Gongcheng Kexue Yu Jishu/Advanced Engineering Science

The Batang—Mangkang section of the G4218 highway is located in the transition zone from the Jinsha River Valley to the plateau, and facing with strong neotectonic activities, broken rock masses and frequent geological disasters. Therefore, the construction and maintenance of the highway in this region are of huge difficulties. Traditional ground geological survey methods face many difficulties in highway route selection, disaster assessment and stability analysis, etc. Combining the optical remote sensing interpretation of geological hazard points with deformation observation by InSAR technology, it is expected that the geological hazard points in this region can be investigated quickly, accurately and efficiently, and reveal their development and distribution rules of geological disaster points.Under the special geological conditions of the high mountains and valleys of the Qinghai–Tibet Plateau, the common types of geological disasters in the region were summarized, and the method of integrated highway remote sensing identification was put forward based on the study of the characteristics of regional disasters and remote sensing technology. Using this method, we carried out disaster surveys on the Batang—Mangkang section, with full knowledge of optical remote sensing visual interpretation technology and InSAR technology, supplemented by field geological survey, GIS spatial analysis, engineering geological analogy , etc. The conclusions of this article are as follows: 1) A total of 670 geological disasters were interpreted by optical visual remote sensing in the study area,and InSAR technology combined with four kinds of SAR data interpreted 220 active geological disasters; 2) The development rules of different types of geological disasters in the study area varied greatly with the change of topographic features, geological conditions and geological disasters and other influencing factors. There were differences in spatial distribution and formation lithology of geologic hazard using the optical remote sensing or InSAR technology; 3) According to the comparative analysis based on the field work, it was concluded that the interpretation results of optical remote sensing and InSAR had a certain relationship with the interpretation methods, imaging conditions of the images and the activity of landslide. The two methods cannot be used for mutual inspection directly;4) The use of comprehensive remote sensing technology was universal in the highway construction of the high mountain valley of the Qinghai–Tibet Plateau. It made full use of the complementarity of optical remote sensing interpretation technology and InSAR deformation observation technology. On the basis of saving time and cost, this method can have a more comprehensive and accurate understanding of the development of regional geological disasters.

The mountain flood disaster is one of the major natural disasters in the world. The global economic loss caused by flash floods in the 21st century has reached more than 46 billion US dollars per year. The area of mountain flood disaster prevention and control accounts for about 40% of the land in China, whereas the fatality caused by mountain flash floods account for approximately 70% of the death toll from flood disasters. In recent years, the construction of mountain torrent disaster prevention and control projects have been carried out in an all-round way in China. A mountain torrent disaster prevention and control system combining specialists and groups has been basically established, and the technical level of mountain torrent disaster monitoring and early warning has been significantly improved. Examples of torrential rain and flash flood disasters show that the flash flood disasters with heavy casualties and property losses often result from the combined effects of flood and sediment. In the past, scientists mostly paid attention to the flood's role while ignoring that the combined effect of flood and sediment would significantly increase the risk of mountain torrent disasters. To further improve the ability to prevent and control mountain flood disasters, it is urgent to study the critical technologies of flood and sediment disaster forecasting and early warning. The project “Research and Demonstration of Key Technologies for Forecasting and Early Warning of Flash Flood and Sediment Disasters in Mountainous Rainstorms” focuses on the joint action of flood and sediment and condenses four critical scientific and technological issues: 1) mutation mechanism of runoff and sediment yield and disaster-causing coupling mechanism of the flood-sediment process and gully-bed drastic change in mountainous area under heavy rain; 2) early identification of flood and sediment disasters and integrated intelligent monitoring technology for disaster-causing elements in mountainous rainstorms; 3) simulation and rapid prediction technology of flash flood and sediment movement process in a mountainous rainstorm; and 4) disaster risk dynamic assessment and early warning and prevention technology based on the dynamic process of mountain flood and sediment disaster. Focusing on the connotation of critical scientific and technological issues, we proposed five key research contents including 1) study on the process of runoff and sediment production in mountainous areas and the disaster mechanism of flood and sediment coupling; 2) early identification and intelligent monitoring technology for flood and sediment disasters in mountainous areas; 3) simulation and rapid prediction technology of flood and sediment movement process in a mountainous rainstorm; 4) dynamic assessment and early warning technology of flood and sediment disaster risk in mountainous areas; 5) construction and demonstration of a platform for forecasting, early warning, and prevention of flood and sediment disasters in mountainous areas. The research results will improve the real-time accuracy and intellectual level of monitoring, early warning, prevention and control of heavy rain and flash flood disasters in China.

