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This paper proposes an approach to reconstruct the time-dependent forces acting on a vibrating structure from pressure measurements. In the approach, the pressures measured in the near field of the structure are related to the exciting forces at the reconstruction points by the transfer functions determined in an experimental way, whereupon the time-dependent forces can be reconstructed with these pressures as inputs. In the reconstruction process, an additional regularization with a mixed l

This paper presents a fast multipole indirect boundary element solver for the thin-body acoustic problems over an infinite impedance plane. The half-space impedance Green’s function involving a complex line source to approximate the porous ground effects is employed in the indirect boundary integral equation (IBIE), which makes that both mass-like and spring-like impedance conditions on the infinite plane are explicitly satisfied. A nonsingular IBIE formulation is derived to implement the fast multipole method (FMM) easily. The image relations of multipole moments are used to avoid the computation and translation of multipole/local expansion coefficients in the image domain. To deal with the numerical instability in the local translation of image multipole moments, a half-space tree structure is elaborately constructed for the FMM. The validity of the method is testified by a benchmark example and the potential of the method is investigated by the numerical simulation of noise barriers with different geometrical configurations.

This letter presents a boundary element scheme for analysis of acoustic resonances in cavities with impedance boundary conditions. The resultant eigenproblem, which is nonlinear and difficult to solve directly, is transformed to a linear one through a contour integral method. A variant-parameter scheme based on the Burton-Miller combined formulation is given to identify spurious eigenfrequencies, which are complex and similar to true eigenfrequencies. A numerical example is used to show the accuracy and effectiveness of the proposed method.

Nearfield acoustic holography based on the compressed sensing theory can realize the accurate reconstruction of sound fields with fewer measurement points on the premise that an appropriate sparse basis is obtained. However, for different types of sound sources, the appropriate sparse bases are diverse and should be constructed elaborately. In this paper, a block sparse Bayesian learning (SBL) equivalent source method is proposed for realizing the reconstruction of the sound fields radiated by different types of sources, including the spatially sparse sources, the spatially extended sources, and the mixed ones of the above two, without the elaborate construction of the sparse basis. The proposed method constructs a block sparse equivalent source model and promotes a block sparse solution by imposing a structured prior on the equivalent source model and estimating the posterior of the model by using the SBL, which can achieve the accurate reconstruction of the radiated sound fields of different types of sources simply by adjusting the block size. Numerical simulation and experimental results demonstrate the validity and superiority of the proposed method, and the effects of two key parameters, the block size, and sparsity pruning threshold value are investigated through simulations.

The compressive-equivalent source method can reconstruct the sound field of the sparsely distributed sound sources through promoting the sparsity of the equivalent source strengths. To reduce the mutual coherence of the sensing matrix, the spatially random sampling is performed. However, different samplings would make the reconstruction results instable, and a fixed sampling would not guarantee satisfied reconstruction results when reconstructing the sound field at different frequencies. To handle this issue, the present paper proposes a sensor array design method for sparse sound field reconstruction. After obtaining the matrix by the sum of the frequency-dependentsensing matrices, the optimization problem of the proposed method is formulated based on the mutual coherence minimization principle, and the solutions indicating the selected positions of the sensors are solved by the gradient projection. Numerical simulation and experimental results show that lower reconstruction errors can be obtained with the designed senor array compared to the spatially random sampling.

This paper proposes a method of measuring the powertrain noise, which enables for the indoor prediction of the sound pressure level (SPL) of pass-by noise in an early stage of vehicle development phase. The proposed method is implemented in two steps. Firstly, the indoor tyre/roller noise is obtained by the indoor coast-by experiment based on the proposed single coast-by approach. Secondly, the powertrain noise is computed by subtracting the tyre/roller noise from the total vehicle noise. Then the powertrain noise is synthesized with the outdoor tyre/road noise energetically to predict the level of pass-by noise, with the purpose of reducing the influence caused by the difference between indoor and outdoor tyre/road noise. The proposed method is validated by experimental comparisons with the existing methods, shielding method and slick-tyre experiment method, respectively. The results show that the proposed method not only produces better prediction accuracy than the existing ones, but also has the ability to predict the pass-by noise SPL for a realistic case in an evaluation time of less than one hour.

