In this paper we construct an extended non-competitive input-occupancy-output model that captures China＇s processing trade and also develop a methodology to estimate the domestic value-added and employment generated ...In this paper we construct an extended non-competitive input-occupancy-output model that captures China＇s processing trade and also develop a methodology to estimate the domestic value-added and employment generated by each unit of total exports, of exports by sector, and of exports by commodity, respectively. We also prove mathematically that the gross value of exports is equal to the sum of total value added and total imports. Based on the methodology proposed here, we compile the 2002 extended Chinese non-competitive input-occupancy-output table and the United States non-competitive input-occupancy- output table, and then estimate and analyze the effects of China＇s exports and US exports on their respective domestic value added and employment.展开更多
Under the background of the energy saving and emission reduction, more and more attention has been placed on investigating the energy efficiency of ships. The added resistance has been noted for being crucial in predi...Under the background of the energy saving and emission reduction, more and more attention has been placed on investigating the energy efficiency of ships. The added resistance has been noted for being crucial in predicting the decrease of speed on a ship operating at sea. Furthermore, it is also significant to investigate the added resistance for a ship functioning in short waves of large modern ships. The researcher presents an estimation formula for the calculation of an added resistance study in short waves derived from the reflection law. An improved method has been proposed to calculate the added resistance due to ship motions, which applies the radiated energy theory along with the strip method. This procedure is based on an extended integral equation （EIE） method, which was used for solving the hydrodynamic coefficients without effects of the irregular frequency. Next, a combined method was recommended for the estimation of added resistance for a ship in the whole wave length range. The comparison data with other experiments indicate the method presented in the paper provides satisfactory results for large blunt ship.展开更多
The numerical prediction of added resistance and vertical ship motions of one ITTC （Intemational Towing Tank Conference） S-175 containership in regular head waves by our own in-house unsteady RANS solver naoe-FOAM-S...The numerical prediction of added resistance and vertical ship motions of one ITTC （Intemational Towing Tank Conference） S-175 containership in regular head waves by our own in-house unsteady RANS solver naoe-FOAM-SJTU is presented in this paper. The development of the solver naoe-FOAM-SJTU is based on the open source CFD tool, OpenFOAM. Numerical analysis is focused on the added resistance and vertical ship motions （heave and pitch motions） with four very different wavelengths （ 0.8Lpp 〈 2 〈 1.5L ） in regular head waves. Once the wavelength is near the length of the ship model, the responses of the resistance and ship motions become strongly influenced by nonlinear factors, as a result difficulties within simulations occur. In the paper, a comparison of the experimental results and the nonlinear strip theory was reviewed and based on the findings, the RANS simulations by the solver naoe-FOAM-SJTU were considered competent with the prediction of added resistance and vertical ship motions in a wide range of wave lengths.展开更多
The added resistance of KVLCC2 in short and regular head waves has been studied theoretically and experimentally. Model tests are performed to determine how well the asymptotic formula （Faltinsen et al. 1980） predic...The added resistance of KVLCC2 in short and regular head waves has been studied theoretically and experimentally. Model tests are performed to determine how well the asymptotic formula （Faltinsen et al. 1980） predicts the typical level of added resistance in short waves. Because the asymptotic formula neglects the effects of ship motions, it is combined with theoretical methods to calculate the added resistance in long waves using an function to predict the added resistance in the intermediate wavelength region where both ship motions and wave reflection are important. A unique feature of this experiment is that the ship model is divided into three segments to explore the added resistance distribution with respect to hull segment. This paper discusses the sensitivity of experimental results to the quality of the incident regular head waves. Moreover, a novel procedure for analyzing added resistance is described. Finally, the experimentally determined added resistance of KVLCC2 is compared with theoretical results. It is shown that the added resistance from the combined theoretical methods agrees well with experimental results in both the intermediate and short wave regions. The use of hull segments shows that added resistance is concentrated primarily at the bow.展开更多
