Visualization of Word Usage in Fluid Mechanics Abstracts

The fluid dynamics video linked in the document shows how `keywords' from abstracts contained in three journals--Physics of Fluids (A) from 1970, Experiments in Fluids from 1983, and Journal of Fluid Mechanics from 1954--have changed over time

Theory of electrostatically induced shape transitions in carbon nanotubes

A mechanically bistable single-walled carbon nanotube can act as a variable-shaped capacitor with a voltage-controlled transition between collapsed and inflated states. This external control parameter provides a means to tune the system so that collapsed and inflated states are degenerate, at which point the tube's susceptibility to diverse external stimuli-- temperature, voltage, trapped atoms -- diverges following a universal curve, yielding an exceptionally sensitive sensor or actuator that is characterized by a vanishing energy scale. For example, the boundary between collapsed and inflated states can shift hundreds of Angstroms in response to the presence or absence of a single gas atom in the core of the tube. Several potential nano-electromechanical devices can be based on this electrically tuned crossover between near-degenerate collapsed and inflated configurations

Mechanics of Rotating Wound Rolls

International audienceIn this paper, we investigate the effect of rotation on the internal loads in a wound roll and the dynamics of a fully wound roll under angular acceleration. Two different types of winding are distinguished: constant transport speed and constant rpm. The original scheme proposed by Benson accounted for large deformation, and used a nonlinear elastic constitutive law; in this paper, the Benson model is first expressed in dimensionless form and extended to account for roll rotation in both cases: constant rpm and constant transport speed. Additionally, tangential dynamics are considered to account for angular acceleration of a fully-wound roll. In general, it is seen that the inclusion of angular velocity in the Benson model alters the lap deformation, interlayer pressure and lap tension profiles compared to the case with no rotation, to an extent determined by the magnitude of angular velocity. A direct consequence of this is that there is now an upper bound on the number of laps that can be safely wound onto the core without loss of contact between the outer-most laps, and this is a function of rotational speed and wrapping tension, among other parameters. A numerical algorithm is then described to account for angular acceleration due to a constant core torque applied after the roll has been completely wound. This allows one to determine the slip profile through the roll at various instants during the motion

Dynamic Analysis of a Serpentine Belt Drive With a Decoupler/Isolator

International audienceBelt drives employing a single, flat serpentine belt tensioned by a passive tensioner are found in automotive engine Front End Accessory Drive (FEAD) where the crankshaft supplies power to accessories like alternators, air-conditioning compressors, pumps, etc. [1]. When the FEAD undergoes forced vibration due to crankshaft excitation, dynamic tension fluctuations can cause the belt to slip on the accessory pulleys [2]. The probability of belt slip increases with the peak drop in belt tension over the pulley during steady state operation [3]. In this paper, one possible solution is analyzed, using a decoupler to isolate/separate the accessory inertia (e.g. alternator) from the FEAD system. This is achieved by placing between the pulley and the accessory a combination of a one-way rigid clutch and an isolator spring. In this study, the rotational response of a typical FEAD is extended to include the clutch and isolator. An analytical solution is then obtained by considering it as a piecewise-linearized system moving about an equilibrium angular displacements. The performance of the ordinary FEAD with regard to tension fluctuation is then compared to that of the system equipped with a decoupler/isolator. The results obtained indicate that within the practical working range of engine speeds, use of either an isolator or a decoupler-isolator could significantly lower the dynamic tension drop across the accessory pulley

Piece-Wise Linear Dynamic Systems With One-Way Clutches

International audienceOne-way clutches and clutch bearings are being used in a wide variety of dynamic systems. Motivated by their recent use as ratchets in piezoelectric actuators and decoupling devices in serpentine belt drives, a method of analysis of systems containing oneway clutches is presented. Two simple systems are analyzed. The goal of the first is the power transmission which would be of concern in an actuator. The goal of the second is decoupling large inertia elements to reduce loads in an oscillating system, the objective of the clutch in a serpentine belt drive. Results show how system parameters can be tuned to meet the desired performance of these piece-wise linear systems

Dynamic analysis of a front-end accessory drive with a decoupler/isolator

International audienceIn automotive Front End Accessory Drives (FEAD), the crankshaft supplies power to accessories like alternators, pumps, etc. When the FEAD undergoes forced vibration due to crankshaft excitation, dynamic tension fluctuations can cause the belt to slip on the accessory pulleys. In this paper, an accessory inertia (e.g. alternator) is isolated/separated from the FEAD by placing between the pulley and accessory a combination of a one-way rigid clutch and an isolator spring. The rotational response of a typical FEAD is extended to include this decoupler-isolator. Analytical solutions are obtained by considering it as a piecewise-linearised system about the equilibrium angular displacements. The tension fluctuation of the ordinary FEAD is then compared to that of the system with a decoupler/isolator. The results indicate that within the practical working range of engine speeds, use of either an isolator or a decoupler-isolator could significantly lower the dynamic tension drop across the accessory pulley

Parallel Optimality Criteria-based Topology Optimization for minimum Compliance Design

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Parallel Optimality Criteria-based Topology Optimization for Minimum Compliance Design

Topology optimization is often used in the conceptual design stage as a preprocessing tool to obtain overall material distribution in the solution domain. The resulting topology is then used as an initial guess for shape optimization. It is always desirable to use fine computational grid to obtain high-resolution layouts that minimize the need for shape optimization and post processing [1], but this approach results in high computation cost and is prohibitive for large structures. To reduce the computation time of such problems, parallel computing in combination with domain decomposition is used. The power law approach has been used as the material distribution method and for locating the optimum solution; an optimality criteria-based optimizer is used [2, 3]. The equilibrium equations are solved using a preconditioned conjugate gradient algorithm. These calculations have been done using a master-slave programming paradigm on coarse grain Multiple Instruction Multiple Data (MIMD) shared memory architecture. In this study, by avoiding assembly of the global stiffness matrix, the memory requirement as well as computation time has been reduced. The results of the current study show that the parallel computing technique is a valuable tool for solving computationally intensive topology optimization problems