Failure analysis of a failed anchor chain link

ARA acknowledges the financial support of Binks Trust through funding made available to the School of Engineering, University of Aberdeen, UK.Peer reviewedPostprin

FIBER REINFORCED COMPOSITE AND METHODS OF FORMING THE SAME

EP1590150B1Granted Paten

The trans-ancestral genomic architecture of glycemic traits

Glycemic traits are used to diagnose and monitor type 2 diabetes and cardiometabolic health. To date, most genetic studies of glycemic traits have focused on individuals of European ancestry. Here we aggregated genome-wide association studies comprising up to 281,416 individuals without diabetes (30% non-European ancestry) for whom fasting glucose, 2-h glucose after an oral glucose challenge, glycated hemoglobin and fasting insulin data were available. Trans-ancestry and single-ancestry meta-analyses identified 242 loci (99 novel; P < 5 x 10(-8)), 80% of which had no significant evidence of between-ancestry heterogeneity. Analyses restricted to individuals of European ancestry with equivalent sample size would have led to 24 fewer new loci. Compared with single-ancestry analyses, equivalent-sized trans-ancestry fine-mapping reduced the number of estimated variants in 99% credible sets by a median of 37.5%. Genomic-feature, gene-expression and gene-set analyses revealed distinct biological signatures for each trait, highlighting different underlying biological pathways. Our results increase our understanding of diabetes pathophysiology by using trans-ancestry studies for improved power and resolution. A trans-ancestry meta-analysis of GWAS of glycemic traits in up to 281,416 individuals identifies 99 novel loci, of which one quarter was found due to the multi-ancestry approach, which also improves fine-mapping of credible variant sets.Peer reviewe

An investigation into the seismic performance and progressive failure mechanism of model geosynthetic reinforced soil walls

Geosynthetic reinforced soil (GRS) walls involve the use of geosynthetic reinforcement (polymer material) within the retained backfill, forming a reinforced soil block where transmission of overturning and sliding forces on the wall to the backfill occurs. Key advantages of GRS systems include the reduced need for large foundations, cost reduction (up to 50%), lower environmental costs, faster construction and significantly improved seismic performance as observed in previous earthquakes. Design methods in New Zealand have not been well established and as a result, GRS structures do not have a uniform level of seismic and static resistance; hence involve different risks of failure. Further research is required to better understand the seismic behaviour of GRS structures to advance design practices. The experimental study of this research involved a series of twelve 1-g shake table tests on reduced-scale (1:5) GRS wall models using the University of Canterbury shake-table. The seismic excitation of the models was unidirectional sinusoidal input motion with a predominant frequency of 5Hz and 10s duration. Seismic excitation of the model commenced at an acceleration amplitude level of 0.1g and was incrementally increased by 0.1g in subsequent excitation levels up to failure (excessive displacement of the wall panel). The wall models were 900mm high with a full-height rigid facing panel and five layers of Microgird reinforcement (reinforcement spacing of 150mm). The wall panel toe was founded on a rigid foundation and was free to slide. The backfill deposit was constructed from dry Albany sand to a backfill relative density, Dr = 85% or 50% through model vibration. The influence of GRS wall parameters such as reinforcement length and layout, backfill density and application of a 3kPa surcharge on the backfill surface was investigated in the testing sequence. Through extensive instrumentation of the wall models, the wall facing displacements, backfill accelerations, earth pressures and reinforcement loads were recorded at the varying levels of model excitation. Additionally, backfill deformation was also measured through high-speed imaging and Geotechnical Particle Image Velocimetry (GeoPIV) analysis. The GeoPIV analysis enabled the identification of the evolution of shear strains and volumetric strains within the backfill at low strain levels before failure of the wall thus allowing interpretations to be made regarding the strain development and shear band progression within the retained backfill. Rotation about the wall toe was the predominant failure mechanism in all excitation level with sliding only significant in the last two excitation levels, resulting in a bi-linear displacement acceleration curve. An increase in acceleration amplification with increasing excitation was observed with amplification factors of up to 1.5 recorded. Maximum seismic and static horizontal earth pressures were recorded at failure and were recorded at the wall toe. The highest reinforcement load was recorded at the lowest (deepest in the backfill) reinforcement layer with a decrease in peak load observed at failure, possibly due to pullout failure of the reinforcement layer. Conversely, peak reinforcement load was recorded at failure for the top reinforcement layer. The staggered reinforcement models exhibited greater wall stability than the uniform reinforcement models of L/H=0.75. However, similar critical accelerations were determined for the two wall models due to the coarseness of excitation level increments of 0.1g. The extended top reinforcements were found to restrict the rotational component of displacement and prevented the development of a preliminary shear band at the middle reinforcement layer, contributing positively to wall stability. Lower acceleration amplification factors were determined for the longer uniform reinforcement length models due to reduced model deformation. A greater distribution of reinforcement load towards the top two extended reinforcement layers was also observed in the staggered wall models. An increase in model backfill density was observed to result in greater wall stability than an increase in uniform reinforcement length. Greater acceleration amplification was observed in looser backfill models due to their lower model stiffness. Due to greater confinement of the reinforcement layers, greater reinforcement loads were developed in higher density wall models with less wall movement required to engage the reinforcement layers and mobilise their resistance. The application of surcharge on the backfill was observed to initially increase the wall stability due to greater normal stresses within the backfill but at greater excitation levels, the surcharge contribution to wall destabilising inertial forces outweighs its contribution to wall stability. As a result, no clear influence of surcharge on the critical acceleration of the wall models was observed. Lower acceleration amplification factors were observed for the surcharged models as the surcharge acts as a damper during excitation. The application of the surcharge also increases the magnitude of reinforcement load developed due to greater confinement and increased wall destabilising forces. The rotation of the wall panel resulted in the progressive development of shears surface with depth that extended from the backfill surface to the ends of the reinforcement (edge of the reinforced soil block). The resultant failure plane would have extended from the backfill surface to the lowest reinforcement layer before developing at the toe of the wall, forming a two-wedge failure mechanism. This is confirmed by development of failure planes at the lowest reinforcement layer (deepest with the backfill) and at the wall toe observed at the critical acceleration level. Key observations of the effect of different wall parameters from the GeoPIV results are found to be in good agreement with conclusions developed from the other forms of instrumentation. Further research is required to achieve the goal of developing seismic guidelines for GRS walls in geotechnical structures in New Zealand. This includes developing and testing wall models with a different facing type (segmental or wrap-around facing), load cell instrumentation of all reinforcement layers, dynamic loading on the wall panel and the use of local soils as the backfill material. Lastly, the limitations of the experimental procedure and wall models should be understood

