Large Dynamic Response Research Articles

Dynamics of mechanical systems involving impact and friction using an efficient contact detection algorithm

In this work, some new results are presented on the dynamics of a class of multibody mechanical systems, involving contact and friction. The main contribution refers to the development of a systematic, accurate and efficient method for detecting contact among the components of a system of solid bodies. For some simple geometries, this task is achieved by employing analytical means. For systems possessing components with complex geometric shapes a more involved numerical methodology is developed. In both cases, once a potential contact point is detected, the common tangent plane and normal vector are located and the penetration depth is calculated, leading to determination of the force arising between the contacting bodies. This information is then passed to a solver, providing the full dynamic response of the system. The validity and numerical efficiency of the methodology developed is first demonstrated by considering a number of examples with relatively small geometric complexity but large traditional value and interesting dynamic response. Some new results are obtained and presented on the dynamics of these systems. Finally, the same methodology is also tested in a more complicated and demanding mechanical application.

VOC-Sensing Properties of Adsorption/Combustion-Type Micro Gas Sensors Using Mesoporous Alumina Co-Loaded with Pt and Metal Oxide

Mesoporous (mp-) Al2O3 powders loaded with n wt% MO (Bi2O3, CeO2, Fe2O3, NiO, RuO2 or ZrO2 (n = 1, 5, 10)) and/or 1 wt% Pt nanoparticles (1.0Pt/nMO-mp-Al2O3) were synthesized by an impregnation or a sonochemical reduction method. The sensor-signal profiles typically consist of one large dynamic response and subsequent static response, which originate from the flash catalytic combustion of these adsorbates and general catalytic combustion, respectively, during the pulse heating. The 1.0Pt/nCeO2-mp-Al2O3 sensor showed the largest static response to all target VOCs (ethanol, ethyl acetate, acetone, benzene and toluene), probably due to the largest specific surface area (ca. 187 m2 g-1) among the sensors examined. In addition, the sensor also showed the largest dynamic response to most of target VOCs except for toluene. On the other hand, 1.0Pt/10Bi2O3-mp-Al2O3 sensor showed the largest dynamic response to toluene and the dynamic response speed of the 1.0Pt/10Bi2O3-mp-Al2O3 sensor to toluene was faster than that of the 1.0Pt/10CeO2-mp-Al2O3 sensor. This is probably because of more accelerated catalytic combustion behavior and the adsorption property of toluene over 1.0Pt/10Bi2O3-mp-Al2O3 than those over 1.0Pt/10CeO2-mp-Al2O3.

Prediction of displacement and stress fields of a notched panel with geometric nonlinearity by reduced order modeling

The focus of this investigation is on a first assessment of the predictive capabilities of nonlinear geometric reduced order models for the prediction of the large displacement and stress fields of panels with localized geometric defects, the case of a notch serving to exemplify the analysis. It is first demonstrated that the reduced order model of the notched panel does indeed provide a close match of the displacement and stress fields obtained from full finite element analyses for moderately large static and dynamic responses (peak displacement of 2 and 4 thicknesses). As might be expected, the reduced order model of the virgin panel would also yield a close approximation of the displacement field but not of the stress one. These observations then lead to two “enrichment” techniques seeking to superpose the notch effects on the virgin panel stress field so that a reduced order model of the latter can be used. A very good prediction of the full finite element stresses, for both static and dynamic analyses, is achieved with both enrichments.

Vehicle-Induced Dynamic Response of Expansion Joints in Long Span Bridges

Due to increasing traffic on long span bridges, behavior of expansion joints is believed to be largely influenced by pounding impact from passing vehicles. In order to precisely understand behavior of expansion joint under vehicle impact loading, a new analysis scheme is proposed which incorporates interaction between vehicle and expansion joint. Mathematical model of vehicle is established and solved with Newmark method. Expansion joint is modeled with refined solid element in Finite element software ABAQUS. The analysis indicates that vehicle loading can induce large dynamic response of expansion joint in long span bridges.

