Jo Apr 29, 2022
In general, knowledge on the mechanical properties of a rock mass is a prerequisite for the numerical simulation and the design of the underground structure, opening-up of mineral deposits and mining processes.
Since the early 1990s, many scholars have proposed a variety of methods to determine the strength and deformation parameters of a rock mass using geological strength index (GSI). The standard GSI chart considers qualitatively the surface condition and blockness of a rock mass, and it is used to estimate values between 0 and 100 representing the overall geotechnical quality of the rock mass. The best outcomes can be achieved only by the collaboration between experienced engineering geologists and geotechnical engineers.
To quantitatively determine the GSI, you have to detect the joints in two-dimensional (2D) photographs of a rock mass surface using image processing technology, then determine the fractal dimension, and finally predict the GSI using artificial neural network (ANN).
The detailed steps for joint detection on the rock mass surface are as follows.
Step 1: Converting the color image of a rock mass into a black and white one
Step 2: Smoothing and sharpening
Step 3: Binary encoding
Step 4: Noise removal
Step 5: Detection of the joints
The fractal dimension of a 2D rock mass surface can be calculated with previous research findings.
A 3-layer BP ANN is used for predicting the GSI of the surface of a jointed rock mass.
On the basis of the GSI chart, an ANN model is established, in which the input neurons are the fractal dimension and surface condition index (i.e. roughness and weathering condition), and the output neuron is a GSI value. And the number of neurons of a hidden layer is first set to three and it is finally determined via learning procedure to establish the most effective ANN structure.
In this way, the GSI of a jointed rock mass can be determined quantitatively and objectively by the interface, coded by using built-in tools of MATLAB 7.0, such as image processing, fractal analysis and ANN.
The details of this can be found in the essay, “Determination of geological strength index of a jointed rock mass based on image processing” by Hong Kun Ui, dean of the Faculty of Mining Engineering, presented to the SCI Journal “Journal of Rock Mechanics and Geotechnical Engineering”.
...
Jo Apr 26, 2022
Materials selection involves a multiattribute decision making whereby materials engineers choose optimal materials among more than two alternatives on the basis of more than two attributes.
Technique for order preference by similarity to ideal solution (TOPSIS) is a well-known multi attribute decision making (MADM) method and it has been widely used in materials selection.
It is based on the principle that the best alternative must have the shortest distance from the positive ideal solution (PIS) and the farthest distance from the negative ideal solution (NIS).
However, the TOPSIS has a non-negligible drawback: rank reversal. It refers to the change in the ranks of the alternatives when one alternative is removed from or added to the list of alternatives.
Although many works have been conducted, the MADM methods such as TOPSIS still suffer from rank reversal, and it is necessary to give further study to perfectly overcome it.
According to the traditional TOPSIS, when the composition of the alternatives is changed, the normalized decision-matrix is changed. The PIS and the NIS are determined from the maximum or minimum value among the attribute values of the present alternatives. When the alternative with maximum or minimum value is removed or added, the PIS and the NIS are changed. Hence, the distances from the alternatives to the PIS and the NIS are changed, and the relative closeness values are also changed, and therefore, rank reversal may be generated.
To overcome the rank reversal, the normalization method and the determination method of the PIS and the NIS should be irrelevant to the composition of alternatives. Therefore, there is a need to improve the normalization method and the determination method of the PIS and NIS.
The normalization of decision-matrix by the linear max-min normalization method can solve this problem.
The application of the improved TOPSIS without rank reversal to select the best absorbent layer material for thin film solar cells (TFSCs) showed that it could fully overcome rank reversal and that it could be applied to many real materials selection problems in practice.
You can find more information about this in “Materials selection method using improved TOPSIS without rank reversal based on linear max-min normalization with absolute maximum and minimum values” presented by Yang Won Chol, a researcher at the Faculty of Materials Science and Technology, to the SCI Journal “Materials Research Express”.
...
Jo Apr 23, 2022
A research team led by Hong Yong Jun, a researcher at the Institute of Electric Engineering, has developed and introduced a single-phase grid connected VSI(Voltage Sourced Inverter). It can not only transfer active power to the national power grid by converting the DC power generated by PV(Photovoltaic) modules into AC active power and synchronizing it with the voltage and frequency of the grid, but also control reactive power independently.
They realized the control of reactive power in the grid-connected VSI by applying the IRP (instantaneous reactive power) theory, the base of the FACTS(flexible AC transmission system). For this control, they had to ensure the exact tracking of the frequency of the grid voltage by introducing the fictitious phase by the SOGI(second-order generalized integrator) and FLL(frequency locked loop).
Then, they took control of grid injected current by a PR(proportional resonant) regulator with proper parameters, and added anti-islanding detection by active frequency drift.
The THD(total harmonic distortion) of grid-injected current is 3.6% and the time required for anti-islanding detection is less than 0.1s.
...
Jo Apr 21, 2022
A research group led by Jang Ki Ho, a section head at the Faculty of Heat Engineering, has developed a 10kV electric boiler designed to use the electricity from a power system directly, and they are now working hard to make further achievements in their research.
