Search

In order to ensure the reliability of the structural design, it is necessary to know the external loads acting on the structure. In this paper, we propose a novel method to identify the dynamic loads based on function principles in the time domain. Assuming the external load remains constant within one micro segment, we establish a linear relationship between external load and structural response in the micro segments based on the mechanical energy conservation law. Next, the external load is obtained by solving the inverse problem in each micro-segment. Finally, the external load in the whole time domain is achieved by fitting the load-identification results in each micro segment. In order to verify the effectiveness and accuracy, single-force and two-force identification, and load identification with noise simulations, are performed on the structures, and the identification results are compared to the ones of the traditional time-domain method with a deviation of less than 5%. The proposed method can effectively solve the problem of cumulative errors in the time-domain method, while its resistance to noise interference is also strong. At last, we verify the experimental performance of the proposed method. The experimental results show the effectiveness and high accuracy of the proposed method. This work presents a first attempt to solve the structural dynamic load with an approach based on a function principle. [ABSTRACT FROM AUTHOR]

A method of assessing equivalent static wind loads that can represent all the real ultimate states of a high-rise building and towering structure has still not been fully determined in wind engineering. Based on random vibration theory, the wind-induced response and equivalent static wind loading of high-rise buildings and towering structures are investigated using the vibration decomposition method. Firstly, the structural wind-induced mean response, background response, resonant response and background and resonant coupled response are studied in the time and frequency domains. Secondly, a new gust load factor (GLF) assessment method suitable for wind-induced displacement, bending moment and shear force response at any height of the structure is proposed, and a typical high-rise building is used as an example for comparison with the previous research results, in order to verify the effectiveness of the method in this paper. The results show the following: for high-rise buildings and towering structures, the percentage of the coupled components in the total pulsation response is less than 2%, and the influence can be ignored; the GLF based on bending moment (MGLF) and the GLF based on shear force (QGLF) increase significantly with height, and the traditional GLF methods underestimate the maximum wind effects. [ABSTRACT FROM AUTHOR]

To explore the spectral radiation characteristics of carbon nanofibers, a finite-difference time-domain method has been applied to study and calculate the scattering/absorption factors of carbon nanofibers with various arrangements, while the filler contents are 61.15%, 53.81%, 48.92%, 44.03% and 39.13% in the spectrum band of 2.5–15 µm. The effects of the nanofiber content, 2D/3D random arrangement and nanofiber radius on scattering/absorption characteristics have been analyzed. The analytical results show that the spectral radiation characteristics of carbon nanofibers have been significantly increased with an increase in the filler content. When the nanofiber content reduced to 48.92%, the random arrangement structure of carbon nanofiber plays an essential role in determining the spectral radiation characteristics. Analytical results prove that the prediction accuracy has been significantly improved by 30.12% by sing the 3D random arrangement model than by using the 2D uniform arrangement model. This study proposed a 3D model to predict the spectral radiation characteristics of carbon nanofibers and their aggregates in engineering nanocomposites.

In order to ensure the reliability of the structural design, it is necessary to know the external loads acting on the structure. In this paper, we propose a novel method to identify the dynamic loads based on function principles in the time domain. Assuming the external load remains constant within one micro segment, we establish a linear relationship between external load and structural response in the micro segments based on the mechanical energy conservation law. Next, the external load is obtained by solving the inverse problem in each micro-segment. Finally, the external load in the whole time domain is achieved by fitting the load-identification results in each micro segment. In order to verify the effectiveness and accuracy, single-force and two-force identification, and load identification with noise simulations, are performed on the structures, and the identification results are compared to the ones of the traditional time-domain method with a deviation of less than 5%. The proposed method can effectively solve the problem of cumulative errors in the time-domain method, while its resistance to noise interference is also strong. At last, we verify the experimental performance of the proposed method. The experimental results show the effectiveness and high accuracy of the proposed method. This work presents a first attempt to solve the structural dynamic load with an approach based on a function principle.