Open-path, quantum cascade-laser-based sensor for high-resolution atmospheric ammonia measurements

Abstract. We demonstrate a compact, open-path, quantum cascade-laser-based atmospheric ammonia sensor operating at 9.06 μm for high-sensitivity, high temporal resolution, ground-based measurements. Atmospheric ammonia (NH3) is a gas-phase precursor to fine particulate matter, with implications for air quality and climate change. Currently, NH3 sensing challenges have led to a lack of widespread in situ measurements. Our open-path sensor configuration minimizes sampling artifacts associated with NH3 surface adsorption onto inlet tubing and reduced pressure sampling cells, as well as condensed-phase partitioning ambiguities. Multi-harmonic wavelength modulation spectroscopy allows for selective and sensitive detection of atmospheric pressure-broadened absorption features. An in-line ethylene reference cell provides real-time calibration (±20% accuracy) and normalization for instrument drift under rapidly changing field conditions. The sensor has a sensitivity and noise-equivalent limit (1σ) of 0.15 ppbv NH3 at 10 Hz, a mass of ~ 5 kg and consumes ~ 50 W of electrical power. The total uncertainty in NH3 measurements is 0.20 ppbv NH3 ± 10%, based on a spectroscopic calibration method. Field performance of this open-path NH3 sensor is demonstrated, with 10 Hz time resolution and a large dynamic response for in situ NH3 measurements. This sensor provides the capabilities for improved in situ gas-phase NH3 sensing relevant for emission source characterization and flux measurements.

Optimized ratiometric calcium sensors for functional in vivo imaging of neurons and T lymphocytes

The quality of genetically encoded calcium indicators (GECIs) has improved dramatically in recent years, but high-performing ratiometric indicators are still rare. Here we describe a series of fluorescence resonance energy transfer (FRET)-based calcium biosensors with a reduced number of calcium binding sites per sensor. These 'Twitch' sensors are based on the C-terminal domain of Opsanus troponin C. Their FRET responses were optimized by a large-scale functional screen in bacterial colonies, refined by a secondary screen in rat hippocampal neuron cultures. We tested the in vivo performance of the most sensitive variants in the brain and lymph nodes of mice. The sensitivity of the Twitch sensors matched that of synthetic calcium dyes and allowed visualization of tonic action potential firing in neurons and high resolution functional tracking of T lymphocytes. Given their ratiometric readout, their brightness, large dynamic range and linear response properties, Twitch sensors represent versatile tools for neuroscience and immunology.

Experimental Aeroelastic Response for a Freeplay Control Surface in Buffeting Flow

A partial control surface is constructed near the midspan of a NACA 0012 airfoil model with and without freeplay gaps. Static and dynamic control surface pitch motion measurements were performed in wind-tunnel tests at higher angles of attack including buffet or von Kármán vortex street flows. Two typical angles of attack, and 40 deg, and four freplay gaps in the pitch stiffness, , 0.5, 0.75, and 1.0 deg, are considered in the tests. This study has measured the static and dynamic responses of the flap pitch motion (with and without freeplay gaps) induced by the buffeting flow. Also, the buffeting frequency has been determined from the measured flap pitch responses. The buffet flow occurs at large angles of attack, and this leads to a larger preload from the aerodynamic forces and a larger static pitch equilibrium position. In this case, there is no limit cycle oscillations of the flap pitch motion induced by the freeplay gap to be found. Because the flap pitch motions are around the upper boundary of the freeplay gap, the dynamic pitch response has only a small change with different freeplay gaps. Buffeting flow excitation leads to a large dynamic response when the buffeting frequency is close to the flap natural frequency.

FRAMEWORK OF WIND–VEHICLE–BRIDGE INTERACTION ANALYSIS AND ITS APPLICATIONS

Under strong winds, bridges may exhibit large dynamic responses. Wind may also endanger the safety of moving vehicles on the roadways as well as on bridges. For regular aerodynamic study of long-span bridges, traffic loads are not typically considered, assuming that bridges will be closed to traffic at high wind speeds. Therefore, bridges are usually tested in wind tunnels or analyzed numerically without considering moving vehicles on them. However, there are numerous possible scenarios under which vehicles may still be on the bridge when higher wind speeds occur. These scenarios include unexpected increase in hurricane forward speed or intensity, evacuation traffic gridlock, accidents/stalled vehicles or rainfall flooding blocking the road ahead, etc. Wind, together with vehicles, will also cause serviceability and bridge fatigue damage issues. The present study will present the framework of wind–vehicle–bridge interaction analysis and its applications, developed in the last decade by the authors' group, focused on the vehicle and bridge safety issues. It consists of the following five parts: (1) A three dimensional finite element analysis framework considering the interaction of wind, bridge and vehicles; (2) experimental facilities development and studies for both static and aerodynamic tests of bridge section models and vehicles; (3) Computation fluid dynamic (CFD) prediction of loading on vehicles; (4) performance evaluation of vehicle safety and bridge fatigue; and (5) bridge vibration mitigations. Case study will also be presented and future research needs are discussed.

