Jo Jan 3, 2023
Thin-walled structures such as ship and offshore structures basically consist of a number of plates stiffened by different types of stiffeners.
Continuous welding may be used for attaching stiffeners to plates, but this technique requires a large amount of welding, adds weight to the structures, and increases construction costs. In order to reduce the costs of labour and materials and save weight of the stiffened plate structures, non-continuous welding is frequently applied to the attachment of plates and stiffeners. This method of fabrication also lowers the magnitudes of welding residual stresses more than continuous welding.
Over the past few decades, the buckling and collapse behaviors of continuously welded stiffened plates under different loading conditions have been widely investigated in order to develop analytical, empirical, numerical and experimental methods.
However, little has been studied on the behavior of intermittently welded stiffened plates and, furthermore, only some numerical and experimental studies have been carried out.
Mun Ji Song, a section head at the Mirae Academy of Science and Technology, has proposed a simplified method for ultimate strength estimation of intermittently welded stiffened plates under uniaxial compression. The plate and stiffener of a stiffened plate were considered as individual beam-columns. The whole span of an intermittently welded stiffened plate was divided into welded and non-welded segments. For modeling the behavior of the intermittently welded stiffened plate, the differential equations which describe the bending of the beam-columns in welded and non-welded segments were considered.
Special attention was paid to the following two cases.
i) Case 1
It was assumed that beam-columns 1 and 2 are deformed in contact and deflections of the beam-columns 1 and 2 are equal to each other.
ii) Case 2
In this case, it was assumed that beam-columns 1 and 2 are deformed in non-contact and behaviors of the beam-columns 1 and 2 are independent of each other.
Based on the model, the Euler limit load of the intermittently welded stiffened plate was calculated. The intermittently welded stiffened plate was changed into a continuously welded one with the equivalent Euler limit load. The Paik’s empirical formulation was used to estimate the ultimate strength of the changed continuously welded stiffened plate under uniaxial compression.
The proposed method demonstrated a good agreement with FEA results. This suggests that ultimate strength of chained and staggered welded stiffened plates can be estimated by the proposed method.
For more information, please refer to his paper “Study on Ultimate Strength Estimation of Intermittently Welded Stiffened Plates under Uniaxial Compression” published in the SCI Journal “Marine Structures”.
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Jo Jan 2, 2023
The knowledge and visions of the map experts in our country in the fifteenth century were not restricted to the country but broaden to the world.
It resulted in two world maps: “Honilgangriryoktaeguktojido” in the early 15th century and “Chonhado” in 1469.
They are elaborate enough to show several tens of names of places in Europe, Africa and even the Middle and Near East
For clear distinction of different parts like lands, seas and deserts, seas are painted in blue and deserts in black, which ensures high visual effect as a map.
They contain not only the maps of our country and the world but also separate ones of other individual countries including then China, Japan, etc.
In conclusion, our ancestors, creators of time-honored and brilliant culture, made great progress in geography, too.
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Jo Dec 30, 2022
Ozone is the second to fluorine in oxidation and sterilization power and it reacts with organic and inorganic materials very well. In addition, it leaves no remainders harmful to the environment. Thus, it has been used not only for food containers but also in fish farming, medical and chemical industries etc. Recently, positive attempts are being made to use it to prevent various infectious diseases.
Accurate measurement of ozone concentration is important for its effective use. One of the most cost-effective measurements is using detector paper.
The ozone detector paper for determining concentration of ozone in the atmosphere has already been developed. When indigo carmine reacts with ozone, the paper turns from blue to white. This principle is used to measure albedo for determination of ozone concentration. The measurement range of the paper is 0~400ppb and the CT value is 0~400ppb×h. The unit of time is hour. It is impossible to precisely measure concentration over the range because the detector paper immediately turns into white completely. The response time of the detector paper is over 30 minutes.
However, research into dissolved ozone detector paper has not been conducted.
Kim Yong Ok, a researcher at the Faculty of Applied Chemistry, has developed detector paper for dissolved ozone.
