Root Mean Square Acceleration Research Articles

Evaluation of dynamic impact factor of existing bridges with road surface damages based on dynamic response under traffic flow loading

When traffic flows pass through existing bridges, the dynamic effect of the vehicle loads increases due to the local surface damage rather than the entire roughness level of the bridge deck. This study presents a method for evaluating a dynamic impact factor (IM) from a bridge dynamic response under a traffic flow considering the local surface damage. The random axle loads of traffic vehicles under the deteriorated roughness conditions are presented using an input load time-history applied to each discretized deck node of a finite element bridge model. The amplification ratios of the root mean square of the simulated acceleration under nominal road surface conditions with respect to the specified IMs in the design stage are calculated. The relationship between the ratios and IMs is determined to evaluate the dynamic impact factors under any surface roughness condition. The method is validated by applying it to two existing bridges with different road surface damage and traffic conditions. The results show that the IMs depend on both the traffic loading and bridge surface roughness conditions. Under the same traffic flow conditions, the values increase when the road surface damage increases. However, the increases in the IMs vary according to the location of the surface roughness deterioration in both of the target bridges.

A Coupling Model of High-Speed Train-Axle Box Bearing and the Vibration Characteristics of Bearing with Defects under Wheel Rail Excitation

A three-dimensional vehicle-axle box bearing coupling model is established. The model can calculate the contact force in three directions and obtain the dynamic response of axle box bearing under the real vehicle running environment. The load distribution on the double row tapered roller bearing and the vehicle is analyzed, and the co-simulation is conducted by comprehensively considering the force transmission between vehicle and bearing. Taking into account the great impact of defects on the bearing, three different types of bearing defects are added into the model, respectively. The simulation results verify the effectiveness of the model. The model is also verified by using the rolling and vibrating test rig of single wheelset. It is concluded that the simulation results show good agreement with experimental results. The influence of track irregularity on the system motion state is studied by using axis trajectory and vibration RMS (Root Mean Square value). The results show that the influence of track irregularity and wheel flat scar on axle box bearing cannot be ignored. The RMS of acceleration will change greatly due to the existence of defects. Wheel flat scar will greatly interfere with the extraction of bearing defect, but it can be selected at high speed and low frequency to monitor the existence of wheel flat scar, and select low speed and high frequency to monitor the existence of bearing defect. The research results are helpful to the detection of wheel flat scar and axle box bearing defect.

Mechanical Structure Design and Experimental Study of Gamma-ray Monitor for Small Satellite Payload

In this paper, a novel mechanical structure for a gamma-ray monitor (GRM) is designed for a small satellite payload. Its structural stiffness, strength and dynamic response are directly related to the performance of the novel GRM, which must meet the static and dynamic characteristic requirements of the structure in a harsh vibration environment. The static and dynamic simulation of the structure are carried out by finite element method (FEM), and the mechanical structure response laws of the novel GRM are analyzed and validated by vibration tests. Through comparing the frequency response simulation results with the vibration test results, the minimum safety factor of the key components of the structure is 4.07, the fundamental frequency error is within 5.04%, the acceleration response error is within 8.5%, the root mean square of total acceleration (Grms) error is within 14.2%, and the sinusoidal characteristic sweep frequency error before and after the vibration test is within 5.0%. The results show that the payload structure has large structural stiffness, high strength and reasonable frequency response characteristics, and meets the design requirements.

Vehicle vibro-acoustical comfort optimization using a multi-objective interval analysis method

Vehicle interior vibro-acoustical comfort, i.e., noise, vibration and harshness (NVH), is important to consumers and automotive manufacturers because it affects the physical and mental health of passengers and impacts the reputations of automotive manufacturers. Although simulations can predict vehicle interior noise and vibration, acoustic treatment and resulting uncertainty may generate considerable errors between the simulation and actual measurement results. Meanwhile, the recursive invocation of a complex simulation model in an optimization leads to a very time-consuming calculation process. These problems make the optimization of vehicle interior vibro-acoustical comfort a challenge for the automotive industry. In this paper, a new method, the multiobjective interval analysis method, was proposed to solve these problems. To implement this method, we carried out a vehicle road test instead of a complicated simulation model to collect data. The vehicle interior noise and vibration were recorded, and the interior sound pressure level (SPL) and total weighted acceleration root mean square (TWA-RMS) values were calculated and used as objectives. Then, a multiobjective interval analysis method was proposed to compute the midpoint and radius of the objective functions under different uncertainties. The preferred average performance and robustness of the vehicle vibro-acoustical comfort was adjusted by tuning the weighting factor. To accelerate the calculation process, a neural network model was developed as an approximate model to construct the numerical relation between the dynamic parameters and the vibro-acoustic metrics. Finally, the effectiveness and accuracy of the proposed method were verified with experimental results.

