Input Acceleration Research Articles

Fatigue stress estimation of metro bogie frame through frequency response functions by using limited sensors

In this paper, the fatigue state estimation of the metro bogie frame is discussed based on limited sensors through frequency domain methods. The middle-frequency and high-frequency vibration fatigue damage cases of one metro bogie frame is discussed. The main excitations come from the wheel/rail interactions including wheel out-of-roundness and rail irregularities. The most common modal vibration of the bogie frame, where the transom bending deformation is dominant, is taken as the research object to study the possibilities of fatigue failure monitoring on concerned points of the bogie frame transom focusing on specific transfer paths. To eliminate unnecessary input signals which are not closely related to the occurrence of large stress amplitudes, the coherence analysis of different loads including the transmission load, carbody load and wheel-rail impact load is conducted through various methods including the short-time Fourier transform spectrum analysis, the magnitude-squared coherence analysis and the partial directed coherence analysis. Then the power spectral densities (PSDs) of the measured accelerations and cross power spectral densities (CPSDs) are calculated to obtain the transfer functions, whose output is the Y-axis stress at the concerned point. The stress PSDs are obtained using the instantly measured input accelerations and the prepared transfer function. Then the spectral moments and the stress amplitudes distribution functions are calculated through the frequency domain method to overcome the computational burden. The stress reconstructions based on inverse fast Fourier transform are analyzed and the fatigue damage results show good consistency with the experimental ones.

Energy Harvesting from Ambient Vibration at Low Force/Acceleration Input

Background: Ambient vibration is a promising source to provide low-power electronic devices with energy. The piezoelectric direct effect is widely used to generate energy from mechanical stress. Generating sufficient power in milliwatts is often obtained with input acceleration greater than 1g (9.81 m/s2) Aim: In this work, the author demonstrated that low acceleration (between 0.1g and 0.9 g) vibration sources can be utilized to generate a satisfactory level of electric power. Method: A low pre-stress was introduced by fixing the piezo structure to the shaker using adhesive tape. the driving force which was less than 0.06 N. The harvester was tested at a vibration frequency of 173 Hz. Result: The maximum power of 1.5 mW was achieved when the harvester resistance matches the load resistance value. At maximum harvested power, the efficiency was found to be 1.6. Conclusion: The results indicated that prestreseed piezoceramics is good candidate for vibration energy harvesting.

Empirical Equations of Changes in Aerodynamic Drag Based on Direct On-Track Road Load Measurements for Multi-Vehicle Platoons

<div class="section abstract"><div class="htmlview paragraph">Considerable effort is currently being focused on emerging vehicle automation technologies. Engineers are making great strides in improving safety and reliability, but they are also exploring how these new technologies can enhance energy efficiency. This study focuses on the changes in aerodynamic drag associated with coordinated driving scenarios, also known as “platooning.” To draw sound conclusions in simulation or experimental studies where vehicle speed and gaps are controlled and coordinated, it is necessary to have a robust quantitative understanding of the road load changes associated with each vehicle in the platoon. Many variables affect the drag of each vehicle, such as each gap length, vehicle type/size, vehicle order and number of vehicles in the platoon. The effect is generally understood, but there are limited supporting data in the literature from actual test vehicles driving in formation. This study uses a practical approach to quantify road load changes in each vehicle using axle torque sensors to directly measure the load required to maintain steady-state speeds while in different platoon configurations (compared to driving solo). Three test vehicles were used, which varied in size and type: a passenger car, a mid-size SUV, and a full-size pickup truck. A control computer in each vehicle sent commands to the vehicle accelerator input to control the speed and gap based on radar feedback. The final product of the test program is a set of empirical equations that estimate drag changes for two- and three-vehicle platoons at highway speeds (88-112 km/hr) with varying vehicle and platoon configuration parameters.</div></div>

