Phil Shorter

Application of the Hybrid FE-SEA Method to Predict Sound Transmission Through Complex Sealing Systems

Currently, the use of numerical and analytical tools during a vehicle development is extensive in the automotive industry. This assures that the required performance levels can be achieved from the early stages of development. However, there are some aspects of the vibro-acoustic performance of a vehicle that are rarely assessed through numerical or analytical analysis. An example is the modeling of sound transmission through vehicle sealing systems. In this case, most of the investigations have been done experimentally, and the analytical models available are not sufficiently accurate. In this paper, the modeling of the sound transmission through a vehicle door seal is presented. The study is an extension of a previous work in which the applicability of the Hybrid FE-SEA method was demonstrated for predicting the TL of sealing elements. A numerical validation of simplified Hybrid FE-SEA model is performed, which is followed by the application of the method to the TL of a car door seal. A full non-linear deformation/contact analysis is used to estimate the deformed geometry of the door seal in real conditions. The geometry is then used in a vibro-acoustic analysis to predict the in-situ transmission loss of the seal using a local Hybrid FE-SEA model. The channel between the door and the car structure where the seal is located is also included in the analysis. Results for the transmission loss are compared with experimental data, showing a good correlation.

Models of the acoustic radiation and transmission properties of complex trimmed structures

A number of advances have been made recently in the development of a hybrid method for rigorously coupling finite element and statistical energy analysis descriptions of the dynamics of a vibro‐acoustic system. The method provides an efficient way to analyze the acoustic radiation and transmission properties of a complex structure across a broad frequency range. In this paper, two case studies of engine components are used to validate the ‘‘hybrid area junction’’ formulation for coupling FE structures with trimmed SEA fluids, and to demonstrate the use of the method in a design process.

Finite element characterization of complex automotive panels for statistical energy analysis (SEA)

Complex panels typical of automotive structures are often difficult to describe using statistical energy analysis (SEA) for vibro‐acoustic prediction at high frequencies. The panels are usually curved, ribbed, with nonhomogenous thickness, and some of these features may be crucial to correctly capture the panels vibro‐acoustic behavior. It is therefore sometimes desirable to include some details in the SEA description of the panel by characterizing the statistical panel properties based on a finite element simulation. In this paper, the key SEA parameters are identified and a general process for obtaining SEA properties from a finite element model is demonstrated on an engine component.

Modeling Interior Noise due to Fluctuating Surface Pressures from Exterior flows

There are many applications in which exterior flow over a structure is an important source for interior noise. In order to predict interior “wind noise” it is necessary to model both: (i) the spatial and spectral statistics of the exterior fluctuating surface pressures (across a broad frequency range) and (ii) the way in which these fluctuating surface pressures are transmitted through a structure and radiated as interior noise (across a broad frequency range). One approach to the former is to use an unsteady CFD model. The use of compressible CFD to characterize exterior fluctuating surface pressures for broadband interior noise problems is relatively new; the accurate prediction of both the convective and acoustic wavenumber content of the flow can therefore present some challenges. This paper presents a numerical investigation of the spatial and spectral statistics contained in the flow downstream of a simplified side-mirror. Two distinct concentrations of energy are observed in wavenumber space at the convective and acoustic wavenumbers. Using wavenumber filtering it is then possible to describe a complex windnoise source in terms of the superposition of two simple analytical sources (that can be fit to CFD data). An example is presented in which the fluctuating surface pressures are applied to a side glass and a SEA model is used to predict interior noise.

Predicting speech transmissibility using ray tracing and statistical energy analysis

Statistical Energy Analysis (SEA) is used across many different industries to predict interior noise, for example the background noise in vehicle interiors due to steady-state exterior sources. SEA describes the reverberant response, however some applications exist where the direct field from interior sources is also important. This includes prediction of audio system sound quality in automobiles, or speech intelligibility for public address systems in trains, coaches, and aircrafts. Computing these indices requires both the background noise level and the impulse response at the listener location due a source representing a loudspeaker. Geometrical methods such as ray tracing are often used for describing the early impulse response where only few reflections of the direct field are involved; however they are not well suited for describing the late impulse response due to the increasing number of reflections. Instead a statistical description similar to transient SEA is typically used for the late time reflections. An SEA model of background noise therefore contains most of the information needed for predicting speech transmissibility: the background noise prediction, a simplified geometry of the acoustic space, and accurate wall impedance models. This paper demonstrates prediction of speech transmissibility by using ray tracing with typical SEA models.

