Fatigue reliability analysis for vibroseis baseplates

Abstract

A B S T R A C T High precision vibroseis are widely used in oil and gas exploration. The key component of a vibroseis is its baseplate, suffered from complicated external load. Cracks could be generated in the baseplate, and fractures could occur in the welding parts of baseplates because of an extreme loading. This failure not only reduces the baseplate life significantly, but also affects the quality and precision of the signal excitation seriously. The objective of this work is to study the fatigue behavior of the baseplate by the finite element analysis (FEA) and fatigue reliability analysis. At first, the solid model of the baseplate is built, and the dynamic characteristics are analyzed by FEA based on the orthogonal design scheme. Then the stress distribution and peak area of baseplate are obtained under a series of loadings, thereby producing the stress-time data of the risky areas. With the S-N curve and the Palmgren-Miner cumulative damage theory, we could therefore predict the baseplate life, and then its fatigue reliability is calculated with the Kriging response surface method. The sensitivity of fatigue reliability with respect to the design parameters is also obtained, and this provides useful information about the importance of design parameters to the fatigue reliability, therefore resulting in the new design that would lead to longer baseplate life, higher quality of the seismic signal excitation, smaller signal distortion and higher accuracy of oil and gas exploration ultimately. Keywords crack; fatigue reliability; Kriging response surface method; S-N curve; sensitivity analysis; vibroseis baseplate. N O M E N C L A T U R E P = hydraulic peak force (MPa) A = piston rod end surface area (m 2 ) D = below cross column diameter (m) S 0 = numbers of the structure response stress level in one load cycle D a = cumulative damage S i = stress level (MPa) n i are numbers of S i appearing in the whole load process N i are maximum cycles of structure under the stress level S i S u = tensile strength of materials (MPa) S = simplified stress response (MPa) S a = amplitude value of alternating stress (MPa) S m = mean value of alternating stress (MPa) S max =maximum value of alternating stress (MPa) S min = minimum value of alternating stress (MPa) h(S) = function of stress L f = stress cycle number or fatigue life L D = designed life of baseplate ∑ m i¼1 1=N j = damage value of one cycle f(x) T = a set of basic functions (e.g. polynomials) α = a vector that gathers together the coefficients of the surface R = correlation matrix Correspondence: Z. Chen.

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