Journal of Science and Technique
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LONGITUDINAL FLYING QUALITY ANALYSIS FOR A SMALL FIXED-WING UAV MODEL
Full text linkThis article presents a detailed analysis of the longitudinal flying qualities of a small fixed-wing unmanned aerial vehicle (UAV). The UAV model is developed using MATLAB/Simulink, supported by the Aerospace Blockset for six-degree-of-freedom dynamic modeling. Aerodynamic coefficients are obtained from Digital DATCOM based on the UAV’s geometry and operating conditions. A trimmed flight state is determined, and the nonlinear model is linearized to extract longitudinal dynamics. The short-period and phugoid modes are analyzed according to MIL-STD-1797A criteria. Results indicate that the UAV meets Level 1 requirements for both modes, with the short-period damping ratio near the lower limit and the natural frequency well above the minimum threshold. These findings clarify the UAV’s inherent dynamic behavior and provide a foundation for future control system development and flight performance optimization
DAMAGE IDENTIFICATION IN BEAM-LIKE STRUCTURE USING RELATIVE NATURAL FREQUENCY SHIFTS
Full text linkVibration-based damage identification methods have demonstrated significant potential for structural health monitoring. Modal parameters, including natural frequencies and mode shapes, serve as global indicators of a structure’s condition. Changes in these parameters can be indicative of damage within the structure. This article proposes an enhanced methodology for damage detection through shifts in natural frequencies. By precisely determining the frequencies of both the intact and damaged structure, frequency shifts can be computed, thereby transforming the damage detection process into a minimization of error in the identification task. This approach involves comparing the measured frequency variations with analytical values, which characterizes the frequency shifts resulting from damage. The effectiveness of the proposed procedure is validated through numerical simulations, followed by experimental testing
ESTIMATING SHALLOW-WATER BATHYMETRY FROM SENTINEL-2 IMAGERY USING MACHINE LEARNING: A CASE STUDY IN COASTAL AREA OF GIA LAI, VIETNAM
Full text linkThis study investigates the potential of applying machine learning algorithms to estimate shallow-water bathymetry from Sentinel-2 satellite imagery in the coastal waters of Gia Lai province, Vietnam. A Sentinel-2 Level-2A image acquired on January 23, 2020, under clear and stable optical conditions, was used after atmospheric correction. In-situ bathymetric data were collected using a GPS-integrated single-beam echo sounder and employed as training and validation datasets. Five machine learning models, including Multiple Linear Regression (MLR), Random Forest (RF), Decision Tree (DT), K-Nearest Neighbors (KNN), and Long Short-Term Memory (LSTM), were developed and compared for bathymetric estimation accuracy. The results indicate that the coefficient of determination (R²) ranges from 0.80 to 0.91, with Root Mean Square Error (RMSE) values between 0.72 m and 1.05 m, and Mean Absolute Error (MAE) values ranging from 0.49 m to 0.72 m. These findings demonstrate the feasibility of integrating Sentinel-2 imagery with machine learning for accurate shallow-water bathymetric mapping. Furthermore, the proposed approach shows strong potential for application to other coastal regions of Vietnam with comparable environmental and optical characteristics
DESIGN AN ADAPTIVE FINITE TIME CONTROLLER FOR INTEGRATED GUIDANCE CONTROL SYSTEMS BY USING FINITE DISTURBANCE OBSERVER AND BACKSTEPPING TECHNIQUE
Full text linkA novel control synthesis approach for Integrated guidance and control (IGC) systems in aerial vehicle (AV), based on Finite-time backstepping (FTB) combined with a Finite-time disturbance observer (FTDO) is proposed. Comparing to the conventional backstepping methods ensuring asymptotic convergence, the proposed approach guarantees finite-time convergence and significantly improves disturbance rejection capability. The controller is designed in a strict-feedback structure containing layers employing nonlinear control laws to satisfy Lyapunov stability conditions. Individual FTDOs are constructed for each state equation to accurately estimate the lumped disturbances and enhance compensation performance. Simulation results show that the proposed method shortens transient response time, reduces control errors, and ensures accurate target tracking even under strong disturbance conditions
ANALYSIS OF BLAST LOADS ON STRUCTURES WITH FACADE OPENINGS USING UFC 3-340-02
Full text linkDesigning blast-resistant structures with openings presents a significant challenge due to the complex propagation and interaction of shock waves with internal structural components. While international design codes have been established to address this issue, engineering practice in Vietnam primarily relies on empirical methods for assessing external blast loads on simple rectangular geometries, often neglecting internal pressure effects due to a lack of experimental data. As an alternative to computationally intensive CFD simulations, this article presents a comprehensive approach utilizing UFC 3-340-02 to determine blast loads acting on both exterior and interior structural surfaces. An automated calculation method is introduced to estimate the determination of these loads and rapidly generate a robust loading database. This study provides Vietnamese engineers with a practical blast loading assessment tool and a new approach to accurately analyze structural components, thereby enhancing the survivability and resilience of structures against explosive events
ALGEBRAIC INTEGRAL BARRIER LYAPUNOV-BASED EVENT-TRIGGERED NONSMOOTH CONTROL FOR N-DOF ROBOTIC MANIPULATORS UNDER NON-LIPSCHITZ UNCERTAINTIES
Full text linkThis study aims to develop a robust control framework for robotic manipulators operating under non-Lipschitz uncertainties and strict state constraints. A novel Algebraic Integral Barrier Lyapunov-Based Event-Triggered Nonsmooth Control (AIBET-NSC) strategy is proposed to achieve fixed-time convergence while minimizing control effort. The method integrates four key components: (i) an algebraic integral observer for noise-resilient state estimation, (ii) a barrier Lyapunov function to strictly enforce joint constraints, (iii) a nonsmooth sliding-mode-based term for fixed-time stability, and (iv) an event-triggered mechanism to reduce control updates. Theoretical analysis proves global fixed-time stability and Zeno-free triggering. Simulation results on a 2-DOF robotic manipulator demonstrate that, compared with conventional sliding mode control, the proposed AIBET-NSC achieves 35-40% lower control torque oscillation, 28% faster settling time, and over 50% fewer control updates, while maintaining accurate trajectory tracking. These results verify the controller’s strong robustness, chattering suppression, and practical feasibility. The proposed framework provides both theoretical and practical contributions toward efficient and constraint-safe control of robotic manipulators under complex uncertain environments
