Abstract: An investigation on the effect of the neutronic behavior on the lattice for a Deuterium
Critical Assembly (DCA) in JNC (Japan Nuclear Cycle Development Institute) has been performed. The DCA, the heavy water moderated and light water cooled pressure-tube type research facility, was designed not only for the core physics research, but also for the development of the core-related technology for the Advanced Thermal Reactor (ATR). The core structure of the ATR is highly
heterogeneous and it is separated from the heavy water moderator by a calandria tube. Therefore, the neutron behavior is quite complicated and sensitive to a change of the core structure. In this study, the assessment of the core physics characteristics such as the multiplication factor and the void coefficient for the DCA was conducted using the WIMS-D5 code and the results were compared with those of both the experimental data and WIMS-AECL.
Abstract: The friction force is the most important factor for the design of control unit in a braking system. For a long time, many researchers have been striving to improve the accuracy in the measurements of friction coefficients [1,2]. However, there were many difficulties because the friction coefficients are affected by a number of conditions and parameters, such as normal force, temperature, characteristics of road condition, and weather. For the development of ABS of the aircraft, the HILS (Hardware-In-the-Loop-Simulation) test and dynamometer test were carried out.
For the calculation of the friction coefficients, the wheel moment was measured using the load cell mounted on the housing of the wheel. The test conditions were dry and greasy, with friction coefficients of 0.7 and 0.4, respectively. In this paper, the test results of the friction coefficients were represented and the improvement method was suggested.
Abstract: Simple methods are developed to predict temperatures of a satellite box during the launch stage. The box is mounted on the outer surface of a satellite and directly exposed to a space thermal environment for the time period from fairing jettison to separation. These simple methods involve solving a 1st order ordinary differential equation (ODE), simplified from the full governing equation when several assumptions are made. The existence of an analytical solution for the 1st order ODE is determined depending on the treatment of the time-dependent molecular heating term. Even for the case that the analytical solution is not available due to the time dependent term, the 1st order ODE can be solved by relatively simple numerical techniques. The temperature difference between two different approaches (analytical and numerical solutions) is relatively small (less than 1°C along the time line) when they are applied to the STSAT-I launch scenario. The present
methods can be generally used as tools to quickly check whether a satellite box is safe against the space environment during the launch stage for the case that the detailed thermal analysis is not available.
Abstract: A control system and ground pilots who operate the system are necessary to control an unmanned vehicle. This paper describes a Ground Control System(GCS) of the unmanned airship developed at KARI. The system is capable of mission planning, real-time data processing, remote real-time data analysis, and data storage and extraction. We estimate the performance of the system and verify its reliability using real-time simulation software. The software relies on a priority-based
multitasking algorithm. No task has delay time and deadlock with semaphore, all of the ground system works in stable during the test flight.
Abstract: An efficient and reliable pressurization system for an oxidizer and fuel of a liquid
propellant rocket is critical for a successful launch. A liquid helium pressurization system employing a heater can reduce its mass, and be made simpler and more reliable than conventional pressurization systems. The key issue to minimize the total mass of the system is the optimization of the size of the liquid helium tank. In this paper, we describe a method to determine the optimal size of a liquid helium tank, and present one set of results under a given set of requirements. In this pressurization system, the heater design is represented by the heater efficiency. To estimate the heater efficiency, the convection heat transfer coefficient should be known beforehand. The guideline how to estimate this convection heat transfer coefficient based on the preliminary experimental data is also presented in this paper.
Abstract: Gravitational lensing (GL) provides the sudden changes in flux densities, when a
compact source crosses a critical curve. Due to lensing, the image of the lensed object is split into at least two images, and merged together upon the source crossing the critical curve. Light paths of the images differ from one another’s, so results time delay to the observer. Asymmetric light curves and the time delay in lensing contain astrophysical information on the GL system: e.g. source structure,
density distribution, and cosmological distance scale. The disalignment of GL system, b, is an important parameter in the GL analysis. We derive b as a function of density parameter of gravitational lens mass. We present an analytical formulation
to determine cosmological distance scales, hence the Hubble parameter, and other properties of GL system. We also discuss degeneracies in the GL mapping.
Abstract: This paper presents the development of a Ka band Input Filter Assembly(IFA) with very low insertion loss and a high temperature stability suitable for a communication satellite transponder. The IFA consists of a cross directional test coupler to check the input signal level of the transponder and an input filter to pass the uplink band signals. The test results show good agreement with the simulation and compliant to the requirements with the temperature range from –20 °C to 60 °C. This IFA will be used for the communication satellite in Korea.
Abstract: We investigate the cosmological perturbations based on the f(R) gravity theory.
Comparing the large angular scale CMBR observation we obtain several important constraints on the inflation model based on the f(R) gravity theory: the ordinary slow-roll assumption during the inflation with the Zel’dovich spectral conditions for the scalar and the tensor-type structures yields R2 gravity as the unique candidate. Also, the considered model predicts the nearly scale-invariant Zel’dovich spectra. We derive the strong constraints on the coupling constants of the R2 term and the
energy scale during the inflation using the COBE-DMR observations. The result shows the gravitational wave contribution is very small. Therefore, future observations of the spectral indices and the gravitational wave contribution to CMBR temperature and polarization anisotropies will subject the current inflation models to a test.
Abstract: Synthetic aperture radar (SAR) provides information different from those gathered by optical sensors and it acquires data day or night regardless of cloud cover through the microwave spectrum. The SAR processing system is an essential requirement in every ground station in order to properly interpret and fully utilize the information contained in these data sets. This paper describes the processing algorithms that generate images from the SAR signal and proposes the application of SAR ground station development to satisfy such requirements. A SAR ground system is implemented using those algorithms. It generates SAR image products according to processing levels. Experiments conducted in this paper show results comparable to the commercial SAR processing software.