Journal of Science and Technique
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PHÂN TÍCH TĨNH VỎ TRỤ FG-CNTRC CHỊU TẢI TRỌNG CƠ NHIỆT VỚI TÍNH CHẤT VẬT LIỆU PHỤ THUỘC VÀO NHIỆT ĐỘ
Get PDFBài báo trình bày kết quả phân tích tĩnh vỏ trụ bằng vật liệu nanocomposite có cơ tính biến thiên gia cường bằng ống nano cacbon (Functionally graded carbon nanotube-reinforced composite - FG-CNTRC) chịu tải trọng cơ nhiệt. Nhiệt độ trong vỏ trụ được giả thiết phân bố theo độ dày và xác định từ phương trình truyền nhiệt. Hệ phương trình cân bằng được thiết lập dựa trên lý thuyết biến dạng cắt bậc cao (Higher-order shear deformation theory - HSDT) có tính đến ứng suất pháp tuyến. Các tính chất của vật liệu phụ thuộc vào nhiệt độ. Sử dụng phương pháp giải tích với chuỗi lượng giác đơn và phép biến đổi Laplace để giải hệ phương trình cân bằng với các điều kiện biên khác nhau. Mô hình tính toán, phương pháp giải và chương trình tính toán được kiểm chứng bằng cách so sánh với các kết quả đã được công bố. Thực hiện khảo sát ảnh hưởng của điều kiện biên và tải trọng nhiệt đến chuyển vị, ứng suất của vỏ trụ FG-CNTRC. Kết quả cho thấy sự biến thiên đột ngột của các thành phần ứng suất tại vị trí biên. Bên cạnh đó, khi nhiệt độ vỏ tăng lên thì trị số tuyệt đối lớn nhất của ứng suất dọc trục tăng, còn của ứng suất vòng giảm
XÂY DỰNG MÔ HÌNH VÀ KHẢO SÁT ĐỘNG LỰC HỌC HỘP SỐ VÔ CẤP TRÊN Ô TÔ
Get PDFHệ thống truyền lực (HTTL) vô cấp sử dụng hộp số CVT cho phép điều chỉnh tỉ số truyền lực một cách linh hoạt để phản ứng linh hoạt với các điều kiện chuyển động và sức cản của mặt đường. Hộp số CVT giúp xe ô tô tăng tốc một cách mạnh mẽ, êm ái và giảm tiêu hao nhiên liệu. Tuy nhiên, những ưu điểm này phụ thuộc chủ yếu vào chất lượng điều khiển của hộp số CVT, đảm bảo rằng tỉ số truyền phù hợp với điều kiện chuyển động. Xây dựng mô hình và thiết kế bộ điều khiển cho hộp số CVT là một chủ đề được nhiều tác giả quan tâm. Trong bài báo này, các tác giả tập trung vào việc xây dựng và khảo sát mô hình HTTL vô cấp, so sánh với HTTL cơ khí có cấp số về mặt động lực học, sự êm ái và đáp ứng của động cơ trong quá trình tăng tốc. Hộp số CVT được lựa chọn trong nghiên cứu này gồm biến mô thủy lực và hệ truyền động đai kim loại. Mô hình động lực học là nền tảng để phát triển luật điều khiển cho hộp số vô cấp
STUDY OF AERODYNAMIC NOISE OF PROPELLER CONSIDERING THE INFLUENCE OF BOUNDARY SURFACE USING CFD METHOD
Get PDFThis article focuses on the aerodynamic and acoustic characteristics of both an isolated propeller model and a propeller - boundary surface model. The study uses the Reynolds-averaged Navier-Stokes (RANS) method combined with Computational Fluid Dynamics techniques to analyze the flow field and wake flow behind the propeller and to determine its basic aerodynamic coefficients. The pressure on the surface of the propeller and boundary surface is used as input for the noise calculations. An acoustic analogy method, based on the Farassat 1A formulation derived from the Ffowcs Williams-Hawkings (FW-H) equation, is employed to calculate the propagation of noise from the surfaces of the propeller and boundary surface to designated positions (microphones). The research results lead to some significant conclusions drawn by the authors
DEVELOPMENT OF METHOD TO OPTIMIZE RAIN GAUGE STATION LOCATION IN DA RANG RIVER BASIN USING SPATIAL INTERPOLATION TECHNIQUE
Get PDFRainfall is one of the crucial data types in meteorological research. In the context of increasingly complex climate change, meteorological forecast data is essential for modeling and predicting natural disasters, especially floods and landslides. To ensure the accuracy of rainfall prediction and the cost of building and operating rain gauge stations, determining the number of stations is crucial. Therefore, this study developed an optimization design for the rain gauge station network in the Da Rang River focusing on the quantity and spatial distribution of rain gauge stations. The geostatistical method combined with spatial interpolation algorithms was applied using rainfall data from 2015-2020. The choice of an appropriate spatial interpolation method influenced the accuracy of the optimization process. The spatial interpolation analysis showed the spatial variation of rainfall types across the entire study area by season, as well as the geographical distribution of rainfall. After determining the optimal number of stations, an approach based on geographic information systems produced a spatial distribution map of the optimal rain gauge station locations. The results indicated that an additional 14 rain gauge stations should be installed, randomly located within the rainy area with a distance of 10 km between stations. These additional stations, along with the existing ones in the area, will provide comprehensive information about rainfall, enabling accurate predictions of rainfall distribution in the research area
INFLUENCE OF TECHNOLOGICAL PROCESS ON THERMAL AND MECHANICAL CHARACTERISTICS OF PYROTECHNIC COMPOSITIONS BASED ON RED PHOSPHORUS
