Showing papers on "Inertia published in 2002"

The aerodynamic effects of wing rotation and a revised quasi-steady model of flapping flight.

Abstract: We used a dynamically scaled model insect to measure the rotational forces produced by a flapping insect wing. A steadily translating wing was rotated at a range of constant angular velocities, and the resulting aerodynamic forces were measured using a sensor attached to the base of the wing. These instantaneous forces were compared with quasi-steady estimates based on translational force coefficients. Because translational and rotational velocities were constant, the wing inertia was negligible, and any difference between measured forces and estimates based on translational force coefficients could be attributed to the aerodynamic effects of wing rotation. By factoring out the geometry and kinematics of the wings from the rotational forces, we determined rotational force coefficients for a range of angular velocities and different axes of rotation. The measured coefficients were compared with a mathematical model developed for two-dimensional motions in inviscid fluids, which we adapted to the three-dimensional case using blade element theory. As predicted by theory, the rotational coefficient varied linearly with the position of the rotational axis for all angular velocities measured. The coefficient also, however, varied with angular velocity, in contrast to theoretical predictions. Using the measured rotational coefficients, we modified a standard quasi-steady model of insect flight to include rotational forces, translational forces and the added mass inertia. The revised model predicts the time course of force generation for several different patterns of flapping kinematics more accurately than a model based solely on translational force coefficients. By subtracting the improved quasi-steady estimates from the measured forces, we isolated the aerodynamic forces due to wake capture.

Time-discretized variational formulation of non-smooth frictional contact

Abstract: The present work extends the non-smooth contact class of algorithms introduced by Kane et al. to the case of friction. The formulation specifically addresses contact geometries, e.g. involving multiple collisions between tightly packed non-smooth bodies, for which neither normals nor gap functions can be properly defined. A key aspect of the approach is that the incremental displacements follow from a minimum principle. The objective function comprises terms which account for inertia, strain energy, contact, friction and external forcing. The Euler–Lagrange equations corresponding to this extended variational principle are shown to be consistent with the equations of motion of solids in frictional contact. In addition to its value as a basis for formulating numerical algorithms, the variational framework offers theoretical advantages as regards the selection of trajectories in cases of non-uniqueness. We present numerical and analytical examples which demonstrate the good momentum and energy conservation characteristics of the numerical algorithms, as well as the ability of the approach to account for stick and slip conditions.

Analysis of Large Flexible Body Deformation in Multibody Systems Using Absolute Coordinates

Abstract: To consider large deformation problems in multibody system simulations afinite element approach, called absolute nodal coordinate.formulation,has been proposed. In this formulation absolute nodal coordinates andtheir material derivatives are applied to represent both deformation andrigid body motion. The choice of nodal variables allows a fullynonlinear representation of rigid body motion and can provide the exactrigid body inertia in the case of large rotations. The methodology isespecially suited for but not limited to modeling of beams, cables andshells in multibody dynamics. This paper summarizes the absolute nodal coordinate formulation for a 3D Euler–Bernoulli beam model, in particular the definition of nodal variables, corresponding generalized elastic and inertia forces and equations of motion. The element stiffness matrix is a nonlinear function of the nodal variables even in the case of linearized strain/displacement relations. Nonlinear strain/displacement relations can be calculated from the global displacements using quadrature formulae. Computational examples are given which demonstrate the capabilities of the applied methodology. Consequences of the choice of shape.functions on the representation of internal forces are discussed. Linearized strain/displacement modeling is compared to the nonlinear approach and significant advantages of the latter, when using the absolute nodal coordinate formulation, are outlined.

Structural Inertia and Organizational Change Revisited III: The Evolution of Organizational Inertia

Abstract: Building on a formal theory of the structural aspects of organizational change initiated in Hannan, Polos, and Carroll (2002a, 2002b), this paper focuses on structural inertia We define inertia as a persistent organizational resistance to changing architectural features We examine the evolutionary consequences of architectural inertia The main theorem holds that selection favors architectural inertia in the sense that the median level of inertia in cohort of organizations presumably increases over time A second theorem holds that the selection intensity favoring architectural inertia is greater when foresight about the consequences of changes is more limited According to the prior theory of Hannan, Polos, and Carroll (2002a, 2002b), foresight is limited by complexity and opacity Thus it follows that the selection intensity favoring architectural inertia is stronger in populations composed of complex and opaque organizations that in those composed of simple and transparent ones

In-Flight Estimation of the Cassini Spacecraft's Inertia Tensor

Abstract: A new methodology for estimating the spacecraft 3-by-3 inertia tensor is proposed in this study.

