The hot corrosion behaviors of Ni–16Cr–xAl（x=4.5%, 6.8%, 9.0%, mass fraction） based alloys in Na2SO4–25% NaCl molten salts at 600 °C were investigated. The effects of pre-oxidation and Al content on the resi...The hot corrosion behaviors of Ni–16Cr–xAl（x=4.5%, 6.8%, 9.0%, mass fraction） based alloys in Na2SO4–25% NaCl molten salts at 600 °C were investigated. The effects of pre-oxidation and Al content on the resistance to hot corrosion were examined. The hot corrosion resistance of Ni–16Cr–xAl based alloy with Al addition from 4.5% to 9.0% increases with increasing Al content. The alloy with Al content of 9.0% shows the highest hot corrosion resistance among the examined alloys because more β–NiAl phases are obtained to sustain the Al2O3 scale repaired during hot corrosion. Pre-oxidized specimens have a superior hot corrosion resistance compared with the as-cast specimens, due to a protective oxide scale formed after pre-treatment.展开更多
Nonlinear time series prediction is studied by using an improved least squares support vector machine （LSSVM） regression based on chaotic mutation evolutionary programming （CMEP） approach for parameter optimizatio...Nonlinear time series prediction is studied by using an improved least squares support vector machine （LSSVM） regression based on chaotic mutation evolutionary programming （CMEP） approach for parameter optimization. We analyze how the prediction error varies with different parameters （σ, γ） in LS-SVM. In order to select appropriate parameters for the prediction model, we employ CMEP algorithm. Finally, Nasdaq stock data are predicted by using this LS-SVM regression based on CMEP, and satisfactory results are obtained.展开更多
By adopting the chaotic searching to improve the global searching performance of the particle swarm optimization (PSO), and using the improved PSO to optimize the key parameters of the support vector machine (SVM) for...By adopting the chaotic searching to improve the global searching performance of the particle swarm optimization (PSO), and using the improved PSO to optimize the key parameters of the support vector machine (SVM) forecasting model, an improved SVM model named CPSO-SVM model was proposed. The new model was applied to predicting the short term load, and the improved effect of the new model was proved. The simulation results of the South China Power Market’s actual data show that the new method can effectively improve the forecast accuracy by 2.23% and 3.87%, respectively, compared with the PSO-SVM and SVM methods. Compared with that of the PSO-SVM and SVM methods, the time cost of the new model is only increased by 3.15 and 4.61 s, respectively, which indicates that the CPSO-SVM model gains significant improved effects.展开更多
This paper examines the effect of equalizing ignition delay in a compression ignition engine.Two sets of tests were conducted,i.e.a set of constant injection timing tests with start of fuel injection at 10°crank ...This paper examines the effect of equalizing ignition delay in a compression ignition engine.Two sets of tests were conducted,i.e.a set of constant injection timing tests with start of fuel injection at 10°crank angle degree(CAD)before top dead center(BTDC)and a set of constant ignition timing tests while also keeping the 10℃AD BTDC injection and adding ignition improver(2-ethylhexylnitrate-,2-EHN)to the fuel mixtures.Soot particles were characterized using DMS-500 instrument in terms of mass,size,and number.The experimental results showed that adding 2-EHN to the model fuel blends reduced the soot surface area,soot mass concentration and soot mean size.Replacing 20 vol%of a C 7-heptane with 20 vol%methyl-decanoate(an oxygenated C 11 molecule)did not affect the ignition delay or rate of fuel air premixing,the peak in-cylinder pressure or heat release rates.Toluene addition(0−22.5 vol%)to heptane increased the mean size of the soot particles generated by only 3%while also resulted in a slight increase in the peak cylinder pressure and peak heat release rates.Blending toluene and methyl-decanoate into heptane without adding 2-EHN increased the premix phase fraction by at least 13%.However,by adding 2-EHN(4×10^(−4)−1.5×10^(−3)),the premixed phase fraction decreased by at least 11%.展开更多
Pipeline of oil and gas have an increased risk because of pipeline punctures and rupture caused by corrosion. Therefore it is very important to have a reliable way for pipeline corrosion prediction. The corrosion dept...Pipeline of oil and gas have an increased risk because of pipeline punctures and rupture caused by corrosion. Therefore it is very important to have a reliable way for pipeline corrosion prediction. The corrosion depth prediction models that based on the support vector machines and chaos were introduced in this paper. A real example was given in this paper. The predicted results showed that the prediction models have a more higher precision. The two corrosion depth prediction models are reasonable in corrosion research, which can supply a scientific basis for pipeline safety management, service life prediction and repair.展开更多