Computationally efficient finite element method for predicting wave propagation in periodic structures

A generic numerical method for predicting the wave propagation in structures with two-dimensional periodicity is presented. The method is based on a combination of Finite Elements and periodic structure theory. A unit cell of the periodic structure is described with finite elements, and a Craig-Bampton reduction is applied to reduce the number of degrees of freedom. Periodic boundary conditions are then applied and the waves propagating in the structure are obtained by solving an algebraic eigenvalue problem. A number of analytical expressions are then used to derive the vibro-acoustic properties of the finite or infinite periodic structure. The method was recently extended to account for heavy fluid loading and material with frequency-dependent properties (typical of acoustic treatments). A number of examples are presented to validate the formulation and demonstrate the possible use of the method for design.

Development of a general SEA subsystem formulation using FE periodic structure theory

Statistical Energy Analysis (SEA) represents a field of study in which statistical descriptions of a system are employed in order to simplify the analysis of complicated vibro‐acoustic problems. In SEA, a vibro‐acoustic system is represented by a collection of subsystems that can receive, store, dissipate and transmit vibro‐acoustic energy. Traditionally, the SEA parameters for a given subsystem are formulated analytically based on consideration of wave propagation through the subsystem. While such analytical algorithms can be readily applied to the majority of systems encountered in practical problems, there are certain types of sections that are difficult to describe using existing analytical formulations. Examples include: isogrid in launch vehicle fairings, extruded aluminum sections in train floors and modern corrugated aircraft fuselage constructions. This paper describes the development of a generic SEA subsystem formulation based on the use of finite element (FE) periodic structure theory. A small...

Development of a general statistical energy analysis subsystem formulation using finite element periodic structure theory

Statistical energy analysis (SEA) represents a field of study in which statistical descriptions of a system are employed in order to simplify the analysis of complicated vibro‐acoustic problems. In SEA, a vibro‐acoustic system is represented by a collection of subsystems that can receive, store, dissipate, and transmit vibro‐acoustic energy. Traditionally, the SEA parameters for a given subsystem are formulated analytically based on consideration of wave propagation through the subsystem. While such analytical algorithms can be readily applied to the majority of systems encountered in practical problems, there are certain types of sections that are difficult to describe using existing analytical formulations. Examples include: Isogrid in launch vehicle fairings, extruded aluminum sections in train floors, and modern corrugated aircraft fuselage constructions. This paper describes the development of a generic SEA subsystem formulation based on the use of finite element (FE) periodic structure theory. A small unit cell of the section is created and computationally efficient algorithms are developed to calculate wave propagation through a large array of such cells. The resulting algorithms are used to calculate the SEA parameters for the section. The approach is described and a number of numerical validation examples are presented.

Vibro‐acoustic analysis using hybrid finite element, boundary element, and statistical energy analysis models

This paper presents an overview of the theory and application of the hybrid FE‐SEA method. The method provides a rigorous way to model the fully coupled response of a vibro‐acoustic system across a broad frequency range using a combination of FE, BEM, and SEA. The theory of the method will be discussed and results from the following applications will be presented: (i) modeling the transmission loss and radiation efficiency of trimmed automotive subassemblies; (ii) creating efficient models of structure‐borne noise in an automotive body‐in‐white; (iii) modeling structure‐borne noise transmission in a commercial aircraft fuselage; and (iv) modeling the response of a satellite antenna to broadband acoustic loading.

Modeling airborne interior noise in full vehicles using statistical energy analysis

SEA is particularly well suited for predicting airborne noise in vehicles. The acoustic sources found in such environment are typically spatially distributed around the vehicle and can be well represented with SEA diffuse acoustic loads. Multiple transmission paths contribute to interior noise levels including (1) mass law transmission through trimmed panels, (2) resonant radiation from vibrating structures, and (3) flanking paths through gaskets, seals, and holes. All these transmission mechanisms may be modeled using SEA techniques. Finally, interior trim (including carpet, headliner, seats) is a key contributor to the acoustic performance of modern vehicles. The vehicle sound package has a significant impact on both the strength of the transmissions paths into the vehicle as well as the acoustic absorption in the cabin. Both these effects can be accounted for with SEA through detailed models of the trim. SEA models of full vehicles are usually validated against experimental results at both component an...