It is widely known that the boundary element method (BEM) without any special treatment suffers from the fictitious eigenfrequency problem for the numerical solutions of exterior acoustic problems. This problem has drawn much attention and been extensively studied over the last several decades. However, this paper is concerned with the existence and influence of the fictitious eigenfrequencies when using the BEM for the numerical solutions of interior acoustic problems. To this end, an eigenvalue analysis technique is developed for the acoustic BEM. The nonlinear eigenvalue problem caused by the acoustic BEM is converted into an ordinary linear one by using a contour integral method. Therefore, the conversion is fulfilled by solving a series of BEM systems of equations without any special or complicated treatment of the governing equations or the linear systems. Three interior acoustic examples including two with simply connected domains and one with a multiply connected domain are used to reveal the existence and influence of the fictitious eigenfrequencies. Furthermore, the Burton–Miller formulation with a variable coupling parameter is found to be able to remove such fictitious eigenfrequencies, and the optimal choice of the coupling parameter is investigated.

This paper presents a boundary element-based scheme for the sensitivity analysis of acoustic eigenfrequencies of both interior and exterior acoustic systems. The nonlinear eigenvalue problem generated by the acoustic boundary element method is first reformulated into a generalized eigenvalue problem of reduced dimension through a contour integral approach. The sensitivity formulations for acoustic eigenfrequencies are then derived based on an adjoint method that uses both the right and left eigenvectors. The adaptive cross approximation in conjunction with the hierarchical matrices is used to reduce the solution burden of the boundary element systems. The Burton-Miller-type combined formulation is applied to shift the spurious eigenfrequencies and their sensitivities, and the strategies to identify the spurious results are suggested. Three numerical examples are used to verify the accuracy and applicability of the developed scheme.

This paper proposes a sound field separation technique based on the time-domain equivalent source method with single layer pressure-velocity measurements to extract the nonstationary sound field radiated by the target source in a reverberant environment. This technique constructs a formulation that relates the pressures and particle velocities on a measurement surface to the strengths of time-domain equivalent sources arranged for modelling the outgoing and incoming waves. By solving the strengths of time-domain equivalent sources, the sounds coming from different sides of the measurement surface can be separated independently. In the proposed technique, the use of a time-domain equivalent source model allows the measurement surface to be arbitrarily shaped, thus providing the ability to analyze the arbitrarily shaped sources in a reverberant environment. Numerical simulations investigated the performance of the proposed technique when using different types of arrays, including planar, semi-cylindrical, and semi-spherical arrays, and an experiment with three loudspeakers located at two sides of the measurement surface was carried out to test the validity of the proposed technique. Both numerical and experimental results demonstrate that the proposed technique can remove the influence of disturbing sources in both time and space domains and separate out the target sound fields effectively.

A time domain angular spectrum method is proposed to reconstruct nonstationary sound fields. In this method, the sound field is expressed as a superposition of a series of plane wave bases, and the plane wave basis is constructed by an impulse response function that relates the time domain angular spectrum to the field point pressure. The impulse response function consists of two parts, the propagating plane waves and the evanescent plane waves, and their physical interpretation is provided. By discretizing the time convolution between the plane wave strength and the impulse response function, the reconstruction can be carried out at each time step, thus providing the advantage of real-time reconstructing sound fields. Since the real-time reconstruction process is non-recursive, it can provide a stable reconstruction. In the reconstruction process, the Tikhonov regularization is introduced at each time step to obtain an appropriate estimation of the plane wave strength. Numerical simulations with an unsteady excitation plate and an experiment with an impacted plate were carried out to demonstrate the feasibility of the proposed method on reconstructing nonstationary sound fields. The effect of numerical parameters on the reconstruction accuracy was also investigated in the numerical simulations.

The equivalent source method (ESM)-based sound field separation technique has been successfully introduced into near-field acoustic holography as a preprocessing tool to eliminate the influence of disturbing sources or reflections from the opposite side of the array. In this paper, that technique is further extended in a sparsity framework, which makes it possible to take the advantage of the theory of compressive sensing to achieve reasonable separation accuracy with a limited number of spatial sampling points. In this study, three sparse bases are considered, including two existing bases that are suitable for spatially sparse and spatially extended sources, respectively, and a more flexible, redundant sparse basis that is constructed by combining the two sparse bases above, and the l 1 - norm minimization is used to promote sparse solutions. Numerical simulation and experimental results demonstrate the validity of the proposed technique and show the superiority of the use of the redundant sparse basis. Besides, the effects of the relative strength of the target source to the disturbing source, the number of spatial sampling points and the signal-to-noise ratio on the separation accuracy are analyzed numerically.