Multi-Threshold Inertial Switch With Acceleration Direction Detection Capability

In this article, we present an inertial switch with three threshold levels, which can provide quantitative acceleration measurements and detect the acceleration direction in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x–y</i> plane. The designed device has four movable electrodes attached to the proof mass (one at every side of the square proof mass) and 12 flexible stationary electrodes (three on each side). When the device is subjected to an acceleration input, the movable electrode can contact one or more of the 12 stationary electrodes based on the acceleration magnitude and direction. The acceleration direction can be determined by identifying the individual electrical switches that are activated. The designed switch is simulated using a finite-element model under different acceleration signals of various magnitudes and directions. A device prototype has been fabricated using the SOIMUMPs process and has been tested by a drop-table system under various shock accelerations in different directions. The experimental and simulation results show good agreement indicating that the acceleration direction detection accuracy and resolution improve with the increase in the number of used electrical switches.

Efficient method based on recurrent neural networks for pavement evenness detection

Surface evenness is an essential indicator for pavement evaluation; however, there is a lack of economical, efficient, and end-to-end assessment methods. This study proposes a pavement evenness estimation framework based on advanced recurrent neural networks. First, the method uses a 3D acceleration sensor to acquire the unsprung mass acceleration signal. The network is trained using a combination of acceleration and velocity inputs. Second, the trained model outputs the power spectral density (PSD) value. The R2 of the results reached 0.9880, and the classification accuracies were all above 91.7%, as evaluated by the simulation tests. Transfer learning is then used to transfer the pre-learned knowledge between similar vehicles. Finally, experiments were conducted in the field to estimate the PSD and to categorize six different pre-selected roads. The experimental results demonstrate that the method is robust to speed. The proposed framework achieves a cost-effective and efficient detection of pavement evenness.

FEM-Inclusive Transfer Learning for Bistable Piezoelectric MEMS Energy Harvester Design

In this article, a bistable piezoelectric MEMS energy harvester is presented to operate in a low-frequency range, around 100–200 Hz. The proposed design has an M-shaped structure with a couple of proof masses to not only lower the operating frequencies but also enlarge the frequency bandwidth. This specific structure has multidegrees of freedom, making it fit for a bistable piezoelectric energy harvester on the MEMS scale. An artificial neural network (ANN) is used to tackle this design in order to facilitate the optimization process and determine proper physical dimensions. To improve the accuracy and boost the training process of deep neural network (DNN), we utilize a transfer learning technique in this work. The analytical modeling and finite-element modeling (FEM) simulation data have been used for the DNN model training. Here, a DNN is first trained with a large dataset computed from the lumped-parameter model, and then, the trained network is transferred to a new DNN model for another round of training with a small dataset of highly accurate FEM simulation data samples to further reduce the estimation error. It is shown that the new model can estimate the device features with over 94% accuracy, which is considerably higher than the regular DNN. Next, the trained model is used as a performance estimator in a genetic algorithm (GA) to optimize the topology of the device to improve the operating frequency range and the generated voltage. An optimized design with a total volume of 1.02 mm3 was fabricated by the micromachining process. Our experimental results confirm that the proposed transfer-learning-based method can not only reduce the prototype’s first and second resonant frequencies to 123.8 and 175.7 Hz, respectively, but also enhance the generated power up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.83 ~\mu \text{W}$ </tex-math></inline-formula> under 0.2-g input acceleration.

How did life become cellular?

How did life become cellular?

Real-Time Risk Assessment Detection for Weak People by Parallel Training Logical Execution of a Supervised Learning System Based on an IoT Wearable MEMS Accelerometer.

