Inertia Components Research Articles

Construcción de un péndulo de torsión para la medida de la fricción interna a bajas temperaturas

In this work we describe the assembly, operation and specifications of an inverted torsion pendulum designed to measure internal friction at low temperatures (from 4.2 K to 500 K). The high precision mechanics allow us to obtain internal friction spectra with low levels of noise from amplitudes as small as 2x10 -7 . The inertia components of the pendulum have been built with specific materials, so that the resonance frequency of the pendulum can be changed within two orders of magnitude (0.1-10 Hz). In addition, the sample can be in situ deformed at any temperature and can be inserted into the pendulum at liquid nitrogen temperature. The operation of the pendulum, all the control processes and data acquisition are completely automated.

Development and characterization of an automatic technique for the alignment of fMRI time series.

An automatic technique for the registration of fMRI time series has been developed, implemented and tested. The method assumes the human brain to be a rigid body and computes a head coordinate system on the basis of three reference points that lies on the directions corresponding to two of the principal axes of the volume at the intersections with the head boundary. Such directions are found computing the eigenvectors of the symmetric inertia matrix of the image. The inertia components were extracted weighting pixels' coordinates with their intensity values. The three reference points were found in the same position, relative to the head, in both the test and the reference images. The technique has been tested using T2*-weighted Magnetic Resonance (MR) images in which known rigid body transformations have been applied. The results obtained indicate that the method offers subvoxel accuracy in correcting misalignment among time points in fMRI time series.

FLUID DAMPING OF AN ELASTIC CYLINDER IN A CROSS-FLOW

Damping characteristics of fluid–structure systems are difficult to measure or calculate. In the past, such data have been rather scarce. This study reports an attempt on the use of a numerical approach to derive damping ratios related to fluid–structure interactions. It is based on an autoregressive moving-average (ARMA) method, which is used to analyse the displacement time series obtained from a numerical simulation of an elastic cylinder in a uniform cross-flow. The damping ratios show a similar trend to those obtained in previous experiments. An alternative way to deduce damping ratios is to decompose the transverse force in the structural dynamics equation into a drag (or out-of-phase) and an inertia (or in-phase) component for analysis. The damping thus deduced is in fair agreement with that obtained from ARMA; however, at or near synchronization, where the natural frequency of the stationary cylinder is close to the vortex shedding frequency, there is a very substantial difference between the two results.

Interactive Mathematical Models of Subjective Alertness and Cognitive Throughput in Humans

The authors present here mathematical models in which levels of subjective alertness and cognitive throughput are predicted by three components that interact with one another in a nonlinear manner. These components are (1) a homeostatic component (H) that falls in a sigmoidal manner during wake and rises in a saturating exponential manner at a rate that is determined by circadian phase during sleep; (2) a circadian component (C) that is a function of the output of our mathematical model of the effect of light on the circadian pacemaker, with the amplitude further regulated by the level of H; and (3) a sleep inertia component (W) that rises in a saturating exponential manner after waketime. The authors first construct initial models of subjective alertness and cognitive throughput based on the results of sleep inertia studies, sleep deprivation studies initiated across all circadian phases, 28-h forced desynchrony studies, and alertness and performance dose response curves to sleep. These initial models are then refined using data from nearly one hundred fifty 30- to 50-h sleep deprivation studies in which subjects woke at their habitual times. The interactive three-component models presented here are able to predict even the fine details of neurobehavioral data from sleep deprivation studies and, after further validation, may provide a powerful tool for the design of safe shift work and travel schedules, including those in which people are exposed to unusual patterns of light.

Squeeze Film Force Modeling for Large Amplitude Motion Using an Elliptical Velocity Profile

Abstract With the aim of seeking a more reasonable solution for the squeeze film force for large amplitude motion with low viscosity fluids, an elliptical velocity profile and the corresponding squeeze film force equations are derived for a two dimensional rectangular plate model using three different approximation methods. Through comparisons with existing theoretical studies which use parabolic velocity profiles for moderate to large Reynolds numbers, it is shown that the squeeze film model using the elliptical profile may be closer to reality. The force level of the dominant temporal inertia component using the elliptical profile (with either the iterative or the energy methods) is between that obtained using the traditional parabolic profile with the momentum method and that obtained with either the iterative or the energy methods.

Concepts for Wave-Excited Offshore Structures

A study of the resultants of the inertia and drag-force intensities induced by waves on offshore structures is made. The relationships between these resultants and the corresponding modal forces that govern the structural response are examined, and information and concepts are reported that elucidate the main factors that control such forces. The demonstration that the inertia and drag components of the modal forces can be expressed in terms of the sea-surface kinematics is a distinguishing feature of the study. More specifically, it is demonstrated that, in deep waters, the inertia modal force is particularly influenced by the horizontal water-particle displacement evaluated at the still-water level. The corresponding drag modal force is shown to be controlled by the square of the vertical water-particle displacement computed at the same level. The analyses for the wave excitations presented in this paper advance the understanding of their characteristics and are potentially useful for the development of efficient design-oriented procedures for offshore platforms. Analyses for the wave-induced structural response are also presented that further enhance the usefulness of the reported information and concepts.

