Multivariate Dam-Site Flood Frequency Analysis of the Three Gorges Reservoir Considering Future Reservoir Regulation and Precipitation

Under a changing environment, the current hydrological design values derived from historical flood data for the Three Gorges Reservoir (TGR) might be no longer applicable due to the newly-built reservoirs upstream from the TGR and the changes in climatic conditions. In this study, we perform a multivariate dam-site flood frequency analysis for the TGR considering future reservoir regulation and summer precipitation. The Xinanjiang model and Muskingum routing method are used to reconstruct the dam-site flood variables during the operation period of the TGR. Then the distributions of the dam-site flood peak and flood volumes with durations of 3, 7, 15, and 30 days are built by Pearson type III (PIII) distribution with time-varying parameters, which are expressed as functions of both reservoir index and summer precipitation anomaly (SPA). The multivariate joint distribution of the dam-site flood variables is constructed by a 5-D C-vine copula. Finally, by using the criteria of annual average reliability (AAR) associated with the exceedance probabilities of OR, AND and Kendall, we derive the multivariate dam-site design floods for the TGR from the predicted flood distributions during the future operation period of the reservoir. The results indicate that the mean values of all flood variables are positively linked to SPA and negatively linked to RI. In the future, the flood mean values are predicted to present a dramatic decrease due to the regulation of the reservoirs upstream from the TGR. As the result, the design dam-site floods in the future will be smaller than those derived from historical flood distributions. This finding indicates that the TGR would have smaller flood risk in the future.

Study on Crack Development of Concrete Lining with Insufficient Lining Thickness Based on CZM Method

The most common structural defect of a tunnel in the operation period is the cracking of concrete lining. The insufficient thickness of tunnel lining is one of the main reasons for its cracking. This study studied the cracking behavior of standard concrete specimens and the failure behavior of tunnel structures caused by insufficient lining thickness using Cohesive Zone Model (CZM). Firstly, zero-thickness cohesive elements were globally inserted between solid elements of the standard concrete specimen model, and the crack development process of different concrete grades was compared. On this basis, a three-dimensional numerical model of the tunnel in the operation period was established. The mechanism and characteristics of crack propagation under different lining thicknesses were discussed. In addition, the statistics of cracks were made to discuss the development rules of lining cracks quantitatively. The results show that the CZM can reasonably simulate the fracture behavior of concrete. With the increase in concrete strength grade, the number of cohesive damaged elements and crack area increases. The insufficient lining thickness changes the lining stress distribution characteristics, reduces the lining structure’s overall safety, and leads to the cracking of the diseased area more easily. When surrounding rock does not contact the insufficient lining thickness, its influence on the structure is more evident than when surrounding rock fills the entire lining thickness. The number of cohesive damaged elements and the size of the crack area increases significantly.

INVESTIGATION OF LIGHT INTENSITY OF LIGHT CURING UNITS AFTER DIFFERENT PERIODS OF USE

Quartz-tungsten halogen light curing units (LCUs) have been the main source of light for the polymerization of resin based composites (RBCs) for several decades. Since the beginning of the 20th century, however, their use has been reduced due to the invention and improvement of LED LCUs. Various factors can cause a decrease in the light intensity of LED LCUs, one of which is diode aging. The aim of the present paper is to study the change in light intensity of LCUs after different periods of intensive use. For this purpose, the light intensity of 94 regularly used LED LCUs aged between 1 and 10 years was measured with a digital radiometer. The devices were used in conventional mode with maximum light intensity. It was found that regardless of the type and model of LCU, there is a direct relationship between the time of use and light intensity - the longer the operation period of a device is and the more used it is, the lower its intensity is. The decrease in light intensity as devices age is different for different models, as well as for different devices of the same model. In the studied LCUs with a 10-year period of use, 77.5% have light intensity lower than the required minimum of 400 mW/cm2, which makes them unusable. It can be concluded that dentists should regularly monitor and measure the light intensity of their LCUs, especially as they age, to ensure the longevity of their restorative procedures.

Characterizing the Economic and Environmental Benefits of LNG Heavy-Duty Trucks: A Case Study in Shenzhen, China

Heavy-duty trucks (HDTs) in road freight are a primary contributor of PM2.5 and NOX emissions in many cities. Shenzhen, a megacity of China, has already made great efforts to promote the green transport transition, including via the Liquefied Natural Gas (LNG) HDTs program, which may be the largest alternative fuel vehicle promotion program in the world. In order to fully understand the actual efficiency of such program, the economic and environmental impacts of LNG HDTs were analyzed in this study. The results revealed that, while the capital cost of LNG HDTs is higher than that of diesel HDTs, the aggregated cost during the entire operation period of LNG HDTs is 10% to 17% lower than that of diesel HDTs. By replacing existing diesel HDTs mode (including China-I to China-V) with LNG HDTs (100%), environmental impact analysis showed that PM2.5 and NOX emissions could be reduced by 96.7% and 73.2% in the city level, respectively. Moreover, the environmental benefits of using purely LNG HDTs versus just China-V diesel HDTs were also compared, which indicated that LNG substitution is superior to China-V, with a reduction of 20.9% for PM2.5 and 35.4% for NOX, respectively. Overall, the effectiveness of the promotion of LNG HDTs is notable in Shenzhen, and these findings could provide references for other cities to promote LNG HDTs and beyond.

Estimation of Shutdown Schedule to Remove Fouling Layers of Heat Exchangers Using Risk-Based Inspection (RBI)

Oil and Gas plants consist of a set of heat exchangers, which are used in recovering the waste heat from product streams to preheat the oil. The heat transfer coefficient of exchangers declines considerably during the operation period due to fouling. Fouling in heat exchangers is a complex phenomenon due to the acceleration of many layers of chemical substances across tubes of heat exchangers resulting from chemical reactions and surface roughness. In this paper, the fouling process was determined as a critical failure in the heat exchanger. Failure is an accelerated fouling layer across the heat exchanger tubes, which can be the reason for the clogging of tubes. Hence, a risk assessment was conducted using the Risk-Based Inspection (RBI) approach to estimate the probability of fouling in heat exchangers. The results showed that the RBI approach can be used successfully to predict the suitable time to shut down the plant and conduct the fouling cleaning process.

System approach to research processes of technological adjustment of machine and tractor units

A substantive interpretation of the main categories of the system approach is formulated in relation to the semantics of the operation of mobile agricultural units from the standpoint of ensuring the technological reliability of the production of field mechanized work by improving the methods and means of measuring control of the state of machine and tractor units and evaluating the parameters of functional diagnostics under shift time conditions. A structural diagram of the systemic image of the production of field mechanized work is proposed, which makes it possible to clarify the hierarchical levels of movement of concepts in the field of managing the state of a complex technical system during the operation period, to highlight the object of research and establish its system elements and connections with the operating environment. The business logic of the implementation of the basic operations of the system of technological adjustment of machine-tractor units to ensure the quality of the technological operation when used for its intended purpose is presented. The theoretical significance of the work is associated with the development of a systematic understanding of the main objects of the processes of machine use in agriculture. The applied and practical significance of the work is confirmed by new technical solutions implemented in projects and organizational and technical documents of an industry scale. The results of the work can be useful both for researchers of the processes of machine-use in agriculture, and for practitioners-subjects of small and medium-sized agribusiness, as well as in organizing the transfer of knowledge of the agro-engineering direction to specialists in agricultural production.