Electromagnetic vibration is an important excitation source for squirrel-cage induction motors. However, the electromagnetic vibration under various loadings has not been sufficiently analyzed. It is proposed in this paper that the electromagnetic vibration of motors under different loads can be obtained by analyzing the amplitude of the electromagnetic force wave. The Maxwell tensor method is employed to derive the spatial and temporal distributions of the radial force. This paper also calculates the radial force using the finite element method and decodes the calculated results using two dimensional fast Fourier transform (2D-FFT) to determine the amplitude of the electromagnetic force at the spatial order under different loads. In addition, through the modal analysis of the stator core, it can be concluded that in the case of nonresonance, the vibration response increases when the electromagnetic force of the first-order and second-order rotor slot harmonic increases. Finally, the conclusion is verified by separating the electromagnetic vibration of the motor using a vibration test rig.

Amidst growing environmental concerns and energy crisis, dc ship hybrid power systems (dc-SHPSs) incorporating energy storage systems (ESSs) has gained widespread applications in the marine industry owing to their flexibility and operability. However, the complex operating modes associated with ESSs and the protection of trade secrets make it difficult to analyze the stability of dc-SHPSs using traditional impedance-based stability criterion. Therefore, this study proposes a new method for analyzing the stability of a dc-SHPS with an ESS by introducing the concept of hybrid H-matrix model. The proposed stability analysis method can guarantee no right half-plane (RHP) poles in the system minor-loop gain, avoiding the need for detailed converter parameters in analyzing system stability. In addition, the method based on the Bode diagram is also proposed to evaluate system stability because assessing it using the Nyquist curve is difficult. This method provides a more intuitive assessment of system stability and is more suitable for engineering applications. Furthermore, some existing impedance-based stability criteria are analyzed and compared with the proposed stability criterion based on the hybrid H-matrix model. Finally, the effectiveness and validity of the proposed stability criterion are verified through time-domain simulations on Matlab/Simulink and experimentation on a hardware-in-the-loop (HIL) platform.

A piston slap is one of the main vibration sources of the reciprocating machinery. Much work has been done in this field, most of which was based on a constant rotating speed. However, in practice, the speed of a crankshaft may always fluctuate due to the uneven load or excitation. The inertia forces of moving components are much different at the fluctuating rotating speed comparing with that at a constant speed. In this paper, the piston slap and the induced vibration are analyzed based on the instantaneous angular speed measured on a single‐cylinder reciprocating compressor. Firstly, the dynamics of a crank‐connecting rod mechanism is analyzed based on the measured instantaneous angular speed which contains the torsional vibration of the air compressor. The time histories of piston slap impact forces considering and without considering torsional vibration are compared. Then, in order to correlate the piston slap impact with the slap‐induced vibration, the corresponding transfer functions between the middle stroke of the outer surface of the cylinder liner and the excitation points are measured. And the excitation force on the main bearing is also taken into account to bring the simulation closer to the experimental results. The effects of a torsional vibration on the vibration of the cylinder liner are analyzed, and the simulation results show that the torsional vibration is a factor that must be taken into account in the vibration analysis of the single‐cylinder reciprocating compressor.

The sound radiation from elastically restrained plates covered by a decoupling layer is studied using the Spectrogeometric Method (SGM), which is a meshless and parametric modeling technique. By adopting the Rayleigh-Ritz procedure and the Rayleigh integral, a vibroacoustic coupling system is established. This model studies the situation when the plate is immersed in heavy fluid, such as water, in which the strong coupling between the structure and sound field should be fully considered. The influence of the boundary conditions on the radiated sound power and sound reduction provided by the decoupling layer based on the locally reacting model is studied. The nonuniform distributed decoupling layer is also studied to analyze the sound reduction effect. The sound intensity on the outer surface of the decoupling layer is investigated and tends to be uniform along the plate scale with increasing thickness of the decoupling layer.