B6377 - Mechanical Vibrations

Learning outcomes

Through the Integrated Course ACOUSTIC AND VIBRATIONAL COMFORT LM, the student acquires fundamental knowledge regarding: acoustic waves in air and their perception by humans; mechanical vibrations and related issues. The student becomes familiar with the main acoustic and vibrational quantities and the methods for measuring them. They learn basic concepts related to signal analysis in the time and frequency domains, as well as the principles of experimental modal analysis. The student gains knowledge of acoustic materials and key technical standards. They also learn the main solutions for noise control and for the reduction and isolation of vibrations on boats, aimed at improving onboard comfort.

Course contents

ACOUSTICS LM

1. Fundamentals of Physical Acoustics and Psychoacoustics
Main acoustic quantities (pressure, particle velocity, speed of sound, intensity, etc.). Acoustic impedance and electrical analogy. Acoustic wave equation and its solutions.
Overview of the human auditory system. Introduction to psychoacoustics.

2. Introduction to Acoustic Signal Analysis
Characteristics of sound signals. Decibel scale. Introduction to frequency analysis. Spectra. Filters. Weighting curves. Sound level measurements. ISO 2923. Sound Quality parameters (ISO 532-1).

3. Instrumentation for Acoustic Measurements
Calibrated measurement chains, measurement uncertainty (ISO/IEC Guide 98-3:2008). Uncalibrated measurement chains: intensity probe, beamforming (overview).

4. Sound-Material Interaction
Sound absorption: fundamental laws and control mechanisms. Sound insulation: fundamental laws and control mechanisms. Acoustic materials: porous materials, membrane and cavity resonators, micro-perforated materials, acoustic metamaterials.

5. Noise Control on Boats
Identification and characterization of noise sources: propulsion and exhaust noise, hydrodynamic and aerodynamic noise, Source-Path-Receiver modeling. Predictive methods. Numerical modeling (overview).
Noise control solutions for boats.
Comfort guidelines (IMO A458, MLC, ABS, RINA, BV, DNV GL, LR).

 

MECHANICAL VIBRATIONS LM

1. Mechanical vibrations.
Fundamentals of mechanical vibrations.
Free and forced vibrations. Resonance. Viscous damping; Coulomb damping; hysteretic damping. One and Two Degrees of Freedom Systems. Multi-degree of Freedom systems. Continuous Systems: mono and bi-dimensional systems. Approximate methods (Rayleigh and Rayleigh-Ritz).

2. Signal analysis
Data sampling: Shannon's theorem; Aliasing. Time and frequency domain. Discrete Fourier Transform. Leakage. Auto- and Cross- Spectrum. Frequency Response Function (FRF) and Coherence function.

3. Vibration measurements and modal analysis.
Vibration measurement scheme. Vibration transducers. Definition of acquisition parameters. Introduction to experimental modal analysis. System excitation: random, impulsive, sinusoidal.

4. Vibration reduction and isolation for onboard comfort.
Main sources of onboard vibration. Overview of relevant standards. Vibration isolation. Dynamic damper. Solutions for passive vibration control.

Readings/Bibliography

ACOUSTICS LM

Lecture notes provided by the instructor on https://virtuale.unibo.it
Book:
Fisher, Boroditsky: “Noise and Vibration Control on Ships. Understanding and Cutting Through the Noise”, Springer, 2024

 

MECHANICAL VIBRATIONS LM

Lecture slides are available on https://virtuale.unibo.it/.
1. Rao S.S., Mechanical vibrations, Sixth edition, Pearson Education, 2018.
2. Inman D.J., Engineering Vibration, 4th edition, Pearson Education, 2014.

Teaching methods

ACOUSTICS LM

Lectures, laboratory tests, and possible in-situ measurements.

 

MECHANICAL VIBRATIONS LM

The course is based on lectures dealing with the theoretical aspects of the course topics and application examples.
Class attendance, although not mandatory, plays a fundamental role in the learning and evaluation process.

Assessment methods

The final exam is oral and includes questions aimed at verifying the acquisition of the knowledge outlined in the course syllabus and at assessing the achievement of the learning objectives.

In accordance with Art. 16 of the current University Didactic Regulations, a negative assessment does not result in the assignment of a grade. In the case of a positive outcome, the grade may be declined only once.

Teaching tools

ACOUSTICS LM

Blackboard, PC.

 

MECHANICAL VIBRATIONS LM

Blackboard, PC.
On the E-learning Platform (https://virtuale.unibo.it/), students may find: slides of the course lectures; exercises and application examples.

Office hours

See the website of Alessandro Rivola