• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.8 s.239
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• pp.934-939
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• 2005

Starting pressure of a supersonic ejector with a second-throat was investigated. In case of mixing chamber length longer than a critical length, starting pressure is in proportion to length of the mixing chamber. In this study, we assumed that the ejector starts when the primary supersonic flow reaches inlet of the second-throat and the distance of the supersonic flow traveling can be expressed by multiplying an empirical factor to the first diamond shock length of overexpanded flow. To calculate the overexpanded supersonic flow, a mixing model was employed to compute secondary flow pressure and the result was applied to back pressure condition of overexpanded flow calculation. In the result, for three cases of primary nozzle area ratio, we could get accurate model of predicting the starting pressure by selecting a suitable empirical factors around 3.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2642-2647
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• 2008

Starting characteristics of the axi-symmetric supersonic exhaust diffuser(SED) with a second throat are numerically investigated. Main purpose of this study is to predict theoretical starting pressure of STED using 1-D normal shock theory and to present the range of optimum starting pressure through parametric study with essential design parameters of STED influencing on starting performance. Renolds-Average Navier-Stokes equations with a standard ${\kappa}-{\varepsilon}$ turbulence model incorporated with standard wall function are solved to simulate the diffusing evolutions of the nozzle plume. Minimum(optimum) starting pressure difference of $20{\sim}25%$ between 1-D theory and experimental evidences validated from previous results[5] is also applied to predict those in this system. The analysis results indicate that dominant parameters for diffuser starting in this system is diffuser expansion ratio($A_d/A_t$), which has optimum value 120 and second throat area ratio($A_d/A_{st}$), which has optimum range $3.3{\sim}3.5$.

• International Journal of Aeronautical and Space Sciences
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• v.9 no.2
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• pp.98-106
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• 2008

The motive gas of a supersonic ejector is supplied from different sources depending on the application. The performance of an ejector that is represented by the secondary flow pressure, starting and unstarting pressures heavily depends on the molecular properties of the motive gas. The effects of specific heat ratio of the motive gas were investigated experimentally for an axi-symmetric annular injection type supersonic ejector. Both the starting pressure and unstarting pressure, however, decreased with the increase of the specific heat ratio of the motive gas. It was discovered that the secondary flow pressure increased as the specific heat ratio of the motive gas decreased even if the stagnation pressure of the motive flow was invariant. However, when the motive gas flow nozzle area ratio is large enough for the motive gas to be condensed, different tendency was observed.

• Earthquakes and Structures
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• v.26 no.2
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• pp.97-115
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• 2024

In this paper, a database consisting of the dynamic shear modulus ratio and damping ratio test data of clay obtained from 406 groups of triaxial tests is constructed with the starting area of Xiong'an New Area as the research background. The aim is to study the nonlinear dynamic properties of clay in this area under cyclic loading. The study found that the effective confining pressure and plasticity index have certain influences on the dynamic shear modulus ratio and damping ratio of clay in this area. Through data analysis, it was found that there was a certain correlation between effective confining pressure and plasticity index and dynamic shear modulus ratio and damping ratio, with fitting degree values greater than 0.1263 for both. However, other physical indices such as the void ratio, natural density, water content and specific gravity have only a small effect on the dynamic shear modulus ratio and the damping ratio, with fitting degree values of less than 0.1 for all of them. This indicates that it is important to consider the influence of effective confining pressure and plasticity index when studying the nonlinear dynamic properties of clays in this area. Based on the above, prediction models for the dynamic shear modulus ratio and damping ratio in this area were constructed separately. The results showed that the model that considered the combined effect of effective confining pressure and plasticity index performed best. The predicted dynamic shear modulus ratio and damping ratio closely matched the actual curves, with approximately 88% of the data falling within ±1.3 times the measured dynamic shear modulus ratio and approximately 85.1% of the data falling within ±1.3 times the measured damping ratio. In contrast, the prediction models that considered only a single influence deviated from the actual values, particularly the model that considered only the plasticity index, which predicted the dynamic shear modulus ratio and the damping ratio within a small distribution range close to the average of the test values. When compared with existing prediction models, it was found that the predicted dynamic shear modulus ratio in this paper was slightly higher, which was due to the overall hardness of the clay in this area, leading to a slightly higher determination of the dynamic shear modulus ratio by the prediction model. Finally, for the dynamic shear modulus ratio and damping ratio of the engineering site in the starting area of Xiong'an New Area, we confirm that the prediction formulas established in this paper have high reliability and provide the applicable range of the prediction model.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.10a
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• pp.6-10
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• 2003

