Static Displacement Research Articles

Model Test of Bearing Characteristics of Fly Ash Foundation under Cyclic Loading

Based on the vertical cyclic model test of the cement-fly ash mixing pile (CFMP) composite foundation, the effects of different dynamic load ratios on the long-term bearing characteristics of the composite foundation were studied. From the perspectives of foundation cumulative settlement, dynamic stiffness, pile axial force, and pile lateral friction, etc., the bearing mechanism of the CFMP fly ash composite foundation under cyclic load was investigated. By virtue of the assay herein, the authors discovered that the cumulative settlement under different load ratios exhibited the “threshold effect”, which could be divided into the attenuation type and destruction type. When the peak value of the cyclic load was close to the ultimate bearing capacity, the dynamic failure of the pile foundation occurred. The cyclic displacement ratio ranged from 1.05 to 1.23, satisfying the relation of quadratic equation. The cyclic load settlement could be predicted by the static load displacement. During cyclic loading, the proportion of the pile side sharing the upper load decreased persistently, and the fatigue degradation of side friction resistance occurred. The degradation could be alleviated by reducing the water content of fly ash and taking waterproof measures during construction.

A discussion regarding reduced-order modelling of inclined elastic and immersed cables under support excitation

This paper investigates the advantages or issues of different reduced-order models (ROMs) for the analysis of elastic cables hanging between two supports at different height. The cable is considered immersed in still fluid and under the action of an imposed boundary motion at the upper support. Nine ROMs are explored, obtained from the combination of three different functions responsible for ensuring the interpolation of the boundary motion with three possible sets of projection functions associated with the degrees of freedom (DOF). For the interpolation functions, the possibilities are: (i) a linear interpolation, (ii) a linear interpolation with a decomposition in axial and transversal directions according to the local angle of each cross-section, or, (iii) a quasi-static approach using the static displacement of the cable due to a unitary displacement applied at the moving boundary. Regarding the number of DOFs, the possible functions sets consists of a single mode of vibration, three modes of vibration, or, a group of five trigonometric functions. The ROMs are then simulated for different conditions and the results are compared to a reference case obtained from Finite Element Method (FEM). Additionally to the numerical analysis, a novel semi-analytical solution is proposed for the single DOF ROMs based on the method of multiple time scales (MMTS). Such solution tackles an issue of using the Morrison damping since it contains an absolute value function in its formulation which makes it unfeasible to compute the integrals that appear in the Galerkin method without knowing the response of the structure. The results show that the choice of the function to interpolate the top motion effects is of top-most importance, since a poor choice of that set of functions leads to low accuracy in the results that cannot be solved by adding more DOFs to the ROM. It is also shown that working with more complex functions instead of simple trigonometric functions leads to a significance enhancement of the computational performance of the simulations.

Flow separation sensing on airfoil using a 3D printed biomimetic artificial hair sensor

Small-scale unmanned air vehicles require lightweight, compact, and low-power sensors that encompass a variety of sensing modalities to enable flight control and navigation in challenging environments. Flow sensing is one such modality that has attracted much interest in recent years. In this paper, a micro-scale artificial hair sensor is developed to resolve both the direction and magnitude of airflow. The sensor structure employs a high-aspect ratio hair structure and a thin flexible membrane to facilitate the transduction of directional airflow to membrane deflection. The sensor readout is based on capacitive sensing and two pairs of electrodes orthogonal to each other are used to obtain airflow directional information. The sensor structure was fabricated using two-photon polymerization and integration onto a miniature printed circuit board to enable simple measurement. The sensor’s responses to static displacement loading from different directions were characterized. The experimental results are in good agreement with the simulation results. Furthermore, the sensor’s capability to measure the direction and magnitude of flow was demonstrated. Finally, the sensor was mounted on an airfoil and its ability to detect flow separation was verified.

