• Journal of Positioning, Navigation, and Timing
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• v.12 no.3
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• pp.307-314
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• 2023

Wide-Area Differential Global Positioning System (WADGPS) is a system that operates a number of reference stations to provide correction information to improve the accuracy of GPS users, and it is available to service users within the area where the wide-area reference stations are installed. Recently, as positioning information has been used in various applications, the need for WADGPS for precise navigation in long-distance spaced areas where the wide-area reference stations cannot be installed has been raised. This paper tested the user navigation performance outside the wide-area reference stations of the WADGPS system, which serves both GPS Precise Positioning Service (PPS) and Standard Positioning Service (SPS) users. Static and dynamic tests were conducted using vehicles, and as a result, position accuracy improvement through WADGPS was confirmed even at points hundreds of kilometers outside the network area of the wide-area reference stations. Through this, the performance of the PPS/SPS correction system and the possibility of expanding the service area were confirmed.

• Journal of Information Processing Systems
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• v.19 no.5
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• pp.563-575
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• 2023

Trajectory planning is a key technology for unmanned aerial vehicles (UAVs) to achieve complex flight missions. In this paper, a terminal constraints conversion-based Gauss pseudospectral trajectory planning optimization method is proposed. Firstly, the UAV trajectory planning mathematical model is established with considering the boundary conditions and dynamic constraints of UAV. Then, a terminal constraint handling strategy is presented to tackle terminal constraints by introducing new penalty parameters so as to improve the performance index. Combined with Gauss-Legendre collocation discretization, the improved Gauss pseudospectral method is given in detail. Finally, simulation tests are carried out on a four-quadrotor UAV model with different terminal constraints to verify the performance of the proposed method. Test studies indicate that the proposed method performances well in handling complex terminal constraints and the improvements are efficient to obtain better performance indexes when compared with the traditional Gauss pseudospectral method.

• Wind and Structures
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• v.38 no.3
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• pp.193-202
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• 2024

Modern high-rise tower designs incorporating recessed balcony cavity spaces can be prone to high-frequency and narrow-band Rossiter aerodynamic excitations under glancing incident winds that can harmonize and compete with recessed balcony volume acoustic Helmholtz modes and facade elastic responses. Resulting resonant inertial wind loading to balcony facades responding to these excitations is additive to the peak design wind pressures currently allowed for in wind codes and can present as excessive facade vibrations and sub-audible throbbing in the serviceability range of wind speeds. This paper presents a methodology to determine Cavity Amplification Factors to account for façade resonant inertial wind loads resulting from balcony cavity aero-acoustic-elastic resonances by drawing upon field observations and the results of full-scale monitoring and model-scale wind tunnel tests. Recessed balcony cavities with single orifice type openings and located within curved façade tower geometries appear particularly prone. A Cavity Amplification Factor of 1.8 is calculated in one example representing almost a doubling of local façade design wind pressures. Balcony façade and tower design recommendations to mitigate wind induced aero-acoustic-elastic resonances are provided.

• Steel and Composite Structures
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• v.50 no.6
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• pp.643-658
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• 2024

The main aim of this study is to quantify the code seismic design coefficients of the RCS system, which consisted of reinforced concrete columns and steel beams, based on the FEMA P-695 methodology. The underlying intention is to evaluate the seismic performance of the RCS system at the system level rather than the connection level. A set of 24 archetype buildings with a various number of stories, beam span lengths, gravity load levels, and seismic load levels are selected and designed based on the prevailing code requirements. Nonlinear analytical models are developed and validated by experimental tests. The pushover and response history dynamic analyses are conducted to evaluate the required data in the performance quantification process. The results show that the design coefficients suggested by the code are acceptable. However, the level of conservatism is very high. Thus, it is possible to use a larger R-factor in the design process or make some relaxations in the design requirements related to this structural system.

• Computers and Concrete
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• v.33 no.6
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• pp.725-738
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• 2024

This study presents a macro-modeling procedure for nonlinear finite element analysis of reinforced and prestressed concrete panels under blast loading. The analysis procedure treats cracked concrete as an orthotropic material based on a smeared rotating crack model within the context of total-load secant stiffness-based formulation. A direct time integration method compatible with the analysis formulation is adapted to solve the dynamic equation of motion. Considerations are made to account for strain rate effects. The analysis procedure is verified by modeling 14 blast tests from various sources reported in the literature including a blast simulation contest. The analysis results are compared against those obtained from experiments, simplified single-degree-of-freedom (SDOF) methods, and sophisticated hydrocodes. It is demonstrated that the smeared crack macro-modeling approach is a viable alternative analysis procedure that gives more information about the structural behavior than SDOF methods, but does not require detailed micro-modeling and extensive material characterization typically needed with hydrocodes.

