Static Amplitudes Research Articles

A compact X-shaped mechanism based 3-DOF anti-vibration unit with enhanced tunable QZS property

Quasi-zero stiffness (QZS) systems for passive vibration isolation have been extensively studied for high static and low dynamic stiffness in practical applications. However, most existing QZS isolators are focused more on suppressing vibration transmission of a single direction, which thus presents a limitation in applications. This study presents a novel X-shaped mechanism based 3 degrees of freedom (3-DOF) anti-vibration unit with enhanced QZS effect in a large stroke, which is expected to achieve low-frequency vibration isolation in three directions simultaneously. The proposed anti-vibration unit exhibits beneficial nonlinear stiffness and damping characteristics, and it can passively achieve excellent and tunable vibration isolation performance in all three directions. The loading capacity, static stiffness and QZS zone in three directions are conducted for understanding such a 3-DOF anti-vibration unit. The influences of several design parameters including the lengths of rods, static equilibrium positions, spring stiffness, damping coefficients and excitation amplitudes on vibration isolation performance are all studied. Compared with typical spring-mass-damper (SMD) isolators, or existing traditional QZS isolators, the proposed anti-vibration structure exhibits much larger QZS area in the main vibration isolation direction, can be flexibly used to construct more DOF vibration isolation in a compact design, and can thus achieve excellent vibration isolation performance in more directions simultaneously with guaranteed stable equilibrium. The results of this study present a new insight into multi-direction passive vibration isolation required in many engineering practices, based on the X-shaped linkage mechanism.

Abnormal static and dynamic brain function in patients with temporomandibular disorders: a resting-state functional magnetic resonance imaging study.

This study was conducted to investigate the brain function of patients with temporomandibular disorders (TMD) by combining the static and dynamic amplitudes of low-frequency fluctuation (ALFF). Thirty patients with TMD and 20 healthy controls were enrolled. All the participants completed their questionnaires, received clinical examinations, and underwent resting-state functional magnetic resonance imaging scanning. We compared the static and dynamic ALFF between the patients and healthy controls by conducting a two-sample t-test with AlphaSim correction for multiple comparisons. The correlation between the static and dynamic ALFF of the brain regions with significant group differences and clinical measurements was analyzed. The patients with TMD showed increased static and dynamic ALFF in the posterior cingulate cortex compared with that of the controls (whole-brain level, uncorrected P=0.005; region of interest level with AlphaSim correction, voxel level P<0.005, cluster level P<0.05). The dynamic ALFF of the posterior cingulate cortex was negatively correlated with bilateral condylar vertical discrepancies. The dynamic ALFF in the medial orbitofrontal cortex of the patients with TMD was greater than that of the controls (whole-brain level AlphaSim correction, voxel level P<0.005, cluster level P<0.05). Our findings revealed that the resting-state brain function of the posterior cingulate cortex and the medial orbitofrontal cortex of patient with TMD increased. These changes probably indicated the potential central mechanisms underlying the increased self-relevant thoughts, negative emotion, and abnormal emotion regulation in TMD.

Effects of Anosognosia on Static and Dynamic Amplitudes of Low-Frequency Fluctuation in Mild Cognitive Impairment.