The time-domain signals of noise sources are of great importance to acoustic design of machinery. One available way to obtain source signals is to reconstruct them from the acoustic signals measured by a microphone array. However, when sources are moving, the acoustic signals sampled by a fixed microphone array are distorted in amplitude and frequency due to the Doppler effect, leading to that the reconstructed source signals may not reflect the real information of sources. This paper first presents a time-wavenumber-domain method to eliminate the Doppler effect in the measured acoustic signals, in which no priori information on the number, frequencies and locations of sources is needed. Then the acoustic signals after eliminating the Doppler effect are used as the input of the passive time reversal method to reconstruct source signals. Numerical simulation and experimental results show that the proposed method can effectively eliminate the Doppler effect and accurately reconstruct the source signals even when the sources emit transient signals. It is also found that the proposed method can work stably when the sources are moving at high speeds if increasing the array aperture and in the situation of low signal-to-noise ratio.

In the Big Data era, data provenance has become an important concern for enhancing the trustworthiness of key data that are rapidly generated and shared across organizations. Prevailing solutions employ authoritative centers to efficiently manage and share massive data. They are not suitable for secure and trustworthy decentralized data provenance sharing due to the inevitable dishonesty or failure of trusted centers. With the advent of the blockchain technology, embedding data provenance in immutable blocks is believed to be a promising solution. However, a provenance file, usually a directed acyclic graph, cannot be embedded in blocks as a whole because its size may exceed the limit of a block, and may include various sensitive information that can be legally accessed by different users. To this end, this paper proposed the BSTProv, a blockchain-based system for secure and trustworthy decentralized data provenance sharing. It enables secure and trustworthy provenance sharing by partitioning a large provenance graph into multiple small subgraphs and embedding the encrypted subgraphs instead of raw subgraphs or their hash values into immutable blocks of a consortium blockchain; it enables decentralized and flexible authorization by allowing each peer to define appropriate permissions for selectively sharing some sets of subgraphs to specific requesters; and it enables efficient cross-domain provenance composition and tracing by maintaining a high-level dependency structure among provenance graphs from different domains in smart contracts, and by locally storing, decrypting, and composing subgraphs obtained from the blockchain. Finally, a prototype is implemented on top of an Ethereum-based consortium blockchain and experiment results show the advantages of our approach.

Stability of the inverse time domain boundary element method (ITBEM) for near-field acoustic holography is investigated. An eigenvalue system is built by reformulating the ITBEM to an iterative format. Through the analysis of the eigenvalue system, a stabilization criterion is derived. Then the stabilization criterion is utilized to reveal the stabilization mechanism of the TSVD method which plays an important role in the ITBEM. Furthermore, a method for properly choosing the ratio of truncated singular values to ensure the stability is provided. Although stability can be managed by using the TSVD method, the accuracy of the results cannot always be guaranteed. To overwhelm this difficulty, an averaging technique is further introduced, and its stabilization mechanism is investigated by incorporating it into the ITBEM formulations. Numerical simulations are carried out to validate the stabilization criterion, and the stabilization mechanisms of TSVD and averaging are shown specifically with extensive eigenvalue analyses.

For path planning and program generation of multi-type holes, this paper presents a method of the path planning, by using the improved genetic algorithm based on chaos algorithm, and develops an interactive programming system for multi-type holes. Users can choose regular holes, and input the parameters and the necessary information, according to their needs. Then the system will combine holes automatically, and calculate the position coordinates of each hole. After that the path planning is carried out by using the improved genetic algorithm. Finally, the system carries out the simulation experiment of the path planning, and outputs NC program. Experiment shows the system can realize the path planning of multi-type holes by a combination of regular holes and generate the NC code after path planning. The optimization of path is better and the operation is more convenient than UG and other professional CAM software.

