scholarly journals In Vitro Validation of Finite-Element Model of AAA Hemodynamics Incorporating Realistic Outlet Boundary Conditions

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Ethan O. Kung ◽  
Andrea S. Les ◽  
Francisco Medina ◽  
Ryan B. Wicker ◽  
Michael V. McConnell ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Numerical Simulations ◽  
In Silico ◽  
Physiological State ◽  
Patient Specific ◽  
Experimental Measurements ◽  
Windkessel Model ◽  
Measured Velocity ◽  
Good Agreement

The purpose of this study is to validate numerical simulations of flow and pressure in an abdominal aortic aneurysm (AAA) using phase-contrast magnetic resonance imaging (PCMRI) and an in vitro phantom under physiological flow and pressure conditions. We constructed a two-outlet physical flow phantom based on patient imaging data of an AAA and developed a physical Windkessel model to use as outlet boundary conditions. We then acquired PCMRI data in the phantom while it operated under conditions mimicking a resting and a light exercise physiological state. Next, we performed in silico numerical simulations and compared experimentally measured velocities, flows, and pressures in the in vitro phantom to those computed in the in silico simulations. There was a high degree of agreement in all of the pressure and flow waveform shapes and magnitudes between the experimental measurements and simulated results. The average pressures and flow split difference between experiment and simulation were all within 2%. Velocity patterns showed good agreement between experimental measurements and simulated results, especially in the case of whole-cycle averaged comparisons. We demonstrated methods to perform in vitro phantom experiments with physiological flows and pressures, showing good agreement between numerically simulated and experimentally measured velocity fields and pressure waveforms in a complex patient-specific AAA geometry.

Experimental Characterization of a T-Shaped Programmable Multistable Mechanism

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Mohamed Zanaty ◽  
Simon Henein
Keyword(s):  
Numerical Simulations ◽  
Reaction Force ◽  
Experimental Measurements ◽  
Experimental Characterization ◽  
Stable States ◽  
Stability Behavior ◽  
The Stability ◽  
Force Characteristics ◽  
Good Agreement

Programmable multistable mechanisms (PMM) exhibit a modifiable stability behavior in which the number of stable states, stiffness, and reaction force characteristics are controlled via their programming inputs. In this paper, we present experimental characterization for the concept of stability programing introduced in our previous work (Zanaty et al., 2018, “Programmable Multistable Mechanisms: Synthesis and Modeling,” ASME J. Mech. Des., 140(4), p. 042301.) A prototype of the T-combined axially loaded double parallelogram mechanisms (DPM) with rectangular hinges is manufactured using electrodischarge machining (EDM). An analytical model based on Euler–Bernoulli equations of the T-mechanism is derived from which the stability behavior is extracted. Numerical simulations and experimental measurements are conducted on programming the mechanism as monostable, bistable, tristable, and quadrastable, and show good agreement with our analytical derivations within 10%.

scholarly journals A Combined In Vivo, In Vitro, In Silico Approach for Patient-Specific Haemodynamic Studies of Aortic Dissection

2020 ◽  
Vol 48 (12) ◽  
pp. 2950-2964
Author(s):  
Mirko Bonfanti ◽  
Gaia Franzetti ◽  
Shervanthi Homer-Vanniasinkam ◽  
Vanessa Díaz-Zuccarini ◽  
Stavroula Balabani
Keyword(s):  
Aortic Dissection ◽  
In Silico ◽  
Clinical Decision ◽  
Patient Specific ◽  
Type B ◽  
Non Invasive ◽  
Cfd Models ◽  
Numerical Predictions

AbstractThe optimal treatment of Type-B aortic dissection (AD) is still a subject of debate, with up to 50% of the cases developing late-term complications requiring invasive intervention. A better understanding of the patient-specific haemodynamic features of AD can provide useful insights on disease progression and support clinical management. In this work, a novel in vitro and in silico framework to perform personalised studies of AD, informed by non-invasive clinical data, is presented. A Type-B AD was investigated in silico using computational fluid dynamics (CFD) and in vitro by means of a state-of-the-art mock circulatory loop and particle image velocimetry (PIV). Both models not only reproduced the anatomical features of the patient, but also imposed physiologically-accurate and personalised boundary conditions. Experimental flow rate and pressure waveforms, as well as detailed velocity fields acquired via PIV, are extensively compared against numerical predictions at different locations in the aorta, showing excellent agreement. This work demonstrates how experimental and numerical tools can be developed in synergy to accurately reproduce patient-specific AD blood flow. The combined platform presented herein constitutes a powerful tool for advanced haemodynamic studies for a range of vascular conditions, allowing not only the validation of CFD models, but also clinical decision support, surgical planning as well as medical device innovation.