Accurate description of starting transient history allows and justifies the use of small margin of safety for the engine parts, resulting in high motor mass ratio in addition to satisfying the control and guidance requirements of the vehicle. Studies have been carried out for the prediction and reduction of ignition peak and pressure-rise rate during the starting transient of solid rocket motors. Numerical studies have been carried out using a two dimensional Navier-Stokes solver. It has been inferred through the parametric studies that, in the case of solid rocket motors with uniform port, high ignition peak is observed at high spread rate and low pressure-rise rate. In the case of the port with sudden expansion configuration, high ignition peak is observed at relatively high average spread rate and high-pressure rise rate. These studies are expected to aid the designer in reducing the ignition peak by altering the propellant properties or igniter characteristics without sacrificing the motor performance.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.9
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• pp.563-570
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• 2017

Experimental and numerical studies were performed to investigate the performance and internal flow characteristics of a supersonic second throat exhaust diffuser (STED) with back pressure ($P_a$). An ejector system was used to vary the back pressure ($P_a$) conditions. The operating gas for the STED and the ejector was high pressure nitrogen at room temperature. When the back pressure ($P_a$) at a constant nozzle inlet pressure $P_0$) decreases, the pressure recovery location moves downstream. If the pressure ratio $P_0/P_a$) is the same, even if the nozzle inlet pressures $P_0$) are different, the diffuser's internal flow pattern and starting pressure ratio ($(P_0/P_a)_{st}$) are almost the same.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.49-53
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• 2003

In this study, the geometric design parameters of ejector system were investigated. The critical parameters were primary nozzle area ratio, 2nd-throat cross sectional area and 2nd-throat L/D ratio. At every geometry cases, primary pressure and secondary pressure were measured simultaneously according to secondary mass flow rate. From the results, the ejector starting pressure, unstarting pressure and minimum secondary flow pressure were found and we got the effect of geometric parameters to ejector performance and the way to optimal design of ejector system for chemical lasers operating. Also the experiments of changing secondary flow temperature were carried out.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.2
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• pp.70-77
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• 2005

An axisymmetric supersonic ejector equipped with a converging-diverging diffuser was built and pressure at various locations along the ejector-diffuser system was recorded with emphasis on the supersonic starting of the secondary flow. In order to find the effects of the opening size of the secondary flow, a number of openings were used with a constant primary pressure. Supersonic starting was possible only for d/D, the ratio of the opening diameter and the diffuser throat diameter, less than 0.306. for larger values of d/D, the ejection begins at subsonic secondary flow condition. With the closure of the opening, the primary flow brings the normal shock downstream of the converging-diverging diffuser And the starting of the ejector continues even after the closure was removed.

• Journal of the Korean Ceramic Society
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• v.39 no.3
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• pp.217-221
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• 2002

Si and ${\alpha}-Si_3N_4$ powder mixtures added with 3 wt% $Y_2O_3$ were reacted under 5 MPa nitrogen pressure. The reaction products contained ${\alpha}-Si_3N_4$ particles with elongated shapes. Length and width of the elongated grains were the maximum when the starting powder mixture of 50 wt% Si - 47 wt% ${\alpha}-Si_3N_4$ and 3 wt% $Y_2O_3$ was used. Aspect ratio of the elongated grains were between 4.4 and 5. When the starting powder mixture contained 70 wt% Si, large particles with irregular shapes appeared. Meanwhile, the reaction did not proceed when the starting powder mixture contained 30 wt% Si and less. The SHS product was easy to crush and the elongated particles obtained from the starting powder mixtures of 40 wt% Si - 57 wt% ${\alpha}-Si_3N_4$ - 3 wt% $Y_2O_3$ and 50 wt% Si - 47 wt% ${\alpha}-Si_3N_4$ - 3 wt% $Y_2O_3$ were good candidates for the seeds.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.299-304
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• 2008

Starting characteristics of the axi-symmetric second throat exhaust diffuser (STED) with zero-secondary flows are numerically investigated. Renolds-Average Navier-Stokes equations with a standard ${\kappa}-{\varepsilon}$ turbulence model incorporated with enhanced wall treatment are solved to simulate the diffusing evolutions of the nozzle plume. Minimum (optimum) starting pressure difference of 20$\sim$25% between 1-D theory and the measured data validated from previous results[5] is also applied to predict the range of an effective diffuser expansion ratio (Ad/At) in this system.