Analysis of aerodynamic loading noise generated by unsteady rotating forces is of great significance in aeroacoustics research. However, it is still difficult to obtain the position and strength information of unsteady rotating loading sources in practice. In this paper, a time-domain inverse method for the localization and quantification of unsteady rotating loading sources is proposed, based on the Farassat integral solution of the Ffowcs Williams-Hawkings equation with the monopole and quadrupole source terms being neglected. In this method, the analytical direct model that relates the unsteady rotating forces to the radiated sound field is first discretized, and then the unsteady rotating forces are reconstructed from the measured pressures via a time-domain inversion procedure. Different from the previous inverse aeroacoustic methods, the proposed method can reconstruct the time histories of the three components of the unsteady rotating forces in the Cartesian coordinate system, thereby accurately locating the source positions and quantitatively estimating the source strengths in a real-time way. Numerical simulations with two unsteady rotating point forces and experiments with the rotating blades of an unmanned aerial vehicle examine the validity of the proposed method.

Real-time nearfield acoustic holography (RT-NAH) is an effective tool to identify nonstationary sound sources and predict the time-dependent sound field via a temporal convolution between the time-dependent wavenumber spectrum on the hologram plane and an impulse response. However, the conventional RT-NAH procedures are developed for sound sources situated in a static medium. As for sound sources located in a moving medium, the conventional RT-NAH procedures cannot be applied directly due to the fact that the impulse response will be changed by flow effects. In this paper, two analytical impulse responses in a uniformly moving medium, corresponding to two cases that the flow direction is parallel to and perpendicular to the hologram plane, are derived first with consideration of flow effects, and then RT-NAH is extended to realize forward and backward propagation of time-dependent signals in the moving medium. Numerical simulations are conducted to check the performances of the proposed method. The results show that the proposed method not only can be used to predict nonstationary sound fields but also can be utilized to identify nonstationary sources in a moving medium for both the parallel and perpendicular cases.

A limitation of the monopole time reversal (MTR) method, which records and retransmits the monopole field only, is that the spatial resolution of the focus cannot be better than half a wavelength, and therefore it is not suitable for locating low-frequency sound sources. In this paper, the time-reversed pressure field obtained by the MTR method is first transformed into the wavenumber domain, and is then decomposed into a filter term that controls the spatial resolution of the focus and a source term that is related to the sound source and focusing plane. Subsequently, a correction is made to the time-reversed pressure field of the MTR method by replacing its filter with the filter for the time-reversed pressure gradient field of the dipole TR (DTR) method, a constant filter and an empirical filter, which makes it possible to include many more evanescent waves and obtain subwavelength focusing. Numerical simulation and experimental results show that compared to the original MTR method, the corrected one is able to dramatically improve the spatial resolution of the focus at low frequencies. It is also found that the constant filter is applicable when the signal-to-noise ratio (SNR) is high (generally above 30 dB), the filter for the time-reversed pressure gradient field of the DTR method works stably even in the situation of low SNR, and the empirical filter performs best when the SNR is above 10 dB.

A time domain boundary element method (TBEM) is applied to predict the horn effect. As the time response calculated by the time domain boundary integral equation contains the resonance components, when transformed to the frequency domain, the result will corrupt at the characteristic frequencies. To overcome this problem, a Burton–Miller-type combined time domain integral equation in half-space is applied. The resonance components are excluded in the time domain calculation, thus the corruptions are avoided in the frequency domain. As a result, the horn effect can be predicted very well at all frequencies. Compared to the frequency domain boundary element method for predicting the horn effect, the TBEM is more efficient due to the lower cost of forming coefficient matrices and solving equations. A numerical simulation is carried out to demonstrate the efficiency of the TBEM, and two experiments are conducted to validate the proposed method in predicting the horn effect. Both numerical and experimental results indicate that the proposed method is reliable and efficient in predicting the horn effect.

A time-domain inverse technique based on the time-domain equivalent source method is proposed for the localization and quantification of rotating sound sources. In this technique, the actual rotating sound sources are modeled by a series of rotating equivalent sources distributed on the source surface. The strengths of these equivalent sources are solved based on the exact transfer relationship between the measured pressure at the receiver time and the desired equivalent source strengths at the source time. Compared to the known time-domain rotating beamforming that just owns the function of source localization, the proposed inverse technique not only can locate rotating sources accurately but also can predict sound fields quantitatively. Moreover, due to the use of retarded time approach, the proposed inverse technique avoids the interpolation of measured pressure that is needed in the time-domain rotating beamforming, thus providing the ability of real-time calculation of source strengths. Numerical simulations and experiments examine the validity of the proposed technique and demonstrate its advantages of locating sources more accurately and enabling to predict sound fields quantitatively by comparing with the time-domain rotating beamforming.

