To address the deficiency in loss diagnostic methods for turbines working at off-design angles of attack,a novel loss decomposition method suitable for cascade flow with large separation is proposed.The method propose...To address the deficiency in loss diagnostic methods for turbines working at off-design angles of attack,a novel loss decomposition method suitable for cascade flow with large separation is proposed.The method proposed has the following advantages over existing methods:(A)It enables refined loss decomposition for cascade flows,capable of identifying the spatial range of specific regions such as shear layers and backflow regions,thereby obtaining the loss characteristics of these regions.(B)The region identification criteria in this method have clear physical meanings,rather than relying on arbitrary area division.(C)The method has good applicability and is suitable for cascade flows under various angles of attack.Validation shows that this method achieves satisfactory results.Based on this method,the loss mechanisms of a low-pressure turbine cascade at a low Reynolds number of 4.3×10^(4)and angles of attack of-5°,-20°,and-45°are investigated using Large Eddy Simulations(LESs).Entropy analysis quantitatively demonstrates significant differences in the composition of losses among flow regions,due to their different flow characteristics.From the perspective of flow regions,wake loss dominates total loss,while loss in backflow region is negligible.Furthermore,the variation mechanisms of loss with incidence differ among different flow regions.展开更多
Rasterization is a conversion process accompanied with information loss, which includes the loss of features＇ shape, structure, position, attribute and so on. Two chief factors that affect estimating attribute accura...Rasterization is a conversion process accompanied with information loss, which includes the loss of features＇ shape, structure, position, attribute and so on. Two chief factors that affect estimating attribute accuracy loss in rasterization are grid cell size and evaluating method. That is, attribute accuracy loss in rasterization has a close relationship with grid cell size; besides, it is also influenced by evaluating methods. Therefore, it is significant to analyze these two influencing factors comprehensively. Taking land cover data of Sichuan at the scale of 1：250,000 in 2005 as a case, in view of data volume and its processing time of the study region, this study selects 16 spatial scales from 600 m to 30 km, uses rasterizing method based on the Rule of Maximum Area （RMA） in ArcGIS and two evaluating methods of attribute accuracy loss, which are Normal Analysis Method （NAM） and a new Method Based on Grid Cell （MBGC）, respectively, and analyzes the scale effect of attribute （it is area here） accuracy loss at 16 different scales by these two evaluating methods comparatively. The results show that： （1） At the same scale, average area accuracy loss of the entire study region evaluated by MBGC is significantly larger than the one estimated using NAM. Moreover, this discrepancy between the two is obvious in the range of 1 km to 10 km. When the grid cell is larger than 10 km, average area accuracy losses calculated by the two evaluating methods are stable, even tended to parallel. （2） MBGC can not only estimate RMA rasterization attribute accuracy loss accurately, but can express the spatial distribution of the loss objectively. （3） The suitable scale domain for RMA rasterization of land cover data of Sichuan at the scale of 1：250,000 in 2005 is better equal to or less than 800 m, in which the data volume is favorable and the processina time is not too Iona. as well as the area accuracv loss is less than 2.5%.展开更多
Probabilistic Seismic Loss Estimation is a methodology used as a quantitative and explicit expression of the performance of buildings using terms that address the interests of both owners and insurance companies. Appl...Probabilistic Seismic Loss Estimation is a methodology used as a quantitative and explicit expression of the performance of buildings using terms that address the interests of both owners and insurance companies. Applying the ATC 58 approach for seismic loss assessment of buildings requires using Incremental Dynamic Analysis （IDA）, which needs hundreds of time-consuming analyses, which in turn hinders its wide application. The Endurance Time Method （ETM） is proposed herein as part of a demand propagation prediction procedure and is shown to be an economical alternative to IDA. Various scenarios were considered to achieve this purpose and their appropriateness has been evaluated using statistical methods. The most precise and efficient scenario was validated through comparison against IDA driven response predictions of 34 code conforming benchmark structures and was proven to be sufficiently precise while offering a great deal of efficiency. The loss values were estimated by replacing IDA with the proposed ETM-based procedure in the ATC 58 procedure and it was fotmd that these values suffer from varying inaccuracies, which were attributed to the discretized nature of damage and loss prediction functions provided by ATC 58.展开更多
