Analytical solutions for contaminant transport are widely used for both theoretical and practical purposes.However,many existing solutions are obtained subject to an initial condition of zero concentration,which is of...Analytical solutions for contaminant transport are widely used for both theoretical and practical purposes.However,many existing solutions are obtained subject to an initial condition of zero concentration,which is often unrealistic in many practical cases.This article proposed a stepwise superposition approximation approach to solve the non-zero initial concentration problem for first-type and third-type boundary conditions by using the existing zero initial concentration solution.Theoretical examples showed that the approach was highly efficient if a proper superposition scheme with relative concentration increments was constructed.The key parameter that controlled the convergence speed was the time increment(△t) multiplied by the rate constant(λ).The approach served also as an alternative way to make a convenient concentration calculation even if the non-zero initial concentration solution of a problem was known.展开更多
The fatigue performance of optimized welded detail has been investigated by fatigue experiments of three welded specimens under different loadings.In addition,local finite element models of this welded detail were est...The fatigue performance of optimized welded detail has been investigated by fatigue experiments of three welded specimens under different loadings.In addition,local finite element models of this welded detail were established using finite element software ANSYS.The influences of different factors such as plate thickness,plate gap and initial geometric imperfections on the stress concentration coefficient(SCC) were discussed.The experimental results indicate that the fatigue life of three specimens for this welded detail is 736,000,1,044,200 and 1,920,300 times,respectively.The web thickness,the filler plate thickness and the initial geometric imperfection have relatively less effect on the SCCs of this welded detail.However,cope-hole radius is influential on the SCCs of the web and the weld.The SCC of weld is significantly affected by the weld size and plate gap,but the SCCs of other parts of the welded detail are hardly affected by the plate gap.展开更多
Low-concentration methane(LCM) has been one of the biggest difficulties in using coal mine methane.And previous studies found that premixed combustion in porous media is an effective method of low calorific gas utiliz...Low-concentration methane(LCM) has been one of the biggest difficulties in using coal mine methane.And previous studies found that premixed combustion in porous media is an effective method of low calorific gas utilization. This paper studied the combustion of LCM in a divergent porous medium burner(DPMB) by using computational fluid dynamics(CFD), and investigated the effect of gas initial temperature on combustion characteristic, the distribution of temperature and pollutant at different equivalence ratios in detail. Besides, the comparison of divergent and cylindrical burners was also performed in this paper. The results show that: the peak temperature in DPMB increases as the increasing of equivalence ratio, which is also suitable for the outlet NO discharge; the linear correlation is also discovered between peak temperature and equivalence ratios; NO emission at the initial temperature of 525 K is 5.64 times,larger than NO emission at the initial temperature of 300 K. Thus, it is preferable to balance the effect of thermal efficiency and environment simultaneously when determining the optimal initial temperature range. The working parameter limits of divergent burner are wider than that of cylindrical one which contributes to reducing the influence of LCM concentration and volume fluctuation on combustion.展开更多
To further understand the prediction skill for the interannual variability of the sea ice concentration(SIC)in specific regions of the Arctic,this paper evaluates the NCEP Climate Forecast System version 2(CFSv2),in p...To further understand the prediction skill for the interannual variability of the sea ice concentration(SIC)in specific regions of the Arctic,this paper evaluates the NCEP Climate Forecast System version 2(CFSv2),in predicting the autumn SIC and its interannual variability over the Barents–East Siberian Seas(BES).It is found that CFSv2 presents much better prediction skill for the September SIC over BES than the Arctic as a whole at 1–6-month leads,and high prediction skill for the interannual variability of the SIC over BES is displayed at 1–2-month leads after removing the linear trend.CFSv2 can reasonably reproduce the relationship between the SIC over BES in September and such factors as the surface air temperature(SAT),200-hPa geopotential height,sea surface temperature(SST),and North Atlantic Oscillation.In addition,it is found that the prescribed SIC initial condition in August as an input to CFSv2 is also essential.Therefore,the above atmospheric and oceanic factors,as well as an accurate initial condition of SIC,all contribute to a high prediction skill for SIC over BES in September.Based on a statistical prediction method,the contributions from individual predictability sources are further identified.The high prediction skill of CFSv2 for the interannual variability of SIC over BES is largely attributable to its accurate predictions of the SAT and SST,as well as a better initial condition of SIC.展开更多
Four sequence batch reactors(SBRs) fed by fermented sugar cane wastewater were continuously operated under the aerobic dynamic feeding(ADF) mode with different configurations of sludge retention time(SRT), carbo...Four sequence batch reactors(SBRs) fed by fermented sugar cane wastewater were continuously operated under the aerobic dynamic feeding(ADF) mode with different configurations of sludge retention time(SRT), carbon and initial biomass concentrations to enrich polyhydroxyalkanoate(PHA) accumulating mixed microbial cultures(MMCs) from municipal activated sludge.The stability of SBRs was investigated besides the enrichment performance. The microbial community structures of the enriched MMCs were analyzed using terminal restriction fragment length polymorphism(T-RFLP). The optimum operating conditions for the enrichment process were: SRT of 5 days, carbon concentration of 2.52 g COD/L and initial biomass concentration of3.65 g/L. The best enrichment performance in terms of both operating stability and PHA storage ability of enriched cultures(with the maximum PHA content and PHA storage yield(YPHA/S) of61.26% and 0.68 mg COD/mg COD, respectively) was achieved under this condition. Effects of the SRT, carbon concentration and initial biomass concentration on the PHA accumulating MMCs selection process were discussed respectively. A new model including the segmentation of the enrichment process and the effects of SRT on each phase was proposed.展开更多
