Seafloor interaction with steel catenary risers

This paper describes the key features of a seafloor-riser interaction model. The soil is represented in terms of non-linear load-deflection (P- y) relationships, which are also able to account for soil stiffness degradation due to cyclic loading. The analytical framework considers the riser-seafloor interaction problem in terms of a pipe resting on a bed of springs, and requires the iterative solution of a fourth-order ordinary differential equation. A series of simulations is used to illustrate the capabilities of the model. Thanks to the non-linear soil springs with stiffness degradation it is possible to simulate the trench formation process and estimate moments in a riser. Copyright © 2008 by The International Society of Offshore and Polar Engineers (ISOPE).

Centrifuge testing of monopile in clay under monotonic loads

The monopile is at present the most widely applied foundation concept for offshore wind turbines. Monopiles are designed utilising the well-established p-y method. Despite being well-established, there are multiple issues and limitations regarding its use. Investigation into the lateral behaviour of monopiles was carried out by performing monotonic and cyclic lateral load tests on an aluminium model monopile in the centrifuge. The monotonic responses and the behaviour of the monopile are described. Differences between the experimental and DNV design p-y curves and their implications are discussed. Efforts to characterise the shear force acting at the pile toe are also discussed. The results highlight the possible deficiencies of utilising the conventional DNV design p-y curves to design monopiles to resist cyclic lateral loads and the importance of research into the cyclic loading behaviour of monopiles to better improve their design to resist long-term cyclic loads. © 2014 Taylor & Francis Group.

Foundations for offshore wind turbines

Offshore wind turbines impose unique combinations of loads on their foundations. They impose large lateral loads in relation to vertical loading which must be resisted, but are also subject to approximately a million cycles of loading through their design life. As the performance of these systems is dominated by their dynamic response, the stiffness of the foundations becomes critical in design. Conventional design codes which are conservative by virtue of predicting a lower stiffness than might be observed in practice may not be conservative for these problems. By utilizing centrifuge modeling the behaviour of monopile foundations in both sands and clays under cyclic loading can be investigated in order to predict the dynamic behaviour of these systems. © 2010 Taylor & Francis Group, London.

Undrained behaviour of two silica sands and practical implications for modelling SSI in liquefiable soils.

The aim of the present study is twofold. Firstly, the paper investigates the undrained cyclic and post-cyclic behaviour of two silica sands by means of multi-stage cyclic triaxial tests. Secondly, based on the post-cyclic response observed in the element test, the authors formulate a simplified stress–strain relationship that can be conveniently used for the construction of p–y curves for liquefiable soils. The multi-stage loading condition consists of an initial cyclic loading applied to cause liquefaction, followed by undrained monotonic loading that aimed to investigate the post-cyclic response of the liquefied sample. It was found that due to the tendency of the liquefied soil to dilate upon undrained shearing, the post-liquefaction strain–stress response was characterised by a distinct strain–hardening behaviour. The latter is idealized by means of a bi-linear stress–strain model, which can be conveniently formulated in terms of three parameters, i.e.: (i) take-off shear strain, γto, i.e. shear strain required to mobilize 1 kPa of shear strength; (b) initial secant shear modulus, G1, defined as 1/γto; (c) post-liquefied shear modulus at large strain, G2 (γ⪢γto). Based on the experimental results, it is concluded that these parameters are strongly influenced by the initial relative density of the sample, whereby γto decreases with increasing relative density. Differently both shear moduli (G1 and G2) increases with increasing relative density. Lastly, the construction of new p–y curves for liquefiable soils based on the idealized bi-linear model is described.

Predicting optimal process conditions for flip-chip aassembly using copper column bumped dies

Recently, research has been carried out to test a novel bumping method which omits the under bump metallurgy (UBM) forming process by bonding copper columns directly onto the Al pads of the silicon dies. This bumping method could be adopted to simplify the flip chip assembly process, increase the productivity and achieve a higher I/O count. Computer modelling methods are used to predict the shape of solder joints and response of the flip chip to thermal cyclic loading. The accumulated plastic strain energy at the comer solder joints is used as the damage indicator. Models with a range of design parameters have been compared for their reliability. The ranking of the relative importance of these parameters is given. Results from these analyses are being used by our industrial and academic partners to identify optimal design conditions.

