We propose an automobile driven by piston motion, which is driven by water-laser coupling. The automobile can load a solar-pumped fiber laser or can be driven by ground-based lasers. The vehicle is much useful for the use in other planet in which usual combustion engine cannot be used. The piston is in a closed system and then the water will not be exhausted into vacuum. In the preliminary experiment, we succeeded to drive the cylindrical piston of 0.2g (6mm in diameter) on top of water placed inside the acrylic pipe of 8 mm in inner diameter and the laser is incident from the bottom and focused onto the upper part of water by the lens (f=8mm) attached to the bottom edge.
We performed 1.5-dimensional simulation of the Fokker-Planck equation using the CIP method to investigate femto-second-laser heating processes. We found that the heat flux in the solid part approaches the classical thermal conduction theory like Spitzer-Harm theory in quite a short time scale ωpt<100, while the heat flux on the vacuum side becomes free streams which don’t depend on temperature gradient. On the basis of this result, we performed hydrodynamic simulation using the CIP method with classical thermal conduction and the experimental ablation depth was replicated very well showing that even fs pulse laser processing can be satisfactorily described by the classical heat conduction. As an application to nanosecond laser, we tried to drill a crack-free high-aspect-ratio hole through glass by YAG laser of 1μm wavelength, 5ns pulse width and 30-630mJ/pulse. The hole is 25.5mm long with 500 μm radius and no crack is observed even in atmospheric condition. This success is due to translucent adhesive tape pasted on glass surface in which the temperature is controlled and thermal stress is reduced.
The CIP method is used to calculate macroscopic plume expansion combined with the Zeldovich-Raiser theory for cluster formation process such as nucleation and growth. The effect of background gas and latent heat is examined in one-dimensional case. The latent heats keep the plume temperature at 2500K for a long period and this explains the delayed photoluminescence. Two contradicting experiments on the size dependence on ambient pressure are clearly explained and are attributed to the difference of laser energy. In two dimensional simulation, mushroom-like plume shape is replicated consistent with experimental results.
Laser supported propulsion of multi-layered target is investigated by the CIP-CUP (Cubic-Interpolated Pseudoparticle Combined Unified Procedure) based hydrodynamic code PARCIPHAL and experiments by pendulum and semi-conductor load cell. The momentum coupling efficiency of 5000 [N.s/MJ] has been achieved by ORION experiments that agree with the simulation code. Time evolution of ablation process and subsequent acceleration is investigated by load cell experiment and simulation. The double-layered target that consists of transparent tamper (Exotic Target) shows higher acceleration rate even with small laser. A propulsion concept is proposed to drive and control a micro-airplane that can be used for observation of climate and volcanic eruption where no one can access directly. In this concept, it is necessary to irradiate a micro-airplane repetitively. Therefore the double-layered target attached a liquid overlay is useful because the device that supplies the surface with liquid can be simple and light. In this paper, the simple device using water as an overlay is presented. Furthermore, from the results of experiments and simulation, it is clear that the mechanism of ablation process differs between the target attached a water layer and the target attached a solid layer.
Laser supported propulsion of a micro-airplane with water-covered ablator is demonstrated. The repetitive use of overlay structure is experimentally demonstrated with specially-designed water supply. The various transparent overlay is investigated by the CIP-based hydrodynamic code and experiments by pendulum and semi-conductor load cell. The momentum coupling efficiency of 5000 N-sec/MJ has been achieved by ORION experiments that agree with the simulation code. With the maximum efficiency approximately 105 N- sec/MJ predicted by the simulation, 30 pulses of MJ laser can give the sound speed to 10tons airplane. The concept can also be used for driving a micro-ship inside human body and a robot under the accidental circumstance of nuclear power reactor in which large amount of neutron source makes electronic device useless.
An experimental and numerical study was conducted on ablation form ns-laser heated aluminum. The goal of present study is to clarify the laser ablation phenomena. In experiments, a YAG laser of 650mJ in 4-7nsec was used to perpendicularly illuminate an aluminum target. Time-resolved measurements were conducted using high-speed camera system. Also, a numerical simulation was conducted using CIP method. The experimental results of time-resolved measurements indicate that the target surface itself is melting until late after the laser irradiation. The SEM pictures of the irradiated indicate that the target surface itself is melting until late after the laser irradiation. The SEM pictures of the irradiated target surface are showing the generation of many minute protrusions. These protrusions near the part that laser is irradiated are facing toward the laser beam path and those of the surroundings are facing toward circumference. It is found by numerical simulation that this is due to the appearance of the critical point just after the laser irradiation. Since the laser beam goes around the critical point, the damaged part expands toward circumference.
We have succeeded for the first time to simulate dynamic phase transition from metal to vapor. This success is due to the CIP method that can treat solid, liquid and gas together and can trace a sharp interface with almost one grid. We report here the application to laser-induced evaporation for nanosecond and femtosecond lasers. In both cases, aluminum is evaporated well after the laser beam ended. In the nanosecond laser, evaporation occurs with a large angle to the target normal causing filamentary structure. In the femtosecond laser, evaporation front is formed and shows discontinuous solution that continues over a long time.
The condensation of vapor within the expanding plume produced by ns-laser ablation is discussed in the framework of Zeldovich and Raizer theory of condensation. The spherical plume expansion is described by numerical solution of hydrodynamic equations by CIP method. This permits to analyze the role of initial distributions in density and pressure onto the size distribution function for nanoclusters. With parabolic distributions (for the plume expansion into vacuum), calculations reproduce the same results, as those found with particular solutions of gas-dynamic equations. When initial distributions deviate from parabolic, the size distribution function varies. For the rectangular plume, size distribution function for nanoclusters demonstrates to maximums. The similar effect can be found due to the ambient gas influence.
We have succeeded for the first time to simulate dynamic phase transition from metal to vapor. This success is due to the CIP (Cubic-Interporated Pseudoparticle/Propagation) method that can treat solid, liquid and gas together and can trace a sharp interface with almost one grid. We report here the application to laser-induced evaporation and welding process. In the former case, aluminum is evaporated well after the laser beam ended and evaporation occurs with a large angle to the target normal leading to large debris. In the latter case, a deep penetration welding of SUS304 by YAG laser has been successfully replicated the experiments and the simulation clarifies the formation mechanism of keyhole.
We have succeeded for the first time to simulate phase transition from metal to vapor. This success is due to the CIP method that can treat solid, liquid and gas together and can trace a sharp interface with almost one grid. For these types of problems such as welding and cutting processes, we need to treat topology and phase changes of the structure simultaneously. Furthermore, the grid system aligned to the solid or liquid surface has no meaning and sometimes the mesh is distorted and even broken up. The CIP method developed by the authors does not need adaptive grid systems and therefore removes the problems of grid distortion caused by structural break up and topology change. In this paper, we will give a brief introduction of the CIP method, then report here the application to laser-induced evaporation and welding process. In the former case, aluminum is evaporated well after the laser beam needed and evaporation occurs with a large angle to the target normal leading to large debris. In the latter case, a deep penetration welding of SUS304 by TAG laser has been successfully replicated the experiments and the simulation clarifies the formation mechanism of keyhole.
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