Unit Impulse Response Function Research Articles

A time-domain soil structure interaction analysis for wave scattering in 3D layered half-space

A direct time-domain Soil Structure Interaction (SSI) model is proposed to analyze the scattering problems in 3D horizontal layered half-space. This model uses the scaling surface based Scaled Boundary Finite Element Method (SBFEM) to simulate the infinite domain. Additionally, it employs a combined approach, merging the Domain Reduction Method (DRM) with ray tracking algorithm to calculate the effective nodal forces of seismic input. Compared to the original SBFEM, the scaling surface based SBFEM overcomes the limitation of scaling requirements, and the acceleration unit-impulse response function computed by this method satisfies the radiation damping of 3D horizontal layered half-space. For the seismic input, seismic waves are introduced to the system through effective nodal forces, which are applied exclusively to a single layer of elements adjacent to the truncated boundary in the near field. Importantly, these forces only depend on the free field motion. The accuracy and applicability of the proposed SSI analysis model in solving scattering problems in 3D horizontal layered half-space are demonstrated through various examples.

A convolution-based in vitro-in vivo correlation model for methylphenidate hydrochloride delayed-release and extended-release capsule.

Delayed-release and extended-release methylphenidate hydrochloride (JORNAY PM®) is a novel capsule formulation of methylphenidate hydrochloride, used to treat attention deficit hyperactivity disorder in patients 6 years and older. In this paper, we develop a Level A invitro-in vivo correlation (IVIVC) model for extended-release methylphenidate hydrochloride to support post-approval manufacturing changes by evaluating a point-to-point correlation between the fraction of drug dissolved invitro and the fraction of drug absorbed invivo. Dissolution data from an invitro study of three different release formulations: fast, medium, and slow, and pharmacokinetic data from two invivo studies were used to develop an IVIVC model using a convolution-based approach. The time-course of the drug concentration resulting from an arbitrary dose was considered as a function of the invivo drug absorption and the disposition and elimination processes defined by the unit impulse response function using the convolution integral. An IVIVC was incorporated in the model due to the temporal difference seen in the scatterplots of the estimated fraction of drug absorbed invivo and the fraction of drug dissolved invitro and Levy plots. Finally, the IVIVC model was subjected to evaluation of internal predictability. This IVIVC model can be used to predict invivo profiles for different invitro profiles of extended-release methylphenidate hydrochloride.

On Time-Domain Solutions to the Free Vibration of SDOF Systems with Linear Hysteretic Damping

This article focuses on the free vibration of single-degree-of-freedom (SDOF) systems with linear hysteretic damping and investigates the consistency and convergency of the solution to the free vibration in time domain. The criteria associated with the unit-impulse response function at [Formula: see text] are suggested to check the consistency of possible solutions. Exhaustive and systematic derivations are presented to clarify the confusing results in the literature. Subsequently, the integration in the Hilbert term proves to be nonconvergent when an exponential term ([Formula: see text]) is assumed to be the general form of displacement solutions. Hence, it can be concluded that the exact solution to the free vibration of SDOF systems with linear hysteretic damping is still an open question. At last, a numerical verification method is proposed to assess the accuracy of possible solutions.

A Scaling Surface Based SBFEM for the Acceleration Unit-Impulse Response Function of 3D Non-Homogeneous Half-Space

A computational model for the acceleration unit-impulse response function (AUIRF) of wave motion based on the scaled boundary finite element method (SBFEM) is proposed in this study for the 3D non-homogeneous half-space. In this model, a surface parallel to the structure-foundation interface for the infinite domain is defined as the scaling center. An expression of characteristic length used in the dimensionless frequency is proposed, which makes it possible to transform the derivative of dynamic stiffness at the structure-foundation interface of 3D non-homogeneous half-space with respect to spatial coordinate into that with respect to frequency. Hence, the governing equations of the AUIRF can be obtained from those of dynamic stiffness in frequency domain by the inverse Fourier transform and solved by the numerical time integration method. The accuracy of the proposed method is demonstrated by comparing the dynamic responses of the homogeneous, horizontally layered half-space, and 3D non-homogeneous half-space subjected to the near-field excitation with those obtained by the finite element method.

