Equivalent Acceleration Research Articles

Dynamic Response of a Cat Head Type Transmission Tower-line System under Strong Wind

Transmission tower plays important role in the power system and it is security sensitive in various working conditions, such as wind and ice. In this paper, a method to obtain the dynamic response of a cat head type transmission tower under strong fluctuating wind was proposed. The coupled tower-lines finite element model was established in ABAQUS, and the equivalent acceleration of fluctuating wind was simulated by MATLAB. Then the displacements and stresses time histories were obtained. The method introduced in this paper can be used to assess the safety of tower under different fluctuating wind with different directions and provide a reference of the tower in the design stage.

Modelling and ride comfort analysis of a coupled track-train-seat-human model with lateral, vertical and roll vibrations

A coupled track-train-seat-human model with lateral, vertical and roll vibrations was developed to investigate the ride comfort of high-speed trains. The ride comfort was assessed by the total equivalent acceleration defined according to ISO 2631-1. It was found that the track flexibility had a minor influence on the lateral, vertical and roll floor vibrations below 20 Hz, while the total equivalent acceleration was overestimated by over 10% at high speed using a rigid track. The flexibility of the carbody generated dramatic floor vibration in lateral, vertical and roll directions above 7.5 Hz, so the rigid carbody model significantly underestimated the total equivalent acceleration. The total equivalent acceleration tended to increase with the increase of speed. The equivalent accelerations for two symmetric seat positions illustrated analogous trends with the increasing speed. The ride comfort was the worst close to the carbody ends, followed by the carbody centre at high speed. The vertical acceleration on the seat pan was the most severe whatever the seat position and speed are. The neighbouring subject brought about a reduction of the total equivalent acceleration for the subject under evaluation. The carbody damping can reduce the total equivalent acceleration effectively in the whole speed range.

Effect of Earthquake Coefficient Selection on Seismic Performance of Gravity Block Type Quay Walls

Gravity block type quay walls are one of the main options when the seabed has a suitable bearing capacity. Today, the design of quay walls is based on its seismic performance, and the pseudo-static method is the most common design method. In this method, the force caused by the earthquake is considered as the product of the equivalent acceleration coefficient in the effective mass of the structure. The choice of the value of this coefficient, consisting of horizontal (kh) and vertical (kv) components, is of great importance. Therefore, in this paper, the effect of selecting the earthquake equivalent acceleration coefficient on the seismic performance of the hunch-back quay wall of Pars Petrochemical Port has been studied as a case study. In this regard, the recommendations and relationships reflected in the old and new editions of the Japanese Maritime Codes (OCDI, 2002, 2009) are more comprehensive and complete than other codes, especially in the seismic design of berths. The results illustrated that the proposed relationships of horizontal earthquake acceleration coefficient (kh) based on the new version of the Japanese code is more suitable and helps predict the seismic performance of this type of quay walls more accurately and their realistic design. Moreover, in this research, based on acceleration time-histories resulted from seismic hazard studies at the site, using FLAC2D software, the values of horizontal displacement of the quay wall crown have been investigated, and based on that, earthquake coefficient values have been predicted for each relevant time-history.

Multi-Function Microelectromechanical Systems Implementation with an ASIC Compatible CMOS 0.18 μm Process.

A multi-function microelectromechanical system (MEMS) with a three-axis magnetometer (MAG) and three-axis accelerometer (ACC) function was implemented with an application-specific integrated circuit (ASIC)-compatible complementary metal-oxide-semiconductor (CMOS) 0.18 μm process. The readout circuit used the nested chopper, correlated double-sampling (CDS), noise reduction method; the frequency division multiplexing method; the time-division multiplexing method; and the calibration method. Sensing was performed by exciting the MEMS three-axis magnetometer at X/Y/Z axes mechanical resonant frequencies of 3.77/7.05/7.47 kHz, respectively. A modest die-level vacuum packaging resulted in in-plane and out-of-plane mechanical quality factors of 471–500 and 971–1000, respectively. The sensitivities of both the three-axis magnetometer with 2 mA driving current and the three-axis accelerometer were 7.1–10.7 uV/uT and 58.37–88.87 uV/ug. The resolutions of both the three-axis magnetometer with 2 mA driving current and three-axis accelerometer resolution were 44.06–87.46 nT/√Hz and 5.043–7.5 ng/√Hz. The resolution was limited by circuit noise equivalent acceleration (CNEM) and Brownian noise equivalent magnetic field (BNEM).

