Rhodri Bevan, P. Nithiarasu, Igor Sazonov, Raoul van Loon, Heyman Luckraz, Michael Collins and Andrew Garnham
The purpose of this paper is to numerically study blood flow through a subject‐specific carotid artery with a moderately severe stenosis, also to thoroughly analyse the wall shear…
Abstract
Purpose
The purpose of this paper is to numerically study blood flow through a subject‐specific carotid artery with a moderately severe stenosis, also to thoroughly analyse the wall shear stress (WSS), oscillatory shear index (OSI) and WSS angular deviation (WSSAD). One of the important aspects of this study is the investigation on the influence of the extensions attached to the domain outlets.
Design/methodology/approach
The segmentation of the carotid artery is carried out using a deformable model based on a level set method. A geometric potential force (GPF) is employed to deform the level set to obtain the carotid artery geometry. The initial surface meshing is generated using an advanced marching cubes (MC) method, before improving the quality of the surface mesh via a number of mesh cosmetic steps. The volume mesh generation has two parts. In the first part, a quasi‐structured, boundary layer mesh is generated in the vicinity of the geometry walls. The second part of the meshing involves unstructured tetrahedral meshing of the inner part of the geometry. After the meshing stage, the flow boundary conditions are generated by numerically solving the Helmholtz equation in both space and time. Finally, the explicit characteristic‐based split (CBS) method is employed in a parallel environment to produce a detailed analysis of wall quantities.
Findings
In general, WSS is very high in the vicinity of the carotid artery apex and in the proximity of the stenosis. From the results obtained, it is clear that the influence of outlet domain extension is marginal. While the peak instantaneous WSS differs by a maximum of 5.7 per cent, the time‐averaged WSS difference due to extended domain is only 1.3 per cent. Two other derived parameters are also examined in the paper, the oscillating shear index and the WSSAD. Both these quantities also display minor or negligible differences due to domain extension.
Originality/value
It has been perceived that domain extension is essential to avoid wrong application of boundary conditions. The results obtained, however, conclusively show that the outlet domain extension has only a moderate influence on WSS. Thus, outlet extension to the domains may not be essential for arterial blood flows. It is also observed that the dramatic values of peak WSS obtained near the stenosis is the result of high resolution mesh along with boundary layers used in this study. Both the outcomes represent the originality of this paper.
Details
Keywords
Rhodri LT Bevan and P Nithiarasu
In the present work, a novel dual time stepping approach is applied to a quasi-implicit (QI) fractional step method and its performance is assessed against the classical versions…
Abstract
Purpose
In the present work, a novel dual time stepping approach is applied to a quasi-implicit (QI) fractional step method and its performance is assessed against the classical versions of the QI procedure for the solution of incompressible Navier-Stokes equations. The paper aims to discuss these issues.
Design/methodology/approach
In the proposed method, a local time stepping algorithm is utilised to accelerate the solution to steady state, while the transient solution is recovered through the use of a dual time step. It is demonstrated that, unlike the classical fractional step method, the temporal convergence rate of the proposed method depends solely upon the choice of the time discretisation.
Findings
While additional stabilisation is the prerequisite for obtaining higher order accuracy in the standard QI methods, the proposed dual time stepping approach completely eliminates this requirement. In addition, the dual time stepping approach proposed achieves the correct formal accuracy in time for both velocity and pressure. It is also demonstrated that a time accuracy beyond second order for both pressure and velocity is possible. In summary, the proposed dual time approach to QI methods simplifies the algorithm, accelerates solution and achieves a higher order time accuracy.
Originality/value
The dual time stepping removed first order pressure error.
Details
Keywords
Rhodri L.T. Bevan, Roland W. Lewis and Perumal Nithiarasu
The purpose of this paper is to numerically model forced convection heat transfer within a patient‐specific carotid bifurcation and to examine the relationship between the…
Abstract
Purpose
The purpose of this paper is to numerically model forced convection heat transfer within a patient‐specific carotid bifurcation and to examine the relationship between the temperature and wall shear stress.
Design/methodology/approach
The procedure employs a parallel, fully explicit (matrix free) characteristic based split scheme for the solution of incompressible Navier‐Stokes equations.
Findings
The arterial wall temperature, rather than the blood temperature dominates the regions of low wall shear stress and high oscillating shear stress. Additionally, negligible temperature gradient was detected proximal to the arterial wall in this locality.
Originality/value
The presented results demonstrate a possible mechanism for cold air temperature to influence the atherosclerotic plaque region proximal to the stenosis. The proposed patient‐specific heat transfer analysis also provides a starting point for the investigation of the influence of induced hypothermia on carotid plaque and its stability.
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Rhodri LT Bevan, Etienne Boileau, Raoul van Loon, R.W. Lewis and P Nithiarasu
The purpose of this paper is to describe and analyse a class of finite element fractional step methods for solving the incompressible Navier-Stokes equations. The objective is not…
Abstract
Purpose
The purpose of this paper is to describe and analyse a class of finite element fractional step methods for solving the incompressible Navier-Stokes equations. The objective is not to reproduce the extensive contributions on the subject, but to report on long-term experience with and provide a unified overview of a particular approach: the characteristic-based split method. Three procedures, the semi-implicit, quasi-implicit and fully explicit, are studied and compared.
Design/methodology/approach
This work provides a thorough assessment of the accuracy and efficiency of these schemes, both for a first and second order pressure split.