Sensitivity of patient-specific numerical simulation of cerebal aneurysm hemodynamics to inflow boundary conditions

2007 ◽  
Vol 106 (6) ◽  
pp. 1051-1060 ◽  
Author(s):  
Prem Venugopal ◽  
Daniel Valentino ◽  
Holger Schmitt ◽  
J. Pablo Villablanca ◽  
Fernando Viñuela ◽  
...  
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Boundary Conditions ◽  
Numerical Simulations ◽  
Flow Rate ◽  
Artery Aneurysm ◽  
Blood Flow Rate ◽  
Patient Specific ◽  
Stress Distributions ◽  
Flow Rates

Object Due to the difficulty of obtaining patient-specific velocity measurements during imaging, many assumptions have to be made while imposing inflow boundary conditions in numerical simulations conducted using patient-specific, imaging-based cerebral aneurysm models. These assumptions can introduce errors, resulting in lack of agreement between the computed flow fields and the true blood flow in the patient. The purpose of this study is to evaluate the effect of the assumptions made while imposing inflow boundary conditions on aneurysmal hemodynamics. Methods A patient-based anterior communicating artery aneurysm model was selected for this study. The effects of various inflow parameters on numerical simulations conducted using this model were then investigated by varying these parameters over ranges reported in the literature. Specifically, we investigated the effects of heart and blood flow rates as well as the distribution of flow rates in the A1 segments of the anterior cerebral artery. The simulations revealed that the shear stress distributions on the aneurysm surface were largely unaffected by changes in heart rate except at locations where the shear stress magnitudes were small. On the other hand, the shear stress distributions were found to be sensitive to the ratio of the flow rates in the feeding arteries as well as to variations in the blood flow rate. Conclusions Measurement of the blood flow rate as well as the distribution of the flow rates in the patient's feeding arteries may be needed for numerical simulations to accurately reproduce the intraaneurysmal hemodynamics in a specific aneurysm in the clinical setting.

scholarly journals Design and fabrication of a freeform mirror generating a uniform illuminance distribution in a rectangular region

2020 ◽  
Vol 44 (4) ◽  
pp. 540-546
Author(s):  
E.S. Andreev ◽  
E.V. Byzov ◽  
D.A. Bykov ◽  
М.А. Moiseev ◽  
L.L. Doskolovich
Keyword(s):  
Numerical Simulations ◽  
Assignment Problem ◽  
Transportation Problem ◽  
Design Method ◽  
Experimental Measurements ◽  
Mass Transportation ◽  
Rectangular Region ◽  
Linear Assignment Problem ◽  
Linear Assignment ◽  
Good Agreement

The design of a freeform mirror generating a uniform illuminance distribution in a rectangular region with angular dimensions of 30°x15° is presented. The design method is based on the formulation of the problem of calculating the "ray-mapping" as a Monge-Kantorovich mass transportation problem and its subsequent reducing to a linear assignment problem. We describe a mirror fabrication process with the use of milling technology and present results of experimental measurements of the light distribution generated by the mirror. The experimental results are in good agreement with the results of numerical simulations and thus confirm the manufacturability of mirrors designed by the method proposed.

Thermal study of clogging during filament-based material extrusion additive manufacturing: Experimental-numerical study

2021 ◽  
Author(s):  
Zahra Taheri ◽  
Ali Karimnejad Esfahani ◽  
Abas Ramiar
Keyword(s):  
Additive Manufacturing ◽  
Numerical Simulations ◽  
Numerical Study ◽  
Thermal Conditions ◽  
Experimental Measurements ◽  
Clear Understanding ◽  
Material Extrusion ◽  
Series Of Experiments ◽  
Detailed Picture ◽  
Good Agreement

