Trang: 1110-1124 Van Trang Phung, Thanh Lich NguyenTóm tắtRolling bearing faults have been capturing substantial research attention as they are the root causes of malfunctions in mechatronics systems than any other factors. The detection of rolling bearing faults in the early stage is therefore a mandatory requirement demanded by reliable industrial plants. To release the dependence of diagnostic methods on human expertise and system’s understanding, this work proposes a fault classification method for rolling bearings that is based on a deep learning framework. The framework consists of a minimax entropy domain adaptation algorithm augmented with a signal generalization algorithm. The function of the signal generalization algorithm is to reduce the domain shift between training and testing datasets that are often obtained experimentally from different working conditions. The generalized signal is then represented in the form of Fourier series whose coefficients contain intrinsic information that associated with different types of bearing faults. A convolutional neural network extracts the hidden information of bearing faults buried in the Fourier coefficients and then categorises the working condition of the bearing under test. By combining the advantages of both signal processing techniques in the frequency domain and the minimax entropy domain adaptation, the novel diagnostic framework is able to detect bearing faults from different working conditions. The effectiveness of the proposed diagnostic algorithm is experimentally verified by two case studies that were prepared with different types and levels of bearing faults.
Analysis of factors affecting vehicle choice behavior in Hanoi city
Trang: 1125-1139 Vu Thi Huong, Nguyen Thanh Chuong, Vu Trong TichTóm tắtMotorcycles are rapidly changing transportation in Vietnamese cities. Motorcycles are dominant in all sixty-three provinces/cities of Vietnam and accounted for nearly 80 percent of passenger transportation. The sharp rise in motorcycle ownership and usage has contributed to several unique motorcycle-related transportation challenges in Vietnam, which are different from those in developed countries where car usage is predominant. These challenges include a high frequency of motorcycle-related accidents and fatalities; and increasing motorcycle-related pollution and congestion. To address these challenges, policymakers in Vietnam have introduced policies that promote alternative transportation modes replacing motorcycles. This study adopts a vehicle user perspective to elucidate the factors influencing the choice of alternative means of transportation instead of motorbikes. The study was conducted through 800 sample surveys among individuals in Hanoi. In addition to the conventional factors included in the model, such as demographics and socio-economic characteristics, trip attributes, vehicle characteristics, subjective norms, awareness, and the appeal of alternative transport modes… This study introduces two additional factors: attitude to vehicles and health awareness. These additions are based on the cultural characteristics and transportation context unique to the capital. The research demonstrates that cultural factors influence the choice of transportation means. Specifically, family structure and attitudes towards vehicles emerge as major barriers to altering the preference for motorbikes in urban areas. Additionally, health awareness is shown to be a factor influencing transportation choices. The findings of this research will contribute to the theoretical foundation for shaping the vehicle management policies of Hanoi capital in the future.
Trang: 1140-1148 Nguyen Ngoc Long, Nguyen Chau Lan, Bui Tien Thanh, Nguyen Thi Cam NhungTóm tắtVietnam is currently undertaking numerous transportation and infrastructure projects in urban areas, particularly in densely populated cities such as Hanoi and Ho Chi Minh City. These cities have high traffic density and frequent traffic congestion, which necessitates the use of construction equipment such as vibratory rollers and pile drivers. However, these machines can cause vibrations that affect the surrounding structures. This study investigates the impact of roller compaction-induced vibration on the building structure of Ring road No.2 in Hanoi, Vietnam. The finite element method (Plaxis 2D) was applied to evaluate the impact of vibration on surrounding structures. The maximum measured velocity is similar to the values derived from numerical analysis. The Finite element method (FEM) results exhibited a high degree of correlation with the actual velocity measurement and frequency dominant structure responses caused by ground-borne vibration induced by roller compaction within the frequency range of 5 Hz to 10 Hz.
Early strength enhancement of high-volume fly ash mortar using accelerating admixtures
Trang: 1149-1158 Vu Viet Hung, Le Van QuangTóm tắtHigh-volume fly ash mortar is considered a "green" material, a sustainable development solution for the construction industry, in which the fly ash replacement Portland cement content is over 50%. However, this material has the major disadvantage of slow strength development, especially at an early age, which limits its applicability. To overcome the above disadvantage, the individual or combined addition of lime Ca(OH)2, silica fume, and/or accelerating admixtures including sodium thiocyanate (NaSCN), diethanolamine (DEA), and glycerol (Gly), etc. have been interested recently. In this study, to enhance the early strength of mortars with fly ash content to replace 60÷80% of Portland cement, a three-component accelerating admixture of NaSCN, DEA, and Gly (2:1:0.5 by the mass) was used with different ratios of 0.21÷0.49 % by the total powder mass, combined with a reasonable amount of lime, silica fume supplement as presented in previous research. Experimental results showed that the optimal accelerating admixture content is 0.35% by weight of powder, combined with 6% silica fume and the additional amount of lime is 5%; 10%; and 15% corresponding to mortars using fly ash of 60%; 70% and 80%, respectively to improve early strength of mortars that are suitable for structural use (R3 ≥ 13MPa, 3 days old). In addition, the influence of the additives used on the initial setting time of high-volume fly ash mortars was also discussed.
