Abstract: The Rayleigh damping model is widely used in simulating the dynamic charac-teristics of drill strings to reflect the effect of damping (including drilling fluid damping). However, the basis for choosing this model has not been sufficiently investigated, and its damping coefficient is mainly determined by experience. In this study, the dynamic fi-nite element model of a drill string was established by first considering the nonlinearity and damping effect of the drilling fluid to simulate the dynamic characteristics of the drill string in a borehole. Subsequently, the mechanisms and internal relations of the typical Rayleigh damping, Caughey damping, and Clough damping models were investigated. Finally, the effects of these three models on the dynamic characteristics of the drill string were investigated using a practical example, and the lateral displacement, lateral acceleration, whirl trajectory, and whirl velocity of the drill string under different damping models were compared. The results show that the damping value of the Caughey damping model with l within the range of −2 ∼ 1 is negligible to effectively provide viscous damping, and the damping value is extremely large when l assumes other values. This implies that the Caughey damping model with four terms is not suitable for the dynamic simulation of drill strings. The Rayleigh and Clough damping models can effectively reflect the damping effect of drilling fluid, and the dynamic characteristics of the drill string obtained are consistent with the actual vibration. By contrast, the Rayleigh damping model is simple in form and easy to calculate; therefore, it is suitable for the dynamic simulation of drill strings in drilling engineering.

Key words: drill string, Rayleigh damping model, drilling ?uid, dynamic characteristics, ?nite element analysis