bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of Advanced Vortex Method to Simulation of Self-Excited Vibration of a Circular Cylinder in Two-Dimensional Uniform Flow
Authors: Matsumoto Hiroaki , Kamemoto Kyoji , Yokoi Yoshifumi
Published: March 2022

An advanced vortex method with moving boundary condition is applied to the simulation of freely oscillating circular cylinder in a uniform flow at high Reynolds number in order to investigate validity and applicability to the analysis of the flow induced vibration problems. The motion of a circular cylinder is calculated from the motion of equation consisting of the damper c, mass m par unit length, natural frequency fn and fluid force acting on the cylinder. The fluid force is evaluated by solving pressure-Poisson equation using the boundary element method. The calculation conditions are given as the Reynolds number Re (= U∞D/v) = 105, damper c/2πmfn = 1.53 × 10−2, natural frequency fn/fK = 0.5, 1.0, 2.0, 2.5, 3.0, mass ratio m/ρD = 5.15, where D, U∞, ρ and fK are the diameter of circular cylinder, reference velocity, density of the flow and the frequency of Karman vortex shedding from a fixed cylinder, respectively. The computational results, such as the flow pattern and motion of a circular cylinder, are in reasonable agreement with experimental results. It is confirmed that the advanced vortex method is useful to predict complex phenomena related to the flow-induced vibration problems.
Computational Navier-Stokes Solutions of Unsteady Confined Flows Based on Time-Dependent Coordinate Transformations for Unsteady Fluid-Structure Interaction Problems
Authors: Mateescu D. , Païdoussis M. P.
Published: March 2022

This paper presents recent computational solutions for unsteady confined viscous flows with oscillating boundaries, aimed at solving fluid-structure interaction and flow-induced vibration problems. A time-integration method based on a time-dependent coordinate transformation and using artificial compressibility is developed for these problems, in order to obtain accurate solutions applicable to the case of larger amplitude oscillations, of interest for the engineering applications.

Numerical solutions are presented for 2-D unsteady confined viscous flows over a backward-facing step with an oscillating floor, and for 2-D and 3-D unsteady annular viscous flows with oscillating walls.
Symmetric Formulations for Modal Analysis of Internal Fluid Structure Systems
Authors: Ohayon Roger
Published: March 2022

This paper deals with appropriate computational methods for modal analysis of elastic structures containing an inviscid fluid (gas or liquid). These methods, based on Ritz-Galerkin projection using appropriate functional basis, allow us to construct reduced models expressed in terms of physical displacement vector field u in the structure, and generalized coordinates vector r describing the behavior of the fluid. Those reduced models lead to symmetric generalized eigenvalue matrix system involving a reduced number of degrees of freedom for the fluid. More precisely, we construct symmetric matrix models of the fluid considered as a subsystem, by considering the response of the fluid to a prescribed normal displacement of the fluid-structure interface. Two distinct situations are analyzed, namely linear vibrations of an elastic structure completely filled with a compressible gas or liquid and linear vibrations of an elastic structure containing an incompressible liquid with free surface effects due to gravity. The first case is a structural acoustic problem with modal interaction between structural modes with acoustic modes in rigid motionless cavity. Wall impedance can also be easily introduced in order to take into account fluid-structure interface dissipation, for further forced response studies. The second case is a hydroelastic-sloshing problem with modal interaction between incompressible hydroelastic structural modes with incompressible liquid sloshing modes in rigid motionless cavity, involving an elastogravity operator related to the wall normal displacement of the fluid-structure interface. For the construction of reduced models, the static behavior at zero frequency play an important role. This is why we start from “well-posed” variational formulations of the problem, in the sense that zero-frequency behavior must be well retrieved in the equations. It should be noted that the so-called “quasi-static correction” term plays a fundamental role in the Ritz-Galerkin procedure (error truncation). The general methodology corresponds to dynamic substructuring procedures adapted to fluid-structure modal analysis. For general presentations of computational methods using appropriate finite element and dynamic substructuring procedures applied to modal analysis of elastic structures containing inviscid fluids (sloshing, hydroelasticity and structural-acoustics), we refer the reader to Morand and Ohayon (1995).
Investigation of Boundary Layer Behavior on Single and Tandem Cylinders
Authors: Lee T. , Panagakos A.
Published: March 2022

The boundary layers developing on a single and two tandem circular cylinders were examined using multiple hot-film sensor arrays for Re = 2.4 – 5.1 × 104. Hot-wire and surface pressure measurements were also made to better understand the flow pattern and the evolution of the vortex street. The results show that, by use of the sensor arrays in conjunction with a bank of constant-temperature anemometers, (i) the effects of the upstream cylinder on the boundary layer developing on the downstream cylinder, (ii) the frequency of the vortex shedding, and (iii) the locations of flow separation and reattachment can be determined non-intrusively and simultaneously. These measurement capabilities will provide a practical means for the characterization and manipulation of unsteady flow phenomena.
Numerical Study on Aeroelastic Instability of a Rectangular Cylinder in Heaving Oscillations
Authors: Tamura Tetsuro , Itoh Yoshiaki
Published: March 2022

