A method based on potential theory for calculating air ca formation of an air cavity resistance reduction ship

This research is intended to provide academic reference and design guidance for further studies to determine the most effective means to reduce a ship’s resistance through an air-cavity. On the basis of potential theory and on the assumption of an ideal and irrotational fluid, this paper drives a method for calculating air cavity formation using slender ship theory then points out the parameters directly related to the formation of air cavities and their interrelationships. Simulations showed that the formation of an air cavity is affected by cavitation number, velocity, groove geometry and groove size. When the ship’s velocity and groove structure are given, the cavitation number must be within range to form a steady air cavity. The interface between air and water forms a wave shape and could be adjusted by an air injection system.

Laparoscopic approach for managing intussusception in children:Analysis of 65 cases

BACKGROUND Intussusception can be managed by pneumatic reduction,ultrasound-guided hydrostatic reduction,open or laparoscopic surgery,but laparoscopy in such cases remains controversial.AIM To explore the clinical characteristics,effectiveness,and complications of surgical reduction for intussusception using laparoscopy in children.METHODS This study was a retrospective case series of pediatric patients with intussusception who underwent surgical reduction by laparoscopy from May 2011 to April 2016 at Taizhou Hospital of Zhejiang Province.Clinical characteristics(operation time,intraoperative blood loss,conversion rate of laparotomy,reasons for conversion,postoperative hospital stay,and adverse events)were described.RESULTS The 65 patients included 45 boys and 20 girls.The average age was 2.3 years(27.5±24.5 mo).Of the 65 patients,61 underwent surgical reduction by laparoscopy after a failed enema reduction of intussusception,and four underwent the procedure directly.All patients were treated successfully and 57(87.7%)patients underwent successful laparoscopic surgery,two of which had a spontaneous reduction.Among the remaining cases,one was converted to open surgery via right upper quadrant incision,and seven required enlarged umbilical incisions.Intestinal resection was performed in 5 patients because of abnormal bowel lesions.There were no complications(intestinal perforations,wound infections,or intestinal adhesions)during the follow-up of 3 years to 8 years.Two patients experienced a recurrence of intussusception;one was resolved with pneumatic reduction,and the other underwent a second laparoscopic surgery.CONCLUSION Laparoscopic approach for pediatric intussusception is feasible and safe.Bowel resection if required can be performed by extending umbilical incision without the conventional laparotomy.

Numerical study of air layer drag reduction of an axisymmetric body in oscillatory motions

The air layer drag reduction(ALDR)of an axisymmetric body in oscillatory motions is investigated in this paper with open source toolbox OpenFOAM.The unsteady Reynolds-averaged Navier-Stokes(URANS)equations are used to determine the viscous flow and the volume of fluid(VOF)model is adopted to capture the interface of the air-water two-phase flow.The k-e turbulence model is adopted to simulate the turbulence.The dynamic mesh technique is applied to model the movement of the axisymmetric body.Firstly,the ALDR results are validated by the experimental data.Then,the effects of the movements of the body on the drag reduction during the ALDR state are investigated.Two representative kinds of movements are considered,namely,the pitch and the heave.The numerical results show that the drag reduction varies during the movements and the average drag reduction rates will be reduced.The variation of the drag reduction is related to the morphological change of the air layer.The heave motion is more likely to reduce the effects of the ALDR than the pitch motion.For both oscillatory motions,the large motion amplitude and the low motion period are not conductive to improving the effects of the ALDR.The effects of the oscillatory motion on the ALDR are more sensitive at high water speeds than at low water speeds.Besides,increasing the air flow ratio can be considered as one way to improve the effects of the ALDR.

Quantification of emission reduction potentials of primary air pollutants from residential solid fuel combustion by adopting cleaner fuels in China

Residential low efficient fuel burning is a major source of many air pollutants produced during incomplete combustions, and household air pollution has been identified as one of the top environmental risk factors. Here we compiled literature-reported emission factors of pollutants including carbon monoxide（CO）, total suspended particles（TSPs）, PM2.5, organic carbon（OC）,elemental carbon（EC） and polycyclic aromatic hydrocarbons（PAHs） for different household energy sources, and quantified the potential for emission reduction by clean fuel adoption. The burning of crop straws, firewood and coal chunks in residential stoves had high emissions per unit fuel mass but lower thermal efficiencies, resulting in high levels of pollution emissions per unit of useful energy, whereas pelletized biofuels and coal briquettes had lower pollutant emissions and higher thermal efficiencies. Briquetting coal may lead to 82%–88% CO, 74%–99%TSP, 73%–76% PM2.5, 64%–98% OC, 92%–99% EC and 80%–83% PAH reductions compared to raw chunk coal. Biomass pelletizing technology would achieve 88%–97% CO, 73%–87% TSP, 79%–88%PM2.5, 94%–96% OC, 91%–99% EC and 63%–96% PAH reduction compared to biomass burning. The adoption of gas fuels（i.e., liquid petroleum gas, natural gas） would achieve significant pollutant reduction, nearly 96% for targeted pollutants. The reduction is related not only to fuel change, but also to the usage of high efficiency stoves.

