Browsing by Author "Huang, C. S."

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Accurate frequencies and mode shapes for moderately thick, cantilevered, skew plates
(2007-09-01)
Leissa, A. W.
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Huang, C. S.
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Chang, M. J.
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土木工程學系
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Department of Civil Engineering
Accurate free vibration frequencies and mode shapes are presented for complete sets of moderately thick, cantilevered skew plates of triangular, trapezoidal and parallelogram shape. These accurate results are obtained by using the Ritz method applied to the Mindlin plate theory. Two sets of functions are employed simultaneously for each of the three dependent variables: transverse displacement (w) and bending rotations (phi(x) and phi(y)). One set is the widely used algebraic polynomials. The other is the set of corner functions which provide the proper stress singularities in the reentrant clamped-free corner, and accelerates the convergence of the solutions. The extensive frequencies presented are exact to the four digits shown. Corresponding mode shapes are also shown, by means of nodal patterns, most of which are novel in the published literature.
Accurate vibration analysis of thick, cracked rectangular plates
(2011-04-25)
Huang, C. S.
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Leissa, A. W.
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Li, R. S.
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土木工程學系
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Department of Civil Engineering
This work applies the Ritz method to accurately determine the frequencies and nodal patterns of thick, cracked rectangular plates analyzed using Mindlin plate theory. Two types of cracked configuration are considered, namely, side crack and internal crack. To enhance the capabilities of the Ritz method in dealing with cracked plates, new sets of admissible functions are proposed to represent the behaviors of true solutions along the crack. The proposed admissible functions appropriately describe the stress singularity behaviors around a crack tip and the discontinuities of transverse displacement and bending rotations across the crack. The present solutions monotonically converge to the exact frequencies as upper bounds when the number of admissible functions increases. The validity and accuracy of the present solutions are confirmed through comprehensive convergence studies and comparison with the published results based on the classical thin plate theory. The proposed approach is further employed to investigate the effects of the length, location, and orientation of crack on frequencies and nodal patterns of simply supported and cantilevered cracked rectangular plates. The results shown are the first ones available in the published literature. (C) 2010 Elsevier Ltd. All rights reserved.
An analytical solution for tidal fluctuations in unconfined aquifers with a vertical beach
(2010-10-22)
Yeh, H. D.
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Huang, C. S.
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Chang, Y. C.
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Jeng, D. S.
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環境工程研究所
The perturbation technique has been commonly used to develop analytical solutions for simulating the dynamic response of tidal fluctuations in unconfined aquifers. However, the solutions obtained from the perturbation method might result in poor accuracy for the case of the perturbation parameter being not small enough. In this paper, we develop a new analytical model for describing the water table fluctuations in unconfined aquifers, based on Laplace and Fourier transforms. In the new approach, the mean sea level is used as the initial condition and a free surface equation, neglecting the second-order slope terms, as the upper boundary condition. Numerical results show that the present solution agrees well with the finite different model with the second-order surface terms. Unlike Teo et al.'s (2003) approximation which restricts on the case of shallow aquifers, the present model can be applied to most of the tidal aquifers except for the very shallow one. In addition, a large-time solution in terms of sine function is provided and examined graphically with four different tidal periods.
An Application of Gram-Schmidt Process on Structural Modal Parameters Identification
(2017-01-01)
Su, W. C.
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Huang, C. S.
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土木工程學系
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Department of Civil Engineering
Structural modal parameters identification based on the measured responses of structure is a major topic for structural health monitoring. This work presents the use of a Gram-Schmidt process to improve. the accuracy of the identified modal parameters. The wavelet transforms is applied to the measured acceleration responses of a structural system, and to reconstruct the autoregressive with exogenous input (ARX) model in wavelet domain. Next, the identified modal parameters would be calculated from the coefficients matrix. Finally, correcting the identified mode shapes via Gram-Schmidt process. The accuracy of this procedure is numerically confirmed; the effects of the wavelet parameters and noise on the ability to accurately estimate the dynamic characteristics are also investigated.
Application of Cauchy wavelet transformation to identify time-variant modal parameters of structures
(2016-12-01)
Huang, C. S.
