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Seminar on Mechanical Science and Bioengineering
77th |
Date: Sep. 3, 2012 Time: 13:00 - 15:00 Place: Sigma Hall Seminar Room |
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| A capsule consists of some internal medium enclosed by a semi-permeable membrane that controls exchanges between the environment and the internal contents and has thus a protection role. Natural capsules are cells, bacteria, eggs or lipid vesicles. Artificial capsules are widely used in many industries such as pharmaceutical, cosmetic, food industries for controlled release of active principles, aromas or flavours. The mechanics of the capsule wall may be governed mostly by shear and area dilation forces (polymerized membrane of artificial capsules), by bending forces (constant area lipid bilayer of vesicles) or by shear and bending forces (red blood cell membrane). When a capsule is suspended into another flowing liquid, it is deformed by viscous fluid stresses that may cause break-up. Understanding this process is crucial for assessment of the membrane mechanical properties, artificial capsule design and burst control. The simplest capsule model consists of a liquid droplet enclosed by a very thin elastic membrane. Assuming the particle Reynolds number to be small, the capsule motion is due to inertialess interactions between the viscous flow of two liquids (inside and outside the capsule) and the large deformation of a thin membrane. It thus involves the solution of a complicated fluid-structure interaction problem. The fluid equations can be solved with different techniques (e.g., immersed boundaries, boundary integrals). The main challenge is to model properly a solid deformable membrane that has a non-linear constitutive law and that undergoes large displacements and deformations. Some classical modeling procedures will be presented and discussed for the motion and deformation of different types of capsules in shear flow. A new model that couples a boundary integral solution for the fluids and a finite element approach for the wall will be presented and discussed. It will be shown how this model allows to capture the motion and deformation of artificial capsules, vesicles or cells in different flows such as unbounded shear flow or confined pore flow. | |
Prof. Dominique Barth`es-Biesel Universit´e de Technologie de Compi`egne Biom´ecanique et Bioing´enierie UMR CNRS 7338 |
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75th |
Date: May 28, 2012 Time: 15:50 - 17:00 Place: Sigma Hall Seminar Room |
| Human unvoiced sibilant fricative [s] speech production involves the noise produced by a complex fluid-structure interaction between a moderate Reynolds number turbulent jet (100 < Re < 10000) issued from a constriction somewhere in the vocal tract and incisors. To contribute to the physical study of sibilant fricative speech production, two types of simplified in-vitro tooth-shaped (single and dual) obstacle replicas are experimentally investigated. Acoustic measurements of the noise emitted by an airflow passing through each of the two replicas are performed at several moderate Reynolds numbers relevant to fricative production. Several geometric parameters of the two replicas, as well as inlet and outlet conditions, are varied in order to study their influence on the produced sound. In addition to the in-vitro study, the current work at Wada-lab is to simulate some of the experimentally tested configurations and to compare numerical results to corresponding measurements. | |
Dr. Yo Fujiso GIPSA-lab, Grenoble University Grenoble, France |
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74th |
Date: May 28, 2012 Time: 14:40 - 15:50 Place: Sigma Hall Seminar Room |
| The acoustic radiation force (RF) is, in general, defined as period-averaged action of sound wave on the medium. The concept of “radiation pressure” in acoustics was developed since early 20th century by many outstanding physicists including Rayleigh, Bjerknes, Brillouin, and Langevin. In the recent years, a new field of biomedical ultrasound applications based on the use of the RF has emerged. In particular, nonlinear methods based on using RF in medical diagnostics and imaging of tissues have been developed. One of such methods uses the radiation force created by focused ultrasound that induces highly localized shear displacements, which can be visualized by ultrasonic or MRI methods in order to obtain an image of the investigated tissue including that with lesions and tumors. Another group of methods is the use of ultrasonic waves in resonators for mixing and stirring, and manipulating particles and bubbles in small volumes of fluid. A new, promising area of application is detection, monitoring, and concentrating very small (micron-range) particles, such as somatic cells and bacteria, in standing ultrasonic waves. The cylindrical standing wave system performance was tested for the E.coli bacteria in water and for a multi-component system containing fat globules and somatic cells in milk. In this presentation we discuss selected theoretical and experimental problems associated with RF in fluids and tissues, as well as possible applications. | |
