Optimization of Noise and Vibration Emission of Ship Hull on Stage of Conceptual Design

Maritime industry more and more involved in questions of noise and vibration emitted by ships. Currently, requirements for permissible vibration levels are regulated by marine classification societies. Design organizations and vessel owners may impose additional requirements for vibration and noise levels in certain areas. A special field of modern scientific and technological research is predicting the Navy's underwater noise levels.shaft line

As is known from experience, a lot of factors affect radiated vibration and noise: hull and propeller design, the intensity of the vibration sources, arrangement of propulsion components, application of vibration absorbers and dampers, and other factors.

One of the most important parameters affecting achieved noise and vibration levels is a simultaneous design of the ship hull and propulsion system that has a suppressive effect on the structure-borne noise and vibration at low frequencies.

This post covers some aspects of intelligence optimization during the conceptual design of ship propulsion units and ship hull to minimize emitted structural born vibration and noise.

The optimization module, which is described in this post, is based on Ph.D. graduation, correspondent research articles.

Innovative Approach of Ship Noise and Vibration Prediction

There are the following most important factors which affect vibration and noise levels:

• Ship hull and propeller design

• Propulsion complex arrangement

• Imposed loads

• Ship foundations and devices for vibration absorption

From project implementation experience, it is seen a weak relationship between the stage of a ship hull design and propulsion complex design and calculation. This leads to an increase in the project time and errors at the documentation development stage. In addition, given the weak communication in the transmission of calculated data, the noise and vibration of the project may not be optimal.

Example of ship propulsion complex arrangement

Individual parameters of the ship shaft line in different ways affect the dynamic performance of the whole system. effortAs a result, there is a possible field to the target function (resulting noise/vibration), for which there are a number of possible minimums. The challenge is to determine a function with minimum time and effort using mathematical modeling.

Example of the ship propulsion complex arrangement at the ship hull

The collection of the above modern mathematical methods, collectively known as “artificial intellect” (algorithms that use the principles of self-learning and artificial neural networks) provide the ability to create a mathematical model of the behavior of the ship and its prediction of vibro-acoustic characteristics.

Scheme of individual parameters of a ship propulsion complex affecting a function of radiated noise

A generalized mathematical model can be presented as follows:

P = f(a,b,c, …, x, y, z),

where P – noise/vibration level; f – a function of dependence of noise/vibration on design parameters; a, b, c, …, x, y, z – values of design parameters.

For particular case P=f(a,b), diagram may be presented as a 3D surface as follow:

𝑎 ∈ 𝐴, …, z ∈ 𝑍

where A, …, Z – set of permissible values of the parameters of design components.

The task is to determine such f, a, b, c, …, x, y, z for which the equality:

P ⇒ min ⁡and ∇(a,b,c, …, x, y, z), P-P ̃⇒ min,

where P ̃ – noise/vibration level obtained on the computational model.