Monocrystalline silicon is widely used in the field of photoelectric systems, and it is easy to cause its thermal damage and change of performance under the action of laser. For the urgent needs of high-precision laser weapons and laser fine processing industry, the thermal damage of monocrystalline silicon irradiated by pulse train of millisecond laser andthe relationship among the laser energy density, number of pulses and other important parameters of thermal damage were analyzed, and the damage law and mechanism were explored. Thermal damage of monocrystalline silicon by pulse train of millisecond laser was studied from both simulation and experimental aspects. Based on the heat conduction equation, a thermal damage model of monocrystalline silicon irradiated by pulse train of millisecond laserwas established, finite element and finite difference methods were used to solve temperature field of monocrystalline silicon treated by pulse train of millisecond laser. The equivalent specific heat capacity was introduced into the model to deal with the phase change after melting and vaporization, and the temperature rise of the model was corrected. The temperature measurement system of millisecond pulse laser damage monocrystalline silicon was constructed, and the high-precision spot temperature meter was used to measure the laser irradiation center point temperature in real time. Research indicated that when a pulsed laser is applied to monocrystalline silicon target, the center point of the laser irradiation and the radial and axial positions have a temperature accumulation effect, and the radial temperature rise range is much larger than the axial direction; With the increase of laser energy density, the temperature accumulation effect is significant; As the number of pulses increases, the melting time of monocrystalline silicon and the time from the melting point to the normal temperature are lengthened; when the number of laser pulses is increased to 90;The thermal damage threshold of monocrystalline silicon decreases to 73.8% of the single pulse damage threshold; When the number of pulses increases, the damage area of monocrystalline silicon increases. Comparing the experimental and simulation results, it can be seen that the laws of the two aspects are basically the same. The simulation model can reasonably describe the process of millisecond pulse laser damage to monocrystalline silicon.

Inverted planetary roller screw (IPRS) is a kind of linear transmission mechanism which has advantages of high load carrying capability, long fatigue life, high transmission accuracy and low noise. Due to these advantages, it has wide application prospect in the fields of aerospace, weapon equipment, CNC machine tools and petrochemical industry. Up to the present, there is little research about this mechanism. Therefore, a model was derived to calculate load distribution, axial deformation and contact fatigue life. Firstly, surface equation of screw, roller and nut was established. Based on Surface meshing theory, the meshing points of the roller with the screw and nut in a pitch were derived respectively. According to the surface equations and the location of contact points, an accurate method to calculate the elastic deformaion between the meshing surface was derived. Secondly, A model of IPRS's load distribution was obtained based on the geometric relationships between Hertz deformation, thread deformation and axial deformation. Based on its load distribution condition and motion principle, a fatigue life model was deduced using Lundberg-Palmgren equation. Then, a program was compiled in the MATLAB Environmet to calculate load distribution axial deformation and contact fatigue life. By comparing calculationg result with the expriments, the load distribution and axial deformation model was verified. The influence of the key parameters on the performance of IPRS was analyzed and the following results were derived. The load distribution was mainly influenced by the number of teeth, the number of rollers and the helix angle, and increased with the increases of these three factors. The axial stiffness was mainly influenced by the number of teeth, the number of rollers, the helix angle and the outer diameter of the nut, and increased with the increases of the number of rollers and the outer diameter of the nut, increased first and then decreased with the increase of the number of teeth and the helix angle. The contact fatigue life was mainly influenced by the number of teeth, the number of rollers, the contact angle and the radius of thread profile, and increased with the increases of the number of teeth, the number of rollers and the radius of thread profile, decreased with the increase of contact angle.

In order to find out the damage evolution rule of the concrete with initial damage caused by early freezing under the coupling of freeze-thaw cycle and sulfate erosion, initial damage to concrete specimens by freezing and thawing them at the 7th and 14th day during the preparation of concrete specimens was carried. Based on this, different initial damage degree on macro performance and internal structure was researched. Then according to the principle of damage mechanics, the dynamic modulus of elasticity and compressive strength were defined as damage variables, by regression fitting analysis of damage process of variable, and the damage evolution equation of different initial damage specimen caused by early freeze-thaw was established in corrosion and freezing environment. The results indicated that two kinds of concrete specimens with different initial damage are affected by early freeze-thaw in the decay process of their mechanical properties and their form are " lead effect", which is closely related to the degree of initial damage. At the same time, the comparison and analysis of the change process of ultrasonic pulse propagation velocity and internal defect zone of concrete inferred that early freeze-thaw accelerates the propagation speed of cavity and crack, and the initial value of macroscopic mechanical properties of concrete and the ability of resisting salt and freezing in later stage are affected. The dynamic modulus of elasticity and the damage evolution equation of compressive strength can be used as a general formula for the attenuation of mechanical properties of concrete with similar damage degree, which can provide a theoretical basis for evaluating the service status and predicting the life of structures in similar environments. At the same time, the damage relationship between dynamic modulus of elasticity and compressive strength can be deduced from each other, which can reduce the limitation of data acquisition due to the shortage of instruments.