Quantitative composition determination by ADF-STEM at a low-angular regime: a combination of EFSTEM and 4DSTEM

High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) is a valuable method for composition determination of nanomaterials. However, light elements do not scatter efficiently into the scattering angles employed for HAADF-STEM which hinders the composition determination of material systems containing light elements by HAADF-STEM. This makes the usage of lower scattering angles favourable. Moreover, static atomic displacements (SADs) caused by the small covalent radius of the substituting light elements in semiconductor alloys increase the scattering intensity at low angles. Nevertheless, at low angles, a quantitative match between complementary image simulations and experiments is not straight forward, since e.g. inelastic scattering and correlated phonon movement is often neglected in simulations.In this study, we establish a method to quantify material systems containing light elements at low angles by resolving the remaining sources of discrepancy. An outstanding agreement between simulations and experiments is achieved by using a combination of an in-column energy filter and a fast pixelated detector. By applying this method to GaNxAs1-x quantum wells, a good agreement of the TEM results with results from high-resolution x-ray diffraction is obtained. The method developed enables the nanoscale analysis of functional materials containing light elements, especially in the presence of SADs.

A Numerical Study on Mechanical Seal Dynamic Characteristics Within a Reactor Coolant Pump

Unstable flow within a reactor coolant pump (RCP)’s mechanical seal may cause the change of its sealing parameters, possibly threatening RCP’s safe operations. In this study, based on the moving grid technology, a 3D fluid–structure interaction analysis model is established, where the influence of parameters such as the inlet pressure fluctuation, closing force fluctuation, and speed fluctuation on mechanical seal performance characteristics within an RCP is numerically studied. Study results have shown that when pressure and closing force fluctuations are applied, the static ring displacement, the inlet-to-outlet temperature difference, and the leakage difference show similar variational rules. In addition, it is found that the sealing parameters are more sensitive to the step form of fluctuation. When the step change of 4% closing force was applied, the static ring displacement was more than 36.7%, the change of the temperature difference between inlet and outlet zones exceeded 53.5%, and the leakage difference was more than 127.2%. The change of speed has also been found to significantly affect the temperature difference between the RCP mechanical seal’s inlet and outlet, but the effect on the leakage and opening force was negligible.

Geometric Tuning of Stress in Predisplaced Silicon Nitride Resonators.

We introduce a novel method to geometrically tune the tension in prestrained resonators by making Si3N4 strings with a designed predisplacement. This enables us, for example, to study their dissipation mechanisms, which are strongly dependent on the stress. After release of the resonators from the substrate, their static displacement is extracted using scanning electron microscopy. The results match finite-element simulations, which allows a quantitative determination of the resulting stress. The in- and out-of-plane eigenmodes are sensed using on-chip Mach-Zehnder interferometers, and the resonance frequencies and quality factors are extracted. The geometrically controlled stress enables tuning not only of the frequencies but also of the damping rate. We develop a model that quantitatively captures the stress dependence of the dissipation in the same SiN film. We show that the predisplacement shape provides additional flexibility, including control over the frequency ratio and the quality factor for a targeted frequency.

Flexibility matrix identification using the moving vehicle induced responses for beam type bridge

Bridge flexibility matrix is widely used in damage detection and condition assessment. As the mass-normalized mode shapes with high spatial resolution are required in formulating the flexibility matrix, the difficult tasks of measuring excitation and arranging a large number of sensors are normally involved. This paper proposes a flexibility matrix identification method by using the moving vehicle induced responses for beam type bridges. Firstly, the proportional relationship between the modal flexibility matrix and the matrix formulated by the bridge influence lines (ILs) of several points is derived theoretically. Then the quasi-static component response of the moving vehicle induced responses is extracted through the analytical mode decomposition (AMD), and the IL of the measurement point is obtained via polynomial fitting accordingly. Finally the flexibility matrix is formulated based on the measured ILs and the derived proportional relationship, and employed to estimate the static displacement of the bridge. Numerical and experimental examples are conducted to verify the accuracy and feasibility of the proposed method. The results indicate that it can identify the bridge flexibility matrix and estimate the static displacement with high accuracy and efficiency at the cost of few sensors. Besides, the proposed method is insensitive to vehicle parameters (velocity, spring stiffness, wheelbase, and weight), road surface roughness and measurement noise.

