Development of Simplified Analysis Process for Multidisciplinary Design Optimization (MDO) of Exhaust Manifold During Concept Stage

The exhaust manifold is one of the key components of an engine exhaust system. Exhaust manifold simulations are time-consuming as they require modeling of complex thermal loading and multiple non-linearities like friction and plasticity. This proves to be a big constraint for using Multidisciplinary Design Optimization (MDO) for exhaust manifolds as it involves running a large number of models specified by a Design of Experiments (DOE). Also, during the initial phase of design development, it seems reasonable to compromise the accuracy of simulations at the cost of speed for getting correct feedback on design direction. Hence, the main objective of the current work was to a develop simplified analysis process for Thermomechanical Fatigue (TMF) and modal analysis of exhaust manifold. At the concept stage, due to the lack of availability of accurate thermal Boundary Conditions (BCs) and the goal to simplify modeling, thermal BCs are assumed with the help of thermal data history instead of accurate thermal BCs from test cells. Similarly, other aspects such as ‘level of component assembly required’, ‘mechanical loading’, and ‘outputs to be monitored for making design decisions were also investigated to come up with a simplified approach. The proposed approach was quick compared to the conventional one. This approach was implemented on a few heavy-duty and mid-range engine programs to check repeatability. It was observed that the proposed analysis approach provides correct design direction with a significantly reduced computational time of up to 80%. Incorporating the simplified approach for the MDO process has made it more practical and feasible for implementation during the concept design cycle in the early stage of an engine development program.