The sloshing test system consists of excitation, support, lifting system, test tank, liquid filling and discharge system, measurement system and other subsystems. The push-pull equipment adopts a mechanical eccentric part with a frequency of 0 ~ 5Hz and a thrust of 10kN. The transmission device connects the test piece with the push-pull equipment, including clutch and braking devices. The supporting device can be used for the installation, lifting, weighing and turnover of the test tank. A small water pump is used to fill and discharge liquid in the tank. The filling liquid capacity for various filling ratio are calibrated by a load cell. Displacement measurement is performed by laser displacement sensor. Π type sensor is used to measurement the sloshing force and moment, as shown in Fig. 4.
The test system is shown in Fig. 5. The test supporting device with a height of 4 meters is set up and hanged with 4 pull rods which connects the load cell in the middle of the pull rod to measure the liquid filling ratio of the tank. The rectangular structure is a supporting beam, which is arranged along the sloshing direction. The spacing for the rectangular structure can be adjusted. Π Type sensors are installed in the middle of the beam and used to fix the test tank. When the test tank is installed vertically, the liquid sloshing direction is horizontal (X direction), as shown in Fig. 5. When the tank is installed horizontally (θ = 0), the horizontal sloshing of the liquid is in the X direction and the longitudinal direction is in the Z direction. The front cross beam of rectangular structure is connected with the driving rod of the push-pull equipment to transmit the horizontal movement, and the clutch braking device is connected in series in the middle of the driving rod. The rear cross beam of the rectangular structure is connected with the laser displacement sensor to measure the horizontal movement of the test tank. Since the tank is an axial symmetrical structure, the sloshing results in X and Y directions are consistent.
The installation and excitation application direction of sloshing test are shown in Fig. 6.
Sloshing tests of the tank were carried out at the condition of constant ground gravity (1go). Liquid sloshing parameters of the tank required for the design of attitude and orbit control system during launch, satellite apogee orbit change and position maintenance are obtained, including sloshing frequency, sloshing mass and sloshing damping at various working conditions. The above data are transformed into an equivalent pendulum model and the corresponding parameters are obtained. The sloshing force and sloshing torque can be tested by Π type sensors. The other parameters are fitted by free attenuation test and forced sloshing test. The free attenuation test is to obtain the sloshing frequency, sloshing center of mass height and sloshing damping value. The forced sloshing test can obtain the sloshing mass and the total mass centroid height. The height sloshing center of mass height is the distance from the center of mass to the bottom of the tank.
Experimental information for sloshing test is shown in Table 1.
Table 1
No.
|
Experimental subject
|
Installation direction
|
Excitation direction
|
Test methods
|
Number of experiments
|
1
|
Tank without PMD
|
vertical
|
X
|
forced sloshing test
|
24
|
3
|
Tank with PMD
|
horizontal
|
X
|
forced sloshing test
|
104
|
resonance attenuation sloshing test
|
78
|
4
|
horizontal
|
Z
|
forced sloshing test
|
32
|
resonance attenuation sloshing test
|
24
|
5
|
X
|
forced sloshing test
|
32
|
resonance attenuation sloshing test
|
24
|
During the forced sloshing test, the positioning displacement excitation was adopted. The sloshing equipment was started, and the vibration frequency was adjusted. After the movement was stable, the time history of sloshing displacement, force and torque of the test tank was recorded. More than 50 vibration cycles were recorded for each test. According to the recorded time history data, the amplitude, phase and frequency of displacement, force and torque could be calculated. The value of frequency response function could be estimated. After changing the vibration frequency, the recording process was repeated until tests of all frequencies were completed. The test frequency shall covered 0.5 ~ 2 times the first-order sloshing frequency.
During the resonance attenuation sloshing test, the vibration frequency of the sloshing equipment was set up with the liquid resonance frequency. The rectangular structure was lock after the sloshing amplitude reached a certain range. the time history data of the sloshing force was recorded to calculate the sloshing damping coefficient and sloshing frequency. Each test repeated for 6 ~ 8 times.
The appropriate test medium for liquid sloshing test is selected according to the analysis of similarity criteria and similar conditions. In order to simulate the conditions of launch, satellite apogee ignition and position maintenance, the sloshing tests of the tank in X, Y and Z directions were performed. The acceleration generated by satellite remote ignition was about 0.06 ~ 0.12m/s2, and the acceleration under east-west and North-South maintenance conditions was about 0.0045 ~ 0.009m/s2.
In order to reduce the measurement error caused by temperature change, it was required to measure the specific gravity of the test medium (ρ) and viscosity coefficient (ν). The Galileo number of the test medium before each test should be calibrated. According to the requirements of similar criteria, the mixture of 60% glycerol and water was used as the test liquid.
Liquid sloshing test was carried out under 14 working conditions of liquid filling ratio. As shown in Table 2, tests with selected working conditions were carried out under the vertical installation state and horizontal installation state of the test tank. Weights of liquid in tank under different liquid filling ratios are shown in Table 2.
Table 2
Weights of liquid in tank under different liquid filling ratios
No.
|
Filling ratio
|
Propellant weight of fuel tank
(kg)
|
Propellant weight of oxidant tank
(kg)
|
1.
|
0.95
|
731.33
|
1209.05
|
2.
|
0.90
|
692.84
|
1145.42
|
3.
|
0.85
|
654.35
|
1081.78
|
4.
|
0.77
|
592.77
|
979.97
|
5.
|
0.75
|
577.36
|
954.51
|
6.
|
0.70
|
538.87
|
890.88
|
7.
|
0.65
|
500.39
|
827.24
|
8.
|
0.60
|
461.90
|
763.61
|
9.
|
0.45
|
346.42
|
572.71
|
10.
|
0.30
|
230.95
|
381.80
|
11.
|
0.25
|
192.46
|
318.17
|
12.
|
0.20
|
153.96
|
254.54
|
13.
|
0.15
|
115.47
|
190.90
|
14.
|
0.10
|
76.98
|
127.27
|