Trang: 1159-1168 Tran Anh Tuan, Tran Thi Bich ThaoTóm tắtIn recent years, the prediction of the effective transport properties have received a great number of investigations. The present work is dedicated to determining the effective permeability of two-dimensional (2D) doubly porous materials made of an isotropic permeable solid matrix in which elliptical shaped pores of any size are embedded. At the interface between the fluid and the solid, the Beaver–Joseph–Saffman conditions are applied. To achieve this objective, the Boundary Element Method (BEM) is first elaborated in the simulation of velocity and pressure solution fields of two coupled Stokes and Darcy problems. Afterwards, with the help of this solution results, the effective permeablity of the doubly porous material under investigation can be determined. For the purpose of assessing the accuracy and convergence of the BEM solution, the results obtained for the velocity and pressure fields are compared with the ones provided by the finite element method (FEM). Finally, several numerical examples are carried out to analyze the fluid/solid interface influence, the effect of area fraction and geometrical properties of pores, such as the size and distribution of the pores within the matrix phase.
Simulation of four-point bending tests for the viscoelastic fracture properties of concrete
Trang: 1169-1182 Tran Nam Hung, Nguyen Thi Thu NgaTóm tắtUnderstanding the fracture properties of concrete, such as crack propagation behavior and fracture energy, is crucial for designing and evaluating concrete structures. Experimental results are insufficient and cannot be directly employed for a comprehensive analysis of the fracture behavior of concrete structures under load, particularly when considering concrete as viscoelastic with the presence of cracks. Recognizing the time and cost constraints of traditional experimental testing, this research leverages numerical simulations as a cost-effective alternative to determine viscoelastic material parameters. Thus, the critical evaluation of concrete fracture properties, fundamental for the design and assessment of concrete structures, is addressed. Employing a finite element method for four-point bending tests, the study systematically investigates parameters such as initial crack depth, displacement acceleration, and time step. The material properties of concrete are described using viscoelastic models. The findings provide valuable insights into crack propagation behavior and deformation characteristics, emphasizing the significant influence of the modulus of elasticity on both maximum load values and displacement. These findings contribute to a deeper understanding of the structure's response and underscore the importance of considering these parameters in similar simulations. The study highlights the importance of considering these parameters in simulations to enhance the understanding of concrete fracture behavior. The paper's contributions can extend to optimizing concrete mixtures, formulating repair strategies, and improving structural assessments. Further research is suggested to improve the accuracy of simulations and investigate material properties under various conditions.
Trang: 1183-1197 Nguyen Tuan AnhTóm tắtWood, an environmentally friendly construction material, is characterized by a critical attribute that significantly influences its mechanical properties and durability: its moisture absorption behavior. This study expands upon an existing one-dimensional model to develop an innovative two-dimensional numerical framework for simulating moisture propagation within wood. Utilizing the finite difference method, this approach offers a more detailed analysis of moisture behavior in wood structures. The research adopts an inverse modeling technique, integrating a simplex optimization algorithm programmed in VBA software. This algorithm is employed to deduce diffusion parameters from the evolution of moisture content over time. Focusing on the analysis of moisture diffusion parameters, the study examines both longitudinal and transverse directions in two temperate species (Beech and Fir) and two tropical species (Moabi and Ozigo). The findings provide insightful data on the hygroscopic behavior of these woods, revealing significant distinctions between temperate and tropical species. This research offers valuable information for the application of these wood species in construction and other fields, enhancing the understanding of their moisture-related properties.
Enhancing vibration control in stay cables: a modified damping formulation with NS-HDR damper
Trang: 1198-1212 Luu Xuan Le, Hiroshi Katsuchi, Binh Xuan Luong, Linh Ngoc Vu, Quan Van HaTóm tắtCables in cable-stayed bridges have low intrinsic damping, and dampers are often used as a countermeasure for cable vibration control. This paper presents an innovative asymptotic formula for calculating the additional damping in stay cables equipped with Negative Stiffness High Damping Rubber dampers (NS-HDR). The NS-HDR damper incorporates negative stiffness through a pre-compressed spring. The analysis employs models of flexural cables with fixed-fixed or hinged-hinged ends to derive the formulation of attainable damping ratio. The results of the study reveal that the NS-HDR damper, with its negative stiffness feature, exhibits a significantly higher added damping ratio in comparison to the conventional HDR damper configuration. To quantify this increased added damping resulting from negative stiffness, a modification factor is proposed. The accuracy and effectiveness of the proposed damping formula are successfully validated using the Finite Difference Method (FDM). Subsequently, the methodology is applied to design the damping of two existing stay cables (137.82m and 167.18m in length). Field measurements reveal that the damping in these cables falls below the required threshold of 0.5%. The proposed NS-HDR damper offers a viable solution to achieve the required damping ratio. These findings contribute significantly to the understanding and optimization of damping in stay cables employing HDR dampers, presenting potential applications in the field of bridge engineering. The research opens up new possibilities for enhancing vibration control and safety in cable-stayed bridges.