Influence of Interference between Vertical and Roll Vibrations on the Dynamic Behaviour of the Railway Bogie

This paper investigates the dynamic behaviour of a two-axle bogie under the influence of interference between the vertical vibrations of bounce and pitch—generated by the track irregularities—and the roll horizontal vibrations—excited by the asymmetry in the suspension damping that can be caused by the failure of a damper during exploitation. For this purpose, the results of numerical simulations are being used, as developed on the basis of two original models of the bogie-track system, namely the model of the bogie with symmetrical damping of the suspension—track and the model of the bogie with asymmetrical damping of the suspension—track, respectively. The dynamic behaviour of the bogie with symmetrical/asymmetrical damping is evaluated in five reference points of the bogie regime of vibrations, based on the Root Mean Square of acceleration (RMS acceleration). The results thus obtained highlight the characteristics regarding the symmetry/asymmetry of the regime of vibrations in the bogie reference points and the location of the critical point of the bogie regime of vibrations. The influence of the suspension asymmetry upon the dynamic behaviour of the bogie is analysed in an original manner, hence leading to conclusions that might establish themselves as the starting point of a new fault detection method of the dampers in the primary suspension of the railway vehicle.

Investigation on the Reliability of an Ablation Thermal Protection Coating with Adjustable Thickness under Aerothermal–Vibration Coupling Environment

Advanced thermal protection system is the core component of supersonic vehicles. A novel hydroxyl‐terminated silicone oligomer‐bridged epoxy resins (PSG)‐based ablation thermal protection coatings (ATPCs) with different thickness are fabricated. The thermal insulation and structural reliability of the coatings are investigated by an aerothermal–vibration coupling test system. During the test, the heat flux of the surface of ATPCs ranges from 400 to 700 kW m−2. Meanwhile, the vibration load is a random vibration with frequency range of 20–2000 Hz and root mean square of total acceleration (Grms) of 15 g. The maximum surface and back‐face temperatures of the coating with the thickness of 2 mm reach 771.8 and 113.6 °C, respectively. Compared with epoxy resin‐based ATPCs, the PSG‐based ATPCs show excellent structural reliability during the test. Finally, the comprehensive properties of ATPCs with different thickness are also carefully studied. Results show that the reduction of thickness obviously suppresses the surface temperature (≈743.4 °C) and increase in back‐face temperature (≈241.5 °C) yet maintaining much higher structural reliability. This study provides a solution for obtaining excellent thermal insulation performance ATPCs with high structural reliability, which is highly desired in supersonic vehicles.

Thermal insulation and anti-vibration properties evaluation of modified epoxy resin-based thermal protection coatings in arc-jet

Thermal protection system (TPS) is crucial for hypersonic flight vehicles to effectively protect them against the aerothermal effect imposed on them during flying with high Mach number. A novel hybrid ablation thermal protection coatings (FHMP-ATPCs) on the surface of stainless steel substrate were prepared by doping iron trioxide (Fe2O3) powder, hollow glass microspheres (HGM) and mica powder (MP) into hydroxyl-terminated silicone oligomer-bridged epoxy resins (PSG) copolymer. The thermal insulation and structural reliability of the FHMP-ATPCs were investigated by a novel aerothermal-vibration coupling test system. During the test, the heat flux of the surface of coatings ranged from 400 kW/m2 to 700 kW/m2. Meanwhile, the vibration load was a random vibration with frequency range of 20–2000 Hz and root mean square of total acceleration (Grms) of 10.8 g. The maximum surface and back-face temperature reached 714.9 °C and 141.3 °C, respectively. Compared with epoxy resin based coatings，the PSG-based coatings showed excellent structural reliability during the test. This study demonstrates the robust effect of strategy of modifying epoxy resin with organosilicon in improving thermal insulation performance yet maintaining the structural reliability of the ablation thermal protection coatings, providing a promising route to achieve high-performance coatings.