Background: Anosognosia is a significant symptom in patients with mild cognitive impairment (MCI) while the underlying neurological mechanism behind it is still unclear.Methods: A total of 121 subjects were included and classified into three groups, including 39 normal controls (NCs), 42 individuals with MCI without anosognosia (MCI-NA), and 40 individuals with MCI with anosognosia (MCI-A), based on their everyday cognition (ECog) questionnaire (discrepancy score). Resting-state functional MRIs were acquired from all the subjects, and the static amplitudes of low-frequency fluctuation (sALFF) and dynamic ALFF (dALFF) variance were investigated to evaluate the intrinsic functional network strength and stability, respectively, and both were corrected by age, sex, education, and gray matter volume. Eventually, correlation analyses were conducted to explore the relationship between brain activity changes and cognitive status in all the subjects.Results: No significant difference was found between MCI-A and MCI-NA (P > 0.05) in cognitive ability. Regarding intrinsic brain activity, MCI-A had increased sALFF and dALFF variance in the anterior cingulate cortex (ACC) relative to MCI-NA, as well as decreased sALFF and dALFF variance in the precuneus relative to MCI-NA and controls. Moreover, MCI-A had decreased sALFF in the inferior temporal gyrus (ITG) and paracentral lobule (PCL) compared to MCI-NA. Among all the subjects, correlation analyses showed that the sALFF and dALFF variance in the precuneus was related to the Ecog discrepancy score (r = 0.232 and 0.235, respectively), immediate story recall (r = 0.200 and 0.277, respectively), and delayed story recall (r = 0.255 and 0.298, respectively).Conclusion: Alterations of intrinsic brain activation in the ACC and precuneus seem to be associated with the anosognosia symptom in patients with MCI.

Structural dynamic responses of a stripped solar sail subjected to solar radiation pressure

The stripped solar sail whose membrane is divided into separate narrow membrane strips is believed to have the best structural efficiency. In this paper, the stripped solar sail structure is regarded as an assembly made by connecting a number of boom-strip components in sequence. Considering the coupling effects between booms and membrane strips, an exact and semi-analytical method to calculate structural dynamic responses of the stripped solar sail subjected to solar radiation pressure is established. The case study of a 100 m stripped solar sail shows that the stripped architecture helps to reduce the static deflections and amplitudes of the steady-state dynamic response. Larger prestress of the membrane strips will decrease stiffness of the sail and increase amplitudes of the steady-state dynamic response. Increasing thickness of the boom will benefit to stability of the sail and reduce the resonant amplitudes. This proposed semi-analytical method provides an efficient analysis tool for structure design and attitude control of the stripped solar sail.

Application of 1-D and 2-D Discrete Wavelet Transform to Crack Identification in Statically and Dynamically Loaded Plates

The paper presents the problem of damage detection in thin plates while considering the influence of static and dynamic characteristics, especially with regard to the modes of vibration as well as the excitation by static loads. The problem of Kirchhoff plate bending is described and solved by the Boundary Element Method (BEM). Rectangular plates supported on boundary or plates supported on boundary and resting on the internal columns are examined. A defect is introduced by the additional edges forming a crack in the plate domain. The analyses of static and dynamic structural responses are carried out with the use of Discrete Wavelet Transform (DWT). Signal decomposition according to the Mallat pyramid algorithm is applied. To obtain a more adequate input function subjected to DWT the white noise disturbing the signal is considered together with the structural response. In the dynamic experiments the plate undergoes vibrations similar to natural modes. The measured variables are static deflections and vertical displacement amplitudes. All of them are established at internal collocation points distributed alongside the line parallel to selected plate edge.

Simple discrete models for dynamic structure-soil-structure interaction analysis

Simple models are presented for dynamic analyses of Structure-Soil-Structure Interaction (SSSI). Structures built on rigid, circular surface foundations resting on a homogeneous, elastic soil half-space are considered. The proposed models consist of discrete mass and spring elements that represent inertial, stiffness, and damping characteristics of an SSSI system. Frequency-dependent springs are developed to simulate Foundation-Soil Interaction (FSI) and Cross-Interaction (CI) between adjacent foundations, both being affected by the number and arrangement of neighbouring foundations. The stated springs are developed using a novel approach that approximates the through-the-soil interaction between adjacent footings using existing solutions to soil-structure interaction (SSI) analyses. Static stiffness matrices are obtained by means of compliance matrices using well known analytical solutions of surface displacement field to a ‘single-disk’ problem and a suggested displacement averaging rule. Dynamic stiffness matrices are created by applying modification factors to their static counterparts. To this end, a practical expression for dynamic modification factors that relate static and dynamic amplitudes of surface displacement field is provided. Equations of motion are formulated and solved in both time and frequency domains, taking into account time-lagging effects on input motion at separate foundations due to their vibration and wave passage. Validation results against more advanced numerical models prove the effectiveness of the proposed models. Finally, the limitations and potential improvements on the models are discussed.