Development of Economic Velocity Planning Algorithm for Plug-in Hybrid Electric Vehicle

The energy consumption of a plug-in hybrid electric vehicle (PHEV) is directly related to its velocity. Considering the influence of road condition information such as traffic velocity, road speed limit and slope on the energy economy of PHEV, the economic velocity planning algorithm is designed in this study. Firstly, based on the actual vehicle test data, the polynomial fitting energy consumption models with the input parameters of vehicle speed and acceleration for charging of depleting mode and charging of sustaining mode are developed. The economic velocity planning model based on traffic flow velocity and road speed limit on flat roads is established adopting the Pontryagin’s minimum principle (PMP). Afterwards, the road gradient information is introduced into the economic velocity planning algorithm based on the equivalent acceleration. Finally, the planned economic velocity and traffic flow speed are compared by the hardware-in-the-loop energy consumption tests. The results show that compared with the traffic flow speed, the economic velocity improves the vehicle energy economy by more than 4%, and the output torques of the engine and driving motor are more stable, which are more conducive to the energy economy of the vehicle. The designed economic velocity planning algorithm based on road information for PHEV improves the adaptability of PHEV control strategy to actual road conditions, and expands the optimization dimension of energy-saving driving. Thus, it has high practical application value.

Field axial cyclic loading tests of screw micropiles in cohesionless soil

Screw micropile is a new type of steel pipe pile that consists of a smooth, threaded segment and a tapered segment. It is installed using the torque method. To examine the axial cyclic behavior of the piles, six one-way compressive and load-controlled axial cyclic tests were performed at a sandpit site. The axial cyclic load, with 15 cycles and an equivalent peak vertical acceleration ranging from 0.4 g to 0.6 g, was meant to replicate the vertical motion of an earthquake load. In-situ geotechnical investigation and lab testing were undertaken to determine the soil stratigraphy and properties. Three of the piles were instrumented with strain gauge to measure the unit shaft distribution. The pile-head cumulative displacement, stiffness and equivalent damping ratios were obtained. The effect of initial factor of safety on the cyclic behavior was examined. The re-distribution of unit shaft resistance of individual segments was obtained. Segment equivalent damping ratio and stiffness of the unit shaft resistance hysteresis were determined. The contribution of each pile segment to global pile behavior was delineated.

Using Electrostatic Spring Softening Effect to Enhance Sensitivity of MEMS Resonant Accelerometers

Micromachined resonant accelerometers (MRAs) are very attractive for high-precision measurement applications due to their high sensitivity, frequency output, and large dynamic range. The sensitivity is one of critical metrics in MRA sensors. In order to enhance this metric, a micro-lever is usually used. However, the micro-lever may suffer from the attenuation of effective amplification ratio and increasing the structure complexity. Lowering spring stiffness of suspension structure and enlarging the proof mass are alternative methods, but these methods are restricted in real devices due to the trade-offs for the device sizes, cross-axis sensitivity, robustness and fabrication yield. This paper presents a novel method to improve sensitivity of MRAs by using electrostatic spring softening effect without sacrificing the mechanical robustness or enlarging footprint size of the device. Besides, this method can on-line adjust the sensitivity of MRAs, which is another potential advantage for specific applications. The prototype has been designed, fabricated and characterized in both open-loop and close-loop ways. In agreement with the proposed device model, the experiment results demonstrated that the sensitivity of the prototype device increased from 492.7 Hz/ ${g}$ ( ${g}$ being the gravity acceleration) to 2277 Hz/ ${g}$ by using a sensitivity enhancing bias voltage of 67V in a linear scale range of $\pm 1~{g}$ . Moreover, the prototype’s equivalent input acceleration noise reduces down from 5.5 ug / $\surd $ Hz to 1.6 ug / $\surd $ Hz within 1Hz bandwidth, and the bias-instability is down from 6.1 ug to 2.2 ug .