Sensitivity-based, space rod system multi-objective design of straddle-type monorail vehicle with single-axle bogies

In order to study the influence of the space linkage system on the stability of the straddle-type monorail vehicle with single-axle bogies, the sensitivity analysis of the space linkage system is identified based on the Pearson coefficient method to determine the importance of each component of the single-axle bogies. The dynamics model of straddle-type monorail vehicle with single-axle bogies is established by the multi-rigid body dynamics. The Pearson analysis method is used to identify the key parameters of the space linkage system. Based on that, dynamic response optimization model of space bar system is developed to carry out a multi-objective suspension design optimization process. The results show that the maximum sensitivity parameter for the RMS value of yaw acceleration and pitch angle acceleration is the length of the longitudinal tow bar; there is a correlation of approximately 0.088 between the stiffness K and the damping coefficient C of the hydraulic shock absorber. After optimization the root mean square of lateral acceleration of the optimized single-axle bogie vehicle is reduced by 6.0%.

Applied Assessment Method for Varus Thrust during Walking in Patients with Knee Osteoarthritis Using Acceleration Data Measured by an Inertial Measurement Unit.

We developed a novel quantitative method to assess varus thrust during walking using acceleration data obtained from an inertial measurement unit (IMU). This study aimed to examine the reliability of the developed index and to evaluate its ability to distinguish patients with knee osteoarthritis (OA) with varus thrust from healthy adults. Overall, 16 patients with knee OA and 16 healthy adults walked on a treadmill with IMUs attached to the tibial tuberosity and lateral femoral condyle. As an index of varus thrust, we used the root mean square (RMS) of acceleration in the mediolateral direction. This value was adjusted by dividing it by swing speed while walking (adjusted RMS, A-RMS) because the RMS of the acceleration was strongly coupled with the speed of motion. The intraclass correlation coefficients of A-RMS of the tibia and femur were 0.85 and 0.73, respectively. Significant differences were observed in the A-RMSs of the tibia and femur, with large effect sizes between the patients with knee OA and healthy adults (Cohen’s d: 1.23 and 0.97, respectively). Our results indicate that A-RMS has good test–retest reproducibility and can differentiate patients with varus thrust from healthy adults.

Damage detection for prefabricated building modules during transportation

Transportation of prefabricated modules is a critical process in modular construction and can cause additional stresses which may damage individual modules, leading to additional costs and time during the installation and operational phase if damaged parts are not timely restored or replaced. Therefore, utilizing a tracking and condition monitoring system is useful for modular building manufacturers to detect damaged modules upon arrival to the project job site. The tracking system, developed in this study, consists of a acceleration-sensor-based data acquisition (DAQ) module and a storage module, along with automated data analysis module to assess the structural condition of prefabricated building modules during transportation. The system uses the acceleration Root Mean Square (RMS) parameter and unsupervised clustering algorithms for damage detection. After detailed analysis, using performance measurement techniques: confusion matrix and accuracy score, it was found that the DBSCAN clustering algorithm yielded full accuracy score in the case of more than one level of damage compared to k-means, mean shift, and agglomerative clustering algorithms, which yielded accuracy scores of 0.81, 0.79, and 0.78 respectively. The developed system addresses existing challenges of cost and complexities associated with commercially available hardware systems and can provide evidence to support manufacturers' insurance claims on repair and/or replacement costs. However, the developed system should be tested further on more prefabricated building modules instrumented with a larger number of sensors.

