Study on monitoring broken rails of heavy haul railway based on ultrasonic guided wave

Real-time monitoring of broken rails in heavy haul railways is crucial for ensuring the safe operation of railway lines. U78CrV steel is a common material used for heavy haul line rails in China. In this study, the semi-analytical finite element (SAFE) method is employed to calculate the dispersion curves and modal shapes of ultrasonic guided waves in U78CrV heavy steel rails. Guided wave modes that are suitable for detecting rail cracks across the entire cross-section are selected based on the total energy of each mode and the vibration energy in the rail head, web, and foot. The excitation method for the chosen mode is determined by analyzing the energy distribution of the mode shape on the rail surface. The ultrasonic guided wave (UGW) signal in the rail is analyzed using ANSYS three-dimensional finite element simulation. The group velocity of the primary mode in the guided wave signal is obtained through continuous wavelet transform to confirm the existence of the selected mode. It is validated that the selected mode can be excited by examining the similarity between the vibration shapes of a specific rail section and all modal vibration shapes obtained through SAFE. Through simulation and field verification, the guided wave mode selected and excited in this study demonstrates good sensitivity to cracks at the rail head, web, and foot, and it can propagate over distances exceeding 1 km in the rail. By detecting the reflected signal of the selected mode or the degree of attenuation of the transmitted wave, long-distance monitoring of broken rails in heavy-haul railway tracks can be achieved.

Extraction and selective promotion of zero-group velocity and cutoff frequency resonances in bi-dimensional waveguides using the electromechanical impedance method

This study showcases the electromechanical impedance (EMI) technique for extracting and promoting zero-group velocity (ZGV) and cutoff frequency resonances in a waveguide structure. We identify the mechanisms of multiple resonances in the EMI spectra via a wave propagation perspective. Both simulation and experiments reveal the fact that sharp resonances in the conductance spectra are associated with either ZGV or cutoff frequency points. Consequently, we design four test configurations to enhance local resonances by aligning induced motions with considered mode shapes. Reasonable agreement between simulation and experiment results is observed. We evaluate the performance of considered configurations in terms of mode enhancement, and configurations that can selectively promote certain mode families are summarized. This study also shines the light on the EMI technique for quantitative non-destructive evaluation (NDE) by potentially supporting the inverse characterization of mechanical properties of host structures.

Comparison of nitrogen losses from different manure treatment and application management systems in China

There is a worldwide focus on reducing the environmental impacts of livestock manure management. In China, there are different manure treatment and application modes, including complete treatment to remove nitrogen (N) for direct discharge into watercourses. But we lack a systematic quantitative comparison of the environmental losses that occur from different management modes. We used an example farm of 10,000 finisher pigs to quantitatively analyze the annual N losses from land application (LA) and treatment to remove N from manure to the level of discharge consent (DS) under 24 sub-modes. This is an important study to unravel the effect of choice of different manure management systems on subsequent N losses. The results showed that the N losses from the LA mode (52.6% of total N excretion) were significantly lower than that from the DS mode (75.9%). Compared with other sub-modes, N emission from whole slurry injection was the smallest, accounting for 43.2% of total N excretion. NH₃-N was the main source of N loss which accounted for 72.9% and 50.2% in LA and DS mode, respectively. The lowest N emission of LA mode with mitigation options, including slurry store covers, composting with bio-filter deodorization and injection application, was 28.8% of total N excretion, which is only 42.2% of N emission from DS mode with mitigation options. Insights from this systematic study of different manure management modes in China show the imperative of control ammonia emission for China, and provide guidance to the sustainable manure management in rapidly developing countries.

Impact of coronavirus pandemic on sharing mode of manufacturer

Service platform has developed rapidly in car-sharing, consumers often buy or own cars but not fully utilize and share them. Since the coronavirus pandemic has affected sales and people's attitudes towards car-sharing, which brought both opportunities and challenges to the platform and changed the operating mode of manufacturers, some traditional manufacturers have motivated to cooperate with third-party platform. In this paper, we develop an analytical framework to examine the pricing decisions and optimal mode selection of manufacturer under the COVID-19 epidemic. Considering the supply chain consists of a manufacturer and a third-party sharing platform. We analyze three scenarios including no sharing, customers-to-customers, and mixed sharing, then employ a game theoretic approach to get equilibrium solutions and analytically derive the optimal mode choice. Our analysis shows that when the operation and maintenance cost is low, manufacturer will join the third-party platform, and the sharing price increase in operation and maintenance cost, while the selling price decrease in operation and maintenance cost. When the value perception factor less than the threshold, the manufacturer will retain sales channel, and the selling demand decrease in value perception factor in the growing market, the sharing demand has the same trend, vice versa. Furthermore, we find that if the operation and maintenance cost is low and value perception factor is high, mixed sharing is the best choice for the manufacturer, while the manufacturer will choose no car-sharing when the value perception factor is relatively low.

An ultrasonic guided wave excitation method at constant phase velocity using ultrasonic phased array probes

High-order ultrasonic guided wave modes have recently been attracting interest in a variety of nondestructive testing applications, ranging from thickness gauging to bond characterization. Accurate control of the transmitted ultrasonic guided wave mode is paramount when working at frequencies above the cutoff of the first high-order mode. The high number of modes available makes this range of frequency-thickness products difficult to exploit in practice. Many papers and textbooks have showed that multielement probes, such as comb transducers, are able to target a specific wavelength which depends on the elementary pitch. This method can be enhanced by adding an elementary delay law. However, this method of excitation has major drawbacks as the areas of excitation in a dispersion curves depends on the frequency and the technique is not unidirectional. This paper demonstrate that a conventional phased array transducer for which the elementary pitch is small relative to the targeted wavelength is able to excite high order guided wave modes at a constant phase velocity (independently of the frequency). The aim is to excite different regions of the dispersion curves by controlling the input signal bandwidth and the angle of the generated beam. The paper describes the theoretical background and details the differences between the various methods of excitation of ultrasonic guided waves, especially with the comb transducer method. Finite element simulations are presented to verify the analytical predictions and quantify the unidirectional and diffraction properties of the transmitted beam. Experiments conducted on an aluminum plate show striking agreement with finite element simulations, including the possibility of exciting a single mode in a narrow region at high frequency-thickness products. Experiments conducted on a CFRP plate demonstrates that the method can be adapted to other materials.

Mode perturbation method for optimal guided wave mode and frequency selection

With a thorough understanding of guided wave mechanics, researchers can predict which guided wave modes will have a high probability of success in a particular nondestructive evaluation application. However, work continues to find optimal mode and frequency selection for a given application. This "optimal" mode could give the highest sensitivity to defects or the greatest penetration power, increasing inspection efficiency. Since material properties used for modeling work may be estimates, in many cases guided wave mode and frequency selection can be adjusted for increased inspection efficiency in the field. In this paper, a novel mode and frequency perturbation method is described and used to identify optimal mode points based on quantifiable wave characteristics. The technique uses an ultrasonic phased array comb transducer to sweep in phase velocity and frequency space. It is demonstrated using guided interface waves for bond evaluation. After searching nearby mode points, an optimal mode and frequency can be selected which has the highest sensitivity to a defect, or gives the greatest penetration power. The optimal mode choice for a given application depends on the requirements of the inspection.