Activity monitoring has become a necessary demand for weak people to guarantee their safety. The paper proposed a Parallel Training Logical Execution (PTLE) system using machine learning (ML) models on a microelectromechanical system (MEMS) accelerometer to detect coughs, falls, and other normal activities. When there are many categories, the ML prediction can be confused between these activities with each other. The PTLE system trains several models in parallel with more specific activity classes in each dataset. The shared tasks between parallel models relieve the complexity for a single one. There are six additional parameters for accelerometer characteristics, which were calculated from three axes accelerations as input features to improve the ML's consciousness. Once all models were trained, the system was ready to receive the input accelerations and activated the logical flow to manage link operation between these ML models for output predictions. Random Forest (RF) had the highest potential among the ML classification algorithms after the validation. In the experiment, the comparison between the PTLE model and the regular ML model were carried out with real-time data from an M5stickC wearable device on the user's chest to the trained models on PC. The result showed the advancement of the proposed method in term of precision, recall, F1-score with an overall accuracy of 98% in the real-time test. The accelerations from the wearable device were sent to ML models via Wi-Fi with Message Queue Telemetry Transport (MQTT) broker, and the activity predictions were transferred to the cloud for the family members or doctor care based on Internet of Things (IoT) communication.

Effect of film thickness on output power of a piezoelectric vibration energy harvester using hydrothermally synthesized (K,Na)NbO3 film

The dependence of the output power of piezoelectric vibration energy harvesters on film thickness was systematically investigated using {100} c -oriented epitaxial (K,Na)NbO3 films prepared on single-crystal SrTiO3 substrates by the hydrothermal deposition technique. First, we measured the vibration energy harvesting properties by a unimorph Pt/(K,Na)NbO3//SrRuO3//SrTiO3 cantilever. Based on the fact that the elastic stiffness of (K,Na)NbO3 is lower than that of SrTiO3 substrate, it can be understood that increasing film thickness leads to decreasing Q m, resulting in the decrease in output power as film thickness increased under the same input acceleration condition. In the next step, these cantilevers were attached to an Al plate having a much larger volume than the Pt/(K,Na)NbO3//SrRuO3//SrTiO3 cantilever. The output power of this type of harvester was more than 400% greater when the film thickness was increased from 3.5 to 22.3 μm due to the almost constant Q m value.

Optimal Calibration Method of PIGA’s Orthogonal Poses for Gravity Field Testing

With the increasing requirements for accuracy of pendulous integrating gyroscopic accelerometer (PIGA), the key to the development of accuracy of PIGA is the advanced calibration methods. This paper focuses on the calibration method of the main error coefficients of PIGA on the indexing head table. The precise input accelerations and angular velocities are deduced and the complete error calibration model is established based on the corresponding coordinate systems. Then, the orthogonal 4‐pose calibration method of dual PIGAs is proposed to identify the harmonic term coefficients of angle error. The calibration uncertainty and efficiency of equal angle sequency and equal acceleration sequency calibration schemes are analyzed. Then, the optimal calibration method is proposed and the complete test process is designed, which can accurately and efficiently calibrate PIGA by compensating with the angle error and combining the two different sequency schemes. Simulation results show that 22‐position equal acceleration sequency scheme can calibrate bias and scale factor more accurately and the test cost of equal angle sequency scheme is lower. After compensation with angle error, the magnitudes of calibration uncertainties are decreased from 10−6 to 10−7 and the maximum value of relative fitting accuracy is decreased from 6.6 × 10−5 to 2.7 × 10−5 g by the proposed 22‐position optimal calibration method.

Experimental investigation on minimizing degradation of solar energy generation for photovoltaic module by modified damping systems

With the rapid increase in solar energy generation, it is common to see solar photovoltaic modules mounted on structures subjected to dynamic loading. These dynamic loads induce vibration in solar photovoltaic modules, which generate cracks and micro-cracks. This deteriorates the solar photovoltaic modules' performance and life, effectively reducing solar energy generation. In this context, this paper deals with modal and harmonic response analysis of solar photovoltaic modules. The photovoltaic module's natural frequencies and mode shapes for ten different mounting configurations are determined using the composite plate Finite Element Model for three separate solar photovoltaic technologies. The finite element model is validated by comparing it with experimental and published results. Acceleration, velocity and displacement responses are determined in harmonic response analysis for base excitation and body acceleration inputs separately. Moreover, harmonic response analysis is performed, for which the amplitude and Frequency of induced vibrations are decided based on measured metro train vibrations levels in the vicinity of the metro rail. It is observed that mounted natural frequencies are considerably affected by the mounting configuration. A comparison of first mode natural frequency between the first and last mounting configurations shows a difference of 214.9%. Harmonic response analysis gives the resonant acceleration, velocity and displacement peak levels for all ten mounting configurations. Based on the least number of resonant peaks and lower value of response amplitudes, the best and worst mounting configurations are identified for all three solar photovoltaic technologies. This study provides a basis for selecting the best mounting arrangements to achieve the best solar energy conversion efficiency with minor degradation of the solar photovoltaic modules subjected to induced vibrations.