Entanglement harvesting for Unruh-DeWitt detectors in circular motion

We study the properties of the transition probability and entanglement harvesting phenomenon for circularly accelerated detectors locally interacting with massless scalar fields. The dependence of the transition probability on the parameters associated with the circular motion is first analyzed in detail. By a cross-comparison with the situation of the uniformly accelerated motion, we obtain that the transition probability and the possible thermalization behavior for detectors rotating with an extremely large circular radius are analogous to that for uniformly accelerated detectors, but for a very small linear speed and a large acceleration, the effective temperature which characterizes the detectors' thermalization in a finite duration is much lower than that for uniformly accelerated detectors. We then focus on the phenomenon of entanglement harvesting in two special situations of circular trajectories, i.e., the coaxial rotation and the mutually perpendicular axial rotation by examining the concurrence as the entanglement measure in detail. We find that when two circularly accelerated detectors have equivalent acceleration and size of circular trajectory, the harvested entanglement rapidly decays with increasing acceleration or separation between two detectors. In contrast with the situation of uniform acceleration, the angular velocity would have significant impacts on entanglement harvesting. Especially for those detectors circularly moving in different directions, both the acceleration and trajectory radius play an important inhibiting role in entanglement harvesting. When two circularly accelerated detectors have different values of acceleration or angular velocity, we find that the entanglement can still be extracted by such detectors, even in the situation that one detector is at rest and the other is in a circular motion.

An investigation of rocking derailment of railway vehicles under the earthquake excitation

The rocking derailment mechanism of railway vehicles due to the earthquake-induced roll motion is investigated through a coupled vehicle/track dynamic model together with a simplified roll-plane vehicle model. The coupled vehicle/track dynamic model is formulated through a typical high-speed train model incorporating with a track model to study dynamic responses and rocking derailment procedure under earthquake excitations. The results indicate that the lateral earthquake excitation can impose significant effects on the running safety of vehicle, and further lead to the rocking derailment. A simplified roll plane vehicle model subjected to the lateral earthquake excitation is thus developed to derive the critical condition of rocking derailment, which further contribute to a criterion for earthquake- induced rocking derailment. Moreover, a conservative limit, in term of equivalent acceleration of lateral earthquake excitation, has been identified considering different earthquake excitations. This could serve as a threshold for assessment of operational safety of rail vehicle in the presence of earthquake condition.

Acceleration Factors and Life Predictions

Abstract Acceleration factors (AF) are key to designing an effective accelerated life test (ALT). They represent the ratio of the time in field to the time in test for a particular event to occur (typically a failure event related to a specific failure mechanism). Time to failure for a device generally correlates with the amount of stress applied (the higher the stress, the quicker the device will fail), and failure models exist to mathematically define that correlation for various failure mechanisms. This allows for use of a higher stress in test than in the field, thereby providing an acceleration factor that shortens the time in test to demonstrate a failure-free time period. ALT can take the form of qualitative or quantitative testing. The latter is used to determine the life characteristics of the device with some reliability and confidence level. Usage rate acceleration and higher stress acceleration can be used. It is important to consider the design limits of the device based on its specification and material properties, and limit the stress levels in test so as not to induce failure mechanisms that the device would not otherwise have experienced in the field. ALT results are used to make life predictions for the device tested. With no failures, the test results demonstrate the required reliability and confidence level metrics for the failure mechanism of interest. With several failures, a reliability software tool can be used with the appropriate analysis method, rank method, and confidence bounds method chosen in order to extrapolate to an expected life in test. The equivalent field life is based on multiplying the expected life in test by the AF. If the field stress and/or test stress are not constant, there are multiple acceleration factors to utilize. As a result, an equivalent acceleration factor needs to be calculated and used as the AF when predicting equivalent field life.

