Showing papers on "Inertia published in 2009"

Adaptive Speed Control for Permanent-Magnet Synchronous Motor System With Variations of Load Inertia

Abstract: Considering the variations of inertia in real applications, an adaptive control scheme for the permanent-magnet synchronous motor speed-regulation system is proposed in this paper. First, a composite control method, i.e., the extended-state-observer (ESO)-based control method, is employed to ensure the performance of the closed-loop system. The ESO can estimate both the states and the disturbances simultaneously so that the composite speed controller can have a corresponding part to compensate for the disturbances. Then, considering the case of variations of load inertia, an adaptive control scheme is developed by analyzing the control performance relationship between the feedforward compensation gain and the system inertia. By using inertia identification techniques, a fuzzy-inferencer-based supervisor is designed to automatically tune the feedforward compensation gain according to the identified inertia. Simulation and experimental results both show that the proposed method achieves a better speed response in the presence of inertia variations.

Inertia-driven spin switching in antiferromagnets

Abstract: Magnetic switching is typically accomplished by using a driving field that stays on until the magnetization is rotated to its final position. An experiment demonstrates that, in antiferromagnets, inertial effects can be harnessed, such that only a short ‘kick’ is required to transfer sufficient momentum to the spin system for it to reorient. It is generally accepted that the fastest way to reorient magnetization is through precessional motion in an external magnetic field1,2,3,4,5,6,7. In ferromagnets, the application of a magnetic field instantaneously sets spins in motion and, in contrast to the inertial motion of massive bodies, the magnetization can climb over a potential barrier only during the action of a magnetic-field pulse. Here we demonstrate a fundamentally different scenario of spin switching in antiferromagnets, where the exchange interaction between the spins leads to an inertial behaviour. Although the spin orientation hardly changes during the action of an optically generated strong magnetic-field pulse of 100 fs duration, this pulse transfers sufficient momentum to the spin system to overcome the potential barrier and reorient into a new metastable state, long after the action of the stimulus. Such an inertia-based mechanism of spin switching should offer new opportunities for ultrafast recording and processing of magnetically stored information.

About the validity of Reynolds equation and inertia effects in textured sliders of infinite width

Abstract: Numerous recent studies focus on modelling the lubricant flow in macro-textured configurations, using the Navier-Stokes, Stokes, and Reynolds equations. Several of these studies show that important, lift generating inertia effects are present in textured configurations, and conclude that Reynolds assumptions do not hold true for such contacts. A similar analysis is performed in this paper, for parallel sliders of infinite width, but with quite different conclusions. Two main observations are made based on the results presented herein: (a) inertia effects cannot be analysed by single texture cell models - for example, in the case of partial inlet texturing, inertia shows a clear negative influence, contradicting the previously reported lift generating effects; (b) the validity of Reynolds equation in textured sliders cannot be decided by the Reynolds number (Re) alone, and the texture aspect ratio (λ) has an equally important influence on Reynolds equation validity. Finally, charts presenting the r...

Grain alignment induced by radiative torques: effects of internal relaxation of energy and complex radiation field

Abstract: Earlier studies of grain alignment dealt mostly with interstellar grains that have strong internal relaxation of energy which aligns the grain axis of maximum moment of inertia (the axis of major inertia) with respect to the grain's angular momentum. In this paper, we study the alignment by radiative torques for large irregular grains, e.g., grains in accretion disks, for which internal relaxation is subdominant. We use both numerical calculations and the analytical model of a helical grain introduced by us earlier. We demonstrate that grains in such a regime exhibit more complex dynamics. In particular, if initially the grain axis of major inertia makes a small angle with angular momentum, then radiative torques can align the grain axis of major inertia with angular momentum, and both the axis of major inertia and angular momentum are aligned with the magnetic field when attractors with high angular momentum (high-J attractors) are available. For alignment without high-J attractors, beside the earlier studied attractors with low angular momentum (low-J attractors), there appear new low-J attractors. In addition, we also study the alignment of grains in the presence of strong internal relaxation, but induced not by a radiation beam as in earlier studies but instead induced by a complex radiation field that can be decomposed into dipole and quadrupole components. We found that in this situation the parameter space q max, for which high-J attractors exist in trajectory maps, is more extended, resulting in the higher degree of polarization expected. Our results are useful for modeling polarization arising from aligned dust grains in molecular clouds.