Lab-scale experiments were conducted to investigate the effect of initial concentration,temperature and pH on the removal of bezafibrate(BF)by activated sludge under aerobic condition.The results showed that adsorptio...Lab-scale experiments were conducted to investigate the effect of initial concentration,temperature and pH on the removal of bezafibrate(BF)by activated sludge under aerobic condition.The results showed that adsorption of BF onto activated sludge was negligible,and biodegradation was the main removal mechanism of BF.The removal of BF in the aqueous phase by the activated sludge can be described by a pseudo-first-order reaction.The reaction rate constants had a negative relationship with the initial concentration of BF,and dramatically reduced from 0.050 to 0.007 h^-1,when the temperature dropped from 20℃to 10℃.Variation of pH between 5.0 and 9.0 did not have significant influence on the removal of BF,indicating a high adaptation of microorganism in the activated sludge responsible for BF degradation to a wide pH range.The findings of this study are helpful to improve the removal of pharmaceuticals during the wastewater treatment plants by selecting the appropriate process variables,and eventually eliminate their release to the environment.展开更多
The effect of initial concentrations on solidification of ammonium chloride water solution is numerically investigated in detail.The solidifying process.with the cold wall temperature lower than the eutectic temperatu...The effect of initial concentrations on solidification of ammonium chloride water solution is numerically investigated in detail.The solidifying process.with the cold wall temperature lower than the eutectic temperature,is assumed to be one-dimensional,and controlled by heat conduction only.The simulation reveals that:(1) The solid-mush interface grows in a linear manner,while the growth rate of the mush-liquid interface decreases in a parabolic manner,with increasing initial concentrations.(2) The temperature field in the whole region has parabolic characteristics,but is shows a linear feature in the solid zone and mushy zone.(3) The concentration always has linear characteristics in the much.(4)The solid fraction distribution is strongly affected by the initial concertration.The solidification process shows quite different features,especially at small and high initial concentrations.展开更多
基金supported by the National Natural Science Foundation of China (No. 40872151)the Key Project in the National Science and Technology Pillar Program of China (No. 2006BAC06B05)
文摘Analytical solutions for contaminant transport are widely used for both theoretical and practical purposes.However,many existing solutions are obtained subject to an initial condition of zero concentration,which is often unrealistic in many practical cases.This article proposed a stepwise superposition approximation approach to solve the non-zero initial concentration problem for first-type and third-type boundary conditions by using the existing zero initial concentration solution.Theoretical examples showed that the approach was highly efficient if a proper superposition scheme with relative concentration increments was constructed.The key parameter that controlled the convergence speed was the time increment(△t) multiplied by the rate constant(λ).The approach served also as an alternative way to make a convenient concentration calculation even if the non-zero initial concentration solution of a problem was known.
基金supported by the National Natural Science Foundation of China(51308467 and 51378431)China railway corporation research and development of science and technology key project(2013G001-A-2)
文摘The fatigue performance of optimized welded detail has been investigated by fatigue experiments of three welded specimens under different loadings.In addition,local finite element models of this welded detail were established using finite element software ANSYS.The influences of different factors such as plate thickness,plate gap and initial geometric imperfections on the stress concentration coefficient(SCC) were discussed.The experimental results indicate that the fatigue life of three specimens for this welded detail is 736,000,1,044,200 and 1,920,300 times,respectively.The web thickness,the filler plate thickness and the initial geometric imperfection have relatively less effect on the SCCs of this welded detail.However,cope-hole radius is influential on the SCCs of the web and the weld.The SCC of weld is significantly affected by the weld size and plate gap,but the SCCs of other parts of the welded detail are hardly affected by the plate gap.
基金the supports by the National Basic Research Program of China (No. 2011CB201205)the National Natural Science Foundation of China (No. 51204169)+1 种基金the Research Fund for the Doctoral Program of Higher Education of China (No. 20110095120017)the Fund of China Postdoctoral Science Foundation of China (No. 20110491482)
文摘Low-concentration methane(LCM) has been one of the biggest difficulties in using coal mine methane.And previous studies found that premixed combustion in porous media is an effective method of low calorific gas utilization. This paper studied the combustion of LCM in a divergent porous medium burner(DPMB) by using computational fluid dynamics(CFD), and investigated the effect of gas initial temperature on combustion characteristic, the distribution of temperature and pollutant at different equivalence ratios in detail. Besides, the comparison of divergent and cylindrical burners was also performed in this paper. The results show that: the peak temperature in DPMB increases as the increasing of equivalence ratio, which is also suitable for the outlet NO discharge; the linear correlation is also discovered between peak temperature and equivalence ratios; NO emission at the initial temperature of 525 K is 5.64 times,larger than NO emission at the initial temperature of 300 K. Thus, it is preferable to balance the effect of thermal efficiency and environment simultaneously when determining the optimal initial temperature range. The working parameter limits of divergent burner are wider than that of cylindrical one which contributes to reducing the influence of LCM concentration and volume fluctuation on combustion.
