Publications

This study investigated the validity of using OpenSim to measure muscle-tendon unit (MTU) length of the bi-articular lower limb muscles in several postures (shortened, lengthened, a combination of shortened and lengthened involving both joints, neutral and standing) using 3D freehand ultrasound (US), and to propose new personalized models. MTU length was measured on 14 participants and 6 bi-articular muscles (semimembranosus SM, semitendinosus ST, biceps femoris BF, rectus femoris RF, gastrocnemius medialis GM and gastrocnemius lateralis GL), considering 5 to 6 postures. MTU length was computed using OpenSim with three different models: OS (the generic OpenSim scaled model), OS + INSER (OS with personalized 3D US MTU insertions), OS + INSER+ PATH (OS with personalized 3D US MTU insertions and path obtained from one posture). Significant differences in MTU length were found between OS and 3D US models for RF, GM and GL (from − 6.3 to 10.9%). Non-significant effects were reported for the hamstrings, notably for the ST (− 1.5%) and BF (− 1.9%), while the SM just crossed the alpha level (− 3.4%, p = 0.049). The OS+ INSER model reduced the magnitude of bias by an average of 4% for RF, GM and GL. The OS + INSER+ PATH model showed the smallest biases in length estimates, which made them negligible and non-significant for all the MTU (i.e. ≤ 2.2%). A 3D US pipeline was developed and validated to estimate the MTU length from a limited number of measurements. This opens up new perspectives for personalizing musculoskeletal models using low-cost user-friendly devices.

Background/Objectives: The aim of this study was to evaluate changes in trunk height and variations in spino-pelvic parameters during trunk self-elongation. Two populations were studied: non-athletes and gymnasts, who differ in their engagement with core-strengthening exercises. Methods: EOS biplanar radiographs were taken on 14 non-athletes and 24 gymnasts in both neutral and trunk self-elongation positions. Three-dimensional reconstructions of the pelvis and spine were used to calculate effective trunk height, thoracic and lumbar contributions, and spino-pelvic parameters. Results: Trunk self-elongation resulted in a significant increase in trunk height for both groups (7 mm on average, range: −1 to 14 mm), accompanied by a reduction in thoracic kyphosis for all participants (−10° for non-athletes and −17° for gymnasts, on average) and a reduction in lumbar lordosis in most participants (−5° for non-athletes and −7° for gymnasts, on average). However, some individuals in both groups exhibited an increase in lumbar lordosis, which reduced the contribution of the lumbar region to overall trunk height. Conclusions: Trunk self-elongation instruction effectively increases trunk height, but additional instructions, such as pelvic retroversion, may enhance its effectiveness.

The simulation of the sand gravity casting process is complicated due to its multiscale and multiphysics nature. Although there are many commercial software options available, it remains extremely difficult to accurately predict the filling, solidification, and defects such as oxidation. Smoothed particle hydrodynamics (SPH) is a Lagrangian simulation approach that is particularly well-suited for modeling the gravity casting process. To validate the results of the filling, cooling, and solidification steps of the SPH method, it is interesting to introduce and design a 3D universal experimental test case of the gravity casting process that can be modeled in 2D. This universal test case is developed so that the hydrodynamic filling process can be analyzed in 2D while the cooling and solidification processes can be investigated in 1D. After comparing ProCAST, a commercial 3D mesh-based software, with the 2D SPH method, the results highlight the unique advantages of each approach in analyzing filling step and temperature evolution. The SPH simulations are better at capturing the essential aspects of fluid motion.