This paper provides a non-contact approach to reconstruct the distributed or concentrated force applied to a plate in the time domain. This approach is based on sound pressure measurements and is realized by coupling the techniques of real-time near-field acoustic holography (RT-NAH) and force reconstruction. A microphone array is used to measure the sound pressures in the near field of the plate. The measured sound pressures are taken as the inputs of the RT-NAH to reconstruct the vibration responses, including the normal acceleration, velocity, and displacement, on the surface of the plate. With the reconstructed vibration responses, the equation of motion governing the forced vibration can be further processed to reconstruct the force applied to the plate in the time domain. In the process of reconstructing the vibration responses, a displacement–pressure impulse response function is derived for the first time and is used in the RT-NAH. Results of numerical simulations as well as experiments demonstrate that the proposed approach can identify the location of the force accurately and reconstruct the time history of the force effectively, thereby helping to diagnose the mechanical cause of the radiated noise.

Background Anaplastic thyroid carcinoma (ATC) is a refractory and poor prognosis tumor Present study aimed to investigate the underlying biological functions and pathways involved in the development of ATC and to identify potential hub genes and candidate biomarkers of ATC. Materials and methods Bioinformatics analyses were performed to identify the differentially expressed genes (DEGs) between ATC tissue samples and adjacent normal tissue samples. Protein-protein interaction (PPI) networks of the DEGs were constructed using Search Tool for the Retrieval of Interacting Genes online tool and Cytoscape software and divided into sub-networks using the Molecular Complex Detection (MCODE) plug-in. DEGs in each module was analyzed by enrichment analysis of the KEGG Orthology Based Annotation System (KOBAS) web software version 3.0. Eventually, the hub genes from bioinformatics analysis were verified by qRT-PCR assay in different ATC cell lines. Results Thirty hub genes were selected and three modules were built by the Cytoscape software from the PPI network. Seven genes (CDK1, CCNB2, BUB1B, CDC20, RRM2, CHEK1 and CDC45) were screened from thirty hub genes. Enrichment analysis showed that these hub genes were primarily accumulated in ‘cell cycle’, ‘p53 signaling pathway’, ‘viral carcinogenesis’, ‘pyrimidine metabolism’ and ‘ubiquitin mediated proteolysis’. The results of qRT-PCR indicated that seven hub genes were unregulated in three ATC cell lines compared with normal thyroid gland cell. Conclusions These findings suggest that CDK1, CCNB2, BUB1B, CDC20, RRM2, CHEK1 and CDC45 may serve as novel diagnosis biomarkers and potential therapeutic target for ATC.

Transient nearfield acoustic holography based on the time domain equivalent source method suffers from the instability that is caused by the use of the time marching scheme. In this paper, the time marching scheme is reformulated to a large iterative scheme. By conducting the eigenanalysis of this large iterative scheme, a necessary condition for stability, i.e., the maximum magnitude of eigenvalues should not be larger than one, can be obtained. Moreover, the causes of instability are analyzed according to the eigenvalues distribution. By virtue of the eigenanalysis, the mechanisms and drawbacks of three previous stabilization methods based on the Tikhonov regularization, the truncated singular value decomposition (TSVD), and the multistep approach are analyzed. To overcome their drawbacks, the classical golden section method is applied to search the regularization parameters and filter parameters based on the necessary condition for stability. Furthermore, the time averaging technique is introduced into the stabilization methods based on the Tikhonov regularization and the TSVD to eliminate the high-frequency oscillation and release the difficulty of searching the filter parameter, respectively. Numerical simulation results indicate that all the improved methods can realize the stabilization of solutions.

