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Wonkyu Moon - One of the best experts on this subject based on the ideXlab platform.

  • a piezoelectric micro cantilever bio sensor using the Mass micro balancing technique with self excitation
    2007
    Co-Authors: Yeolho Lee, Geunbae Lim, Wonkyu Moon
    Abstract:

    A biosensor was developed for using in a Lab-On-a-Chip (LOC). The sensor detects the change in the resonance frequency of a micro-cantilever with a piezoelectric film. This is the Mass micro-balancing technique, which has been successfully used for detecting bio-materials in the quartz crystal microbalance (QCM). The PZT film, a piezoelectric film, is designed to act as both sensor and actuator. The geometry of the micro cantilever is optimized to maximize the sensitivity and minimize the environmental Effects such as viscous damping and Added Mass Effect in liquid. The fabricated sensor is composed of a 100 μm long, 30 μm wide, and 5 μm thick cantilever with a 2.5 μm thick piezoelectric (PZT) layer on it. The ratio of thickness to length of the micro cantilever is very high compared to others in micro cantilever-based studies. This high aspect ratio is the key to maximize the sensitivity and minimize the environmental Effects. The fabricated micro sensor was tested by detecting the mussel gluing protein, the insulin-anti insulin binding protein and the poly T-sequence DNA.

  • a self excited micro cantilever biosensor actuated by pzt using the Mass micro balancing technique
    2006
    Co-Authors: Yeolho Lee, Geunbae Lim, Wonkyu Moon
    Abstract:

    A micro biosensor, which can be applied to a Lab-On-a-Chip (LOC), is developed in order to detect biomaterials such as protein or DNA. The biomaterials are detected by Mass micro-balancing technique, which measures the change of the resonant frequency of the sensor structure. The sensor structure consists of a micro cantilever actuated by piezoelectric PZT film. The PZT film is designed to act as both a sensor and an actuator. The geometry of the micro cantilever is determined so as to maximize the sensitivity of the sensor, and environmental Effects such as Added Mass Effect in liquid are also considered in the structural analysis. The micro cantilever is 100 μm in length, 30 μm in width and 5 μm in thickness, and the PZT film thickness and length are 2.5 and 50 μm, respectively. The first resonant frequency of the PZT micro cantilever is 1.2 ∼ 1.3 MHz. Lastly the fabricated micro-biosensor using the self-excited PZT-micro cantilever is tested by detecting the human insulin-anti human insulin binding protein, the poly T-sequence DNA, the K20-Thiol DNA and the K40-Thiol DNA in air.

  • A piezoelectric micro-cantilever bio-sensor using the Mass-micro-balancing technique with self-excitation
    2005
    Co-Authors: Wonkyu Moon
    Abstract:

    A micro biosensor, which can be applied to a lab-on-a-chip (LOC), is developed in order to detect biomaterials such as protein or DNA. The biomaterials are detected by the Mass micro-balancing technique, which measures the change of the resonant frequency of the sensor structure. The sensor structure consists of a micro cantilever actuated by piezoelectric PZT film. The PZT film is designed to act as both a sensor and an actuator. The geometry of the micro-cantilever is determined so as to maximize the sensitivity of the sensor, and environmental Effects such as Added Mass Effect in liquid are also considered in the design procedure. The microcantilever is 100 /spl mu/m in length, 30 /spl mu/m in width and 5 /spl mu/m in thickness, and the PZT film thickness is 2.5 /spl mu/m. The first resonant frequency of the PZT-micro cantilever is 1.2/spl sim/1.3 MHz. Lastly, the fabricated micro biosensor using the self-exciting PZT-micro cantilever is tested by detecting the insulin-anti insulin binding protein and poly T-sequence DNA.

Miguel A. Fernández - One of the best experts on this subject based on the ideXlab platform.

  • Incremental displacement-correction schemes for incompressible fluid-structure interaction
    2013
    Co-Authors: Miguel A. Fernández
    Abstract:

    In this paper we introduce a class of incremental displacement-correction schemes for the explicit coupling of a thin-structure with an incompressible fluid. These methods enforce a specific Robin–Neumann explicit treatment of the interface coupling. We provide a general stability and convergence analysis that covers both the incremental and the non-incremental variants. Their stability properties are independent of the Added-Mass Effect. The superior accuracy of the incremental schemes (with respect to the original non-incremental variant) is highlighted by the error estimates, and then confirmed in a benchmark by numerical experiments.

