SAM
https://sam.ensam.eu:443
The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sun, 26 May 2019 05:41:08 GMT2019-05-26T05:41:08ZNumerical investigation of the real and ideal gap profiles in the calculation of the pressure distortion coefficient and piston fall rate of an LNE 200 MPa pressure balance
http://hdl.handle.net/10985/8914
Numerical investigation of the real and ideal gap profiles in the calculation of the pressure distortion coefficient and piston fall rate of an LNE 200 MPa pressure balance
WONGTHEP, Padipat; RABAULT, Thierry; NOGUERA, Ricardo; SARRAF, Christophe
This paper aims to investigate, by means of numerical simulation, the effect of gap profiles on the calculation of the pressure distortion coefficient (λ) and the piston fall rate (vf) of two piston-cylinder units used in a Laboratoire National de Métrologie et d'Essais (LNE) 200 MPa pressure balance. The ideal mean gap width between the piston and the cylinder was obtained after measuring the piston fall rate at a low pressure, while the piston radius was obtained from the cross-float experiments at a low pressure. The real gap width was obtained from dimensional measurements by measuring the diameter and straightness of the piston and the cylinder. The piston and cylinder radial distortions were calculated using the finite element method. The pressure distribution in the gap was calculated on the basis of the Navier-Stokes equation for Newtonian viscous flow. The results such as pressure distributions, radial distortions, the pressure distortion coefficient and the piston fall rate were presented for the free-deformation operating mode of the assemblies. The calculation resulted in ideal and real gap profiles indicating that the average pressure distortion coefficient was in good agreement within 0.017 × 10-6 MPa-1 and the calculations of piston fall rate depended on the gap profile especially at the inlet and outlet zones of the engagement length.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/89142013-01-01T00:00:00ZWONGTHEP, PadipatRABAULT, ThierryNOGUERA, RicardoSARRAF, ChristopheThis paper aims to investigate, by means of numerical simulation, the effect of gap profiles on the calculation of the pressure distortion coefficient (λ) and the piston fall rate (vf) of two piston-cylinder units used in a Laboratoire National de Métrologie et d'Essais (LNE) 200 MPa pressure balance. The ideal mean gap width between the piston and the cylinder was obtained after measuring the piston fall rate at a low pressure, while the piston radius was obtained from the cross-float experiments at a low pressure. The real gap width was obtained from dimensional measurements by measuring the diameter and straightness of the piston and the cylinder. The piston and cylinder radial distortions were calculated using the finite element method. The pressure distribution in the gap was calculated on the basis of the Navier-Stokes equation for Newtonian viscous flow. The results such as pressure distributions, radial distortions, the pressure distortion coefficient and the piston fall rate were presented for the free-deformation operating mode of the assemblies. The calculation resulted in ideal and real gap profiles indicating that the average pressure distortion coefficient was in good agreement within 0.017 × 10-6 MPa-1 and the calculations of piston fall rate depended on the gap profile especially at the inlet and outlet zones of the engagement length.A new model of fluid flow to determine pressure balance characteristics
http://hdl.handle.net/10985/8900
A new model of fluid flow to determine pressure balance characteristics
WONGTHEP, Padipat; RABAULT, Thierry; NOGUERA, Ricardo; SARRAF, Christophe
Some projects such as the EUROMET project 463 have underlined the lack of agreement between experimental measurements and calculations by the finite element method (FEM), used to determine the piston fall rate of a high-pressure balance used in primary standards. This is significant because the piston fall rate is an essential parameter to characterize experimentally the mean gap between the piston and the cylinder and to determine the effective area (A p) at each pressure (p) point. By improving the method used to estimate the piston fall rate it is possible to improve the determination of the gap, the effective area and consequently the pressure distortion coefficient. One possible cause of the lack of agreement between the calculated and measured piston fall rates could be inappropriate modelling of the fluid flow. In fact, the former quasi-1D Stokes model assimilates the gap between the piston and the cylinder as formed by two parallel walls, which is an approximation. In addition, the velocity of the piston wall was neglected. In order to evaluate the influence of this model, the equations of the fluid flow are modified and are presented in this paper. Equations that were defined in a parallel-plane model are defined in an annular gap model. In addition to this, corrections due to the velocity of the piston wall are inserted. This research work is applied on a Desgranges et Huot DH 7594 piston-cylinder unit of PTB with a pressure up to 1 GPa, in the continuity of the EUROMET project 463 in order to quantify the influence of each correction that has been inserted in the new equations. This is carried out using the FEM. This analysis will allow us to evaluate the improvement of our knowledge of the behaviour of piston gauges and consequently to better evaluate the uncertainties due to the models.