Journal of Science and Technique
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A HYBRID METHOD IN DETERMINING SKIN FRICTION FIELDS ON THE SURFACE OF FLYING OBJECTS
Get PDFThe study of friction fields on object surfaces plays an important role in fluid mechanics. In this study, a hybrid method, which combines the cross-correlation algorithm and the optical flow algorithm, is developed to calculate the skin-friction field based on the oil distribution on the surface. The scientific basis of the method is presented. Based on this, a computational program is developed and applied to flow calculations over different object surfaces, including an aircraft wing at a high angle of attack, a wing with a low aspect ratio, a delta wing, and the axisymmetric boattail of a flying object. The computational results show that this method effectively determines the flow characteristics of the surface skin-friction field. Flow characteristics, including separation and reattachment locations, are analyzed. Additionally, the influence of computational parameters on the results is specifically presented. This method demonstrates high efficiency and can be applied to future research and aircraft designs
A NEW BUCK-BOOST CONVERTER WITH HIGH VOLTAGE CONVERSION RATIO AND REDUCED VOLTAGE AND CURRENT STRESS ON SWITCHES AND DIODES
Get PDFThis study presents an improved Buck-Boost converter configuration capable of achieving a high voltage conversion ratio while significantly reducing voltage and current stress on critical components such as MOSFETs and diodes. The proposed design enhances operational efficiency, extends component lifespan, and ensures maximum system reliability. To provide an objective assessment, experimental evaluations were conducted to compare output voltage overshoot, input current characteristics, and overall efficiency with existing converters. The results demonstrate that the proposed converter not only overcomes the limitations of conventional topologies but also maintains high efficiency and stable operation across a wide voltage conversion range. With these advantages, the proposed design holds strong potential for applications requiring high performance and long-term stability
LASER ATTENUATION AND OBSCURANT EFFICIENCY OF SCREENING SMOKE
Get PDFThe concealment capability is one of the most important characteristics of smoke screens used in military camouflage. In this article, the influence of several factors (i.e., the formulation, sample mass, and environmental conditions) on the obscurant capabilities (including the degree of the 1.064 µm laser attenuation, the mass extinction coefficient, the Yield factor, and the Figure of Merit) was investigated and evaluated. The findings indicate that red phosphorus-based smoke compositions exhibit higher obscurant characteristics, providing superior laser attenuation to traditional anthracene-based formulations. The research findings can be used to develop a method for determining the laser attenuation capability of smoke screens
CRACK WIDTH CONTROL IN THE DESIGN OF REINFORCED CONCRETE BEAMS IN MARINE ENVIRONMENTS
Get PDFReinforced concrete beams are extensively used in construction, and understanding crack development is essential to ensure the safety and durability of structures, particularly in marine environments. This study investigates the influence of tensile steel reinforcements on crack width in reinforced concrete beams through analytical calculations. The objective is to evaluate crack width behavior under varying amounts and configurations of reinforcement, providing recommendations for optimal load-carrying steel arrangements to limit crack width. The research methodology involves numerical simulations using ETABS and adheres to the design guidelines specified in TCVN 5574:2018, IS 456:2000, and TCVN 9346:2012. The results show that both the quantity and arrangement of tensile reinforcement significantly affect crack formation and width. Notably, the study reveals that meeting both structural strength and crack width requirements for reinforced concrete beams in marine structures is challenging. Ensuring a maximum crack width of 0.05 mm under harsh environmental conditions, such as tidal seawater exposure, poses significant difficulties. These findings offer valuable insights for engineers in designing marine concrete structures and optimizing reinforcement layouts to meet performance and durability criteria under aggressive exposure conditions
STATISTICAL MODELING OF UNIT SKIN FRICTION BETWEEN PILES AND CORAL GRAVELLY SAND USING IN-SITU SPT DATA
Get PDFThis paper presents a statistical analysis of unit skin friction between piles and coral sand layers, based on 245 in-situ Standard Penetration Test (SPT) records collected from a coral reef area. The unit skin friction was estimated using Meyerhof’s empirical correlation. Field data were used to assess the statistical characteristics of the pile-soil interface in coral sand. The results reveal that the distribution of unit skin friction does not follow a single normal (Gaussian) distribution, as is typical for terrestrial granular soils, but instead indicating the presence of multiple distinct geotechnical regimes. This distinctive feature reflects the unique interaction mechanism between piles and calcareous soil, which should be carefully considered in the foundation design of coastal and island structures
CARBON FELT MODIFICATION WITH HNO3 FOR THE ELECTRO-FENTON PROCESS OF DEGRADATION ORGANIC POLLUTANTS IN THE AQUATIC ENVIRONMENT
