Papers by Keyword: Time-Step

Abstract: The aircraft's navigation system routinely makes use of the Global Navigation Satellite System (GNSS) during numerous phases of a flight. A primary concern is Ionospheric Gradients, which might impact the global positioning system's positional accuracy. Data from a single GNSS reference station is required for Ionospheric Spatial Gradient estimation using the well-known Time-Step Method. Temporal decorrelation faults are one type of inaccuracy that accompany the Time-Step Method. Conversely, the Station-Pair technique uses two GNSS reference stations that are closely separated to estimate the Spatial Gradient. When GNSS stations are far apart, the Station-Pair Method is ineffective in determining delay gradients in ionospheric plasma at short baselines. An attractive alternative is Satellite-Pair Method which uses observations from a single GNSS reference station. Satellite-Pair approach compares the Ionospheric delays of two satellites that are being monitored by the same receiver at the same time. GNSS data for the year of January to December 2021 was obtained from the mid latitude stations p502 (Imperial County, California) with Geographical Latitude and Graphical Longitude 32°58'55.2"N and 115°25'19.2"W and p509 (Holtville, California) with Geographical Latitude and Graphical Longitude 32°48'40.18"N and 115°22'48.95"W located in California, USA. The maximum Ionospheric Spatial Gradient for disturbed day (15 June 2021) using Satellite-Pair Method is found to be 4.6047 mm/100km, whereas for Existing Time-Step and Station-Pair Methods are 2.2089 mm/100km and 1.8859 mm/100km.The Spatial Gradients are found to be occurred mostly between 2000hrs to 2200hrs UT.

Abstract: A 2D CFD numerical method based on loose coupling algorithms was adopted to simulate vortex induce vibration of a spring-mounted cylinder. As the accuracy and reliability were focused, the effect analysis of time-step was applied to three typical reduced velocities, which was represented initial branch, upper branch and lower branch respectively. Under the effective courant number, there exist a time-step which would lead to the highest efficiency and the best match for experiment. Because of the limit of RANS method, the predicted vibration amplitude at the upper branch would be lower than experiment value, while the phase angle is sensitive to time step.

Abstract: The heat transfer during the casting solidification process includes: the heat radiation of the high temperature casting and the mold, the heat convection between the casting and the mold, and the heat conduction in the casting and the casting to the mold. In this paper, a formula of time step in simulation of solidification is derived, considering the heat radiation, convection and conduction based on the conservation of energy. The different heat transfer condition between the ordinary sand casting and the permanent mold casting is taken into account in this formula. The characteristic of heat transfer in the interior and surface of the casting is also considered. The numerical experiments show that this formula can avoid radiation of the computation, and can improve the computational efficiency about 20% in the simulation of solidification process.