An improved method for calculating the corona power loss and the ground-level electric field on HVAC transmission lines induced by corona is proposed.Based on a charge simulation method combined with a method of succe...An improved method for calculating the corona power loss and the ground-level electric field on HVAC transmission lines induced by corona is proposed.Based on a charge simulation method combined with a method of successive images,the proposed method has the number and location of the simulated charges not arbitrary.When the surface electric field of a conductor exceeds the onset value,charges are emitted from corona into the space around,and the space ions and the surface charges on each sub-conductor are simulated by using the images of the other sub-conductors.The displacements of the space ions are calculated at every time step during corona periods in both the positive and the negative half cycles.Several examples are calculated by using the proposed method,and the calculated electric field at the ground level and the corona power loss agree well with previous measurements.The results show that simulating 12 charges in each conductor during 600 time steps in one cycle takes less time while guarantees the accuracy.The corona discharge from a 220 kV transmission line enhances slightly(less than 2%) the electric field at the ground level,but this effect is little from a 500 kV line.The improved method is a good compromise between the time cost and the accuracy of calculation.展开更多
Exact simulation of the acoustic performance is essential to the engineering application for a vehicle intake system. The rectangular-pulse method based on the computational fluid dynamics approach was employed for ca...Exact simulation of the acoustic performance is essential to the engineering application for a vehicle intake system. The rectangular-pulse method based on the computational fluid dynamics approach was employed for calculating the transmission loss. Firstly, the transmission loss of the single-cavity element was simulated without any airflow, and the effects of different structural parameters on the acoustic performance were investigated comprehensively. Secondly, the static transmission loss of the perforated intake pipe was obtained by the rectangular-pulse method, which is proved to be accurate enough compared with the result by finite element method. Thirdly, under the different conditions of the mean airflow and the operating temperature, the specific transmission loss was acquired respectively. In general, the peaks of the transmission loss are shifted to the lower frequency range because of the reverse airflow, but the amplitudes are irregularly changed. Besides, when the operating temperature increases, the peaks are shifted to the higher frequencies. Finally, with the designed perforated pipe installed to the intake system, the road tests were proceeded to evaluate the actual acoustic performance, and the result indicates that the intake sound pressure level is greatly attenuated. Typically in the range of 600–1500 Hz, the insertion loss of the intake noise at the decelerating moment is almost 20 d B(A), and the overall noise is reduced more than 14.2 d B(A). In conclusion, the perforated intake pipe has been proved excellent in improving the acoustic performance of intake system and could provide the guidance for the automotive engineering application.展开更多
In this study, we examined the varia- tions between the difference method and the enzyme- hydrolyzed casein method for determining endogenous amino acid loss and the true amino acid digestibility in ducks fed normal p...In this study, we examined the varia- tions between the difference method and the enzyme- hydrolyzed casein method for determining endogenous amino acid loss and the true amino acid digestibility in ducks fed normal protein-containing diets. These methods were compared to the nitrogen-free （N-free） diet method. The difference method was based on soy- bean meal as the only protein source, with the experi- mental diets containing crude protein levels at 15% and 20%. The enzyme-hydrolyzed casein method was based on enzyme-hydrolyzed casein meal as the pro- tein source, with the experimental diet containing a crude protein level of 17.5%. The N-free diet was prepared with starches and paper fibers. In each meth- od,64 Tianfu meat drakes （7-weeks-old） with an av- erage body weight of 2.77±0.16 kg were used and divided into four groups, and fed four different diets. Each group contained four replicates of four drakes and they were force fed trial diets according to the Sirbald method for detecting their apparent amino aciddigestibility, endogenous amino acid loss and true a- mino acid digestibility. The results demonstrated that using the difference, enzyme-hydrolyzed casein and N-free diet methods, endogenous amino acid losses were 0. 9946,1. 2243 and 0. 9297 mg/g dry matter in- take （ DMI）, respectively. The true amino acid digest- ibility measured by the difference method was 88.93 %±4.43 %. Using the enzyme-hydrolyzed ca- sein method with two dietary crude protein levels of 15% and 20%, the digestibility was 91.15%±4.33% and 91.97%±4. 16%, respectively, and by the N-free diet methods with two dietary crude protein levels of 15% and 20% ,it was 88.55%±4.29% and 88.82 %±4.61%, respectively. The results suggested that when the dietary protein level was 15% to 20 %, the true amino acid digestibility and endogenous ami- no acid loss as determined by the difference method was more accurate than the values determined by the enzyme-hydrolyzed casein method.展开更多