The inverse boundary element method (IBEM) is a powerful tool for realizing sound field reconstruction of sources with arbitrarily-shaped surfaces. In the conventional IBEM, the Tikhonov regularization is generally used and the number of sampling points is required to be larger than that of nodes on the boundary surface to guarantee to obtain a unique solution. Meanwhile, it requires that the minimum discretization interval on the boundary surface should be less than one-sixth wavelength to ensure to obtain enough calculation accuracy. Therefore, the number of sampling points may be dramatically large at high frequencies. In this paper, acoustic radiation modes, which are composed of the eigenvectors of the resistive impedance matrix, are used as the sparse basis of source surface velocities. Based on this sparse basis, sparse regularization is introduced into the IBEM. Compared to the Tikhonov regularization, the sparse regularization can provide a higher accuracy for the reconstruction of source surface velocities and can reduce the number of sampling points by taking advantage of the theory of compressive sensing. Both numerical simulation and experimental results demonstrate the superiority of the proposed method. Meanwhile, the effects of the number of sampling points and the signal-to-noise ratio on the reconstruction accuracy are analyzed numerically.

In practical situations, vibrating objects are usually located above a reflecting plane instead of exposing to a free field. The conventional nearfield acoustic holography (NAH) sometimes fails to identify sound sources under such situations. This paper develops two kinds of equivalent source method (ESM)-based half-space NAH to reconstruct the sound field above a reflecting plane. In the first kind of method, the half-space Green's function is introduced into the ESM-based NAH, and the sound field is reconstructed based on the condition that the surface impedance of the reflecting plane is known a prior . The second kind of method regards the reflections as being radiated by equivalent sources placed under the reflecting plane, and the sound field is reconstructed by matching the pressure on the hologram surface with the equivalent sources distributed within the vibrating object and those substituting for reflections. Thus, this kind of method is independent of the surface impedance of the reflecting plane. Numerical simulations and experiments demonstrate the feasibility of these two kinds of methods for reconstructing the sound field above a reflecting plane.

The accuracy, resolution, and economic cost of near-field acoustic holography (NAH) are highly dependent on the number of spatial sampling points. Generally, higher accuracy and resolution require more spatial sampling points, which may increase the workload of measurement or the hardware cost. Compressive sensing (CS) is able to solve the underdetermined problems by utilizing the sparsity of signals, and thus it can be applied to NAH to reduce the number of spatial sampling points but at the same time provide a high-resolution reconstruction image. Based on the CS theory, this paper proposes a compressed modal equivalent point source method (CMESM). In the method, a sparse basis that is obtained from the eigen-decomposition of the power resistance matrix is introduced to compress the equivalent point source strengths, and the l1-norm minimization is used to promote sparse solutions. Both numerical simulation and experimental results demonstrate the validity of the proposed CMESM and show its advantage over the existing methods when the number of spatial sampling points is reduced.

Tamura proposed the well-known spatial Fourier transform method for measuring the reflection factor at oblique incidence, which is based on measurements of pressure on two planes (PP-method). In the present paper, that spatial Fourier transform method is modified by allowing the input data to be measurements of pressure and particle velocity on one plane (PV-method) or particle velocity on two planes (VV-method). Numerical simulations and experiments are carried out to examine the feasibility of the PV- and VV-methods and to show their performances in comparison with the PP-method. It is shown that the PV-method provides almost the same results as the PP-method under all conditions. Meanwhile, the VV-method provides good results at angles of incidence less than a certain value (around 60? if the radial measurement line is about 100 cm long) when a dipole source is used, but leads to significant deviations at larger angles of incidence except for (nearly) rigid material. Also, the VV-method performs better than the other two methods when the flow resistivity of the absorbing material is large or when the frequency is high.

The analytical passive time reversal method (APTRM) is a powerful technique for sound source localization. In that technique, it generally requires that the frequency response function relating the measurement point to the focusing point should be known in advance. However, inside an enclosure of arbitrary shape, there is no theoretical formulation of this frequency response function, and using the APTRM with the free-field Green's function might lead to inaccurate localization of sound sources. This paper proposes a method combining the APTRM with the equivalent source method (ESM) to locate sound sources in an enclosure of arbitrary shape. In this method, the frequency response function relating the measurement point to the focusing point inside the enclosure is first calculated numerically using the ESM, and then the APTRM with this numerical frequency response function is used to realize the localization of sound sources. Numerical simulations in a rectangular enclosure and an enclosure of arbitrary shape as well as an experiment in a rectangular wooden cabinet are performed to verify the validity of the proposed method. The results demonstrate that the frequency response function in an enclosure can be accurately calculated using the ESM; based on measurements with a spherical array composed of 48 microphones, the proposed method can effectively locate the sound sources in enclosures of different shapes and work stably under the situation of low signal-to-noise ratio.

