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In order to prevent pipe blockage and reduce transportation costs, submarine pipes usually use the method of heating and pressurizing the pipe when transporting liquids. The high temperature and high pressure will cause the axial ...
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In order to prevent pipe blockage and reduce transportation costs, submarine pipes usually use the method of heating and pressurizing the pipe when transporting liquids. The high temperature and high pressure will cause the axial deformation of the submarine pipe, but due to the existence of the boundary between the two ends of the pipe, the axial deformation cannot be released and a certain axial force is generated. When axial force accumulates to a certain extent, buckling failure may occur, that is, thermal buckling of submarine pipes. In the process of buckling prediction, the axial force is an important input parameter. In the current engineering application, the non-bonded flexible pipe is often regarded as a steel pipe for fast calculation of the axial force value. However, since the geometry of the non-bonded pipe is very complex, the radial mutual extrusion and interlayer interaction will affect the axial deformation of the pipe. Therefore, it is not appropriate to simply use the deformation of the steel pipe to obtain the equivalent of the deformation of the non-bonded pipe to obtain the value of the axial force. In this paper, an analytical model for calculating the structural response of non-bonded pipes under high temperature loads and axisymmetric loads is proposed, and the structural responses of non-bonded pipes under high temperature loads and internal and external pressures are analyzed. The axial force is compared with the results obtained by the calculation methods commonly used in the current engineering. Further, the impact of these differences on the soft soil seabed upheaval buckling forecast is analyzed.
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With more and more MMC-HVDC connected to the AC network, the short-circuit current contributed by converter station should be taken into account when the short-circuit fault occurs at the AC-side. In this paper, the characteristic...
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With more and more MMC-HVDC connected to the AC network, the short-circuit current contributed by converter station should be taken into account when the short-circuit fault occurs at the AC-side. In this paper, the characteristics of short-circuit current contributed by MMC are analyzed and a simple and convenient method to calculate the fault current is proposed. Study shows that the characteristics of short-circuit current depend on the control method that MMC adopted. The development of short circuit current can be divided into transient-state and steady-state stage according to whether the controller responds completely or not. Considering the margin of IGBT, current limiters are set both in inner and outer controller. It can limit the bridge arm current and avoid overload. Therefore, AC-side current will change within the limit value. A practical method for the short-circuit current calculation is proposed based on the controllers and limiters. Through this method, both the symmetrical and asymmetrical fault short-circuit current can be calculated after the controllers enters steady state. The analysis in this paper shows that MMC can be equivalent to the current source at steady-state and participate in the calculation of AC system short-circuit. Finally, the accuracy of the proposed method is verified in the PSCAD simulation.
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摘要 :
With more and more MMC-HVDC connected to the AC network, the short-circuit current contributed by converter station should be taken into account when the short-circuit fault occurs at the AC-side. In this paper, the characteristic...
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With more and more MMC-HVDC connected to the AC network, the short-circuit current contributed by converter station should be taken into account when the short-circuit fault occurs at the AC-side. In this paper, the characteristics of short-circuit current contributed by MMC are analyzed and a simple and convenient method to calculate the fault current is proposed. Study shows that the characteristics of short-circuit current depend on the control method that MMC adopted. The development of short circuit current can be divided into transient-state and steady-state stage according to whether the controller responds completely or not. Considering the margin of IGBT, current limiters are set both in inner and outer controller. It can limit the bridge arm current and avoid overload. Therefore, AC-side current will change within the limit value. A practical method for the short-circuit current calculation is proposed based on the controllers and limiters. Through this method, both the symmetrical and asymmetrical fault short-circuit current can be calculated after the controllers enters steady state. The analysis in this paper shows that MMC can be equivalent to the current source at steady-state and participate in the calculation of AC system short-circuit. Finally, the accuracy of the proposed method is verified in the PSCAD simulation.
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In view of requirements of high current medium voltage DC circuit breaker for faster opening speed and greater contact pressure in closing position, a fast mechanical switch based on double spring permanent magnet operation and el...
