**Background**

There are a number of different causes of noise of fully submerged vessels corresponding to noise generated by (1) turbulent flow induced noise caused by movement of the vessel through the water, (2) propeller noise and (3) noise from on-board machinery, as shown in Figure 1. The focus of this project is on turbulent flow induced noise and on-board machinery noise. The relative motion between the vessel and water produces a turbulent boundary layer (TBL) that surrounds the vessel surface. Hydroacoustic noise is generated by the fluctuating velocity and pressure fields within this turbulent boundary layer. The pressure field beneath the TBL also excites the structure and causes vibrations; a part of the noise due to the vibrations of the vessel is radiated to the far field and also partially transmitted into the vessel. Similarly, noise generated by on-board machinery, modeled by acoustic diffuse filed (ADF), excites the vessel structure and cause acoustic radiation into the ocean. As such, at the design stage it is important to understand how the structure reacts to TBL/ADF excitation and how this excitation produces radiated underwater noise. There has been considerable interest in the response of structures to random pressure fields (Maxit et al. 2019a,b; Karimi et al. 2019a,b). The objectives of such investigations vary from minimizing structural fatigue damage to reducing noise radiation from the structure (Leibowitz et al. 1975 and Boily et al. 1999). In addition to challenges in predicting hydroacoustic noise, the effect of sea free surface and seabed on the scattered and radiated noise is not well understood. The latter may be significant due to radiation from large surfaces as in the case of marine vessels. This proposal aims to develop numerical capabilities that will address this knowledge gap.

**Aims and objectives**

This project will develop an analytical model of a finite cylindrical shell to investigate the vibroacoustic responses of an underwater vessel in a heavy fluid under TBL/ADF excitations. The project comprises four major phases:

1. In the first phase, a comprehensive literature review will initially be carried out. Vibroacoustic responses of an infinite cylindrical shell under TBL/ADF excitation will then be formulated analytically. The model will include the effects of sea surface and sea bed on the radiated power.

2. In the second phase, the analytical method will be extended to model a finite cylindrical shell excited by TBL/ADF considering the effect of sea surface and sea bed. This model allows us to understand the effect of the finite length of the structure on the radiated sound power in the presence of sea surface and seabed.

3. The project will be extended to include stiffeners and bulkheads in the interior of cylindrical shell to investigate their influence on the radiated power. This is of particular interest for submarine hull analysis (Maxit et al. 2019a). Considering stiffened cylindrical shell under ADF excitation is important to understand the transmission of the acoustic noise induced by the internal machinery of a submarine into water.

4. To verify the analytical model of finite cylindrical shell, a fully coupled FEM-BEM solver (structural solver based on the FEM and acoustic solver based on the BEM (Karimi et al. 2016, 2017)) will be used to model a finite cylindrical shell. This will be done by using uncorrelated wall plane wave (UWPW) technique to compute the incident pressure field on a body due to the fluctuating pressure waves from the turbulent flow (Karimi et al. 2019b) or acoustic diffuse field. The incident pressure field will be then used as the input to the coupled FEM-BEM (Peters et al. 2012, Meyer et al. 2018).

**Supervisors:**

Dr. Mahmoud Karimi (UTS, Sydney). Email: Mahmoud.Karimi@uts.edu.au

A/Prof. Laurent Maxit (INSA Lyon, France). Email: Laurent.Maxit@insa-lyon.fr

Application deadline: 15 January 2020

Commencement date: 1 July 2020

**Location**: The PhD student will need to work full time at UTS in Sydney, Australia.

**Funding:** A PhD stipend of A$30000 per year is available for 3 years with possibility of extension to 3.5 years to cover living expenses in Sydney.

Applicant needs to apply for the PhD program at UTS and win a scholarship to cover the tuition fees.

**Selection criteria:** Strong background in the fields of acoustics, dynamics and vibrations with sound skills in mathematics and computer programming are required.

If you are a motivated student and interested in this project, please send your CV, a copy of your academic transcripts and results of an English language test, to the supervisors of this project.

**References**

Boily, S. and Charron, F. (1999) The vibroacoustic response of a cylindrical shell structure with viscoelastic and poroelastic materials, Applied Acoustics, 58(2), pp. 131-152.

Karimi, M., Croaker, P., Maxit, L., Robin, O., Skvortsov, A., Marburg, S., Kessissoglou, N. (2019a). A hybrid numerical approach to predict the vibrational responses of panels excited by a turbulent boundary layer, Journal of Fluids and Structures.

Karimi, M., Croaker, P., Skvortsov, A., Moreau, D., Kessissoglou, N., Numerical prediction of turbulent boundary layer noise from a sharp-edged flat plate, Int J Numer Meth Fl 90 (2019b) 522-543.

Karimi, M., Croaker, P., & Kessissoglou, N. (2017). Acoustic scattering for 3D multi-directional periodic structures using the boundary element method. The Journal of the Acoustical Society of America, 141(1), 313-323.

Karimi, M., Croaker, P. and Kessissoglou, N. (2016) Boundary element solution for periodic acoustic problems, Journal of Sound and Vibration, 360, pp. 129-139.

Leibowitz, R.C., (1975). Vibroacoustic response of turbulence excited thin rectangular finite plates in heavy and light fluid media, Journal of sound and Vibration, 40(4), pp. 441-495.

Maxit, L., Guasch, O., Meyer, V., Karimi, M. (2019a). Noise radiated from a periodically stiffened cylindrical shell excited by a turbulent boundary layer. Journal of Sound and Vibrations.

Maxit, L, Karimi, M, Meyer, V, Kessissoglou, N (2019b), 'Vibroacoustic responses of a heavy fluid loaded cylindrical shell excited by a turbulent boundary layer', Journal of Fluids and Structures.

Peters, H., Marburg, S., & Kessissoglou, N. (2012). Structuralâacoustic coupling on nonâconforming meshes with quadratic shape functions. International Journal for Numerical Methods in Engineering, 91(1), 27-38.