Analysis on Natural Vibration and Dynamic Response of Footbridge

According to vibration problem of the footbridge, the dynamic characteristics and dynamic responses of the footbridge were analyzed under pedestrian load. Based on one 22m×10 straight line footbridge, this paper established the spatial finite element model to analyze its natural vibration characteristics and discuss the effects on the natural vibration characteristics induced by both connection factors of beam ends and pedestrians weight. And then the dynamic responses of the footbridge caused by pedestrian dynamic load were calculated to analyze the structure stress. In addition, to analyze the calculation result of displacement responses so as to evaluate the comfort of pedestrians. The results show that the natural frequency is lower, and it will probably induce the resonance and larger dynamic response value under pedestrian load although the footbridge structure is safe. Moreover, reducing vibration methods and treatment measures to the footbridge were introduced, and the effective measure was suggested to reduce vibration amplitude at last.

Research on Dynamic Load and Static Load Combination Effects on the Railway Bridge and Piers Impact

Using modal analysis to train and bridges and piers for dynamics analysis, we got a theoretical solution. Using wireless sensor network architecture monitoring system for Bridges and piers of the acceleration and the settlement monitoring, in considering static load loading situation, through contrast train before and after the settlement of piers the quantity change and Bridges and piers acceleration size, draw piers vertical stiffness of the bridge vibration impact is not significant. Study of the bridge piers and transverse vibration characteristics, it is concluded that the piers lateral stiffness is far less than that of the vertical stiffness, piers and bridges in transverse have larger dynamic response to produce.

Structural dynamic modeling and stability of a rotating blade under gravitational force

Turbine blade lengths have been increasing in recent wind energy system designs in order to enhance power generation capacity. A longer blade length makes the structural system more flexible and often results in an undesirable, large dynamic response, which should be avoided in the design of the system. In the present study, the equations of motion of a rotating wind turbine blade undergoing gravitational force are derived, while considering tilt and pitch angles. Since the gravitational force acting on the rotating blade creates an oscillating axial force, this results in oscillating stiffness terms in the governing equations. The validity of the derived rotating blade model is evaluated by comparing its transient responses to those obtained by using a commercial finite element code. Effects of rotating speed, tilt angle, and pitch angle of the wind turbine blade on its dynamic stability characteristics are investigated.

Brain and effort: brain activation and effort-related working memory in healthy participants and patients with working memory deficits

Despite the interest in the neuroimaging of working memory, little is still known about the neurobiology of complex working memory in tasks that require simultaneous manipulation and storage of information. In addition to the central executive network, we assumed that the recently described salience network [involving the anterior insular cortex (AIC) and the anterior cingulate cortex (ACC)] might be of particular importance to working memory tasks that require complex, effortful processing.Method: Healthy participants (n = 26) and participants suffering from working memory problems related to the Kleine–Levin syndrome (KLS) (a specific form of periodic idiopathic hypersomnia; n = 18) participated in the study. Participants were further divided into a high- and low-capacity group, according to performance on a working memory task (listening span). In a functional magnetic resonance imaging (fMRI) study, participants were administered the reading span complex working memory task tapping cognitive effort.Principal findings: The fMRI-derived blood oxygen level dependent (BOLD) signal was modulated by (1) effort in both the central executive and the salience network and (2) capacity in the salience network in that high performers evidenced a weaker BOLD signal than low performers. In the salience network there was a dichotomy between the left and the right hemisphere; the right hemisphere elicited a steeper increase of the BOLD signal as a function of increasing effort. There was also a stronger functional connectivity within the central executive network because of increased task difficulty.Conclusion: The ability to allocate cognitive effort in complex working memory is contingent upon focused resources in the executive and in particular the salience network. Individual capacity during the complex working memory task is related to activity in the salience (but not the executive) network so that high-capacity participants evidence a lower signal and possibly hence a larger dynamic response.