A loss model for the mixed-flow pump impellers was developed by summarizing a variety of loss calculation formulas systematically.The internal flow field of the impeller was obtained by employing the iterative calcula...A loss model for the mixed-flow pump impellers was developed by summarizing a variety of loss calculation formulas systematically.The internal flow field of the impeller was obtained by employing the iterative calculation for S 1 and S 2 stream surfaces to solve the continuity and motion equations of fluid.Based on the calculation method of the flow field and the loss model,it is achieved to predict the impeller performance of the mixed-flow pump and the performance curves of a mixed-flow pump model with adjustable blades.Compared with the test data,the loss model of the mixed-flow pump based on the iterative calculation can predict the impeller performance quickly and accurately,which has a high value on the engineering applications.Based on the test verification,curves of various kinds of losses varied for the flow rate were analyzed under different blade angles.In addition,the mechanisms of various kinds of losses inside the mixed-flow pump impeller were discussed in-depth.展开更多
The application and fundamental study on turbulent premixed combustion of hydrogen enriched natural gas is reviewed in this paper.Discussions include the combustion characteristics of direct injection engine fueled wi...The application and fundamental study on turbulent premixed combustion of hydrogen enriched natural gas is reviewed in this paper.Discussions include the combustion characteristics of direct injection engine fueled with hydrogen enriched natural gas,visualization study of direct injection combustion of hydrogen enriched natural gas using a constant volume vessel,and the fundamental study of turbulent premixed combustion of hydrogen enriched natural gas.The effect of additional hydrogen on the combustion process of natural gas engine is investigated from the fundamental view of the interaction between combustion reaction and turbulent flow.展开更多
Wind energy is a clean and renewable energy for which technology has developed rapidly in recent years.Wind turbines are commonly supported on tubular steel towers.As the turbine size is growing and the towers are ris...Wind energy is a clean and renewable energy for which technology has developed rapidly in recent years.Wind turbines are commonly supported on tubular steel towers.As the turbine size is growing and the towers are rising in height,steel towers are required to be sufficiently strong and stiff,consequently leading to high construction costs.To tackle this problem,a new type of prestressed concrete tower was designed employing a novel tower concept having a regular octagon cross section with interior ribs on each side,which was optimized by comparing the natural frequency and stress difference under the same lateral load in different directions of the tower.The designed tower features a tapered profile that reduces the area subjected to wind;the tapered profile reduces the total weight,applied moment and the capital cost.An optimization method was developed employing ABAQUS software and a genetic algorithm.A target function was defined on the basis of the minimum cost of the concrete and prestressed tendon used,and constraints were applied by accounting for the stress,displacements and natural frequency of the tower.Employing the method,a 100 m prestressed concrete tower system for a 5 MW turbine was optimized and designed under wind and earthquake loads.The paper also reports a systematic design procedure incorporating the finite element method and the optimization method for the prestressed concrete wind-turbine towers.展开更多
基金Project (2009AA032601) supported by the National High-tech Research and Development Program of China
文摘The hot corrosion behaviors of Ni–16Cr–xAl（x=4.5%, 6.8%, 9.0%, mass fraction） based alloys in Na2SO4–25% NaCl molten salts at 600 °C were investigated. The effects of pre-oxidation and Al content on the resistance to hot corrosion were examined. The hot corrosion resistance of Ni–16Cr–xAl based alloy with Al addition from 4.5% to 9.0% increases with increasing Al content. The alloy with Al content of 9.0% shows the highest hot corrosion resistance among the examined alloys because more β–NiAl phases are obtained to sustain the Al2O3 scale repaired during hot corrosion. Pre-oxidized specimens have a superior hot corrosion resistance compared with the as-cast specimens, due to a protective oxide scale formed after pre-treatment.
基金The project supported by National Natural Science Foundation of China under Grant No. 90203008 and the Doctoral Foundation of the Ministry of Education of China
文摘Nonlinear time series prediction is studied by using an improved least squares support vector machine （LSSVM） regression based on chaotic mutation evolutionary programming （CMEP） approach for parameter optimization. We analyze how the prediction error varies with different parameters （σ, γ） in LS-SVM. In order to select appropriate parameters for the prediction model, we employ CMEP algorithm. Finally, Nasdaq stock data are predicted by using this LS-SVM regression based on CMEP, and satisfactory results are obtained.
基金Project(70572090) supported by the National Natural Science Foundation of China
文摘By adopting the chaotic searching to improve the global searching performance of the particle swarm optimization (PSO), and using the improved PSO to optimize the key parameters of the support vector machine (SVM) forecasting model, an improved SVM model named CPSO-SVM model was proposed. The new model was applied to predicting the short term load, and the improved effect of the new model was proved. The simulation results of the South China Power Market’s actual data show that the new method can effectively improve the forecast accuracy by 2.23% and 3.87%, respectively, compared with the PSO-SVM and SVM methods. Compared with that of the PSO-SVM and SVM methods, the time cost of the new model is only increased by 3.15 and 4.61 s, respectively, which indicates that the CPSO-SVM model gains significant improved effects.