Numerical study on the wave pattern characteristic of air layer in cavity and the effects of multiple influence factors

Air-layer drag reduction (ALDR) technology for ship energy saving is getting more and more attention in recent years because of the outstanding drag reduction effect. In order to promote practical application, it is necessary to fully understand the two phase flow characteristics of the air layer. Recent experimental studies have shown that the surface of the air layer presents wave pattern, which has an important influence on its damage risk. However, it is difficult to measure the wave pattern quantificationally due to the interference of equipment. The main goal of the present paper is to investigate the wave pattern characteristic of air layer in cavity using numerical simulation method. On this basis, the effect of flow and geometric influence factors are discussed to understand the key control conditions. A computational fluid dynamics (CFD) numerical method based on Reynolds averaged Navier-Stokes (RANS) equations and volume of fluid (VOF) interface capturing method is established, and has been successfully applied in the simulation of air layer wave pattern. Both 2-D and 3-D simulations are carried out, aiming at analyzing air-water interface flow and vortex flow directly. Based on the simulation results, several important conclusions about the mechanism of air layer wave pattern can be obtained. Firstly, it is found to be an inherent characteristic that the wave height of the upstream air layer is higher than that of the downstream. The extremely high wave peak is easy to contact with the flat plate, leading to the breakup of air layer and a “central blank area” phenomenon. With the help of flow analysis, it is found that this characteristic is mainly caused by the strong counterclockwise vortex behind the bow wedge block. Secondly, the air layer stability is reduced with the increase of water flow velocity by affecting the wave height. There is a saturation point of air flow rate to reach maximum thickness of air layer. Thirdly, cavity configuration has obvious influence on air layer stability by influencing vortex flow field. The increase of cavity depth and width can aggravate the unsteady and nonlinear characteristics of air layer. Finally, comprehensive design criteria are concluded from the view of geometrical configuration and flow conditions. A cavity with the moderate depth and width can avoid the upstream damage of air layer. Longitudinal position of air nozzles should be set within the low pressure zone behind the wedge block for stable air layer formation.

City level CO_(2) and local air pollutants co-control performance evaluation: A case study of 113 key envir on mental protection cities in China

‘Co-control',or synergistically reducing CO_(2)and local air polluta nt emissions,is an important strategy for cities to achieve'low carb on'and'blue sky'simultaneously.However,there were few studies to evaluate and compare the level of co-control of CO_(2) and local air pollutants in cities year.The present study proposed qualitative and quantitative methods to evaluate the level of co-control of CO_(2)and three local air pollutant(SO_(2).NOX,and particulate matter PM)emissions in key environmental protection cities in China over two periods(2012-2015 and 2015-2018).Statistical analysis found that,though three local air pollutant emissions positively correlated with CO_(2) emission,no significantly positive correlation was found between local air pollutants emission reductions and CO_(2) emission reductions,indicating that co-control effects were poor in general.By using the co-control effect coordinate system,qualitative evaluation showed that less than half of the sample cities could achieve co-control of the total amount of CO_(2) and local air pollutants.By employing the indicator of emission reduction equivalence(EReq),quantitative evaluation showed that the co-control level of the sample cities improved in 2015-2018 compared with 2012-2015.Further regression analysis showed that,reducing coal consumption and economic development significantly enhanced the co-control performance of the observed cities.The present case study proved that the proposed methods for evaluation and comparison of the city co-control performance works well,and can be used in other countries and regions to promote global cities racing to carbon and local air pollutants co-control.

Air pollutant emissions induced by rural-to-urban migration during China's urbanization(2005-2015)

As the world's most populous country,China has witnessed rapid urbanization in recent decades,with population migration from rural to urban(RU)regions as the major driving force.Due to the large gap between rural and urban consumption and investment level,large-scale RU migration impacts air pollutant emissions and creates extra uncertainties for air quality improvement.Here,we integrated population migration assessment,an environmentally extended inputeoutput model and structural decomposition analysis to evaluate the NOx,SO2 and primary PM2.5 emissions induced by RU migration during China's urbanization from 2005 to 2015.The results show that RU migration increased air pollutant emissions,while the increases in NOx and SO2 emissions peaked in approximately 2010 at 2.4 Mt and 2.2 Mt,accounting for 9.2%and 8.7%of the national emissions,respectively.The primary PM2.5 emissions induced by RU migration also peaked in approximately 2012 at 0.3 Mt,accounting for 2.8%of the national emissions.The indirect emissions embodied in consumption and investment increased,while household direct emissions decreased.The widening gap between urban and rural investment and consumption exerted a major increasing effect on migration-induced emissions;in contrast,the falling emission intensity contributed the most to the decreasing effect benefitting from end-of-pipe control technology applications as well as improving energy efficiency.The peak of air pollutant emissions induced by RU migration indicates that although urbanization currently creates extra environmental pressure in China,it is possible to reconcile urbanization and air quality improvement in the future with updating urbanization and air pollution control policies.

A review of transition metal chalcogenide/graphene nanocomposites for energy storage and conversion

To meet the ever-increasing energy demands, advanced electrode materials are strongly requested for the exploration of advanced energy storage and conversion technologies, such as Li-ion batteries, Li-S batteries, Li-]Zn-air batteries, supercapacitors, dye-sensitized solar cells, and other electrocatalysis process （e.g., oxygen reductionlevolution reaction, hydrogen evolution reaction）. Transition metal chalcogenides （TMCs, Le., sulfides and selenides） are forcefully considered as an emerging candidate, owing to their unique physical and chemical properties. Moreover, the integration of TMCs with conductive graphene host has enabled the significant improvement of electrochemical performance of devices. In this review, the recent research progress on TMC]graphene composites for applications in energy storage and conversion devices is summarized. The preparation process of TMC]graphene nanocomposites is also included. In order to promote an in-depth understanding of performance improvement for TMC/graphene materials, the operating principle of various devices and technologies are briefly presented. Finally, the perspectives are given on the design and construction of advanced electrode materials.