A method of assessing equivalent static wind loads that can represent all the real ultimate states of a high-rise building and towering structure has still not been fully determined in wind engineering. Based on random vibration theory, the wind-induced response and equivalent static wind loading of high-rise buildings and towering structures are investigated using the vibration decomposition method. Firstly, the structural wind-induced mean response, background response, resonant response and background and resonant coupled response are studied in the time and frequency domains. Secondly, a new gust load factor (GLF) assessment method suitable for wind-induced displacement, bending moment and shear force response at any height of the structure is proposed, and a typical high-rise building is used as an example for comparison with the previous research results, in order to verify the effectiveness of the method in this paper. The results show the following: for high-rise buildings and towering structures, the percentage of the coupled components in the total pulsation response is less than 2%, and the influence can be ignored; the GLF based on bending moment (MGLF) and the GLF based on shear force (QGLF) increase significantly with height, and the traditional GLF methods underestimate the maximum wind effects.

Wave attenuation is a widespread physical phenomenon in most acoustic tests, but there is a scarcity of quantitative investigations into the influence of wave attenuation on the determination of shear wave travel time in bender element tests. To ascertain this attenuation effect, a series of bender element tests were conducted on clay samples with different lengths under unconfined conditions. The experimental results suggest that the real first peak of the received signal attenuates gradually with the increase of the sample length and even becomes undistinguished when the sample length exceeds a limit. This phenomenon results in misinterpretation of the wave travel time using the time domain method. In this study, the shear wave travel time is misinterpreted when wave travel distance over approximately 80 mm, leading to underestimation of the VS by 17% for the peak-to-peak approach and 10% for the arrival-to-arrival method. Therefore, besides the near field effect and boundary reflection, the wave attenuation effect turned out to be an important factor influencing the determination of VS using the time domain method. Accordingly, it is advisable to predetermine the limit test distance for a specific testing system under conditions, particularly for long distance testing.

LLC resonant converter is utilized for a 3.3-kW on-board charger (OBC), where high efficiency and wide output voltage are required. In this paper, the resonant frequency and the magnetizing inductor of the converter are first optimized based on the required efficiency. Then, the resonant inductor and the resonant capacitor are designed considering the required maximum output voltage. The energy equations and the KCL and KVL equations about the converter are established by the time domain method to find out the information about peak resonant current, peak magnetizing current, and minimum switching frequency. The above-mentioned information is used to accurately design the converter`s magnetic components. A 3.3-kW prototype applied for OBC is developed. Its output voltage ranges from 230 to 430 V. Its peak efficiency is higher than 97.6%. The experimental results verify that the proposed method can accurately design the efficiency, the voltage gain, and the magnetic components of LLC resonant converter in a wide output voltage range.

• A preconditioned least square QR-factorization approach is developed for moving force identification. • The regularization matrix L is introduced to improve the ill-posed problems. • The number of iterations j is introduced to avoid noise disturbance and ensure the robustness. • Preconditioned least square QR-factorization approach is validated through numerical simulation. This paper develops a novel method for moving force identification (MFI) called preconditioned least square QR-factorization (PLSQR) method. The algorithm seeks to reduce the impact of identification errors caused by unknown noise. The biaxial moving forces travel on a simply supported bridge at three different speeds is used to generate numerical simulations to assess the effectiveness and applicability of the algorithm. Results indicate that the method is more robust towards ill-posed problem and has higher identification precision than the conventional time domain method (TDM). In addition, the robustness and ill-posed immunity of PLSQR are directly affected by two kinds of regularization parameters, namely, number of iterations j and regularization matrix L. Compared with the standard form of least square QR-factorization (LSQR), i.e., the regularization matrix L being the identity matrix I n , the PLSQR with the optimal number of iterations j and regularization matrix L has many advantages on MFI and it is more suitable for field trials due to better adaptability with type of sensors and number of sensors. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Signal Processing is the property of Journal of Signal Processing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Harbin University of Science & Technology is the property of Journal of Harbin University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Vibration Engineering is the property of Nanjing University of Aeronautics & Astronautics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper develops a modified preconditioned conjugate gradient (M-PCG) method for moving force identification (MFI) by improving the conjugate gradient (CG) and preconditioned conjugate gradient (PCG) methods with a modified Gram-Schmidt algorithm. The method aims to obtain more accurate and more efficient identification results from the responses of bridge deck caused by vehicles passing by, which are known to be sensitive to ill-posed problems that exist in the inverse problem. A simply supported beam model with biaxial time-varying forces is used to generate numerical simulations with various analysis scenarios to assess the effectiveness of the method. Evaluation results show that regularization matrix L and number of iterations j are very important influence factors to identification accuracy and noise immunity of M-PCG. Compared with the conventional counterpart SVD embedded in the time domain method (TDM) and the standard form of CG, the M-PCG with proper regularization matrix has many advantages such as better adaptability and more robust to ill-posed problems. More importantly, it is shown that the average optimal numbers of iterations of M-PCG can be reduced by more than 70% compared with PCG and this apparently makes M-PCG a preferred choice for field MFI applications. [ABSTRACT FROM AUTHOR]