Performance of the Machine Learning on Controlling the Pneumatic Suspension of Automobiles on the Rigid and Off-Road Surfaces

To enhance the ride comfort and control performance of the semi-active pneumatic suspension system (PSS) of automobiles on the different road surfaces, a machine learning method (MLM) developed on the optimal control rules of the fuzzy logic control is proposed for the semi-active PSS. A nonlinear dynamic model of the automobile with eight degrees of freedom (DOF) is established to compute the results. The root mean square (RMS) accelerations of the vertical driver’s seat and the pitching angle and rolling angle of the automobile are selected to evaluate the ride comfort of the automobile on the rigid road and off-road terrain surfaces. The research results show that the off-road terrain surfaces remarkably affect the ride comfort of the automobile, especially at a high moving speed range of the automobile over 17.5 m/s. The performance of the MLM in improving the ride comfort of the automobile is better than the fuzzy logic control under various simulation conditions. Particularly, the RMS accelerations of the vertical driver’s seat and the pitching angle and rolling angle of the automobile with the MLM are smaller than that of the fuzzy logic control by 14.6%, 9.6%, and 5.3% on the rigid road surfaces and reduced by 14.9%, 8.7%, and 9.8% on the soil terrain of off-road terrain surfaces, respectively. However, the research results also indicate that the performance of the MLM significantly depends on the data map of the learning process. Thus, to further enhance the performance of the MLM, the data map for the machine learning process should be expanded under different operating conditions of the automobile.

Identification, tracking and warning of vortex induced vibration using k-means clustering method

Identifying, tracking and warning of the vortexed induced vibration (VIV) are essential for long-span suspension bridges because VIV might cause the driving safety problem. This study proposes an automatic method to identify and track the start and evolution of the VIV. Two feature indices, i.e. the energy concentration coefficient (ECC) and similarity ratio of amplitude (SRA), are utilised to form a feature index vector to identify and track the VIV. The Hilbert transform is utilised to process the vibration signal, based on which the SRA can be extracted. The k-means clustering method is introduced to automatically identify and track the VIV through automatically separating the feature index vectors into several clusters, and multi-level warming is established based on the acceleration root mean square (ARMS) value. The proposed method is validated using the in-field monitoring data of a suspension bridge suffering the VIV. The results indicate that the proposed automatic method can successfully distinguish the VIV from ambient vibration and can identify the forming of the VIV and track the evolution without any manual intervention, even for the VIV with low vibration amplitude. The multi-level warning can also be achieved based on the ARMS value when the VIV is identified.

Monitor wind characteristics and wind‐induced responses of a skyscraper during two typhoons

SummarySkyscrapers are wind‐sensitive structures due to their large slenderness ratio and good flexibility. Understanding the wind characteristics and wind‐induced response from the actual data provides first‐hand information for wind resistance design. This paper reports the wind properties and dynamic performance of a 632 m high‐rise building in Shanghai during the passage of typhoons Jongdari and Rumbbia. Field measurements obtained from the structural health monitoring system include acceleration and wind speed. The data analysis of turbulence intensity, turbulence integral length, and gust factor are compared and discussed. For the identification of dynamic characteristics, the stochastic subspace method and enhanced frequency domain decomposition method are employed to identify the modal parameters. Besides, the comfort assessment using peak value and root mean square of accelerations is compared with different standards. Studying the wind characteristics during the passage of typhoons and their impact on high‐rise buildings in a metropolis is expected to gain an insight into the dynamic mechanism of high‐rise buildings and collect a database for wind resistance design in typhoon‐prone regions.

An experimental study of tuned liquid column damper controlled multi-degree of freedom structure subject to harmonic and seismic excitations.

A tuned liquid column damper (TLCD) is a passive vibration control device that not only mitigates unwanted structural vibrations but also acts as a water storage facility in a building. These aspects of TLCD make its application specifically suited for building structures. Previously, many experimental works on TLCDs have been conducted considering a single degree of freedom (SDOF) structure. However, the performance of TLCDs to control the response of multi-degree of freedom (MDOF) structure has rarely been studied experimentally. Therefore, this study has investigated the performance of a tuned liquid column damper (TLCD) on a multi-degree of freedom (MDOF) structure using shake table testing. A four-storey steel frame structure equipped with TLCD at the top of the fourth storey has been studied. Experimental normalized frequency response curves for MDOF structure equipped with TLCD have been determined. For this purpose, a series of harmonic loadings including frequencies 0.65 Hz, 1.17 Hz, 1.30 Hz, 1.43 Hz and 1.95 Hz have been applied in addition to historic earthquake loading. Peak and root-mean-square (RMS) accelerations have been discussed in detail for all the applied loadings at each storey level of the structure. For comparison purposes, the percentage reductions in peak and RMS accelerations have been calculated and compared. Also, RMS displacements and inter-storey drifts have been presented for resonant and seismic excitations. Both in time and frequency domains, responses of controlled MDOF structure have been analyzed and compared with uncontrolled structure. Results confirmed that TLCD has improved the MDOF structure responses at harmonic loadings frequencies near resonance and historic earthquake excitations. Furthermore, the improvement in the responses of MDOF structure with TLCD is more prominent at harmonic loadings compared to historic earthquake loading.