Force resultants for deep-water wave-excited offshore structures

Concepts are developed which lead to an improved understanding of the characteristics of the wave forces that act on deep-water, jacket-type offshore structures. These concepts are the result of comprehensive examinations of both the inertia and the drag force components of the wave excitation. It is shown that, under conditions which are of practical importance, the resultants of the inertia and drag force components can both be expressed in terms of the motion of the sea surface. Fundamental modal forces which govern fundamental modal responses for offshore structures are also examined, and the relationships between these modal forces and the resultants of the inertia and drag force components are established. The structural response itself is further examined, and valuable information is developed which is believed to be of practical importance.

Expectations and Preferences in British General Elections

We address two questions: How do people form their expectations about the likely winner of the next general election? and What are the links between expectations and votes? Using data collected by the Gallup organization in Great Britain, we find that the expectations formation process (1) has a significant inertia component but also a rapid adjustment to current information; (2) reflects voters' ability to translate economic expectations into political forecasts; and (3) is “time-bounded,” possessing special characteristics immediately before and after a general election. The analysis also confirms the existence of a small bandwagon effect, whereby expectations that one party will win inflate that party's vote. The ability of voters to make reasonable forecasts without being unduly influenced by their own preferences suggests that under normal circumstances voters are expressing real preferences and not simply following the crowd.

Dynamic Modal Responses of Wave‐Excited Offshore Structures

Examinations are made of the dynamic effects associated with modal responses of deep‐water, wave‐excited offshore structures. Such examinations are intended to assess the influences that variations in several parameters involved have on the dynamic structural response. Variations in the following parameters are considered: the distributions of the structural volume and projected area, the distributions of the inertia and drag force coefficients, the relative magnitude of the inertia and drag force components, the natural modes of vibration of the structure, and the random phase angles used for the generation of the wave loading. The response is examined for a wide range of values of the natural frequencies of the system, and the relative importance of the effects of changes in the parameters considered is elucidated. The results of the study provide valuable insight into the response of offshore structures to wave forces, and may contribute to forming a basis for the development of future, efficient desig...

Inertia components of motor development in infants

Inertia components of motor development in infants

Frequency Domain Analysis of In-Line Forces on Circular Cylinders in Random Oscillatory Flow

Experiments were conducted to study random hydrodynamic loading of smooth, rigidly mounted circular cylinders exposed to random oscillatory flow conditions. The experiments were conducted in a water tunnel for statistical Keulegan-Carpenter numbers ranging from KCr = 6.8 to 11.6 and statistical Reynold’s numbers from Rer = 8211 to 20169 under broad and narrow-band flow conditions. A two-input/single-output frequency domain model for the in-line force is used to directly identify frequency-dependent inertia and drag coefficients. This model was also used to show the relative strength of the inertia and drag components in the frequency domain for different random flow conditions parameterized by KCr, Rer and the velocity spectral width, q. This analysis illustrates the effect of statistical flow parameters (KCr, Rer and q) on the nonlinear behavior of the in-line forces. Estimates of the in-line force power spectral density under random flow conditions are determined using the two-input/single-output model and compared to the method for estimating wave forces on a cylindrical structure by Borgman (1967, 1972).

General structure of time-optimal control of robotic manipulators moving along prescribed paths

Abstract The structure is addressed of time-optimal control of robotic manipulators along a specified geometric path subject to constraints on control torques. Both regular and singular (where one or more effective inertia components is/are zero on any finite time interval) cases are studied by using the extended Pontryagin's minimum principle and a parametrization method. It is shown that the structure of the time-optimal control law requires either (a) one and only one control torque to be always in saturation in every finite time interval along its optimal trajectory, while the rest of them adjust their values so that the motion of the robot is guaranteed along the constrained path, or (b) at least one of the actuators to take on its extremal values. The first form of the control law dominates the robot motion along the optimal trajectory although the second form may exist. The theoretical results are verified by various existing numerical examples.

Sensitivity of the dynamic response of simple offshore structural models

Comprehensive analyses are made of the dynamic response of simple models of offshore structures to assess the effects of numerous factors involved. Useful information and concepts of structural behavior are developed, and valuable insight is provided into the response of such structures. After evaluating the effects on the response of changes in the relative magnitudes of the inertia and drag force components, of the current velocity, and of fluid-structure interaction, the effects of the random phase angles and of wave cancellation are examined, and the importance of each of these effects on the response is elucidated.

