Critical Evaluation of Resistive Force Theory using a Machine Learning Assisted Model

The hydrodynamic forces on a slender rod in a fluid medium at low Reynolds number can be modeled using resistive force theories (RFTs) or slender body theories (SBTs). The former represent the forces by local drag coefficients and are computationally cheap; however, they are physically inaccurate when long-range hydrodynamic interaction is involved. The later are physically accurate but require solving integral equations and, therefore, are computationally expensive. This paper investigates RFTs in comparison with state-of-the art SBT methods. During the process, a neural network-based hydrodynamic model that -- similar to RFTs -- relies on local drag coefficients for computational efficiency was developed. However, the network is trained using data from an SBT (regularized stokeslet segments method).The $R^2$ value of the trained coefficients were $\sim 0.99$ with mean absolute error of $1.6\times10^{-2}$. The machine learning resistive force theory (MLRFT) accounts for local hydrodynamic forces distribution, the dependence on rotational and translational speeds and directions, and geometric parameters of the slender object. We show that, when classical RFT fails to accurately predict the forces, torques, and drags on slender rods under low Reynolds number flows, MLRFT exhibits good agreement with physically accurate SBT simulations. In terms of computational speed, MLRFT forgoes the need of solving an inverse problem and, therefore, requires negligible computation time in comparison with SBT. MLRFT presents a computationally inexpensive hydrodynamic model for flagellar propulsion can be used in the design and optimization of biomimetic flagellated robots and analysis of bacterial locomotion.Comment: 9 pages, 10 figure

Coupled radiative and convective heat losses from preterm infant inside an incubator with radiant heaters

Preterm infants face difficulties in maintaining their body temperature due to low metabolic rates of heat generation. Therefore, using incubators and radiant warmers is crucial for their comfort and health. The objective of the present work is to analyze the heat transfer processes for a preterm infant nursed in a simplified incubator under two different operating conditions: in the first one a classical simple incubator is considered and in the second case radiant heaters are used. This is achieved by using ANSYS Fluent 19.0 which his based on the finite volume method to discretize the Navier-Stokes, energy and radiation transfer equations. Conduction, convection and radiation heat transfer modes are modelled in the simulations and coupled to empirical correlations for metabolic heat generation and evaporative heat losses. The different incubator scenarios considered here are compared in terms of convection and radiation heat losses and skin temperature to access the thermal comfort of the preterm infant

Recueil des actes de la 12ème conférence sur les vibrations induites par un écoulement.

Paris-Saclay 5-8 July 2022International audienceFlow-Induced Vibration remains a challenge for design engineers and operators acrossmultiple industries, including vehicle manufacturing and power production, among manyothers. Despite decades of research and development, there is still much to be learned inthis domain. Specific areas warrant special attentions, such as fluid-elastic instability oftube bundles, multiphase flows and their effects on flexible structures, vortex shedding intheir many manifestations, and the intricacies of axial flow instabilities. Even seeminglysimple scenarios, like a single cylinder in crossflow, continue to intrigue researchers,leading to the publication of new scientific articles

Conception et dimensionnement d’un échangeur-réacteur PCHE innovant - Rapport d'étape

SF

Mixing enhancement in a novel type of "Split And Recombine" static mixer

International audienceMixing in laminar flow regimes is crucial for many engineering applications in which highly viscous and fragile fluids are used. Moreover, the compactness of laminar mixers is a great challenge due to the large mixing time required to obtain the desired homogeneity. The "Split And Recombine" (SAR) static mixers are a promising solution for this challenge. This type of mixers consists of a network of separated and then recombined channels in which two fluids are introduced separately and mixed by a multi-lamination process. The SAR static mixers perform a series of baker's transforms on the concentration profile enhancing thus the mixing process at very low Reynolds numbers. In the present study, numerical simulations are carried out to analyze the mixing process in a new topology of SAR mixer with double separation and recombination in order to increase the lateral gradients and destroy the concentration profile faster. The new geometry proposed here is compared to two SAR configurations widely studied in the open literature namely the Gray and the Chen SAR configurations. The results show a good enhancement of the mixing process in the new double SAR configuration with decrease in the power dissipation. INTRODUCTION Efficient mixing remains a challenging process in many engineering applications such as food processing

Conception et dimensionnement d’un échangeur-réacteur PCHE innovant - Rapport d'étape

SF

Design of a Hybrid Photovoltaic Thermal System in Lebanon

Due to global warming and the high toxic gas emissions of traditional power generation methods, renewable energy has become a very active topic in many applications. This study focuses on one versatile type of solar energy: Hybrid Photovoltaic Thermal System (hybrid PV/T). Hybrid PV/T combines both PV and thermal application and by doing this the efficiency of the system will increase by taking advantage of the temperature loss from PV module. The solar radiation and heat will be harnessed to deliver electricity and hot water simultaneously. In the present study a solar system is designed to recycle the heat and improve the temperature loss from PV module in order to supply both electricity and domestic hot water. The project was tested twice in Zouk Mosbeh - Lebanon; on May 18, 2016, and June 7, 2016. The average electrical efficiency was around 11.5% with an average electrical power output of 174.22 W, while with cooling, the average electrical efficiency reaches 11% with a power output of 200 W. The temperature increases by about 7 degrees Celsius from the inlet. The 1D conduction model is also performed in order to design the hybrid PV/T system

Numerical evaluation of the convective and radiative heat transfer coefficients for preterm neonate body segments inside an incubator

International audienc

Hygrothermal Comfort of Neonates Nursed inside Incubators

National audienc