Shaking table tests and numerical study of a sliding isolation bearing for the seismic protection of museum artifacts

Isolation bearings are a seismic strengthening technique widely applied in building structures. However, sliding isolation bearings are seldom used for the seismic protection of artifacts housed in museums. The purpose of this study is to investigate the ability of the designed sliding isolation bearing to protect museum artifacts during earthquakes considering floor acceleration amplification. To better explore the effect of the magnification of the floor acceleration response on the seismic performance of the sliding isolation bearing, a three-story reinforced concrete frame structure was constructed, and a sliding isolation bearing-showcase-artifact system was placed on the floor of the structure. The seismic effectiveness of the proposed system was then evidenced by carrying out shaking table tests. It was observed from the tests that the sliding isolation bearing can effectively reduce the peak input acceleration, thus ensuring the safety of the artifact. Moreover, a seismic fragility analysis method is developed to evaluate the seismic performance of the sliding isolation bearing in the museum-showcase-artifact system subjected to unidirectional ground motions. Furthermore, the influences of the horizontal stiffness and the sliding displacement limitation of the bearing on the protective effect of artifacts are discussed based on the seismic performance assessment of the sliding isolation bearing.

Bandwidth Optimization of MEMS Accelerometers in Fluid Medium Environment.

There is a constraint between the dynamic range and the bandwidth of MEMS accelerometers. When the input acceleration is comparatively large, the squeeze film damping will increase dramatically with the increase in the oscillation amplitude, resulting in a decrease in bandwidth. Conventional models still lack a complete vibration response analysis in large amplitude ratios and cannot offer a suitable guide in the optimization of such devices. In this paper, the vibration response analysis of the sensing unit of an accelerometer in large amplitude ratios is first completed. Then, the optimal design of the sensing unit is proposed to solve the contradiction between the dynamic range and the bandwidth of the accelerometer. Finally, the results of the vibration experiment prove that the maximum bandwidth can be achieved with 0~10g external acceleration, which shows the effectiveness of the design guide. The new vibration analysis with the complete model of squeeze film damping is applicable to all sensitive structures based on vibration, not limited to the MEMS accelerometer studied in this thesis. The bandwidth optimal scheme also provides a strong reference for similar structures with large oscillation amplitude ratios.

Ultracompact single-layer optical MEMS accelerometer based on evanescent coupling through silicon nanowaveguides

In this paper, a novel optical MEMS accelerometer is proposed based on evanescent coupling between parallel silicon nanowaveguides. The coupling length between nanowaveguides changes due to the input acceleration, leading to a great change of coupling efficiency. As a result, the applied acceleration can be obtained by measuring the transmission of waveguiding light. Simulation results with optical displacement sensing sensitivity of 32.83%/upmu m within measurement range of 1.68 g is obtained. This design shows high compactness with no need of assembly, suggesting great potential in applications such as integrated photonic circuits.