Prof. L. A. Ostrovsky Zel Technologies and the University of Colorado, Boulder, Colorado, USA |
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73th |
Date: May 21, 2012 Time: 15:00 - 15:50 Place: Seminar Room D404-408 |
| The determination of the parameters in constitutive model of bird material in bird strike simulation In general case, three kinds of constitutive model equations that are used to simulate the bird: Elastic Plastic constitutive model with failure, the Isotropic Elastic Plastic Hydrodynamic solid, and the Murnaghan Equation of State for Solid Element. However, the parameters for these constitutive equations are difficult to choose from different sources in numerical simulation. In the present representation, the experiments of bird impact on a plate perpendicularly at the velocity of 70m/s, 120m/s and 170m/s were performed respectively. The displacements, strains of the plate as well as the reaction force were measured. The smooth particles Hydrodynamic (SPH) combing the finite element method were used to model the bird impacting on a plate with the fixture of the experiments using PAM-CRASH. The dynamic response of the plate such as displacements, strain and the reaction force of the fixture were calculated corresponding to the experiment. The measured strains and maximum displacements of the plate are used to deduce constitutive model parameters of the bird using optimization inversion methods performed in integrated environmental software iSIGHT. |
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Dr. Jun Liu and Dr. Yulong Li Department of Aircraft Engineering, Northwestern Polytechnical University, Xi’an 710072, China |
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72th |
Date: May 21, 2012 Time: 14:00 - 14:50 Place: Seminar Room D404-408 |
| Temperature and strain rate sensitivities of ultrafine-grained copper under uniaxial compression As ultrafine-grained (UFG) materials with grain size in the range of tens to several hundreds of nanometer show many unique mechanical and physical properties, their mechanical properties have attracted considerable attention in recent years. It is widely accepted that plastic deformation of metals is a thermally activated process which always depends on both strain rate and temperature. Thus, investigations on the strain rate and temperature dependence of mechanical properties of ultrafine-grained (UFG) materials are essential to extend our understanding on these unusual solids. In this work, uniaxial compressive experiments of ultrafine-grained copper fabricated by equal channel angular pressing method were performed at temperatures ranging from 77 to 573K under quasi-static and dynamic loading conditions. Based on the experimental results, the influence of temperature on flow stress, strain hardening rate and strain rate sensitivity were investigated carefully. |
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Dr. Tao Suo, Dr. Yulong Li, and Dr. Feng Zhao School of Aeronautics, Northwestern Polytechnical University, Xi’an 710072, China |
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70th |
Date: Nov. 21, 2011 Time: 14:40 - 16:10 Place: Seminar Room D404-408 |
| In plane Couette flow (PCF), the transition to turbulence is characterized by a whole range [R_g,R_t] of Reynolds number where laminar and turbulent flow coexist in the form of alternating oblique bands. R_g is the global stability threshold below which laminar flow prevails in the long time limit, while above R_t turbulence is essentially space-filling. We report on the dynamics of PCF around R_g, studied using direct numerical simulations in systems extended enough for several bands to exist. We consider both how the bands break and decay as R is decreased slightly below R_g and how they grow out of a localized turbulent germ slightly above R_g. Decay involves a two-stage process involving the rupture of a band and next its slow shrinking. Growth is complicated by the fact that two orientations are permitted by the general symmetries of PCF. All these processes are attributed to the transient nature of chaos taking place at the scale of the Minimal Flow Unit in the range of R of interest, which generates a local stochastic process. Band opening during decay as well as nucleation of turbulent buds during growth are proposed to result from large deviations (rare events) depending sensitively on R. | |
Dr. Paul Manneville Laboratoire d'Hydrodynamique, Ecole Polytechnique |
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68th |
Date: Nov. 15, 2011 Time: 14:40 - 16:10 Place: B204 |