Moving force identification of simply supported bridges through the integral time domain method

This paper presents a new form of inversion matrix, which aims to obtain more accurate moving force identification results from the responses of a simply supported bridge deck to vehicles passing over it. The load identification process of the modal superposition method discretizes the time-domain integral equation of the load response, obtains the load inversion matrix, and converts the load identification problem into a linear equation solving problem. The inversion matrix formation process of this traditional time domain method (TDM) can introduce the load compression error and the discretization error of the unit impulse response function, which affect the load solution. To reduce the source of error and maintain the stability of the solution, the discretized unit impulse response function is replaced by an integral form, thereby eliminating the discretization error. This method is called the integral time domain method (ITDM). A supported beam subjected to a single force and two forces is illustrated as a numerical example. Through numerical analysis, the effects of the two methods in single time-varying force identification are analyzed. Using two moving forces analysis, when noise is included, the influence of discretization error on the load solution is analyzed. Numerical results show that the discretization error has a greater impact on the load inversion using the acceleration response than the bending moment and displacement response inversion, and the ITDM should be used to avoid the interference of discrete error.

Vibration load identification in the time-domain of high arch dam under discharge excitation based on hybrid LSQR algorithm

The identification of vibration load is of great importance in studying the vibration induced by discharge of high arch dam. Considering the ill-posedness in time-domain identification of vibration load, a hybrid least squares QR (LSQR) iterative identification method is proposed. The system response is expressed as the convolution of the unit impulse response function and the excitation load. It is discretized into a set of linear equations, and the mathematical model of the inverse problem of load identification is established. On the basis of vibration signal filtering and noise reduction, Tikhonov regularization method is used to pre optimize LSQR iterative algorithm. This process is performed because the LSQR algorithm is prone to nonconvergence when the error of observation data is large. Thus, a hybrid LSQR algorithm is obtained to improve the ill-posedness of the inverse problem. Numerical examples show that the proposed method can recognize multiple vibration loads effectively and stably under different noise levels, and the recognition accuracy is better than the conventional regularization method. The proposed method is applied to an engineering example. Results show that the proposed method is feasible and effective for the time-domain identification of vibration load of a high arch dam.

Efficient flexibility identification method using structured target rank approximation and extended Prony's method

An accurate estimation of the structural flexibility is crucial in applications such as deflection prediction, damage detection, and finite element model updating. By introducing a unit impulsive response function (UIRF) matrix estimated from noisy input and output signals collected through impact testing, this paper proposes a new method for estimating the structural flexibility matrix from a noisy UIRF. The advantages lie in the way the noise and decoupling modes of the impulse response signal are handled in the time domain. The proposed method consists of three steps: (1) Constructing an enhanced unit impulse response function (EUIRF) from the UIRF by utilizing the orthogonality of the displacement mode shapes for mode decoupling, (2) Noise removal from the constructed EUIRF to obtain a filtered one by implementing the improved Cadzow's algorithm for the structured target rank approximation (STRA) of the Hankel matrix constructed from the EUIRF, and (3) Structural flexibility identification from the EUIRF using the extended Prony's method to identify the basic modal parameters and modal scaling factors for a single-mode impulse response function with one degree of freedom. To validate the applicability of the proposed method, numerical and laboratory case studies were performed. A noisy impact test was simulated for a three-span continuous beam bridge, and the identified modal parameters and structural flexibility matrix were found to be accurate. Moreover, an impact test was conducted on a simply supported beam in a laboratory, and the results showed that the deformation predicted from the identified flexibility matrix and the one measured from the static load test are in good agreement.

Convolution-based time-domain simulation for fluidelastic instability in tube arrays

A convolution-based numerical algorithm is presented for the time-domain analysis of fluidelastic instability in tube arrays, emphasizing in detail some key numerical issues involved in the time-domain simulation. The unit-step and unit-impulse response functions, as two elementary building blocks for the time-domain analysis, are interpreted systematically. An amplitude-dependent unit-step or unit-impulse response function is introduced to capture the main features of the nonlinear fluidelastic (FE) forces. Connections of these elementary functions with conventional frequency-domain unsteady FE force coefficients are discussed to facilitate the identification of model parameters. Due to the lack of a reliable method to directly identify the unit-step or unit-impulse response function, the response function is indirectly identified based on the unsteady FE force coefficients. However, the transient feature captured by the indirectly identified response function may not be consistent with the physical fluid-memory effects. A recursive function is derived for FE force simulation to reduce the computational cost of the convolution operation. Numerical examples of two tube arrays, containing both a single flexible tube and multiple flexible tubes, are provided to validate the fidelity of the time-domain simulation. It is proven that the present time-domain simulation can achieve the same level of accuracy as the frequency-domain simulation based on the unsteady FE force coefficients. The convolution-based time-domain simulation can be used to more accurately evaluate the integrity of tube arrays by considering various nonlinear effects and non-uniform flow conditions. However, the indirectly identified unit-step or unit-impulse response function may fail to capture the underlying discontinuity in the stability curve due to the prespecified expression for fluid-memory effects.

