scholarly journals Efficiently Simulating an Endograft Deployment: A Methodology for Detailed CFD Analyses

2020 ◽  
Vol 48 (10) ◽  
pp. 2449-2465
Author(s):  
Faidon Kyriakou ◽  
Craig Maclean ◽  
William Dempster ◽  
David Nash
Keyword(s):  
Numerical Models ◽  
Flow Analysis ◽  
Endovascular Aneurysm Repair ◽  
Computational Cost ◽  
Element Analysis ◽  
Fea Model ◽  
Order Of Magnitude ◽  
Modelling Methodology ◽  
Computationally Intensive ◽  
Cfd Analyses

Abstract Numerical models of endografts for the simulation of endovascular aneurysm repair are increasingly important in the improvement of device designs and patient outcomes. Nevertheless, current finite element analysis (FEA) models of complete endograft devices come at a high computational cost, requiring days of runtime, therefore restricting their applicability. In the current study, an efficient FEA model of the Anaconda™ endograft (Terumo Aortic, UK) was developed, able to yield results in just over 4 h, an order of magnitude less than similar models found in the literature. The model was used to replicate a physical device that was deployed in a 3D printed aorta and comparison of the two shapes illustrated a less than 5 mm placement error of the model in the regions of interest, consistent with other more computationally intensive models in the literature. Furthermore, the final goal of the study was to utilize the deployed fabric model in a hemodynamic analysis that would incorporate realistic fabric folds, a feature that is almost always omitted in similar simulations. By successfully exporting the deployed graft geometry into a flow analysis, it was illustrated that the inclusion of fabric wrinkles enabled clinically significant flow patterns such as flow stagnation and recirculation to be detected, paving the way for this modelling methodology to be used in future for stent design optimisation.

Femtogram-Level Thermophysical Property Measurement of Polymeric Samples Using Heated Microcantilevers

2011 ◽  
Author(s):  
Andrew M. Gauffreau ◽  
Keunhan Park
Keyword(s):  
Thermophysical Property ◽  
Computational Cost ◽  
Thermal Conductance ◽  
Element Analysis ◽  
Modified Model ◽  
Fea Model ◽  
Order Of Magnitude ◽  
Property Measurement ◽  
Polymeric Samples ◽  
Thermophysical Property Measurement

This article investigates thermophysical property measurement of femtogram-level polymeric samples by using the 3ω method on a heated microcantilever probe. A localized thermal scooping method was employed to acquire 449 fg of polyethylene terephthalate (PET) sample, measured gravimetrically, directly onto the heater of the cantilever. It is shown that the sample case has a 3ω signal that is smaller in magnitude than the bare case, suggesting that sample properties could be determined using the processes discussed here. A finite element analysis (FEA) model was also developed to compute the steady periodic behavior of the cantilever in the frequency domain. In order to drastically reduce the computational cost and consider the transient effect of the surrounding air, the FEA model implements the complex thermal conductance of the air as the boundary condition rather than modeling the air as a separate domain. The comparison of the modified model with the model that includes the air in the system reveals that the running time has improved by one order of magnitude while showing excellent agreement. The obtained results will expand the characterization and functionality of microcantilevers leading to advancements in localized thermal analysis.

scholarly journals Coupling ice flow models of varying orders of complexity with the Tiling method

2012 ◽  
Vol 58 (210) ◽  
pp. 776-786 ◽  
Author(s):  
Helene Seroussi ◽  
Hachmi Ben Dhia ◽  
Mathieu Morlighem ◽  
Eric Larour ◽  
Eric Rignot ◽  
...  
Keyword(s):  
Numerical Models ◽  
Computational Cost ◽  
Higher Order ◽  
Ice Flow ◽  
Flow Models ◽  
Continental Scale ◽  
Critical Areas ◽  
Warming Climate ◽  
Computationally Intensive ◽  
A New Technique

AbstractIce flow numerical models are essential for predicting the evolution of ice sheets in a warming climate. Recent research emphasizes the need for higher-order and even full-Stokes flow models, instead of the traditional shallow-ice approximation, whose assumptions are not valid in certain critical areas. These higher-order models are, however, computationally intensive and difficult to use at the continental scale. Here we present a new technique, the Tiling method, to couple ice flow models of varying orders of complexity. The goal of the method is to limit the spatial extent of where higherorder models are applied to reduce the computational cost, while maintaining the model precision. We apply this method on synthetic geometries to demonstrate its practical use. We first use a geometry for which all models yield the same results to check the consistency of the method. Then we apply our method to a geometry for which a full-Stokes model is required in the vicinity of the ice front. Our results show that the hybrid models present significant improvements over mono-model approaches and reduce computational times.

