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Abstract
In this research, modal tests and analyses are performed for a simplified and scaled first-stage model of a space launch vehicle using liquid propellant. This study aims to establish finite element modeling techniques for computational modal analyses by considering the liquid propellant and flange joints of launch vehicles. The modal tests measure the natural frequencies and mode shapes in the first and second lateral bending modes. As the liquid filling ratio increases, the measured frequencies decrease. In addition, as the number of flange joints increases, the measured natural frequencies increase. Computational modal analyses using the finite element method are conducted. The liquid is modeled by the virtual mass method, and the flange joints are modeled using one-dimensional spring elements along with the node-to-node connection. Comparison of the modal test results and predicted natural frequencies shows good or moderate agreement. The correlation between the modal tests and analyses establishes finite element modeling techniques for modeling the liquid propellant and flange joints of space launch vehicles.
Highlights
Liquid propulsion launch vehicles are widely used because of their high specific impulse and easy control of thrust, despite their drawbacks such as combustion instability, complicated structure, and high production cost
The natural frequencies of space launch vehicles using liquid propellant change during flight because liquid propellant is rapidly consumed. This change in natural frequencies has a significant influence on the dynamics, loads, and vibration characteristics of launch vehicles
Modal tests are usually used to investigate the modal characteristics of launch vehicles, but they are inefficient in terms of time and manpower
Summary
Liquid propulsion launch vehicles are widely used because of their high specific impulse and easy control of thrust, despite their drawbacks such as combustion instability, complicated structure, and high production cost. The natural frequencies of space launch vehicles using liquid propellant change during flight because liquid propellant is rapidly consumed. This change in natural frequencies has a significant influence on the dynamics, loads, and vibration characteristics of launch vehicles. Modal tests are usually used to investigate the modal characteristics (natural frequencies and mode shapes) of launch vehicles, but they are inefficient in terms of time and manpower. Computational modal analyses using an advanced finite element (FE) method have been used to replace or assist modal tests for launch vehicles. It is not easy to establish the FE modeling techniques for the computational modal analysis of space launch vehicles that contain liquid propellant
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