Fatigue assessment of sedentary office workers using smartphones: a preliminary study

Objectives. Smartphone-based gait assessment provides a novel method to evaluate fatigue. This study aimed to examine self-reported fatigue and gait parameters recorded using a smartphone before and after an 8-h work day in bank workers, and identify the relationship between self-reported fatigue and gait parameters. Methods. One hundred bank workers (aged 20–45 years) were tested before and after an 8-h work day using a reaction time test, self-reported fatigue scale and gait test. Spearman correlation coefficient analysis and partial least squares regression were used to identify the relationship between self-reported fatigue and gait parameters. Results. Reaction time and self-reported fatigue increased significantly after work. Gait parameters (step frequency, minimum acceleration, acceleration root mean square, step regularity and step counts) decreased; step time and step time variability increased significantly (p < 0.05). We found a significant correlation between changes (Δ) for Δwork engagement and Δstep frequency (r = −0.20, p < 0.05), Δwork engagement and Δstep time (r = 0.21, p < 0.05), and Δwork tasks and Δstep symmetry (r = −0.20, p < 0.05). Conclusion. This study suggests that step frequency, step time and step symmetry measured using a smartphone have the potential to be used as predictors of work fatigue.

Vertical Negative Effect Suppression of In-Wheel Electric Vehicle Based on Hybrid Variable-Universe Fuzzy Control

To suppress a negative effect brought by introducing hub motor in vertical vibration of the body and that of a hub motor, a suppressing vertical negative effect algorithm of in-wheel electric vehicle is proposed based on hybrid variable universe fuzzy control (VUFC). Vertical accelerations of the body and that of the hub motor are taken as optimization objects, and to control the main suspension damper and in-wheel damper simultaneously, the semi-actively VUFC algorithm is adopted to improve vertical vibration characteristics effectively. The simulated results show that the peak and root mean square (RMS) of body vertical acceleration (VA) are optimized by 21.0% and 19.6%, respectively, after optimization compared to the original in-wheel electric model, the peak and RMS of hub motor VA are optimized by 30.1% and 32.5%, respectively, and the vertical negative effect is suppressed significantly.

The Effect of Fit Clearance between Outer Race and Housing on Vibration Characteristics of a Cylindrical Roller Bearing with Localized Defects

Due to bolt looseness or operating ambient temperature, fit clearance can often be found between the outer ring and housing. The vibration characteristics of a cylindrical roller bearing with localized defects are greatly affected by the fit clearance and the accuracy of bearing fault diagnosis may be reduced. Thus, a mathematical model for a cylindrical roller bearing was constructed and the interaction between the outer ring and housing was described. The classical localized defects were modeled, such as the inner ring defect, outer ring defect and roller defect. The relative experiments were conducted to check the constructed model. Then, it was found that the RMS (Root Mean Square) of housing acceleration decreased with increasing housing stiffness and viscous damping. When the fit clearance and friction coefficient increased, the RMS values increased. Except for housing stiffness and viscous damping, there were no uniform change rules of defect frequency amplitudes for other conditions. In the bearing with an outer ring defect or roller defect, the shock times of housing acceleration and the contact force between outer ring and housing were delayed, while fit clearance decreased. However, contrary variation trends were found for the inner ring defect. If the phase difference between defect location and rotor unbalanced force increased, the RMS and acceleration fluctuation amplitudes for the inner ring defect decreased. When the location angle of the outer ring defect increased, RMS and frequency amplitudes increased and RMSy/RMS decreased. The calculated results may provide the theoretical foundation for condition monitoring rotating machinery systems.