| Inertial particles in turbulence: preferential concentration Turbulent flows laden with inertial particles occur in many industrial and environmental situations (pollutant dispersion, plankton, engine optimization…). During the last forty years, many properties of these flows have been evidenced, nevertheless, a model equation describing them is still out of reach, particularly regarding the back reaction of the particles on the carrier fluid or regarding the possible collective effects on the particles dynamics. We show experimental results on the strong heterogeneities appearing in the concentration fields and try to identify possible collective effects leading to the existence of clusters that can live for times long compared to the large turbulent scales. We also review the various tools used to evidence and quantify preferential concentration. |
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Dr. Romain Monchaux ENSTA-ParisTech |
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67th |
Date: Nov. 11, 2011 Time: 14:40 - 16:10 Place: Seminar room C419-423 |
| Laminar-turbulent patterns in plane shear flows In this talk we will focus on the large-scale laminar-turbulent patterns found at the onset of transition towards sustained turbulence in subcritical plane shear flows such as plane Couette flow and plane Poiseuille flow. Using high-performance computing we will demonstrate how this onset of turbulence can be delayed to larger values of the Reynolds number in the presence of stabilising forces such as rotation, stratification or Lorenz forces. The fate of these laminar-turbulent patterns in the high-Re case will be discussed. |
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Dr. Yohann Duguet Laboratoire d'Informatique pour la Mecanique et les Sciences de l'Ingenieur, CNRS |
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66th |
Date: Nov. 11, 2011 Time: 13:00 - 14:30 Place: A403 |
| Functional imaging using positron emission tomography - Engineered approaches toward clinical apprications - Positron emission tomography (PET) can visualize various functionalities such as a regional metabolic rate of glucose and a density of neuroreceptors. For fully quantitative imaging, however, a behavior of administered radiopharmaceutical in tissues should be considered, and a model based analysis is utilized. In this lecture, some engineered approaches are introduced with showing clinical PET images. |
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Dr. Yuichi KIMURA National Institute of Radiological Sciences |
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65th |
Date: Nov. 7, 2011 Time: 10:30 - 12:00 Place: A403 |
| Vortex Flows in the Wake of a Blunt Trailing Edge Periodic vortex shedding, also known as Karman vortex shedding, is a common phenomenon that occurs in the wake of a nominally two dimensional blunt trailing edge due to interaction between two separated shears layers from opposite sides. We have employed numerous methods, both active and passive, to suppress this alternate vortex shedding in order to alleviate its detrimental effects such as high form drag, flow induced vibration and noise. In active control method, one of the shear layers at the trailing edge of a blunt based aerofoil was either sucked in or tangentially blown just before the separation. With increasing strength of the suction and blowing, a complete suppression of the vortex shedding could be achieved. The efficacy of the blowing technique was further improved significantly by making it from steady to pulsating. The pulsating blowing was applied in open-loop mode with two control parameters ? blowing strength and pulsating frequency. For the frequency of blowing being twice the unforced vortex shedding frequency and the active phase of the cycle being just 20%, not only a complete suppression of the vortex shedding was achieved but also the wake was found to gain momentum. In passive control method, the spanwise vortex dislocation was introduced by certain geometric cutouts provided at the model trailing edge. The serration shapes were found to introduce strong streamwise vortices in pairs of either co-rotating or contra-rotating by choice. The regular vortex shedding was effectively suppressed resulting in about 34% reduction in the form drag. Moreover, the pairs of contra-rotating vortices were found to generate lift even at zero angle of incidence due to wake vectoring (downwash) effect. |
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Dr. S.D. Sharma Professor and Head, Aerospace Engineering Department, Indian Institutes of Technology, Bombay, INDIA |
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42nd |
Date: Jul. 3, 2009 Time: 14:40 - 16:10 Place: Seminar room D404-408 |
| Computing unstable manifolds in turbulent shear flow with multiple shooting | |
Prof. Lennaert van Veen Faculty of Arts and Science, |
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41st |
Date: Feb. 27, 2009 Time: 15:00 - 16:00 Place: Seminar room of Bioengineering (J_3F) |
| Sudies on bone biomechanics and hip fracture risk | |
Prof. Timo Jamsa Department of Medical Technology |