Boilers are largely divided into two types, i.e. a low voltage electric boiler (LVEB) and a high voltage electric boiler (HVEB).
In a LVEB, heat is generated by Joule heating effect in an electrical resistor as an electrical heating element below 380V and is transferred to fluids. Usually, the electrical heating element used in a LVEB produces several kilowatts of thermal power.
However, hundreds or thousands of kilowatts are needed to heat various kinds of liquid for swimming pools, ponds used for aquaculture, sensitive products used in chemical and agro alimentary processes and buildings. The heat power output of boilers used for controlling the load in a wind power station or a nuclear power station is the same. Even if several heating elements below 380V can be used as one, it remains uneconomic, because it needs a transformer that maintains the supply system voltage at 380V, and it also causes a considerable energy loss.
On the contrary, an HVEB(10kV) offers several advantages: it produces thousands of kilowatts of high electro-thermal power, it needs comparatively low investment, it is easy to make, and it can be operated without a transformer from the direct supply from an electric power system.
The problem is the safety of a high-voltage electric boiler. It is difficult to predict the amount of thermal power in the step of its design because it depends on the temperature, velocity and specific resistance of the fluid that are also changed in relation to each other. To solve these problems, they proposed a 10kV electric boiler equipped with a ceramic insulation tube inside and determined its geometrical sizes and operation parameters through a numerical analysis of coupled thermal, hydro mechanical and electrical fields in the water heating process. On the basis of this, they completed it through tests and practices.
The investment of an 10㎸ electric boiler is under ½, and the installation area under ¼, compared to a LVEB of the same capacity. And there is no consumed power due to the operation of a transformer.
...
Jo Apr 19, 2022
See-saw is one of the folk games enjoyed by the Korean people.
There exist several arguments for the origin of see-saw. Some historians claim that it originated from a woman who went on the see-saw outside the wall of the prison to see her imprisoned husband in the period of the Koryo Dynasty while some others believe that it started from the women’s practice of looking over the fence on a piece of board in the yard as a sign of resistance to feudal restraints. It is also said to be derived from the principle of a treadmill used for pounding cereal in the past.
See-saw used to be done mostly on the Lunar New Year’s Day and Jongwoldaeborum (January 15 by the lunar calendar). That was because it was appropriate time for people to enjoy themselves breathing in as much fresh air as they wanted in the currents of warm spring air after the long period of the severe cold striking from morning to evening.
It was so good for women’s health and life that there went an old saying, “A see-saw in January keeps pricks away from soles that year.”
As it is easy and can be played everywhere, middle-aged women as well as young girls can train themselves jumping up and down merrily. In addition, it is in accordance with active and optimistic Korean women’s sentiments of life.
Thanks to the policy of the national heritage conservation of our Party and state, see-saw, the Korean folk game, is still encouraged as the one enjoyed by our women and as one of the national sporting events.
...
Jo Apr 18, 2022
There are a great number of world-famous specialities in the DPRK, the land of beautiful mountains and rivers, and among them is Koryo Insam.
Koryo Insam, a special medicinal plant in the DPRK with a time-honoured tradition, has such a mysterious and unique medicinal effect that it is well-known all over the world as a cure-all and a tonic bringing eternal youth.
Even though a lot of kinds of plants in the insam(jinseng) family are growing and are being cultivated in many countries and regions in the world, none of them is more effective, greater in demand and more time-honoured than it.
The word insam originated from its root which resembles a human body. We call those growing naturally in the mountains wild insam while those cultivated artificially is called insam.
Well-known insam plants that have been used by people all around the world so far include Koryo(Korean) Insam, Chinese Insam(Samchil), Japanese Insam(Jukjol insam), Siberian Insam(eleuterococcus senticosus), Western Insam(Hwagisam), etc.
The most famous of all these is none other than Koryo Insam.
The custom of cultivating and using Koryo Insam was nominated as part of the national intangible cultural heritage and the method of cultivating and processing it has still been inherited.
It is classified into two according to the processing method: hongsam(red) and paeksam(white).
Hongsam is insam steamed and dried at a certain temperature and paeksam refers to insam which is cleaned and dried. Insam in its original state is called susam.
As insam is rich in essential amino acid, various vitamins and minerals, etc., it is used as a basic ingredient for a variety of Koryo medicine and tonics.
It, in addition, renews vigor, relieves fatigue, improves mental and physical abilities and promotes health.
Nowadays a large number of insam products such as insam tea, insam extract, insam liquor, insam sweet medicine, etc. are making an active contribution to the improvement of our people’s health and cosmetics produced with insam as major ingredients are also in great demand.
A foreign specialist in crude drug wrote that the value of insam is represented clearly by the international market price and Koryo Insam cultivated in the DPRK is twice to four times more expensive than those from China or Japan although they are of the same kind, and that it is mainly attributable to the cultivation techniques including choice of superior kind, fertile soil, scientific manuring and prevention from blights and harmful insects.
Under the wise leadership and warm care of our Party, farms, factories and institutes for professional cultivation, processing and research are well established in Kaesong, the original home of insam, and they are working hard to conserve and preserve the peculiar features of Kaesong Koryo Insam, a speciality of our country, and to boost its yield.
...
