Showing papers on "Inertia published in 1987"

High velocity flow in porous media

Abstract: Experimental observations have established that the proportionality between pressure head gradient and fluid velocity does not hold for high rates of fluid flow in porous media. Empirical relations such as Forchheimer equation have been proposed to account for nonlinear effects. The purpose of this work is to derive such nonlinear relationships based on fundamental laws of continuum mechanics and to identify the source of nonlinearity in equations.

Robot control apparatus

Abstract: A robot control apparatus stores the result of operation on the inertia term of an equation of motion depending upon the position of the robot arm, so that the operation period on the inertia term is set longer than the operation period on the drive torque. In controlling the robot with the same precision, therefore, the drive torque can be calculated in a short period of operation time.

SHORT COMMUNICATION Mode shape corrections for dynamic response to wind

Abstract: It is now standard practice to carry out wind tunnel tests of tall buildings greater than 30-40 storeys in height for the dynamic response induced by wind action. Such tests are either aeroelastic tests in which the inertia and stiffness properties of the structure are modelled 1 or force balance tests designed to determine the generalized force spectrum in the first mode of vibration. 2 Both the force balance tests and aeroelastic tests in which a rigid model, pivotted at the base, is used, produce information relevant to a building with a fundamental mode shape varying linearly with height in the form :

Effect of Fluid Inertia on Squeeze-Film Damper Forces for Small-Amplitude Circular-Centered Motions

Abstract: Fluid-film forces generated by squeeze-film dampers (SFD) in response to small-amplitude centered motions are of special interest for stability analyses of rotating machinery employing SFDs with strong centering springs. They form the basis for calculation of linearized damping and inertia force coefficients obtained by subjecting the journal center to very small perturbations in velocity and acceleration. The analysis considers the fluid flow in an open-ends SFD due to small-amplitude circular-centered motions. Simplified governing equations are derived; and regarding the flow to be stable and laminar, the linear flow equations are solved exactly for arbitrary values of the Reynolds number. Exact damping and inertia force coefficient are then derived for open ends SFDs with arbitrary L/D ratios. Presented at the 41st Annual Meeting in Toronto, Ontario, Canada May 12–15, 1986

Inertia effects on natural convection in a vertical porous cavity

Abstract: Inertia effects on buoyancy-driven flow and heat transfer in a vertical porous cavity are examined by using the Forchheimer-extended Darcy equation of motion for flow through porous media. A dimensional analysis indicates that in the inertial flow regime a new dimensionless parameter, the Forchheimer number Fs, which characterizes the porous matrix structure and its confinement, must be considered together with the Rayleigh and Prandtl numbers, Ra* and Pr*. Finite-difference numerical results obtained for a wide range of parameters indicate that the effect of Prandtl number and aspect ratio remains unchanged with an enhancement in the inertia effects, whereas the dependence on Grashof and Forchheimer numbers changes substantially. Indeed, for a Nusselt number correlation Nu = CGr*pPr*qFs−rA−s, q and s remain the same as those obtained for Darcy flow, but p and r change in such a way that p + r is always equal to the value of p in the Darcy regime. The criteria for the Darcy and inertial flow limits are al...

Hydraulic pressure control for reducing engagement shock of automatic transmission

Abstract: A hydraulic pressure control system for reducing engagement shock of a frictional element in an automatic transmission, comprises an electromagnetically operated valve for generating a hydraulic pressure supplied to the frictional element, and a control unit for controlling the hydraulic pressure such that the level of the hydraulic pressure generated is adjusted to a target value. In the control unit, the difference in the torque applied to the transmission output shaft owing to a shifting operation is determined, the length of time from the beginning of an inertia phase to the end of the inertia phase is determined, the mean rate of change in the torque of the output shaft during the length of time is determined, and the target value is determined such that the torque on the transmission output shaft varies at the mean rate of change during the inertia phase.

Experimental Measurement of the Dynamic Pressure Distribution in a Squeeze-Film Bearing Damper Executing Circular-Centered Orbit

Abstract: A review of previous experimental measurements of squeeze film damper (SFD) forces is given. Measurements by the authors of SFD pressure fields and force coefficients, for circular centered orbits with epsilon = 0.5, are described and compared with computer predictions. For Reynolds numbers over the range 2-6, the effect of fluid inertia on the pressure fields and forces is found to be significant.

Variable inertia energy storage system

Abstract: A variable inertia energy storage system for storing large amounts of mechanical energy for an extended period of time on land or on a mobile vehicle includes a fly wheel having a rotating hub with spoke appendages each having an associate mass the center of which can be controllably changed with respect to the hub axis of rotation. The energy storage system also includes motor/­generator elements for providing rotation forces to input mechanical energy to the flywheel or for generating electrical power for use on demand by a subsystem or the like.

