Damage Detection Applied to a Full-Scale Steel Bridge Using Temporal MomentsRead the full article
Shock and Vibration publishes papers on all aspects of shock and vibration, especially in relation to civil, mechanical and aerospace engineering applications, as well as transport, materials and geoscience.
Chief Editor, Dr Thai, is based at the University of Melbourne and his current research focuses on high strength materials for sustainable construction of buildings, bridges and other infrastructure.
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High Frequency Modal Testing of the Multiblade Packets Using a Noncontact Measurement and Excitation System
High cycle failure of blades and vanes caused by the vibration is one of the major causes reducing the lifetime of turbomachines. For multiblade packets, the failure may occur at vibrations with high frequencies that can reach up to tens of kHz. The experimental modal testing of blades is crucial for the validation of numerical models and for the optimization of turbomachine design. In this paper, the test rig and procedure for measurements of dynamic characteristics of lightweight multiblade packets in wide and high frequency ranges are developed. The measurements are based on a noncontact excitation and noncontact measurement method, which allows the determination of the modal characteristics of the packets with high accuracy in wide frequency ranges. The responses of the multiblade packets are measured using a Scanning Laser Doppler Vibrometry (SLDV), while vibrations are excited by the acoustic excitation technique. Modal tests of the blade packet comprising 18 vane blades connected by shrouds are performed. The measurements are performed within the high frequency range of 0–30 kHz, and the natural frequencies and mode shapes are obtained for first 97 modes. To capture the complex high frequency blade mode shapes, each blade in the packet is scanned over 25 reference points uniformly distributed over the blade concave surface. In order to obtain the high frequency resolution, the frequency range used for the measurements is split into several frequency intervals accordingly to the number of spectral lines available in the used data acquisition system, and for each such interval, the test is performed separately. The finite model of the packet is created, and the numerical modal analysis is performed to compare the calculated natural frequencies and mode shapes with the experimental measurements. The comparison shows the satisfactory with those from finite element analysis. It illustrates the measurement method described in this work is effective and reliable.
Experimental and Analytical Study on the Vibration Performance of U-Shaped Steel-Concrete Composite Hollow Waffle Slab
The large-span floor system being lightweight with low frequency and low damping is prone to suffer severe vibration under human excitations. In this research, the vibration performance of an innovative large-span U-shaped steel-concrete composite hollow waffle (CHW) slab was studied based on field testing and theoretical analysis. First, the modal properties of CHW slab including mode shapes, frequencies, and damping ratio were captured by on-site tests and validated by the finite element method, indicating the CHW slab is a low-frequency floor system with a low damping ratio. Second, the vibration responses of CHW slab under heel-drop and jumping excitations were studied considering the impacts of spatial position, tester number, and activity types. Third, the CHW slab shows excellent vibration serviceability proved by the frequency, accelerations, and human perceptions threshold with the current codes. Meanwhile, the paper gives appropriate threshold values for the CHW slab under impulsive excitation. Finally, the natural frequency formula for the CHW slab derived by the Rayleigh–Ritz energy method agrees well with the measurements.
Mine Pressure Behavior Characteristics and Control Methods of a Reused Entry that Was Formed by Roof Cutting: A Case Study
Noncoal pillar mining with automatic formation of a roadway is a new coal mining method that is tailored to improve the coal resource recovery rate and reduce the investment in roadway tunneling. Using this proposed method, a reuse entry is formed by roof cutting instead of tunneling. In this paper, the S1201-II working face of the Ningtiaota Coal Mine was used as a case study. The stress distribution of surrounding rock and the roof deformation characteristics of the reused entry during the mining process of the second working face were studied through FLAC3D numerical simulations combined with field measurements. The results indicate that the zone close to the reused entry led to higher stress in advance. If this stress is superimposed with the lateral pressure of the adjacent mined working face, it will be more difficult to maintain the reused entry. In the engineering case study described here, the reused entry created a stress increase zone and a severe deformation zone in the range of 0–80 m in front of the working face, and its range was approximately 37.5% larger than an ordinary entry. The stress peak in the stress increase zone increased by approximately 34.7% over that of an ordinary entry. The maximum amount of deformation within the severe deformation zone increased by 94.4% over that of an ordinary entry. To properly control the surrounding rock stress and deformation of the reused entry, a dynamic pressure bearing support in front of the working face with adaptability to the large roof deformation and high support strength is proposed here. Field application results showed that the final roof deformation with the dynamic pressure bearing support can be satisfactorily controlled within 110∼130 mm. These findings can provide a reference for researchers and field engineering technicians when engaging in the support work of reused entry.
