Theory of passive localization for underwater sources based on acoustic ray modeling

I.IntroductionLongrangeMFPpassivelocalizationisahotpointinunderwateracousticsstudyinrecentyears.Thekeyworkistointroducethesoundfieldsinformationindeterminingthesourcelocation.MFPlocalizationutilizesmuchmoreinformationofseaenvironmentandthereforeobtainsmuchbetterperformancewhencomparingwiththetraditionalmulti-subarraypassivelocalization.PeoplehaveplungedilltothestudyofMFPlocalizationwithgreatzeal.ThestudiesofMFPlocaJizationconcentrateontheoreticalresearchandsimulations,whilesuccessfulexpe…     

Research on acoustic emission monitoring of pitting corrosion on 304 stainless steel

In order to study acoustic emission(AE) characteristics of pitting corrosion on 304 stainless steel under higher than normal temperature,pitting corrosion process of 304 stainless steel in 6%ferric chloride solution at 70°was monitored by AE technology.Conventional parameter-based approach and signal-based analysis were combined to deal with recorded AE signals,and micrographic observation was performed for further verification.The results showed that AE hit and energy increased gradually with time and reached the peak at certain time, and then declined and maintained a stable condition.Signal waveform was mainly composed of low-frequency(< 100 kHz) flexural wave with larger amplitude and energy and high-frequency (> 100 kHz) expansion wave with lower amplitude and energy.The research results have some certain significance for AE monitoring of pitting corrosion on 304 stainless steel under higher than normal temperature.     

Preparation of ZIF-8 membranes supported on macroporous carbon tubes via a dipcoating–rubbing method

In the present work, a new dipcoating–rubbing method (DCRM) was developed to seed the surface of a macroporous carbon tube with a mixture of graphite and ZIF-8 nanoparticles. A continuous and low-defect ZIF-8 membrane was well formed on the seeded carbon tube by solvothermal growth. The DCRM involved a two-step process including first dipcoating a thin layer of the composite of graphite and ZIF-8 nanoparticles on the carbon surface and then rubbing the layer to form a stable seed layer. The graphite in the composite acting as binding agent could have two functions: (1) anchoring the ZIF-8 seeds onto the carbon surface; (2) smoothing the coarse surface of the macroporous carbon tube, thus forming a high quality ZIF-8 membrane. The as-prepared membrane was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and single gas permeation and was proved to be continuous and low-defect. The ideal selectivity of H₂/CH₄ is 7.9 with a H₂ permeance of 7.15×10⁻⁸ mol Pa⁻¹ s⁻¹ m⁻², which is higher than its corresponding Knudsen diffusion value. We could therefore expect the ZIF-8 membrane supported on macroporous tubular carbon to achieve a high selectivity of H₂ over CH₄ through a molecular sieving effect.     

Research on acoustic holography method for identification of sound sources

This paper presents the method named acoustic holography which can be used to identify noise sources. A new formula of holography reconstruction is obtained, based on the Kirchhoff integral formula. Some simulating tests are carried out using the new formula. The comparison with other reconstruction formulas proves that the new formula is more effective. By using acoustic holography method, some interesting results about the noise of a vehicle are shown. The results proves that acoustic holography is an effective method for the identification of the complex noise sources.     

Analysis of factors affecting beam shaping quality of geometric steady-phase method based on SLM北大核心

基于几何稳相法求解调制相位,使用傅里叶透镜进行傅里叶变换,在后焦面处聚焦,得到对应的平顶光束,从而将圆形高斯光束整形为方形平顶光束,其中光路参数对整形质量将产生较大影响。实验中发现,方形平顶光束受零级光影响均匀性较差,因此详细分析了零级光产生的原因,提出了有效的解决方法,并对实验结果中出现的零级光通过叠加闪耀光栅直接移除。实验结果表明:移除零级光后方形平顶光束的能量利用率为72.3%,光束均匀性高达97.2%,优于传统整形方法。最后进一步分析了全息图与入射光束偏移量、离焦以及入射光束束腰半径对几何稳相法整形质量的影响,为几何法光束整形的应用提供了便利。     

Calculation of the multimode Franck–Condon factors based on the coherent state method

The equivalence of two ways for the calculation of overlap integrals, i.e. the Sharp–Rosenstock generating function method and the Doktorov coherent state method, has been proved. On the basis of the generating function of the overlap integrals, a new closed form expression for the Franck–Condon integrals for overlap multidimensional harmonic oscillators has been exactly derived. In addition, some useful analytical expressions for the calculations of the multimode Franck–Condon factors have been given.     