• Journal of the Korean Society of Industry Convergence
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• v.27 no.5
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• pp.1175-1180
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• 2024

The fuel supply pipe connected to the hydrogen fueled vehicle hydrogen tank is very complicated. Therefore, the fixed portion of the pipe should be determined according to the external vibration. In particular, in order to avoid the resonance frequency range of the hydrogen fueled vehicle, it is necessary to examine the vibration characteristics of the fuel supply pipe and the stress concentration generation part for each frequency. Therefore, the purpose of this study is to understand the resonance potential for the natural frequency of the fuel supply pipe for hydrogen fueled vehicles and the excitation force(vibration of the motor etc.) applied to the external excitation frequency range(1-40Hz). Vibration characteristics were analyzed using the finite element method(FEM) to secure basic data for future seismic vibration tests of fuel supply pipes and to evaluate the safety of fuel supply pipe system.

• International Journal of Highway Engineering
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• v.2 no.3
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• pp.129-144
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• 2000

This paper presents the characteristics of viscoelastic properties and fatigue performance of SBS modified asphalt mixtures depending on the aggregate gradation. Dynamic shear rheometer (DSR) and uniaxial tensile creep tests are performed to analyze the thermomechanical behavior of asphalt binders and mixtures, respectively. Uniaxial tensile fatigue tests for seven different asphalt mixtures are conducted to evaluate the effects of aggregate gradations and SBS modifier on the fatigue performance of the mixtures. DSR and uniaxial tensile creep tests results show that the SBS modified asphalt mixtures have better rutting resistance than the unmodified mixtures at high temperatures regardless of the aggregate gradations used. Fatigue factor $G^*sin\delta$ in Superpave binder specification may not be adequate for evaluating the fatigue Performance of asphalt mixtures. It is observed from uniaxial tensile fatigue tests that SBS modified asphalt mixtures compared to unmodified mixtures have ten times longer fatigue lives regardless of the aggregate gradations(dense, SMA, and Superpave gradations) used in the mixtures. The better fatigue performance of the SBS modified mixtures is observed even after long-term aging process. The effect of aggregate gradations on the fatigue performance is not as significant as the SBS modifier. The cellulose fiber added in the SMA mixture has negligible effects on the viscoelastic Properties and fatigue performance of the mixture, but is effective in reducing draindown. Although the SBS modified asphalt binder is used, it may be necessary to add the cellulose fiber into the SMA mixture to prevent the draindown.

• International Journal of Highway Engineering
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• v.3 no.3 s.9
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• pp.119-133
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• 2001

The stiffness of chemcrete modified asphalt mixtures increase rapidly with time in the presence f oxygen and high temperature, Sometimes the asphalt pavements that have chemcrete modified asphalt mixture applied on the surface none show premature cracking because of the excessive increase in the stiffness f the asphalt mixtures. To mitigate this premature cracking, the chemcrete modified mixtures have been used as a base course material. In this study, the performance of the chemcrete modified asphalt binder and mixtures are investigated through a course of various laboratory tests including dynamic shear rheometer and bending beam rheometer tests for binders and uniaxial tensile fatigue, wheel tracking, and moisture damage tests for the mixtures. And also the resilient modulus of the conventional and chemcrete modified mixtures are compared based on the test results conducted on the specimens obtained from various in-situ test sections. It can be concluded from the tests results that the chemcrete modified mixtures show better rutting resistance than conventional mixtures. The chemcrete modified mixtures may have low temperature cracking when it is applied in the cold region. The stiffness of chemcrete modified mixtures is approximately 50 percent higher than that of conventional mixtures more than two years after the chemcrete modified mixture was applied in the base course.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.5
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• pp.333-340
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• 2019

Tests using a middle velocity propulsion impact machine (MVPIM) were performed to verify the impact resistance capability of sandwich concrete panels (SCP) in a modular liquefied natural gas (LNG) outer tank, and numerical models were constructed and analyzed. $2{\times}2m$ specimens with plain sectional characteristics and specimens including a joint section were used. A 51 kg missile was accelerated above 45 m/s and impacted to have the design code kinetic energy. Impact tests were performed twice according to the design code and once for the doubled impact speed. The numerical models for simulating impact behaviors were created by LS-DYNA. The external steel plate and filled concrete of the panel were modeled as solid elements, the studs as beam elements, and the steel plates as elasto-plastic material with fractures; the CSCM material model was used for concrete. The front plate deformations demonstrated good agreement with those of other tests. However the rear plate deformations were less. In the doubled speed test for the plain section specimen, the missile punctured both plates; however, the front plate was only fractured in the numerical analysis. The impact energy of the missile was transferred to the filled concrete in the numerical analysis.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.5 no.3
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• pp.127-136
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• 1985

A simplified single degree of freedom analog with mass-spring-dashpot is proposed in this study. The simplified analog can describe the dynamic behavior of a rigid circular footings whose contact pressures are parabolic. The analog proposed in this study shows remarkable agreement when compared with the elastic half-space theory the analog is also compared with vertical vibration test results of model concrete footings. For the vibration experiments, 11 circular footings with different mass ratio are constructed. The elastic half-space is represented by compacted sand layer. A constant force excitation vibrator is used for the dynamic loading. The frequency range for vibration tests is 30 to 100 Hz. From the dynamic experiments, it is found that the measured resonant frequencies agree very well with the analog results, however, the ratio of theoretical and measured resonant amplitudes vary between 0.5 and 1.7. It is also found that, when the dynamic force is increased, the resonant frequency is decreased slightly and the resonant amplitude is increased slightly.