Effects of Fluid Inertia on Finite-Length Squeeze-Film Dampers

Abstract: The influence of fluid inertia on the SFD force response to circular-centered motions of arbitrary amplitude is analyzed in detail, For finite length, locally sealed SFDs, integro-differential equations are derived in terms of the mean flow components. Numerical predictions, using the finite-element method, show that the damping and added mass coefficients remain invariant as the Reynolds number increases from small values to a moderate Reynolds number equal to 10. An approximate, finite-length, solution for the fluid-film forces has been analytically obtained which accounts for the fluid-inertia effect as well as local end seal effects in symmetric SFD configurations. The approximate solution, strictly valid for small Reynold numbers (Re < 1), agrees well with the results from the numerical solution for most SFD configurations and orbit radii considered. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Tribology Conference in Pittsburgh, Pennsylvania, October 20–22, 1986

Shift shock alleviating system for automatic transmission

Abstract: A rate of the proceeding of a shifting operation during an inertia phase is adjusted to a target value such that a transmission output torque varies without any rapid change during the inertia phase and agrees smoothly with an output torque value to be established after the gear shift at the ending of the inertia phase.

FEM-analysis of transverse vibrations of an axially moving membrane immersed in ideal fluid

Abstract: Transverse vibrations of an axially moving (travelling in its own plane) membrane submerged in ideal fluid are analysed using the FEM. The discrete equations differ from the equations of the common coupled problem in that there appear two additional inertia terms due to the convective acceleration. The effect of the density of the element mesh, the effect of the truncation distance and the effect of various lumping techniques on the accuracy of the results are studied. The FEM-results are compared with available analytical and experimental results. The agreement seems to be rather good.

A Fully Coupled Variable Properties Thermohydraulic Model for a Cryogenic Hydrostatic Journal Bearing

Abstract: The goal set forth here is to continue the work started by Braun et al. (1984-1985) and present an integrated analysis of the behavior of the two row, 20 staggered pockets, hydrostatic cryogenic bearing used by the turbopumps of the Space Shuttle main engine. The variable properties Reynolds equation is fully coupled with the two-dimensional fluid film energy equation. The three-dimensional equations of the shaft and bushing model the boundary conditions of the fluid film energy equation. The effects of shaft eccentricity, angular velocity, and inertia pressure drops at pocket edge are incorporated in the model. Their effects on the bearing fluid properties, load carrying capacity, mass flow, pressure, velocity, and temperature form the ultimate object of this paper.

Finite Element Analysis of a Steady‐State Rotating Tire Subjected to Point Load or Ground Contact

Abstract: A radial automobile tire undergoing steady‐state rotation is analyzed by a finite element method. A special formulation is used which allows the finite element equations to be solved as a quasi‐static problem using static analysis solution procedures, rather than as a dynamic problem requiring solution in the time domain. This is accomplished through a transformation of variable that changes time derivatives, present through inertia, to spatial derivatives. Solution time for the analysis is thereby shortened. The tire is modeled first as a two‐dimensional ring on an elastic foundation, then in its full three‐dimensional geometry. Rotational speeds are those at which resonance occurs so that the dynamics can be easily visualized and the response easily verified. The models are subjected to point load excitation or ground contact. Point load is used to predict resonance responses of the undamped tire. Results agreed well with experimental measurements. The effect of inertia components and damping o...

Flap-lag equations of motion of rigid, articulated rotor blades with three hinge sequences

Abstract: A derivation of coupled flap-lag equations of motion for a rigid articulated rotor with hinge springs and viscous dampers is reported. Three different flapping-lag-pitch hinge sequences are considered and the Lagrange method is used to derive the equations. The effects of the complete six degrees-of-freedom aircraft motions are included and all the inertia dynamic terms are retained; no small-angle assumptions are used in the development. Comparisons of the results with those available in the literature are made. Sources of terms missing in previous analyses, especially those of the inertia dynamics, are identified.

Inertia, resonant frequency, stiffness and kinetic energy of the human forearm

Abstract: The biodynamics of the forearm of a number of relaxed human subjects have been investigated using a printed motor as a torque generator. Oscillation in the horizontal plane at the resonant frequency has been maintained by feed-back of a modified velocity signal. By means of negative position feed-back the stiffness could be artificially increased and the resonant frequency accordingly elevated. From these changes it has been possible to calculate limb inertia and muscle stiffness, treating the limb as a torsion pendulum. The correlation of inertia with the fifth power of limb length has been studied, this relationship being predicted on theoretical grounds. A significant correlation was found between resonant frequency and the square root of the reciprocal of inertia, a relationship also predicted on theoretical grounds. As the limb was kept on resonance the motion was limited solely by the damping. When the rate of oscillation was increased by the use of added stiffness the peak velocity increased, indicating that the damping was reduced. The mean inertia and mean stiffness values for the men were higher than those for the women. The kinetic energy of rapid voluntary movements was greater in men than in women.

