Reduced modal models and negative concept modifications in dynamic analysis E. Mucchi(*), S. Donders (**), R. Hadjit (**), W. Desmet (*), P. Sas (*) (*) K.U.Leuven, Department Mechanical Engineering Celestijnenlaan 300 B, B-3001, Heverlee, Belgium (**) LMS International, Interleuvenlaan 68, B-3001 Leuven, Belgium email: stijn.donders@lms.be Abstract In this paper a concept CAE approach to efficiently modify the properties of beam-like sections and joint connections of a vehicle body is presented. Negative concept modifications in the beams and in the joints are analyzed using reduced models. Standard beam elements are used to implement the modifications in the beam-like section, where the joint modifications are considered through Guyan superelements. Examples are presented for beam thickness and joint stiffness modifications, but one can consider any properties: it will be shown that by adding beams to the beam model and by applying Guyan superelements to the joint model one thus obtains a much smaller models for fast modification analysis. The proposed approach is then demonstrated on an industrial vehicle model to quickly and accurately optimise the low-medium frequency behaviour. 1 Introduction In order to achieve a true “Design Right First Time” which leads to shorter time-to-market and reduced costs as compared to conventional “Test Analyze & Fix”, one must apply predictive Computer-Aided- Engineering (CAE) methods in all stages of the design process. A major challenge and ongoing revolution in digital product development consists of achieving an “Analysis leads Design” process, in which an upfront engineering analysis phase essentially precedes the detailed (geometrical) design (CAD and CAE) and in which CAE supports concept analysis to define the design requirements in order to meet the functional performance targets. For this purpose, the authors have developed a concept CAE approach, also known as simplified modelling, which uses approximations that reduce the size and complexity of the large FE model. The concept models are characterized by subdividing the structure into beam-like and joint-like components as shown in Figure 1. The properties of the beam-like structures are obtained directly from the refined FE model, and then represented by equivalent beam elements. Similarly, the stiffness characteristics of the body joints (between the beam-components) are derived from the FE model, and the joints are represented by small-sized static superelements (system matrices). 1421