The unsteady three-dimensional flows around a forced-oscillating or freely oscillating rectangular cylinder are numerically simulated by means of the direct finite difference method without any turbulence model. We discuss the accuracy of the present method for prediction of unsteady aerodynamic forces and responses to various dynamic properties. First we examine the aerodynamic forces in case of forced oscillation with D/B = 2 of a rectangular cylinder through the comparison with experiments. Also, in order to understand fundamental behaviors of unstable oscillations of a rectangular cylinder, which is elastically mounted in heaving mode in uniform flow, the effect of various dynamic parameters such as mass ratio, damping ratio or the Scruton number, on aeroelastic instabilities is individually investigated.
Calculation of Vibro-Impact Dynamics of Loosely Supported Rods
Authors: Knudsen J. , Massih A. R. , Johansson L.
Published: March 2022

Vibro-impact dynamics of a loosely-supported rod subject to harmonic and random forces are analyzed. A rod constrained by unilateral contact against springs at contact sites located at different positions is modeled. The beam equations of motion for the rod, with appropriate boundary conditions, are discretized in space by finite element method and in time. The contact forces are computed from the displacements. The model has been used to simulate one span of a rod fixed at one end and loose at the other end. Impact forces, and displacements are calculated as a function of time for different friction coefficients when the rod at one end is subject to sinusoidal or random forces. Lissajous figures and phase plane maps for the system are plotted. Further, the wear rate of the rod is predicted. Some of the predictions are compared with experiments and the results are satisfactory.
Multibody Systems in Nonlinear Waves
Authors: Kral R. , Kreuzer E. , Schlegel V.
Published: March 2022

Almost all offshore structures have to be modeled as multibody systems. Only ships or single pontoons can be modeled as a single rigid body. The dynamic behavior of the multibody system is significantly influenced by fluid-structure interactions. So far, most available methods for analyzing these interactions are restricted to single bodies, small wave amplitudes and body motions, or both.

In the present paper a two-dimensional boundary integral approach with fully nonlinear boundary conditions on the free surface is used to simulate the behavior of elastically coupled floating multibody systems in gravity waves. This method will be applied to analyze the dynamics of two floating bodies moored to a quay.

The results of numerical simulations for selected configurations are shown.
Identification of Fluid Dynamic Coefficients for Multiple Mode Vibrations of a Lightly Damped Rectangular Prism in Cross Flow
Authors: Kerenyi K. , Staubli T. , Drobir H. , Massinger N.
Published: March 2022

An experimental investigation of lightly damped multiple-mode vibrations of a rectangular prism in cross flow will be described. The identification of the fluid dynamic force coefficients is performed by means of a regression analysis (Least-Squares-Procedure) accompanied by online numerical simulation, which allows minimization of errors. Non-linear modelization of the equation of motion is shown, which is needed for stability discussion and to describe the response beyond the stability limit. The fluid dynamic damping will be chosen as the responsible control parameter in the model test for a supercritical Hopf bifurcation.
Fluid-Structural-Acoustical Interactions of a Thin Plate in a Cannel With Flowing Fluid
Authors: Zolotarev I.
Published: March 2022

The dispersion properties of the structural and acoustic waves in the coupled plate-fluid system are presented. The thin elastic plate considered as a simply supported one in the first case and as a part of an unlimited wall of a cannel with flowing fluid in the second case. The linear potential flow theory for inviscid fluid is used. The frequency and modal characteristics are analysed in the range of parameters where the coupling effects between vibration of plate and fluid are either weak or dominant.

The properties of simply supported steel plate interacting with air in cannel for some dimensionless parameters of system was studied by using ANSYS finite element code. As a result of this calculation some dispersion characteristics and fluid pressure distribution in the cannel were obtained.

The frequencies and modal properties of this system as a result of numerical solution (by using ANSYS modelling) are compared with some experimental results.

It is shown that in the fluid-elastic system the strongest acoustic-structural coupling exists if the resonances of acoustic and mechanical systems are sufficiently close. In this case the coupled fluid-mechanical system has two different natural frequencies that are neither pure structural properties nor acoustical. Consequently the fluid-plate arrangement can not be studied separately for the structural and acoustical resonances. Even a light medium can significantly change the spectrum of natural frequencies of a structure. Some expressions for calculation of critical flow velocities are derived.
Flow/Acoustic Interactions for Two Cylinders in Cross Flow
Authors: Fitzpatrick J. A. , Nitti F.
Published: March 2022