Numerical analysis on ship to ship gap influence on resonance

The advantage of ship to ship transfer, especially when berthing of VLCC and ULCC is difficult, is cost effectiveness. However, such operations are associated with safety risks such as hull damages, personnel safety risks and pollution due to operation accidents. Therefore, it is imperative to understand the nature and effects of the environmental factors especially involving sea waves during ship-to-ship operations. Two major aims are outlined in this dissertation: to understand how the gap distance between the ships influences the dependent variables such as wave elevation and to further scrutinise the hydrodynamic interactions regarding this phenomenon. Numerical simulation is firstly done to verify the Airy wave model at wave amplitude 1.05m and period 5s. However, wave pattern unexpectedly exhibit nonlinear characteristics such as sharp crests and flat troughs. This is followed by a ship to ship numerical study with conditions similar to Xu et al. (2014) numerical study at gap widths of 3m, 6m and 12m with 5 equal distance data points at the gap region. The results then show that narrower gap width correlates strongly with larger wave elevations and smaller periods. Velocity vectors and pressure contours from the numerical study also show higher values during gap resonance motion. Next, to establish a local baseline for the findings, Li et al. (2016) barge to barge numerical study is replicated. It is observed that the wave elevation values from this replicated study agrees poorly with what was found in Li et al. (2016) study where replicated study show a lower trend than the original. All numerical computations in this dissertation are done using ASPIRE1 HPC with 168 core processors.Master of Science (Mechanical Engineering

Performance of pulsed plasma thrusters

A pulsed plasma thruster (PPT) is a type of electromagnetic propulsion system which uses plasma as the working fluid to electromagnetically accelerate the fluid to high exhaust velocities. The PPT is primarily designed for long duration satellite missions for attitude control as well as interplanetary and deep space missions. The auto-initiated PPT is one variant of the PPTs developed. This work is a numerical work on the performance of an auto-initiated pulsed plasma thruster. The goal is to compare with the experimental results obtained from the work done at the Indian Institute of Technology, Kanpur. The plasma acceleration phase is modeled by a simple 1-D analytical model, as well as a set of integro-differential equations from the slug, and snowplow model. The different modes of EM acceleration for plasma (steady, and unsteady) is also explored. The case study of Hartmann flows that is investigated is a case for steady plasma acceleration flows. The results provide an understanding that ideal magnetohydrodynamic (MHD) models for steady electromagnetic accelerations do not need to solve for the magnetic induction equation in Maxwell's equations, which results in a significant simplification in the equations that needs to be solved for the 1-D case. As for the unsteady case, the analytical, slug, and snowplow models are developed and the results compared against the experimental data. The results show that the slug model relates the best amongst the three models to the experimental data within 20% of the impulse bit at pressure levels greater than 5 mbar. This suggests that the auto-initiation PPT operates using a slug mode of operation. This also shows that the slug model can be a very useful tool for the conceptual design phase of a solid ablation PPT. This work can be further improved by coupling the resistive MHD equations with the external circuit equations to include resistive effects in the plasma sheet.Bachelor of Engineering (Aerospace Engineering