Selective sensitivity of open chaotic flows on inertial tracer advection: catching particles with a stick.

Abstract: We investigate the effects of finite size and inertia of a small spherical particle immersed in an open unsteady flow which, for ideal tracers, generates transiently chaotic trajectories. The inertia effects may strongly modify the chaotic motion to the point that attractors may appear in the configuration space. These studies are performed in a model of the two-dimensional flow past a cylindrical obstacle. The relevance to modeling efforts of biological pathogen transport in large-scale flows is discussed. Since the tracer dynamics is sensitive to the particle inertia and size, simple geometric setups in such flows could be used as a particle mixture segregator separating and trapping particles.

A New Optimization Method for Dynamic Design of Planar Linkage With Clearances at Joints—Optimizing the Mass Distribution of Links to Reduce the Change of Joint Forces

Abstract: This paper presents a new optimization method for dynamic design of planar linkage with clearances at joints. The general consideration is to optimize the mass distribution of links to reduce the change of joint forces. The mass, the center position of mass and the moment of inertia the moving links are taken as the optimizing variables. The objective functions are taken as the changes of the amplitude and direction of the joint forces and they are minimized. The optimized result shows that the magnitude of joint force can be controlled hardly to change and the direction of joint force can be controlled to change smoothly with respect to the crank angle, although the clearances exist at the joints. The link shape can be formed with the optimized variables by using the small element superposing method (SESM) and a design example is given.

On-line gyro-based, mass-property identification for thruster-controlled spacecraft using recursive least squares

Abstract: Spacecraft control, state estimation, and fault-detection-and-isolation systems are affected by unknown variations in the vehicle mass properties. It is often difficult to accurately measure inertia terms on the ground, and mass properties can change on-orbit as fuel is expended, the configuration changes, or payloads are added or removed. Recursive least squares-based algorithms that use gyro signals to identify the center of mass and inverse inertia matrix are presented. They are applied in simulation to 3 thruster-controlled vehicles: the X-38 and Mini-AERCam under development at NASA-JSC, and the S4, an air-bearing spacecraft simulator at the NASA-Ames Smart Systems Research Lab (SSRL).

The Inertia Tensor Versus Static Moment and Mass in Perceiving Length and Heaviness of Hand-Wielded Rods

Abstract: In 2 experiments, participants haptically estimated length and heaviness of handheld rods while wielding without seeing them. The sets of rods had been constructed such that variation of static moment and the 1st eigenvalue of the inertia tensor (I 1) were separated. Consistent with previous findings, perceived rod length correlated strongly with I1. However, multiple regressions on current data as well as data from previous studies showed a comparable strong correlation between perceived rod length and static moment plus mass. Contrary to previous findings, perceived heaviness correlated strongly with static moment and only weakly with the eigenvalues of the inertia tensor. These results suggest that the inertia tensor does not provide the sole foundation for a theory of dynamic touch. In the past decade or so, significant strides have been made in understanding the perception of properties of objects that are held in the hand but not seen. A large body of experimental data has been presented in support of the hypothesis that many instances of haptic perception are governed by a single yet multivalued physical entity, the inertia tensor ( I). This 3 3 tensor is symmetrical and thus contains six independent numbers. In diagonalized form—that is, when the tensor is expressed with respect to the unique set of axes of symmetrical mass distribution (the so-called principal axes of inertia)—the inertia tensor consists of three elements denoted as the principal moments of inertia or eigenvalues. These principal moments define an object’s (invariant) resistance against rotational acceleration around its principal axes of inertia and have been found to be related to perception of an object’s length (Solomon & Turvey, 1988; Solomon, Turvey, & Burton, 1989a, 1989b), width and height (Turvey, Burton, Amazeen, Butwill, & Carello, 1998), and heaviness (Amazeen & Turvey, 1996). In addition, the eigenvectors of the inertia tensor (defining the direction of the principal axes of inertia of the object) have been found to be related to the perception of an object’s orientation (Pagano & Turvey, 1998; Turvey, Burton, Pagano, Solomon, & Runeson, 1992). More recently, it has been suggested that perception of grip position is a function of the off-diagonal elements of the inertia tensor (i.e., the products of inertia; Pagano, KinsellaShaw, Cassidy, & Turvey, 1994) and that the perception of an object’s partial forward length (i.e., the distance from the hand to the forward-directed endpoint of the rod) is a function of both the moments and products of inertia (Carello, Santana, & Burton, 1996; Pagano, Carello, & Turvey, 1996). In the majority of the studies cited, the invariance of I as well as the fact that it provides information about both magnitude and direction, has been emphasized to support the inertia tensor hypothesis. However, when an object is held as still as possible, it appears difficult to perceive its properties through I because, by definition, an object’s resistance to rotation manifests itself only when the object is rotated. Under static conditions, physical properties such as the static moment (i.e., the first moment of mass

