4.3 Design and Verification of Lunar Lander Structure
119
The modal superposition method was usually used in frequency response analysis.
The selection of frequency range should be determined according to the frequency
range of forced excitation, at least all modes in the range of forced excitation
frequency should be included. In ordered to improve the accuracy of analysis, the
frequency range of modal truncation shall be broadened furthermore.
The selection of modal damping was generally determined based on past test data
or empirical data, which had an important impact on the analysis results. Due to
the complex mechanism of damping, there was a large error in the measurement of
damping in the test, and there was no other analysis method to make up the shortage
of the test. Therefore, the modal damping issue had been puzzling the improvement
of the analysis accuracy. The modal damping of structures with different magnitudes
of sinusoidal vibration was also different, and generally increases with the increase
of excitation leveled.
In the analysis of frequency response, for acceleration analysis and load analysis,
the model was the same as that used in modal analysis. For stressed analysis, issues
that should be considered in the analysis model were similar to that in static analysis,
and the element mesh was refined in the area with the stressed concentration. Therefore, the frequency response analysis model integrated the characteristics of modal
analysis and static analysis.
4.3.3 Structural Tests of Lunar Lander
Structural tests are generally used to verify that structural products meet design
requirements during and after the relative environment, and are the primary methods
for structural design validation, and are also the most effective and direct methods.
There were four types of tests for verification of structural design requirements:
development test, qualification test, acceptance test and validation test.
The purpose of the development test is to demonstrate the design scheme and
obtain the necessary information for design. For structural design, the strength test
of local structure is usually carried out. Development tests are usually carried out at
the early stage of phase A to phase C.
The purpose of the qualification test is to verify whether the design is reasonable
and meet the requirements. The experimental magnitude is 1.3~1.5 times of the
maximum load, and the qualification test is usually carried out at phase C.
The purpose of the acceptance test is to check the defects of materials, processes
and so on, so as to verify the adaptability of the hardware. The acceptance test is
mainly to verify the tested hardware, not to verify the design, and the operation load
is generally used. Normally, the acceptance test of the structure is not carried out
alone, but with the acceptance test of the whole probe.
The purpose of validation test is to confirm the validity of the analysis and provide
test data to confirm the key analysis, or to modify the analysis model. The validity
confirmation test has no damage to the tested hardware. Stiffness test and modal test
are typical validation tests.
119
The modal superposition method was usually used in frequency response analysis.
The selection of frequency range should be determined according to the frequency
range of forced excitation, at least all modes in the range of forced excitation
frequency should be included. In ordered to improve the accuracy of analysis, the
frequency range of modal truncation shall be broadened furthermore.
The selection of modal damping was generally determined based on past test data
or empirical data, which had an important impact on the analysis results. Due to
the complex mechanism of damping, there was a large error in the measurement of
damping in the test, and there was no other analysis method to make up the shortage
of the test. Therefore, the modal damping issue had been puzzling the improvement
of the analysis accuracy. The modal damping of structures with different magnitudes
of sinusoidal vibration was also different, and generally increases with the increase
of excitation leveled.
In the analysis of frequency response, for acceleration analysis and load analysis,
the model was the same as that used in modal analysis. For stressed analysis, issues
that should be considered in the analysis model were similar to that in static analysis,
and the element mesh was refined in the area with the stressed concentration. Therefore, the frequency response analysis model integrated the characteristics of modal
analysis and static analysis.
4.3.3 Structural Tests of Lunar Lander
Structural tests are generally used to verify that structural products meet design
requirements during and after the relative environment, and are the primary methods
for structural design validation, and are also the most effective and direct methods.
There were four types of tests for verification of structural design requirements:
development test, qualification test, acceptance test and validation test.
The purpose of the development test is to demonstrate the design scheme and
obtain the necessary information for design. For structural design, the strength test
of local structure is usually carried out. Development tests are usually carried out at
the early stage of phase A to phase C.
The purpose of the qualification test is to verify whether the design is reasonable
and meet the requirements. The experimental magnitude is 1.3~1.5 times of the
maximum load, and the qualification test is usually carried out at phase C.
The purpose of the acceptance test is to check the defects of materials, processes
and so on, so as to verify the adaptability of the hardware. The acceptance test is
mainly to verify the tested hardware, not to verify the design, and the operation load
is generally used. Normally, the acceptance test of the structure is not carried out
alone, but with the acceptance test of the whole probe.
The purpose of validation test is to confirm the validity of the analysis and provide
test data to confirm the key analysis, or to modify the analysis model. The validity
confirmation test has no damage to the tested hardware. Stiffness test and modal test
are typical validation tests.