Transient Dynamics Model Research Articles

Characterisation of the haemodynamics of the superior mesenteric artery

In contrast to its prevalence in the surrounding vasculature, occurrence of primary atherosclerotic disease in the superior mesenteric artery (SMA) is rare (Glagov et al., 1988. Hemodynamics and atherosclerosis, Insights and perspectives gained from studies of human arteries. Archives of Pathology and Laboratory Medicine 112(10), 1018–1031; Hansen et al., 2004. Mesenteric artery disease in the elderly. Journal of Vascular Surgery 40(1), 45–52). We hypothesise that this sparing might be attributed to more favourable haemodynamic characteristics in the SMA than in other vessels locally. Dynamic magnetic resonance imaging (MRI) images established that the SMA is highly mobile (Jeays, 2006. Investigation of blood flow in the superior mesenteric artery and its potential influence on atheroma and gut ischaemia. Ph.D. Thesis, University of Sheffield), and thus that an analysis based on rigid geometry might be inappropriate. This paper describes an efficient methodology for the construction of a patient-specific, time-dependent model of an arterial segment and reports the results of a haemodynamic characterisation of the SMA for one individual. A transient computational fluid dynamic (CFD) model was constructed by morphing a parametric mesh constructed from simple geometric primitives. This process has the merit that it is easy to control the element size distribution mapped onto the original geometric primitives. It is robust in operation, and is ideally suited to the generation of dynamic CFD meshes of arterial systems that are free from major pathology. Flow boundary conditions were determined based on phase contrast MRI velocity measurements. Comparative studies with rigid walls and with moving walls, based on the transient data, indicated that, despite the significant motion of the SMA (radial dilation of the order of 10% and translation of the order of the radius), the maximum (spatially and temporally-resolved) wall shear stresses changed by no more than 21.6% of a global norm, and the average change was less than 2.1%.

SELF-SUSTAINED OSCILLATION OF A SUBMERGED JET IN A THIN RECTANGULAR CAVITY

Self-sustained oscillating jet flow of water in a rectangular cavity, having thickness which is small relative to its width, is measured using LDA and PIV, and predicted using a transient two-dimensional computational fluid dynamic model which incorporates a resistance coefficient for cross-flow. The basic geometry represents a scale model of a mould typical of thin slab steel casting. The frequency of the oscillation was found to be independent of cavity thickness. It also increased as the cavity width decreased down to some critical value, after which the oscillation ceased. The frequency was observed to increase with nozzle diameter and was found to decrease with increasing length/width ratio of the cavity. The numerical model, with a fixed dimensionless cross-flow resistance coefficient, was shown to predict the Strouhal number of the oscillation and the dimensionless mean velocity profiles in the jet extremely well.

Dynamic Analysis of Melting in Injection Extruder

Abstract Melting is one of the most important process in plastics processing. Admit the extensive use of plastic injection moulding machine in industry, most studies were on extruders which were simpler to model. This paper studies the melting process and derives its transient (dynamic) model for predicting the characteristics of melting in feeding stage of injection extruder. Based on this transient model, factors affecting the melting speed in injection extruders are exposed. Simulation results agree with the results from experiments.

Efficient multiwavelength dynamic model for erbium-doped fiber amplifier

An efficient full spectrum (1480-1600 nm) large-signal transient dynamic model of an erbium-doped fiber amplifier (EDFA) is developed. A technique to speed up the simulation by a factor of 1000 using artificial delay lines based on the transmission-line model (TLM) is presented. Simulations and experimental results show the delay line method is not detrimental to the accuracy of the model. The efficiency of this model means it is ideal for simulating the dynamics of large wavelength division multiplexed (WDM) networks if included in a network simulator.

Transient pattern dynamics and domain growth

Abstract General results for transient pattern dynamics in the context of spinodal decomposition as well as domain-wall formation in the Freedericksz transition in nematics are reviewed. The question of wavelength selection and the relevance of finite-size effects in this issue are considered in a general model of transient pattern dynamics. A finite-size scaling law for domain growth is shown to be satisfied by this model.

The formation of wear patterns on rail tread

Short wavelength corrugations of railway tracks are described by a linear model of transient dynamics and a wear feedback loop. The description is based on the Fourier decomposition of the profile irregularities. The presented results show that corrugations are a direct consequence of the resonance peaks of the dynamical components, e.g. the pinned-pinned mode of the track, and depend strongly on the initial profile irregularities.