It is well-recognized that a transfer system response delay that reduces the test stability inevitably exists in real-time dynamic hybrid testing （RTDHT）. This paper focuses on the delay-dependent stability and adde...It is well-recognized that a transfer system response delay that reduces the test stability inevitably exists in real-time dynamic hybrid testing （RTDHT）. This paper focuses on the delay-dependent stability and added damping of SDOF systems in RTDHT. The exponential delay term is transferred into a rational fraction by the Pad6 approximation, and the delay-dependent stability conditions and instability mechanism of SDOF RTDHT systems are investigated by the root locus technique. First, the stability conditions are discussed separately for the cases of stiffness, mass, and damping experimental substructure. The use of root locus plots shows that the added damping effect and instability mechanism for mass are different from those for stiffness. For the stiffness experimental substructure case, the instability results from the inherent mode because of an obvious negative damping effect of the delay. For the mass case, the delay introduces an equivalent positive damping into the inherent mode, and instability occurs at an added high frequency mode. Then, the compound stability condition is investigated for a general case and the results show that the mass ratio may have both upper and lower limits to remain stable. Finally, a high-emulational virtual shaking table model is built to validate the stability conclusions.展开更多
Since 2001, the exports of foreign-invested enterprises （FIEs） have accounted for more than 50percent of China＇s total exports. As foreign capital occupies a high proportion of the total capital of FIEs, most FIEs ...Since 2001, the exports of foreign-invested enterprises （FIEs） have accounted for more than 50percent of China＇s total exports. As foreign capital occupies a high proportion of the total capital of FIEs, most FIEs ＇ capital gains are foreign factor income. Although these gains are calculated as apart of China＇s GDP, they do not belong to China＇s national income. To determine the real contribution of exports to China ＂s welfare, the present paper analyses the impact of exports on China ＂s national income using a non-competitive input output model capturing processing trade. The results show that every US$1000 of China＇s exports generates US$506.8 of national income. The real contribution of exports to China ＂s welfare is much smaller than what we expected. This suggests that China should endeavor to improve the gains from international markets orfind another engine to maintain its economic growth.展开更多
An integral equation approach is utilized to in- vestigate the added mass and damping of floating produc- tion, storage and offloading system （FPSO system）. Finite water depth Green function and higher-order boundar...An integral equation approach is utilized to in- vestigate the added mass and damping of floating produc- tion, storage and offloading system （FPSO system）. Finite water depth Green function and higher-order boundary ele- ment method are used to solve integral equation. Numeri- cal results about added mass and damping are presented for odd and even mode motions of FPSO. The results show ro- bust convergence in high frequency range and can be used in wave load analysis for FPSO designing and operation.展开更多
Computational fuid dynamics （CFD） has been widely used to study the hydrodynamics of gas-solid fluidization; however, its applications in liquid-solid fluidization are relatively rare. In this study, CFD simulations...Computational fuid dynamics （CFD） has been widely used to study the hydrodynamics of gas-solid fluidization; however, its applications in liquid-solid fluidization are relatively rare. In this study, CFD simulations of a liquid-solid fluidized bed are carried out, focusing on the effect of drag correlation and added mass force on the hydrodynamics of liquid-solid fluidization. It is shown that drag correlation has a significant effect on the simulation results and the correlation proposed by Beetstra et al. （2007） gives the best agreement with experimental data. We further show that the added mass force does play an important role in CFD simulation of liquid-solid fluidization, and therefore should not be ignored in CFD simulations,展开更多
以中小企业板2007年以前上市的制造类企业为样本,将企业分为成长期和成熟期,探讨了股权属性、股权集中度和股权制衡度与EVA(economic value added)的关系.多元线性回归模型的实证结果得出,国有股比例与企业绩效负相关;流通股比例对企业...以中小企业板2007年以前上市的制造类企业为样本,将企业分为成长期和成熟期,探讨了股权属性、股权集中度和股权制衡度与EVA(economic value added)的关系.多元线性回归模型的实证结果得出,国有股比例与企业绩效负相关;流通股比例对企业绩效影响不大;股权集中度和股权制衡度对企业绩效的影响比较复杂.总体上,成长期较高的股权集中度、成熟期较高的股权制衡度对企业绩效有积极作用.展开更多
In the experiment, the brown rice whose moisture content was 12.5% was used as raw material. The brown rice was grouped, then moisturized differently and milled. While milling, the energy consumption, the rate of brok...In the experiment, the brown rice whose moisture content was 12.5% was used as raw material. The brown rice was grouped, then moisturized differently and milled. While milling, the energy consumption, the rate of broken rice and the crack rate were tested. It is confirmed that the stress crack owing to the moisture added to the brown rice can be avoided when the moisture amount added once is limited to no more than 1.5%. It is also proved that the energy consumption can be reduced, the yielding rate of rice can be increased and that the quality of rice can be improved.展开更多
