Jo Feb 18, 2023
Recently, under the increasing ecological awareness and stringent regulations for marine environmental protection, we often meet vessels in which stern tube water-lubricated plastic bearings are applied to the propulsion shafting.
It is because plastic bearings offer simplicity, low initial and operating costs, and no risk of oil pollution, compared with oil-lubricated white metal bearings or water-lubricated rubber bearings.
A research team led by Kim Chun Il, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has developed a water-lubricated stern bearing with plastic material.
First, they conducted a test on the suitable composition of plastic sliding bearings and their characteristics. Then, they determined the lubrication characteristics of stern tube plastic bearings such as the allowable load capacity of bearings, the stiffness and damping coefficients of water lubricating films, and the maximum allowable radial clearance of bearings.
The friction coefficient (against brass) is 0.003 and the dilatation (radial direction) is 0.005.
Compared with a stern tube rubber bearing, the load capacity is raised by 1.2 times and the lifetime is prolonged by 1.5 times thanks to the smaller value of frictional coefficient and higher breaking-in capacity. In addition, it results in the reduction in initial cost by one fifth and in labour and time by one third as it needs no non-ferrous metal and natural rubber.
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Jo Feb 16, 2023
Choe Chol Min, a researcher at the Faculty of Electronics, has developed a portable photocolorimetric ozone meter for regular calibration of a real-time ozone meter at disinfection stations, based on indigo carmine spectrophotometry.
Ozone disinfection process needs both correct real-time measurement of ozone concentration at disinfection stations and regular calibration of ozone meters.
All over the world, indigo carmine spectrophotometry is the choice of the standard method for measurement of ozone concentration and it is being widely used for the air and ozone generators.
The photocolorimetric ozone meter is based on Lambert-Beer’s law, which explains that absorbance is proportional to the concentration of chemical sorts absorbing the light when a solution absorbs the light of given wavelength and the thickness of the solution layer is fixed.
The photocolorimetric ozone meter consists of a driving circuit for light source, a light detection circuit, a filtering and amplifing circuit, a source supply stabilizing circuit and a microprocessor.
The driving circuit for light source contains a constant-current source circuit to stabilize the maximum of light source brightness. The light source driving current can be changed from 0mA to 22mA. For exact driving current, an operational amplifier AD8602 with 80㎶ of input bias voltage, 0.2pA of bias current, and 80dB of PSRR is used in the constant-current source circuit.
In the light detection circuit, higher accuracy of measurement is provided by the difference in the light intensity from the light source (I0) and that passed through the sample (I). Here, a low noise operational amplifier OPA111 is used.
The technical characteristics of the device are as follows.
Measuring range: 0~200ppm
Relative error: Less than 0.4%FS
Relative standard deviation: Less than 1% (n=11)
At persent, the meter is in wide use at several disinfection stations.
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Jo Feb 12, 2023
Flexible metallic film temperature sensors play an important role in some modern engineering applications such as temperature measurements of curved surfaces or interlayer structures with narrow gaps of industrial equipment (e.g. iron cores of generators, motors and transformers).
Platinum is generally used for metallic film temperature sensors thanks to its high accuracy and stability, but it is expensive. Recently, copper film temperature sensors are widely utilized for temperature measurement instead of platinum sensors as the design based on PCB technology allows cost-efficient fabrication, easy handling, and simple retrofitting and replacement. However, defects existing on the PCB leads result in the decline of the performance and stability of the sensor.
A research team led by Pak Yong Thaek, head of Semiconductor Institute, has developed a temperature measurement system for generator protection in consideration of the operation characteristics of generators. For this, they designed a new structure of temperature sensors and proposed a method to design the most suitable thermometer and communication hub for the conditions of power plants.
The system consists of sensors, one-channel and multi-channel thermometers and communication hubs.
The one-channel and multi-channel thermometers measure in real-time the temperature of local points, display the temperature values and output alarm sounds and protection relay signals. The thermometers also transmit measured data to the communication hub.
In order to avoid the lethal defects of PCB leads like disconnection and fall, detour leads are added to the new design. Thus, the copper film resistive lead of the sensor consists of four parts: main resistive lead, detour lead, correction lead and pads. In addition, 3-line mode is used to prevent low accuracy due to the connection wire from the sensor to the amplifing circuit.
The measurement range is -50~170℃ and the error is 0.5℃.
Tested for a long time of over 3 000 hours at 150℃, the sensor proved its reliability. The deviation rate of resistance of the sensor is less than 0.1%. TCR is 4.1×10-3℃-1 and the maximum current is 10mA.