Vibrations of turbo-molecular vacuum pumps with high stable magnetic bearings operating within electronic microscope systems

In order to operate Electronic Microscopes vibration free, it is necessary to assemble the apparatus on a vibration free isolated desk. Similarly, strict requirements, regarding vibrations, are demanded from the attached vacuum pump which provides vacuum for the system. The rotor and rotating shaft of Turbo Molecular Pumps with mechanical bearings are connected to the pump housing by means of ball bearings. The inertia and vibration component resulting from the ball bearing dynamic effects produce the vibration results as indicated in Fig. 1.In order to design a Turbo Molecular Pump with minimum vibration effects it was necessary to provide the pump with a magnetic bearing system containing 4 passive and 1 active controlled axis. This magnetic bearing system is less sensitive to vibration and simpler in assembly than other existing more complicated 5-axis active controlled versions. However it is more complication than the mechanical bearing type. The magnet bearing is provided with a touch-down bearing. Larger pump movements due to high or low frequency stimulation recieved via the microscope desk could result in forcing the shaft out of its magnet-bearing-centre position, the touch-down bearing now re-centres the shaft allowing immediate magnetic bearing centre recovery.

Determining and accounting for a parachute virtual mass

The concept of virtual mass is described, and experiments are outlined in which virtual mass and virtual inertia components for a parachute canopy were determined. Results show that these components depend on the canopy shape and its attitude relative to the airflow; they also depend on the dimensionless acceleration, or acceleration number, of the parachute. Except at high values of acceleration number, these virtual inertia terms are of greater magnitude than corresponding values determined by potential flow methods, and this is characteristic of unsteady bluff-body flows. Their significance is indicated in dynamic behavior prediction for the descending fully deployed parachute canopy.

Forces on Vertical Cylinder Due to Random Waves

Random wave forces consisting of drag and inertia components are analyzed. The forces were measured in a wave tank experiment with circular cylinders at low Keulegan‐Carpenter numbers. The values of the hydrodynamic coefficients were chosen from the corresponding tests in regular waves. The method used in choosing these values applicable to the case of random waves is discussed. The nonlinear drag force contribution is linearized so that the spectral approach may be applied directly. Good correlations between the measured force spectra and the computed spectra were obtained in several cases of random waves. The short‐term distribution of the in‐line and transverse forces is shown. It is found that the in‐line force amplitudes follow the Rayleigh distribution reasonably well. The relations of the transverse force to an exponential distribution are exhibited.

Optimizing the compression/briquetting of fibrous agricultural materials

A compression ratio model, and a repeated compression concept have been used to analyse the effect of chopping and grinding material samples, hold time and initial charge density on the compaction process in a closed die. The specific energy of compaction was separated into inertia and elastic components, and the proportion expended on overcoming frictional resistance quantified. The inertia stage is shown to account for 14 to 38% of the total specific energy. The recovery of the compacted material in a die was evaluated, leading to the definition of a true compression energy, which reflects the “hidden” additional energy associated with the postcompression recovery of a material. The control of in-die recovery, which accounts for 42 to 73% of the total relaxation, is identified as a necessary condition for effective wafering. Although less specific energy was required for compressing ground straw, long straw produced the most stable wafers. Chopping the material was found undesirable both in terms of energy requirement and the stability of the wafer produced. Optimum hold times of 5 and 2·5 s, respectively, were identified for long and ground straw. The optimum initial charge density for ground straw in a 53 mm die is 104 kg/m 3. Based on the findings of the study, a four-stage compaction process, which reflects the inertia and elastic phases of compression, is proposed.

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 on vibrational response of the tire was studied by imposing ground contact at one of the resonance speeds. Damping is included in the model through a two-element Kelvin-Voight viscoelastic material model. Responses of the models were similar to standing wave deformations in a tire.

Dynamic response of dolos armor units

Concrete armor units are commonly employed for the protection of shorelines and rubble structures. Their design is primarily based on hydrodynamic stability, but their structural response to wave loading is poorly understood. In this study a wave force model is presented, which includes drag, inertia, kinetic and buoyant force components, to estimate hydrodynamic loads on the concrete armor unit, dolos. These loads are employed in a three-dimensional FEM analysis to determine the dynamic states of stress in a 42-ton dolos.

Mathematical modeling and simulation of stepping motor systems

A mathematical model is developed for a variable reluctance stepping motor and then a numerical simulation is provided in view of studying the behaviour of the motor chiefly in dynamic start regime. The voltage equations are written considering the magnetic circuit unsaturated and the torque equation contains inertia, viscous friction and load torque components. The six first order differential equations of the model are solved using Basic language programs for a Wang 2200 computer. The motor is tested by numerical simulation in dynamic start regime with constant frequency of input pulses and also with different laws for varying this frequency determing the optimal law for motor acceleration. The method presented here for this aim is generally valid for a wide range of VR stepping motors.