A rigorous stability analysis of the previously published semi-explicit time domain discontinuous Galerkin (DG) H– $\Phi $ approach for eddy current simulations is presented. The considered DG finite-element method (FEM) enables explicit time stepping in electrically conducting regions and eliminates the need for solving large sparse ill-conditioned equation systems. The considered method utilizes the magnetic scalar potential in electrically non-conducting regions computed by using the nodal finite elements. The theoretical stability limit of the considered semi-explicit time domain approach is obtained by applying the z-transform on the discrete time domain DG-FEM equations and by performing an eigenvalue analysis of the underlying elemental DG-FEM matrices. The obtained results are tested on simple 3-D examples, and an excellent agreement between the theoretical stability limit and the empirically obtained values was found. [ABSTRACT FROM AUTHOR]

Ａ ｔｉｍｅ ｄｏｍａｉｎ ｉｄｅｎｔｉｆｉｃａｔｉｏｎ ｍｅｔｈｏｄ ｆｏｒ ｄｉｓｔｒｉｂｕｔｅｄ ｄｙｎａｍｉｃ ｌｏａｄｓ ｏｎ １Ｄ ｓｐａｔｉａｌ ｓｔｒｕｃｔｕｒｅｓ ｗａｓ ｐｒｏｐｏｓｅｄ． Ｂａｓｅｄ ｏｎ ｔｈｅ ｉｄｅａ ｏｆ ｓｐａｔｉａｌ ａｎｄ ｔｅｍｐｏｒａｌ ｄｉｖｉｓｉｏｎｓ， ｔｈｅ ｆｏｒｍｕｌａ ａｎｄ ｐｒｏｃｅｓｓ ｆｏｒ ｌｏａｄ ｔｉｍｅ ｈｉｓｔｏｒｙ ｉｄｅｎｔｉｆｉｃａｔｉｏｎ ｗｅｒｅ ｄｅｒｉｖｅｄ． Ｔｈｅ ｌｏａｄ ｉｄｅｎｔｉｆｉｃａｔｉｏｎ ｐｒｏｇｒａｍ ｗａｓ ｃｏｍｐｉｌｅｄ ｂｙ ｍｅａｎｓ ｏｆ ＭＡＴＬＡＢ， ａｎｄ ｔｈｅ ｉｄｅｎｔｉｆｉｃａｔｉｏｎ ｍｅｔｈｏｄ ｗａｓ ｖｅｒｉｆｉｅｄ ｔｈｒｏｕｇｈ ２ ｅｘａｍｐｌｅｓ： ａ ｓｉｍｐｌｙ ｓｕｐｐｏｒｔｅｄ ｂｅａｍ ｓｕｂｊｅｃｔｅｄ ｔｏ ｄｉｓｔｒｉｂｕｔｅｄ ｄｙｎａｍｉｃ ｌｏａｄｓ ａｎｄ ａ ｐｏｗｅｒ ｌｉｎｅ ｓｕｂｊｅｃtｅｄ ｔｏ ｓｔｏｃｈａｓｔｉｃ ｗｉｎｄ ｌｏａｄｓ． Ｍｏｒｅｏｖｅｒ， ｔｈｅ ｅｆｆｅｃｔ ｏｆ ｎｏｉｓｅ ｏｎ ｔｈｅ ｌｏａｄ ｉｄｅｎｔｉｆｉｃａｔｉｏｎ ｗａｓ ｉｎｖｅｓｔｉｇａｔｅｄ ｔｈｒｏｕｇｈ ｎｕｍｅｒｉｃａｌ ｓｉｍｕｌａｔｉｏｎ． Ｉｔ ｉｓ ｓｈｏｗｎ ｔｈａｔ ｔｈｅ ｄｉｓｔｒｉｂｕｔｅｄ ｌｏａｄｓ ｃａｎ ｂｅ ａｃｃｕｒａｔｅｌｙ iｄｅｎｔｉｆｉｅｄ ｆｏｒ ｌｉｎｅａｒ ｐｒｏｂｌｅｍｓ ａｎｄ ａｐｐｒｏｘｉｍａｔｅｌｙ ｉｄｅｎｔｉｆｉｅｄ ｆｏｒ ｗｅａｋｌｙ ｎｏｎｌｉｎｅａｒ ｐｒｏｂｌｅｍｓ ｗｉｔｈ ｔｈｅ ｐｒｅｓｅｎｔｅｄ ｍｅｔｈｏｄ， ｗｈｉｃｈ ｐｒｏｖｉｄｅｓ ａｎ ｅｆｆｉｃｉｅｎｔ ｗａｙ ｔｏ ｉｄｅｎｔｉｆｙ ｄｉｓｔｒｉｂｕｔｅｄ ｌｏａｄｓ ｏｎ ｅｎｇｉｎｅｅｒｉｎｇ ｓｔｒｕｃｔｕｒｅｓ． [ABSTRACT FROM AUTHOR]