The motion responses of ships carrying liquid cargo are affected not only by external wave excitation, but also by internal sloshing-induced forces and moments. Sloshing flow is coupled with the ship motion. This mean...The motion responses of ships carrying liquid cargo are affected not only by external wave excitation, but also by internal sloshing-induced forces and moments. Sloshing flow is coupled with the ship motion. This means the added resistance in waves may change when sloshing occurs inside the tank of the ship. In this study, the motion responses and added resistance of a ship, coupled with the sloshing-induced internal forces and moments are considered by using the linear potential theory. The three-dimensional Rankine panel method, in which the physical quantities are represented by using B-spline basis function, is applied. The sloshing flow of inner tanks is also simulated by Using the Rankine panel method and linearized boundary value problem. To study the added resistance, a near-field method, which integrates the second-order pressure on a body surface, is applied. The model ship is a blunt modified Wigley model with two inner tanks. Numerical results obtained without inner tanks are compared with the experimental data, and then the effect of filling ratio of inner tanks on ship motion and added resistance are observed. The components that induce added resistance are examined, and the effects of surge motion on sloshing flow and added resistance are briefly considered. This study shows that the sloshing flow inside the inner tanks may significantly influence not only the motion responses, but also added resistance, especially, when the incident wave frequency approaches the resonance frequency of the sloshing flow.展开更多
A numerical method is developed to obtain the added mass coefficients of a vehicle running with cavity in numerical simulation for the multiphase flow of the vehicle which is imposed an added vibration and analyzing i...A numerical method is developed to obtain the added mass coefficients of a vehicle running with cavity in numerical simulation for the multiphase flow of the vehicle which is imposed an added vibration and analyzing its hydrodynamic loads. The method is verified through the cases of non-cavitating sphere and ellipsoid. The changing rule of the added mass of a sphere during water exit is gained. Then the influence of cavitation on the added mass of a cylinder is studied. The results show that λ 11, λ22, λ26, λ66 all decrease as the cavitation number reduces and the length of the attached cavity increases. There is almost a linear relationship between the cavity length and λ22 .The base cavity has great influence on λ11 its contribution decreases more than 60%, when the cavitation number changes from 0.6 to 0.2.展开更多
The objective of this paper is to present and to validate a new hybrid coupling （HC） algorithm for modeling of fluid-structure interaction （FSI） in incompressible, viscous flows. The HC algorithm is able to avoid ...The objective of this paper is to present and to validate a new hybrid coupling （HC） algorithm for modeling of fluid-structure interaction （FSI） in incompressible, viscous flows. The HC algorithm is able to avoid numerical instability issues associated with artificial added mass effects, which are often encountered by standard loosely coupled （LC） and tightly coupled （TC） algorithms, when modeling the FSI response of flexible structures in incompressible flow. The artificial added mass effect is caused by the lag in exchange of interfacial displacements and forces between the fluid and solid solvers in partitioned algorithms. The artificial added mass effect is much more prominent for light/flexible struc- tures moving in water, because the fluid forces are in the same order of magnitude as the solid forces, and because the speed at which numerical errors propagate in an incom- pressible fluid. The new HC algorithm avoids numerical instability issues associated with artificial added mass effects by embedding Theodorsen＇s analytical approximation of the hydroelastic forces in the solution process to obtain better initial estimates of the displacements. Details of the new HC algorithm are presented. Numerical validation studies are shown for the forced pitching response of a steel and a plastic hydrofoil. The results show that the HC algorithm is able to converge faster, and is able to avoid numerical insta- bility issues, compared to standard LC and TC algorithms, when modeling the transient FSI response of a plastic hydrofoil. Although the HC algorithm is only demonstrated for a NACA0009 hydrofoil subject to pure pitching motion, the method can be easily extended to model general 3-D FSI response and stability of complex, flexible structures in turbulent, incompressible, multiphase flows.展开更多