scholarly journals Qualitative Order of Magnitude Energy-Flow-Based Failure Modes and Effects Analysis

2013 ◽  
Vol 46 ◽  
pp. 413-447 ◽  
Author(s):  
N. A. Snooke ◽  
M. H. Lee
Keyword(s):  
Energy Flow ◽  
Power Flow ◽  
Failure Modes ◽  
Numerical Models ◽  
Flow Analysis ◽  
Heating System ◽  
Worst Case ◽  
Power Sources ◽  
Power Domain ◽  
Order Of Magnitude

This paper presents a structured power and energy-flow-based qualitative modelling approach that is applicable to a variety of system types including electrical and fluid flow. The modelling is split into two parts. Power flow is a global phenomenon and is therefore naturally represented and analysed by a network comprised of the relevant structural elements from the components of a system. The power flow analysis is a platform for higher-level behaviour prediction of energy related aspects using local component behaviour models to capture a state-based representation with a global time. The primary application is Failure Modes and Effects Analysis (FMEA) and a form of exaggeration reasoning is used, combined with an order of magnitude representation to derive the worst case failure modes. The novel aspects of the work are an order of magnitude(OM) qualitative network analyser to represent any power domain and topology, including multiple power sources, a feature that was not required for earlier specialised electrical versions of the approach. Secondly, the representation of generalised energy related behaviour as state-based local models is presented as a modelling strategy that can be more vivid and intuitive for a range of topologically complex applications than qualitative equation-based representations.The two-level modelling strategy allows the broad system behaviour coverage of qualitative simulation to be exploited for the FMEA task, while limiting the difficulties of qualitative ambiguity explanation that can arise from abstracted numerical models. We have used the method to support an automated FMEA system with examples of an aircraft fuel system and domestic a heating system discussed in this paper.

Reliability-Based Assessment of Safe Excavation Pressure for Dented Pipelines

2020 ◽  
Author(s):  
Chike Okoloekwe ◽  
Matthew Fowler ◽  
Amandeep Virk ◽  
Nader Yoosef-Ghodsi ◽  
Muntaseer Kainat
Keyword(s):  
Numerical Models ◽  
Mechanical Damage ◽  
Structural Response ◽  
Assessment Method ◽  
Full Scale ◽  
Burst Pressure ◽  
Operating Pressure ◽  
Element Analysis ◽  
Fea Model ◽  
Full Scale Tests

Abstract Dents in a pipe result in alteration of its structural response when subjected to internal pressure. Excavation activities further lead to change in load and boundary conditions of the pipe segment which may exacerbate the stress state within the dented region. Depending on the severity of a dent, excavation under full operating pressure may lead to failure, injuries or fatalities. Although uncommon, an incident has been reported on a gas pipeline where a mechanical damage failed during investigation leading to one death and one injury [10]. While current pipeline regulations require that operators must depressurize a line to ensure safe working conditions during repair activities, there are no detailed provisions available in the codes or standards on how an operator should determine such a safe excavation pressure (SEP). As a result, the safe excavation process of dents has received attention in the industry in recent years. A detailed review of the recent research on dent SEP showed that the current recommendations are primarily dependent on one of two aspects: careful assessment of inline inspection (ILI) data, or a fitness for service (FFS) assessment of the dent feature leveraging numerical models. Enbridge Liquid Pipelines had previously demonstrated a feature specific assessment approach which incorporated both ILI data and finite element analysis (FEA) to determine the SEP. This assessment also accounted for uncertainties associated with material properties and ILI tool measurement. In the previous publication, the authors demonstrated a methodology for assessing the SEP of dents at a conceptual level from both deterministic and reliability-based standpoints. In this paper, a validation study has been performed to compare the results of fracture mechanics based FEA models against ten full scale burst tests available in literature. The study showed good agreement of the burst pressure of dent-crack defects predicted by FEA models with those observed in the full-scale tests. The assessment method is further streamlined by incorporating the API 579 [14] Failure Assessment Diagram (FAD) method on an uncracked FEA model as opposed to explicitly incorporating the crack geometry in the FEA model. The results of FEA in conjunction with FAD are compared with the full-scale tests to ensure accuracy and conservatism of burst pressure prediction. A reliability-based approach is then designed which accounts for the uncertainties associated with the analysis. A case study is presented where the reliability-based SEP assessment method has been implemented and feature specific SEP has been recommended to ensure target reliability during excavation.