The noise generated by two cylinders placed in tandem (i.e. the second in the wake of the first) has been investigated for spacings of 5, 4 & 3 diameters. Measurements of turbulence were obtained between the two cylinders and of fluctuating pressure for the near field region for these cylinder spacings using a microphone with a nose cone. Turbulence levels in the test section were varied using a grid upstream and tests were conducted at different flow velocities and incident levels of turbulence. Although, for a number of cases, up to four peaks related to vortex shedding were evident in the spectrum, most measurements exhibited two peaks, a dominant one at the vortex shedding frequency with a secondary peak at twice this value. The measurements show that the vortex noise is strongest at the mid point between the cylinders and at the rear cylinder with levels of 130 dB. The harmonic component was strongest at the downstream cylinder where peak values of 110 dB were obtained.
Three Dimensional CFD-Analyses of Tube Vibrations Induced by Cross Flow
Authors: Kassera Volker
Published: March 2022

A three dimensional CFD code is applied to the analysis of a single elastically mounted tube in cross flow. The unsteady Navier-Stokes equations are solved in a finite volume mesh with a differential Reynolds-Stress model for turbulence. The tube is supported at both ends by a spring and dashpot system in the cross-flow direction. Fluid forces, tube acceleration, tube velocity and tube displacements are computed after each time step due to the actual flow field. The results for rigid and vibrating tubes are analyzed and compared with experimental data given in the literature. Particular attention is given to the influence of vibration amplitude on the correlation length. In the conclusions the lack of models is discussed critically as well as the aspects of computation time. Suggestions are given for improvement and extension of the model to cover multiple tube rows and tube bundles.
A Time Domain Solution of Fluid-Elastic Instability in Steam Generator Tubes
Authors: Brenneman B. , Gurdal R. J.
Published: March 2022

Because of the gaps between the tubes and support plates, the method of solving flow-induced vibration and wear problems in steam generators must involve nonlinear dynamics and the time domain solution of the differential equations. This paper presents several innovations that make the solution practical for today’s personal computers. The method was used to calculate the critical velocity, and the responses and normal work-rates at critical locations on a tube in a commercial steam generator. In the particular steam generator considered, the critical velocity was found to be insensitive to the tube-to-support plate clearances. Also, if turbulence is the only excitation mechanism, the normal work-rate (and hence the wear-rate) decreases with an increase of the tube-to-support plate clearance. However, in the presence of turbulence and the proposed fluid-elastic mechanism, the normal work-rate increases with the tube-to-support plate clearance, even though the cross-flow velocity remains below the critical velocity.
Flow Periodicity and Acoustic Resonance in Parallel Triangle Tube Bundles
Authors: Oengören Abdullah , Ziada Samir
Published: March 2022

Parallel triangle tube arrays with pitch ratios in the range of 1.2 to 4.2 have been tested at Reynolds numbers up to 90000 to investigate the vorticity shedding and acoustic resonance mechanisms. The tests included measurements of the pressure fluctuations on the tubes and on the test section wall, as well as extensive flow visualisation and hot film measurements of the unsteady flow activities.

Three different components of flow periodicities have been observed. The flow periodicity with the highest Strouhal number (S3) is caused by a shear layer instability and is the weakest component. The S2 component is associated with small scale vortex shedding at the first row. The third component has the lowest Strouhal number (S1) and is the strongest. It is generated by large scale, alternating vortex shedding at deeper rows, and it becomes dominant at all rows at high Reynolds numbers.

For tube arrays with pitch ratio less than 3.4, the onset of acoustic resonances could not be related to the natural flow periodicities mentioned above. This behaviour is in contrast with that of normal triangle arrays, but similar to the acoustic behaviour of in-line arrays. The similarity with in-line arrays seems to stem from the fact that both arrays allow the flow to proceed along free flow lanes between the tube columns, resulting in a similar acoustic resonance mechanism. Strouhal number charts for the natural vorticity shedding and the onset of acoustic resonances have been developed.
Tube Rupture in High Pressure Heat Exchangers
Authors: Goyder H. G. D.
Published: March 2022

A high pressure heat exchanger may have a gas at 100 to 400 bar inside the tubes and cooling water at 20 bar outside the tubes. If a tube ruptures the high pressure gas is released into the water and the pressure quickly rises within the shell. The shells of these heat exchangers may only be capable of withstanding relatively low pressures and a level of safety is achieved by providing bursting disks and pressure relief systems. However, such pressure relief systems do not act instantaneously. The problem is to determine if the rapid pressure rise that follows a tube rupture can rupture a shell before the pressure relief system can act to vent the pressure.
Flow-Induced Vibration Failure in a Steam Condenser and its Successful Redesign
Authors: Escoe A. Keith
Published: March 2022