Phase Demodulation of Rotor Torsional Vibration Measurement under Time-Varying Speed

When torsional vibration is measured with the zebra-tape method, the modulation signals can be contaminated by electrical noise, environmental noise, step noise, sensor nonlinearities, and so on. Although the amplitudes of these types of noise are very weak relative to the amplitude of the ideal pulse test signal, they may introduce large-scale random broad-spectrum noise to the signal phases. Such noise is difficult to remove using frequency domain, time-frequency-domain, or threshold sampling methods and seriously affects the accuracy of torsional vibration measurements. This paper presents a phase demodulation algorithm based on downsampling and local resampling (DSLR) to improve the accuracy of torsional vibration measurements. To verify the proposed DSLR algorithm, torsional vibration simulations and experiments are conducted under a time-varying rotation speed. The results show that the angular displacement signal obtained from the torsional vibration test using zebra tapes is the superposition of the dynamic and static angular displacements, with the latter generated because of the varying rotation speed with respect to time. The DSLR algorithm effectively reduces the phase noise and demodulates the pulse signal phases. The work in this paper provides a method for obtaining reference torsional vibration measurements of rotors based on the zebra-tape method under time-varying speeds.

Structural analysis of composite sandwich plates with enhanced pyramid lattice core using VAM-based reduced-order equivalent model

To overcome the issues of low face sheet–core interface strength and out-of-plane bearing capacity in the traditional pyramid lattice sandwich structure, a composite sandwich plate with enhanced pyramid lattice core (CSP-EPL) is investigated. A two-dimensional reduced-order equivalent model (2D-REM) based on the variational asymptotic approach is developed to study its static and dynamic responses. The accuracy and efficiency of the proposed model are verified by comparison with three-dimensional finite element (3D-FEM) results under different boundary conditions, including global static displacement, global buckling, local field recovery, and free and forced vibration. The predicted results of 2D-REM are in good agreement with those of 3D-FEM, and the computational efficiency is improved. Finally, the influence of geometric parameters of type III reinforcements on the equivalent stiffness is thoroughly examined, which helps to further reduce the weight and improve the bearing capacity of CSP-EPL.

The 21 May 2021 Mw 6.1 Yangbi Earthquake—A Unilateral Rupture Event with Conjugately Distributed Aftershocks

Abstract An Mw 6.1 earthquake occurred in Yangbi, Yunnan province, China, at 13:48:34 (UTC time) on 21 May 2021. It exhibited a typical foreshock–mainshock–aftershock sequence in the northwestern Yunnan rifting area. We used the first P-arrival time from regional broadband seismic stations to check the location of the mainshock’s hypocenter. The updated location of the epicenter is 99.88° E, 25.66° N. The focal mechanisms of nine earthquakes, including the mainshock and the largest foreshock and aftershock, were investigated using the general cut-and-paste method based on regional seismic waveforms to set up the fault geometry and to calculate the static coulomb stress change. The rupture process of the mainshock was constrained by 33 unclipped regional broadband seismic records from 15 stations and nine static displacements from three Global Navigation Satellite System stations. The results showed that the Yangbi earthquake was a unilateral rupture event propagating toward the southeast along-strike direction. The moment was 1.81×1018 N·m, and the corresponding magnitude was Mw 6.1. The peak slip value, the weighted rupture velocity, and the duration time of the mainshock were 0.95 m, 2.2 km/s, and 9.1 s, respectively. At 10 km southeast of the mainshock’s epicenter, the conjugately distributed aftershocks were observed, and the moment density of the mainshock along the strike direction decreased sharply (78% of the total moment released in the first 10 km), suggesting that the sharply decelerating rupture could be the reason for the conjugately distributed aftershocks. The changes in static coulomb stress due to the largest foreshock and mainshock were calculated. The results showed positive Coulomb stress on the major slip zone in the mainshock fault plane triggered by the largest foreshock. Moreover, the 0.01 MPa contour due to the mainshock radiated out of the bend zone of the Weixi–Qiaohou–Weishan fault.

Short Range Order and Static Displacements of Atoms in Polycrystalline Solid Solution of Fe-5 at. %Re

Intensity of X-ray diffuse scattering depends onscattering vector q...

High speed time-of-flight displacement measurement based on dual-comb electronically controlled optical sampling.

We demonstrate a direct time-of-flight approach that utilizes dual-comb electronically controlled optical sampling (ECOPS) to measure small displacements. ECOPS is enabled by electrically controlling the repetition rate of one laser via an intracavity electric-optical modulator (EOM). The acquisition rate is set by the EOM modulation frequency, which is much higher than commonly used asynchronous optical sampling (ASOPS). In a proof-of-principle experiment, an 80-kHz acquisition rate is obtained with a pair of ∼105 MHz repetition rate Er-fiber lasers. At an average time of 30 ms, a measurement precision evaluated with Allan deviation reaches 26.1 nm for a 40-µm static displacement. In a dynamic measurement, a 500-Hz sinusoidal vibration with 15 µm amplitude has also been identified. The high-precision and high-speed displacement measurement technique can be potentially used in 3D surface profilometry of microelectronic step-structures and real-time monitoring of high frequency mechanical vibrations, etc.

