Jo Apr 15, 2024
Energy and environmental problems are two challenges today and production and use of recycled energy is the focus of world attention. More and more attention is being drawn to more reliable solar power generating systems, and more than 50GW solar power generating capacity is being constructed in the world every year.
At present, there are two widely-used types of solar power systems—central or distributed. The main problems in the construction of distributed solar power systems are to guarantee flexibility of distributed power sources, stability of voltage and frequency of the weak grids, optimized management and distribution of electric systems and improvement of electric power quality.
O Yong Nam, a section head at the Faculty of Physical Engineering, has designed a novel phase synchronization method for distributed power systems by combining good harmonic and DC offset cancellation characteristics of the discrete Fourier transform (DFT) and frequency adaptation characteristics of phase locked loop (PLL). The validation of the suggested method has been simulated with Microsoft Excel and MATLAB Simulink software.
The proposed method has shown to be effective for grid voltage signal synchronization in non-ideal grid conditions with frequency variation and harmonic distortion and for reference signal synchronization in multi-inverter standalone systems. Also, it is not sensitive to the DC offset in the measurement process.
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Jo Apr 14, 2024
Parallel robot mechanisms have been and are being used in a wide variety of applications such as motion simulators, high speed manipulation, machine tools and even nano-manipulators. Parallel robot mechanisms are closed-loop mechanisms presenting very good performances in terms of accuracy, rigidity and ability to manipulate large loads.
Researches on parallel robots can be divided into kinematics, dynamics and control, the most fundamental and important being the structural synthesis of parallel robot mechanisms in kinematics. Of many mechanisms that may be made by spatial combination of links and joints, finding a configuration of mechanisms with appropriate performances for applying to a necessary object as a parallel robot mechanism makes us understand the complexity and difficulty of the problems for the structural synthesis of parallel robot mechanisms. Here, quick calculation of correct degree of freedom is the basic requirement for the structural synthesis of parallel robot mechanisms.
Kim Yong Ho, a researcher at the Faculty of Mechanical Science and Technology, has proposed a new method of deriving information on mechanism’s degree of freedom by automatic generation of velocity constraint equations on computer without using any special analytical tools.
Under the condition that the endpoints of open kinematic chains－the legs of parallel robot mechanisms－are connected to one link, he automatically generated the symbolical velocity constraint equations to calculate the degree of freedom of parallel robot mechanisms by using the rank. The proposed method was applied to CPM mechanism, Bennett mechanism and Bricard mechanism. The results showed that the proposed method is correct, useful and prospective.
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Jo Apr 12, 2024
Nowadays taper threads and variable pitch threads are widely used in mechanical, medical, and other sectors. Taper threads are generally used for fixing objects to others such as wood. Variable pitch threads are mainly useful for fastening objects to soft materials with some elasticity due to their fastening characteristics changed with forward movement. For this reason, screws with the two characteristics combined are now designed and widely used. However, there are some disadvantages for machining these screws.
Kim Hak Song, a section head at the Faculty of Mechanical Science and Technology, has put forth the problems arising in the design and machining of variable pitch threads, and proposed a method for calculation of tool path and generation of NC program for cutting them on 5-axis CNC tool grinder and for virtual cutting simulation by virtual cutting simulation program VERICUT8.2.
The proposed method can be used in the design and manufacturing of implants and transmission system of taper threads with variable pitch.
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Jo Apr 10, 2024
Quantitative analysis of diffraction data usually refers to determination of amounts of different phases in multi-phase samples by using standard sample or simulation method. Quantitative analysis may also be understood as determination of particular characteristics of single phases including precise determination of crystal grain size and its structure and shape.
There are several methods of X-ray diffraction to quantify phases, but the Rietveld method has been perhaps the most useful tool in recent years as it accounts for the factors that affect the reproducibility of the intensity peaks (peak overlapping, presence of amorphous phases, and preferred orientation of crystallites).
Ro Thae Min, a researcher at the General Assay Office, has observed the quantitative value change when lattice constant is used, and not used, for fitting in the quantitative phase analysis of TiO2 by the Rietveld method.
The conclusions are as follows.
In qualitative analysis, the corresponding phase may not be correctly identified or unreconciled lattice constant in the ICSD database may be used. To avoid such mistakes, in the quantitative phase analysis, correct lattice parameters must be used for fitting. When lattice parameters are correct, Rietveld method is better than other X-ray diffraction quantitative phase methods such as internal standard method and direct method because it employs insturments, structure parameters and lattice constant of analogue phases altogether. Sometimes, however, lattice constant is not used for fitting. In this case, various lattice defects (crystallite size, rms strain, stacking and twin fault probabilities, etc.) are found in the whole diffraction pattern improvement process. Therefore, in the quantitative phase by Rietveld method, lattice constant should not be ignored to get correct quantitative value.
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Jo Apr 8, 2024
Short bed ion exchange technology utilizes fine mesh resin beads, a fully packed resin bed, and counter-current regeneration. These unique features help to improve exchange kinetics, reduce regenerant consumption and increase the concentration of strip solutions. Commercially, this technology has been extensively used in the following areas: separation and purification of strong mineral acids, removal and recycle of dissolved metals in the surface finishing industries, and production of high purity water.
The most frequent questions concerning short-bed ion exchange relate to flow distribution, because the column is only a few centimeters tall and it has to treat tremendous amount of solution in a short time.
There have been a lot of introductions of the advantages of a short-bed ion exchange column, but no articles on its detailed geometric size and design have been published yet. What is more, no information has been found on the influence of the structure and geometric size of a flow distribution plate on the flow distribution characteristics of the short-bed ion exchange column and on the optimal design based on the influence.
Kim Yong Min, a section head at the Faculty of Chemical Engineering, has discussed the influences of several parameters on flow distribution in Recoflo by using CFD program and consequently done some research to design a reasonable flow distribution plate for optimization of ion exchange processes and enhancement of separation efficiency.
The simulation results showed that 60 radial flow channels and 3 circumferential flow channels were the reasonable parameters for ensuring even flow distribution through the bed in the short-bed ion exchange column.
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Jo Apr 7, 2024
Kyuhyonginjiui, the first surveying instrument invented in Korea in 1467, was used to identify targets and directions on the ground and measure heights and distances.
It was also called injiui.
The instrument consists of two parts; a vertical axis and a horizontal scale plate that revolves around the axis vertically.
Kyuhyong, a device for aiming at target objects is attached to the axis, goes up and down vertically.
There are 24 directions inscribed on the plate for direction finding.
You can aim at any objects by turning the vertical axis round and moving kyuhyong up and down along the axis.
The compass installed on the instrument helped correct aiming.
Kyuhyonginjiui survey was, in principle, the same as present plane table surveying.
Such instrument for surveying was not found in European countries until the late 16th century, and a similar one to Kyuhyonginjiui was finally built in a German factory in the 17th century.
The fact that Korean ancestors made and used such a surveying instrument as Kyuhyonginjiui a century before other countries demonstrates their high creative wisdom and talent.
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