基金co-supported by the National Natural Science Foundation of China(No.52176033)the National Science and Technology Major Project,China(No.J2019-II-0012-0032)the Science Center for Gas Turbine Project,China(No.P2022-B-II-009-001)。
文摘To address the deficiency in loss diagnostic methods for turbines working at off-design angles of attack,a novel loss decomposition method suitable for cascade flow with large separation is proposed.The method proposed has the following advantages over existing methods:(A)It enables refined loss decomposition for cascade flows,capable of identifying the spatial range of specific regions such as shear layers and backflow regions,thereby obtaining the loss characteristics of these regions.(B)The region identification criteria in this method have clear physical meanings,rather than relying on arbitrary area division.(C)The method has good applicability and is suitable for cascade flows under various angles of attack.Validation shows that this method achieves satisfactory results.Based on this method,the loss mechanisms of a low-pressure turbine cascade at a low Reynolds number of 4.3×10^(4)and angles of attack of-5°,-20°,and-45°are investigated using Large Eddy Simulations(LESs).Entropy analysis quantitatively demonstrates significant differences in the composition of losses among flow regions,due to their different flow characteristics.From the perspective of flow regions,wake loss dominates total loss,while loss in backflow region is negligible.Furthermore,the variation mechanisms of loss with incidence differ among different flow regions.
基金The Independent Research of the State Key Laboratory of Resource and Environmental Information System,No.O88RA100SAThe Third Innovative and Cutting-edge Projects of Institute of Geographic Sciences andNatural Resources Research, CAS, No.O66U0309SZ
文摘Rasterization is a conversion process accompanied with information loss, which includes the loss of features＇ shape, structure, position, attribute and so on. Two chief factors that affect estimating attribute accuracy loss in rasterization are grid cell size and evaluating method. That is, attribute accuracy loss in rasterization has a close relationship with grid cell size; besides, it is also influenced by evaluating methods. Therefore, it is significant to analyze these two influencing factors comprehensively. Taking land cover data of Sichuan at the scale of 1：250,000 in 2005 as a case, in view of data volume and its processing time of the study region, this study selects 16 spatial scales from 600 m to 30 km, uses rasterizing method based on the Rule of Maximum Area （RMA） in ArcGIS and two evaluating methods of attribute accuracy loss, which are Normal Analysis Method （NAM） and a new Method Based on Grid Cell （MBGC）, respectively, and analyzes the scale effect of attribute （it is area here） accuracy loss at 16 different scales by these two evaluating methods comparatively. The results show that： （1） At the same scale, average area accuracy loss of the entire study region evaluated by MBGC is significantly larger than the one estimated using NAM. Moreover, this discrepancy between the two is obvious in the range of 1 km to 10 km. When the grid cell is larger than 10 km, average area accuracy losses calculated by the two evaluating methods are stable, even tended to parallel. （2） MBGC can not only estimate RMA rasterization attribute accuracy loss accurately, but can express the spatial distribution of the loss objectively. （3） The suitable scale domain for RMA rasterization of land cover data of Sichuan at the scale of 1：250,000 in 2005 is better equal to or less than 800 m, in which the data volume is favorable and the processina time is not too Iona. as well as the area accuracv loss is less than 2.5%.
文摘Probabilistic Seismic Loss Estimation is a methodology used as a quantitative and explicit expression of the performance of buildings using terms that address the interests of both owners and insurance companies. Applying the ATC 58 approach for seismic loss assessment of buildings requires using Incremental Dynamic Analysis （IDA）, which needs hundreds of time-consuming analyses, which in turn hinders its wide application. The Endurance Time Method （ETM） is proposed herein as part of a demand propagation prediction procedure and is shown to be an economical alternative to IDA. Various scenarios were considered to achieve this purpose and their appropriateness has been evaluated using statistical methods. The most precise and efficient scenario was validated through comparison against IDA driven response predictions of 34 code conforming benchmark structures and was proven to be sufficiently precise while offering a great deal of efficiency. The loss values were estimated by replacing IDA with the proposed ETM-based procedure in the ATC 58 procedure and it was fotmd that these values suffer from varying inaccuracies, which were attributed to the discretized nature of damage and loss prediction functions provided by ATC 58.
