• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.1
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• pp.42-49
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• 2015

The pressure oscillation induced by inhibitor in a solid rocket motor has been investigated by 3D large eddy simulation(LES) and proper orthogonal decomposition(POD). The vortex generation and breakdown at inhibitor are periodically observed between the inhibitor and the nozzle by flow-acoustic coupling mechanism. The excitation of pressure oscillation occurs as the flow impinges on the submerged nozzle head which recirculate in the cavity in rear dome of the motor chamber. The vortex generation frequency is closely related with the shedding frequencies of the detached vorticities at the inhibiter, which fairly compared with the experimental data.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.6
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• pp.45-52
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• 2020

In this paper, a subminiature solid rocket motor(SSRM) was designed to develop a miniature smart-bullet and the designed propellant grain was made of thermoplastic propellant for production convenience of inner shape. The internal ballistics analysis and ground test were performed to investigate the performance of SSRM. And a numerical simulation was carried out to obtain basic data on the design of safety distance between the nozzle outlet and a gunner, the temperature distribution of exhaust gas was analyzed by comparing a numerical simulation and the results of IR camera.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.6
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• pp.635-642
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• 2014

In this paper, an efficient technique is developed to predict failure probability of three failure modes(case rupture, fracture and bolt breakage) related to solid rocket motor case due to the inner pressure during the mission flight. The overall procedure consists of the steps: 1) design parameters affecting the case failure are identified and their uncertainties are modelled by probability distribution, 2) combustion analysis in the interior of the case is carried out to obtain maximum expected operating pressure(MEOP), 3) stress and other structural performances are evaluated by finite element analysis(FEA), and 4) failure probabilities are calculated for the above mentioned failure modes. Axi-symmetric assumption for FEA is employed for simplification while contact between bolted joint is accounted for. Efficient procedure is developed to evaluate failure probability which consists of finding first an Most Probable Failure Point(MPP) using First-Order Reliability Method(FORM), next making a response surface model around the MPP using Latin Hypercube Sampling(LHS), and finally calculating failure probability by employing Importance Sampling.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.11
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• pp.1055-1064
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• 2017

Since a device such as a rocket motor requires very high reliability, a reasonable reliability design process is essential. However, Korea has implemented a design method for applying a safety factor to each component. In classic reliability analysis, input variables such as mean and standard deviation, used in the limit state function, are treated as deterministic values. Because the mean and standard deviation are determined by a small amount of data, this approach could lead to inaccurate results. In this study, reliability analysis is performed for bolted joints and o-ring seals, and the Bayesian approach is used to statistically estimate the input variables. The estimated variables and failure probability, calculated by the reliability analysis, are derived in the form of probability distributions.

• Aerospace Engineering and Technology
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• v.13 no.1
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• pp.129-141
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• 2014

Since 2006, an annual rocket competition for university students in America has been held by management of NASA to support the Space Launch System. This paper describes the significance and operational aspects of NASA Student Launch, a rocket competition for university students organized by NASA Marshall Center's Academic Affairs Office, to inspire students to pursue education and careers in science, technology, engineering, or mathematics (STEM) fields, which is Furthermore, It describes briefly activities of Korean national rocket competition for university students.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.232-235
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• 2011

A typical unsteady internal ballistic analysis model was developed to take account the erosive burning of a solid rocket motor. The variance of local velocity and pressure along grain surface were analyzed by using the continuity and momentum equation. The coefficients of erosive burning were drew from comparing experiment data with analysis. It was investigated that the grain shapes of propellant affect the erosive burning.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.31-37
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• 2011

Detail flow structure in a large solid rocket motor with two inhibitors has been investigated using 3D Large Eddy Simulation and Proper Orthogonal Decomposition(POD) analysis. Vortex shedding frequencies periodically occurred by inhibitors are coupled with flow acoustics induced by the impinging of vorticity on nozzle head. As a result of 3D analysis, it was observed that the nozzle exit flow causes roll-torques from the vortex being decomposed in unbalanced shape for the impinging of vorticity on the nozzle head.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.253-257
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• 2011

Vortex generation mechanism by inhibitor in a solid rocket motor have been investigated by 3D Large Eddy Simulation turbulent model. Most of the result of the present study are in good agreement with experimental data and previous numerical calculation. Vortex generation and breakdown behind inhibitor are periodically observed between inhibitor and nozzle head by flow-acoustic coupling mechanism. Vortex generation frequency is the same as the second-mode frequency in the motor. The roll shape vortex generation behind inhibitor induces non-uniform flow field at the nozzle entrance and its throat.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.233-236
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• 2009

In this study, the characteristic of the hybrid rocket motor with $LN_2O$(Liquid Nitrous oxide) was investigated experimentally. HDPE(High Density PolyEthlene) was used as fuel with different sized single port. When used $LN_2O$, combustion efficiency is lower than using $GN_2O$(Gas Nitrous oxide), because of completeness of vaporization of droplet and mixing. And regression rate was changed by different oxidizer phase. This behavior was considered that flame temperature and combustion of solid fuel front/end surface.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.1
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• pp.29-36
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• 2014

Hybrid rocket displays many different low frequency pressure oscillations during combustion. Thermal lag between solid and gas phase is the primary mechanism to trigger low frequency pressure oscillations of around 10Hz, and Helmholtz or $L^*$ mode also produces other types of low frequency oscillations above 10 Hz which is associated with the change in combustion volume. Since the flow characteristics in hybrid rocket is very similar to those in solid rocket combustion, it is not surprising to observe similar pressure oscillation behaviors. Experimental test shows that combustion pressure suddenly turns into to a big amplitude oscillation around 10Hz then followed by returning to an original pressure level after a short period combustion. Further investigations show that this instability is independent of the change in O/F ratio at all. One of the possible candidates is the vortex shedding dynamics over the backward step in the post combustion chamber. It is required to investigate the low frequency oscillation mechanism in the future study.