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Liu, C. Y.
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Su, W. C.
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交大名義發表
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National Chiao Tung University
This work proposes a procedure for accurately identifying instantaneous modal parameters of a linear time-varying system using a time-varying autoregressive with exogenous input (TVARX) model with the continuous Cauchy wavelet transform (CCWT). An appropriate TVARX model is established using the velocity and displacement responses of the system under consideration. The time-varying coefficients of the TVARX are expanded as piecewise polynomial functions. CCWTs with various scale parameters are then applied to the TVARX model to evaluate the instantaneous modal parameters of different modes. The CCWTs of the velocity and displacement responses are analytically obtained from the CCWT of the measured acceleration responses. The effectiveness and accuracy of the proposed procedure are validated by numerical simulations of single and multiple degrees of freedom systems that have periodically varying and sharply varying stiffness and damping coefficients. The effects of noise, the Cauchy wavelet function and the order of the polynomial on the evaluation of the modal parameters are explored in processing the numerically simulated acceleration responses of systems with a single degree of freedom subjected to base excitation. Finally, the proposed procedure is adopted to determine the modal parameters of a five-story symmetric steel frame from its measured acceleration responses in a shaking table test. The measured strains reveal the yielding of columns in the first story. The variations of the identified instantaneous natural frequencies and modal damping ratios with time are consistent with the physical phenomena that are observed from the measured strains and base excitation acceleration. (C) 2016 Elsevier Ltd. All rights reserved.
Corner stress singularities in an FGM thin plate
(2007-05-01)
Huang, C. S.
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Chang, M. J.
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土木工程學系
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Department of Civil Engineering
Describing the behaviors of stress singularities correctly is essential for obtaining accurate numerical solutions of complicated problems with stress singularities. This analysis derives asymptotic solutions for functionally graded material (FGM) thin plates with geometrically induced stress singularities. The classical thin plate theory is used to establish the equilibrium equations for FGM thin plates. It is assumed that the Young's modulus varies along the thickness and Poisson's ratio is constant. The eigenfunction expansion method is employed to the equilibrium equations in terms of displacement components for an asymptotic analysis in the vicinity of a sharp corner. The characteristic equations for determining the stress singularity order at the corner vertex and the corresponding corner functions are explicitly given for different combinations of boundary conditions along the radial edges forming the sharp corner. The non-homogeneous elasticity properties are present only in the characteristic equations corresponding to boundary conditions involving simple support. Finally, the effects of material non-homogeneity following a power law on the stress singularity orders are thoroughly examined by showing the minimum real values of the roots of the characteristic equations varying with the material properties and vertex angle. (c) 2006 Elsevier Ltd. All rights reserved.
DETECTION OF DAMAGE LOCATION USING A NOVEL SUBSTRUCTURE-BASED FREQUENCY RESPONSE FUNCTION APPROACH WITH A WIRELESS SENSING SYSTEM
(2012-07-01)
Lin, T. K.
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Hung, S. L.
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Huang, C. S.
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土木工程學系
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Department of Civil Engineering
"This paper intends to detect the damage locations for building structures under an earthquake excitation using a novel substructure-based FRF approach with a damage location index (SubFRFDI). An Imote2.NET-based wireless structural health monitoring system was developed and employed in the experimental studies for the sake of deployment flexibility, low maintenance cost, low power consumption, self-organization capability, and wireless communication capability. The feasibility of the proposed approach for damage detection was examined using the numerical response of a six-storey shear plane frame structure subjected to a base excitation. The results demonstrate that the SubFRFDI can be successfully used to identify the damage of different levels at a single site or multiple sites. The SubFRFDI is independent of the responses to various input earthquake excitations. Even with the addition of noises, the SubFRFDI still functions well. The feasibility and robustness of the proposed Imote2.NET-based wireless structural health monitoring system were assessed using a 1/8-scale three-storey steel-frame model. Following this, the proposed SubFRFDI was further applied to identifying the damage locations in a 1/4-scale six-storey steel structure with the proposed Imote2.NET-based wireless monitoring system. It was confirmed experimentally that good data transportation quality can be achieved via reliable data transmission and sensing protocol in identifying the structural dynamic properties, and the proposed SubFRFDI can be used to identify the damage locations effectively."