Abstract One of the major drawbacks of material extrusion additive manufacturing (AM) is hot-end clogging. This study aims to answer the question, “What thermal conditions lead to clogging during filament-based material extrusion?” Answering this question requires a clear understanding of temperature distribution inside the liquefier. However, this could not be achieved only through experimental measurements. Therefore, numerical simulations were also carried out by developing a 3D finite volume model of the hot-end. The results obtained from numerical simulations show good agreement with experimental measurements. They also give us a detailed picture of the temperature gradient near the nozzle. Moreover, a series of experiments were performed to determine when clogging occurs, and some criteria for avoiding clogging were presented. These results were also compared and combined with the numerical results to investigate the thermal condition leading to clogging. As the results show, overheating the heat barrier increases the length of the filament, whose temperature is above the glass transition temperature. As this length exceeds a critical value, the filament buckles under the extruder motor force and clogging occurs.

PIV-Measured Versus CFD-Predicted Flow Dynamics in Anatomically Realistic Cerebral Aneurysm Models

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Matthew D. Ford ◽  
Hristo N. Nikolov ◽  
Jaques S. Milner ◽  
Stephen P. Lownie ◽  
Edwin M. DeMont ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Cardiac Cycle ◽  
Flow Dynamics ◽  
Cfd Modeling ◽  
Patient Specific ◽  
Flow Loop ◽  
Cfd Simulations ◽  
Flow Through

Computational fluid dynamics (CFD) modeling of nominally patient-specific cerebral aneurysms is increasingly being used as a research tool to further understand the development, prognosis, and treatment of brain aneurysms. We have previously developed virtual angiography to indirectly validate CFD-predicted gross flow dynamics against the routinely acquired digital subtraction angiograms. Toward a more direct validation, here we compare detailed, CFD-predicted velocity fields against those measured using particle imaging velocimetry (PIV). Two anatomically realistic flow-through phantoms, one a giant internal carotid artery (ICA) aneurysm and the other a basilar artery (BA) tip aneurysm, were constructed of a clear silicone elastomer. The phantoms were placed within a computer-controlled flow loop, programed with representative flow rate waveforms. PIV images were collected on several anterior-posterior (AP) and lateral (LAT) planes. CFD simulations were then carried out using a well-validated, in-house solver, based on micro-CT reconstructions of the geometries of the flow-through phantoms and inlet/outlet boundary conditions derived from flow rates measured during the PIV experiments. PIV and CFD results from the central AP plane of the ICA aneurysm showed a large stable vortex throughout the cardiac cycle. Complex vortex dynamics, captured by PIV and CFD, persisted throughout the cardiac cycle on the central LAT plane. Velocity vector fields showed good overall agreement. For the BA, aneurysm agreement was more compelling, with both PIV and CFD similarly resolving the dynamics of counter-rotating vortices on both AP and LAT planes. Despite the imposition of periodic flow boundary conditions for the CFD simulations, cycle-to-cycle fluctuations were evident in the BA aneurysm simulations, which agreed well, in terms of both amplitudes and spatial distributions, with cycle-to-cycle fluctuations measured by PIV in the same geometry. The overall good agreement between PIV and CFD suggests that CFD can reliably predict the details of the intra-aneurysmal flow dynamics observed in anatomically realistic in vitro models. Nevertheless, given the various modeling assumptions, this does not prove that they are mimicking the actual in vivo hemodynamics, and so validations against in vivo data are encouraged whenever possible.

Abstract 15923: A Combined In Silico and In Vitr o Approach for Surgical Planning of Pediatric Coarctation Repair

Circulation ◽  
2020 ◽  
Vol 142 (Suppl_3) ◽  
Author(s):  
Fanette Chassagne ◽  
Sujatha Buddhe ◽  
Lester C Permut ◽  
David MCMULLAN ◽  
Stephen P Seslar ◽  
...  
Keyword(s):  
Surgical Treatment ◽  
Aortic Arch ◽  
In Silico ◽  
Cfd Simulation ◽  
Patch Repair ◽  
Recirculation Region ◽  
Patient Specific ◽  
Congenital Cardiac Malformation

