Onboard Monitoring Technique For Detection Of Impact On Manned Pressurized Cabin By Space Debris

The increasing of space debris pose a serious threat to the spacecraft, particularly with the rapid development of our spacecraft industry, promotes a need for onboard monitoring technique. At present, the application prospect of AE onboard monitoring technique such as real-time senses, location and damage identification, has been confirmed by the studying of single projectile impact flat panel AE events. But there are ribs, welds and bulks disturbed on the surface of manned pressurized cabin, that cause the AE signal and its propagation property complicated. Firstly, secondary debris cloud produced by space debris penetrates the shielding panel impact the module wall will create a mount of punctate AE source. Secondly, the monitoring system also pick up the shielding panel AE signal propagate into the module wall through the braced columns. Lastly, the protrusions on module wall will induce scattering phenomenon that affect the waveform and the attenuation characteristic of AE signals. complex structure of manned pressurized cabin bring difficulty to the engineering applications of AE onboard monitoring technique, especially the damage identification function.This thesis take a typical pressured cabin as research object, has made thorough research to the time sequence characteristic of secondary debris cloud AE source, the attenuation characteristic of the signals propagate in the module wall and the signal coupling phenomenon induced by braced columns. AE sensors arrangement has been made, key technology such as debris cloud AE source location method and impact damage identification has been broken through, establish a technical foundation for the engineering applications of AE onboard monitoring technique. The main contents, novel techniques and original theoretical contributions of this thesis are presented as follows:Firstly, concepts of most fast point and most fast ring were proposed, time sequence characteristic function was established and the virtual wave front method was introduced to solve the debris cloud impact location problem. Based on the movement characteristics of debris cloud, the impact sequence of the particles and the propagation sequence characteristics of the signals emitted by punctate AE sources have been analyzed, then a time sequence characteristic function was established, and a concept of most fast point was proposed for representing debris cloud AE source. By study the relative position of impact center, most fast point and sensor, a concept of most fast ring was proposed. Furthermore, the virtual wave front method was introduced to solve the debris cloud impact location problem. The anisotropic wave velocity will cause the location result deviate from the impact center, to verify the feasibility of the location method, the concept of most fast point was used to presented the AE source, time sequence characteristic function was used to calculate the arrival time, virtual wave front method was used to calculate the impact position, the result indicated that the relative location error less than 0.13%, the virtual wave front method could solve the location problem of secondary debris cloud impact module wall.Secondly, numerical simulation was adopted to study the effect of the protrusions on the attenuation characteristic of hypervelocity impact(HVI) AE signals, an attenuation ratio function for primary wave first valley amplitude was established, the attenuation characteristic of HVI AE signals in module wall was obtained. AE signals induced by projectile impact flat and stiffened panel were obtained through a series numerical simulations, the effect of the protrusions on the waveform were studied by comparing the waveform of the 2 different kind signals, the results indicated that the waveform of AE signals in the module wall could be divided into 2 parts, primary wave(P wave) and secondary wave(S wave). To quantitatively describe the attenuation characteristic of P wave, a concept of decay ratio of the 1st valley amplitude(DRA) was proposed, then DRA was used to study the effect of protrusions on the attenuation characteristic, the results indicated that the decay ratio mainly related to the size and number of protrusions, the signal propagation distance and direction, an attenuation ratio function for P wave was established based on this basis, and proved the validity of the attenuation ratio function through testing. AE source location experiment was carried out on the typical pressured cabin with a electrical imitation gun for a qualitative investigation on the attenuation characteristic of S wave, the results indicates that use a isosceles triangle array(base 3200 mm, height 2000mm) arrival time with certain precision of each channel signal can be obtained, the location error would be less than 95.2mm.Thirdly, HVI experiments were carried out to study the propagation characteristic of AE signal in Whipple shield structure, the result indicates that put the sensors inside non-coupling area can avoid the shield/module-wall AE waveform coupling problem. HVI experiments against dual-wall structure were performed, AE signal induced by projectile impact front panel were recorded and wavelet transform was used to identify the mode characteristic of the recorded signals, the results suggest that the braced columns act like a geometric filter, and AE signals pass through the braced columns into the back panel would completely convert to A0 mode wave. Based on the result, a prediction function for arrival time interval between signals from the front and back panel was established, and proved the validity of the prediction function through a series HVI tests. A Whipple structure was taken as an example, use the prediction function analysis the relations between the sensors location and the arrival sequence characteristic of shield/module-wall AE waveform, the results indicates that there are non-coupling area on the module wall, the shield AE signal would always arrival before the module-wall AE signal if AE sensor was placed inside the non-coupling area, that can avoid the coupling problem.Fourthly, based on the achievements of the attenuation characteristic and the propagation characteristic, a sensor layout was designed for the pressurized cabin. Firstly, the prediction function for arrival time interval was adjusted to fit the cylindrical shape of the pressurized cabin, and then evaluate the size of non-coupling area. Secondly, based on the attenuation characteristic of AE signals in module wall, AE sensors were placed inside the non-coupling area form a sensor array with 30 sensors. This sensor array can avoid the shield/module-wall AE waveform coupling problem and obtain location results with certain precision.Finally, a series HVI tests were carried on polyvinylidene fluoride piezoelectric film(PVDF), the characteristic of HVI signals were obtained, an impact damage identification technology based on PVDF for module wall was presented was proposed. Debris cloud impact AE source contains a mount of punctate AE source and the protrusions on module wall would cause the shape of the waveform change, compared with single projectile impact flat plate case, the AE phenomena is more complex cause difficulties to obtain impact damage information of module wall. In order to meet the urgent demand of the damage identification technology, PVDF was introduced to solve the damage identification problem, the characteristic of HVI signals were obtained through a series HVI tests, a technical scheme of damage identification was proposed, Use PVDF film surround the whole module wall inside the pressurized cabin to monitor the debris cloud produced by module wall penetration, thus monitor the penetration damage in the module wall.The conclusion of this paper has important reference value for developing onboard monitoring system for our future space station.