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In view of requirements of high current medium voltage DC circuit breaker for faster opening speed and greater contact pressure in closing position, a fast mechanical switch based on double spring permanent magnet operation and electromagnetic repulsion double-acting mechanism is proposed. The action process of the double acting mechanism involves multi-field coupling of electromagnetic field, temperature field, dynamic field and displacement field. In this paper, based on the finite element method, the multi-physical field coupling calculation is carried out for the fast mechanical switching based on the dual-spring permanent magnet operator and the electromagnetic repulsive double-acting mechanism, and the influence of the input of the driving coil of the permanent magnet operator and the different driving coil currents on the opening process of the switch is analyzed. The simulation results show that the springback phenomenon can be avoided when the driving coil of permanent magnet operating mechanism and the opening coil of electromagnetic repulsion mechanism are put into operation at the same time. Moreover, due to the large electromagnetic repulsion force at the initial opening stage, the input of the driving coil of the permanent magnet operating mechanism has little impact on the initial opening stage. After the electromagnetic repulsion disappears, the greater the current of the driving coil of the permanent magnet operating mechanism in a certain range, the greater the speed when reaching the rated opening distance. Compared with the coil current and stroke curves obtained in the opening process of the actual prototype, they have good consistency, which provides a certain simulation method and theoretical reference for the optimal design of this kind of high current fast mechanical switch.
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In this paper, the mechanism of DC overvoltage is discussed, which caused by block fault in the converter station connected with the active network, and the dynamic process of DC voltage is analyzed in detail according to the equi...
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In this paper, the mechanism of DC overvoltage is discussed, which caused by block fault in the converter station connected with the active network, and the dynamic process of DC voltage is analyzed in detail according to the equivalent circuit and the operating state of sub-module. Moreover, the DC overvoltage caused by the blocking of converter station is studied with the consideration of different blocking time. It is found that the development process of DC overvoltage is independent of fault time, and the virtual overvoltage is generated in steady state mainly contributed by the defect of simulation software that the disconnection of circuit breakers could not be truly reflected in the simulation software. The study of DC overvoltage can provide recommendation for the safety and stability of practical project and the design of insulation grade and protection. Finally a two-terminal MMC-HVDC simulation model built on PSCAD/EMTDC shows the effectiveness of the proposed analysis method.
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摘要 :
In this paper, the mechanism of DC overvoltage is discussed, which caused by block fault in the converter station connected with the active network, and the dynamic process of DC voltage is analyzed in detail according to the equi...
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In this paper, the mechanism of DC overvoltage is discussed, which caused by block fault in the converter station connected with the active network, and the dynamic process of DC voltage is analyzed in detail according to the equivalent circuit and the operating state of sub-module. Moreover, the DC overvoltage caused by the blocking of converter station is studied with the consideration of different blocking time. It is found that the development process of DC overvoltage is independent of fault time, and the virtual overvoltage is generated in steady state mainly contributed by the defect of simulation software that the disconnection of circuit breakers could not be truly reflected in the simulation software. The study of DC overvoltage can provide recommendation for the safety and stability of practical project and the design of insulation grade and protection. Finally a two-terminal MMC-HVDC simulation model built on PSCAD/EMTDC shows the effectiveness of the proposed analysis method.
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Present imaging techniques used in in vitro fertilization (IVF) clinics are unable to produce accurate cell counts in developing embryos past the eight-cell stage. We have developed a method that has produced accurate cell counts ...
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Present imaging techniques used in in vitro fertilization (IVF) clinics are unable to produce accurate cell counts in developing embryos past the eight-cell stage. We have developed a method that has produced accurate cell counts in live mouse embryos ranging from 13-25 cells by combining Differential Interference Contrast (DIC) and Optical Quadrature Microscopy. Optical Quadrature Microscopy is an interferometric imaging modality that measures the amplitude and phase of the signal beam that travels through the embryo. The phase is transformed into an image of optical path length difference, which is used to determine the maximum optical path length deviation of a single cell. DIC microscopy gives distinct cell boundaries for cells within the focal plane when other cells do not lie in the path to the objective. Fitting an ellipse to the boundary of a single cell in the DIC image and combining it with the maximum optical path length deviation of a single cell creates an ellipsoidal model cell of optical path length deviation. Subtracting the model cell from the Optical Quadrature image will either show the optical path length deviation of the culture medium or reveal another cell underneath. Once all the boundaries are used in the DIC image, the subtracted Optical Quadrature image is analyzed to determine the cell boundaries of the remaining cells. The final cell count is produced when no more cells can be subtracted. We have produced exact cell counts on 5 samples, which have been validated by Epi-Fluorescence images of Hoechst stained nuclei.