The influence of the vertical cantledge mass on the vibratory drum vibrations during the material compaction

The road roller vibratory drum is considered as a three-mass vibration system consisting of the eccentric weight mass m1, vibratory drum mass m2, additional mass m3, which is transmitted to the vibratory drum axis through the roller frame. Differential equations of vertical vibrations were formulated, they were solved, analytical expressions were obtained of the amplitude A1 of the vibrator drum vertical vibrations and of the amplitude A2 of the additional mass m3 vibrations, rigidly connected with the road roller frame. The dependences of the vertical vibration amplitudes A1 and A2 on the vibration frequency, mass ratio (m1 + m2) and m3, stiffness factors and viscous friction factors of the soil and rubber-metal shock absorbers have been established. The additional mass m3 is considered as an additional shock absorber that protects the roller frame from vibration. The differential equation of the additional mass m3 vertical vibrations has been obtained, which are excited by the harmonic inertia force. The analytical dependence conclusion for the determination of the dynamic factor Kd as the ratio of the dynamic and static vibration amplitudes of the additional mass m3 of the vibratory drum have been specified. The specified dependence of the driving force transfer factor K determination on mass m3 to the roller frame has been obtained. The diagrams of the dependence of Kd and K factors on the frequency ratio of forced and natural vibrations of the mass m3 are constructed.

Short-Term and Long-Term Behavior of EPS Geofoam

Abstract Expanded Polystyrene Styrofoam (EPS) geofoam is widely used in various civil engineering applications. To predict the responses of structures to external loading, when in the presence of geofoam, understanding physical and mechanical behavior of geofoam, both short and long term, is very essential. A series of laboratory experiments was conducted on EPS15, EPS20, and EPS25 geofoam specimens under different loading conditions. To understand the short-term behavior, static uniaxial compression and cyclic uniaxial compression (CUC) tests were performed; however, for long-term behavior, accelerated creep and pseudo long-term tests were conducted on geofoam samples. CUC tests were performed at different static and cyclic stress amplitudes and loading frequencies for 5,000 load cycles, and the results reveal that, irrespective of geofoam density, secant modulus (Edyn) decreases and the damping ratio of geofoam increases with the increase in cyclic axial strain. Also, it was observed that an increase in cyclic axial strain and the number of loading cycles reduced the Poisson’s ratio of geofoam from positive to negative values. From the time-temperature-stress superposition accelerated creep testing method, creep strains developed in EPS15, EPS20, and EPS25 geofoam samples at the end of 100 years were 2.12, 2.4, and 2.11 %, respectively. From pseudo long-term tests, the estimated Young’s modulus (E) of geofoam decreases with the increase in compressive creep strain for all three densities of geofoam.

Static and Dynamic Transmission Error Measurements of Helical Gear Pairs With Various Tooth Modifications

This paper presents a set of motion transmission error data for a family of helical gears having different profile and lead modifications operated under both low-speed (quasi-static) and dynamic conditions. A power circulatory test machine is used along with encoder and accelerometer-based transmission error measurement systems to quantify motion transmission behavior within wide ranges of torque and speed. Results of these experiments indicate that the tooth modifications impact the resultant static and dynamic transmission error amplitudes significantly. A design load is shown to exist for each gear pair of different modifications where static transmission error amplitude is minimum. Forced response curves and waterfall plots are presented to demonstrate that the helical gear pairs tested act linearly with no signs of nonlinear behavior such as tooth contact separations. Furthermore, static and dynamic transmission error amplitudes are observed to be nearly proportional, suggesting that static transmission error can be employed in helical gear dynamic models as the main gear mesh excitation. The data presented here is intended to fill a void in the literature by providing means for validation of load distribution and dynamic models of helical gear pairs.

