• Strategy21
• /
• s.42
• /
• pp.5-52
• /
• 2017

Debates about introducing nuclear submarines have been a main issue in Korea. The highest officials and the government has started to think seriously about the issue. Yet there were no certain decision to this issue or any agreements with US but it is still necessary to review about introducing nuclear submarines, the technologies and about the business. The reason for such issues are the highest officials of Korea to build nuclear submarine, nK's nuclear development and SLBM launching. ROKN's nuclear submarine's necessity will be to attack(capacity to revenge), defend(anti-SSBN Operation) and to respond against neighboring nation's threat(Russia, Japan, China). Among these nations, US, Russia (Soviet Union), Britain, France had built their submarines in a short term of time due to their industrial foundation regarding with nuclear propulsion submarines. However China and India have started their business without their industrial foundation prepared and took a long time to build their submarines. Current technology level of Korea have reached almost up to US, Russia, Britain and France when they first built their nuclear propulsion submarines since we have almost completed the business for the Changbogo-I,II and almost up to complete building the Changbogo-III which Korea have self designed/developed. Furthermore Korea have reached the level where we can self design large nuclear reactors and the integrated SMART reactor which we can call ourselves a nation with worldwide technologies. If introducing the nuclear submarine to the Korea gets decided, first of all we would have to review the technological problems and also introduce the foreign technologies when needed. The methods for the introduction will be developments after loans from the foreign, productions with technological cooperations, and individual production. The most significant thing will be that changes are continuous and new instances are keep showing up so that it is important to only have a simple reference to a current instances and have a review on every methods with many possibilities. Also developing all of the technologies for the nuclear propulsion submarines may be not possible and give financial damages so there may be a need to partially introduce foreign technologies. For the introduction of nuclear propulsion submarines, there must be a resolution of the international regulations together with the international/domestics resistances and the technological problems to work out for. Also there may be problem for the requirement fees to solve for and other tough problems to solve for. However nuclear submarines are powerful weapon system to risk everything above. This is an international/domestically a serious agenda. Therefore rather than having debates based on false facts, there must be a need to have an investigations and debates regarding the nation's benefits and national security.

• Journal of Powder Materials
• /
• v.31 no.1
• /
• pp.16-22
• /
• 2024

Composite-based piezoelectric devices are extensively studied to develop sustainable power supply and self-powered devices owing to their excellent mechanical durability and output performance. In this study, we design a lead-free piezoelectric nanocomposite utilizing (Ba_0.85 Ca_0.15)(Ti_0.9Zr_0.1)O₃ (BCTZ) nanomaterials for realizing highly flexible energy harvesters. To improve the output performance of the devices, we incorporate porous BCTZ nanowires (NWs) into the nanoparticle (NP)-based piezoelectric nanocomposite. BCTZ NPs and NWs are synthesized through the solid-state reaction and sol-gel-based electrospinning, respectively; subsequently, they are dispersed inside a polyimide matrix. The output performance of the energy harvesters is measured using an optimized measurement system during repetitive mechanical deformation by varying the composition of the NPs and NWs. A nanocomposite-based energy harvester with 4:1 weight ratio generates the maximum open-circuit voltage and short-circuit current of 0.83 V and 0.28 ㎂, respectively. In this study, self-powered devices are constructed with enhanced output performance by using piezoelectric energy harvesting for application in flexible and wearable devices.

• Journal of Sensor Science and Technology
• /
• v.33 no.1
• /
• pp.34-39
• /
• 2024

Energy harvesting technology that converts the wasted energy resources into electrical energy is emerging as a semipermanent power source for self-powered electronics and wireless low-power sensor systems. Among the various energy conversion techniques, flexible piezoelectric energy harvesters (f-PEHs), using materials with piezoelectric effects, have attracted significant interest because they can harvest a small mechanical energy into electrical signals without constraints of time and space in various environments. In this study, we used a flexible piezoelectric composite film fabricated by dispersing BaHf_xTi_(1-x)O₃ (x = 0, 0.01, 0.05, 0.1) piezoelectric powders inside a polymeric matrix to facilitate f-PEHs. The fabricated f-PEH with optimal Hf contents (x = 0.05) generated a maximum output voltage of 0.95 V and current signal of 130 nA with stable electrical/mechanical disabilities under periodically bending deformations. In addition, we demonstrated a cantilever-type f-PEH and investigated its potential as a sensor by characterizing the output performance under mechanical vibrations at various frequencies. This study provides the breakthrough for realizing self-powered energy harvesting and sensing systems by adopting the lead-free piezoelectric composites under vibrational environments.

• Journal of Power Electronics
• /
• v.15 no.5
• /
• pp.1305-1317
• /
• 2015

Distributed generation systems (DGSs) have been getting more and more attention in terms of renewable energy use and new generation technologies in the past decades. The self-excited induction generator (SEIG) occupies an important role in the area of energy conversion due to its low cost, robustness and simple control. Unlike synchronous generators, the SEIG has to absorb capacitive reactive power from the outer device aiming to stabilize the terminal voltage at load changes. This paper presents a novel static VAR compensator (SVC) called a magnetic energy recovery switch (MERS) to serve as a voltage controller in SEIG powered DGSs. In addition, many small scale SEIGs, instead of a single large one, are applied and devoted to promote the generation efficiency. To begin with, an expandable mathematic model based on a d-q equivalent circuit is created for parallel SEIGs. The control method of the MERS is further improved with the objective of broadening its operating range and restraining current harmonics by parameter optimization. A hybrid control strategy is developed by taking both of the stand-alone and grid-connected modes into consideration. Then simulation and experiments are carried out in the case of single and double SEIG(s) generation. Finally, the measurement results verify that the proposed DGS with SVC-MERS achieves a better stability and higher feasibility. The major advantages of the mentioned variable reactive power supplier, when compared to the STATCOM, include the adoption of a small DC capacitor, line frequency switching, simple control and less loss.