Characteristics of spatial variability of shear wave velocity on seismic response of slopes

The soil shear wave velocity has long been recognized as an effective parameter in the assessment of the seismic response of slopes. However, most seismic analyses have been carried out by deterministic models considering just a single realization of soil shear wave velocity. In other words, only a small number of researchers have explored the spatial variability effects of soil shear wave velocity on the seismic response of slopes. This paper investigates this phenomenon stochastically, and the auto-correlation matrix decomposition method based on Monte Carlo Simulation was applied to generate the stationary random fields in order to simulate the spatial variability of soil shear wave velocity. This framework includes interpreting the coefficient of the soil shear modulus variation and auto-correlation length effected on maximum horizontal equivalent acceleration. The results showed that the spatial variation of shear wave velocity might have a significant effect on the dynamic response of the sliding mass if slopes were subjected to weak ground motions. By contrast, it could have a significant effect on maximum horizontal equivalent acceleration induced in slopes subjected to intense ground motions.

Analysis of ride comfort of high-speed train based on a train-seat-human model in the vertical direction

A rigid-flexible coupled train-seat-human model was developed for studying ride comfort of rail vehicles. The weighted acceleration r.m.s. value at the seat pan was used for assessing ride comfort. The contribution of different modes of the carbody to ride comfort was defined from the perspective of power spectral density. The role of first bending mode was more important than other bending modes when bogie and seat positions are far from the nodes of first bending mode. Under this situation, the bogie spacing filter effect of first bending mode can be adopted to predict peaks and troughs of the equivalent acceleration on the floor or human-seat interface varying with speed or first bending frequency. The incorporation of human-seat system was necessary in order to accurately evaluate ride comfort. The ride comfort exhibited a global trend of improvement with increased bending rigidity or reduced speed. Increasing the damping ratio of bending modes improved ride comfort effectively. Increasing stiffness or decreasing damping of human-seat vertical contact on the seat pan worsened ride comfort. Equivalent accelerations at symmetrical seat positions showed analogous tendency as the speed. Ride comfort was worst at two ends whatever the speed was, followed by carbody centre at high speed.

A digital low-frequency geophone based on 4th-order sigma-delta modulator and single-coil velocity feedback

Widely deployed conventional moving-coil geophones lack the responses needed at low frequencies for detecting long-period seismic waves, and rely heavily on the A/D conversion chips for data acquisition. This work reports on a digital low-frequency geophone based on the PID force balancing technique and a single loop 4th-order sigma-delta modulator. The system is studied by Simulink modeling and is designed to satisfy demanding bandwidth and stability requirements. In addition, the hardware implementation adopts a readout interface for a geophone that consists of two parts: the analog part picks off the coil voltage while driving a control balancing force; and the digital part performs a real-time time DF integrators filtering in an FPGA for high-order noise shaping. The experimental results confirm the design concept of the proposed digital geophone. The balancing loop extends the low-frequency response of a commercial 4.5 Hz geophone down to 0.16 Hz. Within a 200 Hz bandwidth, the sigma-delta modulator achieves an equivalent acceleration noise floor of 4.3 ng/√Hz @ 1.0 Hz and shapes the in-band quantization noise to a level below other noises in the system. This investigation shows its potential to detect low-frequency seismic waves for efficient and high precision deep Earth exploration and hazard predictions.