  • stabilization of explicit coupling in fluid structure interaction involving fluid incompressibility
    2009
    Co-Authors: Erik Burman, Miguel A. Fernández
    Abstract:

    Abstract In this work, we propose a stabilized explicit coupling scheme for fluid–structure interaction problems involving a viscous incompressible fluid. The coupled discrete formulation is based on Nitsche’s method with a time penalty term giving L 2 -control on the fluid pressure variations at the interface. For a linear model problem, we prove that the scheme is stable, in the energy norm, irrespectively of the so-called Added-Mass Effect, namely, the fluid–structure density ratio and the geometry of the domain. Numerical experiments, in the linear and non-linear case, show that optimal time accuracy can be obtained by performing one defect-correction iteration.

  • a projection algorithm for fluid structure interaction problems with strong Added Mass Effect
    2006
    Co-Authors: Miguel A. Fernández, Jean-Frédéric Gerbeau, Céline Grandmont
    Abstract:

    Abstract This Note aims at introducing a semi-implicit coupling scheme for fluid–structure interaction problems with a strong Added-Mass Effect. Our main idea relies on the splitting of Added-Mass, viscous Effects and geometrical/convective non-linearities, through a Chorin–Temam projection scheme within the fluid. We state some theoretical stability results, in the linear case, and provide some numerical experiments. The main interest of the proposed scheme is its efficiency compared to the implicit approach. To cite this article: M.A. Fernandez et al., C. R. Acad. Sci. Paris, Ser. I 342 (2006).

Jean-Frédéric Gerbeau - One of the best experts on this subject based on the ideXlab platform.

  • a projection algorithm for fluid structure interaction problems with strong Added Mass Effect
    2006
    Co-Authors: Miguel A. Fernández, Jean-Frédéric Gerbeau, Céline Grandmont
    Abstract:

    Abstract This Note aims at introducing a semi-implicit coupling scheme for fluid–structure interaction problems with a strong Added-Mass Effect. Our main idea relies on the splitting of Added-Mass, viscous Effects and geometrical/convective non-linearities, through a Chorin–Temam projection scheme within the fluid. We state some theoretical stability results, in the linear case, and provide some numerical experiments. The main interest of the proposed scheme is its efficiency compared to the implicit approach. To cite this article: M.A. Fernandez et al., C. R. Acad. Sci. Paris, Ser. I 342 (2006).

  • Added Mass Effect in the design of partitioned algorithms for fluid structure problems
    2005
    Co-Authors: Paola Causin, Jean-Frédéric Gerbeau, Fabio Nobile
    Abstract:

    The aim of this work is to provide a mathematical contribution to explain the numerical instabilities encountered under certain combinations of physical parameters in the simulation of fluid-structure interaction (FSI) when using loosely coupled time advancing schemes. It is also shown how the same combinations of parameters lead, in the case of strongly coupled schemes, to problems that demand a greater computational effort to be solved, requiring for example a high number of subiterations. The application that we have in mind is FSI simulation for blood flow in large human arteries, but the discussion applies as well to several FSI problems in which an incompressible fluid interacts with a thin elastic structure. To carry out the mathematical analysis, we consider a simplified model representing the interaction between a potential fluid and a linear elastic thin tube. Despite its simplicity, this model reproduces propagation phenomena and takes into account the Added-Mass Effect of the fluid on the structure, which is known to be source of numerical difficulties. This allows to draw conclusions that apply to more realistic problems, as well.

  • A projection semi-implicit scheme for the coupling of an elastic structure with an incompressible fluid
    2005
    Co-Authors: Miguel Angel Fernández, Jean-Frédéric Gerbeau, Céline Grandmont
    Abstract:

    We address the numerical simulation of fluid-structure systems involving an incompressible viscous fluid. This issue is particularly difficult to face when the fluid Added-Mass acting on the structure is strong, as it happens in hemodynamics for example. Indeed, several works have shown that, in such situations, implicit coupling seems to be necessary in order to avoid numerical instabilities. Although significant improvements have been achieved during the last years, solving implicit coupling often exhibits a prohibitive computational cost. In this work, we introduce a semi-implicit coupling scheme which remains stable for a reasonable range of the discretization parameters. The first idea consists in treating implicitly the Added-Mass Effect, whereas the other contributions (geometrical non-linearities, viscous and convective Effects) are treated explicitly. The second idea, relies on the fact that this kind of explicit-implicit splitting can be naturally performed using a Chorin-Temam projection scheme in the fluid. We prove (conditional) stability of the scheme for a fully discrete formulation. Several numerical experiments point out the efficiency of the present scheme compared to several implicit approaches.

  • A Quasi-Newton Algorithm Based on a Reduced Model for Fluid-Structure Interaction Problems in Blood Flows
    2003
    Co-Authors: Jean-Frédéric Gerbeau, Marina Vidrascu
    Abstract:

    We propose a quasi-Newton algorithm for solving fluid-structure interaction problems. The basic idea of the method is to build an approximate tangent operator which is cost Effective and which takes into account the so-called Added Mass Effect. Various test cases show that the method allows a significant reduction of the computational effort compared to relaxed fixed point algorithms. We present 2D and 3D fluid-structure simulations performed either with a simple 1D structure model or with shells in large displacements.