Get PDFThis study studied the technological process of pyrotechnic compositions based on red phosphorus (RP). In addition, the influence of the RP mixing method on thermal and mechanical characteristics was also investigated. Measurements such as scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX) are used to evaluate the completeness of samples; Burning rate, burning temperature, and thermogravimetry/ differential thermal analysis (TG/DTA) are used to assess thermal characteristics; Compressive strength is used to determine compressive strength, in addition, ignition temperature and friction sensitivity are also used to evaluate the safety of samples. The results showed that the samples had good completion, and the compatibility of the ingredients in the pyrotechnic composition was high. Samples with RP mixed after granulation have high friction and temperature sensitivity but have better compressive strength than samples with 100% RP mixed before granulation. The samples have similar mass burning rates in the range of 0.035 - 0.063 g.cm-1, and the burning temperature of these samples is in the range of 1100 - 1500oC
A METHOD FOR CONSTRUCTING DIGITAL SIGNATURE SCHEMES BASED ON NEW HARD PROBLEM ON THE ELLIPTIC CURVE
Get PDFIn this paper, the authors propose a solution to improve the secure of digital signature schemes, this solution is implemented on two levels of digital signature scheme construction. At the first level, the authors propose a new hard problem, this hard problem belongs to the class of hard problems for which there is currently no solution (except by “brute force attack" method). At the second level, the authors propose a method to construct new digital signature algorithms based on this hard problem
TEXTKNOCKOFF: KNOCKOFF NETS FOR STEALING FUNCTIONALITY OF TEXT SENTIMENT MODELS
Get PDFMost commercial machine learning models today are designed to require significant amounts of time, money, and human effort. Therefore, intrinsic information about the model (such as architecture, hyperparameters, and training data) needs to be kept confidential. These models are referred to as black boxes, and there is an increasing amount of research focused on both attacking and protecting them. Recent publications have often concentrated on the field of computer vision; in contrast, there is still relatively little research on methods for attacking black box models with textual data. This article introduces a research method for extracting the functionality of a black box model in the task of text sentiment analysis. The method has been effectively tested based on random sampling techniques to reconstruct a new model with equivalent functionality to the original model, achieving high accuracy (94.46% compared to 94.92%) and high similarity (96.82%)
DETERMINING SEASONAL SEAFLOOR DEPTH CHANGES AROUND OFFSHORE ISLANDS OF VIETNAM USING SENTINEL-2 AND GOOGLE EARTH ENGINE
Get PDFThis study focuses on determining bathymetric changes around offshore islands of Vietnam using remote sensing data available on the Google Earth Engine (GEE) cloud platform. Sentinel-2 multispectral satellite imagery was collected over three time periods, January 14, 2020, June 5, 2020 and June 15, 2021, coinciding with the wind season to analyze and calculate bathymetric changes. The results of the bathymetry compared to the field measurement points have coefficients of determination (R2) ranging from 0.83 to 0.94. The RMSE (Relative Mean Square Error) results obtained were 0.066 m, 0.048 m and 0.079 m, initially providing a map of seasonal bathymetry changes consistent with reality. This method demonstrates the efficiency and automation potential for tracking depth changes in the Vietnamese coastal region, especially around offshore islands. Moreover, it highlights the importance of continuous monitoring for environmental protection, navigation, and resource management
FACIAL RECOGNITION-BASED APPROACH FOR EFFICIENT PERSONAL INFORMATION RETRIEVAL IN CYBERSPACE
Get PDFThe paper proposes an artificial intelligence system that can perform face searches on the Internet. Face search is the search for images or videos that contain a specific person’s face in cyberspace. The proposed system integrates four key components: the Data Collection Module, Data Storage Mechanism, Search Module, and Analysis Module. By integrating advanced deep learning models, the system achieves high precision and reliability in detecting and recognizing faces. Moreover, our system leverages advanced processing technologies such as parallel computing and optimization techniques to speed up the face search process and handle large-scale data. Experimental results demonstrate that the system achieves remarkable accuracy and efficiency in operation
ANALYSIS OF OUTAGE PROBABILITY AND INTERCEPT PROBABILITY TRADE-OFF FOR SECURE TWO-WAY RELAYING SCHEMES BETWEEN TWO CLUSTERS OF NODES USING FOUNTAIN CODES
Get PDFThis paper presents two secure two-way relaying schemes between two clusters of nodes: i) 3-phase two-way relaying using Digital Network Coding; ii) conventional 4-phase two-way relaying. In the proposed schemes, one node selected from each cluster will use Fountain codes to encode the original data, and then send encoded packets to nodes in the remaining cluster, with the help of a common relay node. Explicit mathematical expressions are derived to evaluate the outage probability (system outage probability) and intercept probability (system intercept probability) of the proposed schemes over the Rayleigh fading channel. Our results show a reliability-security trade-off as well as the impact of system parameters on the network performances