Effect Of Rigid Body Motion Research Articles

Nonlinear Dynamics of a Space Tensioned Membrane Antenna during Orbital Maneuvering

Due to the super flexibility and strong nonlinearity of space membrane antennas, the dynamic response of a space membrane antenna will be affected by the rigid–flexible coupling effect in the process of orbital maneuvering. In this case, the dynamic model of a tensioned membrane antenna is significantly different from that under the general condition (fixed boundary). In this study, a nonlinear dynamic model of a tensioned space membrane antenna experiencing maneuvering is established, and the influence of the rigid–flexible coupling effect on structural stiffness and damping characteristics is described. Through a numerical solution, the effects of rigid body motion and structural natural frequency on the rigid–flexible coupling effect are discussed. The results show that the vibration frequency and amplitude of the antenna are positively correlated with the acceleration and initial velocity of rigid body motion. With the increase of the natural frequency of the antenna, the vibration frequency increases but the amplitude decreases. The rigid–flexible coupling nonlinear dynamic model proposed in this work is more applicable in intelligent vibration control compared to finite element software.

Effect of rigid body motion in phase-field models of solid-state sintering

In the last two decades, many phase-field models for solid-state sintering have been published. Two groups of models have emerged, with and without the contribution of rigid body motion. This paper first describes the previously published phase-field model with an advection term driven by rigid body motion. The model is then used to investigate the differences between models with and without rigid body motion in new benchmark geometries exhibiting markedly different behavior. Sensitivity studies concerning the parameters of the rigid-body motion model are conducted and their effects on equilibrium and kinetic properties explored. In particular, it is shown by simulations that a shrinkage rate independent of system size requires the inclusion of an advection term. Finally, the reason behind this behavior is explored and implications for diffusion-only models are drawn.

Low-frequency vibration control of two flexible appendages using a joint with actively tunable stiffness

Low-frequency and large-amplitude vibration of flexible appendages in space can be induced when a spacecraft performs attitude maneuvers and thermal alternations during orbit operation. In this paper, a novel joint mechanism combined with a semi-active method for variable stiffness control is proposed to suppress the low-frequency vibrations of flexible jointed appendages. The variable stiffness of the joint is derived from the linear relationship between its output torque and rotation angle when direct current (DC) power is applied to the coils. Based on the Lagrange equation and the assumed mode method, the coupling dynamic relationships of the active joint and two flexible appendages are established, and semi-active vibration control simulations are performed. A ground experimental platform is built to simulate the microgravity environment in space. The frequency shift effect of rigid body motion and elastic vibration under impact disturbance are investigated. In addition, the effect of variable stiffness control on the elastic deformation of flexible appendages is studied. The simulation and experimental results indicated that the proposed method can control both the rigid body motion of the system and the elastic vibration of the appendages. It has been found that the major frequency bandwidth of the interference signal is within 0.3–1.0 Hz with a substantial vibration attenuation of 1.82–16.62 dB for the joint and 4.86–11.48 dB for the flexible appendages.

A Universal Approach to Tire Forces Estimation by Accelerometer-Based Intelligent Tire: Analytical Model and Experimental Validation

ABSTRACT Efforts to improve the performance and safety of vehicles include placing active sensing components (e.g., embedded microsensors) within tires result in intelligent tires. One application of intelligent tire is tire force estimation based on accelerometers. However, its development is limited due to the difficulty of relating the tire force to kinematical information by model-based theory. In this manuscript, a universal approach to tire forces estimation by the accelerometer-based intelligent tire is formulated and experimentally validated. First, a microelectromechanical system accelerometer-based intelligent tire prototype is established with the function of on-board monitoring of tire forces. Then, a theoretical rolling kinematics model is proposed for illustrating the mechanisms of acceleration fields, resulting from the coupling effect of rigid body motion and elastic deformation. An analytical model is formulated to estimate the vertical force in real time. Furthermore, the beam model is adopted to describe lateral deformations of the tire belt, directly linking lateral acceleration and lateral force. Finally, the lateral force can be estimated by lateral acceleration and vertical force already estimated. Based on a universal analytical model, the lateral force estimation method realizes high accuracy under different circumstances, even with unified coefficients, by clarifying and eliminating the influence of ply steer. A field test and two bench experiments have been conducted to fully validate the developed model. It can be concluded that the theoretical-analysis-based estimation model realizes an encouraging tire force estimation application with an intelligent tire hardware system.