Findings
In transient problems, the quasi-implicit form significantly outperforms the fully explicit approach. The second order (pressure) fractional step method displays significant convergence and accuracy benefits when the quasi-implicit projection method is employed. The fully explicit method, utilising artificial compressibility and a pseudo time stepping procedure, requires no second order fractional split to achieve second order or higher accuracy. While the fully explicit form is efficient for steady state problems, due to its ability to handle local time stepping, the quasi-implicit is the best choice for transient flow calculations with time independent boundary conditions. The semi-implicit form, with its stability restrictions, is the least favoured of all the three forms for incompressible flow calculations.
Originality/value
A comprehensive comparison between three versions of the CBS method is provided for the first time.
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Keywords
Christopher Edmunds and Kerry KilBride
The purpose of this paper is to recount 12 months of a pioneering collaboration between the Aneurin Bevan University Health Board, five local authorities and nine registered…
Abstract
Purpose
The purpose of this paper is to recount 12 months of a pioneering collaboration between the Aneurin Bevan University Health Board, five local authorities and nine registered social landlords in South East Wales. It will aim to share the understanding that has emerged, demonstrating how a large number of agencies, many of which have different purposes or which have traditionally been in competition with each other, have been able to work collaboratively, to meet the interests of some very vulnerable people.
Design/methodology/approach
This reflective approach draws on the views of a large number of staff from each of the three constituent public sector service areas and their experience of collaborative working using action research principles. The study will use people’s own words to highlight real experiences, but analysed against similar collaborative activity elsewhere reflected in the literature. As there has been no established pathway for the collaboration to follow, we have adopted a Plan-Do-Study-Act cycle to capture the evolving “In One Place” (IOP) process.
Findings
This paper highlights the inherent systemic barriers that have to be identified and overcome if the authors are to move from wishful thinking to pragmatic realism, both within and between organisations. The sense of public sector agencies being able to work together, simply because it makes good sense, is challenged and the paper identifies both cultural and professional factors that made a difference in this collaboration, which could be harnessed elsewhere.
Originality/value
From the outset, a key driver for the IOP has been to align health, social care and housing processes by bringing together practitioners and senior managers to identify need and to plan and deliver services locally, offering a real benefit to individuals with complex needs. This is set within the context of increasing demand on public services, financial austerity and the history of “housing” being on the margins of discussion when considering the integration of health and social care services. The authors are able to demonstrate the benefit of housing being at the centre of such discussions.
Diben
Mae’r astudiaeth hon yn adrodd hanes deuddeg mis cyntaf cydweithrediad arloesol rhwng Bwrdd Iechyd Prifysgol Aneurin Bevan (ABMUHB), pum Awdurdod Lleol a naw Landlord Cymdeithasol Cofrestredig (RSL) yn Ne Ddwyrain Cymru. Nod yr astudiaeth hon fydd rhannu’r ddealltwriaeth sydd wedi dod i’r amlwg yn dangos sut mae nifer fawr o asiantaethau, llawer ohonynt â dibenion gwahanol neu sydd wedi bod mewn cystadleuaeth â’i gilydd yn draddodiadol, wedi gallu gweithio’n gydweithredol, i fodloni budd rhai pobl agored iawn i niwed.
Cynllun/methodoleg/dull
Mae’r dull adlewyrchol hwn yn defnyddio safbwynt nifer fawr o staff o bob un o 3 maes gwasanaeth sector cyhoeddus yr etholaeth a’u profiad o weithio’n gydweithredol gan ddefnyddio egwyddorion ymchwil weithredol. Bydd yr astudiaeth yn defnyddio geiriau pobl i amlygu profiadau gwirioneddol, ond wedi ei ddadansoddi yn erbyn gweithgaredd cydweithredol tebyg sydd wedi ei adlewyrchu rhywle arall yn y llenyddiaeth. Gan nad oes unrhyw lwybr wedi ei sefydlu i’r gydweithrediaeth ei ddilyn, rydym wedi mabwysiadu cylch Cynllunio-Gwneud-Astudio-Gweithredu (CGAG) i gyfleu’r broses ‘Mewn Un Lle’ sy’n esblygu.
Canfyddiadau
Mae’r erthygl hon yn amlygu’r rhwystrau systemig cynhenid y mae’n rhaid eu nodi a’u goresgyn er mwyn symud o ddymuno i realaeth ymarferol, o fewn a rhwng sefydliadau. Mae’r syniad bod asiantaethau’r sector cyhoeddus yn gallu cydweithio, dim ond am fod hynny’n gwneud synnwyr, yn cael ei herio ac mae’r papur yn nodi ffactorau diwylliannol a phroffesiynol a wnaeth wahaniaeth yn y cydweithrediad hwn, y gellid eu defnyddio rhywle arall.
Gwreiddioldeb/gwerth
O’r cychwyn, ysgogwr allweddol ar gyfer y rhaglen ‘Mewn Un Lle’ oedd alinio prosesau iechyd, gofal cymdeithasol a thai trwy ddod ag ymarferwyr ac uwch reolwyr o’r sectorau gwahanol hyn ynghyd i nodi angen ac i gynllunio a chyflenwi gwasanaethau yn lleol, pan fo hynny o fudd gwirioneddol i unigolion ag anghenion cymhleth. Mae hyn wedi ei nodi o fewn cyd-destun cynyddu’r galw am wasanaethau cyhoeddus, cynildeb ariannol a hanes ‘tai’ ar ymylon trafodaeth wrth ystyried integreiddio gwasanaethau iechyd a gofal cymdeithasol. Yn yr enghraifft hon rydym yn gallu dangos buddion gwneud tai yn ganolog i drafodaethau o’r fath.