Background technology
For realizing lunar surface soft landing detection mission, lunar orbiter system will experience two large processes: flight landing process and the lunar surface course of work.According to current achievement in research, the moon does not have geology activity substantially, so after safe landing, except a small amount of disturbance that each mechanism kinematic of detector system produces, without typical mechanical environment.So the main mechanical environment of detector system is all embodied in flight landing process.Flight landing process can be divided into again carrier rocket transmitter section, month transfer leg, ring month section and four parts of power descending branch.Wherein first three section and conventional satellite, particularly the mechanical environment of ring month explorer satellite experience is basically identical, mainly comprise the mechanical environment that transmitter section is transmitted by carrier rocket, the noise circumstance of endoatmosphere flight, and the detector shock environment that engine ignition produces while becoming rail.
Power descending branch is the distinctive mission phase of soft lunar landing task, and at its latter end, detector can be from the height free-falling of about 4m to moonscape.Can, in landing shock process, detector need to experience a transient impact load, hold out against the key that this mechanical environment is soft landing success.Therefore be necessary just this environment to be made to indication in the schematic design phase, to formulate design and the test condition of equipment.Three kinds of methods of the general employing of indication of mechanical environment: testing method, analog structure extrapolation method and mathematical model prediction method.The method of experimental test just can be carried out after need to waiting until the detector first sample stage, in the schematic design phase, is infeasible.Detector planet landing task still belongs to the first time in China's survey of deep space activity, and the mechanical environment that its landing shock section experiences does not have relevant experience and measured data accumulation, and the method for analog structure extrapolation is also infeasible.Therefore, indicate that its landing shock mechanics environment just need to adopt the method for mathematical model prediction in the detector scheme design phase.
So far, conventional lunar orbiter mathematical model is broadly divided into three classes in the world: Rigid Body Dynamics Model, Rigid-flexible Coupling Dynamics model and nonlinear finite element model.Rigid Body Dynamics Model counting yield is high, but does not consider structural flexibility, shock response that can not actual response detector useful load.Rigid-flexible Coupling Dynamics model cannot be described the elastic-plastic deformation of lunar soil, and the interaction of detector buffer gear and lunar soil depends on experimental formula.Nonlinear finite element model can be good at considering the impact of detector plastic deformation and various non-linear factors, and testing surface adopts the analysis result of nonlinear finite element model to be better than the above two.But among three kinds of models, nonlinear finite element model solution efficiency is minimum, affects designer's work efficiency, therefore how obtaining an accurate and efficient mathematical model becomes one of gordian technique of detector soft landing ballistics environment indication.
Summary of the invention
The object of the invention is must not the shock response of actual response detector useful load for solution problem, a kind of moon detector in flexible landing ballistics environment predicting method based on non linear finite element analysis is proposed, be applicable to the detector scheme design phase.
Technical scheme of the present invention specifically comprises lunar orbiter modeling method and mechanical environment analytical approach: first, set up the nonlinear finite element model of detector lunar surface soft landing, utilize broad sense dynamic condensation method to carry out model reduction to detector, reach the object that improves solution efficiency; Then reduced-order model is carried out to nonlinear finite element and solve, obtain the dynamic response of sounder structure; Obtaining being concerned about after the acceleration responsive of position, adopting the shock response spectrum of recurrence digital filtering method computation structure acceleration responsive, for describing the mechanical environment of detector landing shock; Finally adopt the method for envelope spectrum to obtain greatest hope environment, for formulating design and the test condition of equipment.
A moon detector in flexible landing ballistics environment predicting method, specifically comprises the steps:
Step 1: lunar orbiter is encouraged to prediction, the dynamic response while selecting finite element prediction method prediction detector to land according to the feature of excitation.
Step 2: the method for employing mathematical model prediction is obtained the acceleration responsive of measuring point on detector, and described measuring point is the whole finite element nodes on the plate of cabin.
Step 2.1: set up the dynamic (dynamical) nonlinear finite element model of moon detector in flexible landing.Described nonlinear finite element model comprises centrosome, fuel tank, lunar rover, buffer gear and lunar soil finite element model.
In the present lunar soil material of model non-linear body and buffer gear in the moulding constitutive relation of bullet of padded coaming and the contact relation of buffer gear and lunar soil.
Step 2.2: utilize broad sense dynamic condensation method to carry out model reduction to detector centrosome finite element model.
Step 2.3: to the detector centrosome finite element model loaded load after depression of order, carry out Nonlinear FEM Simulation, obtain the acceleration responsive of all measuring points.
Step 3: ballistics environment when detector is landed is described.The present invention uses the ballistics environment of the shock response profiling detector of acceleration.
Step 3.1: the acceleration responsive that extracts all measuring points on the plate of the same cabin of detector centrosome.
Step 3.2: the acceleration responsive of all measuring points on the plate of same cabin is converted to shock response spectrum with recurrence digital filtering algorithm.