This paper is a study of an inadequate FIV design of a steam condenser. The condenser failed because of lack of tube support baffles. The flow distribution varied widely at different parts of the exchanger. The vibration assessment based on conventional technology showed the exchanger experiencing both fluidelastic instability and turbulence buffeting. The exchanger failed within the first six months of operation, which would suggest FEI as the mechanism of failure. A consulting firm came in and added stakes within the top portion of the tubes. The FIV steadily got worse over a period of twelve years, as operations increased the shell side flow velocity. The increased velocity and leaks suggested low cycle fatigue failures typical of turbulence buffeting. What makes this study interesting is the long unsupported length of the tubes resulted in very low natural frequency of the tubes and tube collisions. The study of tube collisions and the consequences unravel a unique situation. Numerous attempts were made to correct the problem, but were marginally successful. The final and successful “fix” was a new rod baffle design. This design differed from the classical rod-baffle design, because of the large diameter (20 ft). The magnitude of the diameter normally limits the rod baffle design. Modifications of the rod baffle design were to compensate the flexibility of the long length of the tube support rods. This paper will discuss these modifications, showing the corresponding FIV computations, using finite element studies of the tubes and a new FIV software package. This paper will be a unique study of the failure and successful fix of a FIV failure.
Flow-Induced Wear in Steam Generator Tubes: Prediction Versus Operational Experience
Authors: Au-Yang M. K.
Published: March 2022

Many nuclear steam generators have accumulated more than ten effective-full-power-years of operation. Eddy-current inspections revealed that a number of these steam generator tubes, notably those located in high local cross-flow regions, have indications of wear at some support plate elevations after five to ten years of effective-full-power operations. In the last five years, a number of technical papers on non-linear tube bundle dynamics has been published to address the effect of tube and support plate interactions. At the same time, test data relating wear and tube wall thickness losses for different material combinations and different support plate geometries became available. Based on the available data in the literature, as well as data obtained in the author’s affiliation, this paper assesses the cumulative tube wall wear after 5, 10 and 15 effective-full-power years of operation of a typical commercial nuclear steam generator, using different wear models. It is hoped that this study will shed some light on the probable mechanism that caused the observed wear in today’s operating nuclear steam generators.
Active Feedback Control of Combustion Oscillations
Authors: Ziada Samir , Graf Hans R.
Published: March 2022

Combustion oscillations are excited by a feedback mechanism which results from the coupling between the flame instability and an acoustic resonance mode of the combustion chamber. The most important event of this mechanism is believed to be the upstream feedback from the acoustic resonance to the initial region of the flame, where new disturbances are generated. A control system has been implemented into a household burner to counter act this upstream feedback. This is achieved by means of pulsating either the fresh air for combustion or the fuel. The actuators are activated by the signal of a sensor measuring the pulsation inside the combustion chamber. Combustion oscillations of this burner have been eliminated altogether, without destabilising other acoustic modes, resulting in 35 dB reduction in the amplitude of pressure pulsations.
Fluid-Elastic Force Measurements Acting on a Tube Bundle in Two-Phase Cross Flow: Fluid-Elastic Forces Acting on the Oscillated Tube and Tubes Surrounding the Oscillated Tube
Authors: Inada Fumio , Kawamura Koji , Yasuo Akira
Published: March 2022

Fluid-elastic forces acting on a square tube bundle (P/D = 1.42) in air-water two-phase cross flow were considered experimentally. A tube in the tube bundle was oscillated in the direction perpendicular as well as parallel to the two-phase flow, and fluid elastic forces acting on the oscillated tube as well as tubes surrounding the oscillated tube were measured. Measured fluid elastic forces were separated into coefficients of acceleration, velocity, and displacement of the oscillated tube, and the coefficients were nondimensionalized with two-phase mixture characteristics, which were obtained using the drift-flux model. It was found that the fluid elastic force coefficients could collapse very well as a function of void fraction and/or nondimensional gap velocity. These coefficients were used to estimate the critical gap velocity of fluid elastic vibration. The results agreed qualitatively with previous experimental results of Nakamura et al. (1986a,b).
Fluid-Structure Interaction in Hydraulic Networks
Authors: Bouabdallah Saïd , Massouh Fawaz
Published: March 2022

In this study, we consider the fluid-structure interaction in hydraulic networks, with a simplified representation of the structure thanks to the Timoshenko beam theory. This allows us to write the coupled equations which represent both the fluid flow and the structure deformations effects. These equations are solved by the method of characteristics. This last method involves different kinds of characteristics.

In this paper we consider only the longitudinal mode of propagation, which the pipe undergoes in traction and compression. In this case two families of compatibility equations with different characteristic paths must be solved together. For the computation a numerical scheme with a reach-back time interpolation will be used.
Coupled and Uncoupled Bending-Torsion Responses of Twin-Tail Buffet
Authors: Kandil Osama A. , Sheta Essam F.
Published: March 2022

The effect of coupled and uncoupled bending and torsion modes on flexible twin-tail buffet is considered. This multidisciplinary problem is investigated using three sets of equations on a multi-block grid structure. The first set is the unsteady, compressible, full Navier-Stokes equations which are used for obtaining the flow-filed vector and the aerodynamic loads on the twin tails. The second set is the coupled aeroelastic equations which are used for obtaining the bending and torsional deflections of the twin tails. The third set is the grid-displacement equations which are used for updating the grid coordinates due to the tail deflections. The configuration is pitched at 30° angle of attack and the freestream Mach number and Reynolds number are 0.3 and 1.25 million, respectively. Keeping the twin tails as rigid surfaces, the problem is solved for the initial flow conditions. Next, the problem is solved for the flexible twin tails responses due to the unsteady loads produced by the vortex breakdown flow of the delta-wing leading-edge vortex cores. The configuration is investigated for the effect of coupled and uncoupled bending and torsion modes using two different separation distances of the twin-tail; the inboard and the outboard positions.
Parametric Vibration of Elastic Cavitating Wing in Unsteady Flow
Authors: Kovinskaya S. I. , Amromin E. L.
Published: March 2022