Erik Burman - One of the best experts on this subject based on the ideXlab platform.

  • Explicit strategies for incompressible fluid-structure interaction problems: Nitsche type mortaring versus Robin-Robin coupling
    2014
    Co-Authors: Erik Burman
    Abstract:

    We discuss explicit coupling schemes for fluid-structure interaction problems where the Added Mass Effect is important. In this paper we show the close relation between coupling schemes using Nitsche's method and a Robin-Robin type coupling. In the latter case the method may be implemented either using boundary integrals of the stresses or the more conventional discrete lifting operators. Recalling the explicit method proposed in Comput. Methods Appl. Mech. Engrg. 198(5-8):766-784, 2009 we make the observation that this scheme is stable under a hyperbolic type CFL condition, but that optimal accuracy imposes a parabolic type CFL conditions due to the splitting error. Two strategies to enhance the accuracy of the coupling scheme under the hyperbolic CFL-condition are suggested, one using extrapolation and defect-correction and one using a penalty-free non-symmetric Nitsche method. Finally we illustrate the performance of the proposed schemes on some numerical examples in two and three space dimensions.

  • stabilization of explicit coupling in fluid structure interaction involving fluid incompressibility
    2009
    Co-Authors: Erik Burman, Miguel A. Fernández
    Abstract:

    Abstract In this work, we propose a stabilized explicit coupling scheme for fluid–structure interaction problems involving a viscous incompressible fluid. The coupled discrete formulation is based on Nitsche’s method with a time penalty term giving L 2 -control on the fluid pressure variations at the interface. For a linear model problem, we prove that the scheme is stable, in the energy norm, irrespectively of the so-called Added-Mass Effect, namely, the fluid–structure density ratio and the geometry of the domain. Numerical experiments, in the linear and non-linear case, show that optimal time accuracy can be obtained by performing one defect-correction iteration.

Eduard Egusquiza - One of the best experts on this subject based on the ideXlab platform.

  • Numerical study on the influence of acoustic natural frequencies on the dynamic behaviour of submerged and confined disk-like structures
    2017
    Co-Authors: Matias Bossio, Eduard Egusquiza, David Valentín, Alexandre Presas, David Ramos Martin, Carme Valero, Mònica Egusquiza
    Abstract:

    Abstract The dynamic response of disks has been deeply studied in the last years given that their dynamic characteristics present similarities with more complex disk-like structures used in real engineering applications, such as hydraulic turbine runners. Because of disk-like structures could present fatigue damage or critical failures as a result of resonance conditions, it is of paramount importance to determine their natural frequencies. The dynamic response of disk-like structures is heavily affected by the Added Mass Effect when they are surrounded by a heavy fluid. This Added Mass is greatly affected by the proximity of walls. Furthermore, the surrounding fluid cavity has its own natural frequencies and mode shapes, called acoustic natural frequencies and acoustic mode-shapes. All studies of submerged and confined disks have been carried out considering that the acoustic natural frequencies of the surrounding fluid cavity are much higher than the natural frequencies of the disk, so they do not affect each other. However, in some cases the acoustic natural frequencies are close to the natural frequencies of the submerged structure, which can be affected considerably. This case has not been deeply discussed yet. In this paper, the influence of the acoustic natural frequencies of a cylindrical fluid cavity on the natural frequencies of a disk has been analysed numerically. First, the Effect of the Added Mass of the fluid has been estimated when the acoustic natural frequencies of the fluid cavity are much higher than the natural frequencies of the disk. For this case, different geometrical and material parameters have been considered. Then, the parameters that affect the acoustical natural frequencies of the fluid cavity have been identified. Finally, the case with acoustic natural frequencies close to the structural natural frequencies is studied in detail and the affectation between both is discussed. All the results presented in this paper have been dimensionless in order to be used for a wide range of disk-like structures. Therefore, with this study it is possible to identify for which conditions the dynamic response of a generic disk-like structure will be affected by the acoustic natural frequencies of its surrounding fluid cylindrical cavity.