Bayesian inference of dense structural response using vision-based measurements

As-built structures typically behave differently than their analytical models because of uncertainties in material properties, boundary conditions, loading scenarios, or other modeling assumptions. Therefore, to perform structural health monitoring effectively, analytical models need to be calibrated or updated to match the measured responses from as-built structures. Bayesian model updating provides a rigorous framework to integrate data and parameter uncertainty and has been applied successfully in numerous application settings employing traditional sensors that are often sparsely distributed. Computer vision has shown tremendous success for the measurement of static and dynamic displacements of structures. Vision-based measurements have the potential to be transformative for model updating of large-scale civil infrastructure, as measurements can be obtained for dense array of points within the camera frame using a single device. However, model updating using vision-based measurements to date has been limited to the use of a few points selected manually, leading to the investigation of simple structures or their global behaviors (e.g. first few modal responses); developing a systematic and highly automated procedure for estimating structural displacement and its uncertainty densely, registering the measured data to the finite element model, and then updating the model based on all the available data remains a challenge. This study proposes Bayesian inference using dense vision-based measurements to estimate the localized response of the entire structure. Finite element models are incorporated into the three-dimensional displacement measurement and registration process (model-informed approach), and then the Markov chain Monte Carlo method is applied to enable the Bayesian inference for large and complex civil infrastructure. The proposed method is applied to a laboratory-scale three-dimensional steel truss to perform inference of the overall system response based on the a posteriori knowledge. The results demonstrate the adequacy of performing Bayesian inference of structural response using vision-based measurements.

Design methods and manufacturing techniques applicable in constructing dynamically scaled airplane models

The article describes methods and techniques intended for designing and manufacturing scaled airplane models applicable in experimental flight testing. Reduced model with resized geometric dimensions should be constructed in such way to preserve similarity of its structural properties with properties of the real aircraft. Having kept the similarity of weight, stiffness and aerodynamic load distribution and maintaining properly scaled values of thrust-to-weight and wing loading ratios we can prepare scaled model showing in-flight features identical to the real airplane.A series of measuring and technological activities have to be undertaken to develop full CAD model mapping airframe geometry and structure of the real aircraft. The process chain includes measuring, design and technological activities. The development of the geometry model includes: scanning outer geometry of the real airframe, development of the surface geometry model in the CAD environment and then introducing inner geometry items which together with outer skin face make a completely assembled model of the aircraft. For the needs of constructing scaled model the full-size CAD model has to be reduced. The structure of that resized model do not have to be the same as the real one. Materials and structural elements can be quite different but after assembling them the similarity of static and dynamic structural effects should be proved. Within the manufacturing phase there are some necessary stages like preparing molds for laminating components, milling solid elements, assembly of structural components, surface finishing of the model-body surface. The final model was subjected to a load test in a special test stand to check its deformability under specific load. In the same way the numerical static analysis of the full-size FEM model was conducted. The distribution of static displacement results obtained in both cases were compared. The other way of checking structural properties of the scaled model is comparable analysis of resonant vibrations. However, in this case, vibration measurements were not carried out and model verification stopped on a comparative analysis of construction mass distribution.The procedure and results were elaborated on the example of the Tu-154M aircraft, of which the reduced model was developed in the Faculty of Mechatronics, Armament and Aerospace of the Military University of Technology (FMA MUT Warsaw, PL). Constructing and testing dynamically scaled model is one of many tasks solved in the framework of complex research project, of which the general purpose was to give numerical and experimental results useful in explaining the circumstances of the Smolensk disaster.

