Section properties of palm petioles, Part 1: The influence of section shape on the flexural and torsional properties of selected palm petioles

Shape factors have been used to calculate the shape efficiency of palm leaf petiole sections in order to understand how palms compensate for the torsional and bending forces put upon them by their environment. That part of the palm leaf that is similar in form to the leaf stalk (petiole) in dicot leaves will be referred to as a petiole in this paper, whilst recognising that it is probably not an exact homologue. Wind and rain on the blade generate combined flexural and torsion loads on the petiole and a question arises as to how the section properties of the petiole deal with this loading. By isolating the shape from the size of the sections through the use of shape factors, the effects of the petiole section shape can be analysed on its own. Thus micro structural and material factors become a separate issue and will be discussed in a later paper. Cross section profiles from seven palm petioles are modelled, independent of their sizes, in order to calculate and plot the flexural and torsional coupling efficiencies for comparison with other plants and typical engineering cross sections

Structural and torsional properties of the Trachycarpus fortunei palm petiole

The Trachycarpus fortunei palm is a good example of a palm with a large leaf blade supported by a correspondingly large petiole. The way in which the material and functional properties of the petiole interact is analysed using engineering and botanical methods with a view to understanding how the petiole functions from a structural standpoint. Initially, the histological aspects of the petiole are analysed at a microscopic level from sections of the petiole taken at regular intervals along its axis, in order to determine the density and location of the vascular bundles. A modified torsion rig was used to measure the torsion and shear stress variation along petiole sample lengths. Knowledge of vascular bundle placement within the petiole sections and their torsional loading characteristics contribute to understanding the petiole function

A new approach to planning in vitro and in vivo experiments for cardiovascular stents. (1) Fundamentals of design procedures

Copyright @ 2000 Pacini Editore SpAWhile the use of cardiovascular stents is internationally widespread re-stenosis remains a common problem. There are a number of different designs, and this project seeks for design improvements leading to a reduction in re-stenosis rates. The haemodynamics of the stent as used in a patient is viewed as one of the major concerns, and the authors have already applied Computational Fluid Dynamics in investigating this. In this more comprehensive study, however, the novel approach of applying two formal engineering design procedures is used, namely Genetic Algorithms (GA) and Robust Engineering Design (RED). In this paper, the two procedures are explained and compared in the context of their application to the design of stents

Genetic algorithm search for stent design improvements

Copyright @ 2002 SpringerThis paper presents an optimisation process for finding improved stent design using Genetic Algorithms. An optimisation criterion based on dissipated power is used which fits with the accepted principle that arterial flows follow a minimum energy loss. The GA shows good convergence and the solution found exhibits improved performance over proprietary designs used for comparison purposes

Wall shear stress and arterial performance: two approaches based on engineering

This is the Abstract of the Article. Copyright @ 2009 Oxford University.This crucially important subject generates a very wide literature and the recent authoritative ‘in vivo’ review of Reneman et al [1] (& [2]), with Vennemann et al [3], are taken as seminal. In this paper we use approaches based on conventional engineering to address two key issues raised in [1]. The first is that of basic theory. To what extent can underlying fluid flow theory complement the in vivo understanding of wall shear stress (WSS)? In [1], which is sub-titled Discrepancies with Theory’, Poiseuille’s Law is used, extended to Murray’s Law in [2]. But they do ’not hold in vivo’ [2] because ‘we are dealing with non-Newtonian fluid, distensible vessels, unsteady flows, and too short entrance lengths’ [1].This comment coincides with the four factors Xu and Collins identified in their early Review of numerical analysis for bifurcations [4]. Subsequently they addressed these factors, with an engineering-based rationale of comparing predictions of Computational Fluid Dynamics (CFD) with Womersley theory, in vitro and in vivo data. This rationale has yet to be widely adopted, possibly due to computing complexities and the wide boundary condition data needed. This is despite uncertainties in current in vivo WSS [2]. Secondly, [1] and [2] focus on endothelial function. WSS is an ‘important determinant of arterial diameter’ and ‘mean (M)WSS is regulated locally’. One pointer is the possible importance of the glycocalyx, so that ‘endothelial cells are not seeing WSS’ and which ‘may be involved in the regulation of the total blood flow’ [3]. A typical glycocalyx is shown in [3]. Such a model should focus on adaptation of arterial diameter by ‘nitric oxide and prostaglandins’ [1]. So, using an engineering approach, can we construct a model for local regulation of MWSS? Again, remarks from [1]-[3] resonate with the conclusions of a review of nanoscale physiological flows [5] undertaken as part of an early Nanotechnology Initiative of the UK’s EPSRC. In [5] is illustrated the fractal nature of the intestinal villi-glycocalyx geometry, together with an engineering-style control loop for nitric oxide release and arterial diameter-flow rate control. Within our discussion we report two studies to obtain CFD predictive data very close to the endothelial surface. In both cases we compared two independent codes, respectively two CFD codes, and CFD and Lattice Boltzmann solvers. We also give an updated version of the endothelium control loop