Step 4: determine greatest hope environment (Maximum expected environment, MEE).Greatest hope environment is the upper limit of an expection of detector landing shock mechanics environment, and it can retrain the prediction frequency spectrum of all putting in region, guarantees that any point can seriously not surpass spectral range.In order to guarantee that test can produce a conservative result, the present invention adopts maximum spectrum as greatest hope environment.
Concrete definite method is: on the same cabin of the detector centrosome plate that step 3.2 is obtained, the shock response spectrum of all measuring point acceleration carries out envelope.Then the multiple typical condition running in landing according to detector changes the landing attitude of detector, and operating mode repeating step 2.3 of every change is to step 3.2, obtains under every kind of operating mode the envelope spectrum of the shock response spectrum of all measuring point acceleration on the plate of same cabin.Finally the envelope spectrum of the shock response spectrum of all measuring point acceleration on same cabin plate under above-mentioned all typical conditions is got to envelope again, the greatest hope environment of this cabin plate during as detector landing shock.
Described multiple typical condition comprises that detector lands and lands in horizontal lunar surface and have the landing leg of initial level speed, detector to land and land successively in slope lunar surface in the landing leg of slope lunar surface, detector with symmetric mode in horizontal lunar surface and without initial level speed, detector.
Step 5: formulate the test condition of detector landing shock mechanics environment, for Change In Design and the optimization of useful load on detector provides decision information.The testing standard of the mechanical environment of timing considerations same frequency segment processed, other stage of existing detector (carrier rocket transmitter section, month transfer leg, ring month section).Method is that the mechanical environment condition in other stage is converted to corresponding shock response spectrum, sees the greatest hope environment that whether can cover landing impact section.If can cover, do not need to formulate extra test condition.If can not cover, consider improve original test condition or formulate extra test condition.
Beneficial effect
The present invention utilizes the mathematical model of lunar orbiter to indicate the mechanical environment of its landing shock, can provide the restrictive condition in design for numerous useful load such as the radar on detector, camera, antenna, vector engine, masts in starting stage of lunar orbiter design, do not rely on any test figure, saved product design costs; Before moon detector in flexible landing dynamics is analyzed, adopt the method for broad sense dynamic condensation to carry out model reduction to detector central body model, improved solution efficiency, shortened the product design cycle.
Embodiment
The centrosome top board (panel detector structure finite element model is shown in Fig. 2) of take is example, formulates its ballistics Environment Design and test condition.
Step 1: excitation is predicted, selects the dynamic response of suitable method predict according to the feature of excitation.
For soft lunar landing detector, amplitude limit effect due to Landing Buffer device, the excitation energy acting in detector matrix main structure mainly concentrates on low-frequency range, therefore the dynamic response of detector main structure also concentrates on low-frequency range, according to NASA handbook < < NASA-HDBK-7005 > >, the prediction that can respond by Finite Element Method, i.e. detector soft landing dynamic response is the Transient Dynamics problem of a low frequency.
Step 1.1: the Rigid Body Dynamics Model of setting up the soft landing of lunar orbiter lunar surface.(most conventional rigid dynamics software and the rigid dynamics solver of Nonlinear Finite meta software can be realized, as MSC.ADAMS, Abaqus, HyperWorks etc.Setting up Rigid Body Dynamics Model is in order to improve the speed of solving.)
Step 1.2: solve and obtain the exciting force-time curve of damper leg to detector centrosome.
Step 1.3: the load-time curve in step 1.2 is carried out to Fourier transform, obtain the amplitude-versus-frequency curve (as shown in Figure 3) of exciting force.
Step 1.4: the amplitude-versus-frequency curve that analytical procedure 1.3 obtains, determine the main frequency component of exciting force, scope is [0,500] Hz.This 500Hz is using the mode cutoff frequency during as model reduction for step 2.2.
Step 2: response prediction, adopts the method for mathematical model prediction to obtain the acceleration responsive of measuring point on detector.
Step 2.1: utilize Abaqus software to set up the dynamic (dynamical) nonlinear finite element model of moon detector in flexible landing.
Step 2.2: utilize " broad sense dynamic condensation " method that in Abaqus software, Substructure module provides to carry out model reduction to detector centrosome.
Step 2.2.1: detector centrosome is carried out to free vibration model analysis, obtain the 900th rank model frequency and be about 500Hz.(most business finite element softwares can carry out model analysis, and the present invention utilizes the Linear perturbation analysis module of Abaqus for simplicity)
Step 2.2.2: the cutoff frequency of broad sense dynamic condensation method is got 500Hz, main degree of freedom is got 72 degree of freedom on 12 nodes that damper leg is connected with centrosome.In the Substructure of Abaqus software module, centrosome is carried out to dynamic condensation, then assemble with Nonlinear Free degree (snubber assembly and lunar soil).
Step 2.3: utilize Abaqus/Standard solver to carry out Nonlinear FEM Simulation to detector with 5 kinds of typical conditions of different attitude soft landings, wherein moon acceleration is got 1.63m/s
2.