This paper proposes a new methodology for moving force identification (MFI) from the responses of bridge deck. Based on the existing time domain method (TDM), the MFI problem eventually becomes solving the linear algebraic equation in the form Ax = b . The vector b is usually contaminated by an unknown error e generating from measurement error, which often called the vector e as ‘‘noise’’. With the ill-posed problems that exist in the inverse problem, the identification force would be sensitive to the noise e . The proposed truncated generalized singular value decomposition method (TGSVD) aims at obtaining an acceptable solution and making the noise to be less sensitive to perturbations with the ill-posed problems. The illustrated results show that the TGSVD has many advantages such as higher precision, better adaptability and noise immunity compared with TDM. In addition, choosing a proper regularization matrix L and a truncation parameter k are very useful to improve the identification accuracy and to solve ill-posed problems when it is used to identify the moving force on bridge. [ABSTRACT FROM AUTHOR]

A semi-explicit time domain method for solving eddy current problems is presented. The suggested method is based on the discontinuous Galerkin (DG) finite-element approach and the H- $\Phi $ formulation of eddy current problem. The DG-technique allows for explicit time stepping in electrically conducting domains without solving a large sparse ill-conditioned linear equations system. The H- $\Phi $ field formulation enables the use of the magnetic scalar potential in electrically non-conducting domains that are discretized by using nodal finite elements. The application of the method is demonstrated by a 3-D example and the obtained results are verified by comparison with the corresponding frequency domain solution. [ABSTRACT FROM AUTHOR]

An efficient and simplified procedure is proposed for the reduction of high‐frequency oscillations and erroneous magnitude peaks in electromagnetic transient simulations in power transmission systems modelled by the lumped electric parameters approach. This procedure consists of the inclusion of analogue filters in the equivalent representation of multiconductor transmission lines without modifying its electromagnetic propagation characteristics. The analogue filter modelling is conducted as a function of the line length and line parameters. The proposed simulation methodology is applied directly in the line modelling, which means that the filtering/correction process represents a real‐time process during simulations, without post‐processing filtering techniques using digital filters or variations in the solution methods. The results obtained directly in the time domain by the proposed modelling/simulation methodology are compared with simulations obtained from well‐established line models using the numerical Laplace transform and the Bergeron method. [ABSTRACT FROM AUTHOR]

The fatigue assessment plays an increasing role for the offshore structural safety. Many fatigue assessment methods have been developed for this purpose. Among those methods, the time domain method is regarded as the most accurate method but less adopted in practice due to time consuming. In order to improve the efficiency of the time domain method, an innovative block partition and equivalence method of the wave scatter diagram is developed for offshore structural fatigue assessment. After the wave scatter diagram is partitioned into several blocks, the newly developed method, involves determination of the equivalent wave height, wave period and occurrence probability of the representative sea states based on modified energy equivalent principle. The equivalent wave period of the representative sea state is calculated via the spectral moment formula in which the equivalent spectral moments of zero and second order are obtained based on the weighted averaging principle. Combining with the determined wave period, the equivalent significant wave height can be determined by reversing the wave spectrum integral formula, where the equivalent wave energy of a divided block of the wave scatter diagram is modified by introducing a factor to compensate the effect of low- and high-amplitude cycles fatigue damage. The equivalent occurrence probability is equal to the summation of the original sea states’ occurrence probability within the divided block. The developed method has the advantage of preserving the stochastic characteristics of the short term sea states within the divided block during determining the representative sea state. At the same time the newly developed method has no limitation on block partition and can be applied on different offshore structure. Two structural models, a fixed mono-pile platform and a floating semi-submersible platform, are demonstrated in the numerical examples. Results indicate that the newly developed method is robust, computationally affordable, and accurate within engineering expectations. [ABSTRACT FROM AUTHOR]

