• Structural Engineering and Mechanics
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• v.17 no.2
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• pp.245-266
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• 2004

Incremental launching method is one of the highly competitive techniques for construction of concrete bridges. It avoids costly and time consuming form work and centralizes all construction activities in a small casting yard, thus saving in cost and time against conventional bridge construction. From the quality point of view, it eliminates the uncertainty of monolithic behaviour by allowing high repetitiveness and industrial environment. But, from analysis and design point of view, the most characteristic aspect of incrementally launched bridges is that, it has to absorb the stresses associated with the temporary supports that are gradually taken on by the deck during its launch. So, it is necessary to analyse the structure for each step of launching which is a tedious and time consuming process. Effect of support settlements or temperature variation makes the problem more complex. By using transfer matrix method, this problem can be handled efficiently with minimal computational effort. This paper gives insight into method of analysis, formulation for optimization of the structural system, effect of support settlement and temperature gradient, during construction, on the stress state of incrementally launched bridges.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.2
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• pp.73-82
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• 2020

Additively manufactured, small rocket engines are perhaps the focal activities of space startups that are developing low-cost launch vehicles. Rocket engine companies such as SpaceX and Rocket Lab in the United States, Ariane Group in Europe, and IHI in Japan have already adopted the additive manufacturing process in building key components of their rocket engines. In this paper on technology trends, an existing valve housing of a rocket engine is chosen as a case study to examine the feasibility of using additively manufactured parts for rocket engines.

• Current Industrial and Technological Trends in Aerospace
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• v.6 no.1
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• pp.116-123
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• 2008

In the launch mission, mission control systems and tracking systems need time synchronization for data monitoring and data analysis. There are several standards for time synchronization and an adequate standard is selected according to the requirement of time accuracy and cost among time synchronization standards. Oscillators are used to maintain time accuracy. There are some kinds of oscillators with diverse characteristics and an adequate oscillator can be adopted according to time accuracy. In this paper, we will specify characteristics of several oscillators and standards generally used for time synchronization. And we will also introduce TSDN(time synchronization and display network) for time synchronization in Naro Space Center.

• The Journal of Engineering Geology
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• v.24 no.4
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• pp.455-461
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• 2014

The Honam-Jeju, Korea-Japan, and Korea-China subsea tunnel construction projects have drawn significant attention since the early 2000s. These subsea tunnels are much deeper than most existing natural shallow sea tunnels linking coastal areas. Thus, the need for developing new technologies for the site selection and construction of deep subsea tunnels has recently emerged, with the launch of a research project titled "Development of Key Subsea Tunnelling Technology" in 2013. A component of this research, an analysis of deep subsea geological structure, is currently underway. A ground investigation, such as a borehole or geophysical investigation, is generally carried out for tunnel design. However, when investigating a potential site for a deep subsea tunnel, borehole drilling requires equipment at the scale of offshore oil drilling. The huge cost of such an undertaking has raised the urgent need for methods to indirectly assess the local geological structure as much as possible to limit the need for repeated borehole investigations. This study introduces an indirect approach for assessing the geological structure of the seafloor through a submarine bathymetry analysis. The ultimate goal here is to develop an automated approach to the analysis of submarine geological structures, which may prove useful in the selection of future deep subsea tunnel sites.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.7
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• pp.3671-3689
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• 2019

Software defined networking brings unique security risks such as control plane saturation attack while enhancing the performance of wireless sensor networks. The attack is a new type of distributed denial of service (DDoS) attack, which is easy to launch. However, it is difficult to detect and hard to defend. In response to this, the attack threat model is discussed firstly, and then a DDoS attack prevention extension, called FuzzyGuard, is proposed. In FuzzyGuard, a control network with both the protection of data flow and the convergence of attack flow is constructed in the data plane by using the idea of independent routing control flow. Then, the attack detection is implemented by fuzzy inference method to output the current security state of the network. Different probabilistic suppression modes are adopted subsequently to deal with the attack flow to cost-effectively reduce the impact of the attack on the network. The prototype is implemented on SDN-WISE and the simulation experiment is carried out. The evaluation results show that FuzzyGuard could effectively protect the normal forwarding of data flow in the attacked state and has a good defensive effect on the control plane saturation attack with lower resource requirements.

