysed using ANSYS. As the first step towards a detailed seismic analysis, free vibration response of different geometries is studied for their mode shapes and frequencies. Typical pattern of free vibration responses in different frequencies with change in geometry is observed. Further, three different seismic loading histories are chosen with various characteristics to find the structural response of different geometries under seismic loading. Effect of variation in pylon shape, cable arrangement with variation in span is found to have typical characteristics with different structural response under seismic loading. From the study, it is observed that the structural response is very much dependent on the geometry of the cable-stayed bridge and the characteristics of the seismic loading as well. Further, structural responses obtained from the study would help the design engineers to take decisions on geometric shapes of the bridges to be constructed in seismic prone zones.

Numerical analysis on the behaviour of reinforced concrete frame structures in fire

  • Dzolev, Igor M.;Cvetkovska, Meri J.;Ladinovic, Dorde Z.;Radonjanin, Vlastimir S.
    • Computers and Concrete
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    • v.21 no.6
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    • pp.637-647
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    • 2018
  • Numerical approach using finite element method has been used to evaluate the behaviour of reinforced concrete frame structure subjected to fire. The structure is previously designed in accordance with Eurocode standards for the design of structures for earthquake resistance, for the ductility class M. Thermal and structural response are obtained using a commercially available software ANSYS. Temperature-dependent nonlinear thermal and mechanical properties are adopted according to Eurocode standards, with the application of constitutive model for the triaxial behaviour of concrete with a smeared crack approach. Discrete modelling of concrete and reinforcement has enabled monitoring of the behaviour at a global, as well as at a local level, providing information on the level of damage occurring during fire. Critical regions in frame structures are identified and assessed, based on temperatures, displacements, variations of internal forces magnitudes and achieved plastic deformations of main reinforcement bars. Parametric analyses are conducted for different fire scenarios and different types of concrete aggregate to determine their effect on global deformations of frame structures. According to analyses results, the three-dimensional finite element model can be used to evaluate the insulation and mechanical resistance criteria of reinforced concrete frame structures subjected to nominal fire curves.

One-dimensional nonlinear consolidation behavior of structured soft clay under time-dependent loading

  • Liu, Weizheng;Shi, Zhiguo;Zhang, Junhui;Zhang, Dingwen
    • Geomechanics and Engineering
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    • v.18 no.3
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    • pp.299-313
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    • 2019
  • This research investigated the nonlinear compressibility, permeability, the yielding due to structural degradation and their effects on consolidation behavior of structured soft soils. Based on oedometer and hydraulic conductivity test results of natural and reconstituted soft clays, linear log (1+e) ~ $log\;{\sigma}^{\prime}$ and log (1+e) ~ $log\;k_v$ relationships were developed to capture the variations in compressibility and permeability, and the yield stress ratio (YSR) was introduced to characterize the soil structure of natural soft clay. Semi-analytical solutions for one-dimensional consolidation of soft clay under time-dependent loading incorporating the effects of soil nonlinearity and soil structure were proposed. The semi-analytical solutions were verified against field measurements of a well-documented test embankment and they can give better accuracy in prediction of excess pore pressure compared to the predictions using the existing analytical solutions. Additionally, parametric studies were conducted to analyze the effects of YSR, compression index (${\lambda}_r$ and ${\lambda}_c$), and permeability index (${\eta}_k$) on the consolidation behavior of structured soft clays. The magnitude of the difference between degree of consolidation based on excess pore pressure ($U_p$) and that based on strain ($U_s$) depends on YSR. The parameter ${\lambda}_c/{\eta}_k$ plays a significant role in predicting consolidation behavior.

Influences of porosity on dynamic response of FG plates resting on Winkler/Pasternak/Kerr foundation using quasi 3D HSDT

  • Addou, Farouk Yahia;Meradjah, Mustapha;Bousahla, Abdelmoumen Anis;Benachour, Abdelkader;Bourada, Fouad;Tounsi, Abdelouahed;Mahmoud, S.R.
    • Computers and Concrete
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    • v.24 no.4
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    • pp.347-367
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    • 2019
  • This work investigates the effect of Winkler/Pasternak/Kerr foundation and porosity on dynamic behavior of FG plates using a simple quasi-3D hyperbolic theory. Four different patterns of porosity variations are considered in this study. The used quasi-3D hyperbolic theory is simple and easy to apply because it considers only four-unknown variables to determine the four coupled vibration responses (axial-shear-flexion-stretching). A detailed parametric study is established to evaluate the influences of gradient index, porosity parameter, stiffness of foundation parameters, mode numbers, and geometry on the natural frequencies of imperfect FG plates.

