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This paper presents a method for structural modifications for achieving desired eigenstructures based on receptances, by adding multiple mass-spring systems to some locations of the primary system. This method has the benefit that not only neither analytical nor modal models are needed, but also the original mass and stiffness of the primary system are maintained. Moreover, when a complex structure or machine is designed for some special functions so that its inner structure is not allowed to be modified, it is an effective way in practice to achieve desired dynamical performance resulted from adding several external simple substructures. The theory is presented in this paper, which is suitable for linear undamped systems. Numerical experiment is set up, and the results of the modifications are compared with the method proposed by Braun and Ram. Both theoretical derivation and numerical results demonstrate the effectiveness of this method. [ABSTRACT FROM AUTHOR]

• A fracture failure of a marine diesel engine timing gear is investigated in detail. • Both experimental and numerical investigations are performed. • Influence of associated structures is considered while analyzing the fracture. • Two models, one is with inclusion and the other is non-inclusion, are constructed. • Results indicate the fracture is a fatigue fracture and is caused by the inclusion. In this paper, a fracture failure of a marine diesel engine timing gear in a chemical tanker was investigated in detail using both experimental analysis and numerical analysis. The experimental analysis includes macroscopical inspection, Scanning Electron Microscope analysis, Energy Dispersive Spectroscopy analysis, metallographic investigation and mechanical property investigation. The numerical analysis includes torsional vibration analysis and finite element method (FEM) simulations. In the torsional vibration analysis, the coupling influence of the associated structures on the timing gear system was taken into account, not only analyzing the fault gear itself. In the FEM simulations, two models, one is with inclusion and the other is non-inclusion, were constructed. Both investigations indicate that the fracture is a fatigue fracture and the initial cracks are caused by the inclusion. Further investigation should pay attention to finding a way to overcome the problem of fatigue fracture. [ABSTRACT FROM AUTHOR]