Channel hydrological response function considering inflow conditions and hydraulic characteristics

To bypass the problem of numerical instability in conducting the channel routing system, the application of an impulse response function based on the linearization of Saint Venant equations has been an alternative for predicting streamflow discharge. However, the distribution type of the impulse response function proposed by Dooge et al. (1987a) is restricted during a flood, so this approach cannot adequately describe flow response in practical applications. In considering that the flow response in a natural channel is usually influenced by the shape of the cross-section, the terrain of channel bed and the discharge of the moving flood, this study focuses on improving the original unit impulse function by conducting two aspects of analysis: (1) the distribution of unit impulse response function was changed with time by adjusting the reference parameters according to the inflow condition and the hydraulic variables; (2) the outcome of this modified linear approach was thoroughly examined by comparing the simulated results with that adopting the original linear channel method and the numerical scheme based on the nonlinear Saint Venant equations. Moreover, for achieving the simulation of a whole river basin, a complete executing procedure was provided to explain the connection between the upstream inflows, lateral flows, and the linear channel response of each channel reach. A series of tests showed that the proposed method can produce approximated hydrographs in comparison with numerical simulation results owing to the flexibility of the impulse response function although the linear channel routing adopts simplified mathematical operations. A case study of a natural river basin also demonstrated the applicability of the modified channel response system.

MIMO Sonar DOA Estimation with Joint Matched-Filtering Based on Transmission Diversity Smoothing

There is a class of methods based on transmission diversity smoothing by multiple-input multiple-output(MIMO) sonar called MIMO-TDS which is considered as one of the most effective methods for estimation of direction-of-arrival(DOA) using MIMO sonar systems. MIMO-TDS produced by orthogonal signal transmission for active sonar can be immediately implemented with high resolution algorithms such as MVDR to estimate the direction of received signals. However, the orthogonal transmission mode of MIMO-TDS is doomed to a loss of transmission array gain indirectly leading to the problem that the echoes are not equipped with as high SNR as enough for an accurate target localization, especially in scenarios in which the targets are far away from array. In order to solving the "low SNR" problem, a solution using all transmitted signals simultaneously to design a joint matched-filter intended for received signal is proposed to improve the performance of MIMO-TDS, which is inspired by the match-filtering concept of "MIMO sonar virtual array method" simplified as MIMO-VA. And accordingly, the unit impulse response function of proposed joint matched-filter is the equivalent of linear sum of all orthogonal transmitted signals and the modified MIMO-TDS is named as "joint matched-filtering MIMO sonar transmission diversity smoothing DOA estimation method", which could be simplified as MIMO-TDS-MF. The characteristic of proposed method is analyzed theoretically and compared to MIMO-TDS and MIMO-VA in this paper:Compared with MIMO-TDS, the proposed method not only retains the advantage of transmission diversity smoothing but also improves the SNR by joint match-filtering; What's more, compared with MIMO-VA, MIMO-TDS-MF is equipped with substantially less computation than the former due to an employment of much fewer matched-filters and is in possession of a superior robustness to that of MIMO-VA. Numerical experiments demonstrate the efficiency of proposed MIMO-TDS-MF.

Probability Weighted Moments–Based Parameter Estimation for Kinematic Diffusion and Muskingum-Based Distributions

AbstractHydrologic series in arid and semiarid areas often contain zero values. For such data, the unit impulse response function (irf) of a kinematic diffusion model and a Muskingum flood routing ...