Controlling angular oscillations through mass reconfiguration: a variable length pendulum case

Abstract: The control of angular oscillations or energy of a system through mass reconfiguration is examined using a variable length pendulum. Control is accomplished by sliding the end mass towards and away from the pivot as the pendulum oscillates. The resulting attenuation or amplification of the angular oscillations are explained using the Coriolis inertia force and by examining the energy variation during an oscillation cycle. Simple rules relating the sliding motion to the angular oscillations are proposed and assessed using numerical simulations. An equivalent viscous damping ratio is introduced to quantify the attenuation/amplification phenomena. Sliding motion profiles for achieving attenuation have been simulated with the results being discussed in detail.

Force control of redundant robots in unstructured environment

Abstract: In this paper, a method for force control of redundant robots in an unstructured environment is proposed. We assume that the obstacles are not known in advance. Hence, the robot arm has to be compliant with the environment while tracking the desired position and force at the end-effector. First, the dynamic properties of the internal motion of redundant manipulators are considered. The motion is decoupled into the end-effector motion and the internal motion. Next, the dynamic model of a redundant manipulator is derived. Special attention is given to the inertial properties of the system in the space where internal motion is taking place; the authors define a null-space effective inertia and its inverse. Finally, a control method is proposed which completely decouples the motion of the manipulator into the task-space motion and the internal motion and enables the selection of dynamic characteristics in both subspaces separately. The proposed method is verified with simulation and with experimental results of a four-degrees-of-freedom planar redundant robot.

On the Dynamics of Variable Mass Systems

Abstract: This paper accomplishes two things. It presents a derivation of the equations of motion of variable mass systems. The method presented here is based on Kane's formalism, and is complete, efficient, and mathematically rigorous—avoiding heuristics and many other pitfalls of previous attempts at such derivation. The paper also presents a detailed discussion of the meaning and importance of the various terms of the equations of motion, and the circumstances under which each term can be neglected. It is found that certain judiciously simplified versions of the equations of motion are adequate for most studies. The most important forces contributed by mass variability appear to be the thrust vector and the Coriolis force. The jet damping moment and the moment due to inertia variation are the dominant moments due to mass variability. The study ends with specific equations that are recommended for use in the study of the dynamics of variable mass systems. These equations capture all the important features of the ...

The effect of weak inertia on the emptying of a tube

Abstract: We present an extension of the classical axisymmetric Bretherton theory giving the thickness of the liquid film left on the walls of a drained tube, treating the case of weak inertia by a regular perturbation method. The results obtained by numerical integration fit Taylor’s [J. Fluid Mech. 10, 161 (1961)] experiments, obtained with viscous fluids (glycerine and strong sucrose solutions), and Aussillous and Quere’s [Phys. Fluids 12, 2367 (2000)] experiments with low viscosity liquids (hexamethyldisiloxane and water) when inertia becomes important. The discrepancies observed between the theory and high Reynolds numbers experiments (Re>1000) are commented on.

Coupled Torsion-Lateral Stability of a Shaft-Disk System Driven Through a Universal Joint

Abstract: Understanding the instability phenomena of rotor-shaft and driveline systems incorporating universal joints is becoming increasingly important because of the trend towards light-weight, high-speed supercritical designs. In this paper, a nondimensional, periodic, linear time-varying model with torsional and lateral degrees-of-freedom is developed for a rotor shaft-disk assembly supported on a flexible bearing and driven through a U-joint. The stability of this system is investigated utilizing Floquet theory. It is shown that the interaction between torsional and lateral dynamics results in new regions of parametric instability that have not been addressed in previous investigations. The presence of load inertia and misalignment causes dynamic coupling of the torsion and lateral modes, which can result in torsion-lateral instability for shaft speeds near the sum-type combinations of the torsion and lateral natural frequencies. The effect of angular misalignment, static load-torque, load-inertia, lateral frequency split, and auxiliary damping on the stability of the system is studied over a range of shaft operating speeds. Other than avoiding the unstable operating frequencies, the effectiveness of using auxiliary lateral viscous damping as a means of stabilizing the system is investigated. Finally, a closed-form technique based on perturbation expansions is derived to determine the auxiliary damping necessary to stabilize the system for the least stable case (worst case). ©2002 ASME

