Joshua W.R. Meggitt

University of Salford · Acoustics Research Centre

Transfer Path Analysis (TPA) is a test-based methodology used to analyse the propagation of noise and vibration in complex systems. In this paper we present a covariance based framework for the propagation of experimental uncertainty in classical, blocked force, and component-based TPA procedures. The presence of both complex and correlated uncerta...

Conventional model updating methods are based on frequency response functions (FRFs) and/or modal parameters estimates obtained from freely suspended, or sometimes rigidly constrained, sub-structures. These idealised boundary conditions are however often difficult to realise in a practical scenario. Furthermore, they are in conflict with the requir...

To accurately model the dynamics of a complex built-up structure it is often necessary to forgo the assumption of ideal rigid coupling between components. The dynamic behaviour of inter-component connections, or joints, can have a significant impact on the performance, even survivability, of an assembled structure. For complex structures, where man...

Blocked forces have become an increasingly popular means of characterising the operational behaviour of vibrating machines (such as pumps, engines, gearboxes, electric motors, etc.). Nevertheless, their characterisation and application remains somewhat inaccessible, often requiring many years of experience to master. This document intends to provi...

Across many industries there is a need to develop products with improved vibro-acoustic performance. Whether the aim is to reduce the radiated sound level in a vehicle cabin, or to minimise the vibration level of sensitive components, the problem may be interpreted as an issue of power transmission from vibration generating components to receiving...

This paper describes the development and testing of an alternative method of sound transmission measurement , ideally suited to low frequencies. The standard approach to measuring sound transmission (detailed in ISO 10140) relies on the assumption of a diffuse field from which radiated sound power can be estimated. While adequate for higher frequen...

Transmissibility functions are used to identify and locate damage in critical structures for health monitoring purposes. Their appeal over conventional signal or frequency response-based functions lie in a unique property; sub-structural invariance. It has been shown that the transmissibility of an assembled structure, when obtained correctly, can...

The round-trip method enables the indirect determination of point mobilities along interfaces that cannot be easily excited. One embodiment of the method requires excitation at a subset of points either side of the interface, while responses are measured along it. This is typically done by instrumented hammer or shaker. In the present paper, we inv...

The paper outlines some major developments in Virtual Acoustic prototyping. The story starts in the 1980s (four decades ago) when the prediction accuracy for structure-borne sound of 40 dB (four decades) was considered normal! The group's key innovation has been in describing sources in terms of 'blocked forces' which not only can be measured in-si...

The dynamic properties of joints, or inter-component connections, are a principal source of uncertainty when modelling complex built-up structures. In the present paper, we propose an interval-based sensitivity analysis (SA) to establish the contribution, or influence, of a structure's uncertain joint dynamics towards the uncertainty of its coupled...

A common problem that arises during modal testing is the inability to directly excite degrees-of-freedom to obtain frequency response functions (FRFs). It has been shown previously that reliable reproduction of FRFs via indirect excitation is difficult. This issue led to further investigation into the reconstruction of FRFs, with the most successfu...

There are numerous methods for characterising sound insulating and impact noise reducing compo-nents and systems, each with their own advantages and disadvantages. Two of the predominant mod-elling techniques for prediction of transmission loss through partitions are finite element analysis (FEA)and the transfer matrix method (TMM). FEA has the adv...

In noise and vibration engineering, a structure’s passive dynamic properties are often quantified by frequency response functions (FRFs). This paper focuses on acquiring FRFs from experimental tests, considering both, translational (x, y, z) and rotational (e.g. moments around these axes) terms. In practical applications, test structures may not al...

The purpose of this paper is to present a case study whereby a hybrid experimental-numerical model is used to analyse the structure-borne radiation from a domestic product (vacuum cleaner head). The passive (including radiative) properties of the structure considered are modelled using the Hybrid FE-SEA method. The product's operational activity, w...

In-situ Transfer Path Analysis is a diagnostic method used to analyse the propagation of noise and vibration through complex built-up structures. Its defining feature is the invariant characterisation of an assembly's active components (i.e. vibration sources) by their blocked forces. This invariant characterisation enables the downstream structura...

The vibro-acoustic analysis of complex structures over a broadband frequency range is an extremely challenging problem that may often require the use of a hybrid deterministic-statistical approach. Due to manufacturing imperfections, the frequency response functions (FRFs) of an ensemble of nominally identical systems can be considered to be random...

Modern manufacturers usually need to know at a design stage if their products will meet certain vibro-acoustic requirements. In many cases the use of physical prototyping becomes significantly expensive, and engineers opt for the development of predictive computational models. In these cases, a hybrid deterministic-statistical approach can overcome...

In-situ Transfer Path Analysis (TPA) is a diagnostic method used to analyse the propagation of noise and vibration through complex built-up structures. Its defining feature is the independent characterisation of an assembly's vibratory source in terms of its blocked force, an invariant property that is unchanged by the dynamics of neighbouring comp...

There is a clear need in modern industries for models that can predict the vibro-acoustic response of their manufactured products at the design stage. Models based on the hybrid deterministic-statistical method are a suitable solution to overcome the challenge of predicting the response of complex built-up systems in the mid-frequency range. Despit...

Blocked forces can be used to describe, independently, the operational characteristics of a vibratory source. Their use within a computational model avoids the need to represent explicitly the complex mechanisms that lead to vibratory excitation. To obtain and apply an experimental blocked force with confidence it is important that likely sources o...

Dynamic sub-structuring (DS) is the procedure by which the passive properties (i.e. frequency response functions) of an assembled structure are predicted from those of its constituent sub-structures. In this paper we are concerned with the propagation of correlated uncertainty through such a prediction. In this work a first-order covariance based p...

