Research On Laser De-icing Technology For Electrified Railway Tunnel

The rapid development of infrastructure construction,especially the rapid development of railway industry,has provided a strong driving force for the improvement of China's overall economic strength.At present,the total amount of railway tunnels in China has exceeded50,000,which is one of the key points of railway daily maintenance work.Among them,the top of the tunnel has subtle cracks which cause water to flow out and the water flow is easy to condense into ice in winter in the north.These ice columns will continue to increase and grow with the continuous seepage.It is easy to cause short-circuit grounding failure of high voltage part of the railway contact network in the tunnel,which seriously threatens the normal and safe operation of equipment and locomotives in the railway tunnel and is the first cause of winter failure of the contact network in the tunnel.It can be seen that ice damage caused by tunnel seepage is an important problem that needs to be solved urgently.To solve this problem,different methods have been proposed by railway departments and research institutes.However,considering the actual cost and the difficulty of implementation,the most commonly used methods are still artificial ice beating or electric heating.Artificial ice-beating requires a lot of manpower.De-icing workers may need to deice several times a day.Each road tour takes several hours,the working environment of the workers is very bad,and the working time is very limited.Electric heating is used to prevent ice from forming by erecting the electric heating equipment in the seepage crevice position in the tunnel and maintaining the temperature at the location by means of thermal radiation or thermal contact through electric current heating.This method is relatively simple,but it costs a lot to set up,consumes a lot of energy,and wastes a lot of heat energy.In order to effectively,reliably and easily solve the problem of ice damage in tunnels,this paper puts forward the idea of using laser to irradiate the ice roots,melt the ice layer that touches the top wall of tunnels,make the ice fall and remove the ice.The feasibility and validity of this method are demonstrated through theoretical analysis,simulation calculation and experimental test.This article mainly does the following work:In the aspect of electromagnetic propagation theory,the energy theorem of electromagnetic field,laser propagation,and Gauss beam are discussed.Firstly,the general energy theorem of electromagnetic field is deduced from the Maxwell equation system,starting from the fluctuation of laser,and the basic calculation method for quantitatively calculating the thermal effect of laser is given.Then,starting from the homogeneous Helmholtz equation,the solutions of the laser wave equation in the case of plane and spherical waves are derived.On this basis,the common Gaussian beams in practice,their characteristic parameters and propagation properties are derived.In terms of the theory of the effect of electromagnetic fields on matter,the principles of polarization,reflection and transmission are discussed.Starting from the material nature of the electromagnetic field,the mechanism of the interaction between the electromagnetic field and the object is demonstrated.Then,starting with the refraction-transmission theorem derived from the boundary conditions of the electromagnetic field and combining with the particle nature of the light wave,the generalized absorption parameters are analyzed and derived.Then,the Bill-Lambert law is introduced with the generalized absorption parameter as the fulcrum.In terms of the theory of laser absorption by materials,this paper mainly considers the BillLambert law and explains it from the point of view of the particle nature of high frequency light waves.In terms of heat transfer theory,this paper takes the internal heat transfer of solid as the main research object,and deduces the control equation of the system studied.In fluid mechanics,due to limited academic capacity,only the effect of a simple fully developed flow on the study is considered.In order to deal with the ice-water phase transition and its "material loss" in the theoretical model,a new method,the equivalent material method,is proposed.By extending the thermal conductivity of a material in Fourier's law,the method enables the material to have some special properties that simplify the calculation of phase transition without affecting the original phase transition process.Based on this,a simulation calculation model for laser deicing of electrified railway tunnels is established.It is found that a laser with a wavelength of 940 nm,a power of 20 W and a light spot diameter of 9 mm is used to illuminate a cylindrical icicle with initial temperature of-10 ?,a height of 150 mm and a diameter of 10 mm from oblique bottom.After 150 s,a hole with a depth of 10 mm and a diameter of 18.5mm appears on the icicle.And continuing to illuminate to 300 s,the depth of the hole changes to 21 mm,and the diameter remains unchanged to 18.5 mm.When heated to steady state,the temperature of concrete increases from-10 to 25 degrees ?.indicating that the temperature rise caused by this type of laser has no negative effect on the tunnel wall.Subsequently,laboratory experiments were carried out under the same parameters.The results show that after 300 seconds of irradiation,a circular hole appeared on the ice column with clear and sharp edges,a diameter of about 20 mm and a depth of about 19 mm.No ice residue or ice-water mixture was found inside the hole.It was also observed that during the heating process of continuous irradiation,no evident softening,dripping or structural changes were observed in the rest of the ice column except for the area directly irradiated.It indicates that the deicing process has no effect on the non-operational area and will not affect other railway equipment and facilities that may exist nearby.The above results can prove the applicability and correctness of the equivalent material method proposed in this paper and the established laser deicing model for electrified railway tunnels.The theoretical and experimental results also prove that the method of removing ice hanging by laser heating in electrified railway tunnels is effective and feasible.