114
4 Structure and Mechanism Technology of Lunar Lander
most fundamental and must be considered, and these problems were exactly what
structural analysis could solve. A reasonable design could be determined with structural analysis of different design, comparison of analysis results and comprehensive
consideration of other factors.
Structural design should meet a variety of design requirements or design
constraints. The most fundamental requirement was to meet the requirements of
static characteristics (static strength) and dynamic characteristics of the structure.
Therefore, after the design was completed, a very important issue was how to verify
that the design had met these requirements, i.e. the verification of the structural
design. Verification of structural design was also an integral part of structural design.
Structural analysis was one of the common methods for verification. Compared with
structural tests, structural analysis could be performed without structural hardware,
therefore saved development time and costs. For some issues that were difficult to
conduct ground tests, it was more necessary to solve them through analysis. The
analysis could also guide the test and predict the test results.
The central task of structural analysis was to quantitatively evaluate the mechanical properties of the structure. The most widely used analysis method at present was
the finite element method. The mechanical basis of the finite element method was
the variational principle of elastic-plastic mechanics.
The analysis model was the basis of structural analysis. In structural analysis,
it was crucial to establish a valid model. The model should commonly contain all
the mechanical properties of the structure. In general, the main issues that should
be considered in establishing a structural analysis model (referred to as modeling)
included: idealization of structures, selection of finite element types and division of
cell grids, preparation of cell characteristics, determination of boundary (and initial)
conditions and load conditions, etc., as well as the specific content and accuracy
requirements of analysis. All above issues were not isolated and they were organically
related with each other. Therefore, they must be considered in a unified manner.
There was not much difference between the structural analysis of lunar lander and
general spacecraft. The attention should be paid to additional landing load conditions
(including the corresponding boundary conditions)and the accuracy of the fuel tanks
model.
1. Modal Analysis
The lander modality was an inherent property of the lander instead of the lander
structure. The lander modality was determined by the stiffness of lander structure,
mass distribution and boundary conditions.
The requirements of the lander modality were the basic requirements for structural
design of the lander. Because the lander modality was determined by the stiffness of
lander structure, the modality requirements of the lander were sometimes referred to
as the stiffness requirements of structure. When the lander structure was designed,
at first it was necessary to consider the requirements of the modality. Therefore,
the modal analysis of the lander was one of the important aspects of the structural
analysis as well as basic aspect of structural analysis.
4 Structure and Mechanism Technology of Lunar Lander
most fundamental and must be considered, and these problems were exactly what
structural analysis could solve. A reasonable design could be determined with structural analysis of different design, comparison of analysis results and comprehensive
consideration of other factors.
Structural design should meet a variety of design requirements or design
constraints. The most fundamental requirement was to meet the requirements of
static characteristics (static strength) and dynamic characteristics of the structure.
Therefore, after the design was completed, a very important issue was how to verify
that the design had met these requirements, i.e. the verification of the structural
design. Verification of structural design was also an integral part of structural design.
Structural analysis was one of the common methods for verification. Compared with
structural tests, structural analysis could be performed without structural hardware,
therefore saved development time and costs. For some issues that were difficult to
conduct ground tests, it was more necessary to solve them through analysis. The
analysis could also guide the test and predict the test results.
The central task of structural analysis was to quantitatively evaluate the mechanical properties of the structure. The most widely used analysis method at present was
the finite element method. The mechanical basis of the finite element method was
the variational principle of elastic-plastic mechanics.
The analysis model was the basis of structural analysis. In structural analysis,
it was crucial to establish a valid model. The model should commonly contain all
the mechanical properties of the structure. In general, the main issues that should
be considered in establishing a structural analysis model (referred to as modeling)
included: idealization of structures, selection of finite element types and division of
cell grids, preparation of cell characteristics, determination of boundary (and initial)
conditions and load conditions, etc., as well as the specific content and accuracy
requirements of analysis. All above issues were not isolated and they were organically
related with each other. Therefore, they must be considered in a unified manner.
There was not much difference between the structural analysis of lunar lander and
general spacecraft. The attention should be paid to additional landing load conditions
(including the corresponding boundary conditions)and the accuracy of the fuel tanks
model.
1. Modal Analysis
The lander modality was an inherent property of the lander instead of the lander
structure. The lander modality was determined by the stiffness of lander structure,
mass distribution and boundary conditions.
The requirements of the lander modality were the basic requirements for structural
design of the lander. Because the lander modality was determined by the stiffness of
lander structure, the modality requirements of the lander were sometimes referred to
as the stiffness requirements of structure. When the lander structure was designed,
at first it was necessary to consider the requirements of the modality. Therefore,
the modal analysis of the lander was one of the important aspects of the structural
analysis as well as basic aspect of structural analysis.