Calculation and design of ship vibration isolation by integrating isolator spectrum data and FEM

Objective Traditional simulations of ship floating raft isolation systems often exhibit significant discrepancies from experimental results due to inaccurate dynamic parameters of rubber isolators. Existing approaches lack effective integration between isolator spectrum data and finite element method (FEM), resulting in the absence of an engineering-oriented prediction tool for rapid evaluation of single- and double-layer isolation performance and isolator selection during the design stage. To address the challenge of accurate dynamic modeling for rubber isolators, this paper proposes a coupled simulation framework to improve the design accuracy of acoustic and vibration isolation systems for marine machinery.

Method Geometric dimensions, static stiffness, nominal dynamic stiffness and damping data are extracted from the standard spectrum data of ship vibration isolators. Three parameter acquisition schemes are established, including static stiffness, spectrum-specified dynamic stiffness, and dynamic stiffness converted from measured driving-point impedance. In Abaqus, isolators are simplified as spring-dashpot elements, and finite element models of single-layer and double-layer floating raft systems are developed. A series of validation tests, including mechanical impedance measurements, raft admittance calibration and full-scale vibration transmission experiments, are conducted to compare full-band vibration responses under different parameter inputs. Furthermore, the proposed method is applied to batch-evaluate five types of rubber isolators with identical load capacities.

Results Dynamic stiffness converted from measured driving-point impedance shows the best agreement with experimental results, with the maximum frequency deviation limited to 3.5 Hz within the 400 Hz frequency range. Cross-point impedance is affected by interference from external support structures, resulting in lower prediction accuracy. Double-layer isolation shows superior vibration attenuation performance in the medium- and high-frequency ranges compared with single-layer schemes. Among the tested products, JQ-120 and 6JX-100 isolators exhibit the best isolation performance, whereas the E-120 isolator shows the poorest performance.

Conclusion The spectrum-FEM coupled method can accurately predict vibration transmission characteristics of floating raft systems and effectively avoid system resonance, providing support for rapid isolator selection during the design stage. It can be further developed into dedicated prediction software, providing a complete engineering technical scheme for vibration isolation optimization of low-noise marine machinery and acoustic stealth design of ships.