A major challenge in automotive NVH engineering is to approach complex structure-borne sound and vibration problems with sufficient accuracy but reasonable experimental effort. Typical issues encountered are poor correlation between objective component performance criteria tested for during bench validation and corresponding subjective targets eval...

Transfer path analysis (TPA) has become a widely used diagnostic technique in the automotive and other sectors. In classic TPA, a two-stage measurement is conducted including operational and frequency response function (FRF) phases from which the contribution of various excitations to a target quantity, typically cabin sound pressure, are determine...

div class="section abstract"> Transfer path analysis (TPA) has become a widely used diagnostic technique in the automotive and other sectors. In classic TPA, a two-stage measurement is conducted including operational and frequency response function (FRF) phases from which the contribution of various excitations to a target quantity, typically cabin...

The vibro-acoustic response of complex structures with uncertain properties is a problem of great concern for modern industries. In recent years, much research has been devoted to the prediction of this response in the mid-frequency range where, because neither finite element analysis nor statistical energy analysis are appropriate, a hybrid determ...

Modern industries usually need to ensure that their manufactured products meet certain vibro-acoustic requirements. Therefore, they have a clear need for models that can predict the broadband dynamic response of structural components at the design stage. The use of a hybrid deterministic-statistical formulation has been shown to be a suitable solut...

Inverse problems are widely encountered in fields as diverse as physics, geophysics, engineering and finance. In the present paper, a covariance based framework for the estimation of their uncertainty is presented and applied to the problem of inverse force identification. A key step in its application involves the propagation of frequency response...

This paper is concerned with the development of an experimental method capable of independently characterising low Mach number, in-duct fluid machines, such as pumps, fans, etc. The aim is to propose and test a source characterisation method that is suitable for acoustic simulation and the construction Virtual Acoustic Prototypes. Such a requiremen...

Frequency response functions (FRFs) are routinely used within experimental structural dynamics, among other fields. The uncertainty associated with their measurement is typically modelled on the simplified assumption that additive uncorrelated noise is present. This treatment of FRF uncertainty is questioned here by demonstrating that the notion of...

The context of this paper is the increasing need for vibro-acoustic simulation across many sectors. A procedure is derived for decoupling the components of resiliently mounted assemblies. An independent characterisation of the components is obtained such that they can be mathematically recombined with other elements to form virtual assemblies or Vi...

This paper is concerned with Shorter and Langley's hybrid method [JSV, 288(3):669-699, 2005] and the incorporation of experimental subsystems. In particular, this paper will address the form of the experimental data required and the procedures necessary to obtain it. Further discussion regarding the theoretical construction of the hybrid model will...

A crucial step in sub-structuring, vibration source characterisation and transfer path analysis is to correctly define the interfaces between coupled sub-structures. In particular, it is necessary to identify the degrees of freedom through which coupling occurs. Even for experienced engineers, identification of the degrees of freedom required to fu...

The vibro-acoustic response of complex structures with uncertain properties is a problem of great concern for modern industries. In recent years, much research has been devoted to the prediction of this response in the mid-frequency range where, because neither finite element analysis nor statistical energy analysis are appropriate, a hybrid determ...

The independent characterisation of a structural component is an essential requirement in many vibro-acoustic problems, including the construction of virtual assemblies and virtual acoustic prototypes. Typically, a complete characterisation involves the determination of both active and passive component properties. This paper concerns the latter, o...

A drive towards leaner engineering has seen the use of physical prototypes become a limiting factor in the development of new products. Consequently, alternative prototyping methods are of interest. With their ability to reduce cost, accelerate time to market, and optimize products to higher levels of performance and reliability, virtual methods of...

The context of the paper is the need across many industries for prediction and simulation of vibro-acoustic response of assembled structures. One of the main areas of difficulty is to know the excitation forces. The blocked force method allows vibration sources to be characterised independently using conventional measurements similar to those used...

In the field of experimental vibro-acoustics the ability to predict the response of a coupled assembly from the properties of its constituent parts can prove advantageous, particularly in the development of mechanical goods, such as domestic products, vehicles, and other machinery. A notable example is its use within virtual acoustic prototyping (V...

This paper concerns the development and application of an in-situ characterisation method for induct sources. Such sources may be attributed to many of the noise problems faced by acoustic engineers, and therefore reliable methods for the analysis and prediction of sound generation and propagation due to induct installations are of interest. Based...

An in situ method for the measurement of a resilient elements dynamic transfer stiffness is outlined and validated. Unlike current methods, the proposed in situ approach allows for the characterisation of a resilient element whilst incorporated into an assembly, and therefore under representative mounting conditions. Potential advantages of the pro...

During the development of complex assemblies such as aircraft the noise from installed components must be considered. For airborne sound sources this issue has been resolved to some extent by standard measurement procedures which allow equipment suppliers to transfer data to end users in an agreed form. The same cannot be said for structure borne s...

This paper investigates techniques for auralising continuous broadband sounds both with and without tonal components. This work is part of a wider project to develop a virtual acoustic prototype of a domestic appliance. The ultimate objective is to simulate the acoustic output of the device as a function of its design parameters and operating condi...

Internal University of Salford conference poster

An in-situ method for the measurement of a resilient elements dynamic transfer stiffness is outlined and validated. Unlike current methods, the proposed in-situ approach allows for the characterisation of a resilient element whilst incorporated into an assembly, and therefore under representative mounting conditions. Potential advantages of the pro...