Background: Transmission of loads between the prosthetic socket and the residual limb is critical for the comfort and walking ability of people with transfemoral amputation. This transmission is mainly determined by the socket tightening, muscle forces, and socket ischial support. However, numerical investigations of the amputated gait, using modeling approaches such as MusculoSkeletal (MSK) modeling, ignore the weight-bearing role of the ischial support. This simplification may lead to errors in the muscle force estimation. Objective: This study aims to propose a MSK model of the amputated gait that accounts for the interaction between the body and the ischial support for the estimation of the muscle forces of 13 subjects with unilateral transfemoral amputation. Methods: Contrary to previous studies on the amputated gait which ignored the interaction with the ischial support, here, the contact on the ischial support was included in the external loads acting on the pelvis in a MSK model of the amputated gait. Results: Including the ischial support induced an increase in the activity of the main abductor muscles, while adductor muscles' activity was reduced. These results suggest that neglecting the interaction with the ischial support leads to erroneous muscle force distribution considering the gait of people with transfemoral amputation. Although subjects with various bone geometries, particularly femur lengths, were included in the study, similar results were obtained for all subjects. Conclusions: Eventually, the estimation of muscle forces from MSK models could be used in combination with finite element models to provide quantitative data for the design of prosthetic sockets.

Cross-Flow Fans (CFFs) have been widely applied in the automotive and domestic air conditioning industries in recent decades. They are high-pressure coefficient turbomachines compacted diametrically, and thus, the complex interactions of these fans require thorough evaluation. Their innovation has opened up new directions in turbomachinery, and both academic research and industry have seen numerous efforts to develop these types of fans. Despite extensive work, optimizing and improving their performance remains a challenge. Enhancing their efficiency necessitates improvements in structural characteristics, aerodynamic features, and acoustic properties. In this review, we aim to demonstrate the essential aspects of CFFs by introducing their fundamentals and primary characteristics. Furthermore, we delve into a discussion on the acoustic performance of these fans. We also summarize the flow characteristics and different flow-field patterns in CFFs and their impact on aeroacoustic behavior. The main objective of this review paper is to provide an overview of the research in this field, summarizing the critical factors that play a significant role in studying CFFs’ performance.

This article provides a comprehensive investigation into the resin-bonded sand gravity casting process, with a focus on the filling, cooling, and solidification steps. The research combines numerical simulations and experimental validation in a three-dimensional (3D) configuration, utilizing a realistic filling system. The study employs three approaches—experimental tests, Smoothed Particle Hydrodynamics (SPH) simulations, and ProCAST simulations—to analyze the filling, cooling, and solidification steps. Two different molds were used in the experiments. The first mold has a transparent glass component in front of the plate, enabling observation and recording of the filling process, while the second mold, used solely for thermal analysis, did not incorporate any glass component. The SPH approach yields more accurate results for the filling time, liquid level height, and morphology when compared to ProCAST. The discrepancy in final filling time for the desired casting part between the experiment and SPH is 5.13 %, and the difference between the experiment and ProCAST is 15.38 %. Additionally, the cooling and solidification steps are investigated through an analysis of cooling curves. The numerical methods demonstrate slightly higher cooling rates and deviations in solidification times compared to the experimental data, mainly due to the thermal Neumann boundary condition. Furthermore, the average discrepancy in solidification time for five points of the intended casting component between the experiment and SPH is 8.60 %, whereas when compared with ProCAST, the discrepancy increases to 9.13 %.

Efficient chaotic microdevices have major importance across many potential applications in industrial processes and operations, which form essential parts of microfluidic devices. In microfluidics, The Two-Layer Crossing Channels Micromixer (TLCCM) exhibits notable characteristics in terms of mixing of Newtonian fluids which motivated us to compare it with other micromixers using pseudoplastic fluids. The examined micromixers are: L-Shape, OH, and OX. CFD code is utilized to numerically solve Navier-Stokes, the mass conservation and species transport equations. Therefore, the species transport model was selected to analyze the mixing process. The pseudoplastic fluids consist of carboxymethyl cellulose (CMC) solutions, which are characterized using the power-law model, the flow behavior index ranging from 0.49 to 1 and generalized Reynolds number (Reg) varies from 0.2 to 70. The effectiveness of mixing was assessed through the mixing degree across various cross-sectional areas. To address this, the analysis encompassed mass fraction contours, velocity profiles, streamlines, flow rates, and the associated mixing energy costs. Our findings report that the TLCCM micromixer presents the elevated mixing degree, where their obtained values vary between 0.80526 and 0.99765. It appears that the occurrence of secondary flows has an additional benefit to improve the mixing performances. Moreover, it requires less mixing energy costs versus other micromixers, where their values vary between 0.00036 and 0.49 W.