The dissolved ozone reacts with KI to produce iodine, which then reacts with starch to turn the paper blue. This means that the paper turns from white to blue according to the ozone concentration. Thus, the chromaticity of the paper helps determine concentration of dissolved ozone.
This paper guarantees precise and quick measurement for up to 8ppm of concentration of ozone within a short time of 30~40s.
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Jo Dec 28, 2022
High-efficiency electric drive systems claim not only optimally designed electric machines but also efficiency-oriented control strategies.
Taking machines and drives into synergetic consideration, Jong Hak Chol, a section head at the Faculty of Electrical Engineering, has proposed a fresh particle crowd optimization (FPCO) of efficiency-oriented control algorithm called maximum outer torque per ampere (MOPA) control and maximum efficiency per ampere (MEPA) control, aiming to maximize the efficiency of interior permanent magnet synchronous machines in operation.
Differently from conventional id = 0 or maximum torque per ampere control, MOPA and MEPA fully consider the cross effect Core loss, iron loss, supplementary loss and mechanical loss.
In order to identify the accuracy of the efficiency-oriented control algorithm, he built an efficiency-oriented controlled system based on FPCO using nonsingular terminal sliding (NTS) controller, and on the basis of this, he inspected the stabilization of current trajectory and the voltage vector from simulation and testing. After that, he verified the higher effectiveness of MOPA and MEPA through the operation experiment of IPMSM whose capacity is 82 kW.
You can find more information about it in his paper “Fresh particle crowd optimization of efficiency-oriented control in interior permanent magnet synchronous motor during operation” published in the SCI Journal “International journal of power and energy conversion”.
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Jo Dec 27, 2022
Every country has their symbolic animals that reflect the history and culture, excellent dispositions and extraordinary abilities of their people. Among them is a dog.
Phungsan Dog is a native breed of Korea that has left an indelible mark in the history of our nation for thousands of years. It has been tamed for ages by our ancestors in severe natural environments of the northern uplands where there were a large number of beasts such as a tiger, a bear, a wild boar, a wolf, etc.
Well adapted to the topography and climate of the mountainous forest areas in our country, the dog has features of a typical hunting dog. It is famous for its cleverness, persistence, bravery and swiftness. Though this dog is of smooth nature and quite obedient to its keeper at ordinary times, it shows a strong fighting spirit and bravery at the time of hunting and it never gives a fight up. Full of vitality, it is resistant to the cold and diseases.
It was registered as a state natural monument in April, 1956 thanks to the state measure taken by President
When visiting Ryanggang Province in May, 1958, the President said that Phungsan Dog thoroughbred is a very good breed, underscoring the need to survey its thoroughbred.
Chairman
On November 7, 2014, the respected Comrade
Today, Phungsan Dog is widely known as a national dog that symbolizes the spirit of properous Juche Korea and as a world’s famous dog.
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Jo Dec 25, 2022
Time-dependent deformations of rock are important factors for the design and construction of tunnels in the rock masses with time-dependent strength and deformation properties. Therefore, determination of the displacement and the stable time of tunnels is an indispensable task in geotechnical engineering, especially the design and construction of underground structures.
However, in some types of rock masses, tunnel displacement may increase for months or years after excavation owing to the rheological behavior of the surrounding rock masses, which greatly influences the selection of an initial tunnel support system, excavation layout, and determination of its load-carrying capacity.
Therefore, Han Un Chol, a researcher at the Science Engineering Institute, has made it possible to predict the final displacement of rock mass surrounding a tunnel, which is gradually stabilized in the shape of an S-type saturated curve by using the improved nonequidistant grey Verhulst model (INGVM) with Fourier series.
The traditional non-equidistance grey model (NGM(1,1)) and non-equidistance grey Verhulst model (NGVM) were compared to examine the feasibility of INGVM application. He only used the monitored displacements during excavation to predict the final displacement and stable time of the tunnel excabated in time-dependent rock mass.
The results showed that the proposed model was highly accurate and adaptable.
The details of this are carried in his paper “Prediction of Final Displacement of Tunnels in Time-Dependent Rock Mass Based on the Nonequidistant Grey Verhulst Model” published in the SCI Journal “Mathematical Problems in Engineering”.
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