Analysis of Influence of Material Damping on the Dynamic Response of Concrete-Filled Square Steel Tubular Columns

The damping characteristic and dynamic responses of the concrete-filled square steel tubular (CFST) columns were numerically investigated in this paper. Finite element iteration method in the hysteretic damping system for CFST materials was presented, and an improved method considering viscous damping dynamic equilibrium equation with hysteretic damping model was also proposed. Based on the proposed methods, the loss factor and dynamic response of CFST columns subjected to the earthquake and harmonic loadings were effectively calculated. The results indicate that the stress-dependent damping method induces a larger dynamic response, and the loss factor of the CFST columns increases with the increase of the stress amplitude and lower steel ratio.

Experimental Characterization of Aerodynamic Behavior of Membrane Wings in Low-Reynolds-Number Flow

An experimental study of the aerodynamic characteristics of a flat-plate membrane wing was conducted. Three different values of membrane prestrain (5, 7, and 10%) were investigated, along with a rigid flat plate, at Reynolds numbers of 13,700, 22,600 and 36,300 and angles of attack up to 27 deg. It was found that 1) the dependence of the prestall mean lift on model prestrain is negligible, 2) prestall mean lift at a given level of prestrain is a strong function of Reynolds number, and 3) the mean drag increased with a decrease in model prestrain. In addition, the stall angle of attack is weakly dependent on prestrain and increases with increasing Reynolds number. With the exception of the highest Reynolds number, the flexible-model stall angles were found to be similar to the rigid flat-plate results. At the largest Reynolds number, dynamic results for the flexible models revealed large rms values of lift and drag, which generally decrease with increasing angle of attack. In comparison to the flexible models, the rms values for the rigid flat plate were insignificant. An aeroelastic flutter instability is postulated to be the cause of the large dynamic response for the flexible models. This hypothesis is supported by results that were generated using a potential flow- based computational aeroelastic model. These aeroelastic instability-induced vibrations are also proposed as the mechanism by which the flexible models showed better stall characteristics at the highest-tested Reynolds number.

OPTICAL SENSING PROPERTIES OF WO3 NANOSTRUCTURED THIN FILMS ON SAPPHIRE SUBSTRATE TOWARD HYDROGEN

Many studies have identified tungsten trioxide (WO3) as a promising candidate for optical gas sensing applications. WO3 , coated with thin catalytic metals such as Pd , was reported to show a color change from transparent to dark blue upon exposure to oxidizing gas such as hydrogen (H2). Reliable hydrogen sensor is widely used in medical and energy application area. In this work, WO3 nanostructured thin films were deposited onto sapphire substrates via pulsed laser deposition (PLD) technique by using ArF Excimer laser operating at very short wavelength of 193 nm, the shortest wavelength used in the fabrication of semiconductor oxide thin films. By ablating the target oxides by high energy photons, we could fabricate good crystalline nanostructure thin films. Electron microscopy studies revealed that the uniform and homogeneous WO3 nanostructured films consist of nanorods of about 50 nm sizes. XRD and Raman studies verified good crystalline formation. Absorbance response toward H2 gas was investigated for a WO3 film coated with 25 Å thick palladium (Pd). The Pd/WO3 nanostructured thin films exhibited excellent gasochromic response toward H2 when measured in the visible-NIR range at 100°C. As low as 0.06% H2 concentration was clearly sensed. The larger dynamic response was measured at NIR wavelength of 900 nm as compared to the response at visible wavelength of 500 nm. The dynamic response of the films observed in the range of 500–800 nm showed more significant response toward H2 with low concentrations (0.06%–1%) than the one at single wavelength. As a result, H2 with very low concentration was able to be sensed reliably in real time. The response and recovery times were found to be < 2 min. The results indicated that the Pd/WO3 nanorod films on sapphire substrates responded to very low H2 concentration (0.06%) which is well below its lower explosive level threshold (4%).