Step 3: mechanical environment is described, ballistics environment is described by the frequency spectrum of certain type conventionally, China GB GB2423, IEC68-2-27 and IEC721-3, American army mark MIL-STD-810D and the mark DEF STAN07-55 of the British army require to adopt acceleration as test data.So use the ballistics environment of the shock response profiling detector of acceleration in the present invention, shock response spectrum principle as shown in Figure 4.
Step 3.1: the acceleration responsive that extracts all finite element nodes on centrosome top board.
Step 3.2: the acceleration responsive of all nodes on top board is converted to shock response spectrum with recurrence digital filtering algorithm.(amplification factor Q gets 10)
Step 4: the determining of greatest hope environment (Maximum expected environment, MEE).Greatest hope environment is the upper limit of an expection of detector landing shock mechanics environment, and it can retrain the prediction frequency spectrum of all putting in region, guarantees that any point can seriously not surpass spectral range.In order to guarantee that test can produce a conservative result, the present invention has adopted maximum spectrum as greatest hope environment.
Step 4.1: respectively under 5 kinds of typical conditions to centrosome top board on the acceleration shock response spectrum of all nodes carry out envelope, corresponding 1 envelope spectrum of every 1 operating mode.
Described 5 kinds of typical conditions are respectively:
Operating mode 1 detector lands in horizontal lunar surface, and detector is without initial level speed.
Operating mode 2 detectors land in horizontal lunar surface, and detector has the initial level speed of 1m/s.
Operating mode 3 detectors are so that " 2-2 " land in 15 ° of slope lunar surfaces, has 2 to land in lunar surface in 4 of detector foot pads, and then all the other 2 are landed in lunar surface again by symmetrical mode simultaneously simultaneously.
Operating mode 4 detectors land in 15 ° of slope lunar surfaces in " 1-2-1 " symmetrical mode, in 4 of detector foot pads, have at first 1 to land in lunar surface, and then other 2 foot pads land in lunar surface simultaneously, and remaining 1 is finally landed in lunar surface.
Operating mode 5 detectors land in 15 ° of slope lunar surfaces in the mode of " 1-2-3-4 ", and 4 of detector sufficient pads successively (during difference) are landed in lunar surface.
Step 4.2: to the envelope again of 5 envelope spectrums in step 4.1, as the greatest hope environment of centrosome top board.The envelope again of 5 kinds of envelope spectrums as shown in Figure 5.
Step 5: formulate design and test condition.During formulation, can take into full account the testing standard of other stage mechanical environment of the existing detector of same frequency segment, for example, deliver sinusoidal vibration (as shown in table 1) and the random vibration mechanical environment condition (as shown in table 2) of launching phase.Method is that the mechanical environment condition in other stage is converted to corresponding shock response spectrum, sees the greatest hope environment that whether can cover landing impact section.If can cover, do not need to formulate extra test condition.If can not cover, consider improve original test condition or formulate extra test condition.
Step 5.1: the centrosome top board shock response spectrum comparison that sinusoidal vibration environment is equivalent to acceleration shock response spectrum and obtains with step 4.2.The sinusoidal vibration environment of centrosome top board is provided by table 1.Equivalent method is as follows:
In little damping situation, when excitation frequency equals the natural frequency of the system that is energized, acceleration responsive can be determined by following formula
In formula,
the maximum absolute acceleration response of system,
excitation acceleration peak value,
(ξ is damping ratio), N is the sinusoidal excitation cycle, when N is enough large, has
The input amplitude (shown in table 1) of supposing the sinusoidal excitation in regulation frequency range is
, according to formula, the shock environment spectrum value of its equivalence is
if get Q=10, the centrosome top board shock response spectrum being obtained by acceleration shock response spectrum and the step 4.2 of table 1 equivalence more as shown in Figure 6.As seen from the figure, in 0~100Hz frequency range, sinusoidal vibration environment has covered the landing shock environment of centrosome top board completely.
Step 5.2: the centrosome top board shock response spectrum comparison that random vibration environment is equivalent to acceleration shock response spectrum and obtains with step 4.2.The sinusoidal vibration environment of centrosome top board is provided by table 2.Equivalent method is as follows:
The input amplitude (as shown in table 2) of supposing the arbitrary excitation in regulation frequency range is G (f), and the shock environment spectrum value of its equivalence is
In formula, f is frequency (Hz of unit), if get Q=10, the centrosome top board shock response spectrum being obtained by acceleration shock response spectrum and the step 4.2 of table 2 equivalence more as shown in Figure 7.As seen from the figure, in the frequency range more than 100Hz, random vibration environment has covered the landing shock environment of centrosome top board.
Step 5.3: because sinusoidal vibration environment in 5Hz~100Hz has covered the landing shock environment of centrosome top board completely, 100Hz has covered the landing shock environment of centrosome top board with random vibration environment in super band, so do not need to formulate extra test condition for centrosome top board.
Table 1 sine vibration test condition
Table 2 random vibration test condition