Vehicle control apparatus having means for changing inertia torque of engine during shifting action or during switching of operating state of lock-up clutch

Abstract: A control apparatus for an automotive vehicle having an automatic transmission and an engine capable of controlling a resistance to its rotary motion. The control apparatus is adapted to change an output torque of the engine temporarily during a shifting action of the automatic transmission. The control apparatus includes inertia-phase torque changing means for changing an inertia torque of the engine during the shifting action, by controlling the resistance of the rotary motion of the engine. This inertia-phase torque changing means may be adapted to change the inertia torque during a switching of an operating state of a lock-up clutch which is provided in a fluid-operated power transmitting device interposed between the automatic transmission and the engine.

Admittance enhancement in force feedback of dynamic systems

Abstract: A limitation of high-speed contact operations, including robotic assembly, is the magnitude of contact forces resulting from inertial effects. Directly attempting to reduce the apparent inertia of interacting systems through force feedback results in instability. It is shown here that one can introduce a mechanical filter to alter the open-loop system dynamics, making feedback much more effective. Experimental results are presented showing a reduction in apparent inertia by nearly two orders of magnitude.

Non‐linear dynamic behaviour of flexible marine pipes and risers

Abstract: This paper describes the way in which hydrostatic and hydrodynamic forces can be added to the conventional static and inertia forces for the non-linear analysis of 3D flexible pipes and riser systems. Emphasis is placed on elements that use the Reissner–Simo beam theory or a related co-rotational approach. Copyright © 2002 John Wiley & Sons, Ltd.

The fast spinning motion of a rigid body in the presence of a gyrostatic momentum 3

Abstract: In this paper, the rotational motion of a rigid body about a fixed point in the Newtonian force field [1] with a gyrostatic momentum l3 about thez-axis is considered. The equations of motion and their first integrals are obtained and reduced to a quasi-linear autonomous system with two degrees of freedom with one first integral. Poincare's small parameter method [2] is applied to investigate the analytical periodic solutions of the equations of motion of the body with one point fixed, rapidly spinning about one of the principal axes of the ellipsoid of inertia. A geometric interpretation of motion is given by using Euler's angles [3] to describe the orientation of the body at any instant of time.

Control device of automatic transmission

Abstract: PROBLEM TO BE SOLVED: To start inertia phase control in a state of generating a sufficient engaging force by a frictional engaging element, even under a condition of causing reduction in the input shaft rotating speed of a shift gear mechanism during shift control. SOLUTION: A driven state and an undriven state of an engine are determined based on an engine control parameter (such as engine torque or a throttle opening) during the shift control, and the determination of an inertial phase is prohibited by setting an inertial phase determination permitting flag to an off-state at a time t2 when the determination of the engine driving state is switched to the undriven state. The determination of the inertial phase is permitted by setting the inertial phase determination permitting flag to an on-state at a time t3 when a count value of a timer for counting an elapsed time after starting the shift control reaches a predetermined time. Thereafter, a phase is determined whether it is the inertial or a non-inertial phase depending on whether or not an input shaft rotating speed Nt (or the gear ratio) is lower than an inertial phase determining threshold. COPYRIGHT: (C)2008,JPO&INPIT

Measuring the inertia tensor of vehicles

Abstract: SUMMARYA new method for measuring the inertia tensor of rigid bodies has been developed and used for vehicle system dynamics applications.In the first part of the paper a brief state-of-the-art is presented referring to methods for measuring the inertia tensor of vehicles (or other rigid bodies). A number of test-rigs (presented in the literature) are classified and compared.In the second part of the paper a new test-rig, studied and built at the Politecnico di Milano, is introduced. The test-rig allows to measure the inertia tensor of vehicles (of mass up to 3500 kg, or more, after a proper adjustment). The rig is basically a three or four bar pendulum hanging from the ceiling and carrying, by means of a rigid frame the rigid body under investigation, e.g. a full road vehicle. The motion of the hanging vehicle is recorded by means of accelerometers, gyroscopes and inclinometers. The recorded data are numerically processed in order to indentify the full inertia tensor of the vehicle body. The paper presen...

Sensorless Force Estimation for Robots with Friction

Abstract: This paper describes a method for estimating forces applied at the end effector of a robot without the need for force sensors. Servo motor currents and positions are used together with an accurate system model to estimate applied forces. The system model includes inertia, friction and position dependent force components. The signal processing techniques required to extract the force information from the servo motor data are detailed and experimental results from a SCARA robot presented.