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## MECHANICS OF MACHINES

CODE 84414 2019/2020 6 credits during the 2nd year of 8722 Naval Architecture and Marine Engineering (L-9) GENOVA ING-IND/13 Italian GENOVA (Naval Architecture and Marine Engineering) 2° Semester Prerequisites You can take the exam for this unit if you passed the following exam(s): Naval Architecture and Marine Engineering 8722 (coorte 2018/2019) GEOMETRY 56718 PHISYCS 73223 AULAWEB

## OVERVIEW

The module of Mechanics of Machinery aims to provide the tools necessary for the knowledge and analysis of the fundamental mechanical phenomena present in the mechanical power transmissions and the identification of the main components and mechanical systems used, through a functional analysis.

## AIMS AND CONTENT

### LEARNING OUTCOMES

Fundamentals on kinematic and kinetic-static methods of transmitting machines. Analysis of forces in transmissions in the presence of friction. Lubrication elements. Dynamic analysis of transmissions through elementary models with one or more degrees of freedom. Components constituting the naval transmissions: sliding and rolling bearings, gear wheels and gears, belts, chains, wire ropes, cams, couplings, couplings, brakes.

### AIMS AND LEARNING OUTCOMES

The aim of the Mechanics of Machinery module is to provide operational concepts on the functionality of mechanical systems used in the industrial field and, in particular, in the naval field. At the end of the cosmos the student will have acquired the knowledge related to the fundamental mechanical problems, with specific reference to the industrial transmissions and will be able to analyze the fundamental problems of the basic mechanical components.

Specifically, the student will be able to:

•      know the phenomena related to the kinematics and the dynamics of the machines
•      evaluate the mechanical characteristics of the basic components of industrial transmissions
•      discuss the selection of mechanical components available on the market

### PREREQUISITES

To effectively deal with the topics covered in the course, knowledge of:

•      general physics
•      rational mechanics
•      industrial technical drawing

### TEACHING METHODS

The teaching consists of lectures and classroom exercises, carried out in integrated mode on a orientative amount of 60 hours. The theoretical topics treated are associated, individually or in groups, with exercises carried out.

### SYLLABUS/CONTENT

The course program includes the presentation and discussion of the following topics:

•     Elementary kinematics copies and degrees of freedom of mechanisms.
•     Graphic kinematic analysis of plane mechanisms (with particular reference to speed analysis).
•     Kinematic analysis of basic articulated systems (connecting rod-crank, articulated quadrilateral).
•     Dynamic equivalence of rigid systems.
•     Dynamic equivalence of deformable systems: reduction of inertia, couples and elasticity.
•     Dynamics of an engine-reducer-load complex.
•     Return of mechanisms. Yields of mechanisms in series and in parallel.
•     Machines operating on a periodic basis: determination of the moment of inertia of flywheels with the Tredgold method.
•     Phenomenology of sliding friction: main hypotheses, factors that influence the sliding friction factor.
•     Properties and laws of viscous fluids for industrial use (industrial oils). Classification criteria.
•     Fluid lubrication: hydrodynamic lubrication elements (Reynolds equation and simplified hypotheses).
•     Loaded and pushing lubricated rotoidal torques: Gibbs and Mitchell bearings.
•     Phenomenology of rolling friction: dynamics of towed rollers and engines.
•     Rolling bearings: types and selection procedures.
•     Static graphic analysis applied to simple mechanical systems.
•     Dynamic analysis: first and second order models, with one or more degrees of freedom.
•     Natural motion of second-order systems, with a degree of freedom.
•     Response of systems of the second order, to a degree of freedom, with stepped forcing.
•     Response of systems of the second order, to a degree of freedom, with sinusoidal forcing.
•     Factors for dynamic amplification of displacements and forces.
•     Introduction to torsion dynamics: elementary models for analysis of motor-reducer-load systems.
•     Friction wheels: transmissions for parallel, competing, skew axes.
•     Toothed wheels: typologies, tracing of the involute toothing profile.
•     Interference in cylindrical gears: how it manifests itself and avoids it. Minimum number of teeth to avoid interference.
•     Modular proportioning elements of toothed wheels.
•     Determination of the toothing module based on resistance criteria.
•     Gear units with toothed wheels for competing and crooked axles. Screw-wheel transmission.
•     Ordinary and planetary rotations (Willis formula).
•     Practical determination of constant transmission ratios with gears.
•     Transmissions with hoses: law of variation of the tension of the hose on the wrapped section of pulley.
•     Procedure for the selection of trapezoidal belts.
•     Transmissible power with hoses: maximum useful effect speed.
•     Chain transmissions: impact phenomena and polygonal effect.
•     Transmissions with wire ropes: fixed and mobile pulleys, sizes, hoists.
•     Cam transmission: graphic method for the kinematic synthesis of the cam profile and relative problems (sub-cut, cam-releasing cam, ...).
•     Joints: types. Analysis of the joint of Oldham, the gimbal and the homokinetic joints.
•     Grafts: types. Friction clutches and hydraulic couplings.
•     Brakes: analysis of the forces in the drum brakes. Disc brake problems.

The topics covered during the exercises are an integral part of the exam program.

Reference books:

R.Ghigliazza, A.Lucifredi, R.Michelini “Lezioni di Meccanica applicata alle macchine”, Genova, 1974.

R.Ghigliazza et al. “Guida alla progettazione funzionale delle macchine”, Tolozzi ed., Genova, 1980.

Didactic notes and solved exercises are made available on AulaWeb

## TEACHERS AND EXAM BOARD

### Exam Board

MATTEO VEROTTI (President)

LUCA BRUZZONE

PIETRO FANGHELLA

## LESSONS

### TEACHING METHODS

The teaching consists of lectures and classroom exercises, carried out in integrated mode on a orientative amount of 60 hours. The theoretical topics treated are associated, individually or in groups, with exercises carried out.

### LESSONS START

According to the timetable of the Polytechnic School.

### Class schedule

All class schedules are posted on the EasyAcademy portal.

## EXAMS

### EXAM DESCRIPTION

The exam consists of a written test and an oral test. The written test will focus on a similar exercise to those treated during the exercises and in a question with an open answer on one of the topics covered in the course. After this test a partial evaluation will be provided (in thirtieths): all the students who have obtained the 18/30 grade are admitted to the oral exam. The students who have obtained a vote in the circle of sufficiency (indicatively at least 16/30) are also admitted to the oral test. The oral exam will complete the exam with the discussion of other topics included in the course. The final evaluation will globally consider the outcome of the answers (written and oral) of the student.

The written test has a maximum duration of 60 minutes. The date of the oral test will be announced following the corresponding written test and at the time of communication of the results of the written test, with reference to the number of students participating in the single exam session.

### ASSESSMENT METHODS

The written test tends to verify the effective acquisition of basic knowledge on the themes of Mechanicis of machinery, through the solution of an easy exercise in line with those carried out during the module and through the written presentation, in summary form, of a theme among those scheduled.

The oral exam tends to complete the verification of the student's preparation, with discussion of one or more topics explicitly indicated in the exam program.

### Exam schedule

Date Time Location Type Notes
23/06/2020 09:30 GENOVA Scritto + Orale
21/07/2020 09:30 GENOVA Scritto + Orale
03/09/2020 09:00 GENOVA Scritto + Orale
14/09/2020 09:00 GENOVA Scritto + Orale

### FURTHER INFORMATION

The teacher is available for detailed information.