Pressure-impulse diagram method:a fundamental review

Accidental and deliberate explosions stemming from catastrophic events in the petroleum industry, incidents during complex manufacturing processes, mishandling or failure of domestic gas appliances or installations, terrorist attacks and military engagements, are becoming increasingly relevant in structural design. Pressure‐impulse (P‐I) diagrams are widely used for the preliminarily assessment and design of structures subjected to such extreme loading conditions. A typical P‐I diagram provides information concerning the level of damage sustained by a specific structural member when subjected to a blast load. This paper presents a state‐of‐the‐art review describing the development of the P‐I diagram method over the last 70 years, the main assumptions upon which its development is based and the framework through which such the method is applied in practice. The structural analysis methods used for the derivation of P‐I curves are discussed and the existing approaches are categorised according to algorithms used. A review of the P‐I curve formulae proposed to date is performed, where the formulae are classified according to the formulation methods

Ultrasonic cavitation erosion of CFRP composites

To date, cavitation erosion of carbon fibre reinforced polymer (CFRP) composites has attracted only limited scientific attention. This paper investigates this knowledge gap through a series of experiments, in which unidirectional and bidirectional (2x2 twill) CFRP composites were exposed to cavitation clouds produced by an ultrasonic transducer in distilled water. Both composites were bonded with epoxy resin. Cavitation erosion tests were conducted according to the ASTM G32-16 standard using a stationary specimen method. The effect of water absorption on monitoring erosion damage was studied using saturated and dry specimens. Specimen mass loss measurements and microscopy observations were done at regular intervals throughout testing. Erosion imprint topographies were studied using X-ray computed microtomography. Three distinct erosion stages were identified from the erosion process observations. Nonuniformities in surface geometry and properties facilitated nucleation and accelerated local erosion. Surface epoxy thickness, fibre diameter and packing, and thickness and layup of fibre bundles influenced the erosion process. The erosion mechanisms included cracking and debonding of epoxy, and tunnelling and trenching in fibre bundles. Research findings indicated that the composite internal structure can potentially be designed for reduced water absorption and increased erosion resistance. Acoustic impedance was most efficient in predicting material response to cavitation erosion.<br/

Ultrasonic cavitation erosion of CFRP composites

To date, cavitation erosion of carbon fibre reinforced polymer (CFRP) composites has attracted only limited scientific attention. This paper investigates this knowledge gap through a series of experiments, in which unidirectional and bidirectional (2x2 twill) CFRP composites were exposed to cavitation clouds produced by an ultrasonic transducer in distilled water. Both composites were bonded with epoxy resin. Cavitation erosion tests were conducted according to the ASTM G32-16 standard using a stationary specimen method. The effect of water absorption on monitoring erosion damage was studied using saturated and dry specimens. Specimen mass loss measurements and microscopy observations were done at regular intervals throughout testing. Erosion imprint topographies were studied using X-ray computed microtomography. Three distinct erosion stages were identified from the erosion process observations. Nonuniformities in surface geometry and properties facilitated nucleation and accelerated local erosion. Surface epoxy thickness, fibre diameter and packing, and thickness and layup of fibre bundles influenced the erosion process. The erosion mechanisms included cracking and debonding of epoxy, and tunnelling and trenching in fibre bundles. Research findings indicated that the composite internal structure can potentially be designed for reduced water absorption and increased erosion resistance. Acoustic impedance was most efficient in predicting material response to cavitation erosion.<br/

Fidelity of computational modelling of offshore jacket platforms

The development of oil and gas exploitation offshore has a history of about half a century. Many platforms have been built since to facilitate the production of hydrocarbons oil and gas, of which fixed offshore jacket type structures are the most commonly adopted rigs for shallow water depths. The present paper focuses on the modelling of a 4-legged X-braced jacket type platform, representative of a typical fixed platform in the North Sea using nonlinear finite element analysis. Normally, offshore platforms are conservatively designed using linear-elastic models to determine the effects of applied actions. The nonlinear effects of joint flexibility, piled foundations and geometrical imperfections on the platform behaviour are investigated in this paper. Joint flexibility is studied by modelling the jacket using beam elements and introducing rigid or flexible joints. A hybrid model, with the critically loaded leg and connected joints built using shell elements, is applied for the investigation of localised effects on increasing joint flexibility. The soil-pile interaction is modelled implicitly using sets of decoupled springs distributed along the piles. The geometrical imperfections are introduced in the compression legs of the jacket. The imperfect leg shapes are generated based on the failure modes of the platform. The platform is loaded by operational and environmental loads. The environmental loads are gradually increased until platform failure occurs. Eight load cases are considered, where the environmental loads are applied in 4 end-on and 4 broadside directions. The findings of the paper indicate that incorporation of joint flexibility and piled foundation result in the reduction of platform yielding and ultimate strength. The piled foundation affects platform stiffness severely. The imperfections increase platform deformability in the elastic rage and lead to dramatic reduction of jacket base shear capacity

Flat-face epoxy-bonded concrete joints loaded in torsion:Physical modelling

Joints in concrete structures must perform under various complex loads including torsion. This paper reports the results of an experimental programme investigating the static torsional performance of epoxy-bonded concrete joints. Torsion tests were performed using a custom experimental setup able to apply torque on a hollow concrete prism with an epoxy joint in the middle. The tested specimens failed in both cohesive and mixed modes. The cohesive failure mode was characterised by cracking in the body of concrete, while the mixed mode also included partial debonding of the joint. The cohesive mode was dominant, more ductile and exhibited higher torsional strength. The cracking behaviour of the jointed specimens was typical of concrete prisms under torsion except that in the mixed mode a crack developed along the joint on two or three specimen sides. Digital Image Correlation, applied for monitoring surface strain, showed that inclined bands of high shear strain passed across the joint during the tests. The mechanism of concrete-epoxy debonding was investigated using two standard testing methods. The low shear strength of concrete near the epoxy joint was identified as the source for the weaker, stiffer and more brittle response of the mixed failure mode in the torsion tests

Updatable Probabilistic Evaluation of Failure Rates of Mechanical Components in Power Take-Off Systems of Tidal Stream Turbines

This paper presents a method for the probabilistic evaluation of the failure rates of mechanical components in a typical power take-off (PTO) system of a horizontal-axis tidal stream turbine (HATT). The method is based on a modification of the method of the influence factors, when base failure rates, relevant influence factors and, subsequently, resulting failure rates are treated as random variables. The prior (i.e., initial) probabilistic distribution of the failure rates of a HATT component is generated using data for similar components from other industries, while taking into account actual characteristics of the component and site-specific operating and environmental conditions of the HATT. A posterior distribution of the failure rate is estimated numerically based on a Bayesian approach as new information about the component performance in an operating HATT becomes available. The posterior distribution is then employed to obtain the updated mean and lower and upper confidence limits of the failure rate. The proposed method is illustrated by applying it to the evaluation of the failure rates of two key components of the PTO system of a typical HATT—main seal and main bearing. In particular, it is shown that uncertainty associated with the method itself has a major influence on the failure rate evaluation. The proposed method is useful for the reliability assessment of both PTO designs of new HATTs and PTO systems of operating HATTs