Introduction: Coarctation of the aorta is a congenital malformation of the proximal descending aorta that results in severe narrowing of the vessel lumen. It causes significant changes in the aortic hemodynamics, including reduced blood flow and an increased pressure gradient in this area of the vasculature. When this congenital cardiac malformation is associated with aortic arch hypoplasia, a two step-surgery is proposed: first, an end-to-end anastomosis in performed to remove all the ductal tissue surrounding the coarctation, and then the aorta is longitudinally incised and patched to increase its diameter. The design of the patch, based on the surgeon’s experience, is done in the OR. A combined in silico and in vitro approach is proposed to test the possibility of a priori design of the patch. This approach would also open the door to optimization of the patch to restore physiological hemodynamics in the aorta. Methods & Results: CFD simulations of the hemodynamics in the pre-treatment aortic arch were created from the segmentation of patients’ images who received surgical treatment at Seattle Children’s Hospital. In vivo hemodynamics data were used as boundary conditions for the simulation. The design of the patch was created via an in-house code and was based on surgeons’ input: the locations of the start and the end of the lumen enlargement and the length of the aortic segment to be resected. The optimization of the patch design was performed by comparing the simulated hemodynamics (pressure drop, endothelial shear stress, size of the recirculation region, ...) before and after the patch repair. The optimized patch design was then used by the surgeon to perform the in vitro surgical treatment on a physical model of the patient’s anatomy, made in a translucent silicon rubber. The repaired anatomical model was scanned by X-ray microtomography and cast in an optically clear silicone. Time-resolved particle image velocimetry measurements were performed to characterize the post-treatment hemodynamics, and compared to the results of the CFD simulation. Conclusions: This unique in silico and in vitro approach allows surgeons to perform different repairs on patient-specific physical in vitro models and to optimize the design of the patch prior to starting the surgery.

Analysis of Experimental Measurements and Numerical Simulations of a Heat Field in the Light Weight Building Structure

2014 ◽  
Vol 969 ◽  
pp. 33-38 ◽  
Author(s):  
Lenka Lausova ◽  
Iveta Skotnicova
Keyword(s):  
Numerical Methods ◽  
Boundary Conditions ◽  
Numerical Simulations ◽  
Thermal Field ◽  
Temperature Response ◽  
Summer Temperature ◽  
Experimental Measurements ◽  
Light Weight ◽  
Building Structure ◽  
Heat Field

The paper analyses results of the experimental measurements and numerical simulations of the winter and summer temperature response in the light timber structure. In the article there is evaluated the suitability of using of the theoretical numerical methods for a thermal field prediction in a building structure exposed to non-stationary boundary conditions.

scholarly journals Effects of Uncertainty of Outlet Boundary Conditions in a Patient-Specific Case of Aortic Coarctation

2021 ◽  
Author(s):  
Maria Nicole Antonuccio ◽  
Alessandro Mariotti ◽  
Benigno Marco Fanni ◽  
Katia Capellini ◽  
Claudio Capelli ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Aortic Coarctation ◽  
Volume Flow Rate ◽  
Input Parameter ◽  
Stochastic Approach ◽  
Fine Tuning ◽  
Patient Specific ◽  
Computational Domain ◽  
Windkessel Model ◽  
Deterministic Simulations

AbstractComputational Fluid Dynamics (CFD) simulations of blood flow are widely used to compute a variety of hemodynamic indicators such as velocity, time-varying wall shear stress, pressure drop, and energy losses. One of the major advances of this approach is that it is non-invasive. The accuracy of the cardiovascular simulations depends directly on the level of certainty on input parameters due to the modelling assumptions or computational settings. Physiologically suitable boundary conditions at the inlet and outlet of the computational domain are needed to perform a patient-specific CFD analysis. These conditions are often affected by uncertainties, whose impact can be quantified through a stochastic approach. A methodology based on a full propagation of the uncertainty from clinical data to model results is proposed here. It was possible to estimate the confidence associated with model predictions, differently than by deterministic simulations. We evaluated the effect of using three-element Windkessel models as the outflow boundary conditions of a patient-specific aortic coarctation model. A parameter was introduced to calibrate the resistances of the Windkessel model at the outlets. The generalized Polynomial Chaos method was adopted to perform the stochastic analysis, starting from a few deterministic simulations. Our results show that the uncertainty of the input parameter gave a remarkable variability on the volume flow rate waveform at the systolic peak simulating the conditions before the treatment. The same uncertain parameter had a slighter effect on other quantities of interest, such as the pressure gradient. Furthermore, the results highlight that the fine-tuning of Windkessel resistances is not necessary to simulate the post-stenting scenario.

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