Computer modelling of the reliability of flip chips with metal column bumping

Recently, research has been carried out to test a novel bumping method which omits the under bump metallurgy forming process by bonding copper columns directly onto the Al pads of the silicon dies. This bumping method could be adopted to simplify the flip chip manufacturing process, increase the productivity and achieve a higher I/O count. This paper describes an investigation of the solder joint reliability of flip-chips based on this new bumping process. Computer modelling methods are used to predict the shape of solder joints and response of flip chips to thermal cyclic loading. The accumulated plastic strain energy at the comer solder joints is used as the damage indicator. Models with a range of design parameters have been compared for their reliability. The parameters that have been investigated are the copper column height, radius and solder volume. The ranking of the relative importance of these parameters is given. For most of the results presented in the paper, the solder material has been assumed to be the lead-free 96.5Sn3.5Ag alloy but some results for 60Sn40Pb solder joints have also been presented.

Lifetime prediction for power electronics module substrate mount-down solder interconnect

A numerical modeling method for the prediction of the lifetime of solder joints of relatively large solder area under cyclic thermal-mechanical loading conditions has been developed. The method is based on the Miner's linear damage accumulation rule and the properties of the accumulated plastic strain in front of the crack in large area solder joint. The nonlinear distribution of the damage indicator in the solder joints have been taken into account. The method has been used to calculate the lifetime of the solder interconnect in a power module under mixed cyclic loading conditions found in railway traction control applications. The results show that the solder thickness is a parameter that has a strong influence on the damage and therefore the lifetime of the solder joint while the substrate width and the thickness of the baseplate are much less important for the lifetime

Computer simulating a trial of a load-bearing implant: example of an intramedullary prosthesis

Computational modelling is becoming ever more important for obtaining regulatory approval for new medical devices. An accepted approach is to infer performance in a population from an analysis conducted for an idealised or ‘average’ patient; we present here a method for predicting the performance of an orthopaedic implant when released into a population—effectively simulating a clinical trial. Specifically we hypothesise that an analysis based on a method for predicting the performance in a population will lead to different conclusions than an analysis based on an idealised or ‘average’ patient. To test this hypothesis we use a finite element model of an intramedullary implant in a bone whose size and remodelling activity is different for each individual in the population. We compare the performance of a low Young’s modulus implant (View the MathML source) to one with a higher Young’s modulus (200 GPa). Cyclic loading is applied and failure is assumed when the migration of the implant relative to the bone exceeds a threshold magnitude. The analysis for an idealised of ‘average’ patient predicts that the lower modulus device survives longer whereas the analysis simulating a clinical trial predicts no statistically-significant tendency (p=0.77) for the low modulus device to perform better. It is concluded that population-based simulations of implant performance–simulating a clinical trial–present a very valuable opportunity for more realistic computational pre-clinical testing of medical devices.

1-D constitutive model for evolution of stress-induced R-phase and localized Lüders-like stress-induced martensitic transformation of super-elastic NiTi wires

NiTi alloys have been widely used in the applications for micro-electro-mechanical-systems (MEMS), which often involve some precise and complex motion control. However, when using the NiTi alloys in MEMS application, the main problem to be considered is the degradation of functional property during cycling loading. This also stresses the importance of accurate prediction of the functional behavior of NiTi alloys. In the last two decades, a large number of constitutive models have been proposed to achieve the task. A portion of them focused on the deformation behavior of NiTi alloys under cyclic loading, which is a practical and non-negligible situation. Despite of the scale of modeling studies of the field in NiTi alloys, two experimental observations under uniaxial tension loading have not received proper attentions. First, a deviation from linearity well before the stress-induced martensitic transformation (SIMT) has not been modeled. Recent experiments confirmed that it is caused by the formation of stress-induced R phase. Second, the influence of the well-known localized Lüders-like SIMT on the macroscopic behavior of NiTi alloys, in particular the residual strain during cyclic loading, has not been addressed. In response, we develop a 1-D phenomenological constitutive model for NiTi alloys with two novel features: the formation of stress-induced R phase and the explicit modeling of the localized Lüders-like SIMT. The derived constitutive relations are simple and at the same time sufficient to describe the behavior of NiTi alloys. The accumulation of residual strain caused by R phase under different loading schemes is accurately described by the proposed model. Also, the residual strain caused by irreversible SIMT at different maximum loading strain under cyclic tension loading in individual samples can be explained by and fitted into a single equation in the proposed model. These results show that the proposed model successfully captures the behavior of R phase and the essence of localized SIMT.