Virtual synchronous generator control in autonomous wind-diesel power systems

Abstract: This paper addresses the problem of frequency stability in an autonomous wind-diesel power system with energy storage. At high wind penetration levels and due to the lack of controlled rotating machines, wind fluctuation might cause unacceptable frequency excursions in the system and they need to be mitigated. A virtual synchronous machine control is designed to emulate a virtual inertia via power injection from/to the energy storage system. The impact of this control strategy on the system is analyzed. Based on the case study, the major conclusion is that virtual inertia control reduces the maximum rotor speed deviation, but in exchange for increasing the inertia, the system becomes slower and more oscillatory. Possible solutions for the latter are pointed out, but further work is required. Parameters for sizing the energy storage are proposed.

Phase-field-crystal and Swift-Hohenberg equations with fast dynamics.

Abstract: A phenomenological description of transition from an unstable to a (meta)stable phase state, including microscopic and mesoscopic scales, is presented. It is based on the introduction of specific memory functions which take into account contributions to the driving force of transformation from the past. A region of applicability for phase-field crystals and Swift-Hohenberg-type models is extended by inclusion of inertia effects into the equations of motion through a memory function of an exponential form. The inertia allows us to predict fast degrees of freedom in the form of damping perturbations with finite relaxation time in the instability of homogeneous and periodic model solutions.

Multi-touch object inertia simulation

Abstract: The inertia system provides a common platform and application-programming interface (API) for applications to extend the input received from various multi-touch hardware devices to simulate real-world behavior of application objects. To move naturally, application objects should exhibit physical characteristics such as elasticity and deceleration. When a user lifts all contacts from an object, the inertia system provides additional manipulation events to the application so that the application can handle the events as if the user was still moving the object with touch. The inertia system generates the events based on a simulation of the behavior of the objects. If the user moves an object into another object, the inertia system simulates the boundary characteristics of the objects. Thus, the inertia system provides more realistic movement for application objects manipulated using multi-touch hardware and the API provides a consistent feel to manipulations across applications.

Comparison of Various Dynamic Balancing Principles Regarding Additional Mass and Additional Inertia

Abstract: The major disadvantage of existing dynamic balancing principles is that a considerable amount of mass and inertia is added to the system The objectives of this article are to summarize, to compare, and to evaluate existing complete balancing principles regarding the addition of mass and the addition of inertia and to introduce a normalized indicator to judge the balancing performance regarding the addition of mass and inertia The balancing principles are obtained from a survey of literature and applied to a double pendulum for comparison, both analytically and numerically The results show that the duplicate mechanisms principle has the least addition of mass and also a low addition of inertia and is most advantageous for low-mass and low-inertia dynamic balancing if available space is not a limiting factor Applying countermasses and separate counter-rotations with or without an idler loop both increase the mass and inertia considerably, with idler loop being the better of the two Using the force-balancing countermasses also as moment-balancing counterinertias leads to significantly less mass addition as compared with the use of separate counter-rotations For low transmission ratios, also the addition of inertia then is smaller

Derivation of the Dynamics Equations of Receiver Aircraft in Aerial Refueling

Abstract: This paper describes the derivation of a new set of nonlinear, 6{DOF equations of motion of a receiver aircraft undergoing an aerial refueling, including the efiect of timevarying mass and inertia properties associated with the fuel transfer and the tanker’s vortex induced wind efiect. Since the Center of Mass (CM) of the receiver is time{varying during the fuel transfer, the equations are written in a reference frame whose origin is at the CM of the receiver before fuel transfer begins and stays flxed at that position even though the CM is moving during the refueling. Due to the fact that aerial refueling simulation and control deal with the position and orientation of the receiver relative to the tanker, the equations of motion are derived in terms of the translational and rotational position and velocity with respect to the tanker. Further, the derivation of the equations takes into account the momentum transfer into the receiver due to the fuel transfer. The receiver aircraft before fuel transfer is treated as a rigid body made up of ‘n’ particles. The dynamic efiects due to fuel transfer are modeled by considering the mass change to be conflned to a flnite number of lumped masses, which would normally represent the fuel tanks on the receiver aircraft. Once the refueling begins, by using the design parameters such as the shape, size and location of the individual fuel tanks and the rate of fuel ∞owing into each of them, the mass and location of the individual lumped masses are calculated and fed into the equations of motion as exogenous inputs. The new receiver equations of motion are implemented in an integrated simulation environment with a feedback controller for receiver station-keeping as well as the full set of nonlinear, 6{DOF equations of motion of the tanker aircraft and a feedback controller to ∞y the tanker on a U-turn maneuver.

Suppression of friction by mechanical vibrations.