Based on the bender element (BE) international parallel tests, conducted from 2003 to 2005 using Toyoura sand, a standard test method for BE tests was proposed by Yamashita et al. (2009). The proposed method showed that any of the different identification methods would give a comparable travel time if the frequency of the transmitted wave were approximately equal to the frequency of the received wave. The proposed test method, however, did not show any specific procedure for choosing the input frequencies or for calculating the travel time. In the present study, therefore, with reference to the results from several previous studies on BE testing, a conditional expression for determining the input frequency and a calculation formula for the travel time have been defined, and BE testing using 13 different sandy and clayey soils has been conducted. After the testing, it was confirmed that the testing method is able to determine the shear wave velocity of sandy and clayey soils having widely different stiffnesses. Furthermore, the study has found that a reevaluation of the International Parallel Test results using this method has resulted in less variation as compared to the results from the reevaluation by Yamashita et al. (2009). This method is recommended in the "Method for laboratory measurement of shear wave velocity of soils by bender element test" standardized by the Japanese Geotechnical Society (JGS) in 2011 (Japanese Geotechnical Society, 2011). [ABSTRACT FROM AUTHOR]

• Developing a new form of inversion matrix (ITDM) for moving force identification. • The two sources of error in the formation of the inversion matrix are analyzed, one is the load compression error and the other is the unit impulse response dispersion error. • The ITDM eliminates the influence of the discrete error of the unit impulse response on the load solution. • All the results have demonstrated the effectiveness of the ITDM. 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. [ABSTRACT FROM AUTHOR]

• A frequency-domain method is developed to measure the DMD of multimode fibers. • Vector network analyzer is used to measure the complex transfer functions. • The time-domain output pulses can be calculated from CTF with proper procedures. • Frequency-domain method yields DMD results equivalent to the time domain method. • The frequency domain method can conduct DMD measurements at very low optical power. We report a frequency-domain method for measuring the differential mode delay (DMD) and bandwidth of multimode fibers (MMFs). Using a frequency domain instrument, vector network analyzer (VNA), the method measures the complex transfer functions (CTFs) of multimode fibers for a given set of launch conditions. As a result of the fiber length, which is long relative to sampling points used in VNA, the frequency sampling is under-sampled and the measured CTF is aliased. Aliased CTF behaves very differently from fully sampled CTF with dependence on the sampling frequency step. With proper procedures, the CTF can be transformed to local time frame centered around DMD into a modified CTF. The time-domain output pulses can be further recovered through an inverse Fourier transform. By recovering output pulses using complex transfer functions of a multimode fiber at controlled launch offsets, one can subsequently follow the same procedures of existing time domain methods to determine the effective modal bandwidth of the multimode fiber under test (FUT). As a result of the method, DMD and modal bandwidth measurements can be undertaken using frequency domain instruments rather than time domain instruments in a mathematically equivalent manner for multimode fibers. The measurement method utilizes CW light sources that are readily available in a wide range of wavelengths, thus providing greater flexibility for measuring the modal bandwidth of MMFs at different wavelengths, including WDM applications other than 850 nm. The very high sensitivity of the VNA allows the measurement at much lower optical power compared to the time domain instrument. Several measurements at 850 nm have been conducted using the frequency domain method and validated by comparison with the results from the time domain method. The method is suitable for measuring MMFs from a short length of a few hundred meters to a very long length close to 20 km. We have also measured an MMF at 910 nm using the method to demonstrate its flexibility in adopting different wavelengths. [ABSTRACT FROM AUTHOR]

Wave attenuation is a widespread physical phenomenon in most acoustic tests, but there is a scarcity of quantitative investigations into the influence of wave attenuation on the determination of shear wave travel time in bender element tests. To ascertain this attenuation effect, a series of bender element tests were conducted on clay samples with different lengths under unconfined conditions. The experimental results suggest that the real first peak of the received signal attenuates gradually with the increase of the sample length and even becomes undistinguished when the sample length exceeds a limit. This phenomenon results in misinterpretation of the wave travel time using the time domain method. In this study, the shear wave travel time is misinterpreted when wave travel distance over approximately 80 mm, leading to underestimation of the VS by 17% for the peak-to-peak approach and 10% for the arrival-to-arrival method. Therefore, besides the near field effect and boundary reflection, the wave attenuation effect turned out to be an important factor influencing the determination of VS using the time domain method. Accordingly, it is advisable to predetermine the limit test distance for a specific testing system under conditions, particularly for long distance testing. [ABSTRACT FROM AUTHOR]

