Zonglu Guo¹, Deli Gao¹

CMES-Computer Modeling in Engineering & Sciences, Vol.90, No.1, pp. 65-76, 2013, DOI:10.3970/cmes.2013.090.065

Abstract The modeling of the bottomhole assembly (BHA) is an essential problem in directional drilling. Some basic equations for predicting the performance of the BHA are presented in this paper. These equations take into account the effects of the axial displacement. The method of weighted residuals and the Newton-Raphson iterations are used to compute the nonlinear effects of the deformation of the BHA. A computer program is developed for the analysis of the BHA in order to quantitatively predict the performance of the BHA in directional drilling. In addition, a case study is presented to evaluate the effect of the axial… More >

Hui Zhang¹, Deli Gao^1,2, Xiaopin Xie¹

CMES-Computer Modeling in Engineering & Sciences, Vol.90, No.1, pp. 47-64, 2013, DOI:10.3970/cmes.2013.090.047

Abstract In oil & gas drilling engineering, the rock breaking efficiency as well as the trajectory of the Well should be quantitatively and accurately described by an ideal triaxial Rate of Penetration (ROP) model, taking into account the various objective and subjective factors. However, with the existing triaxial ROP models, it is difficult to achieve these goals. The applications of the existing ROP models are limited, especially in under-balanced drilling (air drilling, foam drilling etc.), because the unloading effect (i.e. the effect of the bottom hole differential pressure on the formation force) has been rarely considered. On the basis of a… More >

Tengfei Sun¹, Deli Gao^1,2, Hui Zhang¹

CMES-Computer Modeling in Engineering & Sciences, Vol.90, No.1, pp. 37-46, 2013, DOI:10.3970/cmes.2013.090.037

Abstract Well profile design is one of the critical technologies in extended reach drilling (ERD), because an optimum well profile is an effective means for reducing the torque, drag and cost. This paper proposes a new well profile based on an inverse proportional function, and the new profile design method is analyzed in detail. The new well profile is also compared with other existing well profiles in many aspects such as the hook load, the maximum well curvature, the well length, the torque and so on. The results show that the well profile design based on an inverse proportional curve is… More >

Deli Gao¹, Fengwu Liu¹

CMES-Computer Modeling in Engineering & Sciences, Vol.90, No.1, pp. 17-36, 2013, DOI:10.3970/cmes.2013.090.017

Abstract A down-hole tubular string in an inclined wellbore, under variable axial and torsional loading, may simultaneously undergo a sinusoidal as well as helical buckling, at different sections. In this paper, the buckling equation for a tubular string, in an inclined wellbore, subjected to axial and torsional loading, is established by an equilibrium method. The analytical solutions for the buckling equations, for sinusoidal and helical configurations of buckled tubular string, are obtained by Galerkin and nonlinear scaling methods. Methods for computing the contact forces between the buckled tubular string and wellbore, are developed. The analytical solutions are in good accordance with… More >

Xuejun Hou^1,2, Deli Gao^1,3, Zhonghou Shen¹

CMES-Computer Modeling in Engineering & Sciences, Vol.90, No.1, pp. 1-16, 2013, DOI:10.3970/cmes.2013.090.001

Abstract Diesel tail gas drilling (DTGD) is a type of gas drilling, which uses diesel tail gas (DTG) as a circulating medium. Its cost is slightly higher than that of air drilling, but is cheaper than those of nitrogen drilling and natural gas drilling. When the reservoir is drilled with DTG, just as nitrogen and natural gas, the DTG will prevent the burning and blasting of oil and gas in the bottom hole. In order to reduce costs, the DTG is often used in drilling the reservoir, to prevent the underground explosion. This paper analyzes the composition of the Z12V190 diesel… More >

E.J. Sellountos¹, D. Polyzos², S.N. Atluri³

CMES-Computer Modeling in Engineering & Sciences, Vol.89, No.6, pp. 513-551, 2012, DOI:10.3970/cmes.2012.089.513

Abstract A new meshless Local Boundary Integral Equation (LBIE) method for solving two-dimensional elastostatic problems is proposed. Randomly distributed points without any connectivity requirement cover the analyzed domain and Local Radial Basis Functions (LRBFs) are employed for the meshless interpolation of displacements. For each point a circular support domain is centered and a local integral representation for displacements is considered. At the local circular boundaries tractions are eliminated with the aid of companion solution, while at the intersections between the local domains and the global boundary displacements and tractions are treated as independent variables avoiding thus derivatives of LRBFs. Stresses are… More >

Yonghua Zhou¹, Xun Yang¹, Chao Mi¹

CMES-Computer Modeling in Engineering & Sciences, Vol.89, No.6, pp. 497-512, 2012, DOI:10.3970/cmes.2012.089.497

Abstract The movements of vehicles equipped with various positioning systems such as global and wireless positioning ones have provided beneficial channels to acquire abundant traffic flow information for total road network. However, not all vehicles are mounted with positioning systems and not all equipped positioning facilities are always active. This paper will address how to estimate the number and the states of unequipped vehicles through a series of observations on equipped ones. The proposed estimation process initiates employing the non-analytical microscopic traffic model for particle filter to estimate the number, positions and speeds of unequipped vehicles between an equipped one and… More >

Jinxia Wei¹, Yiming Chen¹, Baofeng Li², Mingxu Yi¹

CMES-Computer Modeling in Engineering & Sciences, Vol.89, No.6, pp. 481-495, 2012, DOI:10.3970/cmes.2012.089.481

Abstract In this paper, we present a computational method for solving a class of space-time fractional convection-diffusion equations with variable coefficients which is based on the Haar wavelets operational matrix of fractional order differentiation. Haar wavelets method is used because its computation is sample as it converts the original problem into Sylvester equation. Error analysis is given that shows efficiency of the method. Finally, a numerical example shows the implementation and accuracy of the approach. More >

A. Ramachandra Murthy¹, Nagesh R. Iyer¹, B.K. Raghu Prasad²

CMES-Computer Modeling in Engineering & Sciences, Vol.89, No.6, pp. 459-480, 2012, DOI:10.3970/cmes.2012.089.459

Abstract This paper presents the details of crack growth study and remaining life assessment of concrete specimens made up of high strength concrete (HSC, HSC1) and ultra high strength concrete (UHSC). Flexural fatigue tests have been conducted on HSC, HSC1 and UHSC beams under constant amplitude loading with a stress ratio of 0.2. It is observed from the studies that (i) the failure patterns of HSC1 and UHSC beams indicate their ductility as the member was intact till the crack propagated up to 90% of the beam depth and (ii) the remaining life decreases with increase of notch depth (iii) the… More >

Leiting Dong^1,2, Satya N. Atluri²

CMES-Computer Modeling in Engineering & Sciences, Vol.89, No.5, pp. 417-458, 2012, DOI:10.3970/cmes.2012.089.417

Abstract Two-dimensional weakly-singular Symmetric Galerkin Boundary Elements (SGBEMs) are developed, following the work of [Han and Atluri (2003)], using non-hypersingular integral equations for tractions. Specifically, the present 2D SGBEM is used to compute the stress intensity factors for arbitrary-shaped line cracks, including embedded, edge, branching, and intersecting cracks. The computed stress intensity factors show high accuracy, even with very coarse meshes. The non-collinear mixed-mode fatigue growth analysis of cracks requires a very minimal effort¡ªsimply extending the cracks by adding an element to each crack tip, in the direction of the crack-growth as determined by a physics-based criterion. Moreover, by rearranging the… More >