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/89002013-01-01T00:00:00ZWONGTHEP, PadipatRABAULT, ThierryNOGUERA, RicardoSARRAF, ChristopheSome projects such as the EUROMET project 463 have underlined the lack of agreement between experimental measurements and calculations by the finite element method (FEM), used to determine the piston fall rate of a high-pressure balance used in primary standards. This is significant because the piston fall rate is an essential parameter to characterize experimentally the mean gap between the piston and the cylinder and to determine the effective area (A p) at each pressure (p) point. By improving the method used to estimate the piston fall rate it is possible to improve the determination of the gap, the effective area and consequently the pressure distortion coefficient. One possible cause of the lack of agreement between the calculated and measured piston fall rates could be inappropriate modelling of the fluid flow. In fact, the former quasi-1D Stokes model assimilates the gap between the piston and the cylinder as formed by two parallel walls, which is an approximation. In addition, the velocity of the piston wall was neglected. In order to evaluate the influence of this model, the equations of the fluid flow are modified and are presented in this paper. Equations that were defined in a parallel-plane model are defined in an annular gap model. In addition to this, corrections due to the velocity of the piston wall are inserted. This research work is applied on a Desgranges et Huot DH 7594 piston-cylinder unit of PTB with a pressure up to 1 GPa, in the continuity of the EUROMET project 463 in order to quantify the influence of each correction that has been inserted in the new equations. This is carried out using the FEM. This analysis will allow us to evaluate the improvement of our knowledge of the behaviour of piston gauges and consequently to better evaluate the uncertainties due to the models.Critical evaluation of three hemodynamic models for the numerical simulation of intra-stent flows
http://hdl.handle.net/10985/9961
Critical evaluation of three hemodynamic models for the numerical simulation of intra-stent flows
CHABI, Fatiha; CHAMPMARTIN, Stéphane; SARRAF, Christophe; NOGUERA, Ricardo
We evaluate here three hemodynamic models used for the numerical simulation of bare and stented artery flows. We focus on two flow features responsible for intra-stent restenosis: the wall shear stress and the re-circulation lengths around a stent. The studied models are the Poiseuille profile, the simplified pulsatile profile and the complete pulsatile profile based on the analysis of Womersley. The flow rate of blood in a human left coronary artery is considered to compute the velocity profiles. “Ansys Fluent 14.5” is used to solve the Navier–Stokes and continuity equations. As expected our results show that the Poiseuille profile is questionable to simulate the complex flow dynamics involved in intra-stent restenosis. Both pulsatile models give similar results close to the strut but diverge far from it. However, the computational time for the complete pulsatile model is five times that of the simplified pulsatile model. Considering the additional “cost” for the complete model, we recommend using the simplified pulsatile model for future intra-stent flow simulations.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/99612015-01-01T00:00:00ZCHABI, FatihaCHAMPMARTIN, StéphaneSARRAF, ChristopheNOGUERA, RicardoWe evaluate here three hemodynamic models used for the numerical simulation of bare and stented artery flows. We focus on two flow features responsible for intra-stent restenosis: the wall shear stress and the re-circulation lengths around a stent. The studied models are the Poiseuille profile, the simplified pulsatile profile and the complete pulsatile profile based on the analysis of Womersley. The flow rate of blood in a human left coronary artery is considered to compute the velocity profiles. “Ansys Fluent 14.5” is used to solve the Navier–Stokes and continuity equations. As expected our results show that the Poiseuille profile is questionable to simulate the complex flow dynamics involved in intra-stent restenosis. Both pulsatile models give similar results close to the strut but diverge far from it. However, the computational time for the complete pulsatile model is five times that of the simplified pulsatile model. Considering the additional “cost” for the complete model, we recommend using the simplified pulsatile model for future intra-stent flow simulations.Comparison of various hemodynamic models for applications to CFD in stent arteries
http://hdl.handle.net/10985/10255
Comparison of various hemodynamic models for applications to CFD in stent arteries
CHABI, Fatiha; CHAMPMARTIN, Stéphane; SARRAF, Christophe; NOGUERA, Ricardo; MAUREL, Blandine
This work assesses three hemodynamic models for the numerical modeling of intra-stent flows. These are the classical Poiseuille model (PM), the simplified pulsatile model (SPM) and the complete pulsatile model (CPM) based on the analysis of Womersley. They are applied to the physiological flow rate of a stented left coronary artery. The CFD package "Ansys Fluent 14.5" is used to compute the main features of the flows. The results show large differences between the steady and unsteady models notably for the wall shear stress and the re-circulation lengths, which are known to promote intra-stent restenosis. The PM is obviously not pertinent to calculate the flows involved in intra-stent restenosis. The CPM and SPM give close results but the latter model is by far less time-demanding and should be preferred.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/102552014-01-01T00:00:00ZCHABI, FatihaCHAMPMARTIN, StéphaneSARRAF, ChristopheNOGUERA, RicardoMAUREL, BlandineThis work assesses three hemodynamic models for the numerical modeling of intra-stent flows. These are the classical Poiseuille model (PM), the simplified pulsatile model (SPM) and the complete pulsatile model (CPM) based on the analysis of Womersley. They are applied to the physiological flow rate of a stented left coronary artery. The CFD package "Ansys Fluent 14.5" is used to compute the main features of the flows. The results show large differences between the steady and unsteady models notably for the wall shear stress and the re-circulation lengths, which are known to promote intra-stent restenosis. The PM is obviously not pertinent to calculate the flows involved in intra-stent restenosis. The CPM and SPM give close results but the latter model is by far less time-demanding and should be preferred.