Abstract: Mechanical vibrations are known to affect frictional sliding and the associated stick-slip patterns causing sometimes a drastic reduction of the friction force This issue is relevant for applications in nanotribology and to understand earthquake triggering by small dynamic perturbations We study the dynamics of repulsive particles confined between a horizontally driven top plate and a vertically oscillating bottom plate Our numerical results show a suppression of the high dissipative stick-slip regime in a well-defined range of frequencies that depends on the vibrating amplitude, the normal applied load, the system inertia and the damping constant We propose a theoretical explanation of the numerical results and derive a phase diagram indicating the region of parameter space where friction is suppressed Our results allow to define better strategies for the mechanical control of friction

Adaptive Control of Uncertain Hamiltonian Multi-Input Multi-Output Systems: With Application to Spacecraft Control

Abstract: A novel adaptive tracking control law for nonlinear Hamiltonian multi-input-multi-output (MIMO) systems with uncertain parameters in the actuator modeling as well as the inertia and/or the Coriolis and centrifugal terms is developed. The physical properties of the Hamiltonian systems are effectively used in the control design and the stability analysis. The number of the parameter estimates is significantly lowered as compared to the conventional adaptive control methods which are based on the state-space form. The developed control scheme is applied for attitude control of a spacecraft with both the inertia and the actuator uncertainties, and numerical examples show that the controller successfully deals with the unknown inertia/actuator parameters.

Inverse dynamics of the 6-dof out-parallel manipulator by means of the principle of virtual work

Abstract: In this paper, the inverse dynamics of the 6-dof out-parallel manipulator is formulated by means of the principle of virtual work and the concept of link Jacobian matrices. The dynamical equations of motion include the rotation inertia of motor–coupler–screw and the term caused by the external force and moment exerted at the moving platform. The approach described here leads to efficient algorithms since the constraint forces and moments of the robot system have been eliminated from the equations of motion and there is no differential equation for the whole procedure. Numerical simulation for the inverse dynamics of a 6-dof out-parallel manipulator is illustrated. The whole actuating torques and the torques caused by gravity, velocity, acceleration, moving platform, strut, carriage, and the rotation inertia of the lead screw, motor rotor and coupler have been computed.

Velocity-gradient statistics along particle trajectories in turbulent flows: The refined similarity hypothesis in the Lagrangian frame

Abstract: We present an investigation of the statistics of velocity gradient related quantities, in particular energy dissipation rate and enstrophy, along the trajectories of fluid tracers and of heavy/light particles advected by a homogeneous and isotropic turbulent flow. The refined similarity hypothesis (RSH) proposed by Kolmogorov and Oboukhov in 1962 is rephrased in the Lagrangian context and then tested along the particle trajectories. The study is performed on state-of-the-art numerical data resulting from numerical simulations up to Reλ∼400 with 20483 collocation points. When particles have small inertia, we show that the Lagrangian formulation of the RSH is well verified for time lags larger than the typical response time τp of the particle. In contrast, in the large inertia limit when the particle response time approaches the integral time scale of the flow, particles behave nearly ballistic, and the Eulerian formulation of RSH holds in the inertial range.

Particle swarm optimization with an oscillating inertia weight

Abstract: In this paper, we propose an alternative strategy of adapting the inertia weight parameter during the course of particle swarm optimization, by means of a non-monotonic inertia weight function of time. Results demonstrate that an oscillating inertia weight function is competitive and in some cases better than established inertia weight functions, in terms of consistency and speed of convergence.

The forced motion of a flag

Abstract: The prevailing view of the dynamics of flapping flags is that the onset of motion is caused by temporal instability of the initial planar state. This view is re-examined by considering the linearized two-dimensional motion of a flag immersed in a high-Reynolds-number flow and taking account of forcing by a ‘street’ of vortices shed periodically from its cylindrical pole. The zone of nominal instability is determined by analysis of the self-induced motion in the absence of shed vorticity, including the balance between flag inertia, bending rigidity, varying tension and fluid loading. Forced motion is then investigated by separating the flag deflection into ‘vortex-induced’ and ‘self’ components. The former is related directly to the motion that would be generated by the shed vortices if the flag were absent. This component serves as an inhomogeneous forcing term in the equation satisfied by the ‘self’ motion. It is found that forced flapping is possible whenever the Reynolds number based on the pole diameter ReD ≳ 100, such that a wake of distinct vortex structures is established behind the pole. Such conditions typically prevail at mean flow velocities significantly lower than the critical threshold values predicted by the linear theory. It is therefore argued that analyses of the onset of flag motion that are based on ideal, homogeneous flag theory are incomplete and that consideration of the pole-induced fluid flow is essential at all relevant wind speeds.

Persistent correlation of constrained colloidal motion.