A two-dimensional unsteady potential flow outside an elastic partially cavitating wing is analyzed numerically by using the Birnbaum equation on hydrofoil chord and the Lagrange-Cauchy integral on the cavity. An angle of attack has a small periodic perturbation, and cavity thickness and length have got perturbations too. Wing vibration is considered as vibration of a variable thickness beam with two clamp bolts near the beam center. A mono-frequency flow perturbation induces mono-frequency flexural vibration of a non-cavitating wing, but the vibration of a cavitating wing is multy-frequency one, and a spectrum of a cavitating wing response can depend on an amplitude of the incoming flow perturbation.

Numerical simulation of NACA-16009 hydrofoil vibration was made for various free-stream speeds, module of elasticity, fluid and wing densities, and as a result, three frequency bands of a vibration increase are found. The low-frequency band is connected with a cavity volume oscillation. There is a considerable effect of cavity length, therefore the cavitation number influences on vibration as a parameter. The high-frequency band is connected with elastic resonances of wing. Besides, resonance-like frequencies were found in the middle band. This phenomenon has not a dependence on cavity dimensions and wing elasticity, but appears as a result of an interaction between hydrodynamic damping and media inertia forces.
Adaptive Feedback Linearization for the Control of a Typical Wing Section With Structural Nonlinearity
Authors: Ko Jeonghwan , Kurdila Andrew J. , Strganac Thomas W.
Published: March 2022

Earlier results by the authors have derived constructions of Lie algebraic partial feedback linearizing control methods for pitch and plunge primary control utilizing a single trailing edge actuator. In addition, a globally stable nonlinear adaptive control method was derived for a structurally nonlinear wing section with both a leading and trailing edge actuator. However, the global stability result described in a previous paper by the authors, while highly desirable, relied on the fact that the leading and trailing edge actuators rendered the system exactly feedback linearizable via Lie algebraic methods. In this paper, the authors derive an adaptive, nonlinear feedback control methodology for a structurally nonlinear typical wing section. The technique is advantageous in that the adaptive control is derived utilizing an explicit parameterization of the structural nonlinearity, and defining a partial feedback linearizing control via Lie algebraic methods that is parametrically dependent. The closed loop stability of the system is guaranteed to be stable via application of LaSalle’s in variance principle.
Reduced Order Aerodynamic Modeling of How to Make CFD Useful to an Aeroelastician
Authors: Dowell Earl H. , Hall Kenneth C. , Romanowski Michael C.
Published: March 2022

In this article, we review the status of reduced order modeling of unsteady aerodynamic systems. Reduced order modeling is a conceptually novel and computationally efficient technique for computing unsteady flow about isolated airfoils, wings, and turbomachinery cascades. Starting with either a time domain or frequency domain computational fluid dynamics (CFD) analysis of unsteady aerodynamic or aeroacoustic flows, a large, sparse eigenvalue problem is solved using the Lanczos algorithm. Then, using just a few of the resulting eigenmodes, a Reduced Order Model of the unsteady flow is constructed. With this model, one can rapidly and accurately predict the unsteady aerodynamic response of the system over a wide range of reduced frequencies. Moreover, the eigenmode information provides important insights into the physics of unsteady flows. Finally, the method is particularly well suited for use in the active control of aeroelastic and aeroacoustic phenomena as well as in standard aeroelastic analysis for flutter or gust response. Numerical results presented include: 1) comparison of the reduced order model to classical unsteady incompressible aerodynamic theory, 2) reduced order calculations of compressible unsteady aerodynamics based on the full potential equation, 3) reduced order calculations of unsteady flow about an isolated airfoil based on the Euler equations, and 4) reduced order calculations of unsteady viscous flows associated with cascade stall flutter, 5) flutter analysis using the Reduced Order Model. The presentation will include our most recent results including the use of A-one Orthogonal Decomposition as an alternative or complement to eigenmodes.
Integrated Design of Controllable Tensegrity Structures
Authors: Sultan C. , Skelton R. E.
Published: March 2022

Tensegrity structures represent a special class of spatial structures, having a continuous network of members in tension and a discontinuous network of members in compression. These members can serve simultaneously as sensors, actuators, and load carrying elements. Hence, structure and control design must be carried out together. This paper illustrates the use of tensegrity structures as adaptive structures. The paper addresses static design problems, presents the mathematical structure of the linear dynamic models, deals with the actuator locations, and integrates structure and controller design for output variance control problems. Through integration of static design, actuator selection and controller design, better performances are achieved compared with the case in which these tasks are carried out separately.
Power Flow Analysis of an Electrostrictive Actuator Driven by a PWM Amplifier
Authors: Zvonar Gregory A. , Lindner Douglas K.
Published: March 2022