Correlation between numerical simulations and measurements to assess uncertainties: a case study on a hydroelectric runner

For fatigue reliability analysis, we need an estimate of the structure response and uncertainty at critical locations where often direct observation from a measurement campaign cannot be obtained. At these critical locations, two types of information are required: static amplitudes and dynamic ranges. In this work, we assume a linear correlation between simulated and measured values to estimate the information needed at critical locations on the runner blades. The proposed methodology is illustrated using the data from a six-blade propeller runner. The methodology enables one to easily transpose information from observed values to a critical location and assess uncertainty for fatigue reliability analysis.

Piezomagnetic behavior: experimental observations and multiscale modeling

This work deals with the study of magnetoelastic coupling in the framework of non-destructive testing. Experimental hysteretic and cyclic piezomagnetic measurements carried out on a dual-phase steel submitted to different magnetic field and stress conditions are reported. The effect of concomitant magnetic field and stress, considering static or variable amplitudes, is discussed. A new multiscale modeling of piezomagnetic hysteresis is finally proposed.

Relations between static and dynamic moduli of sedimentary rocks

ABSTRACTStatic moduli of rocks are usually different from the corresponding dynamic moduli. The ratio between them is generally complex and depends on several conditions, including stress state and stress history. Different drainage conditions, dispersion (often associated with pore fluid effects), heterogeneities and strain amplitude, are all potential reasons for this discrepancy. Moreover, comparison of static and dynamic moduli is often hampered and maybe mistaken due to insufficient characterization of anisotropy.This paper gives a review of the various mechanisms causing differences between static and dynamic moduli. By careful arrangements of test conditions, it is possible to isolate the mechanisms so that they can be studied separately. Non‐elastic deformation induced by the large static strain amplitudes is particularly challenging, however a linear relationship between non‐elastic compliance and stress makes it possible to eliminate also this effect by extrapolation to zero strain amplitude.To a large extent, each mechanism can be expressed mathematically with reasonable precision, thus quantitative relations between the moduli can be established. This provides useful tools for analyses and prediction of rock behaviour. For instance, such relations may be used to predict static stiffness and even strength based on dynamic measurements. This is particularly useful in field situations where only dynamic data are available. Further, by utilizing the possibility for extrapolation of static measurements to zero strain amplitude, dispersion in the range from seismic to ultrasonic frequencies may be studied by a combination of static and dynamic measurements.

Combined Airfoil and Snubber Design Optimization of Turbine Blades With Respect to Friction Damping

A major concern for new generations of large turbine blades is forced and self-excited (flutter) vibrations, which can cause high-cycle fatigue (HCF). The design of friction joints is a commonly applied strategy for systematic reduction of resonance amplitudes at critical operational conditions. In this paper, the influence of geometric blade design parameters onto the damped system response is investigated for direct snubber coupling. A simplified turbine blade geometry is parametrized and a well-proven reduced-order model for turbine blade dynamics under friction damping is integrated into a 3D finite element tool-chain. The developed process is then used in combination with surrogate modeling to predict the effect of geometric design parameters onto the vibrational characteristics. As such, main and interaction effects of design variables onto static normal contact force and resonance amplitudes are determined for a critical first bending mode. Parameters were found to influence the static normal contact force based on their effect on elasticity of the snubber, torsional stiffness of the airfoil and free blade untwist. The results lead to the conclusion that geometric design parameters mainly affect the resonance amplitude equivalent to their influence on static normal contact force in the friction joint. However, it is demonstrated that geometric airfoil parameters influence blade stiffness and are significantly changing the respective mode shapes, which can lead to lower resonance amplitudes despite an increase in static contact loads. Finally, an evolutionary optimization is carried out and novel design guidelines for snubbered blades with friction damping are formulated.