Analysis of Vibration and Acoustic Characteristics of a Simply Supported Double-Panel Partition under Thermal Environment
Numerical studies on the vibration and acoustic characteristics of a simply supported double-panel partition under the thermal environment are presented by the modal superposition approach and temperature field theory. Many factors are considered in this theoretical research, including acoustic refraction, dynamic response of the panel under thermal and acoustic load, vibroacoustic coupling characteristic analysis, and the variation of material properties. To access the accuracy and feasibility of the theoretical model, a finite element method is proposed to calculate the natural frequencies and mode shapes. The results show that the vibration and acoustic responses change obviously with the change of thermal stress and material properties. The rise of the graded thermal environment and thermal load decreases the natural frequencies and moves response peaks to the low-frequency range. The first valley of sound transmission loss is well consistent with the mode frequency. Finally, the relation between the average sound insulation and the thickness ratio is analyzed.
Sliding Mode Control of Vehicle Equipped with Brake-by-Wire System considering Braking Comfort
For passengers, the most common feeling during running on the bumpy road is continuous vertical discomfort, and when the vehicle is braking, especially the emergency braking, the instantaneous inertia of the vehicle can also cause a strong discomfort of the passengers, so studying the comfort of the vehicle during the braking process is of great significance for improving the performance of the vehicle. This paper presented a complete control scheme for vehicles equipped with the brake-by-wire (BBW) system aiming at ensuring braking comfort. A novel braking intention classification method was proposed based on vehicle braking comfort, which divided braking intention into mild brake, medium comfort brake, and emergency brake. Correspondingly, in order to improve the control accuracy of the vehicle brake system and to best meet the driver’s brake needs, a braking intention recognizer relying on fuzzy logic was established, which used the road condition and the brake pedal voltage and its change rate as input, output real-time driver's braking intention, and braking intensity. An optimal brake force distribution strategy for the vehicle equipped with the BBW system based on slip rate was proposed to determine the relationship between braking intensity and target slip ratio. Combined with the vehicle dynamics model, improved sliding mode controller, and brake force observer, the joint simulation was conducted in Simulink and CarSim. The cosimulation results show that the proposed braking intention classification method, braking intention recognizer, brake force distribution strategy, and sliding mode control can well ensure the braking comfort of the vehicle equipped with the BBW system under the premise of ensuring brake safety.
Dispersion Compensation Method for Lamb Waves Based on Measured Wavenumber
In this study, a delta wavenumber dispersion compensation (∆K-DC) method was developed and applied, not only with the theoretical wavenumber but also with the measured wavenumber. Dispersion compensation can be achieved by the following steps: relative wavenumber measurement, traveling distance estimation, phase compensation, and wave correction. The feasibility of ∆K-DC with the theoretical wavenumber and measured wavenumber was validated with a high-dispersive A0 mode in a 2 mm steel plate experiment. The results showed that phase spectrum measurement was an effective method to construct the wavenumber curve, the propagation distances estimated by SAP2 were very accurate, and the dispersive signals can be compensated perfectly by applying the phase compensation and wave correction methods for each wavepacket. The present results highlight the application of ∆K-DC on dispersion compensation without any material parameters of a waveguide.