Acoustic signature of a submarine hull

A model to predict the acoustic signature of a submarine resulting from the radial vibration of the hull under axial excitation is presented. The simplified physical model of the submarine hull includes complicating effects such the presence of bulkheads, end enclosures, ring stiffeners and fluid loading due to the interaction with the surrounding medium. Under an axial symmetric force, only the ‘breathing’ modes of the cylinder corresponding to the n=0 circumferential modes are excited. To show the sound radiation due to the higher order n≥1 modes, a point axial force acting at one end of the shell has been considered. At low frequencies, the structural wavenumbers are generally subsonic. However, due to the finite cylinder, the wavenumber spectrum is a convolution of the spectrum of an infinite structure and a window generating radiation by means of the presence of supersonic components. The effect of the bulkheads on the structural and acoustic responses of the hull is also presented

Low frequency structural and acoustic responses of a submarine hull under eccentric axial excitation from the propulsion system

A model to describe the low frequency dynamic and acoustic responses of a submarine hull subject to an eccentric harmonic propeller shaft excitation is presented. The submarine is modelled as a fluid-loaded, ring stiffened cylindri-cal shell with internal bulkheads and conical end caps. The stiffeners are introduced using a smeared approach. A harmonic axial force is introduced by the propeller and is transmitted to the hull through the shaft. It results in excita-tion of the accordion modes only if the force is symmetrically distributed to the structure. Otherwise the excitation can be modelled as the sum of a distributed load and a moment applied to the edge of the hull. This leads to excitation of the higher order circumferential modes that can result in high noise signature. Structural and acoustic responses are presented in terms of deformation shapes and directivity patterns for the radiated sound pressure. Results for the case of purely axisymmetric excitation and the case in which an eccentricity is introduced are compared

Prediction of the intramembranous tissue formation during perisprosthetic healing with uncertainties. Part 1. Effect of the variability of each biochemical factor

A stochastic model is proposed to predict the intramembranous process in periprosthetic healing in the early post-operative period. The methodology was validated by a canine experimental model. In this first part, the effects of each individual uncertain biochemical factor on the bone-implant healing are examined, including the coefficient of osteoid synthesis, the coefficients of haptotactic and chemotactic migration of osteoblastic population and the radius of the drill hole. A multi-phase reactive model solved by an explicit finite difference scheme is combined with the polynomial chaos expansion to solve the stochastic system. In the second part, combined biochemical factors are considered to study a real configuration of clinical acts

Acoustic performance of a metascreen-based coating for maritime applications

Time and frequency domain numerical models are developed to investigate the acoustic performance of metascreen-based coatings for maritime applications. The coating designs are composed of periodic air-filled cavities embedded in a soft elastic medium, which is attached to a hard backing and submerged in water. Numerical results for an acoustic coating with cylindrical cavities are favourably compared with analytical and experimental results from the literature. Frequencies associated with peak sound absorption as a function of the geometric parameters of the cavities and material properties of the host medium are predicted. Variation in the cavity dimensions that modifies the cylindrical-shaped cavities to flat disks or thin needles is modelled. Results reveal that high sound absorption occurs when either the diameter or length of the cavities is reduced. Physical mechanisms governing sound absorption for the various cavity designs are described

Prediction of the intramembranous tissue formation during perisprosthetic healing with uncertainties. Part 2. Global clinical healing due to combination of random sources

This work proposes to examine the variability of the bone tissue healing process in the early period after the implantation surgery. The first part took into account the effect of variability of individual biochemical factors on the solid phase fraction, which is an indicator of the quality of the primary fixation and condition of its long-term behaviour. The next issue, addressed in this second part, is the effect of cumulative sources of uncertainties on the same problem of a canine implant. This paper is concerned with the ability to increase the number of random parameters to assess the coupled influence of those variabilities on the tissue healing. To avoid an excessive increase in the complexity of the numerical modelling and further, to maintain efficiency in computational cost, a collocation-based polynomial chaos expansion approach is implemented. A progressive set of simulations with an increasing number of sources of uncertainty is performed. This information is helpful for future implant design and decision process for the implantation surgical act