• Journal of the Korean Society for Precision Engineering
• /
• v.22 no.9 s.174
• /
• pp.107-114
• /
• 2005

With the recent progress in flexible manufacturing systems (FMS) in industry, increasing attention has been given to Automatic Guided Vehicle (AGV) systems. An AGV is a self-powered unit for transporting materials between stations without needing to be controlled by an operator. Such a system has several sensors to recognize the external state, and it is designed to travel between stations automatically without external assistance. To manage each device automatically in real time it requires a distributed controller with a main computer as the host, as well as a number of micro-controllers. In this study, an AGV system with dual motor drive was constructed. A Pentium 4 personal computer was set up as the main host for the distributed control, and this communicated with other micro-controllers in the management of the motor. The speed of each motor was also controlled by a micro-controller.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.11a
• /
• pp.193-193
• /
• 2008

Wearable and ubiquitous micro systems will be greatly growing and their related devices should be self-powered in order to avoid the replacement of finite power sources, for example, by scavenging energy from the environment. With ever reducing power requirements of both analog and digital circuits, power scavenging approaches are becoming increasingly realistic. One approach is to drive an electromechanical converter from ambient motion or vibration. Vibration-driven generators based on electromagnetic, electrostatic and piezoelectric technologies have been demonstrated. Among various generator types proposed so far, piezoelectric generator possesses considerable potential in micro system. To overcome low mechanical-to-electric energy conversion, the piezoelectric device should activate in resonance mode in response to external vibration. Normally, the external vibration excretes at low frequency ranging 0.1 to 200 Hz, whereas the resonant frequencies of the devices are fixed as constant. Therefore, keeping their resonant mode in varying external vibration can be one of important points in enhancing the conversion efficiency. We investigated the possibility of use of multi-bender type piezoelectric devices. To match the external vibration frequency with the device resonant frequency, the various devices with different resonant frequency were chosen.

• Journal of Internet Computing and Services
• /
• v.12 no.6
• /
• pp.129-137
• /
• 2011

In this paper, a fast and reliable emergency broadcasting system for Advanced Television System Committee (ATSC) Mobile DTV is proposed. The proposed protocol is based on the Emergency Alert Message (EAM) standard currently used for cable TV emergency broadcasting in the United States. The protocol is implemented and evaluated to enable fast emergency information propagation. ATSC Mobile DTV enables digital mobile broadcasting without affecting the existing ATSC legacy digital TV system. Since ATSC Mobile DTV devices are mobile and self-powered, they can effectively propagate emergency information. The proposed emergency broadcasting protocol can be applied in all countries adopting the ATSC standard.

• Smart Structures and Systems
• /
• v.6 no.3
• /
• pp.263-275
• /
• 2010

In the last decade, wireless sensor networks have emerged as a promising technology that could accelerate progress in the field of structural monitoring. The main advantages of wireless sensor networks compared to conventional monitoring technologies are fast deployment, small interference with the surroundings, self-organization, flexibility and scalability. These features could enable mass application of monitoring systems, even on smaller structures. However, since wireless sensor network nodes are battery powered and data communication is the most energy consuming task, transferring all the acquired raw data through the network would dramatically limit system lifetime. Hence, data reduction has to be achieved at the node level in order to meet the system lifetime requirements of real life applications. The objective of this paper is to discuss some general aspects of data processing and management in monitoring systems based on wireless sensor networks, to present a prototype monitoring system for civil engineering structures, and to illustrate long-term field test results.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1996.05d
• /
• pp.101-106
• /
• 1996

For the application of the neutron flux mapping, an accurate calculation of the sensitivity is required because the sensitivity is proportional to the neutron flux density. Sensitivity is defined as the current per unit length per unit neutron flux and it mainly depends on the depression factor(f), the escape probability from the emitter($\varepsilon$1) and the charge build-up factor of the insulator layer(c). A Monte Carlo simulation was accomplished to calculate the sensitivity of rhodium emitter material and alumina(Al$_2$O$_3$) insulator with a cylindrical geometry, based on the (n,${\beta}$) interaction and on other interaction including the secondary electron generation for the more accurate estimation of the sensitivity. From the simulation results, factors fur the sensitivity were accurately calculated and compared with other theoretical and experimental values. In addition, the sensitivity linearly increases and saturates as the emitter radius increases. The accomplished method is useful in the analysis for the change of SPND sensitivity as a function of burn-up and in the optimum design of SPND.

• Journal of Electrical Engineering and Technology
• /
• v.7 no.1
• /
• pp.75-80
• /
• 2012

In this paper, a new energy harvesting technology using stray electric field of an electric power line is presented. It is found that energy can be harvested and stored in the storage capacitor that is connected to a cylindrical aluminum foil wrapped around a commercial insulated 220 V power line. The average current flowing into 47 ${\mu}F$ storage capacitor is about 4.53 ${\mu}A$ with 60 cm long cylindrical aluminum foil, and it is possible to operate wireless sensor node to transmit RF data every 42 seconds. The harvested average power is about 47 ${\mu}W$ in this case. Since the energy can be harvested without removing insulating sheath, it is believed that the proposed harvesting technology can be applied to power the sensor nodes in wireless ubiquitous sensor network and smart grid system.