Experimental research on the dynamic responses of the steel-concrete composite beams under the harmonic forces

In order to research the dynamic response of the steel-concrete composite beam under forced vibration, three simply-supported steel-concrete composite beams were designed with the shear connection degree as the parameter, the dynamic model experiments under the harmonic load with different static load components, load amplitudes, and load frequencies were conducted on each test beam, the mid-span acceleration and deflection, and the mean slip and slip amplitude at different measuring points were obtained. The results indicate that, the mean slip value and the slip amplitude at the surface between the steel girder and concrete slab, the mid-span accelerate and dynamic deflection are all show a sine wave shape under the sine harmonic load, and increase with the shear connection degree’s decrease. The mid-span dynamic deflection and mean value of the ship are most influenced by the static load components, the slip amplitude is most influenced by the load amplitude, and the mid-span accelerate is mainly affected by the load frequency and amplitude.

Structure and dynamics of binary liquid mixtures near their continuous demixing transitions

The dynamic and static critical behavior of a family of binary Lennard-Jones liquid mixtures, close to their continuous demixing points (belonging to the so-called model H' dynamic universality class), are studied computationally by combining semi-grand canonical Monte Carlo simulations and large-scale molecular dynamics (MD) simulations, accelerated by graphic processing units (GPU). The symmetric binary liquid mixtures considered cover a variety of densities, a wide range of compressibilities, and various interactions between the unlike particles. The static quantities studied here encompass the bulk phase diagram (including both the binodal and the λ-line), the correlation length, and the concentration susceptibility, of the finite-sized systems above the bulk critical temperature Tc, the compressibility and the pressure at Tc. Concerning the collective transport properties, we focus on the Onsager coefficient and the shear viscosity. The critical power-law singularities of these quantities are analyzed in the mixed phase (above Tc) and non-universal critical amplitudes are extracted. Two universal amplitude ratios are calculated. The first one involves static amplitudes only and agrees well with the expectations for the three-dimensional Ising universality class. The second ratio includes also dynamic critical amplitudes and is related to the Einstein-Kawasaki relation for the interdiffusion constant. Precise estimates of this amplitude ratio are difficult to obtain from MD simulations, but within the error bars our results are compatible with theoretical predictions and experimental values for model H'. Evidence is reported for an inverse proportionality of the pressure and the isothermal compressibility at the demixing transition, upon varying either the number density or the repulsion strength between unlike particles.

Tuning the push–pull configuration for efficient second-order nonlinear optical properties in some chalcone derivatives

Using the density functional theory methods, we effectively tune the second-order nonlinear optical (NLO) properties in some chalcone derivatives. Various unique push–pull configurations are used to efficiently enhance the intramolecular charge transfer process over the designed derivatives, which result in significantly larger amplitudes of the first hyperpolarizability as compared to their parent molecule. The ground state molecular geometries have been optimized using B3LYP/6-311G** level of theory. A variety of methods including B3LYP, CAM-B3LYP, PBE0, M06, BHandHLYP and MP2 are tested with 6-311G** basis set to calculate the first hyperpolarizability of parent system 1. The results of M06 are found closer to highly correlated MP2 method, which has been selected to calculate static and frequency dependent first hyperpolarizability amplitudes of all selected systems. At M06/6-311G** level of theory, the permanent electronic dipole moment (μtot), polarizability (α0) and static first hyperpolarizability (βtot) amplitudes for parent system 1 are found to be 5.139 Debye, 274a. u. and 24.22×10−30esu, respectively. These amplitudes have been significantly enhanced in designed derivatives 2 and 3. More importantly, the (βtot) amplitudes of systems 2 and 3 mount to 75.78×10−30 and 128.51×10−30esu, respectively, which are about 3 times and 5 times larger than that of their parent system 1. Additionally, we have extended the structure-NLO property relationship to several newly synthesized chalcone derivatives. Interestingly, the amplitudes of dynamic frequency dependent hyperpolarizability μβω (SHG) are also significantly larger having values of 366.72×10−48, 856.32×10−48 and 1913.46×10−48esu for systems 1–3, respectively, at 1400nm of incident laser wavelength. The dispersion behavior over a wide range of change in wavelength has also been studied adopting a range of wavelength from 1907 to 544nm. Thus, the present work realizes the potential of designed derivatives as efficient NLO-phores for modern NLO applications.