In this paper we analyze the power flow between stacked electrostrictor actuators and a pulse-width-modulated switching amplifier. An integrated model is developed with includes a dynamic structural model of the actuator, a dynamic model of the power electronics and a nonlinear electro-mechanical coupling mechanism. By analyzing the conversion of mechanical power to and from electrical power, a better understanding is gained of the interaction between the electrical amplifier and the actuators. Furthermore, this new insight provides for the design of more efficient closed loop controllers. This work focuses on the behavior of electrostrictive actuators with nonlinear actuator models. Also, with the inclusion of the dynamic model of the switching amplifier, the power flow can be traced directly back into the original power bus. The effect on the power flow of a nonlinear amplifier controller is also investigated. It is shown that the nonlinear controller, which reduced actuator velocity distortion, also reduces the maximum required power that the amplifier must process.
Simultaneous Optimization of Structural and Controller Parameters of Spring-Supported Beam for Vibration Control
Authors: Zhu Ye , Qiu Jinhao , Tani Junji , Urushiyama Yuta , Hontani Yasuhara
Published: March 2022

The modeling and formulation of simultaneous optimization problems with H2 and H∞ norm objective functions are discussed in the paper. They are applied to the simultaneous optimization of the cross-sectional parameters of a spring-supported beam and the parameters of the controller used to actively suppress the vibration of the beam. The H2 and H∞ norms of the transfer function from external disturbance to measured output are used as the objective functions. Simultaneous optimization is realized by iteratively executing structural optimization and controller optimization. Both serial and parallel approaches to combine structural optimization and controller optimization are investigated. The performance of both output and control input is improved significantly after simultaneous optimization. The simulation results show the great potential advantages of simultaneous optimization over traditional design methods.
A Method for Analysis of Vibration Systems With Integrated Active Elements
Authors: Hornung Thomas , Reimerdes Hans-G. , Günnewig Jochen
Published: March 2022

Designing smart structural systems with induced strain elements, like piezoelectric ceramic actuators, is a comprehensive issue, involving not only geometry and material data but also the behavior of the coupled host system as a main aspect. For an effective control of structural vibration due to external or environmental loads, an accurate description of the system is needed. An analytical based method for the characterization of the complete system under consideration of local increase of stiffness and mass by integrating sensor and actuator elements will be presented in this paper.
Two Dimensional Finite Element Analysis of Myocardial Infarction in the Human Left Ventricle
Authors: Sathyamoorthy Mohan
Published: March 2022

Diseases of the heart and blood vessels are the number one causes of patient mortality in the United States. Of these conditions, myocardial infarctions, more commonly known as heart attacks, are the most feared of cardiovascular pathologies. The American Heart Association has dedicated billions of dollars over the past four decades to basic science and clinical research to help prevent and treat heart attacks. Detailed assessment of three dimensional stress, strain, and deformation histories is important because it has been noted that reduced transmural strain and left ventricular torsion may be indicative of myocardial infarction resulting from ischemia [1]. Previous studies have been limited to clinical and experimental modalities of study. With the evolution of high speed computers and finite element softwares, detailed and effective biomechanical modeling of complex physiological systems such as the heart have been undertaken. The objective of this study is to utilize finite element analysis to assess local and global deformation and stress patterns in normal vs. imposed conditions of myocardial infarction. Such knowledge obtained a priori could be utilized by cardiothoracic surgeons and cardiologists to improve the efficacy of treatment and treatment options for patients suffering from heart disease.
Elastic Properties of 3D Cells for Trabecular Bone: Digital vs. Structural Finite Element Models
Authors: Ominsky Michael S. , Zysset Philippe K. , Goldstein Steven A.
Published: March 2022

Characterizing morphological and elastic properties of trabecular bone is a critical step towards understanding bone fragility. Idealized 3D cells for trabecular bone based on a tetrakaidecahedral geometry have been previously described to study morphology and its relationship to mechanical properties [1,2]. Two types of cells have been proposed: an open cell consisting of rectangular beams and a closed cell with hexagonal plates [Fig. 1]. The morphology of the cell is quantified by measures of structural density (SD) and mean intercept length (MIL). Structural density is mainly controlled by the aspect ratio t/l (thickness/length) of the beams or plates. Mean intercept length is controlled by the angle θ, which changes the cell’s anisotropy.
A Comprehensive Investigation of the Biomechanics of an Artificial Intervertebral Disc
Authors: Todd Dwight T. , Goel Vijay K. , Grosland Nicole M. , Gilbertson Lars G. , Wilder David G. , Pope Malcolm H. , Lankford James
Published: March 2022

