Research On The Impact Dynamic Characteristics Of The Floating Shock Platform

The shipboard equipment having a good shock resistance plays an important role in ship survivability.The naval powers carry out experiments on key equipment to improve the impact resistance of the equipment and have formulated the corresponding shock resistance standard for shipboard equipment at the same time.The equipment with low weight and small size can be tested on the impact testing machine,while the large and medium sized shipboard equipment should be mounted on a FSP(floating shock platform)for the evaluation test.There are still some gaps between our country and western naval powers in the construction of examination norm and facilities for the large and medium sized shipboard equipment.Take the United States who has the most developed navy construction for example,in the respect of examination norm,it has a more mature military standard MIL-S-901D,which has undergone several times of modification and improvement.Meanwhile,it has light,medium impact machine and standard,medium,large floating platform as the evaluation tools of shipboard equipment to match the military standard.On the contrary,our examination norm of the large and medium sized shipboard equipment is lack of reliability and operability,and there is no matched evaluation tool.Only some departments have the small floating shock platform and the standard floating shock platform with 36 tons of the maximum evaluation weigh,and the unity and normalization is poor.Against this background,impact dynamic characteristics of the floating shock platform are studied in this thesis to reveal the mechanism of equipment evaluation using a FSP and analyze characteristics of the FSP’s shock environment.The research contents can provide guidance for the structural design of a LFSP(large floating shock platform)or an IFSP(intermediate floating shock platform).The similarity and correspondence of shock environment between FSP and ship is also analyzed in this paper,which may give a reference for our construction of system and examination norm of the large and medium sized shipboard equipment.According to the research background and actual engineering significance,starting with the more mature and perfect military standards,BV043/85 and MIL-S-901D,the shock request for shipboard equipment and implementation procedure of the investigation test was analyzed.The hardware construction and the technical research situation of FSP at home and abroad were collated and sum up in the meantime.Summarizing the research progress of shipboard equipment assessment by mean of FSP,scientific and engineering problems that need to be solved in our assessment method of shock resistance for the large and medium sized shipboard equipment were presented,which could lay a foundation for the consequent work.FSP as the evaluation tool of shipboard equipment,when analyzing its impulse response,there are two major problems:shock environment and structural strength.On the issue of shock environment,the shock spectrum would be used inevitably when studying the shock environment of equipment provided by the FSP.Therefore,according to the research achievements at this stage,the principle and characteristics of shock spectrum were studied deeply and systematically.The basic concept and physical principles of shock spectrum was illuminated.Meanwhile,the relationships among relative displacement spectrum,relative velocity spectrum,absolute acceleration spectrum and pseudo-velocity spectrum were explained,and the relationship between shock spectrum and Fourier spectrum was also analyzed.Based on the theory of coupled chaotic system to explicate the phenomenon of spectrum dip,the main features of shock spectrum were analyzed to serve the research of shock environment of FSP and ship.For the problem of FSP’s structural strength,the FSP’s shock response under the underwater explosion was analyzed firstly.According to the charge set of assessment conditions and the characteristics of shock wave propagation,with account of the surface truncation effect of the shock wave and the local cavitation at the bottom of the platform,the calculation method of vertical rigid body motion subjected to spherical shock wave was given.Through the numerical simulation and the related experimental data,the rationality of the calculation model and the effectiveness of the simulation calculation were verified.The results show that the main response of the FSP under the underwater explosion is the rigid body motion.Hence,while the FSP’s shock environment loaded to the equipment can meet requirement,the structural intensity and stiffness could be increased to ensure that FSP’s structural strength can meet the needs of repeated tests.According to the FSP’s shock response analysis,combined with BV043/85 and MIL-S-901D,the structural type of American IFSP as a reference,the structure of IFSP that has not yet been put into construction in China was designed by the method of system identification.After getting the FSP’s impact response,based on the verification conditions specified in the MIL-S-901D,the shock environment of American FSP and designed IFSP was analyzed,which was compared with the equipment’s check requirements of BV043/85 to study the similarities and differences between MIL and BV specification.And to meet the installation requirements of frequency for resilient mounting equipment,the principle of DSF(deck simulator fixture)appeared in the MIL-S-901D was interpreted.The impact of DSF,equipment quality and mounting frequency on FSP’s shock environment was discussed.Then the dynamic test simulation technique and experimental calibration method of the FSP were proposed.To further investigate the mechanism of equipment examination by FSP,considering the DSF with the function to meet the installation requirements of frequency for resilient mounting equipment,the impact response of FSP and its equipment under test was theoretically analyzed and numerically simulated.Based on the mathematical model of multiple degree of freedom system with foundation excitation,a theoretical approach of multiple degree of freedom system to compute the response of shipboard equipment under underwater explosion environment was established simultaneously.The influence of shock spectral parameters and the frequency of the excitation force on the shock response of shipboard equipment with different weight and different type were studied,and the rationality of the theoretical analysis was verified by numerical simulation method.In order to study similarity and correspondence of shock environment between the FSP and the real ship,the impulse response and the grillage’s deformation law of the ship cabin,which has similar size and scope with FSP,were investigated experimentally and analyzed theoretically.The complex hull envelope was equivalent to the Taylor plate,and the effect of rigid body motion on ship’s overall response was discussed based on the calculation method of rigid body motion presented in this paper.Meanwhile,the similarities and differences in impact response and shock environment of the ship cabin and FSP were compared and analyzed.Combining the results in the front analysis,it can be seen that there are some differences between FSP and real ship in load input,structural style and impact response,thus causing the difference of shock environment provided to the shipboard equipment by the two.According to the characteristics of shock environment in ships with different displacement subjected to underwater explosion shock waves and research results of the low-pass filtering effect,combined with the influence of shock spectrum on impact response of shipboard equipment,from the statistical perspective,the discriminant analysis on shock spectral parameters at connection place of the FSP and equipment as well as different positions of the ship was carried out by using the Fisher method.The corresponding relation of shock environment between the FSP and the real ship was finally established.