Wideband high-resolution direction of arrival estimation method based on the pressure-velocity combined processing using the acoustic vector sensor array

In order to solve the problem of DOA (Direction of Arrival) estimation of underwater distant wideband targets, a novel coherent signal-subspace method based on the cross spectral matrix of pressure and particle velocity using the Acoustic Vector Sensor Array (AVSA) is proposed in this paper. The proposed method is different from existing AVSA based DOA estimation methods in using particle velocity information of Acoustic Vector Sensor (AVS) as an independent array element. It is entirely based on the combined information processing of pressure and particle velocity, namely, the P-V cross spectrum, has better DOA estimation performance than existing methods in isotropic noise field. By theoretical analysis, both focusing principle and eigendecomposition theory based on the P-V cross spectral matrix are given. At the same time, the corresponding criteria for source number detection is also presented. Computer simulations with data from lake trials demonstrate that the proposed method is effective and obviously outperforms existing methods in resolution and accuracy in the case of low Signal-to-Noise Ratio (SNR).     

Influence of acoustic leakage at fluid–solid interface on interferometric detection of surface acoustic wave

When using laser interferometer to detect surface acoustic wave at fluid–solid interface, there are two factors which will cause the optical path length variation of the probe laser beam: interface deformation, and refractive index changes in fluid induced by acoustic leakage. Influence of acoustic leakage on laser interferometric detection for surface acoustic wave is researched here. A metal plate immersed in an infinite fluid is used as a physical model. Interface deformation due to laser-induced acoustic wave and pressure in fluid due to acoustic leakage are computed for select cases by finite element method. The optical path length variation caused by the two factors are calculated respectively and compared. The results show that the influence of acoustic leakage increases with the increasing acoustic impedance matching of fluid and solid, the peak-to-peak of influence degree increases linearly with the increasing acoustic impedance of fluid, and that decreasing the distance between the interferometer and interface can effectively reduce the influence of acoustic leakage.     

Theoretical modelling,analysis and validation of the shaft motion and dynamic forces during rotor–stator contact

This paper deals with the theoretical study of a horizontal shaft, partially levitated by a passive magnetic bearing, impacting its stator. Rigid body dynamics are utilised in order to describe the governing nonlinear equations of motion of the shaft interacting with a passive magnetic bearing and stator. Expressions for the restoring magnetic forces are derived using Biot Savart law for uniformed magnetised bar magnets and the contact forces are derived by use of a compliant contact force model. The theoretical mathematical model is verified with experimental results, and shows good agreements. However, the simulated contact forces are higher in magnitude compared to the experimental results. The cause of this disagreement is addressed and shows that the formulation of the theoretical contact force model slightly overestimates the forces acting during a full annular backward whirl motion.     

Exact evaluation of the multidimensional Franck–Condon integrals based on the contour integral method

Adopting a different method from the Sharp–Rosenstock generating function method and the Doktorov coherent state method, a closed form expression for the Franck–Condon integrals between arbitrary multidimensional harmonic oscillators is derived exactly under the Duschinsky mixing effects on the base of the contour integral form expression of Hermite polynomials. In addition, an analytical expression for the calculation of the four-mode Franck–Condon factors is presented.     

Investigation on method for measuring dynamic shear modulus of underwater acoustic structure materials

1IfltroductionSince6o's,withthedevelopmentoflargemolecularmaterialsandcompositematerials,structurematerialsinunderwateracousticapplicationshavemadeagreatchanges.Forex-ample,thepropertiesofsonardomesthatmadefromreinforcedpolymersinsteadofstainlesssteelhavebeenimprovedobviously.Inordertodesignrationally,itisnecessaryforengineerstofindouttheiracousticpropertiescompletely.Accordingtotheelastictheories,twokindsofwave:longitudinalwaveandshearwavewillbeexcitedontheboundaryoftwomediumswhilethesoundsar…     

Passive tracking and size estimation of volume target based on acoustic vector intensity

1 IntroductionThe ship detected and tracked at short distance by a passive acoustic device, for instance,by an acoustic fuze, should not be considered to be a dot target, bat a volume target with theradiated-sound sources colltinuously distributed along the fore-and-aft direction. Literature[1]showed that the distribution pattern of the ship-radiated noise sources can be approalmatelysimplexxed to be a thlee radiated-noise highlight model: (1) stern, propeller is the principal noisesource, and…     

Estimation method of glottal vocal efficiency based on conversion function of voice source

This investigation was designed to approach a novel estimation method of glottal vocal efficiency (GVE) based on conversion function of voice source. The conversion function of voice source was defined the ratio of supra-glottal acoustic voice source signal to the glottal air volume flow velocity waveform in frequency domain. A carefully designed in vivo canine larynx experiment and several human experiments including different vowels, pressed, falsetto, breath and typical laryngeal diseases were adopted to demonstrate this alternative GVE method. Compared with other vocal efficiency, it is shown that this method could eliminate the contribution from the super vocal tract transmission and resonance to GVE, and reflect the differences of phonation modes. The average magnitude of this conversion function in frequency domain represents GVE, and the variation of the magnitude in fundamental frequency is identical to AC/DC value.     