In this paper, a half-space fast multipole BEM is developed for the simulation of three-dimensional acoustic problems above an infinite impedance plane. The half-space impedance Green’s function involving a complex line source is used, so that both mass-like and spring-like impedance boundary conditions on the infinite plane can be explicitly satisfied and the infinite plane is not required to be discretized. The Burton–Miller method is employed to tackle the fictitious eigenfrequency problem involved in the conventional boundary integral equation method. Image relations of the multipole expansion coefficients are used and the half-space impedance Green’s function is modified to apply such relations to avoid calculating, translating and saving the multipole/local expansion coefficients in the image domain. An automatic integrator with adaptive interval subdivision is further adopted to calculate the line integral contained in the M2L translation formula accurately and efficiently. Numerical examples are given to show the validity and potential of the method.

In previous studies, an equivalent source method (ESM)-based technique for recovering the free sound field in a noisy environment has been successfully applied to exterior problems. In order to evaluate its performance when applied to a more general noisy environment, that technique is used to identify active sources inside cavities where the sound field is composed of the field radiated by active sources and that reflected by walls. A patch approach with two semi-closed surfaces covering the target active sources is presented to perform the measurements, and the field that would be radiated by these target active sources into free space is extracted from the mixed field by using the proposed technique, which will be further used as the input of nearfield acoustic holography for source identification. Simulation and experimental results validate the effectiveness of the proposed technique for source identification in cavities, and show the feasibility of performing the measurements with a double layer planar array.

Planar near-field acoustic holography has been successfully extended to reconstruct the sound field in a moving medium, however, the reconstructed field still contains the convection effect that might lead to the wrong identification of sound sources. In order to accurately identify sound sources in a moving medium, a time-domain equivalent source method is developed. In the method, the real source is replaced by a series of time-domain equivalent sources whose strengths are solved iteratively by utilizing the measured pressure and the known convective time-domain Green's function, and time averaging is used to reduce the instability in the iterative solving process. Since these solved equivalent source strengths are independent of the convection effect, they can be used not only to identify sound sources but also to model sound radiations in both moving and static media. Numerical simulations are performed to investigate the influence of noise on the solved equivalent source strengths and the effect of time averaging on reducing the instability, and to demonstrate the advantages of the proposed method on the source identification and sound radiation modeling.

A pressure–velocity impulse response is deduced in this work to establish the relationship between the pressure and the particle velocity in the time-wavenumber domain. By virtue of it, real-time nearfield acoustic holography (RT-NAH) is extended to reconstruct the instantaneous surface normal velocity of a vibrating structure from the time-dependent pressure measured in the near field, which provides a non-contact and real-time method to measure and visualize the transient vibration of the structure. An experiment of an impacted steel plate is investigated, in which the surface normal velocity of the plate is measured by laser Doppler vibrometry and reconstructed by RT-NAH. The comparison of surface normal velocities obtained by using these two methods shows a satisfactory agreement not just for the time-evolving surface normal velocity signals but also for the vibration mode shapes. Accordingly, it demonstrates that RT-NAH is a viable approach for reconstructing the instantaneous surface normal velocity.

To identify sound sources situated in a fluid flow, an equivalent source method (ESM)-based nearfield acoustic holography (NAH) in a moving medium is proposed, and two types of acoustic inputs, pressure and particle velocity, are considered. In particular, an analytical relationship between the particle velocity perpendicular to the flow direction and the equivalent source strength is deduced, which makes it possible to realize the reconstruction with particle velocity input. Compared to the planar NAH in a moving medium, the proposed method is applicable to sound sources with more complicated geometries. Numerical simulations with sound sources distributed over two types of geometries including planar geometry and nonplanar one are conducted to test the performances of the proposed method. The results indicate that the proposed method provides satisfactory reconstructed results whatever with pressure input or with particle velocity input, and it is valid and robust over a wide range of flow velocities and frequencies and under different levels of background noise.