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摘要 :
Present imaging techniques used in in vitro fertilization (IVF) clinics are unable to produce accurate cell counts in developing embryos past the eight-cell stage. We have developed a method that has produced accurate cell counts ...
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Present imaging techniques used in in vitro fertilization (IVF) clinics are unable to produce accurate cell counts in developing embryos past the eight-cell stage. We have developed a method that has produced accurate cell counts in live mouse embryos ranging from 13-25 cells by combining Differential Interference Contrast (DIC) and Optical Quadrature Microscopy. Optical Quadrature Microscopy is an interferometric imaging modality that measures the amplitude and phase of the signal beam that travels through the embryo. The phase is transformed into an image of optical path length difference, which is used to determine the maximum optical path length deviation of a single cell. DIC microscopy gives distinct cell boundaries for cells within the focal plane when other cells do not lie in the path to the objective. Fitting an ellipse to the boundary of a single cell in the DIC image and combining it with the maximum optical path length deviation of a single cell creates an ellipsoidal model cell of optical path length deviation. Subtracting the model cell from the Optical Quadrature image will either show the optical path length deviation of the culture medium or reveal another cell underneath. Once all the boundaries are used in the DIC image, the subtracted Optical Quadrature image is analyzed to determine the cell boundaries of the remaining cells. The final cell count is produced when no more cells can be subtracted. We have produced exact cell counts on 5 samples, which have been validated by Epi-Fluorescence images of Hoechst stained nuclei.
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摘要 :
Present imaging techniques used in in vitro fertilization (IVF) clinics are unable to produce accurate cell counts in developing embryos past the eight-cell stage. We have developed a method that has produced accurate cell counts ...
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Present imaging techniques used in in vitro fertilization (IVF) clinics are unable to produce accurate cell counts in developing embryos past the eight-cell stage. We have developed a method that has produced accurate cell counts in live mouse embryos ranging from 13-25 cells by combining Differential Interference Contrast (DIC) and Optical Quadrature Microscopy. Optical Quadrature Microscopy is an interferometric imaging modality that measures the amplitude and phase of the signal beam that travels through the embryo. The phase is transformed into an image of optical path length difference, which is used to determine the maximum optical path length deviation of a single cell. DIC microscopy gives distinct cell boundaries for cells within the focal plane when other cells do not lie in the path to the objective. Fitting an ellipse to the boundary of a single cell in the DIC image and combining it with the maximum optical path length deviation of a single cell creates an ellipsoidal model cell of optical path length deviation. Subtracting the model cell from the Optical Quadrature image will either show the optical path length deviation of the culture medium or reveal another cell underneath. Once all the boundaries are used in the DIC image, the subtracted Optical Quadrature image is analyzed to determine the cell boundaries of the remaining cells. The final cell count is produced when no more cells can be subtracted. We have produced exact cell counts on 5 samples, which have been validated by Epi-Fluorescence images of Hoechst stained nuclei.
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The construction of transportation infrastructure is not only the foundation of regional survival and development, but also the important foundation of realizing regional functional orientation and improving regional comprehensive...
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The construction of transportation infrastructure is not only the foundation of regional survival and development, but also the important foundation of realizing regional functional orientation and improving regional comprehensive competitiveness. The rational allocation of traffic land resources requires the prediction of the limit scale of transportation infrastructure. Through the combination of qualitative analysis, quantitative evaluation and empirical research, a theoretical calculation model for predicting the land scale of highway traffic infrastructure construction based on RR-ARIMA coupling model is proposed. Taking Shandong Province as an example, the total limit scale of regional highway traffic infrastructure from 2022 to 2025 is predicted, and it is concluded that the limit scale of highway infrastructure at the end of the 14th five-year plan is 79.99-91.58 ten thousand hectares.
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