Real-time Visual Simulation And Analysis Method For Rapid Risk Assessment Of Debris Flow Disasters

Debris flows are trigged by intense rainfalls with landslides in a short time.The debris flows have some certain characteristics such as sudden occurrence,rapid expansion,and emergency respond,which bring hazard risks to people's lives and properties.Therefore,it is important to implement numerical simulation and a rapid risk analysis of debris flow disasters,from which accurate disaster information can be obtained,such as inundated area,flow depth and disaster degree.These disaster information can provide scientific support for emergency rescue response,which is of great significance for the debris flow disaster prevention and reduction.Despite the achievements of the simulation and analysis for debris flow disasters have been obtained in previous studies,there are still some shortcomings,such as low efficiency of numerical simulation,poor capability of risk assessment,low cross-platform compatibility of 3D visualization and difficulty in sharing geographic knowledge.It is difficult to provide the rapid analysis of debris flow disasters in emergency situations.Therefore,the method for rapid simulation and analysis of debris flow disasters was studied with the support of high performance computing and WebGL technologies.Key techniques and methods including rapid risk assessment based on refined grid cell sizes,parallel computing simulation of multiple grid cell sizes,and real-time visualization of disaster information were examined in-depth.The emergency simulation and visual analysis of debris flow disasters were carried out.The following was an overview of this dissertation.(1)The refined grid cell sizes were selected as the basic assessment units to study the methods and procedures of rapid risk assessment of debris flow disasters.The appropriate grid sizes were selected to finely grid risk objects including land use,population and social economy,etc.;the analytic hierarchy process function was used to construct the risk assessment functions of debris flow disasters;and the unmanned aerial vehicle(UAV)image,historical data and field survey data were used to obtain the values of risk assessment factors.An overall risk assessment of debris flow disasters was rapidly carried out based on above data.Then,based on the simulation results,a refined risk assessment was conducted to obtain detailed disaster information of the affected population,roads and residential areas under different risk levels.(2)A multiscale parallel optimization method was designed and the proper grid cell sizes for rapid simulation and analysis of debris were selected to improve the simulation computing efficiency of debris flow disasters.The OpenMP framework was used to implement parallel optimization of the debris flow simulation.Several typical grid cell sizes were tested in a sensitivity analysis of the inundated area,maximum flow depths,and maximum flow velocities.The computational efficiency of one simulation step could be completed within 15 ms,and the maximum speedup ratio is approximately 148 when using the proper grid cell size.Thus,the multiscale parallel optimization can support real-time interactive analysis.(3)The methods of dynamic construction and web service-based publishing of debris flow disaster scene were studied,which can support real-time visualization and interactive analysis.With the support of high performance computing and WebGL technologies,the virtual terrain scene was constructed and the dynamic visualization of the debris flow disaster routing process was carried out.Users can obtain the inundated area,flow depth,risk area,and spatial distribution of risk objects at different risk levels and query the disaster information in the debris flow disaster routing process,such as the risk population,risk residential areas,and risk roads.The average efficiency of visual rendering is approximately 35 fps,which can support real-time interactive analysis of debris flow disasters in a virtual geographic scene.(4)By integrating the preceding research achievements,we have developed a prototype system based on virtual geographic environment for rapid simulation and risk analysis of debris flow disasters.The numerical simulation,risk assessment and 3D visualization of the debris flow disasters were tightly integrated into the virtual geographic environment(VGE)system.Typical cases were selected to conduct emergency simulation and risk analysis experiment of debris flow disasters.Experimental results showed that,the proposed methods can support the rapid simulation,dynamic visualization,interactive analysis of debris flow disasters,can share and publish geographic knowledge,and also can provide scientific evidence for crowd evacuation,temporary shelter arrangement,and rescue plan making in emergency situations.