Abstract: We have investigated the motion of a single optically trapped colloidal particle close to a limiting wall at time scales where the inertia of the surrounding fluid plays a significant role. The velocity autocorrelation function exhibits a complex interplay due to the momentum relaxation of the particle, the vortex diffusion in the fluid, the obstruction of flow close to the interface, and the harmonic restoring forces due to the optical trap. We show that already a weak trapping force has a significant impact on the velocity autocorrelation function C(t)= at times where the hydrodynamic memory leads to an algebraic decay. The long-time behavior for the motion parallel and perpendicular to the wall is derived analytically and compared to numerical results. Then, we discuss the power spectral densities of the displacement and provide simple interpolation formulas. The theoretical predictions are finally compared to recent experimental observations.

Decreasing the Apparent Inertia of an Impedance Haptic Device by Using Force Feedforward

Abstract: When using a haptic device in unconstrained movement, the user should experience only minor inertia. For certain tasks, the workspace of the device should be similar or even larger than that of the human arm. This condition tends to lead to large devices that often present high rather than low inertia. This brief describes a method to decrease the inertia felt by users of impedance haptic devices. It has been successfully implemented in the LHIfAM haptic device. The effect that this strategy has on stability and virtual contact is also illustrated.

Design, test and model of a hybrid magnetostrictive hydraulic actuator

Abstract: The basic operation of hybrid hydraulic actuators involves high frequency bi-directional operation of an active material that is converted to uni-directional motion of hydraulic fluid using valves. A hybrid actuator was developed using magnetostrictive material Terfenol-D as the driving element and hydraulic oil as the working fluid. Two different lengths of Terfenol-D rod, 51 and 102 mm, with the same diameter, 12.7 mm, were used. Tests with no load and with load were carried out to measure the performance for uni-directional motion of the output piston at different pumping frequencies. The maximum no-load flow rates were 24.8 cm3 s−1 and 22.7 cm3 s−1 with the 51 mm and 102 mm long rods respectively, and the peaks were noted around 325 Hz pumping frequency. The blocked force of the actuator was close to 89 N in both cases. A key observation was that, at these high pumping frequencies, the inertial effects of the fluid mass dominate over the viscous effects and the problem becomes unsteady in nature. In this study, we also develop a mathematical model of the hydraulic hybrid actuator in the time domain to show the basic operational principle under varying conditions and to capture phenomena affecting system performance. Governing equations for the pumping piston and output shaft were obtained from force equilibrium considerations, while compressibility of the working fluid was taken into account by incorporating the bulk modulus. Fluid inertia was represented by a lumped parameter approach to the transmission line model, giving rise to strongly coupled ordinary differential equations. The model was then used to calculate the no-load velocities of the actuator at different pumping frequencies and simulation results were compared with experimental data for model validation.

Flight Dynamics of Flexible Aircraft with Aeroelastic and Inertial Force Interactions

Abstract: This paper presents an integrated flight dynamic modeling method for flexible aircraft that captures coupled physics effects due to inertial forces, aeroelasticity, and propulsive forces that are normally present in flight. The present approach formulates the coupled flight dynamics using a structural dynamic modeling method that describes the elasticity of a flexible, twisted, swept wing using an equivalent beam-rod model. The structural dynamic model allows for three types of wing elastic motion: flapwise bending, chordwise bending, and torsion. Inertial force coupling with the wing elasticity is formulated to account for aircraft acceleration. The structural deflections create an effective aeroelastic angle of attack that affects the rigid-body motion of flexible aircraft. The aeroelastic effect contributes to aerodynamic damping forces that can influence aerodynamic stability. For wing-mounted engines, wing flexibility can cause the propulsive forces and moments to couple with the wing elastic motion. The integrated flight dynamics for a flexible aircraft are formulated by including generalized coordinate variables associated with the aeroelastic-propulsive forces and moments in the standard state-space form for six degree-of-freedom flight dynamics. A computational structural model for a generic transport aircraft has been created. The eigenvalue analysis is performed to compute aeroelastic frequencies and aerodynamic damping. The results will be used to construct an integrated flight dynamic model of a flexible generic transport aircraft.

Modelling and simulation of mechanical transmission in roller‐screw electromechanical actuators

Abstract: Purpose – The purpose of this paper is to develop accurate model and simulation of mechanical power transmission within roller‐screw electromechanical actuators with special attention to friction, compliance and inertia effects. Also, to propose non‐intrusive experiments for the identification of model parameters with an integrator or system‐oriented view.Design/methodology/approach – At system design level, the actuation models need to reproduce with confidence the energy losses and the main dynamic effects. The adopted modelling methodology is based on non‐intrusive measurements taken on a standard actuator test‐bench. The actuator model is first structured with respect to the bond‐graph formalism that allows a clear identification of the considered effects and associated causalities for model implementation. Various approaches are then combined, mixing blocked or moving load, position or torque control and time or frequency domains analysis. The friction representation model is suggested using a step‐b...