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Two finite element optimization techniques are presented for minimizing automotive engine air induction structural radiated noise and mass. Air induction systems are generally made of thin wall plastic which is exposed to high levels of pulsating engine noise. Weak air induction system walls vibrate excessively creating noise that can be heard by the driver. The conventional approach is to add ribs (many times through trial and error) which increase part weight or by adding “kiss-offs,” which restrict air flow. The finite element optimization methods considered here are shape optimization and topometry optimization. Genesis, a fully integrated finite element analysis and optimization package by Vanderplaats Research & Development, was used to perform finite element optimization. Choice of optimization method is primarily dependent on several factors which are appearance, part interference and flow restriction requirements.

In this paper, finite element shape optimization is used to determine the optimum air cleaner shape and rib design for low shell noise. Shape variables are used to vary the height and location of rib elements, as well as vary the shape of the air cleaner surfaces. The optimization code evaluates each design variation and selects a search direction that will reduce surface velocity. Sound power radiation is calculated for each optimized design using an acoustic code. Large reductions in shell noise were achieved by optimizing the shape of the air cleaner surface and rib design. Optimization of the rib pattern alone yielded a local optimization, as opposed to a global optimization that represented the best possible design.

Plate and shell theory is used to determine the force vibration response of large air cleaner surfaces for the air cleaner breathing modes of vibration. Plate equations are small and can be programmed into a hand held calculator for convenience. The eigenfunction method is used to solve the plate equation to obtain the plate vibration response. Surface reinforcements such as ribs, corrugation and surface curvature are included in the plate equation in terms of structural rigidity. Surface stiffness can be modified by simply changing the stiffener moment of inertia or by changing the number of stiffeners. The approximation technique was used to model a rectangular shallow shell. The predicted shell first natural frequency compared favorably to that of an exact solution to the shallow shell equation. Two air cleaner covers were modeled with the technique. One of the covers was flat and reinforced with ribs while the other was a shallow shell also reinforced with ribs.

Several aspects of the acoustic design optimization of induction systems are considered. The important role of the inlet manifold in the induction system is shown by constructing mathematical models of two levels of sophistication. A plane wave representation of the manifold is adequate when the geometry of the manifold supports only longitudinal acoustic modes. When the geometry supports transverse modes it is necessary to include the acoustic modal structure in the mathematical model comparing three mathematical models. The manifold with a conventional runner arrangement is shown to introduce harmonics of the firing frequency other than the generally assumed multiples of the number of cylinders. A manifold with runners coupled in a common plane is considered as a means of eliminating undesirable harmonics. It is shown by considering the ninth harmonic (order 4.5), that harmonics other than the integer multiples of the number of cylinders are drastically reduced in amplitude.

Two problems that arise in induction system acoustic analysis are addressed in the context of the Acoustic Wave Finite Element (AWFE) procedure. A source model that makes use of measured data to scale the source amplitude is shown to provide good correlation between the predicted and measured inlet manifold noise of a six cylinder engine. Three-dimensional effects due to complex geometry in intake manifolds and air cleaners are modeled using an extension of the AWFE method that introduces three-dimensional wave structure within elements that are comparable to the acoustic wave length. Comparisons are made of the acoustic output of induction system components modeled using simple plane wave elements and using elements with wave structure.

Fiber Optic Technology is being developed for aircraft and offers benefits in system performance and manufacturing cost reduction. The fiber optic systems have high bandwidths that exceeds all of the new aircraft design requirements and exceptional EMI immunity. Additionally, fiber optic systems have been installed in production aircraft proving design feasibility.