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• 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]

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]

• 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]

The wind-induced responses of a large-scale membrane structure, Expo Boulevard, are evaluated in this study. To obtain the wind pressure distribution on the roof surface, a wind tunnel test is performed. A brief analysis of wind pressure on the membrane roof is conducted first and then an analysis of the wind-induced responses of the structure is carried out using a numerical integral method in the time domain. In the process of calculation, the geometrical nonlinearity is taken into account. Results indicate that mean, RSM and peak values of the structure responses increase nonlinearly while the approaching flow velocity increases. Strong nonlinear characteristics are observed in the displacement responses, whereas the responses of nodal stress and cable axial force show minimal nonlinear properties when the membrane structure is subjected to wind loads. Different values of the damping ratio only have a minimal impact on the RSM response of the structure because the background component is a dominant part of the total dynamic response and the resonant component is too small. As the damping ratio increases from 0.02 to 0.05, the RMS responses of vertical displacement, nodal stress and cable axial force decrease by 8.1%, 6.7% and 17.9%, respectively. Since the mean component plays a significant role in the wind-induced response, the values of the gust response factor are not high for Expo Boulevard. [ABSTRACT FROM AUTHOR]

Introduction: Antimicrobial drug resistance is a fast emerging problem worldwide. It is a consequence of the use, particularly of the misuse of drugs. In most of the developing countries, antibiotics can be purchased without prescriptions, even when the practice is not legal. Presently, in India, Schedule H, under the Drug and Cosmetics Act and Rules, provides a list of over 536 drugs which include Antimicrobial Agents [AMAs], which are required to be sold on the prescription of a registered medical practitioner. Objectives: To evaluate the Over the Counter (OTC) sales of antimicrobial agents in allopathic pharmacies [community] within the city corporation limits. To describe the degree of difficulty which is faced in obtaining antibiotics without a prescription. To find out as to what advice, if any, was given by the pharmacists with regards to the administration of the medicines which had been sold. Methods: Three diseases were simulated by two medical students who presented as patients in randomly selected pharmacies at an Urban location. They then requested the pharmacists for medications for their illnesses. AMAs were requested for, if they were not issued at the first instance. Results and Discussion: Nearly 50% of the pharmacists declined to issue AMAs. Amoxicillin was the most common of the AMAs which were dispensed by the pharmacists. The duration and the frequency of the treatment which was advised by the pharmacists were mostly wrong. Conclusion: This study showed that the practice of dispensing AMAs without prescriptions was widely prevalent among the dispensaries which were located even in urban areas. Not only were the AMAs dispensed, but also they were dispensed without taking any history of hypersensitivity. What makes the practice worse is that the duration and the frequency of administration of these drugs are wrongly advised more often than not. [ABSTRACT FROM AUTHOR]

Based on international standard ISO2631 and national standard GB/T4970 Method of random input running test-Automotive ride comfort, the ride comfort tests are conducted on a bus with a study focused on the applicability discrepancy between different algorithms in ride comfort analysis. By applying Parseval theorem, both time and frequency domain algorithms are implemented with FAMOS and VC&MATLAB software development platforms. The results show that the outcomes of calculation with different algorithms don't have significant differences, but each algorithm has its own distinguishing feature. The time domain algorithm is more sensitive to peak factor and can be used to evaluate the ride comfort of vehicle from the perspective of human body comfort, while the frequency domain algorithm is suitable for analyzing the influence of each frequency of one-third octave band on human body vibration and providing bases for ride comfort improvement, but with the defects in lower accuracy and processing efficiency. And in frequency domain, the results of comparison between two spectrum estimation schemes indicate that the Welch classic spectrum estimation technique has poor consistency while the Yule-Walker method using AR model has relatively stable performance. [ABSTRACT FROM AUTHOR]

Abstract: Two methods for analyzing intracranial pressure (ICP) waveforms were compared. The frequency domain (FD) method converts the signal from the time domain to the frequency domain by a fast Fourier transform (FFT), while the time domain (TD) method calculates peak-to-peak value of the pulse waveform directly from the time samples. First, the ICP signal was regenerated from the first harmonic of the FFT and compared against the time domain raw ICP signal. We found that the FD method may underestimate pulse amplitude if there is heart rate variability or a high harmonic distortion. Second, to explore the significance in a larger data set, differences between FD- and TD-derived pulse amplitudes were determined for a total of 50,978 6-s time windows of 79 head injury patients. The mean difference in pulse pressure amplitude was 2.9mmHg for the 50,978 6-s time windows. Differences between TD- and FD-derived pulse amplitudes were ≥2.0mmHg in 58.8% of the 50,978 time windows. In about 33% of time windows FD amplitudes were <2mmHg when TD amplitudes were ≥4mmHg, and vice versa. Hence, the TD method is superior to the FD method for calculation of pulse amplitudes. Nevertheless, in this material both the TD and FD methods revealed significantly elevated pulse amplitudes in head injury patients with bad outcome (i.e. Glasgow Outcome Score 1–3). [Copyright &y& Elsevier]

In many applications, and in particular in seismology, realistic propagation media disperse and attenuate waves. This dissipative behavior can be taken into account by using a viscoacoustic propagation model, which incorporates a complex and frequency-dependent viscoacoustic modulus in the constitutive relation. The main difficulty then lies in finding an efficient way to discretize the constitutive equation as it becomes a convolution integral in the time domain. To overcome this difficulty the usual approach consists in approximating the viscoacoustic modulus by a low-order rational function of frequency. We use here such an approximation and show how it can be incorporated in the velocity-pressure formulation for viscoacoustic waves. This formulation is coupled with the fictitious domain method which permits us to model efficiently diffraction by objects of complicated geometry and with the Perfectly Matched Layer Model which allows us to model wave propagation in unbounded domains. The space discretization of the problem is based on a mixed finite element method and for the discretization in time a 2nd order centered finite difference scheme is employed. Several numerical examples illustrate the efficiency of the method. [ABSTRACT FROM AUTHOR]

The aeroelastic behaviour of vibrating blade assemblies is usually investigated in the frequency domain where the determination of aeroelastic stability boundaries is separated from the computation of linearized unsteady aerodynamic forces. However, nonlinear fluid-structure interaction caused by oscillating shocks or strong flow separation may significantly influence the aerodynamic damping and hence effect a shift of stability boundaries. In order to investigate such aeroelastic phenomena, the governing equations of structural and fluid motion have to be simultaneously integrated in time.In this paper a technique is presented which analyses the flutter behaviour of turbomachinery bladings in the time domain. The structural part of the governing aeroelastic equations is time-integrated according to the algorithm of Newmark, while the unsteady airloads are computed at every time step by a Navier–Stokes code. The link between the two time integrations is an automatic grid generation in which the used mesh is dynamically deformed so that it conforms with the deflected blades at every time step.The computed time series of the aeroelastic simulation of an assembly of highly loaded compressor blades vibrating freely in transonic flow are presented. The energy transfer between fluid and structure is here dominated by vibrating shocks and shock-boundary layer interaction. It is investigated if the predicted aeroelastic stability boundaries differ from those of a linearised method. [Copyright &y& Elsevier]

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]