Parametrisation Scheme for Multidisciplinary Design Analysis and Optimisation of a Floating Offshore Wind Turbine Substructure – OC3 5MW Case Study

The development of novel energy technologies is considered imperative in the provision of solutions to meet an increasing global demand for clean energy. Floating Offshore Wind Turbine (FOWT) is one of the emerging technologies to exploit the vast wind resources available in deeper waters. To lower the levelized cost of energy (LCOE) or optimise the performance response associated with a FOWT system, a detailed understanding of the different disciplines (Aero-Hydro-Servo-Elastic) within the system and the relationship between the FOWT system and the dynamics of the marine environment is required. This requires an efficient Multidisciplinary Design, Analysis and Optimisation (MDAO) framework for FOWT systems to reduce the capital cost and increase dynamic performance. A key component of any MDAO framework is the shape parameterisation scheme, as it enables the modelling of a large array of platform designs with different geometric shapes using limited number of parameters. This work focuses on the B-Spline parameterisation modelling technique of OC3 spar-buoy and the use pattern search optimization algorithm to select the optimal design variants. The parametrisation technique is implemented in an analysis framework, where a B-spline library from Sesam GeniE is used to model each design representation, and a potential flow frequency domain analysis solver (HydroD/Wadam) is used for the hydrodynamic analysis. Validation of the selected designs within the design space is conducted with a benchmark NREL5MW spar-buoy hydrodynamic response results in literature with the hydrodynamic response of the frequency domain modelling approach using Sesam GeniE and HydroD/Wadam. This analysis process shows a high accuracy in response results between the OC3 spar-buoy in literature and the OC3 spar-buoy model design using B-Spline parametrization technique. Key performance metrics like the cost of materials and root mean square (RMS) of the nacelle acceleration also show improvement with the design variants compared to estimation from OC3 design in literature.

Beam width and arm position but not cognitive task affect walking balance in older adults

Detection of changes in dynamic balance could help identify older adults at fall risk. Walking on a narrow beam with its width, cognitive load, and arm position manipulated could be an alternative to current tests. Therefore, we examined additive and interactive effects of beam width, cognitive task (CT), and arm position on dynamic balance during beam walking in older adults. Twenty older adults (69 ± 4y) walked on 6, 8, and 10-cm wide beams (2-cm high, 4-m-long), with and without CT, with three arm positions (free, crossed, akimbo). We determined cognitive errors, distance walked, step speed, root mean square (RMS) of center of mass (COM) displacement and trunk acceleration in the frontal plane. Beam width decrease progressively reduced distance walked and increased trunk acceleration RMS. Step speed decreased on the narrowest beam and with CT. Arm crossing decreased distance walked and step speed. COM displacement RMS and cognitive errors were not affected by any manipulation. In conclusion, distance walked indicated that beam width and arm position, but less so CT, affected dynamic balance, implying that beam walking has the potential to become a test of fall risk. Stability measurements suggested effective trunk adjustments to control COM position and keep dynamic balance during the task.

Condition Monitoring of the Dampers in the Railway Vehicle Suspension Based on the Vibrations Response Analysis of the Bogie.

This paper investigates the possibility of developing a new method for fault detection of a damper in the primary suspension of the railway vehicle, based on the analysis of the vertical vibration’s response of the bogie. To this purpose, experimental data are used, along with results from numerical simulations regarding the Root Mean Square (RMS) accelerations measured/simulated in four reference bogie points—two points on the chassis, against the suspension, and two points located against the axle boxes. The experimental data are utilized to define the normal area of operating and the damper failure area in the bogie primary suspension, as well as a basis for validating the results of numerical simulations. The numerical simulations are developed on the basis of two original models of the vehicle–track system, rigid-flexible coupled type, which take into account the elasticity of the vehicle carbody and the elasticity of the wheel-rail contact: a reference model with 15 degrees of freedom, for simulating the bogie response to vertical vibrations for the normal operating of the primary suspension dampers, and an extended model with 20 degrees of freedom, for simulating the bogie vibration response to the failure damper of a primary suspension. The presented results show that there are clear premises on the possibilities of developing a fault detection method of any of the four dampers of the primary suspension corresponding to a vehicle bogie, based on the RMS accelerations measured only in two reference points of the bogie.