DYNAMIC ANALYSES OF A FLEXIBLE VEHICLE MOVING ALONG A FLEXIBLE GUIDEWAY CONSIDERING THE TIP-OFF EFFECT
(2013-02-01)
Chou, S. N.
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Cheng, F. P.
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Huang, C. S.
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土木工程學系
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Department of Civil Engineering
A semi-analytical solution for the tip-off response of a vehicle moving along a guideway is obtained, considering the dynamic interaction between the two subsystems. The guideway is modeled as an inclined simply-supported uniform flexible beam, and the vehicle as a flexible free-free beam under a pre-specified thrust force. The equations of motion for the vehicle and guideway are developed using the Lagrangian approach and the assumed mode method based on the Euler-Bernoulli hypothesis. In the form of nonlinear differential equations, they are solved by the Petzold-Gear backward differentiation formula (BDF) method. The solutions obtained are validated by comparing them with the published results for the models with a rigid vehicle running over a rigid guideway or a flexible guideway. Comparisons of the present solutions with the existing ones for the vehicle and guideway reveal the advantages of the approach proposed herein. Other effects on the tip-off responses of the vehicle that are investigated include the length of the guideway, distance between the shoes of the vehicle, and mass and rigidity ratios of the vehicle to the guideway. The results presented herein provide valuable information for the design of the vehicle launch system.
Effect of imperfect interfaces on the field response of multilayered magneto-electroelastic composites under surface loading
(2019-11-01)
Kuo, H. Y.
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Huang, C. S.
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Pan, E.
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土木工程學系
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Department of Civil Engineering
Layered magneto-electro-elastic (MEE) composites with imperfect interface have been investigated in recent years for enhancing the important magnetoelectric coupling effect. However, the impact of the imperfect interface on the elastic, electric and magnetic behaviors has not been studied in details so far. In this paper, a simply supported and multilayered MEE plate with one of the typical imperfect interfaces is proposed to deeply understand the response of the layered plate under surface loading, which mimics the simple tests used in experiments. Based on the extended pseud Stroh formalism and the dual variable and position method, the analytical solutions for anisotropic and multilayered MEE plates with imperfect interfaces are derived. In our numerical studies, we choose BaTiO3 (BTO) as the piezoelectric phase and CoFe2O4 (CFO) as the piezomagnetic phase to construct two sandwich plates (BTO/CFO/BTO, and CFO/BTO/CFO). Under surface loading, responses of these two sandwich plates are analyzed which demonstrate the possibility of optimal tuning the elastic, electric and magnetic fields.
Effects of the catalyst pretreatment on CO2 sensors made by carbon nanotubes
(2008-04-01)
Huang, C. S.
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Huang, B. R.
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Hsiao, C. H.
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Yeh, C. Y.
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Huang, C. C.
A novel CO2 sensor was made by carbon nanotubes (CNTs). The CNTs were synthesized by catalystic thermal chemical vapour deposition at 700 degrees C. Prior to the synthesis, the Fe catalysts were pretreated by H-2 plasma for different times. Two terminal resistance of the as-grown CNTs mat was measured under different CO2 concentrations. It was found that without the catalyst pretreatment, the sensitivity was about 4% when the CNTs mat was exposed to 800 mTorr CO2 concentration. However, with various catalyst pretreatment times of 5, 10, 15 and 20 min, the sensitivity was 3.69%, 6.27%, 9.54%, and 12.1%, respectively. The Raman spectroscopy showed the I-D/I-G decreased from 0.668 to 0.539 as the catalyst pretreatment time increased. The XPS also showed the correlation of surface chemical components with the Raman spectroscopy. The Fe catalyst H-2 plasma pretreatment affected both the graphitization and surface binding sites of CNTs. (C) 2007 Elsevier B.V. All rights reserved.
Enhanced planar poly-Si TFT EEPROM cell for system on panel applications
(2007)
Liu, Po-Tsun
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Huang, C. S.
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Chen, C. W.