Effects of stents under asymmetric inflow conditions

This is the post-print version of the Article. The official published version can be accessed from the link below. Copyright @ 2002 IOS PressPatient-to-patient variations in artery geometry may determine their susceptibility to stenosis formation. These geometrical variations can be linked to variations in flow characteristics such as wall shear stress through stents, which increases the risk of restenosis. This paper considers computer models of stents in non-symmetric flows and their effects on flow characteristics at the wall. This is a fresh approach from the point of view of identifying a stent design whose performance is insensitive to asymmetric flow. Measures of dissipated energy and power are introduced in order to discriminate between competing designs of stents

A new approach to planning in vitro and in vivo experiments for cardiovascular stents. (2) Planning of experiments

Copyright @ 2000 Pacini Editore SpAWithin our overall project to improve the design of stents in terms of reduced rates of re-stenosis, there are three main methods, namely computer simulation and in vitro and in vivo experiments. These methods are closely integrated using contemporary design procedures described below, especially to accommodate patient-to-patient variation. Clinical experience shows that a small variation has considerable effects on flow characteristics of stents and in engineering terms may be described as a ‘geometric risk factor’. The Robust Engineering Design procedure readily incorporates this factor which may thus become a component feature in our experimental planning. We envisage that this approach could be applied to other invasive implants with a view to enhancing their quality

Beyond the virtual intracranial stenting challenge 2007: non-Newtonian and flow pulsatility effects

The attached article is a post print version of the final published version which may be accessed at the link below. Crown Copyright (c) 2010 Published by Elsevier Ltd. All rights reserved.The Virtual Intracranial Stenting Challenge 2007 (VISC’07) is becoming a standard test case in computational minimally invasive cerebrovascular intervention. Following views expressed in the literature and consistent with the recommendations of a report, the effects of non-Newtonian viscosity and pulsatile flow are reported. Three models of stented cerebral aneurysms, originating from VISC’07 are meshed and the flow characteristics simulated using commercial computational fluid dynamics (CFD) software. We conclude that non-Newtonian and pulsatile effects are important to include in order to discriminate more effectively between stent designs

Enhanced visualisation of complex thermofluid data: Vertical and horizontal combined convection and microscale heat transfer cases

Copyright @ 2000 UITIn general, convective heat transfer is an 'n-dimensional' problem where n is well in excess of 3 for steady flows. Traditionally, the method of dimensional analysis results in a small number of dimensionless groups. In the case of steady forced convection these can reduce to three, namely the Nusselt (Nu), Reynolds (Re) and Prandtl (Pr) numbers, for heat transfer, fluid flow regime and fluid properties respectively. Again, traditionally, data are presented on log-log graphs, say of Nu versus Re, with Pr being a possible third parameter. For natural convection, the Grashof number (Gr) expresses buoyancy effects in place of Re, while for combined (natural and forced) convection Gr becomes additional to, rather than replacing, Re. Using sets of data for: (a) vertical combined convection in nuclear safety, (b) horizontal combined convection review material, and (c) microchannel heat transfer, in the first part of this paper we survey this problem. We reach the following conclusions: that heat transfer data are presented in either 'holistic' or 'reductive' modes, and that other thermodynamic performance data are related to the generic scientific cases of (a) 3-dimensional space and (b) multi-dimensional space. In the second part of the paper we present a first attempt at applying design-type procedures to specifying this problem. Visualisation priorities are suggested from which particular solutions will be developed in future

Modelling of two-component turbulent mass and heat transfer in air-fed pressurised suits

This article has been accepted for publication in the Flow, Turbulence and Combustion journal.In this paper the modelling of an important industrial problem is addressed, which involves the two-component turbulent flow with heat transfer that takes place inside protective clothing. The geometry of the flow boundaries is reconstructed in a CAD system from photogrammetry scan data. The overall model is sufficiently realistic to allow, after validation, design improvements to be tested. Those presented here allow the reduction of hot spots over the worker’s body surface and increase thermal comfort.This project is funded by the Engineering and Physical Sciences Research Council and the UK Atomic Energy Authority