scholarly journals Ballistic Impact and Virtual Testing of Woven FRP Laminates

2021 ◽  
Vol 5 (5) ◽  
pp. 115
Author(s):  
Ioannis K. Giannopoulos ◽  
Mehdi Yasaee ◽  
Nikolaos Maropakis
Keyword(s):  
Numerical Models ◽  
Progressive Failure ◽  
Computational Cost ◽  
Carbon Composite ◽  
Steel Ball ◽  
Element Analysis ◽  
General Behaviour ◽  
Explicit Finite Element ◽  
The Impact ◽  
Fidelity Model

The aim of the work was to investigate the numerical simulations correlation with the experimental behaviour of steel ball high velocity impact onto a 2 × 2 twill woven carbon composite laminate. The experimental set up consisted of a pressurised gas-gun able to shot steel ball projectiles onto two different composite plate layup configurations of plates made of the same composite material fabric. Subsequently, the experiments were replicated using the LSDYNA explicit finite element analysis software package. Progressive failure numerical models of two different fidelity levels were constructed. The higher fidelity model was simulating each of the plys of the composite panels separately, tied together using cohesive zone modelling properties. The lower fidelity model consisted of a single layer plate with artificial integration points for each ply. The simulation results came out to be in satisfactory agreement with the experimental ones. While the delamination extent was moderately under predicted by the higher fidelity model, the general behaviour was complying with the experimental results. The lower fidelity model was consistent in representing the damage of the panel during the impact and better predicted the impactor residual velocities due to the better matching of the pane stiffness. Despite the competency of the higher fidelity model to capture the damage of the laminate in a more detailed level, the computational cost was 80% higher than the lower fidelity case, which rendered that model impractical against the lower fidelity one, to use in larger models representing more substantial or more complex structures.

Uncertainty Quantification With Maximum Entropy Method for Fatigue Life Estimation

2020 ◽  
Author(s):  
S. M. Nielsen ◽  
H. A. Hougaard ◽  
O. Balling
Keyword(s):  
Fatigue Life ◽  
Maximum Entropy ◽  
Maximum Entropy Method ◽  
Probability Distributions ◽  
Computational Cost ◽  
Entropy Method ◽  
Element Analysis ◽  
Fatigue Life Estimation ◽  
Order Of Magnitude ◽  
General Statistical

Abstract Use of high-fidelity fatigue models that incorporate not only material uncertainty but also part variability and operational uncertainties can improve the accuracy of predictive maintenance and thus decrease operational cost. However, due to the large number of computationally expensive cost function evaluations necessary, little work has been done to explore this field. In this research, the expected life probability distributions with low computational cost is estimated through a general statistical framework that applies Maximum Entropy Method (MEM), fractional statistical moments and Multiplicative Dimensional Reduction (M-DRM). The framework is tested on advanced models of a 6204 SKF ball bearing. The influence of critical part tolerances and load conditions on fatigue life with a probability density function with only 80 function evaluations is quantified in both a finite element analysis and a non-linear analytical model. The number of function evaluations is one order of magnitude lower than necessary for a comparable accuracy achieved by Monte Carlo simulation.

Tire Bead Overheating in Urban Buses and Trucks Using Drum Brake Systems

1998 ◽  
Vol 26 (1) ◽  
pp. 51-62
Author(s):  
A. L. A. Costa ◽  
M. Natalini ◽  
M. F. Inglese ◽  
O. A. M. Xavier
Keyword(s):  
Heat Transfer ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Thermal Energy ◽  
Structural Integrity ◽  
Experimental Temperature ◽  
Temperature Profiles ◽  
Element Analysis ◽  
Drum Brake ◽  
Fea Model

Abstract Because the structural integrity of brake systems and tires can be related to the temperature, this work proposes a transient heat transfer finite element analysis (FEA) model to study the overheating in drum brake systems used in trucks and urban buses. To understand the mechanics of overheating, some constructive variants have been modeled regarding the assemblage: brake, rims, and tires. The model simultaneously studies the thermal energy generated by brakes and tires and how the heat is transferred and dissipated by conduction, convection, and radiation. The simulated FEA data and the experimental temperature profiles measured with thermocouples have been compared giving good correlation.

