有限元接触分析模拟

The Finite Element Analysis of the Rollers in a Rotary Steerable Drilling

Tool

Guangwei Zhang 1, a , Li You

2,b and Zhao Li 3,c

1

School of Mechanical Engineering, Xi'an Shiyou University, China 2CNOOC Information Technology Co., Ltd. Shanghai Branch, China

3

School of Mechanical Engineering, Xi'an Shiyou University, China a zhang-guangwei@, b eimeng@, c lizhao0125@

Keywords: Rollers, Rotary Steerable Drilling Tool, Contact Analysis, Finite Element Analysis.

Abstract: Rotary steerable system (RSS) is a system complete the oriented features in real-time while a drill string rotary drilling. It is a major change since the 1990s in directional drilling technology. RSS’s drilling frictional and torsional resistance is small, has a high drilling speed, low cost, the well trajectory is smooth and easy to control, it is considered to be the development direction of modern steering drilling technology .When the system working ,drilling pressure and torque are passed by the thrust bearings in the controlled bend sub oriented tool; therefore it is necessary to analysis the roller’s load distribution to verify the design parameters of variation cardan shaft, thrust bearings and roller are correct or not, This article analyzed thrust bearing’s rollers by ANSYS. Determine its maximum stress, etc. Providing more intuitive and scientific basis for its structural optimization [1].

Introduction

Rotary steerable drilling technology is a state-of-the-art automated drilling technology developed in the late 20th century, it is one of several key technologies in the international oil industry as the most important, is the research priorities and the development direction of modern steering drilling. Rotary steerable drilling, at the top of the drill equipped with a controlled eccentric, regulation wellbore trajectory while the drillstring rotary drilling. This article describe an intelligent closed loop downhole rotary steerable tool, it can automatically transform working statues according to the control requirements in downhole. Controllable bent sub’s guiding principle is shown in Figure 1[2].

Fig.1 Controllable bent sub’s guiding principle

The section view of the controllable bent sub’ is shown in Figure 2, we should analyze the situation of the contact between the bearings and roller to understand the stress. This article only analyzes the bearing part of the oriented drill and only A-B segment is analyzed. It is shown in Fig.2.

Fig. 2 The section view of the controllable bend sub

Finite Element Contact Algorithm

The contact problem is a highly nonlinear behavior, prevalent in actual engineering practice. Two major difficulties in the processing and calculation are: Users do not know the contact area before solving the problems; most contact issues need to consider the frictions, they are nonlinear, so the friction makes problem become more difficult [3].

Contact problem is typically different in engineering; there are two solutions for these problems: Analytical and numerical method. Analytical method is often referred to as the classical contact mechanics. The classic contact mechanics can only solve some simple geometries, the range of application is limited. With the development of computer and numerical computation theory, especially the rapid development of the theory of finite element, applications of some large dedicated finite element commercial software, people began to try to use numerical solution to study the contact problem. Although numerical solutions can not draw a function of the general contact problem, many complex contact problems can be solved by numerical solution; numerical solution has great practical value in the engineering application and has made many important achievements.

Finite Element Contact Analysis of Roller

Do the following assumptions without affecting the substance of the analytical problem: (1) variation cardan shaft, thrust bearings and roller are isotropic, linear elastic materials;(2) does not consider the contact surface elastic hydrodynamic lubrication mechanism, lubrication consider only the coefficient of friction.

Establish the finite element model [4]

Take variation cardan shaft where a ball shaft segments, thrust bearings and roller for study, the geometric model is shown in Fig. 3.

Material for 40CrNiMo alloy, the elastic modulus is 2.07 × 1011 N/m 2, Poisson's ratio is 0.296, the density of 7.85 × 103 kg/m 3, the yield limit of 835 MPa, ultimate tensile strength of 980 Mpa.The meshed model is shown in Fig.4.

Fig.3 Geometric model Fig.4 Meshed model

Identifying contact pairs When defining contact pairs, the outer surface of the roller is defined as a contact surface, the shaft and bearing ball concave defined as target surface. Using contact wizard can easily generate contact pair; establish 2 contacts pairs on each roller, they are contact of the roller and the shaft and the thrust bearing respectively. The contact type by contact174 and targe170 is to simulate the contact surface and the target surface.