A comprehensive numerical study on the three-dimensional structure of a turbulent jet in crossflow is performed. The jet-to-crossflow velocity ratio (R) varies in the range of 2 - 16; both vertical jets and inclined j...A comprehensive numerical study on the three-dimensional structure of a turbulent jet in crossflow is performed. The jet-to-crossflow velocity ratio (R) varies in the range of 2 - 16; both vertical jets and inclined jets without excess streamwise momentum are considered. The numerical results of the Standard two-equation k-ε model show that the turbulent structure can be broadly categorised according to the jet-to-crossflow velocity ratio. For strong to moderate jet discharges, i.e. R> 4, the jet is characterized by a longitudinal transition through a bent-over phase during which the jet becomes almost parallel with the main freestream, to a sectional vortex-pair flow with double concentration maxima; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless distance of around 20-60. The similarity coefficients are only weakly dependent on R. The cross-section scalar field is kidney-shaped and bifurcated, vvith distinct double concentration maxima; the aspect ratio is found to be around 1.2. A loss in vertical momentum is ob-served and the added mass coefficient of the jet motion is found to be approximately 1. On the other hand, for weak jets in strong crossflow, i. e. R ≥ 2, the lee of the jet is characterized by a negative pressure region. Although the double vortex flow can stili be noted, the scalar field becomes more symmetrical and no longer bifurcated. The similarity coeffcients are al-so noticeably different. The predicted jet flovv characteristics and mixing rates are well supported by experimental and field dala展开更多
The interaction between membrane structures and their environment can be either static or dynamic. Static interaction refers to interaction with static air, while dynamic interaction refers to wind and its effects. Th...The interaction between membrane structures and their environment can be either static or dynamic. Static interaction refers to interaction with static air, while dynamic interaction refers to wind and its effects. They can be evaluated by two parameters, added mass and radiation/aerodynamic damping, which are experimentally investigated in this study. The study includes the effects of both the static and dynamic interaction on structural dynamic characteristics, and the relationship between the interaction parameters and the covered area of a membrane structure for the static interaction and the relationship between the interaction parameters and wind direction and speed for the dynamic interaction. Experimental data show that the dynamic interaction is strongly correlated with the structural modes, i.e., the interaction of the symmetric modes is much larger than the anti-synmletric modes; and the influence of the dynamic interaction is significant in wind-induced response analysis and cannot be ignored. In addition, it is concluded that the structural natural frequency is remarkably decreased by this interaction, and the frequency band is significantly broadened.展开更多
基金This is a translated version of the paper published in Chinese in Social Sciences in China （Zhongguo shehui kexue, 2007, no. 5, pp. 91-103）, which has received the ＂Pei-Kang CHANG Development Economics Award＂ and ＂Sun Yefang Economics Award.＂ The authors are grateful to Mr. Tung Chee- hwa, former President of Hong Kong SAR, Chinese University of Hong Kong and National Natural Science Foundation of China （No. 70810107020, 70871108, 60474063） for their financial support. The authors thank Dr Wang Zhi from US International Trade Commission, and anonymous referees for their useful comments. Usual claims are applied.
文摘In this paper we construct an extended non-competitive input-occupancy-output model that captures China＇s processing trade and also develop a methodology to estimate the domestic value-added and employment generated by each unit of total exports, of exports by sector, and of exports by commodity, respectively. We also prove mathematically that the gross value of exports is equal to the sum of total value added and total imports. Based on the methodology proposed here, we compile the 2002 extended Chinese non-competitive input-occupancy-output table and the United States non-competitive input-occupancy- output table, and then estimate and analyze the effects of China＇s exports and US exports on their respective domestic value added and employment.
基金Supported by the National Natural Science Foundation of China under Grant No.51079032 the Outstanding Youth Science Foundation of Heilongjiang Province,No.200908
文摘Under the background of the energy saving and emission reduction, more and more attention has been placed on investigating the energy efficiency of ships. The added resistance has been noted for being crucial in predicting the decrease of speed on a ship operating at sea. Furthermore, it is also significant to investigate the added resistance for a ship functioning in short waves of large modern ships. The researcher presents an estimation formula for the calculation of an added resistance study in short waves derived from the reflection law. An improved method has been proposed to calculate the added resistance due to ship motions, which applies the radiated energy theory along with the strip method. This procedure is based on an extended integral equation （EIE） method, which was used for solving the hydrodynamic coefficients without effects of the irregular frequency. Next, a combined method was recommended for the estimation of added resistance for a ship in the whole wave length range. The comparison data with other experiments indicate the method presented in the paper provides satisfactory results for large blunt ship.
