Ridesplitting, which is a form of pooled ridesourcing service, has great potential to alleviate the negative impacts of ridesourcing on the environment. However, most existing studies only explored its theoretical environmental benefits based on optimization models and simulations. By contrast, this study aims to reveal the real-world emission reduction of ridesplitting and its determinants based on the observed data of ridesourcing in Chengdu, China. Integrating the trip data with the COPERT model, this study calculates the CO2 emissions of shared rides (ridesplitting) and their substituted single rides (regular ridesourcing) to estimate the CO2 emission reduction of each ridesplitting trip. The results show that not all ridesplitting trips reduce emissions from ridesourcing in the real world. The CO2 emission reduction rate of ridesplitting varies from trip to trip, averaging at 43.15g/km. Then, interpretable machine learning models, gradient boosting machines, are applied to explore the relationship between the CO2 emission reduction rate of ridesplitting and its determinants. Based on the SHapley Additive exPlanations (SHAP) method, the overlap rate and detour rate of shared rides are identified to be the most important factors that determine the CO2 emission reduction rate of ridesplitting. Increasing the overlap rate, the number of shared rides, average speed, and ride distance ratio while decreasing the detour rate, actual trip distance, and ride distance gap can increase the CO2 emission reduction rate of ridesplitting. In addition, nonlinear effects and interactions of the determinants are examined through the partial dependence plots. To sum up, this study provides a scientific method for the government and ridesourcing companies to better assess and optimize the environmental benefits of ridesplitting.
Ultrasonic 3D imaging technology is helpful to visually display the shape and distribution of defects, but when the amount of ultrasonic data is large, the 3D imaging reconstruction of non-defect parts waste computer performance, resulting in slow imaging speed. According to the sparseness of the mapped volume data, a moving cube algorithm based on bounding box is proposed for 3D reconstruction. The above algorithm was verified by experiments. The experimental results show that the improved moving cube algorithm can improve the time of reducing the three-dimensional imaging of ultrasound and improve the drawing speed.
The present work is devoted to the study of underground hydrogen storage in salt caverns. Based on the hydromechanical characteristics of rock salts obtained from some laboratory experiments, we propose a novel model that includes short- and long-term mechanical behaviour. Specifically, the short-term part incorporates the elastoplastic and instantaneous damage mechanisms. Concerning the long-term behaviour, in addition to the primary and secondary creep phases, the tertiary phase takes into account a delayed damage mechanism which is different from the short-term damage. As application, we performed a hydromechanical modelling of two vertical salt caverns subjected to cyclic hydrogen injection and withdrawal (seasonal and daily scenarios). The modelled cavern geometries and depths were based on existing hydrogen gas caverns. Mechanical results indicate that the stability problem of a very deep cavern is more susceptible in comparison with a shallow cavern, as expected. However, the gas extensions around the caverns were similar due to the fact that the gas flow was dominated by diffusion transport. Since field data at very depths are limited, a sensibility analysis of material properties was carried out to provide insight into key mechanisms that may occur. Typically, a decrease in mechanical properties or an increase in initial permeability increases the instantaneous damage extent around deep caverns but did not lead to significant increase in the gas leakage extent. Under the assumptions made, these findings suggest that the use of salt caverns for green hydrogen storage, with aggressive operating conditions to regulate variations between renewable energy production and peak power demands, should not significantly affect the stability of salt cavern nor promote an increase in hydrogen loss.
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