Vibro-acoustic Optimization Research Articles

Vibro-acoustic optimization of an immersed cylindrical structure with a floating-raft system inside by using frequency-response-function-based substructuring sensitivity analysis

Optimization of the vibration transmission of an internal floating-raft system and the resultant sound radiation of the fluid-loaded cylindrical structure is presented. The influences of different objective functions, fluid loading, external loading, and an optimized frequency band on the optimization results are investigated in detail. The frequency-response-function (FRF)-based substructuring method and the coupled finite element method–boundary element method are employed to study the vibration transmission from vibrating machines to the base and the vibro-acoustic behaviour of the fluid-loaded cylindrical structure respectively. An FRF-based substructuring sensitivity analysis is applied to obtain the optimal values of the stiffness of isolators under five objective functions in the low-frequency range. The optimized results demonstrate that some of the objective functions are equivalent to each other and can be replaced by each other. The reasons for the difference in the variation trends of the stiffness of the lower isolators for different objective functions are discussed in detail. The fluid loading does have an impact on the optimal results and it influences the variation trend of only the stiffness of the isolators that support the machines without an externally applied load. The external loading and the optimized frequency band are two factors to be carefully considered in the design stage. This investigation reveals that it should take into account fluid–structure interaction and comprehensively consider different vibration or acoustic objectives in the design stage.

Discrete material optimization of vibrating laminated composite plates for minimum sound radiation

This paper deals with vibro-acoustic optimization of laminated composite plates. The vibration of the laminated plate is excited by time-harmonic external mechanical loading with prescribed frequency and amplitude, and the design objective is to minimize the total sound power radiated from the surface of the laminated plate to the surrounding acoustic medium. Instead of solving the Helmholtz equation for evaluation of the sound power, advantage is taken of the fact that the surface of the laminated plate is flat, which implies that Rayleigh’s integral approximation can be used to evaluate the sound power radiated from the surface of the plate. The novel Discrete Material Optimization (DMO) formulation has been applied to achieve the design optimization of fiber angles, stacking sequence and selection of material for laminated composite plates. Several numerical examples are presented in order to illustrate this approach.

Engine noise potential analysis for a trimmed vehicle body: Optimisation using an analytical sea gradient computation technique

For the optimisation of the vibro-acoustic behaviour of vehicle bodies above 400 Hz, statistical energy analysis (SEA) has become a common tool in recent years. Within this paper we would like to introduce a vibro-acoustic optimisation algorithm which is based on an analytical gradient computation of the energy of a subsystem with respect to SEA coupling and internal loss factors. The suggested interface of the method between vibro-acoustic complete vehicle optimisation with respect to SEA parameters and material optimisation in order to design the SEA loss factors, might offer a suitable work flow between OEM or system supplier and trim material supplier. With the help of the analytical gradient formulation, which is represented in Section 2, we show in Section 3 that the energy of subsystems, which constitutes the optimisation function, does not exhibit local extrema in the loss factor parameter space. Therefore, a straightforward optimisation procedure based on the investigation of the vibro-acoustic potentials of loss factors and the calculation of design targets is introduced in Section 4. After validation in Section 5 the method is applied in Section 6 in order to optimise engine noise of a coupé SEA model.

Vibroacoustic optimization of skin damped structures for noise reduction

Most of the time the widely used passive treatments are designed to obtain the highest achievable damping. Although this might be satisfactory from a vibrational point of view the approach is not optimal for noise reduction. The idea is illustrated in the case study of a plate on which polymer/aluminum thin patches have been bonded. The system acoustic pressure and structure displacement equations are transformed into a single integro differential one governing the plate displacement. The solution is then expanded into a series of resonance modes. These modes are estimated using a perturbation expansion with respect to the fluid/solid density ratio. Numerically, in vacuo resonance modes are firstly computed using a viscoelastic incompressible 3D FE program together with a Newton-type iterative method and a sparse complex matrix solver implementing ARPACK. Radiation modal impedances are then computed to ponderate the in vacuo solution. The numerical model has been experimentally validated. Its specificity lies in the separate computation of three damping components: thermoelastic, skin and acoustic damping, this last one being caused by the fluid/structure coupling. Finally an optimization process determines an optimal system configuration to achieve the lowest acoustic damping while obtaining the highest viscoelastic damping.

Powertrain noise and vibration simulation with hybrid models

As a result of the requirements to shorten the development cycle of new engines, CAE techniques become increasingly important in the early design stages. More specifically, the complex task of vibro-acoustic optimisation, traditionally an end-of-cycle task, is now shifting towards the pre-assembly phase. Structural and acoustic modelling methods, used to predict the performance in terms of noise, vibration, engine dynamics and durability, rapidly evolve to being key tools in the design processes. Traditional CAE analyses of powertrains rely on large-scale FE-models, describing the engine, transmission and auxiliaries in much detail, and lead to high model development times and high computational times. However, because of the limitations currently put on the total design cycle duration, modelling methods need to be able to handle a mixture of pure analytical design models and experimentally obtained dynamic characteristics. Based on analytical vibro-acoustic component models, an initial predictive assembly model is built. Excitation forces resulting from dynamic simulation or from experimental identification on existing engines are used to load the model for the evaluation of the performance or design changes in terms of absolute noise and vibration levels. The noise and vibration quality can thus be evaluated at assembly level and next cascaded down to requirements at component level. Whenever available in a new development phase, the measured dynamic characteristics of prototyped components are integrated into the total model, to refine the virtual prototype of the assembled product (see Figure 1). This paper covers the investigative application of these hybrid vibroacoustic simulation techniques. The described project has been executed as under cooperation between Toyota Motor Corporation and LMS Engineering Services in order to establish the above process and validate the simulation techniques. The Toyota 3S-FE engine is used as a benchmark engine throughout this paper.

Development trends and vibro-acoustic layout criteria for powertrain mounting systems

Improved driving comfort is currently one of the main development focuses of car manufacturers. This concerns not only the structural car’s design but also the vibro-acoustic optimisation of severel susystems. Suppliers in particular are faced with higher demands for comfort in cars. As a development partner to the automotive industry, Freudenberg Dichtungs- und Schwingungstechnik had expanded its products and rnaterials expertise to include holistic system development

Use of genetic algorithms for the vibroacoustic optimization of a plate carrying point-masses

Optimal design of mechanical structures for vibration or noise reduction often requires finding the minima of highly nonlinear multi-dimensional functions. In this paper, genetic algorithms are introduced as a new promising tool for numerical optimization of such problems. The application presented is on the control of the vibroacoustic response of a plate carrying point-masses. Genetic algorithms have been used to determine the optimal positions of the masses on the plate. Several cases are presented, using various optimization criteria, showing the importance of selecting the most appropriate criterion.

Use of genetic algorithms for the vibroacoustic optimization of plates

Genetic algorithms have proven to be helpful for solving complex optimization problems where more traditional gradient-based methods have failed. The optimal design of vibroacoustic systems often leads to complex optimization problems requiring a method able to find a globally optimal solution through a large number of locally optimal solutions. The vibroacoustic behavior of a simply supported plate carrying one or more point masses has been investigated through a genetic algorithm optimization method, in order to determine optimal placement of the masses for maximal sound or vibration attenuation. It has been shown that the use of an optimization method able to search through the whole optimization domain can give unexpected solutions resulting in a higher level of reduction in radiated noise or vibration response, when compared to intuitive solutions like placing the point masses on excitation points. In particular, when a well-defined frequency range is targeted, genetic algorithms can be used for tailoring a special design giving highest reduction in the specified range. [Work supported by the IRSST.]