Explicit modeling of cubic stiffness in large amplitude dynamic response of metal plate under impingement of solid rocket motor plume

Determining the damping characteristics of launch vehicle structures has risen to a high priority issue, since dynamic response in modeling and simulations is directly related to assumed damping. An experiment was conducted wherein an instrumented flat plate was excited by hydrodynamic fringes of the plume of a solid rocket motor. Estimation of damping was performed by variations of maximum entropy parametric spectrum estimation. Equivalent damping ratios of 5% were observed, even though the damping was observed to be amplitude dependent, with lower damping ratios associated with lower amplitudes. Analytic simulations, with fixed damping ratios and large displacement and rotation geometric effects, showed similar characteristics to the measured test responses. The hypothesis was formed that the structure is dominated by cubic stiffness effects under the observed impingement conditions, and that the damping actually remains constant, effectively limiting the dynamic response and giving the appearance of an increased damping ratio. Since one can estimate velocity and displacement time histories by filtering measured acceleration time histories, a time domain maximum entropy model can be formulated. The cubic stiffness terms are linear parameters and all nonlinear terms being computed from the measured kinematic quantities. The estimated results will be compared with analytic simulations.

Determination of a Rubber-Like Material Model as an Inverse Problem

The purpose of this paper is to describe the selection process of a rubber-like material model useful for simulation behaviour of an inflatable air cushion under multi-axial stress states. The air cushion is a part of a single segment of a pontoon bridge. The air cushion is constructed of a polyester fabric reinforced membrane such as Hypalon®. From a numerical point of view such a composite type poses a challenge since numerical ill-conditioning can occur due to stiffness differences between rubber and fabric. Due to the analysis of the large deformation dynamic response of the structure, the LS-Dyna code is used. Since LS-Dyna contains more than two-hundred constitutive models the inverse method is used to determine parameters characterizing the material on the base of results of the experimental test.

Parametric Simulation on Torque-Angle Characteristic of Rotary Electromagnet with Low Inertia

Since conventional electro-mechanical converter of 2D digital valve had limitations of large inertia and low dynamic response, a novel low inertia rotary electromagnet with coreless rotor structure was proposed. The axial magnetic flux generated by permanent magnet and the radial magnetic flux generated by excitation coils were superimposed and then electromagnetic torque was produced to drive rotor to track the input signal simultaneously. Based on the approach of 3D finite element electromagnetic field simulation, the influence of key structure and operating parameters such as excitation ampere turns, working air gap, tooth height, tooth width and wall thickness of coreless rotor on torque-angle characteristic was discussed. The result obtained provides a certain reference value on the structural optimization of electro-mechanical converter of 2D digital valve.

Study on Mine-Used Battery Locomotive Charging System

According to the insufficiency of large volume, high cost and poor dynamic response in the traditional mine-used battery locomotive charging system. This paper presents a design scheme on this system based on DSP TMS320F2801 which directly using SPWM conversion control technology, generating the SPWM wave through DSP control chip and convert the alternating current under the mine into the corresponding pulse charging current. The results show that the system can achieve the goal that well system stability, good dynamic performance, control circuit simplified, high charge efficiency and low cost.

Macromodel-Based Simulation of Progressive Collapse: RC Frame Structures

The potential for progressive collapse of a typical reinforced concrete (RC) moment frame structure initiated through the loss of one or more first-story columns is numerically simulated using a macromodel-based approach. The development of the simulation model is guided by the realization that the characterization of nonlinear behavior associated with the transfer of forces through the joint is critical to predict the large deformation response associated with progressive collapse. A simplified simulation model of a beam-column joint is used to represent essential and critical actions in the floor beams and the transfer of these forces through the joint region to the vertical elements. The validity of the macromodel developed is evaluated through comparison of both overall response and element actions with those obtained from high-fidelity finite-element analyses. Two prototype buildings designed for lateral load requirements in a nonseismic and seismic region are considered in progressive collapse studies. Two-dimensional models of the frames are subjected to gravity loads and then one or more first-story columns are removed, and the resulting large displacement inelastic dynamic response of each frame is investigated. It is demonstrated that the proposed approach using a validated macromodel is a viable methodology for progressive collapse analysis. The study also finds that special RC moment frames detailed and designed in zones of high seismicity perform better and are less vulnerable to progressive collapse than RC frame structures designed for low to moderate seismic risk.