Fatigue Crack Monitoring of T-Type Joints in Steel Offshore Oil and Gas Jacket Platform

Several approaches have been used in the past to predict fatigue crack growth rates in T-joints of the offshore structures, but there are relatively few cases of applying structural health monitoring during the non-destructive testing of jacket platforms. This paper presents an experimental method based on the sensing of the piezoelectric sensors and finite element analysis method for studying the fatigue cracks in the offshore steel jacket structure. Three types of joints are selected in the current research work: T-type plate, T-type tube-plate, and T-type tube joints. The finite element analysis model established in the current study computes and analyzes the high stress and high strain regions in the T-type joints. The fatigue damage in the T-type joints was successfully detected by utilizing both the finite element analysis and experimental methods. The results showed that fatigue cracks of the three types of joints are prone to appear at the weld toe and spread in the welding direction. The fatigue damage location of T-type plate and T-type tube-plate joints is more concentrated in the upper weld toe area, and the fatigue damage location of the T-type tube joint is closer to the lower weld toe area.

Nanoscale Lubrication in Biosystems as Rationalized in Terms of Fractons and Spectral-Mechanical Properties of Networked Biopolymers in Ionic Solutions

Articular cartilage is a natural tribochemical device just-designed by nature. Yet, a vivid debate goes on toward the mechanisms by which its nanoscopic viscoelastic properties facilitate lubrication in terms of ultralow static and kinetic friction coefficients. In this concisely conducted conceptual discussion, we wish to point out that a nanoscale tribomechanistic description based upon certain “viscoelastic quanta”, called fractons, expressing spectral-mechanical properties of viscoelastic nets under the influence of force/pressure factor(s), may contribute substantially to the elucidation of ultralow coefficients of friction in the articular cartilage of predictable relaxational response. Our example unveils a part of a mechanically responsive viscoelastic network, such as a tied piece of hyaluronan molecule, fit in an Edwards type tube, in which upon water–mediated interaction of lipids with the hyaluronan when subjected to loading at the nanoscale, a consecutive stress-field and ion diffusion action is going to occur simultaneously. It results in a natural-logarithmic formula that interrelates a number of hyaluronan’s interactive residues, N, with certain molecular-elastic (an exponent γ) and surface-to-volume (nano-colloid type) characteristics of around 2/3 to emerge near thermodynamic equilibrium, that is to say after a frictional loading action performed. It enables to relate uniquely a value of the exponent 0 < γ < 1/2 with a virtual tribomicellization scenario of the nanoscale friction–lubrication event accompanied by inevitable tubularmilieu viscosity alterations when the quasi-static friction scenario shows up, preferably with γ → 1/3 from above for large enough N –s. A periodic vibrational super-biopolymer’s mode is exploited, leading to a change in the nanoscale friction-lubrication period from which an opportunity to involve an essential contribution to the (nanoscale) coefficient of friction arises.PACS numbers71.10.+x, 81.30.Fb, 05.70.Fh, 05.60.+w

Calculation of the Geometrical Parameters of the Heat Exchanger Type “Pipe in Pipe” with a Spiral-Coiled Channel

The designs of the modern type of twisting devices include spring-twisted channels, which to use as innovative heat exchange elements of tubular apparatuses. The paper presents a method for determining the equivalent diameter of the tube and intertubular space in a heat exchanger apparatus of the type “tube-in-tube” with a spring-twisted channel which composed of tori closely adjacent to each other. Based on the integral calculus, formulas are obtained for calculating the equivalent diameters of the tube and annular space in a tube-in-tube apparatus with a spring-twisted channel. The results of experiments on heat transfer are generalized by criterial equations, in which the equivalent diameter is used as the characteristic size. It is shown that the equivalent diameters of the examined channels differ from each other by no more than 5%. The results of this work can be used in the design and calculations of promising heat exchangers with intensified heat transfer.