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光電工程學系
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顯示科技研究所
In this work an enhanced electrically erasable programmable read-only memory (EEPROM) device comprised of twin low-temperature poly-Si thin-film transistors (TFTs) was fabricated for potential application to system-on-panel technology. Also, two kinds of memory devices with different overlap areas were developed to investigate the gate-coupling effect. The memory window of 4.8 and 4 V can be obtained at a programming voltage of 18 V, separately, for the fully overlapped EEPROM and the one with a 1 mu m length overlap between the gate and source/drain. The excellent memory characteristics of the fully overlapped TFT EEPROM cell are attributed to the enhanced gate-coupling ratio by maximizing the overlap coverage between the gate electrode and the source/drain regions. (c) 2007 The Electrochemical Society.
Fourier series solutions for vibrations of a rectangular plate with a straight through crack
(2016-12)
Huang, C. S.
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Lin, Y. J.
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土木工程學系
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Department of Civil Engineering
The existence of a crack in a rectangular plate makes the exact closed-form solutions for the vibrations of the plate intractable, if they even exist. This work presents analytical solutions for vibrations of horizontally or vertically cracked rectangular plates under various boundary conditions. The solutions are constructed by combining Fourier cosine series with domain decomposition. A rectangular plate with a side crack or an internal crack is divided into four or six rectangular sub-domains, respectively. The series solutions that satisfy the governing equations for the vibrations of a plate are firstly established for each sub-domain based on the classical plate theory. The solutions for each sub-domain are related to each other by satisfying the continuity conditions along the interconnection boundaries between the sub-domains. Finally, the boundary conditions of the cracked plate are imposed on the solutions. Comprehensive convergence studies are performed for intact plates and cracked plates with various boundary conditions, and the presented natural frequencies are compared with the published ones to confirm the correctness of the proposed solutions. Not like a typical energy method, which overpredicts true frequencies if the used shape functions do not exactly satisfy the governing equations for the problem under consideration, the convergence studies reveal that the present solutions converge from the lower bounds to the exact frequencies as the number of series terms increases. The present solutions are further applied to determine the first five frequencies of vibration of rectangular plates with side cracks and internal cracks of various lengths and locations. The results obtained under SSSS, CFFF, FSFS and FFFF boundary conditions are tabulated, and some of these are presented here for the first time. (C) 2016 Elsevier Inc. All rights reserved.
Fourier series solutions for vibrations of a rectangular plate with a straight through crack
(2016-12)
Huang, C. S.
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Lin, Y. J.
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土木工程學系
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Department of Civil Engineering
The existence of a crack in a rectangular plate makes the exact closed-form solutions for the vibrations of the plate intractable, if they even exist. This work presents analytical solutions for vibrations of horizontally or vertically cracked rectangular plates under various boundary conditions. The solutions are constructed by combining Fourier cosine series with domain decomposition. A rectangular plate with a side crack or an internal crack is divided into four or six rectangular sub-domains, respectively. The series solutions that satisfy the governing equations for the vibrations of a plate are firstly established for each sub-domain based on the classical plate theory. The solutions for each sub-domain are related to each other by satisfying the continuity conditions along the interconnection boundaries between the sub-domains. Finally, the boundary conditions of the cracked plate are imposed on the solutions. Comprehensive convergence studies are performed for intact plates and cracked plates with various boundary conditions, and the presented natural frequencies are compared with the published ones to confirm the correctness of the proposed solutions. Not like a typical energy method, which overpredicts true frequencies if the used shape functions do not exactly satisfy the governing equations for the problem under consideration, the convergence studies reveal that the present solutions converge from the lower bounds to the exact frequencies as the number of series terms increases. The present solutions are further applied to determine the first five frequencies of vibration of rectangular plates with side cracks and internal cracks of various lengths and locations. The results obtained under SSSS, CFFF, FSFS and FFFF boundary conditions are tabulated, and some of these are presented here for the first time. (C) 2016 Elsevier Inc. All rights reserved.
Geometrically induced stress singularities in a piezoelectric body of revolution
(2011-09-01)
Huang, C. S.
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Hu, C. N.