Momentum compensated rotary actuator with harmonic drive

Abstract: The momemtum compensated actuator in this invention directly torques the compensating inertia relative to the pointed structure with the harmonic drive used to insure the rotational rate ratio between the compensating inertia and pointed structure is constant at all times. Improvements to the actuator are: 1. a harmonic drive wave generator shaft coupling that is torsionally very stiff with no backlash about the wave generator rotational axis, but is compliant to small wave generator motions orthogonal to the rotational axis due to harmonic drive ring gear-flexspline tooth mesh errors; 2. a shaft link between the pointed structure and the base vehicle with a threaded means to compressional preload all the rotational structure support ball bearings; 3. a means to provide a rotational bias rate to the actuator rotational reference structure assuring that during pointing each rotating structure support ball bearing race has a different rotational rate eliminating non linear stiction friction effects.

Seat belt retractor mechanism

Abstract: There is provided an improvement in a seat belt retractor mechanism of the type having a seat belt reel rotatably mounted in a support frame adapted to be assembled on a movable door of a vehicle, wherein the reel has at least on one end a generally circular ratchet plate for engaging a locking element movably mounted on the support frame between a first position allowing the reel to payout the belt freely and a second position engaging the ratchet plate to hold the reel against rotation to payout the seat belt. An inertia sensing element carried by the support frame shifts this locking element into the locked position upon being moved by inertia forces caused by rapid acceleration or deceleration of the vehicle to which the mechanism is mounted. In addition, an electromagnet is employed for increasing the amount of inertia force needed to move the inertia sensor element during such rapid changes in speed of the vehicle. This electromagnet is energized when the door is opened so that movement of the door itself by the occupant in entering or leaving the vehicle will not trip the sensor element. The improvement is the provision of a generally flat pole surface for the electromagnet and a generally flat keeper surface which are engaged in a generally coplanar relationship to cause the increased inertia force by magnetic attraction between the engaged surfaces upon energizing the electromagnet when the door is open. When the door is closed, there is no magnetic force between the engaging surfaces so that the inertia sensor element is moved by normal inertia forces.

On the Dynamics and Control of Robotic Manipulators with an Automatic Balancing Mechanism

Abstract: Non-linear characteristics and uncertainty in manipulator dynamics caused by payload effects are major hurdles in controller design. To overcome such hurdles the authors have introduced an automatic balancing concept which has been proved to reduce the non-linear complexity in manipulator dynamics as well as to remove gravity loading. This paper examines the characteristic features of balanced manipulator dynamics in more detail and presents an efficient control algorithm suitable for the dynamics. Since the dynamics of a balanced manipulator are characterized by partially configuration-independent inertial properties, the present algorithm adopts two different control concepts ‘the computed torque control’ for the joint having coupled, configuration-dependent inertia and ‘an optimal constant feedback control’ for the joints having configuration-independent inertia. To evaluate the proposed control algorithm, simulation studies were made over a wide range of manipulator speeds and payloads. Based upon the...

Nonlinear flexural vibrations of rectangular plates subjected to in-plane forces using a new shear deformation theory

Abstract: Recently developed shear deformation theory is used to analyse large amplitude, flexural vibrations of laminated rectangular plates subject to in-plane forces. Single mode approach, in conjunction with the Galerkin method, is used to reduce the five coupled equilibrium equations to a single second order ordinary differential equation in time variable by ignoring certain inertia terms. This reduced equation involves quadratic and cubic nonlinearities and the solution of which is obtained by the method of Multiple Scales. Numerical results are presented in tabular form for various parameters of the rectangular plate considered.

Nonlinear Three-Dimensional Dynamic Analysis of Marine Risers

Abstract: Marine risers are modeled as thin-walled, slender, extensible or inextensible, tubular beams subject to nonlinear three-dimensional hydrodynamic loads of interactive nature, torsion and distributed couples, inertia forces and varying axial tension. A finite element, time-incremental algorithm is developed which utilizes equilibrium and kinematic constraints to reduce the required computational time. Iterations are used within each increment to assure convergence of deformation, stiffness matrices and external loads. The algorithm is implemented numerically and the developed computer code is used in several numerical applications to show that a structurally linear model may not be accurate enough and may occasionally be nonconservative in predicting the dynamic riser response.