IDENTIFICATION OF DAMAGE LOCATIONS IN STEEL BEAMS BASED ON CHANGES IN NATURAL FREQUENCIES
Full text linkWhen damage occurs in a structure, it results in changes to its dynamic characteristics including natural frequencies, mode shapes, and damping ratios, compared to an undamaged structure. Based on this principle, several methods have been researched and applied to identify damaged regions in structures. In this article, a cantilever steel beam with constant cross-section is studied by dividing it into regions, where each region is classified based on the first four normalized natural frequencies. The damaged region is identified by classifying the normalized frequencies of the structure through the ratio of the natural frequency of the damaged beam to that of the undamaged beam. A simulation is conducted using SAP2000 for both the intact and damaged cantilever beam to determine its natural frequencies, serving as a basis for identifying the damage location and severity. The identified damage region matches the assumed location and is independent of damage severity. The research results demonstrate that changes in natural frequencies can be utilized to identify damage on cantilever beam structures, providing a basis for the application in detecting damage locations in more complex structures and real-world constructions
NUMERICAL SIMULATION OF BLAST PRESSURE ON ACCESS BLAST DOOR USING ABAQUS SOFTWARE
Full text linkThis article presents the investigation results of reflected blast pressure acting on access blast doors using a numerical simulation method with Abaqus software. The study employs Sadovskii's empirical formula as the theoretical basis for determining shock wave overpressure. Simulations were conducted with parametric variations including: TNT explosive mass ranging from 50 kg to 200 kg, standoff distance from explosion center to protective door (R₀) from 10m to 25m, and incident angle α between shock wave propagation direction and door surface normal from 0° to 60°, under the assumption that the protective door is perfectly rigid and immobile. Results show that the error between Abaqus simulation and empirical formula ranges from 1.123% to 13.65%, demonstrating high reliability of the simulation method. Reflected pressure decreases with increasing standoff distance R₀ and varies complexly with angle α due to the curved surface characteristics of the protective door. The study confirms that Abaqus software is an effective tool for predicting and analyzing blast pressure on protective door structures, contributing to improved efficiency and safety in the design and construction of access tunnel protective doors in practice. Moreover, the influence of the curvature radius of the door surface on the reflected pressure value is complex. When calculating the load acting on the protective door, it is necessary to consider the average reflected pressure on the curved surface to ensure accurate calculations
A SOLUTION TO IMPROVE LOCATION DATA ACCURACY FOR MAP-UPDATING FROM MOBILE DEVICES USING THE KALMAN FILTER
Full text linkWith the increasing prevalence of mobile devices, it is possible to continuously collect geospatial data directly in the field such as image data and coordinates of objects. However, location data collected from mobile devices often contains noise and large errors, thus direct integration into spatial database poses challenges in terms of accuracy. In the context of the continuous expansion and infrastructure changes of industrial parks in Vietnam, the application of GPS-integrated GIS technology enables automatic and accurate updates of internal road maps within the parks. This article proposes a framework for optimizing point-based data used to update digital maps from mobile devices. The article uses the Kalman filter as a solution to improve the location data accuracy when updating maps from mobile devices. Experimental programming of mobile devices utilizes the Flutter and MapLibre GL libraries, while the desktop program employs QGIS software. The database management systems used are PostgreSQL and PostGIS/GeoServer. Experiments on updating data on real mobile devices demonstrate that the proposed method can effectively limit location errors and minimize the risks associated with anomalous data. By applying the proposed method, the positioning error has been reduced from approximately 8.23 meters to only 3.11 meters. The experimental results also show significant improvements in coordinates accuracy, data deduplication, and map-updating efficiency
NUMERICAL ANALYSIS OF THE EFFECTS OF DIFFERENT BEHAVIOR MODELS OF ISOLATORS ON THE SEISMIC RESPONSES OF MULTI-STORY BUILDINGS
Full text linkSeismic base isolation (SBI) is widely recognized as a highly effective solution for earthquake-resistant design, extensively implemented in high-seismicity regions, and increasingly adopted in areas with moderate seismic activity. While structural analysis software provides various behavior models to simulate SBI elements, the suitability of these models for specific analytical applications remains unclear. This study conducts a numerical analysis to assess the impact of different isolator behavior models - including equivalent linear, plastic Wen, bilinear, and rubber isolators - on the seismic response of isolated buildings. Nonlinear time-history analyses are performed on a typical seismically isolated building using the 1994 Northridge earthquake record, scaled to match the target spectrum. The seismic isolators are modeled using link elements with constitutive parameters corresponding to the selected models. Key response parameters, such as isolator behavior, lateral displacements, and base shear forces, are analyzed to compare the structural performance across different isolator models. The results indicate that nonlinear models (plastic Wen, bilinear, and rubber) yield comparable and realistic seismic responses, whereas the linear model significantly overestimates displacements and forces. These findings highlight the limitations of linear assumptions in seismic analysis and underscore the necessity of employing nonlinear models for a more accurate evaluation of structural behavior during earthquakes