In-Car Noise Computation for a High-Rise Lift

The authors have developed an acoustic model of a lift, using a multi-disciplinary approach. The model enables a full understanding of how the lift design is affected by noise requirements inside the car, and in buildings that are still in planning or construction phase. The approach is based on a hybrid model combining structural finite element (FEM); computational fluid dynamics (CFD); boundary element method (BEM) and statistical energy analysis (SEA); to cover both low and relatively high frequency acoustical domains in a sufficiently detailed model with a reasonable computational time. Special attention has been paid to modelling of the noise sources. Structure-borne sources (point forces) due to roller guide shoes and ropes were applied on the system. Forces were determined on grounds of FEM-computed point mobilities and measured vibration velocity responses at the same excitation points. Airborne sources due to flow-induced noise were computed using an incompressible transient CFD analysis. The resulting time variable air surface pressure was then applied on the car walls. The surface pressure spectra were used both directly (the convective source) and as a source for the acoustic propagation (giving the acoustic source). The reverberant sound field in the hoistway, generated by the flow sources, is a significant contributor. This part was modelled using BEM. The time variable pressure field on the car surface was used as a source distribution for BEM. The end result of the computation was applied as a diffuse acoustic field on the car surfaces. All the sources: structure-borne and airborne, were applied as forces and pressures. They were internally converted to power inputs for solving the SEA model. All transfer paths in the sling, car, doors, fairings and hoistway, including relevant leaks were simulated. After validation, the hybrid model now allows the users to quantify and rank noise contribution of each source and make predictions based on changes in the lift structure, hoistway design and car running parameters.