Pollution Contribution Response in Governance and Potential Pollution Factors in Licun River

The development of the city results in deterioration of the water quality of the Licun River. As a result, years of governance have been conducted to improve its water quality. In order to clarify the response changes of water quality in the water governance, the governance process is divided into three stages (2000–2007, 2008–2016, 2017–2020) according to different priorities. Spearman’s rank correlation coefficient and the comprehensive pollution index are applied to analyze the variation of water quality response at various stages. In addition, the main pollution contributions with the governance changes were obtained. It is concluded that flood control and incomplete river pollution interception have a limited effect on water quality improvement, with NH3-N (ammonia nitrogen) and COD (chemical oxygen demand) being the main pollution contributions at the first stage. At the second stage, the point source control and sewage treatment facilities significantly improve water quality, and the main pollution contributions are NH3-N and TP (total phosphorus). At the third stage, sewage treatment facilities and supporting pipelines are improved, water sources are replenished, and the main pollution contribution is TN (total nitrogen). For further treatment, the factors affecting pollution are analyzed, including the contradiction of sewage system, point source pollution caused by pipe network problems, shortage of water resources, sludge pollution, and non-point source pollution

Load quantification and effect evaluation of urban non-point source pollution in the Licun River based on SWAT model

With the gradual control of point source pollution, the impact of urban nonpoint source pollution on river water quality is becoming more prominent. Regarding the current problem that nonpoint source pollution loads in urban basins are difficult to quantify and the impact on water quality is difficult to analyze, the Licun River basin in Qingdao was selected as the research object. Through the field survey and surface accumulation sampling analysis of the basin, the evaluation model of urban nonpoint source pollution was constructed by revising the land type data of the basin and the urban database of the SWAT model. The results showed that concentration of nitrate in precipitation was most sensitive to the simulation of nitrogen loading; organic P in baseflow was most sensitive to the simulation of phosphorus loading. The Nash–Sutcliffe efficiency coefficient (ENS) and the coefficients of determination (R2) of the SWAT model for runoff, total phosphorus (TP), and total nitrogen (TN) in the simulation validation period meet the model requirements,indicating a good model fit. In addition, the spatial and temporal distribution characteristics of urban nonpoint source pollution of TN and TP in 2021 were analyzed. In July, rainfall-runoff from the Licun River basin was the most polluted. HIGHLIGHTS High-accuracy simulation of urban nonpoint source pollution in small-scale basins.; Revising the land type data of the basin and modifying the model's town database.; Realize quantification and impact analysis of urban nonpoint source pollution load.

Machining quality and cutting force signal analysis in UD-CFRP milling under different fiber orientation

Increasing usage of carbon fiber-reinforced polymer (CFRP) components in the airplane industry has led to higher demand in the machining quality of CFRP. In order to meet the quality requirements of final assembly, the signal monitoring of various processing parameters can be used to ensure the machining setup in perfect order. In the present work, a set of experiments for UD-CFRP side milling has been carried out with different fiber cutting angle. The effects of fiber cutting angle on machining surface quality as well as the corresponding milling force signal features have been investigated based on time, frequency domain analysis, and wavelet analysis methods. The analysis results demonstrate that, for the against fiber cutting condition, the cutting force signal has a significant increase for high-frequency component energy percentage, and the higher frequency components are more sensitive. In addition, the fluctuation trend of power percentage for frequency band S3 (1500–2500 Hz) and surface roughness is quite close, which can be employed as a monitoring index for CFRP machining surface roughness