Research On The Dynamics Method Of DTH Drill String Based On Beam Theory And Domain Decomposition Method

With the continuous development of China,infrastructure construction and underground resource mining require equipment to adapt to the complex construction environment,have faster drilling speed,better security,and put forward new requirements for the development of drilling engineering.Drill string dynamics is one of the most challenging problems,which has been studied for many years.In this paper,based on the domain decomposition method,the coupled vibration energy functional of beam theory is established,and the applicability of three-dimensional beam theory energy functional to drill string problem is discussed.The research contents are as follows:1.Based on the plane beam theory,the differences and relations between Euler Bernoulli beam theory and Timoshenko beam theory are compared.On the basis of plane beam theory and displacement superposition method,three-dimensional Euler Bernoulli beam theory's and three-dimensional Timoshenko beam theory's energy functional are derived,and the discrete dynamic equations of these three-dimensional beam theory are established by using the domain decomposition method.The discrete dynamic equations can be used for modal analysis,steady-state and transient dynamic analysis under different boundary conditions.2.In view of the dynamic problems of slender rod structure such as drill string,the influence of shear deformation on the theoretical calculation results of two kinds of three-dimensional beams are analyzed under the conditions of different thickness diameter ratio H / R and slenderness ratio L / R.It is concluded that when L / R >2000 and H / R > 0.1,three-dimensional Euler Bernoulli beam theory can be selected for analysis,which can reduce the overall calculation amount and improve the calculation efficiency while ensuring the calculation accuracy.3.Based on the domain decomposition method and the three-dimensional Euler Bernoulli beam theory,the vibration model of DTH Drill string with non-classical boundary is established,and the energy functional of the coupled vibration of the DTH Drill string is obtained.Taking? 165 mm bit and? 88.9mm drill string as the research object,the longitudinal and torsional vibration responses of drill string are solved under the periodic impact load.