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Jo Feb 9, 2023
It is of great importance to make a proper classification of underwater sediments for protecting the ecological environment and dredging materials such as sand or gravel, mud, etc. in rivers or oceans.
Ri Un Song, a section head at the Faculty of Shipbuilding and Ocean Engineering, has newly defined some characteristic parameters and established Artificial Neural Network (ANN) with these parameters as input layers. By doing so, he has managed to find a way to raise the accuracy of acoustic sediment classification on rough riverbeds.
The neurons of input layers used include the newly-defined roughness and monotonic decreasingness of the tail potion of the first echo signal as well as the roughness index and hardness index usually employed in Rox Ann and QTCView.
The proposed method has raised the accuracy of acoustic classification of sediments in the water areas with rough floors to 95%.
It is now in effective use for search for gravels and sand by dredging vessels on riverbeds, and for classification of sediments accumulated on the dams of floodgates, tidelands, etc.
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Jo Feb 7, 2023
A research team led by Sin Jung Sok, a researcher at the Faculty of Earth Science and Technology, has developed an ultrasonic mixer to improve the combustibility of heavy oil burners by ultrasonic waves generated by the steam in a tubular furnace.
This technology can help to make ultrasonic waves by high pressure steam to change the carbon chain structure of heavy oil whose relative viscosity is over 200 and to decrease the viscosity. It leads to the improvement of spraying characteristics of burners and to the sharp reduction of consumption of heavy oil necessary for oil processing.
The ultrasonic mixer has 1st ultrasonic wave generator, mixing unit of heavy oil ― steam, 2nd ultrasonic wave generator, spraying unit, etc.
In the 1st ultrasonic wave generator, high pressure steam that passes through the jet orifice, resonator and reflector can make ultrasonic waves of 14~17kHz, which enter the heavy oil ― steam distributor.
In the heavy oil ― steam mixing unit, the heavy oil coming in four tangential directions through the heavy oil ― steam distributor is mixed with steam. Then, the mixed liquid is sprayed. At this time, the chain structure of the heavy oil is destroyed primarily by the ultrasonic waves.
When the sprayed liquid causes the 2nd resonance while passing the resonator of the 2nd ultrasonic wave generator, most of the heavy oil particles are pulverized to be smaller than 20㎛. The purpose of the 2nd ultrasonic wave generation is to break up the liquid particles mixed through the heavy oil ― steam distributor into smaller ones.
In the spraying unit, heavy oil and steam are mixed evenly and sprayed through 8 holes. The size of about 90% of heavy oil particles is within the range of 10~20㎛.
The intensity of ultrasonic wave is 200dB at the 1st ultrasonic wave generator and 220dB at the 2nd one.
If the size of heavy oil particles is below 30㎛, the combustion efficiency of heavy oil in tubular furnaces reaches higher than 95%, which equals the case of combustion of heavy oil whose relative viscosity is 100.
The introduction of this device to tubular furnaces for oil processing can lower the flue temperature by 15~20℃ and reduce the consumption rate of oil. It can also improve the spraying quality of liquid and raise the combustion efficiency in the burners of tubular furnaces.
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Jo Jan 31, 2023
Song Man Hyok, a section head at the Faculty of Earth Science and Technology, has proposed a new method to extract image features and to evaluate fractality based on two-dimensional (2D) continuous wavelet transform (CWT).
Multi-directional 2D CWT coefficients are used to determine the direction and magnitude of image intensity gradients directly unlike other methods using gradient components in horizontal and vertical directions. Image feature points are detected by comparing candidate directional 2D CWT coefficients at candidate points and their neighbors instead of gradient magnitudes or 2D CWT moduli used in traditional methods. It enables extracting multiscale image features including line singularities such as corners which are recognized to be hardly extracted by traditional methods. This offers an advantageous condition to study fractal objects consisting of lots of line singularities.
Assuming that the detected multiscale image features can reflect multiscale fractal measures used to evaluate fractality, that is, self-similarity across scales, he has proposed a method to evaluate fractality and calculate fractal dimensions using multiscale image features.
The application of the proposed method to theoretical fractal models proved that it is convenient and effective in extracting the image features of the models consisting of many line singularities and in calculating their fractal dimensions. It is concluded that the method is useful to deal with fractality evaluation of geoscientific objects such as coastlines and stream networks.
For more information, please refer to his paper “Image feature extraction and fractality evaluation based on two-dimensional continuous wavelet transform: Application to digital elevation model data” published in the SCI Journal “Fractals”.
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