  • Influence of the Added Mass Effect and boundary conditions on the dynamic response of submerged and confined structures
    2014
    Co-Authors: David Valentín, Eduard Egusquiza, Alexandre Presas, Carme Valero
    Abstract:

    The dynamic response of submerged and confined disk-like structures is of interest in the flied of hydraulic machinery, especially in hydraulic turbine runners. This response is difficult to be estimated with accuracy due to the strong influence of the boundary conditions. Small radial gaps as well as short axial distances to rigid surfaces greatly modify the dynamic response because the fact of the Added Mass and damping Effects. Moreover, the Effect of the shaft coupling is also important for certain mode-shapes of the structure. In the present study, the influence of the Added Mass Effect and boundary conditions on the dynamic behavior of a submerged disk attached to a shaft is evaluated through experimental tests and structural- acoustic coupling numerical simulations. For the experimentation, a test rig has been developed. It consists of a confined disk attached to a shaft inside a cylindrical container full of water. The disk can be fixed at different axial positions along the shaft. Piezoelectric patches are used to excite the disk and the response is measured with submersible accelerometers. For each configuration tested, the natural frequencies of the disk and the shaft are studied. Numerical results have been compared with experimental results.

  • experimental investigation of Added Mass Effects on a hydrofoil under cavitation conditions
    2013
    Co-Authors: O De La Torre, Xavier Escaler, Eduard Egusquiza, Mohamed Farhat
    Abstract:

    The influence of leading edge sheet cavitation and supercavitation on the Added Mass Effects experienced by a 2-D NACA0009 truncated hydrofoil has been experimentally investigated in a hydrodynamic tunnel. A non-intrusive excitation and measuring system based on piezoelectric patches mounted on the hydrofoil surface was used to determine the natural frequencies of the fluid-structure system. The appropriate hydrodynamic conditions were selected to generate a range of stable partial cavities of various sizes and also to minimize the Effects of other sources of flow noise and vibrations. The main tests were performed for different sigma values under a constant flow velocity of 14 m/s and for incident angles of both 10 and 2. Additionally, a series of experiments in which the hydrofoil was submerged in air, partially and completely submerged in still water and without cavitation at 7 and 14 m/s were also performed. The maximum Added Mass Effect occurs with still water. When cavitation appears, the Added Mass decreases because the cavity length is increased, and the Added Mass is minimum for supercavitation. A linear correlation is found between the Added Mass coefficients and the entrained Mass that accounts for the mean density of the cavity, its dimensions and its location relative to the specific mode shape deformation. (C) 2013 Elsevier Ltd. All rights reserved.

  • modal behavior of a reduced scale pump turbine impeller part 1 experiments
    2010
    Co-Authors: Xavier Escaler, Mohamed Farhat, Eduard Egusquiza, J K Hutter, François Avellan
    Abstract:

    An experimental investigation has been carried out to quantify the Effects of surrounding fluid on the modal behavior of a reduced scale pump-turbine impeller. The modal properties of the fluid-structure system have been obtained by Experimental Modal Analysis (EMA) with the impeller suspended in air and inside a water reservoir. The impeller has been excited with an instrumented hammer and the response has been measured by means of miniature accelerometers. The Frequency Response Functions (FRF's) have been obtained from a large number of impacting positions in order to ensure the identification of the main mode shapes. As a result, the main modes of vibration have been well characterized both in air and in water in terms of natural frequency, damping ratio and mode shape. The first mode is the 2 Nodal Diameter (ND), the second one is the 0ND and the following ones are the 3ND coupled with the 1ND. The visual observation of the animated mode shapes and the level of the Modal Assurance Criterion (MAC) have permitted to correlate the homologous modes of vibration of the fluid-structure system in air and in water. From this comparison the Added Mass Effect on the natural frequencies and the fluid Effect on the damping ratios have been quantified for the most significant modes. With the surrounding water, the natural frequencies decrease in average by 10%. On the other hand, the damping ratios increase in average by 0.5%. In any case, the damping ratio appears to decrease with the frequency value of the mode.

  • fluid Added Mass Effect in the modal response of a pump turbine impeller
    2009
    Co-Authors: Eduard Egusquiza, Q W Liang, Carme Valero, M Coussirat, Ulrich Seidel
    Abstract:

    In this paper, the reduction in the natural frequencies of a pump-turbine impeller prototype when submerged in water has been investigated. The impeller, with a diameter of 2.870m belongs to a pump-turbine unit with a power of around 100MW. To analyze the influence of the Added Mass, both experimental tests and numerical simulations have been carried out. The experiment has been performed in air and in water. From the frequency response functions the modal characteristics such as natural frequencies and mode shapes have been obtained. A numerical simulation using FEM (Finite Elements Model) was done using the same boundary conditions as in the experiment (impeller in air and surrounded by a Mass of water). The modal behaviour has also been calculated. The numerical results were compared with the available experimental results. The comparison shows a good agreement in the natural frequency values both in air and in water. The reduction in frequency due to the Added Mass Effect of surrounding fluid has been calculated. The physics of this phenomenon due to the fluid structure interaction has been investigated from the analysis of the mode-shapes.Copyright © 2009 by ASME