Demountable Bolted Shear Connector for Easy Deconstruction and Reconstruction of Concrete Slabs in Steel–Concrete Bridges

Welded headed studs are used to connect steel girders and concrete slabs in steel composite bridges. However, environmental problems related to welded shear connectors have been reported, including noise and dust generation during the replacement and demolition of damaged or worn concrete slabs. To overcome these issues, demountable shear connectors that enable easy replacement of damaged or worn concrete slabs must be developed. However, conventional bolted shear connectors mainly use embedded nuts, which cannot be used in structures such as bridges because initial slip occurs and the stiffness and shear resistance strength are relatively low. To address these issues, this paper proposes a bolted shear connector that integrates the embedded nut part into the stud bolt and has a tapered shape at the bottom of the expansion column. For performance verification in regard to static shear strength and slip displacement, push-out tests were performed according to Eurocode-4, and the performance of the proposed stud bolt was compared to those of conventional welded headed studs and embedded nut-style bolted shear connectors. In addition, an analytical review was performed using the ABAQUS program for the 1/4 axisymmetric model of the push-out test. As a result of applying the material nonlinear model and the surface contact analysis, the load-slip displacement of each analysis model showed a tendency extremely similar to the experimental results. The proposed demountable bolted shear connector exhibited excellent shear performance and can be used as a satisfactory replacement for conventional welded studs because it meets slip displacement and ductility standards.

Experimental investigation on dynamic performance evolution of double-block ballastless track under high-cycle train loads

This paper aims to investigate the dynamic performance evolution law of double-block ballastless track under long-term train load through a full-size laboratory experiment. The experiments are conducted based on a comprehensive test platform of a full-size double-block ballastless track-subgrade system, and the test contents are composed of the fatigue loading test and dynamic performance test. The full-size acceleration test method is adopted for the fatigue test to simulate the fatigue process of the ballastless track under different accumulative loading cycles. Moreover, the fatigue loading stage is divided into several periods according to the accumulative loading cycles, and the dynamic performance test is conducted after each fatigue loading period to study the dynamic performance evolution law of the ballastless track. The test results show that the static rail displacement relative to the subgrade displacement presents a development progress from initial decline to gradual stability along with the increase of loading cycles. However, the accelerations of the ballastless track structure components present a gradual increase trend with the accumulation of loading cycles. The deformation resistant capacity of the double-block ballastless track decreases gradually with the increase of loading cycles. This study may provide useful reference for scientific operation and maintenance of ballastless track in high-speed railway.

Simple Approximate Solutions for Dynamic Response of Suspension System

An approximate simplified analytic solution is proposed for the one DOF (degree of freedom) static and dynamic displacements alongside the stiffness (dynamic and static) and damping coefficients (minimum and maximum/critical values) of a parallel spring-damper suspension system connected to a solid mass-body gaining its energy by falling from height h. The analytic solution for the prescribed system is based on energy conservation equilibrium, considering the impact by a special G parameter. The formulation is based on the works performed by Timoshenko (1928), Mindlin (1945), and the U. S. army-engineering handbook (1975, 1982). A comparison between the prescribed studies formulations and current development has led to qualitative agreement. Moreover, quantitative agreement was found between the current prescribed suspension properties approximate value - results and the traditionally time dependent (transient, frequency) parameter properties. Also, coupling models that concerns the linkage between different work and energy terms, e.g., the damping energy, friction work, spring potential energy and gravitational energy model was performed. Moreover, approximate analytic solution was proposed for both cases (friction and coupling case), whereas the uncoupling and the coupling cases were found to agree qualitatively with the literature studies. Both coupling and uncoupling solutions were found to complete each other, explaining different literature attitudes and assumptions. In addition, some design points were clarified about the wire mounting isolators stiffness properties dependent on their physical behavior (compression, shear tension), based on Cavoflex catalog. Finally, the current study aims to continue and contribute the suspension, package cushioning and containers studies by using an initial simple pre – design analytic evaluation of falling mass- body (like cushion, containers, etc.).