基金Foundation item： Supported by the National Natural Science Foundation of China （Grant No. 50739004 and 11072154）
文摘The numerical prediction of added resistance and vertical ship motions of one ITTC （Intemational Towing Tank Conference） S-175 containership in regular head waves by our own in-house unsteady RANS solver naoe-FOAM-SJTU is presented in this paper. The development of the solver naoe-FOAM-SJTU is based on the open source CFD tool, OpenFOAM. Numerical analysis is focused on the added resistance and vertical ship motions （heave and pitch motions） with four very different wavelengths （ 0.8Lpp 〈 2 〈 1.5L ） in regular head waves. Once the wavelength is near the length of the ship model, the responses of the resistance and ship motions become strongly influenced by nonlinear factors, as a result difficulties within simulations occur. In the paper, a comparison of the experimental results and the nonlinear strip theory was reviewed and based on the findings, the RANS simulations by the solver naoe-FOAM-SJTU were considered competent with the prediction of added resistance and vertical ship motions in a wide range of wave lengths.
基金part of the research project SeaPro, which is sponsored by Rolls-Royce Marine and the Research Council of Norway
文摘The added resistance of KVLCC2 in short and regular head waves has been studied theoretically and experimentally. Model tests are performed to determine how well the asymptotic formula （Faltinsen et al. 1980） predicts the typical level of added resistance in short waves. Because the asymptotic formula neglects the effects of ship motions, it is combined with theoretical methods to calculate the added resistance in long waves using an function to predict the added resistance in the intermediate wavelength region where both ship motions and wave reflection are important. A unique feature of this experiment is that the ship model is divided into three segments to explore the added resistance distribution with respect to hull segment. This paper discusses the sensitivity of experimental results to the quality of the incident regular head waves. Moreover, a novel procedure for analyzing added resistance is described. Finally, the experimentally determined added resistance of KVLCC2 is compared with theoretical results. It is shown that the added resistance from the combined theoretical methods agrees well with experimental results in both the intermediate and short wave regions. The use of hull segments shows that added resistance is concentrated primarily at the bow.
基金State Key Laboratory of Hydroscience and Engineering Under Grant No.2008-TC-2National Natural Science Foundation of China Under Grant No.90510018,50779021 and 90715041
文摘It is well-recognized that a transfer system response delay that reduces the test stability inevitably exists in real-time dynamic hybrid testing （RTDHT）. This paper focuses on the delay-dependent stability and added damping of SDOF systems in RTDHT. The exponential delay term is transferred into a rational fraction by the Pad6 approximation, and the delay-dependent stability conditions and instability mechanism of SDOF RTDHT systems are investigated by the root locus technique. First, the stability conditions are discussed separately for the cases of stiffness, mass, and damping experimental substructure. The use of root locus plots shows that the added damping effect and instability mechanism for mass are different from those for stiffness. For the stiffness experimental substructure case, the instability results from the inherent mode because of an obvious negative damping effect of the delay. For the mass case, the delay introduces an equivalent positive damping into the inherent mode, and instability occurs at an added high frequency mode. Then, the compound stability condition is investigated for a general case and the results show that the mass ratio may have both upper and lower limits to remain stable. Finally, a high-emulational virtual shaking table model is built to validate the stability conclusions.
基金supported by the National Natural Science Foundation of China(Grant Nos.71003093, 70871108 and 70810107020)
文摘Since 2001, the exports of foreign-invested enterprises （FIEs） have accounted for more than 50percent of China＇s total exports. As foreign capital occupies a high proportion of the total capital of FIEs, most FIEs ＇ capital gains are foreign factor income. Although these gains are calculated as apart of China＇s GDP, they do not belong to China＇s national income. To determine the real contribution of exports to China ＂s welfare, the present paper analyses the impact of exports on China ＂s national income using a non-competitive input output model capturing processing trade. The results show that every US$1000 of China＇s exports generates US$506.8 of national income. The real contribution of exports to China ＂s welfare is much smaller than what we expected. This suggests that China should endeavor to improve the gains from international markets orfind another engine to maintain its economic growth.