Analysis of a Lightweight Aluminum Vehicle Chassis in a Simulation-Based Design Approach

This study investigates different chassis designs through a simulation-based design approach. The inherent aluminum ductility and softness could make chassis a daunting modification if not analyzed properly. Structural finite element analysis is comprehensively performed on a vehicle chassis for static loading cases up to 1G in equivalent acceleration. The analysis of the vehicle chassis of both A36 steel and 6061 aluminum for the scenarios of bump, front impact, side impact and a rollover. The von Mises stresses and displacement results showed that the steel chassis possessed higher safety factor in all load cases. The safety factors for an aluminum clone of the steel chassis in some load cases are below 1.0, hence indicating that the failure criterion has been triggered and failure would occur under the 1G load. The original aluminum chassis deformation is far more severe than steel reaching as high as 9.88 mm for the bump loading. A modified aluminum chassis is proposed, by optimizing the wall thickness of the rectangular bars. The slight increase in weight resulted in overcoming the deficiency of aluminum in load carrying capacity. An evaluation matrix procedure is implemented to analyze the trade offs between cost, weight and safety factor for the three chassis materials.

Downhole Microseismic Monitoring Using Time-Division Multiplexed Fiber-Optic Accelerometer Array

Microseismic monitoring is of importance for several geoscience research aspects and for applications in oil and gas industry. For signals generated by the ultra-weak microseismic events, conventional moving-coil geophone systems have reached their limit in detection sensitivity especially at high frequency range. Here we for the first time present a specially tailored fiber-optic sensing system targeting at downhole microseismic monitoring. The system contains 30 individual interferometric accelerometers and 2 reference sensors, which are time-division multiplexed into a 12-level vector seismic sensor array. The multiplexed accelerometers can achieve ~50 ng/ $\sqrt {\mathrm{Hz}} $ noise equivalent acceleration, which is superior to the commercial available moving-coil geophone systems at frequencies above 200 Hz. The measured sensitivity of the accelerometers can reach ~200 rad/g from 10 Hz to 1 kHz. The dynamic range is above 134 dB over the same frequency range and is higher than its electronic counterpart in the low frequency band. Moreover, the sensors can function properly under the harsh condition of 120 °C temperature and 40 MPa pressure over the 4-hour test duration. The sensor array along with the interrogator has been running uninterruptedly over 3 weeks in a multi-stage hydraulic fracturing stimulation field test. On-site results show that our system can clearly resolve the vector nature of both compressional and shear waves generated by the microseismic events.

Equivalent Acceleration Imitation for Single Wheel of Manned Lunar Rover by Varying Torque on Earth

Owing to different gravities, the same manned lunar rover shows different acceleration properties on the earth and the moon; therefore, it is of great significance for astronauts to be trained on the earth under the condition of the acceleration properties found on the moon. In this article, a novel acceleration imitation method focused on a single wheel is proposed to obtain equivalent acceleration when using the same acceleration driver input under different gravities, and the acceleration imitation algorithm is derived based on a mechanical model of a special metal wheel with a mesh surface. To reduce the complexity and improve the real-time properties of the algorithm, a fitting function for the imitation torque ratio is proposed to adjust the relationship between the acceleration driver input and the driving torque of the wheel. Finally, experiments were conducted to verify the acceleration imitation algorithm, and the results revealed that the wheel with an imitation torque ratio could effectively approximate on the earth the same acceleration experienced by a single wheel of a manned lunar rover on the moon, given equivalent acceleration driver inputs.