Effect of reinforcement and heat treatment on elevated temperature sliding of electroless Ni–P/SiC composite coatings

The investigation is focused on the wear behaviour at elevated test temperature of composite Ni–P/SiC deposit, with varying concentration of the reinforcing SiC particles. The phase evolution measured by X-ray diffraction suggests slight crystallisation during wear testing at 200 °C. In coating without reinforcing particles, adhesive wear is accompanied by microcracks. The thermal heat generated and the cyclic loading could have induced sub-surface microcracks. Owing to the effective matrix-ceramics system in composite coatings, fine grooves, abrasive polishing and uniform wearing are observed. Reinforcing particles in the matrix hinder microcrack formation and significantly reduce the wear rate. Triboxidation is confirmed from energy dispersive X-ray spectrometry.

Utilisation of fibre reinforced polymer (FRP) composites in the confinement of concrete

This paper presents an experimental investigation carried out on concrete cylinders confined with fibre reinforced polymers (FRP), subjected to monotonic and cyclic loading. Carbon fibres (CFRP) were used as confining material for the concrete specimens. The failure mode, reinforcement ratio based on jacket thickness and type of loading are examined. The study shows that external confinement of concrete can enhance its strength and ductility as well as result in large energy absorption capacity. This has important safety implications, especially in regions with seismic activity.

Externally confined concrete columns using FRP tubes

This paper presents an experimental investigation carried out on concrete filled fibre reinforced polymers (FRP) tubes, subjected to monotonic and cyclic loading. Two types of FRP materials were used: glass fibres and carbon fibres. Different failure modes and the effect of concrete fill, type of confinement materials, reinforcement ratio based on tube thickness and type of loading are examined. The study shows that external confinement of concrete by means of modern materials, such fibre reinforced polymers, can enhance its strength and ductility as well as result in large energy absorption capacity. This has important safety implications, especially in regions with seismic activity. A model that predicts the behaviour of confined concrete which takes into account the stiffness and effectiveness of different confinement materials is briefly introduced.

Development and applications of an experimental database for structural engineering education

A great number of research organisations in Japan have been conducting structural steel experiments for many years, particularly seismic tests of steel structures like cyclic-loading and pseudo-dynamic tests, in order to determine their seismic performances. However, the original test data gained by most research organisations are not well stored in an appropriate manner for distribution and possible usage by others. With the rapid development of information networks, structural engineers and researchers are able to exchange various types of test data through the Internet. In this paper, the authors present the development of a distributed collaborative database system for structural steel experiments. The database is made available on the Internet, and the use of Java language enables efficient interactive retrieval. The potential applications of the developed database system for structural engineering education are validated for the retrieval of experimental data and seismic numerical analysis.

Database for structural steel experiments under a distributed collaboration environment

Due to the high requirements of civil infrastructures against the earthquake in Japan, a great number of research organizations have been conducting the structural steel experiments, in particular the seismic tests such as the cyclic loading test and the pseudo-dynamic test, for many years to determine the seismic performances of steel structures. However, the original test data gained by most research organizations are not well stored in an appropriate manner for distribution and possible usage of others. Although a Numerical Database of Steel Structures (NDSS) was developed some years ago to preserve and share experimental data of the ultimate strength tests acquired at Nagoya University, it was not easy to access this database from other computer platform due to the lack of the support of proper communication media. With the rapid development of information networks and their browsers, structural engineers and researchers are able to exchange various types of test data through Internet. This paper presents the development of a distributed collaborative database system for structural steel experiments. The database is made available on the World-Wide Web, and the Java language enables the interactive retrieval efficiently. The applications of the developed database system for the retrieval of experimental data and seismic numerical analysis are validated in the form of examples.