文摘This paper examines the effect of equalizing ignition delay in a compression ignition engine.Two sets of tests were conducted,i.e.a set of constant injection timing tests with start of fuel injection at 10°crank angle degree(CAD)before top dead center(BTDC)and a set of constant ignition timing tests while also keeping the 10℃AD BTDC injection and adding ignition improver(2-ethylhexylnitrate-,2-EHN)to the fuel mixtures.Soot particles were characterized using DMS-500 instrument in terms of mass,size,and number.The experimental results showed that adding 2-EHN to the model fuel blends reduced the soot surface area,soot mass concentration and soot mean size.Replacing 20 vol%of a C 7-heptane with 20 vol%methyl-decanoate(an oxygenated C 11 molecule)did not affect the ignition delay or rate of fuel air premixing,the peak in-cylinder pressure or heat release rates.Toluene addition(0−22.5 vol%)to heptane increased the mean size of the soot particles generated by only 3%while also resulted in a slight increase in the peak cylinder pressure and peak heat release rates.Blending toluene and methyl-decanoate into heptane without adding 2-EHN increased the premix phase fraction by at least 13%.However,by adding 2-EHN(4×10^(−4)−1.5×10^(−3)),the premixed phase fraction decreased by at least 11%.
文摘Pipeline of oil and gas have an increased risk because of pipeline punctures and rupture caused by corrosion. Therefore it is very important to have a reliable way for pipeline corrosion prediction. The corrosion depth prediction models that based on the support vector machines and chaos were introduced in this paper. A real example was given in this paper. The predicted results showed that the prediction models have a more higher precision. The two corrosion depth prediction models are reasonable in corrosion research, which can supply a scientific basis for pipeline safety management, service life prediction and repair.
基金supported by the National Natural Science Foundation of China (Grant No. 51176088)the Open Research Foundation of State Key Laboratory of Hydroscience and Engineering of Tsinghua University(Grant No. 2009T3)
文摘A loss model for the mixed-flow pump impellers was developed by summarizing a variety of loss calculation formulas systematically.The internal flow field of the impeller was obtained by employing the iterative calculation for S 1 and S 2 stream surfaces to solve the continuity and motion equations of fluid.Based on the calculation method of the flow field and the loss model,it is achieved to predict the impeller performance of the mixed-flow pump and the performance curves of a mixed-flow pump model with adjustable blades.Compared with the test data,the loss model of the mixed-flow pump based on the iterative calculation can predict the impeller performance quickly and accurately,which has a high value on the engineering applications.Based on the test verification,curves of various kinds of losses varied for the flow rate were analyzed under different blade angles.In addition,the mechanisms of various kinds of losses inside the mixed-flow pump impeller were discussed in-depth.
基金supported by the National Natural Science Foundation of China(Grant Nos.51376004 and 51006080)the National Basic Research Program of China("973"Program)(Grant No.2013CB228406)
文摘The application and fundamental study on turbulent premixed combustion of hydrogen enriched natural gas is reviewed in this paper.Discussions include the combustion characteristics of direct injection engine fueled with hydrogen enriched natural gas,visualization study of direct injection combustion of hydrogen enriched natural gas using a constant volume vessel,and the fundamental study of turbulent premixed combustion of hydrogen enriched natural gas.The effect of additional hydrogen on the combustion process of natural gas engine is investigated from the fundamental view of the interaction between combustion reaction and turbulent flow.
基金supported by the National Natural Science Foundation of China(Grant No.51078231)
文摘Wind energy is a clean and renewable energy for which technology has developed rapidly in recent years.Wind turbines are commonly supported on tubular steel towers.As the turbine size is growing and the towers are rising in height,steel towers are required to be sufficiently strong and stiff,consequently leading to high construction costs.To tackle this problem,a new type of prestressed concrete tower was designed employing a novel tower concept having a regular octagon cross section with interior ribs on each side,which was optimized by comparing the natural frequency and stress difference under the same lateral load in different directions of the tower.The designed tower features a tapered profile that reduces the area subjected to wind;the tapered profile reduces the total weight,applied moment and the capital cost.An optimization method was developed employing ABAQUS software and a genetic algorithm.A target function was defined on the basis of the minimum cost of the concrete and prestressed tendon used,and constraints were applied by accounting for the stress,displacements and natural frequency of the tower.Employing the method,a 100 m prestressed concrete tower system for a 5 MW turbine was optimized and designed under wind and earthquake loads.The paper also reports a systematic design procedure incorporating the finite element method and the optimization method for the prestressed concrete wind-turbine towers.