Sound radiation from a cylindrical shell with a multilayered resonant coating

The vibroacoustic response of a structurally excited cylindrical shell submerged in water is presented. The shell is coated with a soft elastic material embedded with circumferential arrays of resonant inclusions. The coating is modelled as a multilayered equivalent fluid composed of homogeneous layers of the host soft material and homogenised layers comprising voids or hard inclusions. The radiated acoustic pressure is analytically derived by assembling and solving continuity and kinematic conditions at the interfaces between the cylindrical shell and the multilayered coating. Coating designs with different combinations of homogenised layers are examined. Physical mechanisms governing acoustic performance of the various coating designs are described. We show that the material of the inclusions, tuning the local resonances of the inclusions and the distribution of the homogenised layers within the coating have a significant effect on the shell vibroacoustic response

Propagation d'incertitude par réduction de modèle pour un problème couplé de reconstruction osseuse

Cette communication vise à montrer l'intérêt de l'utilisation d'une réduction de modèle couplée à une technique de morphing pour analyser un problème biomécanique avec une incertitude géométrique pour la reformation osseuse. Une analyse stochastique est réalisée sur le modèle réduit, puis validée et comparée avec une approche de Monte-Carlo. La forme particulière du modèle réduit permet de ne nécessiter qu'une phase de post-processing pour obtenir la loi de probabilité de la quantité d'intérêt étant donnée celle de l'entrée

Active attenuation of the wave transmission through an L-plate junction

Active control is applied to an L-shaped plate in order to attenuate the flexural energy transmission from one plate to the other. The coupled plates are simply supported along two parallel sides, and free at the other two ends. Point forces are used to generate the primary and secondary excitation of the plates. The flexural wave coefficients are determined from the boundary conditions, continuity equations at the driving force locations, and continuity equations at the corner junction of the two plates. Bending, shearing, and longitudinal effects are taken into consideration at the corner junction. Under broadband frequency control at a discrete location in plate 2, both the control shaker and the error sensor are optimally located to achieve the best control performance. Results show that when the control force and error sensor are arbitrarily located, the control performance is dependent on the excitation frequency. When both the control force and error sensor are optimally located with respect to the primary shaker location in a symmetrical arrangement, the control performance is both maximized and independent of the excitation frequency. Using single-frequency control to attenuate the total vibrational response of the coupled plates, the error sensor location is strongly mode dependent. It is shown that using a single, properly located control force and a single, properly located error sensor, global attenuation of the L-shaped plate can be achieved

Active control of the plate energy transmission in a semi-infinite ribbed plate

Active control of the plate flexural wave transmission through the beam in a semi-infinite beam-reinforced plate is analytically investigated. The ribbed plate is modeled as a continuous system, using equations of motion to describe the plate in flexure and the beam in both flexure and torsion. The maximum transmission of the plate flexural waves through the reinforcing beam is found to occur at resonance frequencies corresponding to the optimal coupling between the plate flexural waves and the flexural and torsional waves in the beam. A single control force is applied to the beam, and a cost function is developed to attenuate the far-field flexural energy transmission. It can be observed that the transmission peaks corresponding to the flexural resonances in the beam are reduced. Similarly, the transmission peaks corresponding to the torsional resonance conditions in the beam can be attenuated using a single control moment applied to the beam. Significant attenuation of all the resonance peaks in the flexural wave transmission can also be achieved with the application of a single force and a single moment collocated on the beam. In this paper, the feasibility of attenuating the flexural wave transmission due to both the flexural and torsional resonance conditions by using a single point force and point moment collocated on the beam is demonstrated

Power transmission in L-shaped plates including flexural and in-plane vibration

In this paper, power flow propagation in plates connected in an L-joint is investigated in both the low and high frequency ranges. An exact solution is derived to describe the flexural, in-plane longitudinal and in-plane shear wave motion in the plates. The coupled plates are simply supported along two parallel sides, and free at the other two ends. A point force is used to generate flexural wave motion only. The flexural wave coefficients are determined from the boundary conditions, continuity equations at the driving force locations, and continuity equations at the corner junction of the plates. Structural intensity expressions are used to examine the structural noise transmission in the low and high frequency ranges. The contributions from the individual wave types are also examined