In this paper, we solve a diffusion problem in the presence of two absorbing boundaries in the time-domain. This model is well-known as Oster–Nishijima's model of electronic relaxation. The relaxation dynamics of the initially excited electronic distribution are studied, and the form of the distribution function is assumed to be Gaussian. The results are calculated for a flat-excited state potential, which is an exact consideration near the equilibrium configuration of the molecules. The analytic results of survival probability are presented graphically. For a case with more than one finite boundary, a time-domain solution has been obtained for the first time, and the parametric limitations to the presented method are discussed. • We present the time-domain dynamics of a diffusing probability distribution (Gaussian) in presence of two finite absorbing boundaries. • The solution can be used to solve other multiple boundary problems under transformations. • The time-domain solution has been presented for the first time, and there are parametric limitations to our solution. [ABSTRACT FROM AUTHOR]

This paper presents a novel time-domain method for non-stationary random vibration analysis of linear structures. Specifically, using the well-known spectral representation method, the stochastic excitation process is first decomposed into a set of trigonometric basis functions (TBFs) modulated by a series of orthogonal basis random variables (BRVs). Next, each TBF is used as a deterministic excitation input for the structural model, and the induced structural responses are derived analytically using the modal superposition method. After superposition of each TBF-induced deterministic responses, an explicit closed-form expression between the structural stochastic responses and the BRVs is derived, based on which the response statistics of structures at any time instant can be evaluated easily. Furthermore, the accuracy of the solution is independent of the time step used. Finally, several numerical examples in civil engineering, including a Euler beam under stochastic moving load and a shear frame structure subjected to uniformly modulated or fully non-stationary seismic motions, are studied to illustrate the performance of the proposed method. The obtained structural response statistics are compared with the solutions obtained by the Monte Carlo and evolutionary spectral methods. The results verified the high accuracy and efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

• A modified time domain method is proposed to calculate the noise reduction and acoustic impedance of an intake duct system. • The intake port boundary is modeled by adding a correction pipe requiring no complicated time domain convolution. • Only one simulation run is required to obtain both NR and acoustic impedance. Calculation of noise reduction and acoustic impedance of the duct system is needed for the one-port source model, which is widely used in the field of duct acoustics for extracting the source characteristics and predicting the radiating noise at the open end. The flow field in the duct influences the acoustic characteristics when the flow velocity is relatively high. Recently, the time domain method has been adopted to study the flow effects on the acoustic response of the duct mufflers. However, the existing method only focuses on the calculation of transmission loss (TL) or transfer matrix. In this paper, a modified time domain approach is proposed for the first time to calculate the noise reduction and acoustic impedance of the intake duct system. In the proposed time domain model, the frequency dependent reflection at the intake port, rather the anechoic boundary used for TL calculation, is simulated by simply adding a correction pipe at the port. This approach has effectively simplified the implementation of the traditional time domain method in dealing with frequency dependent reflection at the open end. The porous sound-absorbing material commonly used in the intake system is modelled by modified equations with the material porosity and flow resistivity. The predicted time-domain sound pressure signals are then post-processed to obtain the noise reduction and the acoustic impedance in a different way from the traditional time domain TL calculation approach. The result of validation has shown that the noise reduction and acoustic impedance predicted with the modified time domain approach agree well with the measured results and the results calculated from frequency domain methods in the cases without and with meanflow. [ABSTRACT FROM AUTHOR]

In this paper, we give a time domain method to solve exactly the problem of diffusion of a generic initial distribution in the presence of a sink. The diffusive motion is described by the Smoluchowski equation. The potential is taken to be flat and the sink function is taken to be a finite strength Dirac delta function. We solve this problem for the case of initial Gaussian distribution which is usually done numerically. This simple model has been an unsolved problem for some time and is of considerable importance in understanding the reaction–diffusion system. This method can be applied to solve several related problems. We verify our results numerically. • A new method to solve Smoluchowski equation in time domain is given. • The method can be applicable to far more realistic potentials and considerations. • The solution of the considered model ensures the solution of other realistic models by applying suitable transformations. [ABSTRACT FROM AUTHOR]