基金supported by the Fundamental Research Funds forthe Central Universities (DVT10LK43)the Returned Overseas Chinese Scholars,State Education Ministry (2007[24])
文摘An integral equation approach is utilized to in- vestigate the added mass and damping of floating produc- tion, storage and offloading system （FPSO system）. Finite water depth Green function and higher-order boundary ele- ment method are used to solve integral equation. Numeri- cal results about added mass and damping are presented for odd and even mode motions of FPSO. The results show ro- bust convergence in high frequency range and can be used in wave load analysis for FPSO designing and operation.
文摘Computational fuid dynamics （CFD） has been widely used to study the hydrodynamics of gas-solid fluidization; however, its applications in liquid-solid fluidization are relatively rare. In this study, CFD simulations of a liquid-solid fluidized bed are carried out, focusing on the effect of drag correlation and added mass force on the hydrodynamics of liquid-solid fluidization. It is shown that drag correlation has a significant effect on the simulation results and the correlation proposed by Beetstra et al. （2007） gives the best agreement with experimental data. We further show that the added mass force does play an important role in CFD simulation of liquid-solid fluidization, and therefore should not be ignored in CFD simulations,
文摘以中小企业板2007年以前上市的制造类企业为样本,将企业分为成长期和成熟期,探讨了股权属性、股权集中度和股权制衡度与EVA(economic value added)的关系.多元线性回归模型的实证结果得出,国有股比例与企业绩效负相关;流通股比例对企业绩效影响不大;股权集中度和股权制衡度对企业绩效的影响比较复杂.总体上,成长期较高的股权集中度、成熟期较高的股权制衡度对企业绩效有积极作用.
基金Tenth Eive-Year Plan of the Committee of the Scientific Tech. of Heilongjiang Province (GB02B4040-1)Heilongjiang Education Bureau (10511012)
文摘In the experiment, the brown rice whose moisture content was 12.5% was used as raw material. The brown rice was grouped, then moisturized differently and milled. While milling, the energy consumption, the rate of broken rice and the crack rate were tested. It is confirmed that the stress crack owing to the moisture added to the brown rice can be avoided when the moisture amount added once is limited to no more than 1.5%. It is also proved that the energy consumption can be reduced, the yielding rate of rice can be increased and that the quality of rice can be improved.
基金partly funded by the Ministry of Trade,Industry and Energy(MOTIE),Korea,under Industrial Technology Innovation Program(Grant No.10062881),“Technology Development to Improve Added Resistance and Ship Operational Efficiency for Hull Form Design,”the NICOP project Grant No.N62909-15-1-2020,supported by Office of Naval Research Globalpartly funded by the LRF*–Funded Research Center at Seoul National University
文摘The motion responses of ships carrying liquid cargo are affected not only by external wave excitation, but also by internal sloshing-induced forces and moments. Sloshing flow is coupled with the ship motion. This means the added resistance in waves may change when sloshing occurs inside the tank of the ship. In this study, the motion responses and added resistance of a ship, coupled with the sloshing-induced internal forces and moments are considered by using the linear potential theory. The three-dimensional Rankine panel method, in which the physical quantities are represented by using B-spline basis function, is applied. The sloshing flow of inner tanks is also simulated by Using the Rankine panel method and linearized boundary value problem. To study the added resistance, a near-field method, which integrates the second-order pressure on a body surface, is applied. The model ship is a blunt modified Wigley model with two inner tanks. Numerical results obtained without inner tanks are compared with the experimental data, and then the effect of filling ratio of inner tanks on ship motion and added resistance are observed. The components that induce added resistance are examined, and the effects of surge motion on sloshing flow and added resistance are briefly considered. This study shows that the sloshing flow inside the inner tanks may significantly influence not only the motion responses, but also added resistance, especially, when the incident wave frequency approaches the resonance frequency of the sloshing flow.
基金supported by the National Nature Science Foundation of China(Grant No.10832007)
文摘A numerical method is developed to obtain the added mass coefficients of a vehicle running with cavity in numerical simulation for the multiphase flow of the vehicle which is imposed an added vibration and analyzing its hydrodynamic loads. The method is verified through the cases of non-cavitating sphere and ellipsoid. The changing rule of the added mass of a sphere during water exit is gained. Then the influence of cavitation on the added mass of a cylinder is studied. The results show that λ 11, λ22, λ26, λ66 all decrease as the cavitation number reduces and the length of the attached cavity increases. There is almost a linear relationship between the cavity length and λ22 .The base cavity has great influence on λ11 its contribution decreases more than 60%, when the cavitation number changes from 0.6 to 0.2.