基金Supported by the National Key Research and Development Program of China(2022YFE0106800)National Natural Science Foundation of China(42230603)Innovation Group Project of the Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(311021001)。
文摘To further understand the prediction skill for the interannual variability of the sea ice concentration(SIC)in specific regions of the Arctic,this paper evaluates the NCEP Climate Forecast System version 2(CFSv2),in predicting the autumn SIC and its interannual variability over the Barents–East Siberian Seas(BES).It is found that CFSv2 presents much better prediction skill for the September SIC over BES than the Arctic as a whole at 1–6-month leads,and high prediction skill for the interannual variability of the SIC over BES is displayed at 1–2-month leads after removing the linear trend.CFSv2 can reasonably reproduce the relationship between the SIC over BES in September and such factors as the surface air temperature(SAT),200-hPa geopotential height,sea surface temperature(SST),and North Atlantic Oscillation.In addition,it is found that the prescribed SIC initial condition in August as an input to CFSv2 is also essential.Therefore,the above atmospheric and oceanic factors,as well as an accurate initial condition of SIC,all contribute to a high prediction skill for SIC over BES in September.Based on a statistical prediction method,the contributions from individual predictability sources are further identified.The high prediction skill of CFSv2 for the interannual variability of SIC over BES is largely attributable to its accurate predictions of the SAT and SST,as well as a better initial condition of SIC.
基金supported by the National Natural Science Foundation of China(No.51378142)the Program for New Century Excellent Talents in University(No.NCET-12-0156)+1 种基金the Open Project of the State Key Laboratory of Urban Water ResourceEnvironment(Harbin institute of Technology)(No.2015DX10)
文摘Four sequence batch reactors(SBRs) fed by fermented sugar cane wastewater were continuously operated under the aerobic dynamic feeding(ADF) mode with different configurations of sludge retention time(SRT), carbon and initial biomass concentrations to enrich polyhydroxyalkanoate(PHA) accumulating mixed microbial cultures(MMCs) from municipal activated sludge.The stability of SBRs was investigated besides the enrichment performance. The microbial community structures of the enriched MMCs were analyzed using terminal restriction fragment length polymorphism(T-RFLP). The optimum operating conditions for the enrichment process were: SRT of 5 days, carbon concentration of 2.52 g COD/L and initial biomass concentration of3.65 g/L. The best enrichment performance in terms of both operating stability and PHA storage ability of enriched cultures(with the maximum PHA content and PHA storage yield(YPHA/S) of61.26% and 0.68 mg COD/mg COD, respectively) was achieved under this condition. Effects of the SRT, carbon concentration and initial biomass concentration on the PHA accumulating MMCs selection process were discussed respectively. A new model including the segmentation of the enrichment process and the effects of SRT on each phase was proposed.
基金This research was partly supported by the National Natural Science Foundation of China(21577033,51208199,51408425)the Fundamental Research Funds for the Central Universities(22A201514057)+1 种基金Beijing Key Laboratory for Emerging Organic Contaminants Control,the Foundation of The State Key Laboratory of Pollution Control and Resource Reuse,China(PCRRY 11017)the Specialized Research Fund for the Doctoral Program of Higher Education of China(20130072120033).
文摘Lab-scale experiments were conducted to investigate the effect of initial concentration,temperature and pH on the removal of bezafibrate(BF)by activated sludge under aerobic condition.The results showed that adsorption of BF onto activated sludge was negligible,and biodegradation was the main removal mechanism of BF.The removal of BF in the aqueous phase by the activated sludge can be described by a pseudo-first-order reaction.The reaction rate constants had a negative relationship with the initial concentration of BF,and dramatically reduced from 0.050 to 0.007 h^-1,when the temperature dropped from 20℃to 10℃.Variation of pH between 5.0 and 9.0 did not have significant influence on the removal of BF,indicating a high adaptation of microorganism in the activated sludge responsible for BF degradation to a wide pH range.The findings of this study are helpful to improve the removal of pharmaceuticals during the wastewater treatment plants by selecting the appropriate process variables,and eventually eliminate their release to the environment.
文摘The effect of initial concentrations on solidification of ammonium chloride water solution is numerically investigated in detail.The solidifying process.with the cold wall temperature lower than the eutectic temperature,is assumed to be one-dimensional,and controlled by heat conduction only.The simulation reveals that:(1) The solid-mush interface grows in a linear manner,while the growth rate of the mush-liquid interface decreases in a parabolic manner,with increasing initial concentrations.(2) The temperature field in the whole region has parabolic characteristics,but is shows a linear feature in the solid zone and mushy zone.(3) The concentration always has linear characteristics in the much.(4)The solid fraction distribution is strongly affected by the initial concertration.The solidification process shows quite different features,especially at small and high initial concentrations.