Development of an improved mathematical model for the dynamic response of a sphere located at a viscoelastic medium interface

A comprehensive investigation on the static and dynamic responses of a sphere located at elastic and viscoelastic medium interfaces is performed in this study. First, the mathematical models commonly used for predicting the static displacement of a sphere located at an elastic medium interface are presented and their performances are compared. After that, based on the finite element analyses, an accurate mathematical model to predict the static displacement of a sphere located at an elastic medium interface valid for different Poisson’s ratios of the medium and small and large sphere displacements is proposed. Then, an improved mathematical model for the dynamic response of a sphere located at a viscoelastic medium interface is developed. In addition to the Young’s modulus of the medium and the radius of the sphere, the model takes into account the density, Poisson’s ratio and viscosity of the medium, the mass of the sphere and the radiation damping. The effects of the radiation damping, the Young’s modulus, density and viscosity of the medium and the density of the sphere on the dynamic response of the sphere located at a viscoelastic medium interface are explored. The developed model can be used to understand the dynamic responses of spherical objects located at viscoelastic medium interfaces in practical applications. Furthermore, the proposed model is a significant tool for graduate students and researchers in the fields of engineering, materials science and physics to gain insight into the dynamic responses of spheres located at viscoelastic medium interfaces.

Flexible Fixation Technique for Subtle Lisfranc Injuries

Background: Subtle Lisfranc injuries represent a primarily ligamentous Lisfranc complex injury involving the Lisfranc ligament and the medial and middle cuneiform ligaments. Static radiographic displacement or dynamic instability of the medial cuneiform and 2nd metatarsal typically warrants operative intervention to prevent chronic functional pain, allow for timely return-to-sport, and mitigate posttraumatic osteoarthritis. Flexible fixation techniques offer a unique solution to the issues seen with transarticular screws, plates, and arthrodesis for ligamentous Lisfranc injuries. Indications: We present the case of a 16-year-old female basketball player with a subtle Lisfranc injury sustained during practice. X-rays show isolated widening of the 1st and 2nd metatarsal bases and dynamic diastasis between the medial and middle cuneiforms. Magnetic resonance imaging (MRI) confirmed a rupture of the plantar Lisfranc ligament. After extensive discussion regarding treatment options, the patient and her family decided to proceed with surgical intervention using a suture anchor and button technique to restore stability to the Lisfranc ligament and intercuneiform complexes. Technique Description: A standardized dynamic examination under anesthesia identifies the extent of the injury. Exposure of the base of the 2nd metatarsal and medial cuneiform is performed. Reduction clamps are applied to restore the intercuneiform relationship and interval between the medial cuneiform and base of 2nd metatarsal. The suture anchor and button construct is placed using fluoroscopic guidance. A final dynamic examination is performed to confirm stability of the construct. Results: Biomechanical studies have shown that flexible fixation maintains physiologic motion about the Lisfranc articulations and has comparable stability to transarticular screws in cadaveric models of isolated Lisfranc ligament insufficiency. Clinical results are limited but demonstrate excellent postoperative functional outcome scores with very few fixation-related complications at 1 to 3 years. Discussion: Flexible fixation techniques for subtle Lisfranc injuries offer unique benefits to transarticular screws, plates, and arthrodesis. We highlight the appropriate evaluation of patients with a suspected subtle ligamentous Lisfranc injury, the surgical technique using a suture button and anchor construct, and review postoperative management and expected outcomes based on the present literature.

TOPOLOGICAL OPTIMIZATION OF THE DRIVE LEVER OF THE MODULAR ROTARY PLANT FOR A CITY FARM

The design of automated block-modular devices for growing fresh vitamin products in urban agriculture is becoming urgent. Topological optimization of components and parts of these devices will significantly reduce the cost of products, reduce the material and weight and preserve their strength and rigidity. The article gives an example of topological optimization of the drive lever of a modular rotary installation for city farms. (Research purpose) The research purpose is to optimize topologically the drive lever of a modular rotary installation for city farms, to reduce material consumption and to reduce the weight of the part. (Materials and methods) The SolidWorks program was used as a computer-aided design system, which allows for topological optimization of parts. The methods of manufacturing topologically optimized parts are: additive technologies (3D printing), casting technologies, manufacturing of composite materials under pressure, cutting processing. (Results and discussion) The article presents the stages of topological optimization of the drive lever, including the preparation of computer-aided design of the lever geometry, static analysis of the initial model, creation of a parametric grid, processing of a topologically optimized model of the drive lever, the results of primary static analysis, the output of data plots of static displacement, the output of data plots for the safety margin of the material. (Conclusions) According to the results of the study, the mass of the topologically optimized drive lever decreased by 42 percent, as a result, the safety margin of the part decreases, which entails an increase in the operating stress up to 183 megapascals, but taking into account the strength of steel 45, the stresses remain within acceptable values (530 megapascals).