Influence of interactions between topographic and soil layer amplification on seismic response of sliding mass and slope displacement

In the conventional evaluation of earthquake-induced displacement of slopes, the two-dimensional (2D) full-slope amplification as a result of the interaction of topography, soil layer and seismic ground motion is commonly neglected. To investigate this coupling effect on the evaluation of sliding displacements of earth slopes, linear and non-linear seismic response analyses are conducted on slope models with different inclinations and potential sliding mechanisms, subjected to simplified wavelets and recorded earthquake ground motions with various frequencies and amplitudes. The equivalent acceleration time histories of the sliding masses and the induced sliding displacements are derived. The results indicate that the soil layer amplification generally dominates the overall seismic response of the sliding mass. The controlling factors include the fundamental natural period of the soil deposit, the geometry of the sliding mass, the slope inclination, and the normalized depth of the sliding mass. Predictive models for the equivalent seismic ground motions of sliding masses are developed by including the 2D full-slope responses. Finally, an example application is presented to estimate the seismic response of the sliding mass and the slope displacements by using the proposed model.

Evaluating the Effect of Wheel Polygons on Dynamic Track Performance in High-Speed Railway Systems Using Co-Simulation Analysis

With increases in train speed and traffic density, problems due to wheel polygons and those caused by wheel–rail impacts will increase accordingly, which will affect train operational safety and passenger ride comfort. This paper investigates the effects of polygonal wheels on the dynamic performance of the track in a high-speed railway system. The wheel–rail interaction forces caused by wheel polygons are determined using a dynamic vehicle–track model, and the results are entered into a slab track finite element model. The influence of the harmonic order and out-of-roundness (OOR) amplitude of wheel polygons on the transient dynamic characteristics of the track(von Mises equivalent stress, displacement, and acceleration) is examined under high-speed conditions. The results indicate that the vibration acceleration and von Mises equivalent stress of the rail increase in proportion to the harmonic order and the OOR amplitude and velocity of a polygonized wheel. The vibration displacement of the rail first increases and then decreases with a change in the harmonic order, and reaches a maximum at the ninth order. The dynamic responses of the concrete slab layer, cement-asphalt layer, and support layer increase linearly with the harmonic order and amplitude of wheel polygons and decrease from top to bottom. Through a combination of numerical simulations and real-time monitoring of rail vibrations, this study provides guidance on potential sensor locations to identify polygonized wheels before they fail.

Seismic Performance Analysis of Emergency Diesel Engine Retarder in Nuclear Power Plant

The finite element analysis is used to study the seismic performance of the emergency diesel worm gear retarder in nuclear power plant. By modal analysis of the structure, it is concluded that the first natural frequency is higher than 33 Hz. Then the seismic analysis is performed both on the horizontal and vertical conditions. The analysis results show that under the equivalent earthquake acceleration 4.5g, the stress is low for the retarder case and other components of the worm retarder, and fulfills the material strength requirement. It can be considered that the structure of the retarder is stable and has excellent anti-seismic performance, meeting the seismic requirement for class 3 nuclear safety equipment.

A new model of trajectory in eddy current separation for recovering spent lithium iron phosphate batteries

Eddy current separation (ECS) is an environment-friendly technology for separating nonferrous metallic particles whose size was from 2 mm to 10 mm. No wastes are generated in ECS. ECS quality of nonferrous metals from solid wastes is rather low in the production practice of spent lithium iron phosphate (LFP) batteries recovering. Repeating separation even manual sorting is required in the production. The traditional method of falling point prediction based on eddy current mechanics uses equivalent acceleration to replace separation motion curves. These curves have low precision and are unsuitable for predicting the motion trajectory of small particle size of sorted materials. In this work, eddy current separation of positive and negative plates in a crushed product of spent lithium iron phosphate battery is used as an example to establish the force and kinematics models of different materials in the eddy current separation. An iterative method, rather than average speed method, is used to improve the accuracy of the model. Displacement interval replaces disengagement angle as a separating index to improve the model’s intuitiveness and practical guidance. In the range of 2–20 mm, test results are consistent with simulation results. The copper and aluminium foils at a magnetic roller speed of 800r/min can be separated to a maximum particle size ratio of 1.72, and the maximum particle size ratio of copper and positive electrode sheets can be large. This paper provided an environmental-friendly and effective technology for separating nonferrous metals from crushed spent LFP batteries.