Numerical instability is an important issue that should be addressed in the time-domain equivalent source method (TESM). This study proposes a multistep method to stabilize TESM when using the measured acoustic pressure data to optimize equivalent source strengths. Unlike the conventional single-step method that solves each time step in the time-marching process of TESM, the proposed method performs a one-time solution for several time steps. The multistep solution can potentially reduce the accumulation rate of error, and improves filtering effects by changing the structure of the matrix that needs to be inverted when the truncated singular value decomposition or Tikhonov regularization is used in the time-marching process. Numerical simulations with three examples demonstrate the effectiveness of the multistep method in improving the stability of solutions compared with the single-step method. Effects of the number of merged time steps on the solutions are also discussed to guide the selection process. Finally, the sensitivity of the multistep method to numerical parameters is investigated to demonstrate its consistency under different configurations of numerical parameters.

Quality of teaching in university has a great influence on students’ learning and developing. Nowadays, studies on teaching strategies have attracted more attention, but practical methods to improve teaching abilities are not common. At the same time, most studies focused on how to improve teaching abilities in theory. Teachers need specific and practical methods to help them improve teaching abilities. Classroom teaching is one of the most important aspects in higher education. Therefore, this paper aimed at providing specific implementation methods and recommendation guidelines to improve classroom teaching abilities. We introduced how to improve classroom teaching abilities with Pair Teaching strategy. According to feedbacks from both teachers and students, we got a conclusion that pair teaching can not only improve both teachers’ classroom teaching abilities, but also increase students’ learning output, which improves teaching effectiveness. The significance of the study was that we provided valuable guidance to improve classroom teaching abilities with pair teaching strategy, and we also demonstrated how to apply pair teaching strategy in C programming language in Beijing Institute of Graphic Communication as a case.

To realize the accurate reconstruction of sound field in a moving medium under the condition of limited holographic aperture, a patch nearfield acoustic holography (NAH) in a moving medium is proposed. The proposed method not only reduces the influence caused by the limited aperture effects through sound field extrapolation, but also perfectly suits for sound field reconstruction in a moving medium by improving the shape of the modified Tikhonov regularization filter and the noise estimation method in accordance with flow effects. In the method, two cases that the flow direction is parallel to and perpendicular to the hologram surface are considered. Especially in the perpendicular case, the expression of the wavenumber component in the z direction is improved to make the proposed method suitable for the moving medium at a high Mach number. Simulations are investigated to examine the performance of the proposed method and show its advantages by comparing with NAH in a moving medium and the conventional patch NAH. It is found that, the proposed method is effective and robust at different flow velocities of the medium and different frequencies of the sound source.

Planar nearfield acoustic holography (NAH) is extended to identify the sound source in a noisy environment. The extended method requires the knowledge of the pressures on two closely spaced parallel hologram planes and the plane wave reflection coefficient on the target source surface. First, the incoming field coming from the back side of the microphone array and the scattered field due to the incoming wave falling on the target source are correlated through the plane wave reflection coefficient on the target source surface. Then, the mixed field on the hologram plane can be represented by the field that would be radiated by the target source into free space and the incoming field. Finally, the field that would be radiated by the target source into free space can be extracted by using the pressures measured on two hologram planes, which will be further used to accurately identify the sound source via planar NAH. The validity of the proposed method is demonstrated by simulations and experiment, and the influence of the relative strength of the disturbing source to the target source is also investigated.

This paper is related to the design of an upper-limb motion recognition system based on a new-style MEMS sensor MPU-9150.In order to obtain more accurate deflection Angle, we describe the output of the 3-axis gyroscope and 3-axis accelerometer data with quaternion differential equations and then solving the corresponding equation through the timing incremental method and acceleration value separately. We can get two angles by solving the double integral values, then through the data fusion algorithm for two angle value processing to obtain the stable angle value. Verified, the results of this experiment have small error,had a high accuracy, stability and timeliness.

Information and network technologies have great positive effect on teaching and learning in education. Many companies and researchers have developed various teaching and learning models to promote teaching and learning processes. In higher education, teachers work on different computer environments, which bring teachers many difficulties, such as version control of teachers working and software availability. We presented a cloud based working and teaching system for teachers so that each teacher will work with the same computer environment wherever and whenever they are as long as internet connection is available. With this model, teachers can focus on their work instead of underline computer infrastructure.