Determinants of Credit and Financing Risk: Evidence of Dual Banking System in Indonesia

Given the fact that banking is the backbone of the Indonesian economy with a dual banking system. This paper seeks determinants of default rate in Indonesia. Various techniques of econometric tools such as unit root, co-integration test and Impulse Response Function (IRF) utilized. Bank capital has similar influence on the own credit or financing risks. Overall economic performance has a different result to the risk. Among the recommendations are for the government to maintain economic performance to keep default rate as low as possible. Financing Deposit Ratio-based Reserve Requirement policy (which is adopted only in Indonesia) imposed by the central bank seems to be effective in developing the real sector and should adopt in conventional banks. DOI: 10.15408/aiq.v10i1.5903

Determinants of Credit and Financing Risk: Evidence of Dual Banking System in Indonesia

Given the fact that banking is the backbone of the Indonesian economy with a dual banking system. This paper seeks determinants of default rate in Indonesia. Various techniques of econometric tools such as unit root, co-integration test and Impulse Response Function (IRF) utilized. Bank capital has similar influence on the own credit or financing risks. Overall economic performance has a different result to the risk. Among the recommendations are for the government to maintain economic performance to keep default rate as low as possible. Financing Deposit Ratio-based Reserve Requirement policy (which is adopted only in Indonesia) imposed by the central bank seems to be effective in developing the real sector and should adopt in conventional banks. DOI: 10.15408/aiq.v10i1.5903

Deconvolution-based real-time neutron flux reconstruction for Self-Powered Neutron Detector

Self-Powered Neutron Detector (SPND) is useful for in-core neutron flux measurement in nuclear reactors due to its tiny size, simple structure, ruggedness and self-powered feature. One type of SPNDs with delayed current from instable intermediate nuclides cannot directly represent the real-time in-core neutron flux Φ(t) by their current I(t), which should be avoided during reactor control and protection. In this paper, we proposed a deconvolution-based method to reconstruct real-time neutron flux for SPND. Following the establishment of dynamic model, the unit-impulse response function h(t) was easily obtained when neutron flux was unit-impulse. Then, the iterative compensation relations were established for delay compensation according to the convolution relationship I(t) = Φ(t) * h(t). In the meanwhile, determination methods for initial values were also proposed and the compensation performance for jump neutron flux was demonstrated to be only 0.3 s. Furthermore, the dependences on initial conditions and sampling time interval were studied systematically, indicating our method is effective and robust. Finally, our method has been compared with a typical compensation method and validated with measured current, showing its advantages. This method is very attractive due to its obvious simplicity, high intuitiveness and general applicability.

Optimal Wavelet Selection for the Size Estimation of Manufacturing Defects of Tapered Roller Bearings with Vibration Measurement using Shannon Entropy Criteria

Fault diagnosis of bearings is essential in manufacturing to increase quality. Traditionally, fault diagnosis of tapered roller element bearings is performed by signal processing methods, which handle the nonstationary behaviour of the signal. The wavelet transform is an efficient tool for analysing the vibration signal of the bearings because it can detect the sudden changes and transient impulses in the signal caused by faults in the bearing elements. In this article, manufacturing faults on the outer ring of tapered roller bearings due to the grinding process in manufacturing are investigated. Nine different real values wavelets (Symlet-2, Symlet-5, Symlet-8, db02, db06, db10, db14, Meyer, and Morlet) are compared according to the Energy-to-Shannon-Entropy ratio criteria, and which is efficient for detecting the manufacturing faults is determined. Finally, experiments are carried out on a test rig for determining the geometrical size of the manufacturing faults with all wavelets directly from the vibration signature the result of db02, Symlet-5, and Morlet wavelets are presented. When modelling the bearing structure as an under-damped second-order mass-spring-damper mechanical system, its unit impulse response function is compared to the wavelets on the basis of their Energy-to-Shannon-Entropy ratio to determine the fault size from the vibration signal. The proposed technique has been successfully implemented for measuring defect widths. The maximum deviation in result has been found to be 4.12 % for the defect width which was verified with image analysis methods using an optical microscope and contact measurement.

Stability of initialization response of fractional oscillators

Application of fractional calculus representations, shortly termed as fractional constitute relations becomes an effective and powerful technique to characterize the rheological behavior of viscoelastic materials. Research on fractional oscillators provides a novel approach to deal with viscoelastically damped structures. This paper firstly investigates the memory effects or historical effects on dynamical responses of fractional oscillators via numerical simulations. Then the stability of initialization response is proved based on the unit impulse response function and the Lyapunov stability theorem for fractional differential equations. The main conclusion in this paper is that the stability of initialization responses of fractional oscillators is irrelevant to initial conditions or prehistory.

