Search

Acoustic data were recorded on two vertical line arrays (VLAs) deployed in the New England Mud Patch during the Seabed Characterization Experiment 2017 in about 75 m of water. The sound recorded during the passage of merchant ships permits identification of singular points for the waveguide invariant β for mode pairs (1 , n) : β 1 , n , for n = 2 , 3 , 4 , 5 , in the 15–80 Hz band. Using prior geophysical information and an acoustic data sample from the merchant ship KALAMATA, a geoacoustic model M of the seabed was developed. Then, using data samples from other merchant ships, a feature-ensemble maximum entropy method is employed to infer the statistical properties of geoacoustic parameter values for the sound speeds in a surface mud layer and a deep sand layer. Technical challenges include a sparsity of observed singular points, the unique identification of mode pairs for an observed singular point, and the deviation of the waveguide from horizontal stratification. A geoacoustic model M is developed that reproduced the observed β ≈ − 1 for f < 20 Hz and mode cutoff features at about 15 Hz. The statistical low-frequency inference of the singular point structure from multiple ships provides evidence of an angle of intromission at the water sediment interface with an average sound speed ratio of about 0.986 and an average sound speed for the deeper sand layer of about 1775 m/s. [ABSTRACT FROM AUTHOR]

Cored wires are used in numerous welding processes with or without external gas or flux shielding. Submerged arc welding (SAW) with cored wires, seamed or seamless, for joining mild and low alloyed steel grades is a technique that has demonstrated clear advantages during the three last decades. Ever since its invention, the SAW process has evolved with one main goal: to combine quality with productivity. With low alloy wires, the benefits have already been clearly demonstrated and widely exploited. However, little has been written on SAW and cladding with cored wires for corrosion or heat resisting applications. Its extension to high alloy compositions brings corresponding benefits and adds some specific and unique features. This paper focuses on consumable specificities and on the quality and productivity features of SAW with CRA (corrosion resistant alloy) cored wires. It describes the potential as well as the limitations of this technique. Cored wires are now used for submerged arc welding of almost all stainless steels ranging from soft martensitic to super-duplex, and for a series of nickel base compositions as well as for cladding cobalt base alloys. Examples of industrial applications with austenitic, duplex, martensitic and heat resisting stainless steels are given to illustrate the potential of the cored wire solution. 13 Ref., 4 Tables, 25 Figures. [ABSTRACT FROM AUTHOR]

Cored wires are used in numerous welding processes with or without external gas or flux shielding. Submerged arc welding (SAW) with cored wires, seamed or seamless, for joining mild and low alloyed steel grades is a technique that has demonstrated clear advantages during the three last decades. Ever since its invention, the SAW process has evolved with one main goal: to combine quality with productivity. With low alloy wires, the benefits have already been clearly demonstrated and widely exploited. However, little has been written on SAW and cladding with cored wires for corrosion or heat resisting applications. Its extension to high alloy compositions brings corresponding benefits and adds some specific and unique features. This paper focuses on consumable specificities and on the quality and productivity features of SAW with CRA (corrosion resistant alloy) cored wires. It describes the potential as well as the limitations of this technique. Cored wires are now used for submerged arc welding of almost all stainless steels ranging from soft martensitic to super-duplex, and for a series of nickel base compositions as well as for cladding cobalt base alloys. Examples of industrial applications with austenitic, duplex, martensitic and heat resisting stainless steels are given to illustrate the potential of the cored wire solution. 13 Ref., 4 Tabl., 25 Fig. [ABSTRACT FROM AUTHOR]

An inversion scheme is proposed, relying upon the inversion of the noise of a moving ship measured on a single distant hydrophone. The spectrogram of the measurements exhibits striations which depend on waveguide parameters. The periodic behavior of striations versus range are used to estimate the differences of radial wavenumber between couples of propagative modes at a given frequency. These wavenumber differences are stacked for several frequencies to form the relative dispersion curves. Such relative dispersion curves can be synthesized using a propagation model feeded with a bottom geoacoustic model. Inversion is performed by looking for the bottom properties that optimize the fit between measured and predicted relative dispersion curves. The inversion scheme is tested on simulated data. The conclusions are twofold: (1) a minimum 6 dB signal to noise ratio is required to obtained an unbiased estimate of compressional sound speed in the bottom with a 3 m s-1 standard deviation; however, even with low signal to noise ratio, the estimation error remains bounded and (2) in the case of a multi-layer bottom, the scheme produces a single depth-average compressional sound speed. The inversion scheme is applied on experimental data. The results are fully consistent with a core sample measured around the receiving hydrophone. [ABSTRACT FROM AUTHOR]

This paper introduces a single-receiver geoacoustic-inversion method based on dispersion analysis and adapted to low-frequency impulsive sources in shallow-water environments. In this context, most existing methods take advantage of the modal dispersion curves in the time-frequency domain. Inversion is usually performed by matching estimated dispersion curves with simulated replicas. The method proposed here is different. It considers the received modes in the frequency domain. The modes are transformed using an operator called modal reversal, which is parameterized using environmental parameters. When modal reversal is applied using parameters that match the real environment, dispersion is compensated for in all of the modes. In this case, the reversed modes are in phase and add up constructively, which is not the case when modal reversal is ill-parameterized. To use this phenomenon, a criterion that adds up the reversed modes has been defined. The geoacoustic inversion is finally performed by maximizing this criterion. The proposed method is benchmarked against simulated data, and it is applied to experimental data recorded during the Shallow Water 2006 experiment. [ABSTRACT FROM AUTHOR]

Acoustic propagation in shallow water is characterized by a set of depth-dependent modes, the modal depth functions, which propagate in range according to their horizontal wavenumbers. For inversion purposes, modal depth function estimation in shallow water is an issue when the environment is not known. Classical methods that provide blind mode estimation rely on the singular value decomposition of the received field at different frequencies over a vertical array of transducers. These methods require that the vertical array spans the full water column. This is obviously a strong limitation for the application of such methods in an operational context. To overcome these shortcomings, this study proposes to replace the spatial diversity constraint by a frequency diversity condition, and thus considers the case of a field emanating from an impulsive source. Indeed, because of the discrete nature of the wavenumber spectrum and due to their dispersive behavior, the modes are separated in the time-frequency domain. This phenomenon enables the design of a modal filtering scheme for signals received on a single receiver. In the case of a vertical receiver array, the modal contributions can be isolated for each receiver even when using a partial water column spanning array. This method thus eliminates the receiving constraints of classical methods of modal depth function estimation, although it imposes the use of an impulsive source. The developed algorithm is benchmarked on numerical simulations and validated on laboratory experimental data recorded in an ultrasonic waveguide. Practical applications are also discussed. [ABSTRACT FROM AUTHOR]