Simulation of Two Phase Flow Dynamics in Flexible Riser Exit Geometries for Oil and Gas Applications

2018 ◽  
Vol 39 ◽  
pp. 1-13
Author(s):  
Ikpe E. Aniekan ◽  
Owunna Ikechukwu ◽  
Satope Paul
Keyword(s):  
Oil And Gas ◽  
Two Phase Flow ◽  
Flow Analysis ◽  
Computational Cost ◽  
Maximum Velocity ◽  
Oil Well ◽  
Phase Flow ◽  
Two Phase ◽  
The Third ◽  
Riser Pipe

Four different riser pipe exit configurations were modelled and the flow across them analysed using STAR CCM+ CFD codes. The analysis was limited to exit configurations because of the length to diameter ratio of riser pipes and the limitations of CFD codes available. Two phase flow analysis of the flow through each of the exit configurations was attempted. The various parameters required for detailed study of the flow were computed. The maximum velocity within the pipe in a two phase flow were determined to 3.42 m/s for an 8 (eight) inch riser pipe. After thorough analysis of the two phase flow regime in each of the individual exit configurations, the third and the fourth exit configurations were seen to have flow properties that ensures easy flow within the production system as well as ensure lower computational cost. Convergence (Iterations), total pressure, static pressure, velocity and pressure drop were used as criteria matrix for selecting ideal riser exit geometry, and the third exit geometry was adjudged the ideal exit geometry of all the geometries. The flow in the third riser exit configuration was modelled as a two phase flow. From the results of the two phase flow analysis, it was concluded that the third riser configuration be used in industrial applications to ensure free flow of crude oil and gas from the oil well during oil production.

scholarly journals A Fast Estimator for Binary Choice Models with Spatial, Temporal, and Spatio-Temporal Interdependence

2021 ◽  
pp. 1-7
Author(s):  
Julian Wucherpfennig ◽  
Aya Kachi ◽  
Nils-Christian Bormann ◽  
Philipp Hunziker
Keyword(s):  
Computational Cost ◽  
Choice Models ◽  
Reduced Form ◽  
Binary Choice ◽  
Monte Carlo Experiments ◽  
Binary Choice Models ◽  
Spatio Temporal ◽  
Computationally Intensive ◽  
Pseudo Maximum Likelihood ◽  
Parameter Values

Abstract Binary outcome models are frequently used in the social sciences and economics. However, such models are difficult to estimate with interdependent data structures, including spatial, temporal, and spatio-temporal autocorrelation because jointly determined error terms in the reduced-form specification are generally analytically intractable. To deal with this problem, simulation-based approaches have been proposed. However, these approaches (i) are computationally intensive and impractical for sizable datasets commonly used in contemporary research, and (ii) rarely address temporal interdependence. As a way forward, we demonstrate how to reduce the computational burden significantly by (i) introducing analytically-tractable pseudo maximum likelihood estimators for latent binary choice models that exhibit interdependence across space and time and by (ii) proposing an implementation strategy that increases computational efficiency considerably. Monte Carlo experiments show that our estimators recover the parameter values as good as commonly used estimation alternatives and require only a fraction of the computational cost.

Localization simulation of forming-induced residual stresses of composite using prescribed boundary

2021 ◽  
pp. 073168442094118
Author(s):  
Qi Wu ◽  
Hongzhou Zhai ◽  
Nobuhiro Yoshikawa ◽  
Tomotaka Ogasawara ◽  
Naoki Morita
Keyword(s):  
Residual Stresses ◽  
Representative Volume Element ◽  
Computational Cost ◽  
Volume Element ◽  
Thermoplastic Composite ◽  
Structural Deformation ◽  
Element Analysis ◽  
Micro Scale ◽  
Representative Volume ◽  
Localization Approach

A novel localization approach that seamlessly bridges the macro- and micro-scale models is proposed and used to model the forming-induced residual stresses within a representative volume element of a fiber reinforced composite. The approach uses a prescribed boundary that is theoretically deduced by integrating the asymptotic expansion of a composite and the equal strain transfer, thus rendering the simulation setting to be easier than conventional approaches. When the localization approach is used for the finite element analysis, the temperature and residual stresses within an ideal cubic representative volume element are precisely simulated, given a sandwiched thermoplastic composite is formed under one-side cooling condition. The simulation results, after being validated, show that the temperature gradient has an impact on the local residual stresses, especially on the in-plane normal stress transverse to the fiber, and consequently, influences the structural deformation. This newly designed localization approach demonstrates the advantages of enhanced precision and reduced computational cost owing to the fast modeling of the finely meshed representative volume element. This is beneficial for a detailed understanding of the actual residual stresses at the micro-scale.

Sign in / Sign up

Export Citation Format

Share Document