Given the small wavelengths and wide range of frequencies of the acoustic waves involved in Aeroacoustics problems, the use of very accurate, low-dissipative numerical schemes is the only valid option to accurately capture these phenomena. However, as the order of the scheme increases, the computational time also increases. In this work, we propose a new high-order flux reconstruction in the framework of finite volume (FV) schemes for linear problems. In particular, it is applied to solve the Linearized Euler Equations, which are widely used in the field of Computational Aeroacoustics. This new reconstruction is very efficient and well suited in the context of very high-order FV schemes, where the computation of high-order flux integrals are needed at cell edges/faces. Different benchmark test cases are carried out to analyze the accuracy and the efficiency of the proposed flux reconstruction. The proposed methodology preserves the accuracy while the computational time relatively reduces drastically as the order increases.

In gas turbines, the stator wells play a key role in the efficiency of the turbomachine. The research for performance gains requires a good understanding and an accurate modeling of the flows and heat transfers occurring in these areas. Within the framework of the European program main annulus gas path interaction (MAGPI) WP1, a two-stage axial turbine test rig provided an experimental database used to validate the computational fluid dynamics (CFD) models. The aim of this study is to setup a numerical methodology using the CFD solver ANSYSFluent to accurately predict the conjugate heat transfer in the stator well area. The validation of the methodology relies on thorough comparison of the results with the MAGPI WP1 experimental temperature/pressure measurements. A geometry with axial cooling injection through lock plate slot was chosen. A Reynolds-averaged Navier–Stokes (RANS) three-dimensional sectorized CFD model of the turbine with conjugate heat transfer was used. It includes main gas path, cavities with labyrinths, disks rotor, the casing, and the nozzle guide vanes (NGV). Mixing planes are placed between the static and rotating frames. Different influences (mesh, turbulence model, thermal boundary conditions, radial labyrinths clearances) were studied and compared with experimental data. As a baseline, the first calculations were performed with a cooling flowrate chosen so that hot gas ingresses from the main stream into the stator well cavity. Good agreements between predicted and measured temperatures/pressures were observed, especially in the vicinity of the stator well. Discrepancies were spotted at the first rotor hub endwall and at the upstream wheelspace and will be discussed. Two other cooling configurations were conducted, one with cooling air exiting from the disk rim cavity to the main gas path and the other with the lowest cooling flowrate and so the highest ingress. Finally, the turbine performance under nonadiabatic conditions has been evaluated with an appropriate efficiency definition.

In this study, advanced design technique has been introduced to determine the radial local chord distribution on the rotor blades of Horizontal Axis Wind Turbines (HAWT) based on an inverse Computational Fluid Dynamics (CFD) actuator disk method combined with linearization of both the chord and twist distributions. The overarching goal was to refine HAWT rotor blade design for enhanced aerodynamic performance. The proposed design methodology, embedded into a custom axisymmetric CFD subroutine based on the actuator disk model in OpenFOAM, incorporates key aerodynamic factors such as turbulence, viscosity, and both two-dimensional and three-dimensional flow field properties. Results from this innovative approach indicate that rotor models crafted using our algorithm significantly outperform those based on traditional theories in terms of efficiency and consistency. Comprehensive aerodynamic analyses focusing on the power coefficient and annual energy production (AEP) across various incoming free stream velocities show that the optimized model improves power coefficient by up to 70% and AEP by 17.64% compared to the baseline model. Additionally, the optimized model demonstrates a 15% reduction in velocity deficit, enhancing the potential for optimizing wind farm layouts.