| Hydrogen is recognized as one of the most promising energy in the 21 st century.Unfortunately,it is likely to suffer from explosions in the process of production,storage,transport and usage.Such accidents will cause serious damage and destruction to civil engineering structures such as bridges and buildings,leading to heavy casualties and property losses.As one of the important measures of disaster presentation,explosion venting is a common method in industry and living.However,the research on the structural dynamic responses induced by vented hydrogen explosion is still rarely reported.Explosive load is a special dynamic load that changes rapidly in a very short time,so the characteristics of structural dynamic responses due to explosive load are different from those subjected to seismic and wind excitation.Investigating evolution mechanisms of overpressure loading and structural dynamic responses can gain more in-depth insights into the anti-explosion capacity of the structure and provide a theoretical basis for the design of protective devices.Based on this,funded by National Key Research and Development Plan(No.2016YFE0113400),the experimental platform was set up for vented hydrogen explosions and a number of scenarios were carried out in a large-scale ISO container with the scale of 12 m×2.5 m×2.5 m.The characteristics of overpressure load and structural dynamic responses subjected to hydrogen explosion were studied experimentally.For further analysis,a baseline finite element model of the structure was established based on finite element model updating using dynamic properties of the container.After verifying the accuracy and effectiveness of the numerical model,the parametric analysis was conducted to investigate the effects of the key design parameters on the anti-explosion ability of the structure.The findings of this thesis are expected to lay a foundation for future study on the simplified model of explosion load and evolutional mechanism of the structural dynamic responses subjected to the hydrogen explosion.The main contributions and conclusions of this thesis are outlined as follows:1.The experimental results indicate that when venting through the roof of container,the explosion pressure is mainly dominated by two peak values due to the rupture and the acoustic oscillation.The former can be divided into three stages: the pressure curve increases exponentially at the first stage and the index increases with hydrogen concentration;at the second stage,the curve decays rapidly in an approximate straight line;the pressure rebounds at the third stage,and then the pressure decays slowly to approach ambient pressure.When venting through the end of the enclosure,multiple overpressure peaks were observed due to the rupture,discharge,external explosion as well as unstable combustion and accompanied by the Helmholtz oscillation.In this situation,the overpressure loading can be divided into two stages: the number of peaks depended on the initial condition and a negative overpressure peak was generated at the first stage.The waveform of the second stage changes approximately as a sine function and the amplitude decreases as an exponential function.In addition,the vibration frequency is found to be located within 8 and 13 Hz,but it is highly non-trivial to fit an explicit mathematical function relationship between the frequency and time.The above analysis laid a solid foundation for establishing a simplified model of explosion load,which can play an important role in structural dynamic response prediction and safety assessment for engineering structures subjected to hydrogen explosion in the future.2.The measured data showed that there are two modes available for the structural displacement.When the acoustic oscillation was not considered,the duration of explosion load was longer than the natural period of the structure.In other words,explosion load could be regarded quasi-static.The displacement fluctuated similar to the trend of the overpressure,and a linear relationship was found for the peaks of overpressure and displacement.It is worth noting that,when venting occurs at the end of the container,the ratio of the pressure to the displacement peak during the oscillation phase was smaller than those measured at the beginning of the explosion,which obviously indicated the dynamic effect with the dynamic amplification factor of about 1.89.There was no explicit mathematical function relationship between the peak of structural displacement and negative pressure peak.In addition,when high-frequency acoustic oscillation of the explosion pressure occurred,the energy of the response is obviously concentrated around 20 Hz and 30 Hz,which were close to the first few modal frequencies of the structure.3.Double-peak phenomenon of the structural acceleration with low and high amplitude is clearly seen from the acceleration responses.The low-amplitude vibration was due to the rapid change rate of overpressure in the later stage of the explosion,which caused the structural dynamic behavior.But the external load was still mainly balanced by the restoring force of the structure itself at the moment,so the acceleration amplitude was small.However,the high-amplitude vibration was caused by the acoustic oscillation,which means that the overpressure changed so rapidly that it did not have enough to cause structural deformation.As a result,the external force was mainly balanced by the inertial force,resulting in acceleration with large amplitude.Moreover,the curve waveform was similar to that of the acoustic oscillation.The time-frequency analysis was also conducted to show that the frequency domain characteristics of the high-amplitude vibration were consistent with the overpressure.Specifically,when the hydrogen concentration was 16 vol.%,the energy peaks of both response and overpressure are concentrated around 400 Hz.Furthermore,the vibration frequency band gradually broadened with increase of the hydrogen concentration and the dominated frequency of vibration increased with time.4.Experimental studies cannot accommodate all cases due to limited budget and other kinds of difficulties.The numerical simulation method which can simulate various explosion loads under different conditions,and was also studied as an aid.Therefore,to further analyze the structural dynamic response characteristicsinduced by the vented hydrogen explosion,the raw finite element model of the structure was established using ANSYS,and the theoretical modal analysis was carried out.The results show the structure vibration modes can be regarded as a combination of vibration modes of each panel modelled as rectangular thin plate with four sides fully clamped.Then,the field test was performed for the container under vibration to identify the dynamic properties,and the operational modal analysis was conducted using frequency domain decomposition and data-driven stochastic subspace identification techniques.By minimizing the residual of the dynamic properties calculated from the FE model and those identified from field testing data,the raw finite element model was updated and then a baseline finite element model was established,which will be used to predict the structural dynamic responses subjected to hydrogen explosion.5.The accuracy and effectiveness of the baseline model were verified by comparing the predicted responses with those measured in the experiments.The results show that the structural deformation was continuous without local deformation due to the weaker stiffeners relative to the panel stiffness.As a result,the load transmitted by the panel to the stiffeners caused stiffeners to enter the deformation mechanism quickly.In addition,the parametric analysis demonstrates that the boundary conditions can exert greater influence on structural deformation.The peak values ofthe structural displacement decreased approximately linearly with the increase of the thickness of the panel and the height of the stiffeners... |
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