基金the financial support provided by the Office of Naval Research(ONR) through grant number N00014-09-1-1204 (managed by Dr. Ki-Han Kim)supported in part by the National Research Foundation of Korea (NRF)grant funded by the Korea government (MEST) through the GCRC-SOP Grant No. 2012-0004783
文摘The objective of this paper is to present and to validate a new hybrid coupling （HC） algorithm for modeling of fluid-structure interaction （FSI） in incompressible, viscous flows. The HC algorithm is able to avoid numerical instability issues associated with artificial added mass effects, which are often encountered by standard loosely coupled （LC） and tightly coupled （TC） algorithms, when modeling the FSI response of flexible structures in incompressible flow. The artificial added mass effect is caused by the lag in exchange of interfacial displacements and forces between the fluid and solid solvers in partitioned algorithms. The artificial added mass effect is much more prominent for light/flexible struc- tures moving in water, because the fluid forces are in the same order of magnitude as the solid forces, and because the speed at which numerical errors propagate in an incom- pressible fluid. The new HC algorithm avoids numerical instability issues associated with artificial added mass effects by embedding Theodorsen＇s analytical approximation of the hydroelastic forces in the solution process to obtain better initial estimates of the displacements. Details of the new HC algorithm are presented. Numerical validation studies are shown for the forced pitching response of a steel and a plastic hydrofoil. The results show that the HC algorithm is able to converge faster, and is able to avoid numerical insta- bility issues, compared to standard LC and TC algorithms, when modeling the transient FSI response of a plastic hydrofoil. Although the HC algorithm is only demonstrated for a NACA0009 hydrofoil subject to pure pitching motion, the method can be easily extended to model general 3-D FSI response and stability of complex, flexible structures in turbulent, incompressible, multiphase flows.
文摘A comprehensive numerical study on the three-dimensional structure of a turbulent jet in crossflow is performed. The jet-to-crossflow velocity ratio (R) varies in the range of 2 - 16; both vertical jets and inclined jets without excess streamwise momentum are considered. The numerical results of the Standard two-equation k-ε model show that the turbulent structure can be broadly categorised according to the jet-to-crossflow velocity ratio. For strong to moderate jet discharges, i.e. R> 4, the jet is characterized by a longitudinal transition through a bent-over phase during which the jet becomes almost parallel with the main freestream, to a sectional vortex-pair flow with double concentration maxima; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless distance of around 20-60. The similarity coefficients are only weakly dependent on R. The cross-section scalar field is kidney-shaped and bifurcated, vvith distinct double concentration maxima; the aspect ratio is found to be around 1.2. A loss in vertical momentum is ob-served and the added mass coefficient of the jet motion is found to be approximately 1. On the other hand, for weak jets in strong crossflow, i. e. R ≥ 2, the lee of the jet is characterized by a negative pressure region. Although the double vortex flow can stili be noted, the scalar field becomes more symmetrical and no longer bifurcated. The similarity coeffcients are al-so noticeably different. The predicted jet flovv characteristics and mixing rates are well supported by experimental and field dala
基金National Natural Science Foundation of China Under Grant No. 50725826, 90815021
文摘The interaction between membrane structures and their environment can be either static or dynamic. Static interaction refers to interaction with static air, while dynamic interaction refers to wind and its effects. They can be evaluated by two parameters, added mass and radiation/aerodynamic damping, which are experimentally investigated in this study. The study includes the effects of both the static and dynamic interaction on structural dynamic characteristics, and the relationship between the interaction parameters and the covered area of a membrane structure for the static interaction and the relationship between the interaction parameters and wind direction and speed for the dynamic interaction. Experimental data show that the dynamic interaction is strongly correlated with the structural modes, i.e., the interaction of the symmetric modes is much larger than the anti-synmletric modes; and the influence of the dynamic interaction is significant in wind-induced response analysis and cannot be ignored. In addition, it is concluded that the structural natural frequency is remarkably decreased by this interaction, and the frequency band is significantly broadened.