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土木工程學系
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Department of Civil Engineering
An eigenfunction expansion approach is combined with a power series solution technique to establish the asymptotic solutions for geometrically induced electroelastic singularities in a piezoelectric body of revolution, with its direction of polarization not parallel to the axis of revolution. The asymptotic solutions are obtained by directly solving the three-dimensional equilibrium and Maxwell's equations in terms of displacement components and electric potential. When the direction of polarization is not along the axis of revolution, the assumption of axisymmetric deformation that is often made in the published literature is not valid, and the direction of polarization and the circular coordinate variable can substantially affect the singularities. The numerical results related to singularity orders are shown in graphical form for bodies of revolution that comprise a single material (PZT-4 or PZT-5H) or bonded piezo/piezo (PZT-4/PZT-5H) or piezo/isotropic elastic (PZT-4/Al or PZT-5H/Al) materials. This is the first study to present results for the direction of polarization not along the axis of revolution. (C) 2011 Elsevier Ltd. All rights reserved.
Geometrically Induced Stress Singularities of a Thick FGM Plate Based on the Third-Order Shear Deformation Theory
(2009)
Huang, C. S.
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Chang, M. J.
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土木工程學系
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Department of Civil Engineering
Asymptotic solutions for a functionally graded material (FGM) plate are developed to elucidate stress singularities at a plate corner, using a third-order shear deformation theory. The characteristic equations are given explicitly for determining the order of stress singularity at the vertex of a corner with two radial edges having various boundary conditions. The non-homogeneous elasticity properties are present only in the characteristic equations for a corner with one of its two edges simply supported. The effects of material non-homogeneity on the stress singularities are extensively examined. The present results are very useful for developing accurate numerical solutions for an FGM plate under static or dynamic loading when the plate involves stress singularities, such as a V-notch or crack.
Geometrically-induced singularities in functionally graded magneto-electro-elastic wedges
(2014-12-01)
Huang, C. S.
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Hu, C. N.
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土木工程學系
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Department of Civil Engineering
Asymptotic solutions are proposed for geometrically-induced magneto-electro-elastic (MEE) singularities at the vertex of a rectilinearly polarized wedge that is made of functionally graded magneto-electro-elastic (FGMEE) materials. The material properties are assumed to vary along the thickness, of the wedge, and the direction of polarization may not be parallel or perpendicular to the thickness direction. An eigenfunction expansion approach with the power series solution technique and domain decomposition is adopted to establish the asymptotic solutions by directly solving the three-dimensional equations of motion and Maxwell\'s equations in terms of mechanical displacement components and electric and magnetic potentials. Since the direction of polarization can be arbitrary in space, the in-plane components of displacement, electric and magnetic fields are generally coupled with the out-of-plane components. The solutions are presented here for the first time. The correctness of the proposed solutions is confirmed by comparing the orders of MEE singularities with the published results for wedges under anti-plane deformation and in-plane electric and magnetic fields. The proposed solutions are further employed to investigate the effects of the direction of polarization, vertex angle, boundary conditions and material-property gradient index on the MEE singularities in BaTiO3-CoFe2O4 wedges. (C) 2014 Elsevier Ltd. All rights reserved.
Identification of Instantaneous Modal Parameter of Time-Varying Systems via a Wavelet-Based Approach and Its Application
(2014-04-01)
Su, W. C.
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Liu, C. Y.
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Huang, C. S.
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交大名義發表
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National Chiao Tung University
This work presents an efficient approach using time-varying autoregressive with exogenous input (TVARX) model and a substructure technique to identify the instantaneous modal parameters of a linear time-varying structure and its substructures. The identified instantaneous natural frequencies can be used to identify earthquake damage to a building, including the specific floors that are damaged. An appropriate TVARX model of the dynamic responses of a structure or substructure is established using a basis function expansion and regression approach combined with continuous wavelet transform. The effectiveness of the proposed approach is validated using numerically simulated earthquake responses of a five-storey shear building with time-varying stiffness and damping coefficients. In terms of accuracy in determining the instantaneous modal parameters of a structure from noisy responses, the proposed approach is superior to typical basis function expansion and regression approach. The proposed method is further applied to process the dynamic responses of an eight-storey steel frame in shaking table tests to identify its instantaneous modal parameters and to locate the storeys whose columns yielded under a strong base excitation.