Fault feature extraction of rolling element bearings using sparse representation

Influenced by factors such as speed fluctuation, rolling element sliding and periodical variation of load distribution and impact force on the measuring direction of sensor, the impulse response signals caused by defective rolling bearing are non-stationary, and the amplitudes of the impulse may even drop to zero when the fault is out of load zone. The non-stationary characteristic and impulse missing phenomenon reduce the effectiveness of the commonly used demodulation method on rolling element bearing fault diagnosis. Based on sparse representation theories, a new approach for fault diagnosis of rolling element bearing is proposed. The over-complete dictionary is constructed by the unit impulse response function of damped second-order system, whose natural frequencies and relative damping ratios are directly identified from the fault signal by correlation filtering method. It leads to a high similarity between atoms and defect induced impulse, and also a sharply reduction of the redundancy of the dictionary. To improve the matching accuracy and calculation speed of sparse coefficient solving, the fault signal is divided into segments and the matching pursuit algorithm is carried out by segments. After splicing together all the reconstructed signals, the fault feature is extracted successfully. The simulation and experimental results show that the proposed method is effective for the fault diagnosis of rolling element bearing in large rolling element sliding and low signal to noise ratio circumstances.

Dynamic Characterization of a Transient Surface Temperature Sensor

This paper presents a dynamic characterization setup to calibrate transient surface temperature sensor in radiative conditions. The temperature sensor is a K type (Chromel/Alumel) wire microthermocouple which hot junction is obtained from a layer deposition by PVD process. Three different metallic layers are used (Tungsten, gold and chromium) with two thin film thicknesses (0.4μm and 0.8μm). The aim of this work is to develop a dynamic characterization with a radiation source from a laser focused onto the thermocouple's hot junction. The dynamic performance of the sensor is obtained by measuring its unit-impulse response function (Yag laser) and its periodic response under a chopped continuous laser beam (Argon laser). Experiments are realized at atmospheric pressure. The best results are obtained with deposited probes with gold junction of 0.4μm thickness. The rise-time and decrease-time are equal to 10μs and 80μs respectively (Yag laser).

Substructure damage identification based on wavelet-domain response reconstruction

This article presents experimental verification on damage identification of a substructure using a wavelet-domain response reconstruction technique. The response reconstruction is based on the unit impulse response function in the wavelet domain to form a transformation matrix between two different sets of time-domain response vectors. The initial finite element model updating is performed to achieve an accurate model in the intact stage as a baseline, and measured acceleration responses from the damaged substructure are used for the damage identification. Substructure damage identification is conducted by minimizing the discrepancy between a measured response vector and the reconstructed one. A dynamic response sensitivity-based model updating method is used for the identification of the target substructure. Local damage is identified as a change in the elemental stiffness factors. The adaptive Tikhonov regularization technique is adopted to improve the identification results with measured responses including measurement and environmental noises in laboratory. Experimental studies on a 7-storey plane frame structure are conducted to investigate the accuracy of the presented response reconstruction technique and the performance of substructure damage identification approach. Good response reconstruction accuracy is obtained with the baseline model, and the introduced damages in the substructure can be identified effectively. The damage locations are identified correctly with a close estimation of damage extents.

Unit Impulse Response Estimation for Structural Damage Detection Under Planar Multiple Excitations

An unit impulse response (UIR) function is an inherent system function that depends only on the structure and the locations of excitation. When the structure is under general excitation, the effect can be obtained via Duhamel integral between the UIR function and the excitation. The possibility of the UIR function as a damage detection index under general excitation is studied here. However, the UIRs from multiple excitations will contribute to the identification equation together. Therefore, the estimation of UIRs will most probably become underdetermined with a limited number of measurements leading to an incorrect or nonfeasible solution of the inverse problem. This report addresses this problem by developing a transformation between the UIRs to facilitate the conversion of a multiple excitations problem into an equivalent single excitation problem. However, the method is limited to planar problems and the reference response is confined to those with larger vibration amplitude. The extraction of the UIR via Tikhonov regularization from the measured acceleration is then described. Numerical studies with a 31-bar plane truss structure are used to illustrate the performances of the proposed approach with different damage scenarios with or without noise effect and model errors. The stability of the UIR estimation with different periods of measured data is also studied. Moreover, this paper studies the effect of using a reduced number of sensors and an increased sampling rate. Results show that the regularization-based approach with the new transformation matrix is accurate and effective for the inverse solution and it is robust to measurement noise in the damage detection process.