Analysis and engineering of coupled cavity waveguides based on coupled-mode theory

The analytical expression for the transmission spectra of coupled cavity waveguides （CCWs） in photonic crystals （PCs） is derived based on the coupled-mode theory （CMT）. Parameters in the analytical expression can be extracted by simple numerical simulations. We reveal that it is the phase shift between the two adjacent PC defects that uniquely determines the flatness of the impurity bands of CCWs. In addition, it is found that the phase shift also greatly affects the bandwidth of CCWs. Thus, the engineering of the impurity bands of CCWs can be realized through the adjustment of the phase shift. Based on the theoretical results, an interesting phenomenon in which a CCW acts as a single PC defect and its impurity band possesses a Lorentz lineshape is predicted. Very good agreement between the analytical results and the numerical simulations based on transfer matrix method has been achieved.     

Method based on broadband compressed pulse superposition to measure properties of underwater acoustic materials

1 IntroductionUsually, a nUJnber of acoustic characteristics of underWater acoustic materials can be evaluated by measuring their complex reflection and transmission coefficiellts, such as echo reduction,insertion loss, absorption and attenuation coefficients, etc, which are the typical acoustic parameters. Hence, the meajsuremeats of complex reflection and transmission coefficiellts are thebasis of calculating most ajcoustic parameters for finite sized large area sample panels.R. J. Bobber …     

A scanning distortion correction method based on Ⅹ–Y galvanometer Lidar system

Aiming at the problem of scanning distortion in X-Y galvanometer light detecting and ranging(Lidar) scanning system,we propose a method of image scanning distortion correction with controllable driving voltage compensation.Firstly,the geometrical optics vectors model is established to explain the principle of pincushion distortion in the galvanometer scanning system,and the simulation result of scanning trajectory is consistent with experiments.The linear relationship between the driving voltage and the scanning angle of the galvanometer is verified.Secondly,the relationship between the deflection angle of the galvanometer and the scanning trajectory and the driving voltage is deduced respectively,and an image scanning correction algorithm with controllable driving voltage compensation is obtained.The simulation experiment results of the proposed method show that the root-mean-square error(RMSE) and the corresponding curve between the scan value and the actual value at different distances,have a good correction effect for the pincushion distortion.Finally,the X-Y galvanometer scanning Lidar system is established to obtain undistorted two-dimensional scanned image and it can be applied to the three-dimensional Lidar scanning system in the actual experiments,which further demonstrates the feasibility and practicability of our method.     

Further improvement of edge location accuracy of double fiber spherical coupling sensor using orthogonal Jacobi–Fourier moments

In order to further improve the edge location accuracy of double fiber spherical coupling sensor, an approach based on OJFMs is proposed. In this paper, OJFMs with high order spatial moment and simple calculation is built. Then, its edge location method and fast discrete algorithm is proposed. Finally, the proposed method is tested by locating the edge of standard pattern and the image acquired by double fiber spherical coupling sensor with lot of noise. Experiment results show that the location accuracy is up to 0.05 pixel and 0.08 pixel for standard lines and standard circle, respectively. The accuracy of double fiber spherical coupling sensor is 0.026 pixel in 2σ band and a actual accuracy of 36 nm is obtained by OJFMs after a moving average filter (N = 7).     

Immersed boundary method for the simulation of 2D viscous flow based on vorticity–velocity formulations

A new immersed boundary method based on vorticity–velocity formulations for the simulation of 2D incompressible viscous flow is proposed in present paper. The velocity and vorticity are respectively divided into two parts: one is the velocity and vorticity without the influence of the immersed boundary, and the other is the corrected velocity and the corrected vorticity derived from the influence of the immersed boundary. The corrected velocity is obtained from the multi-direct forcing to ensure the well satisfaction of the no-slip boundary condition at the immersed boundary. The corrected vorticity is derived from the vorticity transport equation. The third-order Runge–Kutta for time stepping, the fourth-order finite difference scheme for spatial derivatives and the fourth-order discretized Poisson for solving velocity are applied in present flow solver. Three cases including decaying vortices, flow past a stationary circular cylinder and an in-line oscillating cylinder in a fluid at rest are conducted to validate the method proposed in this paper. And the results of the simulations show good agreements with previous numerical and experimental results. This indicates the validity and the accuracy of present immersed boundary method based on vorticity–velocity formulations.     

An alternative method for the exact calculation of Wannier–Stark localization in superlattices

We present an alternative method for the exact calculations of the Wannier–Stark (WS) localization in a long periodic potential corresponding to a (50 Å/30 Å) GaAs/Ga_0.7Al_0.3As superlattice. We show that the electric field dependence of the electron wavefunction has unique localization dynamics. One interesting prediction is a small effect involving the change of the dipole field with increasing WS field. It is argued that this may give rise to parasitic effects in Bloch oscillations and, therefore, to noise in coherent terahertz emission.