基金supported by National Basic Research Program of China(973 Program)(2011CB209404)
文摘An improved method for calculating the corona power loss and the ground-level electric field on HVAC transmission lines induced by corona is proposed.Based on a charge simulation method combined with a method of successive images,the proposed method has the number and location of the simulated charges not arbitrary.When the surface electric field of a conductor exceeds the onset value,charges are emitted from corona into the space around,and the space ions and the surface charges on each sub-conductor are simulated by using the images of the other sub-conductors.The displacements of the space ions are calculated at every time step during corona periods in both the positive and the negative half cycles.Several examples are calculated by using the proposed method,and the calculated electric field at the ground level and the corona power loss agree well with previous measurements.The results show that simulating 12 charges in each conductor during 600 time steps in one cycle takes less time while guarantees the accuracy.The corona discharge from a 220 kV transmission line enhances slightly(less than 2%) the electric field at the ground level,but this effect is little from a 500 kV line.The improved method is a good compromise between the time cost and the accuracy of calculation.
基金Project(51705454)supported by the National Natural Science Foundation of China
文摘Exact simulation of the acoustic performance is essential to the engineering application for a vehicle intake system. The rectangular-pulse method based on the computational fluid dynamics approach was employed for calculating the transmission loss. Firstly, the transmission loss of the single-cavity element was simulated without any airflow, and the effects of different structural parameters on the acoustic performance were investigated comprehensively. Secondly, the static transmission loss of the perforated intake pipe was obtained by the rectangular-pulse method, which is proved to be accurate enough compared with the result by finite element method. Thirdly, under the different conditions of the mean airflow and the operating temperature, the specific transmission loss was acquired respectively. In general, the peaks of the transmission loss are shifted to the lower frequency range because of the reverse airflow, but the amplitudes are irregularly changed. Besides, when the operating temperature increases, the peaks are shifted to the higher frequencies. Finally, with the designed perforated pipe installed to the intake system, the road tests were proceeded to evaluate the actual acoustic performance, and the result indicates that the intake sound pressure level is greatly attenuated. Typically in the range of 600–1500 Hz, the insertion loss of the intake noise at the decelerating moment is almost 20 d B(A), and the overall noise is reduced more than 14.2 d B(A). In conclusion, the perforated intake pipe has been proved excellent in improving the acoustic performance of intake system and could provide the guidance for the automotive engineering application.
文摘In this study, we examined the varia- tions between the difference method and the enzyme- hydrolyzed casein method for determining endogenous amino acid loss and the true amino acid digestibility in ducks fed normal protein-containing diets. These methods were compared to the nitrogen-free （N-free） diet method. The difference method was based on soy- bean meal as the only protein source, with the experi- mental diets containing crude protein levels at 15% and 20%. The enzyme-hydrolyzed casein method was based on enzyme-hydrolyzed casein meal as the pro- tein source, with the experimental diet containing a crude protein level of 17.5%. The N-free diet was prepared with starches and paper fibers. In each meth- od,64 Tianfu meat drakes （7-weeks-old） with an av- erage body weight of 2.77±0.16 kg were used and divided into four groups, and fed four different diets. Each group contained four replicates of four drakes and they were force fed trial diets according to the Sirbald method for detecting their apparent amino aciddigestibility, endogenous amino acid loss and true a- mino acid digestibility. The results demonstrated that using the difference, enzyme-hydrolyzed casein and N-free diet methods, endogenous amino acid losses were 0. 9946,1. 2243 and 0. 9297 mg/g dry matter in- take （ DMI）, respectively. The true amino acid digest- ibility measured by the difference method was 88.93 %±4.43 %. Using the enzyme-hydrolyzed ca- sein method with two dietary crude protein levels of 15% and 20%, the digestibility was 91.15%±4.33% and 91.97%±4. 16%, respectively, and by the N-free diet methods with two dietary crude protein levels of 15% and 20% ,it was 88.55%±4.29% and 88.82 %±4.61%, respectively. The results suggested that when the dietary protein level was 15% to 20 %, the true amino acid digestibility and endogenous ami- no acid loss as determined by the difference method was more accurate than the values determined by the enzyme-hydrolyzed casein method.