The biomechanics and wear characteristics of an experimental artificial disc prosthesis have been investigated through a three-part study. This study reports the results of in-vitro cadaveric testing, finite element modeling, and cyclic wear testing. Load-displacement data from the in-vitro testing and finite element model demonstrate that the artificial disc can provide comparable biomechanics to the intact case. The finite element model also predicts increased facet loads in extension. Results from the wear study show little gravimetric wear over two million cycles.
Altered Collateral Ligament Strain Following Total Knee Arthroplasty
Authors: Hairrell E. Nicki , Eberhardt Alan W. , Moeini Reza , Cuckler John
Published: March 2022

The geometric design of a total knee arthroplasty system can cause changes in the wear and fixation of the device, as well as the kinematics of the replaced joint (Nilsonn, et al., 1997). Troubles arise when trying to determine the strain behavior of the collateral ligaments of the knee, due to subject-to-subject variations (Crownshield et al., 1975). This study compared the strain in the collateral ligaments of the knee, before and after a total knee arthroplasty. It is hypothesized that this information can be used to indicate the effects of the TKA on these ligaments. If the strain after a TKA is greater than the normal physiological strain in these ligaments, this may be perceived as a source of discomfort or disfunction for the patient. Such a comparison of strain patterns may be used as a tool in the design of improved total knee arthroplasty system.
Interaction of Airflow With Mucus Simulant in a Channel
Authors: Evrensel Cahit A. , Hassan Amgad A. , Krumpe Peter E.
Published: March 2022

A common symptom of most obstructive airway diseases is the impaired muco-ciliary transport due to increased mucus viscosity and thickness. These persons must rely on the two-phase flow and cough as a lung clearance mechanism. The objective of this study is to understand the dynamics of the interface between the airflow and mucus layer better. This understanding is inherent to designing therapies to enhance the mucus clearance.
Strain Rate Affects Viscoelastic Measurements on Porcine Aortic Heart Valve Tissue Tested in Shear
Authors: Talman Eric , Boughner Derek
Published: March 2022

Mechanical testing of bioprosthetic heart valve tissue is an important aspect of engineering a successful artificial valve. The artificial tissue must be strong enough to withstand the tension associated with back-pressure during systole, yet pliable enough to undergo the complex deformations during valve opening and closing. Current prostheses have adequate strength but their pliability is reduced which may contribute to premature tissue failure.
Mixing Studies in Bioreactors
Authors: Menisher Tewodros , Metghalchi Mohamad , Gutoff Edgar B.
Published: March 2022

Fluid mixing is a very important factor that needs to be considered in the design of bioreactors. Growing cells in bioreactors require sufficient amounts of nutrients and oxygen for their growth. The transfer of these nutrients to the cells can be ensured by sufficient mixing, yet excessive shear can destroy the cells. This study compares two impellers used for mixing: the “Dumbo Ear” impeller and the high efficiency A310 impeller.

Mixing time is used as the criteria of the performance of the impellers. Mixing time is defined as the time taken for the disappearance of the pink color of Phenolphthalein indicator in a basic solution by the rapid addition of acid. A known amount and concentration of sodium hydroxide is added to a bioreactor containing distilled water with a known amount phenolphthalein, turning the solution pink. Using pressure driven dispensing system (Figure 1), excess hydrochloric acid is rapidly injected to neutralize the base. The time it takes for the solution to become colorless is recorded as the mixing time. The mixing time is measured as a function of rotational speed for different locations of the impeller. The results are reported in figures 2–6.

Figure 2 compares Dumbo Ear impeller with the A310 at a clearance-to-height ratio (C/H) of 0.44 for a vertically centered shaft. In all the cases studied, the Dumbo Ear impeller out-performed the A310. The effect of varying clearance of the impeller on the mixing time was also investigated. Unlike the A310, the Dumbo Ear impeller showed better mixing as the clearance is reduced (Figure 3). In studying the effect of shaft angle on mixing time, two ways of pivoting the impeller were utilized. In the first case the impeller was pivoted at the intersection of the tank centerline with the top surface of the liquid. The impeller was also pivoted so as to maintain the bottom of the impeller shaft at the centerline of the tank. Thus in one case the impeller shaft entered the liquid at the centerline of the tank, and in the other case it did not, but the base of the shaft remained at the centerline. The shear forces will be different in the two cases because the clearances will be different. Figure 4 shows the variation in mixing time for a 15° shaft angle. In most of the cases studied, pivoting at the surface of the liquid gives a shorter mixing than pivoting at bottom of the impeller shaft. Figures 5 & 6 compare the mixing times for vertical and pivoted impellers for the two types of pivoting. In both types, tilting impeller reduces the mixing time.