Interaction of two parallel U-notches with tip cracks in PMMA plates under tension using digital image correlation

Stress intensity factors (SIFs) in a polymethyl methacrylate (PMMA) plate with two parallel cracks initiating from U-notch tips under the action of tensile loading were calculated using digital image correlation (DIC). The effect of notch and crack geometry, including crack length, notch depth, and distance between two notches were investigated experimentally. The displacement fields were determined by correlation between reference images and deformed images. The effect of rigid body motion and rotation was eliminated from displacement field, and SIFs were calculated using a least square algorithm. Also, the effect of subset size and number of terms in William’s equation on SIFs was studied. The experimental results were compared with both analytical solution published in literature and Finite Element Method (FEM) simulation. A good agreement between results warrants the accuracy and effectiveness of the experiments. The results show that as the notch distance increases, the values of the mode I stress intensity factor (KI) for two adjacent U-notches approach the obtained KI value for a single notch specimen.

Reproduction of motion artifacts for performance analysis of prospective motion correction in MRI

Despite numerous publications describing the ability of prospective motion correction to improve image quality in magnetic resonance imaging of the brain, a reliable approach to assess this improvement is still missing. A method that accurately reproduces motion artifacts correctable with prospective motion correction is developed, and enables the quantification of the improvements achieved. A software interface was developed to simulate rigid body motion by changing the scanning coordinate system relative to the object. Thus, tracking data recorded during a patient scan can be used to reproduce the prevented motion artifacts on a volunteer or a phantom. The influence of physiological motion on image quality was investigated by filtering these data. Finally, the method was used to reproduce and quantify the motion artifacts prevented in a patient scan. The accuracy of the method was tested in phantom experiments and in vivo. The calculated quality factor, as well as a visual inspection of the reproduced artifacts shows a good correspondence to the original. Precise reproduction of motion artifacts assists qualification of prospective motion correction strategies. The presented method provides an important tool to investigate the effects of rigid body motion on a wide range of sequences, and to quantify the improvement in image quality through prospective motion correction.

The effect of rigid-body motions on the whipping response of a ship hull subjected to an underwater bubble

The dynamic elastic response of a floating ship hull girder to an underwater explosion bubble is normally composed of two parts: rigid-body motion and elastic deformation. However, the effects of rigid-body motion have consistently been neglected in the current literature based on the assumption that they are small. In this paper, our focus is on the study of rigid-body motion effects on the hull girder's elastic deformation, also known as the ‘whipping response’. A theory of interaction between a gas bubble and a hull girder is presented. The bubble dynamic equations combined with the bubble migration, free surface effect and drag force considerations are solved numerically using the Runge–Kutta method. The rigid-body and elastic responses of the hull that are induced by the impulsive pressure of a bubble are calculated using the methods presented herein. Two different examples of real ships are given to demonstrate the effect of rigid-body motion on whipping responses. The numerical results show that rigid-body motions reduce the amplitudes and vibration natural periods of the bending moments of the hull girder. These effects can be ignored for slender hulls, but must be taken into consideration for shorter/wider hulls so as not to underestimate the longitudinal strength.