Get PDFIn this study, we modified the surface of raw carbon felt (CF) using concentrated HNO3 for durations ranging from 0 to 12 hours at temperatures between 30°C and 90°C. The structural morphology of both the raw CF and the modified CF was characterized using SEM, EDX, XRD, and FT-IR methods. The results showed that the CF modified for 6 hours at 30°C exhibited the highest degradation efficiency for LFX. After 90 minutes of reaction, the degradation efficiency for LFX reached 79.65%. Additionally, the modified CF electrodes demonstrated flexibility and high applicability in degrading various organic pollutants such as oxytetracycline, tartrazine, rhodamine B, methyl orange, and methyl blue, achieving degradation efficiencies of 81.07-97.14% after 45 minutes of reaction. Furthermore, long-term stability tests confirmed its relatively stable performance after 3 cycles of reuse
MÔ HÌNH HÓA VÀ PHÂN TÍCH ĐỘNG LỰC HỌC XE NÂNG NGƯỜI DẠNG CẦN GẬP KHI VẬN HÀNH KẾT HỢP CÁC THAO TÁC ĐỂ NÂNG TẢI
Get PDFXe nâng người được sử dụng để phục vụ thực hiện các công việc tại những vị trí cao và khó tiếp cận. Độ ổn định động có ý nghĩa quan trọng trong quá trình triển khai và vận hành đối với xe nâng người. Chính vì vậy, bài báo tiến hành xây dựng mô hình và khảo sát động lực học xe nâng người dạng cần gập khi thực hiện đồng thời các thao tác trong quá trình nâng tải để làm cơ sở xác định ổn định động của xe. Mô hình động lực học xây dựng có xét đến độ nhớt đàn hồi và giảm chấn của các xi lanh thủy lực nâng đốt cần và độ đàn hồi của lốp xe. Phương trình Lagrăng loại II được sử dụng để xây dựng hệ phương trình vi phân mô tả chuyển động của cơ hệ. Trên cơ sở đó, bài báo tiến hành khảo sát các thông số động lực học của xe nâng khi thực hiện đồng thời các thao tác để nâng tải. Kết quả của bài báo là cơ sở cho bài toán phân tích độ ổn định động cũng như bài toán điều khiển xe nâng người dạng cần gập để nâng cao hiệu suất, độ tin cậy trong quá trình vận hành
STATIC BENDING RESPONSE OF VARIABLE THICKNESS FGM PLATES USING NEW SHEAR DEFORMATION PLATE THEORY
Get PDFThis study aims to investigate the static bending behavior of functionally graded material plates with variable thickness using a new shear deformation theory and the finite element method. Material and mechanical models are developed to establish the equations describing mechanical relationships. The calculation program is implemented in MATLAB, and its accuracy is verified by comparison with results from analytical methods presented in reputable scientific publications. The error between methods is no more than 1.5%. The program can calculate plate structures with variable thickness according to different rules such as linear and nonlinear. The effects of geometric and material parameters on the static bending of FGM plates with variable thickness are explored. Following this, the thickness change affects the bending of the plate. These results provide an essential foundation for addressing more complex problems in the future
DYNAMICS AND STATISTICAL VIBRATION CHARACTERISTICS OF A BASE VEHICLE OF MOBILE WATER PURIFICATION STATION MOVING ON RANDOM ROAD SURFACES
Get PDFThe vehicle-mounted VFS-2.5 water filtration station is one of the devices used to provide clean water during rescue and relief missions; therefore, it often operates on complex terrains. This article studies the dynamic model of the mobile water filtration station VFS-2.5 of a base vehicle during movement, taking into account random road surface roughness. Based on the dynamic model of the base vehicle, the Lagrange's Equation II is used to establish a set of differential equations describing the system motion. The article employs the inverse Fourier transform method, statistical techniques, and simulations available in MATLAB to evaluate the probability density distribution, value range, and statistical characteristics of vibration acceleration for road classes C, D, and E, as well as the dynamic parameters when the vehicle moves on the class-C road within a speed of 25 km/h which is the maximum permitted speed on unpaved roads. The obtained results can serve as a basis for assessing stability, vibration effects on operators during movement, and as input parameters for experiments to evaluate the degradation of technical conditions and the reliability of the equipment on the filtration station
BUILDING SOFTWARE FOR ANALYZING MUCK PILES AFTER BLASTING IN LABORATORY CONDITIONS WITH INTEGRATED ARTIFICIAL INTELLIGENCE
Get PDFIn the mining and tunneling industry, the mean particle size (Dtb) of a muck pile after blasting is a key parameter for evaluating blasting efficiency. Numerous solutions exist for determining mean particle size by photographing muck piles after blasting using commercial software such as Split-Desktop and WipFrag, but these incur annual costs of thousands of US dollars. To address this limitation, the study develops software that analyzes images of muck piles after blasting, providing Swebrec, Gate-Gaudin-Schumann, and Rosin-Rammler particle size distribution (PSD) functions and their corresponding mean particle sizes. The software utilizes open-source resources and integrates the SAM2 artificial intelligence model to facilitate editing of each rock fragment detected in the image. The software’s mean particle size results are compared with those from traditional sieving analysis, with differences ranging from 5% to 7% for image segmentation data. These results demonstrate the software’s feasibility as a low-cost, reliable alternative to the sieving process