Improved Response Spectrum Method Based on Real-Complex Hybrid Modal Superposition for Base-Isolated Structures

A novel real-complex hybrid modal response spectrum method (RCHM-RSM) based on the modal superposition of the superstructure is proposed for base-isolated (BI) structures in this paper. In contrast to the traditional analysis method, the method can increase the accuracy of the structural response and avoid complex calculations. Additionally, the direct use of the damping matrix of superstructures for BI structures was found to cause an overestimation of the damping effect and consequently underestimate the deformation of the superstructure. Thus, a new scheme is proposed for determining the damping matrix for BI structures, and general expressions of the damping matrix of the superstructure and the damping constant of the isolation layer are presented. Using the proposed method to construct the damping matrix of BI structures, the equivalent load associated with the coupling damping between the structure and support can be determined when the displacement–velocity input model (D–VIM) is adopted. Analytical expressions of structural matrices are presented for a shear-type model of a BI structure, and a numerical investigation is conducted to demonstrate the feasibility and effectiveness of the proposed methods. The results show that the proposed method (RCHM-RSM) has the advantages of simple calculations and high accuracy. The numerical results obtained also confirm that the direct use of the damping matrix of superstructures for the BI structure will underestimate the superstructure response, while the displacement input model (DIM) overestimates the deformation of the isolation layer and underestimates superstructure responses, the analysis results by using D–VIM are consistent with the acceleration input model (AIM), so the D–VIM should be used instead of the DIM.

Shake table test and numerical analysis of the seismic response of buried long-distance pipeline under longitudinal non-uniform excitation

To investigate the seismic response characteristics of buried pipelines under longitudinal non-uniform seismic excitation, a three-dimensional finite element overall analysis model is established on finite element analysis software based on the shaking table test of buried oil and gas pipelines under longitudinal non-uniform excitation. The calculated results are compared with the experimental analysis results to evaluate the correctness and reliability of the established model. The acceleration response, strain response, and displacement response of buried oil and gas pipelines and surrounding soil under longitudinal traveling wave excitation at different seismic intensities are compared and analyzed using finite element models to supplement the test conditions. The test and analysis results show that the longitudinal displacements at each measurement point under longitudinal non-uniform excitation follow the same pattern except for differences in displacement magnitude and the vibration pattern of the tube and soil when the peak input acceleration reaches 1.00 g. As shown by both experimental and numerical simulation results, the soil acceleration amplification coefficients along the soil height fluctuate between 0.5 and 1.5. The pipe acceleration time curves and Fourier spectrum exhibit the same simulated and experimental pipe acceleration waveforms, and they both show significant amplification in the low to medium frequency band of 5–20 Hz. The testing and numerical simulated pipeline axial strain peak curves are similar and in good agreement, indicating the high reliability of the experimental results.

Influence of facing conditions on the dynamic response of back-to-back MSE walls

This paper presents an experimental study of shaking table tests on two back-to-back mechanical stabilized earth (MSE) walls with full-height rigid facing and modular block facing, respectively, to investigate the influence of facing conditions on the dynamic response. The reduced-scale MSE wall models were designed according to the similitude relationships considering model geometry, reinforcement stiffness, and input motions. The back-to-back MSE wall models were constructed using poorly graded backfill soil and geogrid reinforcement, and then were excited using a series of sinusoidal input motions with increasing acceleration. The threshold acceleration where acceleration amplification factors suddenly increase significantly for the back-to-back MSE walls with modular block facing is smaller than that for the full-height rigid facing walls. The full-height rigid facing walls have smaller facing displacements than those for the modular block facing walls under the same motions and can resist stronger earthquakes in terms of facing displacements. For the back-to-back MSE walls with full-height rigid facing, incremental reinforcement tensile strains increase significantly with increasing input acceleration, while the reinforcement strains of the modular block walls are similar under different input motions for the conditions investigated.