• Journal of Astronomy and Space Sciences
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• v.37 no.4
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• pp.219-228
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• 2020

A CubeSat platform has become a popular choice due to inexpensive commercial off-the-shelf (COTS) components and low launch cost. However, it requires more power-efficient and higher-data rate downlink capability for space applications related to remote sensing. In addition, the platform is limited by the size, weight and power (SWaP) constraints as well as the regulatory issue of licensing the radio frequency (RF) spectrum. The requirements and limitations have put optical communications on promising alternatives to RF communications for a CubeSat platform, owing to the power efficiency and high data rate as well as the license free spectrum. In this study, we analyzed the performance of optical downlink communications compatible with CubeSat platforms in terms of data rate, bit error rate (BER) and outage probability. Mathematical models of BER and outage probability were derived based on not only the log-normal model of atmospheric turbulence but also a transmitter with a finite extinction ratio. Given the fixed slot width, the optimal guard time and modulation orders were chosen to achieve the target data rate. And the two performance metrics, BER and outage data rate, were analyzed and discussed with respect to beam divergence angle, scintillation index and zenith angle.

• ETRI Journal
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• v.44 no.5
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• pp.715-732
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• 2022

Despite the successful launch of Advanced Television Systems Committee (ATSC) 3.0 broadcasting worldwide, broadcasters are facing obstacles in constructing void-less large-scale single-frequency networks (SFNs). The bottleneck is the absence of decent on-channel repeater (OCR) solutions necessary for SFNs. In the real world, OCRs suffer from the maleficent feedback interference (FI) problem, which overwhelms the desired input signal. Moreover, the undesired multipaths between studio-linked transmitters and the OCR deteriorate the forward signals' quality as well. These problems crucially restrict the feasibility of conventional OCR systems, arousing the strong need for cost-worthy advanced OCR solutions. This paper presents an ATSC 3.0-specific solution of advanced OCR that solves the FI problem and refines the input signal. To this end, the FI canceler and channel equalizer functionalities are carefully implemented into the OCR system. The presented OCR system is designed to be fully compliant with the ATSC 3.0 specifications and performs a fast and efficient signal processing by exploiting the specific frame structure. The real product of ATSC 3.0 OCR is fabricated as well, and its feasibility is verified via field and laboratory experiments. The implemented solution is installed at a commercial on-air site and shown to provide substantial coverage gain in practice.

• Journal of the Korea Institute of Military Science and Technology
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• v.26 no.1
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• pp.64-71
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• 2023

In the recent defence industries, it is required to develop the small and low cost embedded systems for guided missiles. According to the characteristics of guided missiles, the mission is conducted with multiple phases, which include a squib activation phase. By considering the unexpected squib activation, the squib system should be disabled after the launch of a guided missile. Therefore, the squib system needs to include the functions of the safe ignition and status check. This paper presents the squib ignition and status check circuits design for the compact embedded systems in guided missiles. Validation results show that for the functions of the squib ignition and status check, the presented circuits design performs well. The designed circuits also were implemented with various electronic devices and validated by the ground and flight tests.

• Journal of Energy Engineering
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• v.16 no.4
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• pp.202-214
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• 2007

The concept of HSA (Home Service Aggregator) is derived from performing the energy IT business efficiently as well as successfully launcing a new service based on BPL (Broadband over Power Line). The HSA business using a BPL can extend the field of energy industry and an give a chance to create a new demand by consumer-oriented services. This study focuses on the exact evaluation of HSA business using BPL, and reasonable trusty evaluation should be the first step to launch the HSA business. In this study, the categories of cost are comprised of equipment (mainly RSM and MGW) cost, instalation cost, and maintenance cost. AMR (Automatic Meter Reading), internet integration billing service, integration charging service, internet service, sorority service, and electricity safety are listed for benefit. In this study, the ROI of HSA business is 0.9594, which is less than 1. However, that value does not consider the electricity safety benefit which is classified as a social benefit. Therefore, the value can be above 1 if it includes social and private benefits.

• Journal of Aerospace System Engineering
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• v.12 no.4
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• pp.64-74
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• 2018

Small high-resolution Earth observation satellites require precise optical alignment at the submicron level. However, misalignments can occur due to the influence of external factors during the launch and operation despite the sufficient alignment processes that take place before the launch. Thus, satellites need to realign their optical elements in orbit in what is known as a refocusing process to compensate for any misalignments. Refocusing algorithms developed for satellites have only considered de-space, which is the most sensitive factor with respect to image quality. However, the existing algorithms can cause correction error when inner and external forces generate tilt amount in an optical system. The present work suggests an improved online refocusing algorithm by considering the tilting effect for application in the case of a de-spaced and tilted optical system. In addition, the algorithm is considered to be efficient in terms of time and cost because it is designed to be used as an online method that does not require ground communication.