In this summary, the background to MHiVec, the project objectives and work description for the first two year reporting period are given along with the results achieved so far and their expected impact.
The background and project objectives:
This proposal is concerned with a new simulation tool for noise, vibration and harshness (NVH) predictions in mechanical structures. The tool is based on an innovative method called Discrete Flow Mapping (DFM) which has been invented in 2011 by the coordinating partners of this consortium, Nottingham Trent University (NTU) and University of Nottingham (UoN), and has been tested on small scale bench-marking projects with the car maker Jaguar Land Rover. As design and construction decisions are increasingly made by means of virtual prototyping and as part of Computer Aided Engineering (CAE), efficient simulation tools in all areas of engineering are prevalent and sought after. A whole simulation industry has emerged serving the needs of the Original Equipment Manufacturers (OEMs).
DFM makes it possible to efficiently compute vibrational energy distributions on structures of arbitrary complexity, making it ideal for an NVH software tool to be used by the non-specialist engineer. Vibrational energy flow can be computed on meshes harnessing the full flexibility of mesh based approaches. Once fully developed, DFM will reduce NVH simulation costs considerably and will provide a reliable everyday tool for the engineer, here with a focus on applications in the car manufacturing industry. The main objective of the proposal is to develop a modelling and simulation tool for a complete car body over the full frequency range up to 20 kHz.
The project consortium is led by NTU and UoN and includes further academic expertise from the world leading Institute of Sound and Vibration Research (ISVR) at the University of Southampton. The academic knowledge will be channelled via two expert SMEs to OEMs. CDH AG (CDH) provide software and modelling expertise with a track record in NVH simulation for the automotive industry. inuTech GmbH (iT) is an expert in numerical solutions and algorithm development with expert knowledge on DFM. The consortium is completed by the associate partner (AP) Jaguar Land Rover (JLR), who will provide benchmark problems and measurements. The main objective will be achieved by delivering the following Science & Technology objectives:
• O1: Structure/components: DFM technology for individual car body parts;
• O2: Interfaces: Hybrid model description of interfaces between individual car body parts;
• O3: Structure-Assembly: Assembling a hybrid model for a whole car Body-in-Blue (BiB);
• O4: Software Integration: Linking the DFM solver to standard software tools;
• O5: Validation: Testing the results against simulations and measurements provided by JLR;
• O6: Product: Providing a user-friendly complete vehicle modelling tool for a BiB.
Objectives O1 and O2 are the focus of this first reporting period for project months 1 to 24.
The work description:
In this first 24 months the majority of the work has taken place within the academic partners, including contributions from members of the industrial partners whilst on secondment. Work at NTU has focussed on extending the capability of DFM in a number of respects. Firstly, the modelling of how curvature effects the energy transport on a curved shell around and below the ring frequency. For sufficiently high frequency the propagation follows geodesic paths, but at lower frequencies curved regions can lead to reflections and in effect leads to vibrations avoiding regions of strong curvature. Secondly, three-dimensional DFM elements have been developed in an efficient manner using semi-analytic and semi-spectral quadrature methods. Efficiency is of vital importance here due to the high dimensionality. Thirdly, global interface problems are being considered at NTU where the a two-dimensional substructure is globally coupled to the three-dimensional elements. Finally, the modelling of uncertainties has been implemented at NTU, in collaboration with UoN, by designing a propagation operator that interpolates between random and deterministic propagation, which can be used in place of the standard DFM propagation operator. This operator can describe both material and geometric uncertainties as well as having nice mathematical properties (compactness) that mean we can prove convergence in certain function space settings.
As well as collaborating with NTU on the work on uncertainties, UoN have also developed a number of enhancements to the DFM methodology. Firstly, acoustic radiation and fluid structure interaction has been modelled leading to predictions of both the sound pressure levels in an interior region and the vibrational energy on the surrounding structure. However, the main focus of work at UoN has been on the wider development of transfer operator approaches to include wave effects in the models and facilitate efficient DFM modelling at so-called mid-frequencies, which are too low for a pure ray treatment like standard DFM approaches and too high for conventional CAE methods such as finite element methods. A wave transfer operator has been developed for including effects such as diffraction. Interface models using transfer operators are being incorporated at UoN, with particular focus on interfaces connecting non-conforming meshes, since these are prevalent in the body-in-blue mesh data from JLR. The secondment of an early career researcher from UoN to iT also resulted in an interface model library being set up for relatively simple cases (multi-plate and simple plate-beam connections) where analytic wave descriptions can be employed to describe the vibrational energy transport.
Work at ISVR has concentrated on local models for small sub-structures where wave effects must be captured. In these cases the wave and finite element method (WFEM) provides a natural counterpart to DFM, since it considers structural vibrations in term of the waves that generate them. ISVR have lead the development of local interface models that can be implemented along with DFM in a hybrid fashion, including the connections most commonly found on vehicle structures. Namely, these connections are gas weld and adhesive line connections, and small circular joints created by either spot welding or self-piercing rivets. In the latter case, the interface models have been developed using the popular CAE software NASTRAN. Here the work drew heavily on the expertise of CDH in both NASTRAN software and spot weld models, facilitated through both secondment and a short visit in March this year. Research at ISVR has also contributed to the modelling of composite elements which can again be implemented in DFM as part of a hybrid DFM/WFEM scheme.
The results achieved and expected impact:
Through the combined work of the consortium members described above, the capability of DFM has been extended considerably to make it a viable for modelling a full vehicle BiB structure. The ability to handle complex curved geometries at mid-frequencies, to model fully three dimensional and composite structures and to include uncertainties in the description of the propagating ray paths are all significant steps forward. In addition to an enhanced library of ‘DFM elements’, a major area of development has been in modelling the connections between different parts of a structure. The major results in this area have been achieved via WFEM and FEM models of the local spot and adhesive joints. The project is currently in a transition stage whereby the results achieved during the first reporting period are being transferred to the SME commercial partners, for whom the knowledge gained from the academic partners will lead to the prospect of becoming main players in the mid-to-high frequency automotive NVH market and leading providers of software and expertise in the NVH CAE area. Associate partner JLR will be the first end-user to learn about the method enabling them to gain a competitive edge by using the method first in product development activities. The long-term impact of the project is envisaged to be that DFM technology will become the method for the NVH simulation market. The successful introduction of these software tools will stimulate further R&D efforts, mainly in a European context, turning Europe into a focus of the NVH simulation world.