Towards the modeling of mucus draining from human lung: role of airways deformation on air-mucus interaction

Chest physiotherapy is an empirical technique used to help secretions to get out of the lung whenever stagnation occurs. Although commonly used, little is known about the inner mechanisms of chest physiotherapy and controversies about its use are coming out regularly. Thus, a scientific validation of chest physiotherapy is needed to evaluate its effects on secretions. We setup a quasi-static numerical model of chest physiotherapy based on thorax and lung physiology and on their respective biophysics. We modeled the lung with an idealized deformable symmetric bifurcating tree. Bronchi and their inner fluids mechanics are assumed axisymmetric. Static data from the literature is used to build a model for the lung's mechanics. Secretions motion is the consequence of the shear constraints apply by the air flow. The input of the model is the pressure on the chest wall at each time, and the output is the bronchi geometry and air and secretions properties. In the limit of our model, we mimicked manual and mechanical chest physiotherapy techniques. We show that for secretions to move, air flow has to be high enough to overcome secretion resistance to motion. Moreover, the higher the pressure or the quicker it is applied, the higher is the air flow and thus the mobilization of secretions. However, pressures too high are efficient up to a point where airways compressions prevents air flow to increases any further. Generally, the first effects of manipulations is a decrease of the airway tree hydrodynamic resistance, thus improving ventilation even if secretions do not get out of the lungs. Also, some secretions might be pushed deeper into the lungs; this effect is stronger for high pressures and for mechanical chest physiotherapy. Finally, we propose and tested two adimensional numbers that depend on lung properties and that allow to measure the efficiency and comfort of a manipulation

Modélisation de l’interaction air/mucus dans l’arbre bronchique. Volume pulmonaire vs débit d’air : contraintes de cisaillement dans l’arbre bronchique

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Definition and calculation of single turn coils’ electrical, magnetic and electro-mechanical parameters for pulsed magnetic technologies with the finite element method and experiments

This paper proposes to compute the electrical behavior, including electromagnetic and electromechanical parameters, of a single-turn toroidal coil which is fed by a transient pseudo-harmonic current pulse at low or medium frequency. Solutions adapted to the specificity of the pulsed high magnetic fields technology are given, including original performance characteristics, independent on the current source, but still taking eddy currents and the skin effect into account. The finite element analysis is carried out progressively; first with time harmonics, then in the transient working condition, and finally by coupling the electromagnetic calculations to the equivalent electrical circuit of the coil. The aim of this study is to first evaluate the accuracy of a 2D axi-symmetrical numerical model by comparing it to 3D reference calculations. The reliability is valued according to measurements. The method then makes it possible to very quickly compute the main interesting coils characteristics, namely the equivalent resistance, inductance, maximum induction coefficient and finally the self and mutual force coefficients. These last new parameters are also defined in the present paper and provide important performance criteria. Finally, a sensitivity analysis will be performed to understand the impact of the main usual parameters (frequency, coil length, coil radius, airgap, electrical conductivity). The 2D model allows to save time and to build an approximate but reliable solution that might make either the transient calculation or the coupling with electrical, mechanical and thermal physics easier. After an introduction (part 2), part 3 gives the model geometry, physics and meshing. Magneto-harmonic calculations of fields and coils’ parameters and a complete sensitivity analysis are performed in part 4. Transient computations are carried out on a single-turn coil made of steel without a field-shaper and are compared to experimental results in parts 5. Finally, an innovative single-turn coil with a field-shaper, both made of a non-standard copper alloy (siclanic®), has been also calculated, tested and measured in part 6. To conclude, the 2D model provides the main interesting intrinsic coil’s characteristics and a fast sensitivity analysis as a function of several parameters, such as the pulse natural frequency. These parameters are needed to couple the electromagnetic process to an electrical circuit or a mechanical workpiece deformation. The present study can estimate if, in given conditions, the forming coil can ensure electromagnetic forces high enough either to initiate the process or to end it with an assembling static pressure

Analytical design model of coil parameters for the electro-magnetic forming technology - Case of the 1-turn coil dedicated to tubular parts forming and crimping with 1D approximation

International audienceIn this paper, we propose an analytical electromagnetic modelling and an electromechanical coupling of the 1-turn bulk coil with a cut, made of conducting steel or copper alloys, and used in the electro-magnetic forming technology. The electromagnetic part of the work is the one created beyond the state of the art. Such analytical models that can quickly solve for key process parameters are extremely desirable but must be completed with a mechanical model able to calculate in the end the deformation. An existing mechanical model to calculate the deformation is used and coupled to our electromagnetic model. First, the basic electromagnetic theory will be summarised and then the One-Dimensional (1-D) axi-symmetrical approximation discussed (part 2). The goal is to be able to determine the magnetic vector potential A diffusion, that will quickly lead to all the parameters needed to characterize, qualify, feed and optimize the use of the coil (ex.: magnetic flux density, equivalent inductance, force coefficients,...). Then the pseudo-harmonic solution of the 1D-problem is expanded with the help of Bessel basis functions, including some specific limit conditions and constraints (part 3). The results are compared to numerical 2-D and 3-D computations, performed, thanks to the Finite Element Method, onto some test cases without and with a tube to deform. The proposed model does not only give the numerical value of each parameter, but it provides analytical formulae, with explicit dependences upon some key geometrical and physical variables (ex.: changeable air-gap between the coil and the tube linked to the deformation). The use of a pseudo harmonic working condition will be justified by comparing it to the transient working condition for which the model is improved. Experimental measurements will be carried out with and without a tube but with no deformation (part 4). The results are close and coherent and useful when sizing the coil with respect to performance criteria and performing an equivalent electrical circuit and an electro-mechanical coupling solution, usable with deformation in the transient working conditions (part 5)