This mixing study showed that in most cases, at the same rotational speeds, the Dumbo Ear impeller gave shorter mixing times than the A310. Also, tilting the Dumbo Ear impeller and having a small bottom clearance gave the shortest blending times. However, in all cases, one has to consider the increased shear forces on cells when clearance between the blades to the walls is reduced.
Hydrodynamics in Cell Rolling and Adhesion
Authors: Zhao Yihua , Skalak Richard , Chien Shu
Published: March 2022

Formulas for the slow viscous motion of a sphere in the presence of a solid wall have been used in analyzing the phenomena of cell rolling and adhesion. The established theories, such as the ones by Brenner and his colleagues [1,2,3], address the ideal situation in which both the sphere and the wall are smooth. However, biological cells such as leukocytes have numerous surface protrusions (microvilli). Therefore, the applicability of the theories of smooth spheres to the problem of cell rolling and adhesion needs to be examined. Also, to facilitate the design and analysis of experiments, it is desirable to have a simple solution that can provides some physical insights into the process.
Computational Fluid Dynamics Analysis of Pulsatile Flow Over an Isolated Intravascular Stent Strut
Authors: Ainsworth Stephen D. , Ochterbeck Jay M. , Langan Eugene M. , LaBerge Martine
Published: March 2022

Knowledge of the distinct fluid dynamic factors created by an intravascular stent, placed in an atherosclerotic artery and subjected to pulsatile flow, is limited. A computational fluid dynamics modeling approach was used in this research to analyze and measure the effect of single stent struts on the flow separation and reattachment points, and re-circulation regions. With the overall goal to effectively model a comprehensive stented atherosclerotic artery, this preliminary study focused on two dimensional flow at various points in the cross-section of a stent subjected to steady and pulsatile flow. The reattachment point is an area of increased wall shear stress gradients, and thus a concern when considering intimal hyperplasia. The results show that the reattachment point is a function of the longitudinal cross sectional geometry of the stent. Pulsatile flow results show the motion of the reattachment point with increasing and decreasing flow, as well as the relationship of the geometrical design of the stent and the existence of reattachment points between struts.
Mechanics of Heterogeneous Atherosclerotic Human Aorta: Correlation With Positive Staining for MMP-1
Authors: Beattie Deborah , Vito Raymond , Bilusic Zrinka , Xu Chengpei , Glagov Seymour
Published: March 2022

We hypothesize that mechanical factors within heterogeneous atherosclerotic human arteries are important, either as primary determinants of plaque stability or as influences on relevant cell activity. We developed an experimental system to measure the finite deformation of diseased human arterial cross sections at physiologic pressures. Strains are calculated using interpolation functions. The distributions of lipid, calcified, healthy and fibrous tissue are measured using differential staining and light microscopy. The presence of matrix metalloproteinase 1 is also quantified. Histologic features and deformations are incorporated into a plane stress finite element model and tissue constituent material properties, stresses and strain energies are determined using an optimization procedure. Results show correlation of stress and strain distributions with histologic make up of the tissue and with staining for matrix metalloproteinase (MMP-1).
Analysis of Instability and Self-Excited Vibration for Collapsible Tube by Distributed Parameter Model
Authors: Hayashi Satoru , Hayase Toshiyuki , Miura Yuji
Published: March 2022

The stability of a Starling resistor type collapsible tube circuit are studied on the basis of a distributed parameter model including no effect of flow separation at the collapsed part of the tube. The governing equations are spatially discretized into 200 sections and rearranged to 401 ordinary differential equations with respect to time. The stability of the circuit is examined by the characteristic equation of linearized governing equations. Transition of the stability according to variation of the flow rate is indicated as a root locus of the eigenvalues. The original nonlinear equations are numerically solved by Runge-Kutta scheme and the theoretical frequency and the amplitude of self-excited vibrations are compared with experimental results.
An Experimental System to Expose Perfused Vascular Segments to Cyclic Bending Ex-Vivo
Authors: Vorp David A. , Severyn Donald A. , Mears Jon R.
Published: March 2022

Portions of coronary and other blood vessels undergo cyclic bending due to attachment to the heart or crossing of joints [1,4,9]. Bending of a vascular segment alters the local transmural stresses and strains [5,13] as well as the shear stresses acting on the endothelial surface [8,11]. Fluctuations in both shear stress and in-plane stretch have been shown to influence endothelial cell and smooth muscle cell biology [12]. The purpose of the present work was to create a model to expose perfused, intact vascular segments to cyclic bending in-vitro. Such a system would enable the assessment of the biologic response of vascular tissue to combined alterations in transmural stress and shear stress produced by cyclic bending.
A Generalized Scheme for Surface-Fit of Dynamic Coronary Artery Tree Data
Authors: Pao Y. C.
Published: March 2022

The earliest geometric model used for computing stresses in the heart was a sphere. As computer tomography becomes increasingly utilized, the true geometry of the heart can be reconstructed three-dimensionally. However, for qualitative finite element analysis of the in vivo heart by applying the advanced theories of mechanics, idealized geometric shapes are still needed We have presented the spline-fitted spatial curve for study of the bending and twisting of the coronary artery tree of a beating heart [1]. The dynamic behavior of arterial branches near a bifurcation has been investigated based on the developed method. Anatomic landmarks such as the bifurcation points are necessary for study of the local behavior. Otherwise, implanted markers would be needed for identifying the investigated region. For global study of the whole heart or coronary artery tree [2], idealized geometry is more practical for approximated analyses.