Experimental analysis of energy harvesting from self-induced flutter of a composite beam

Previous attempts to harvest energy from aeroelastic vibrations have been based on attaching a beam to a moving wing or structure. Here, we exploit self-excited oscillations of a fluttering composite beam to harvest energy using piezoelectric transduction. Details of the beam properties and experimental setup are presented. The effects of preset angle of attack, wind speed, and load resistance on the levels of harvested power are determined. The results point to a complex relation between the aerodynamic loading and its impact on the static deflection and amplitudes of the limit cycle oscillations on one hand and the load resistance and level of power harvested on the other hand.

Structural Dynamics Optimization of Rotor Systems for a Small-Size Turboprop Engine

This paper presents the results of the rotordynamic analysis and design optimization performed for a turboprop engine-rotor system consisting of a free-power turbine and a gas generator. Predictions of static stresses, natural frequencies, and amplitudes are obtained by the in-house finite-element code. A detailed analysis of the finite-element method model (various beam formulations, three-dimensional axisymmetric model, point masses, and one-dimensional rigid disk elements) is provided. A sizing optimization problem of total shaft mass minimization is considered. Design variables are inner radii and wall thicknesses of shaft sections. Constraints are imposed on static stresses, natural frequencies, and amplitudes of the unbalance response. Changes in design variables are constrained to avoid contacts between the shafts of the twin-spool configuration. An in-house implementation of the sequential quadratic programming method is coupled with hybrid, analytical and numerical, sensitivity analysis. Results of the optimization show that a significant mass reduction in comparison with the baseline configuration can be achieved with all constraints being simultaneously satisfied. The optimal designs, however, must be finalized to meet other requirements not considered during the optimization. The Campbell diagram of the free-power turbine rotor system is significantly affected by the optimization.

Comparative Study on Synthesizing Reconfigurable Time- Modulated Linear Arrays using Differential Evolution, Artificial Bee Colony and Particle Swarm Optimization

This paper presents a new technique based on optimization tools to design phase only, digitally controlled, reconfigurable antenna arrays through time modulation. In the proposed approach, the on-time durations of the time-modulated elements and the static amplitudes of the array elements are perturbed in such a way that the same on-time sequence and discrete values of static amplitudes for four bit digital attenuators produces either a pencil or a flat-top beam pattern, depending on the suitable discrete phase distributions of five bit digital phase shifters. In order to illustrate the technique, three optimization tools: differential evolution (DE), artificial bee colony (ABC), and particle swarm optimization (PSO) are employed and their performances are compared. The numerical results for a 20-element linear array are presented.

Design of digitally controlled multiple-pattern time-modulated antenna arrays with phase-only difference

An optimization approach based on differential evolution (DE) is proposed to design multiple-pattern time-modulated linear antenna arrays (TMLAAs) with phase-only control by using 5-bit digital phase shifters. The synthesized multiple patterns include a pencil beam (PB), a flat-topped beam (FTB), and a cosec squared pattern (CSP). The function of the DE is to find, simultaneously, a common, i.e., fixed, set of continuous values of switch-on time durations and discrete static excitation amplitudes for 5-bit digital attenuators, and different sets of discrete excitation phase distributions for 5-bit digital phase shifters; to generate different power patterns in the far field of the TMLAA. By perturbing the static amplitude distribution of a 20-element TMLAA in the discrete search range of “(0.2–1),” the patterns are obtained by reducing side lobe levels (SLLs) to almost −20 dB and sideband levels (SBLs) to less than −25 dB. Towards the end, the same on-time and amplitude distribution is used to produce a symmetric side lobe (S-SL) and asymmetric side lobe (A-SL) CSP, and their usefulness under a noisy signal environment is discussed.