A comparative study of the models to predict aeroelastic vibrations of circular cylinder and chimneys

  • Rahman, Saba;Jain, Arvind K.;Bharti, S.D.;Datta, T.K.
    • Wind and Structures
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    • v.35 no.1
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    • pp.35-54
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    • 2022
  • A comparative study of aeroelastic vibrations of spring-mass cylinder and chimneys, with the help of a few wake oscillator models available in the literature, is presented. The models include those proposed by Facchinetti, Farshidian and Dolatabadi method-I, Farshidian and Dolatabadi method-II, de Langre, Skop and Griffin. Besides, the linear model proposed by Simiu and Scanlan is also incorporated in the study. For chimneys, the first mode oscillation is considered, and the top displacements of the chimneys are evaluated using the considered models. The results of the analytical model are compared with those obtained from the numerical solution of the wake-oscillator coupled equations. The response behavior of the cylinder and three chimneys of different heights are studied and compared with respect to critical parametric variations. The results of the study indicate that the numerical analysis is essential to capture the effect of non-linear aeroelastic phenomena in the solutions, especially for small damping. Further, except for the models proposed by Farshidian and Dolatabadi, other models predict nearly the same responses. The non-linear model predicts a much higher response as compared to the linear model.

Mechanical behavior of RC beams bonded with thin porous FGM plates: Case of fiber concretes based on local materials from the mountains of the Tiaret highlands

  • Benferhat Rabia;Tahar Hassaine Daouadji;Rabahi Abderezak
    • Coupled systems mechanics
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    • v.12 no.3
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    • pp.241-260
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    • 2023
  • The objective of this study is to evaluate the effects of adding fibers to concrete and the distribution rate of the porosity on the interfacial stresses of the beams strengthened with various types of functionally graded porous (FGP) plate. Toward this goal, the beams strengthened with FGP plate were considered and subjected to uniform loading. Three types of beams are considered namely RC beam, RC beam reinforced with metal fibers (RCFM) and RC beam reinforced with Alfa fibers (RCFA). From an analytical development, shear and normal interfacial stresses along the length of the FGP plates were obtained. The accuracy and validity of the proposed theoretical formula are confirmed by the others theoretical results. The results showed clearly that adding fibers to concrete and the distribution rate of the porosity have significant influence on the interfacial stresses of the beams strengthened with FGP plates. Finally, parametric studies are carried out to demonstrate the effect of the mechanical properties and thickness variations of FGP plate, concrete and adhesive on interface debonding, we can conclude that, This research is helpful for the understanding on mechanical behavior of the interface and design of the FRP-RC hybrid structures.

Time-Series Estimation based AI Algorithm for Energy Management in a Virtual Power Plant System

  • Yeonwoo LEE
    • Korean Journal of Artificial Intelligence
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    • v.12 no.1
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    • pp.17-24
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    • 2024
  • This paper introduces a novel approach to time-series estimation for energy load forecasting within Virtual Power Plant (VPP) systems, leveraging advanced artificial intelligence (AI) algorithms, namely Long Short-Term Memory (LSTM) and Seasonal Autoregressive Integrated Moving Average (SARIMA). Virtual power plants, which integrate diverse microgrids managed by Energy Management Systems (EMS), require precise forecasting techniques to balance energy supply and demand efficiently. The paper introduces a hybrid-method forecasting model combining a parametric-based statistical technique and an AI algorithm. The LSTM algorithm is particularly employed to discern pattern correlations over fixed intervals, crucial for predicting accurate future energy loads. SARIMA is applied to generate time-series forecasts, accounting for non-stationary and seasonal variations. The forecasting model incorporates a broad spectrum of distributed energy resources, including renewable energy sources and conventional power plants. Data spanning a decade, sourced from the Korea Power Exchange (KPX) Electrical Power Statistical Information System (EPSIS), were utilized to validate the model. The proposed hybrid LSTM-SARIMA model with parameter sets (1, 1, 1, 12) and (2, 1, 1, 12) demonstrated a high fidelity to the actual observed data. Thus, it is concluded that the optimized system notably surpasses traditional forecasting methods, indicating that this model offers a viable solution for EMS to enhance short-term load forecasting.