A comprehensive suite of FE based structural optimization
computer programs has been developed to minimise vibration
and radiated noise of internal combustion engines. Finite
element based vibration and noise prediction techniques,
dynamic substructuring capabilities and design optimization
methods are the key elements of the program suite. The entire
engine noise generation process, starting from the combustion
pressure and ending with the radiated noise, is within the
scope of the programs. Engine structural member sizes,
material properties, structural damping and the gasket
stiffness and damping between engine components may be used
as design variables. Limited shape optimization capabilities
are also developed, including removal and addition of
structural parts, and geometric modifications without FE mesh
regeneration. The design optimization problem, which may
involve complex design modifications, is finally transformed
into a simple numerical optimization problem with a few
design variables. The programs are so structured that any
established numerical optimization method may be used to
solve the final numerical optimization problem, although
straight forward iterative optimization algorithms are shown
to be inefficient for this application. The numerical
optimization can be carried out either as an integrated part
of the whole procedure or as another separate process.
Extensive studies have been carried out on the various
factors influencing engine noise optimization, including the
characteristics of the radiated sound power as a function of
structural design variables, the effects of damping,
excitation and FE modelling. A comprehensive analysis
starting from crank train loads and ending with radiated
sound power level has been shown to be the basis of a
practical optimization scheme. Sound power level has been identified as a suitable candidate to be used explicitly as
the objective function of the optimization. Excitation models
which fail to include correctly phased loads at main bearings
and cylinders are shown to be inadequate for this
application, although the conclusion may not apply at high
frequencies (say, above 1 KHz) because the phase relationship
at high frequencies might not be correctly predicted.
Because engine FE models inevitably have large numbers of
degrees of freedom, the sound power evaluation process is
computationally very intensive. Therefore, each element of
the procedure has been considered carefully to minimise the
total computational burden without sacrificing important
physical characteristics.
The programs have been tested on a few realistic engine
FE models, although this thesis will only include the results
based on models of a four cylinder in-line diesel engine with
up to 6000 degrees of freedom. The tests suggest that the
noise optimization scheme is not only theoretically sound but
also computationally viable, although further work is
required in the related specialisations to fully realise its
potential.

Structural optimization of reciprocating engines for minimum noise radiation

Following the report of the armitage inquiry and the resulting UK government white paper "lorries, people and the environment", the government initiated a cooperative programme of research and development with the UK commercial vehicle industry to produce quieter lorries for the 1990S. The aim of this programme, known as the qhv90 project and managed by the transport and Road Research Laboratory of the Department of Transport, and the department of trade and industry, is to support commercial vehicle and engine manufacturers in the production of the quieter prototypes required to meet the lower noise levels embodied in the forthcoming eec legislation. This legislation requires a reduction in sound pressure level for the heaviest vehicles from 88 db(a) at present to 84 db(a) in 1989/90. The cost of the work is being borne half by government and half by industry. The principal manufacturers involved include erf, foden, iveco-ford and leyland for the quieter vehicle prototypes and perkins, cummins and Ford for the quieter engines. In addition to the work being carried out by the manufacturers, research on specific aspects of vehicle noise, for example on exhaust and air inlets and engine design, is being done by the motor industry research association, Loughborough university of technology, the British hydromechanics research association, the institute of sound and vibration research and ricardo consulting engineers. This paper will describe the qhv90 project and present some of the results obtained.(a) for the covering abstract see IRRD 816897.

Quiet heavy vehicles for the 1990s - the qhv90 project progress report ---advances in the control and refinement of vehicle noise. proceedings of the institution of mechanical engineers. international conference, 23-24 march 1988, belfry hotel birmingham, england. imeche conference 1988-2

A M Porkess

Papers

Quiet heavy vehicles for the 1990s - the qhv90 project progress report ---advances in the control and refinement of vehicle noise. proceedings of the institution of mechanical engineers. international conference, 23-24 march 1988, belfry hotel birmingham, england. imeche conference 1988-2