Geotechnical Seismic Isolation System Based on Rubber-Sand Mixtures for Rural Residence Buildings: Shaking Table Test

The anti-seismic problem of rural residential buildings is the weak link of seismic retrofitting in China. Recently, geotechnical seismic isolation (GSI) technology based on rubber-sand mixtures (GSI-RSM) using rubber-sand mixtures (RSM) between the structural foundation and the foundation soil has been proven to have the possibility of potential applications in rural residential buildings. Many theoretical studies exist on the effectiveness of seismic isolation of the GSI-RSM system, but few studies on either the seismic response test of model buildings placed on the RSM layer or the large-scale shaking table test exist. Therefore, this study considers a large shaking table test performed on a 1/4 single-story masonry structure model with and without a GSI-RSM system by selecting a standard input ground motion and varying input acceleration amplitudes. The test results show that the GSI-RSM system can reduce the seismic response of superstructures. The isolation effect of the GSI-RSM system is low in small earthquakes and increases with increasing earthquake magnitude. Overall, the RSM layer can filter part of the high-frequency components of the earthquake to transmit to the superstructure and consume more seismic energy by generating friction slip in the interaction with the structural foundation.

Design and Implementation of a Novel Membrane-Island Structured MEMS Accelerometer With an Ultra-High Range

Antioverload high-range accelerometer is playing an increasingly important role in the field of hard target penetration testing, and the demand of higher accuracy and higher range accelerometers is growing consequently. Therefore, a novel accelerometer with a new structure of membrane island is proposed in this article, while the measurement range is significantly improved to 200 000 g. The design is mainly based on the finite-element method. In general, the membrane-island structured piezoresistive accelerometer is formed of a four-clamped membrane that carries a piezoresistor at the four ends. The four piezoresistors form a Wheatstone bridge. Then, based on the Timoshenko plate and shell theory, a mathematical stiffness model of the four-clamped membrane is established. The detailed parameters of the sensor are carried out by the finite-element analysis (FEA) and optimization, and it has a maximum stress of 26.8 MPa and a maximum displacement of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.208~\mu \text{m}$ </tex-math></inline-formula> when applying an input acceleration of 200 000 g. Finally, the sensitivity test, antioverload test, and dynamic test of three membrane-island structured prototypes are carried out, and their sensitivities are 0.579, 0.505, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.532~\mu \text{V}$ </tex-math></inline-formula> /g, respectively; the passband with 5% dynamic error is 14.9, 16.5, and 15.8 kHz, respectively. The accelerometer has an antioverload capability of 250 000 g, which is verified by the Hopkinson bar. The test results show that this membrane-island structured accelerometer has both good antioverload capability and high accuracy.

Shake table test and numerical analyses of a thin-walled Cold-Formed Steel structure: Part 1 — Investigation of the structural skeleton without claddings

CFS structures are classified as structures with low ductility. Due to this, they are not recommended for medium to high seismic areas. The paper presents the results of a complex experimental program coupled with numerical investigations on the behavior of Cold Formed Steel (CFS) structures under seismic actions. The scaled-down model skeleton was made of DX51D+Z C-shaped 89 × 41 × 12 × 1 mm steel elements connected by 4.8 × 16 mm self-tapping screws (STS) and 5.5 × 25 mm self-drilling screws (SDS). This structure represents a replica of constructive solutions for single-story or one or two-storey structures that are frequently met in South-Eastern Europe, including highly active seismic areas.The main purpose of the research program is to gather both quantitative and, more importantly, accurate information regarding structural response to dynamic actions characterized by input accelerations equal in amplitude to the maximum values specified in seismic design codes, up to PGA = 0.40 g. The damage of the joints and the reduction in the structural stiffness due to cyclic loads, such as the ones produced by earthquakes, change the structure’s eigen period and significantly influence the structure’s response to seismic actions. Larger gravitational loads lead to more extensive damage of the joints. The developed numerical model based on the experimentally determined connection axial rigidity can offer accurate results in terms of the fundamental frequency of vibration, relative accelerations and displacements. However, for a more accurate capturing of the local damages and onset of failure mechanisms, more complex numerical models are needed, which take into account non-linear material behavior.The results presented in this paper help to design these structures as only the skeleton and serve as a starting point for future research work aimed to assess the influence of the sheathing on the global response of CFS structures to seismic actions. Additionally, research in the direction of improved joints with better energy dissipation properties is also pursued by the authors.