Alternative stress-integration schemes for large-deformation problems of solid mechanics

In solving nonlinear problems of solid mechanics by the finite-element method, stresses at integration points are usually obtained by integrating nonlinear constitutive equations, given known incremental strains. In a large-deformation analysis, stress–strain relationships must be frame independent such that any rigid-body motion does not induce strain within the material. This principle is generally satisfied by introducing an objective stress rate, such as the Jaumann or Truesdell stress rates, into the constitutive equations. This paper investigates three alternative algorithms for integrating stress–strain relationships in a large-deformation analysis. It is shown that the effect of rigid-body motion is equivalent to a stress transformation and this transformation can be introduced before, after or during integration of the stress–strain constitutive equations. Although there is no theoretical advantage, in terms of accuracy, for selecting one of these strategies over the others, in terms of efficiency of algorithms one is more advantageous than the others. Performance of the proposed algorithms is studied and compared by means of numerical examples. The results of this study can be used in the development of fast and robust algorithms for stress integration of constitutive equations in nonlinear finite-element analysis.

Coupling characteristics of rigid body motion and elastic deformation of a 3-PRR parallel manipulator with flexible links

Modeling of multibody dynamics with flexible links is a challenging task, which not only involves the effect of rigid body motion on elastic deformations, but also includes the influence of elastic deformations on rigid body motion. This paper presents coupling characteristics of rigid body motions and elastic motions of a 3-PRR parallel manipulator with three flexible intermediate links. The intermediate links are modeled as Euler–Bernoulli beams with pinned-pinned boundary conditions based on the assumed mode method (AMM). Using Lagrange multipliers, the fully coupled equations of motions of the flexible parallel manipulator are developed by incorporating the rigid body motions with elastic motions. The mutual dependence of elastic deformations and rigid body motions are investigated from the analysis of the derived equations of motion. Open-loop simulation without joint motion controls and closed-loop simulation with joint motion controls are performed to illustrate the effect of elastic motion on rigid body motions and the coupling effect amongst flexible links. These analyses and results provide valuable insight to the design and control of the parallel manipulator with flexible intermediate links.

Estimation of Size and Depth of Debonds in Laminates From Holographic Interferometry

Double-exposure holography has been shown to be a useful nondestructive testing technique for the detection of debonds in laminates when subjected to vacuum stressing. The size of a debond is estimated from the boundary containing anomalous fringes and subsequently, its depth is estimated from these fringes using a thin-plate model. Rigid-body motion is frequently present during testing, causing ambiguity in the identification of the shape of the debond and hence difficulty in the estimation of its size and depth. In this paper, a simple method is presented which isolates the effects of rigid-body motion so that accurate assessment of the detected debonds can be achieved. Also, the use of a circle to outline the ambiguous boundary is found suitable for square debonds.

Boron‐nitrilotriacetate, N(CH2COO)3B: Synthesis and Crystal‐Structure Determinations at 293K and 110K

AbstractThe title compound is insoluble in aprotic solvents and decomposes in protic ones. Its crystal structure consists of discrete molecules with non‐crystallographic C30‐symmetry and a transannular dative BN bond (1.620(3) (Å). The molecules pack tightly (density 1.804 g cm−2) interacting via O…C contacts between carbonyl groups (2.92–3.05 Å)). The atoms show small vibrational motion which may be interpreted in terms of a rigid body model. Distances and angles obtained at 293 and 110 were corrected for effects of rigid body motion and do not show significant differences.

Simplified Laser-Speckle Strain Gauge

An automatic method of measuring surface strain by electro-optical techniques is described. It is a real-time and point-by-point method in which a specimen surface is illuminated by a thin laser beam and the displacements of the speckle pattern resulting from the surface deformation are detected by linear image sensors followed by a microcomputer. The displacements are calculated as the peak positions of the cross-correlation functions of image sensor signals before and after the deformation. By adopting a differential system consisting of two image sensors positioned symmetrically about the surface normal we can eliminate the effect of rigid body motion. The sensitivity depends on the surface to sensor distance, while the gauge length is given by the diameter of the laser spot. These relations derived from physical optics are verified by experiments using a metal plate specimen subject to tensile strain that is monitored by an electrical resistance strain gauge. The minimum strain value measured was a few ten microstrains with a gauge length of 1 mm. We could also measure thermal strain by this method.