Brilliant LeaderShip

On Munsu Hill

It was April 6, Juche 36(1947). On the day President Kim Il Sung climbed Munsu Hill after attending a grand commemoration ceremony of tree-planting. The President was heartbroken at the sight of the ...

Spring Fragrance on International Women’s Day

On March 8 over a decade ago, there was a performance in the presence of Chairman Kim Jong Il. The women who were enjoying the performance together with him could ...

Criterion of Service Activity

One day in March some years ago, the respected Comrade Kim Jong Un visited the newly built Mirae Shop. Acknowledging that the shop was well built as befits the model of commercial establishments ...

Story of Coming Back

One night after midnight, the respected Comrade Kim Jong Un visited a unit of the Korean People’s Army. He took hours to give valuable instructions concerning the work of the unit. Then, tenderly ...

Teaching in Detail

One spring day Chairman Kim Jong Il visited the park of Mangyongdae Schoolchildren’s Palace (then) for memorial tree-planting. Lest the Chairman, who was always busy with the state affairs, should waste much time ...

Historic Significance Elucidated by the Chairman

Chairman Kim Jong Il was conducting the revolutionary activities at Kim Il Sung University when one day in February, Juche 51 (1962), he shared with his fellow students comments on the Chongsan-ri ...

News

Jo Mar 15, 2024

Welding deformation is one of the most complex problems arising in manufacturing of welded structures and it is impossible to remove or correct it. Welding deformation reduces accuracy in the size and shape of structures and increases the amount of correction work which leads to rise in manufacturing cost. Therefore, predicting and controlling welding deformation is of key importance in manufacturing welded structures. Predicting and controlling of welding deformation can reduce the amount of correction work, thus saving labor and cost and raising productivity.

At present, analysis of welding deformation is conducted by thermal-elastic-plastic (TEP) FEM and inherent strain method. In the past, there were a large number of experiments and numerical models to obtain inherent deformation. Although constraint is, in general, a simple practical method to reduce angle distortion, past researches were focused on numerical analysis of welding deformation, and the control of welding deformation considering the effect of constraint on angle distortion of large structures have not been sufficiently investigated.

Kim Chang Son, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has predicted the welding distortion of a ship panel structure with butt and zigzag joints and determined the reasonable constraint position to reduce fabrication cost by considering the effect of constraint on angle distortion.

First, he investigated the inherent strains of the welded structure by TEP FEM analysis under both constraint and free conditions. Next, through the elastic FEM based on inherent strain, he estimated the welding deformation of ship panel structure under consideration. After that, in order to quantitatively estimate the effect of constraint on angle distortion of welded structure, he performed a numerical analysis in a non-constraint free condition and various constraint positions, and determined the reasonable constraint position. Finally, he compared the angle distortion of ship panel structure under the constraint condition with that under the non-constraint free condition.

The simulation results show that angular distortion can be effectively reduced under a constraint condition.

...

Jo Mar 13, 2024

Laser cutting, which is one of the laser machining technologies, has been widely used in industrial production due to its good processing flexibility, high quality, high cutting speed, high precision and high production rate.

In order to ensure high quality in laser cutting, not only the appropriate process parameters (laser power, focal position, cutting speed, type and pressure of assist gas, etc.) must be set, but the stand-off distance between a work piece and a cutting head has to be kept at a fixed distance.

An Chol Min, a section head at the Faculty of Physical Engineering, has built a precise mathematical model of a truncated cone-shaped capacitive sensor based on the theory related to the electrostatic field and the properties of conductors and dielectrics in the field. He has also proposed limitations and suppositions to get a unique solution of the capacitance while analyzing the model by MATLAB, and verified the correctness of the model through experiments.

The theoretical analysis and the experiments show that the truncated cone sensor has much higher sensitivity than a parallel-plate sensor in laser cutting.

...

Jo Mar 12, 2024

Electron density is a key parameter in designing and constructing a pumping system for high power transversely excited atmospheric (TEA) pressure CO2 laser. It is necessary to ensure uniform volumetric discharge in order to enhance the output power and the efficiency of gas laser. It is, however, very hard for TEA-CO2 laser to achieve electron density of more than 1014cm-3 necessary for volumetric discharge as the pressure of active gas of the laser is higher than atmospheric pressure.

Recent-developed external pre-ionization systems such as those based on high-energy field emission, ultraviolet or X-ray have enabled atmospheric pressure volumetric discharge in a short time of about 1㎲ and raised the output power of pulsed laser up to the level of GW. The main factor of getting higher power (over tens of GW) is to ensure that electron avalanche caused by inelastic collisions between CO2 (or N2 and He) molecule and cold electrons with energy of hundreds of keV is spatially uniform, and that non-self-sustained main discharge is conducted as a uniform volumetric one. It means that finding out the characteristics of change of electron density is of primary importance in developing high power TEA-CO2 laser.

The model of electron density for uniform volumetric discharge is a nonlinear model describing microphysical processes such as pre-ionization, avalanche ionization, recombination, attachment and so on. So far, there have been no general solutions of this model but only special solutions for some extreme cases.

Yun Tu Hon, a researcher at the Faculty of Physical Engineering, has proposed a method of general solutions for the nonlinear model and verified the accuracy and generality of his method by comparing the results with the data reported in the literature. He also reported some new special solutions unknown in the literature and the experimental results for them.

The proposed method will prove to be valuable for high power TEA-CO2 laser of hundreds of MW.

...

Students on “Risang” Local Network (1)

“Risang”, homepage for distance education of Kim Chaek University of Technology, has been making the part-time learners realize their ideal to the full.

Nov 11, 2022