Identification of modal parameters of a time invariant linear system by continuous wavelet transformation
(2007-05-01)
Huang, C. S.
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Su, W. C.
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土木工程學系
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Department of Civil Engineering
The applications of wavelet transforms have received significant attentions in many fields. This work proposes a procedure for identifying modal parameters of a linear system using the continuous wavelet transform. The merits of the proposed procedure over the exiting schemes of applying the wavelet transform to system identification for a linear system are in use of the time invariance property and filtering ability of the transform to enhance the efficiency of identifying the modal parameters of a structure from its earthquake responses or free vibration responses. The effectiveness and accuracy of the proposed procedure are validated via numerical simulations. The effects of noise and wavelet function on identifying the modal parameters of the structure are also explored in processing the numerically simulated acceleration responses of a six-story shear building subjected to base excitation. The dynamic characteristics of close modes are accurately determined. Finally, the proposed procedure is adopted to obtain the modal parameters of a three-story non-symmetric steel frame from its measured acceleration responses in a shaking table test. A total of nine modes are identified, including modes with high frequencies and very small amplitude. (c) 2006 Elsevier Ltd. All rights reserved.
Identification of Time-Variant Modal Parameters Using Time-Varying Autoregressive with Exogenous Input and Low-Order Polynomial Function
(2009)
Huang, C. S.
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Hung, S. L.
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Su, W. C.
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Wu, C. L.
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土木工程學系
This work presents an approach that accurately identifies instantaneous modal parameters of a structure using time-varying autoregressive with exogenous input (TVARX) model. By developing the equivalent relations between the equation of motion of a time-varying structural system and the TVARX model, this work proves that instantaneous modal parameters of a time-varying system can be directly estimated from the TVARX model coefficients established from displacement responses. A moving least-squares technique incorporating polynomial basis functions is adopted to approximate the coefficient functions of the TVARX model. The coefficient functions of the TVARX model are represented by polynomials having time-dependent coefficients, instead of constant coefficients as in traditional basis function expansion approaches, so that only low orders of polynomial basis functions are needed. Numerical studies are carried out to investigate the effects of parameters in the proposed approach on accurately determining instantaneous modal parameters. Numerical analyses also demonstrate that the proposed approach is superior to some published techniques (i.e., recursive technique with a forgetting factor, traditional basis function expansion approach, and weighted basis function expansion approach) in accurately estimating instantaneous modal parameters of a structure. Finally, the proposed approach is applied to process measured data for a frame specimen subjected to a series of base excitations in shaking table tests. The specimen was damaged during testing. The identified instantaneous modal parameters are consistent with observed physical phenomena.
Identifying the Modal Parameters of a Structure from Ambient Vibration Data via the Stationary Wavelet Packet
(2014-11-01)
Su, W. C.
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Huang, C. S.
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Chen, C. H.
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Liu, C. Y.
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Huang, H. C.
Ambient vibration tests are conducted widely to estimate the modal parameters of a structure. The work proposes an efficient wavelet-based approach to determine the modal parameters of a structure from its ambient vibration responses. The proposed approach integrates the time series autoregressive (AR) model with the stationary wavelet packet transform. In addition to providing a richer decomposition and allowing for an improved time-frequency localization of signals over that of the discrete wavelet transform, the stationary wavelet packet transform also has significantly higher computational efficiency than the wavelet packet transform in terms of decomposing time-shifted signals because the former has a time-invariance property. The correlation matrices needed in determining the coefficient matrices in an AR model are established in subspaces expanded by stationary wavelet packets. The formulation for estimating the correlation matrices is shown for the first time. Because different subspaces contain signals with different frequency subbands, the fine filtering property enhances the ability of the proposed approach to identify not only the modes with strong modal interference, but also many modes from the responses of very few measured degrees of freedom. The proposed approach is validated by processing the numerically simulated responses of a seven-floor shear building, which has closely spaced modes, with considering the effects of noise and incomplete measurements. Furthermore, the present approach is employed to process the velocity responses of an eight-storey steel frame subjected to white noise input in a shaking table test and ambient vibration responses of a cable-stayed bridge.