An optimization-based approach for static analysis of multi-segment mooring lines with clump weights
Trang: 1128-1137 Quoc Hoan PhamTóm tắtStatic configuration analysis of multi-segment mooring systems equipped with clump weights poses a significant computational challenge due to the high non-linearity and sensitivity of the governing equations. This study proposes an optimization-based approach to determine the equilibrium shape of mooring lines, bypassing the limitations of traditional trial-and-error or simplified analytical methods. By incorporating the fundamental catenary equations with force balance and displacement continuity conditions into the objective function, the problem is reformulated as a search for the optimal inclination angle at the lower point of each segment. Two metaheuristic algorithms, Particle Swarm Optimization (PSO) and Genetic Algorithm (GA), are implemented to solve the system of equations. Results demonstrate that the proposed method achieves high accuracy when validated against Finite Element Analysis (FEA), yielding negligible discrepancies (maximum error of 0.3% for inclination angles and 0.0% for mooring tensions). The study highlights that PSO exhibits superior convergence speed and stability compared to GA, particularly in complex configurations involving multiple clump weights.
Timing bottleneck characterization in an iterative Keccak-f[1600]/SHA3-256 core: An FPGA/ASIC study
Trang: 1138-1154 Nguyen Thanh Ngoc, Nguyen Dac Khiem, Doan Duc Duy, Tran Trong Hieu, Nguyen Anh Tai, Chu Thi Ngoc QuynhTóm tắtThe Keccak-f[1600] permutation underlies the Secure Hash Algorithm 3 (SHA-3) family of cryptographic hash functions, widely used for data integrity and, increasingly, in post-quantum cryptographic hardware. Iterative implementations reuse one round datapath for all 24 rounds through a wide feedback multiplexer, a resource-efficient choice whose timing has not previously been measured with post-route accuracy. This study analyzes an iterative SHA3-256 core implemented on a Xilinx Artix-7 field-programmable gate array (FPGA) and cross-checked on a Virtex-7 device, comparing post-synthesis and post-route timing and evaluating two fan-out-reduction techniques and a multicycle-path exception. The same design was also taken through a complete register-transfer level (RTL) to GDSII flow on a 45 nm process as an application-specific integrated circuit (ASIC), using an in-house-characterized standard-cell library and a widely used public library, with functional correctness verified against reference test vectors. Post-synthesis estimates underestimate the critical-path delay of the feedback-select path by up to 2.8×, none of the three mitigation techniques improves the operating frequency, and the bottleneck is architecture-induced rather than technology-dependent. The in-house library achieved a signed-off implementation with zero design-rule check (DRC) and layout-versus-schematic (LVS) violations, whereas cell-level verification found manufacturing-grid violations in the public library that prevented a comparable signoff.
A new approach to equilibrium problems via regularized extragradient-type dynamics
Trang: 1155-1169 Nguyen Hai HaTóm tắtNonlinear analysis serves as a fundamental framework for modeling diverse phenomena in modern science and engineering. Within this field, equilibrium problems provide a powerful tool that not only unifies diverse mathematical models, such as variational inequalities and fixed point problems, but also effectively characterizes various phenomena in various scientific disciplines. Over the past decades, dynamical systems have emerged as an effective method for finding solutions to these problems due to their continuous-time nature and stability properties. This paper investigates a novel regularized dynamical system of extragradient-type specifically designed to solve monotone equilibrium problems. The primary challenge addressed is ensuring the existence of a global solution and achieving strong convergence under mild assumptions. Our methodological approach involves constructing a continuous-time trajectory governed by a regularization term and an extragradient-type structure. We first prove the existence and uniqueness of a strong global solution to the proposed system. Subsequently, the asymptotic behavior of the system is analyzed, demonstrating the strong convergence of the generated trajectories toward a specific solution of the original equilibrium problem. Lastly, a time discretization scheme is implemented, leading to a new iterative regularized extragradient-type algorithm enhanced by relaxation parameters. The main results confirm that the proposed dynamical approach not only guarantees theoretical stability but also provides a robust computational platform for monotone equilibrium problems. The findings of this study offer significant insights into the development of efficient continuous-time optimization methods and contribute to the broader understanding of regularization techniques in nonlinear analysis.
Comparative flexural performance of primitive, diamond, and gyroid TPMS concrete beams
Trang: 1170-1184 Tran Anh Tuan, Hoang Viet Hai, Nguyen Hoang Quan, Tran Thi Bich Thao, Tran Bao VietTóm tắtThis study investigates the nonlinear flexural behaviour of Primitive, Diamond, and Gyroid triply periodic minimal surface (TPMS) concrete beams using the Concrete Damaged Plasticity model in Abaqus/Standard. All beams had identical external dimensions, C30/37 concrete properties, and a nominal solid volume fraction of 50%, allowing topology to remain the main variable. A combined geometric-resolution and mesh sensitivity study was conducted, and the R24 models were adopted as the common comparative reference. Structural performance was evaluated using peak load, secant stiffness, accumulated external work up to a common post-peak load threshold, mass-normalized accumulated work, normalized deformation index, and damage distributions. Primitive exhibited the highest secant stiffness (46.5 kN/mm) and peak load (5.12 kN) but showed localized damage, rapid post-peak load reduction, and the lowest accumulated work (0.93 J). Diamond achieved a slightly lower peak load (4.77 kN) while providing the highest accumulated work (1.85 J) and mass-normalized accumulated work (0.39 J/kg), indicating a favorable balance between strength and work accumulation under the adopted numerical assumptions. Gyroid showed the lowest peak load (3.56 kN) but the highest normalized deformation index (2.16). The results demonstrate a clear topology-dependent trade-off among stiffness, strength, accumulated work, and deformation capacity, and provide preliminary numerical insights for future experimental validation and investigation of load-bearing, permeable TPMS concrete structures.
Trang: 1185-1197 Ho Xuan Nam, Nguyen Ngoc LanTóm tắtFlutter is a self-excited aeroelastic instability that controls the wind design of long-span cable-stayed bridges. It is usually assessed by wind tunnel tests or costly simulations. This study examines whether a probabilistic machine learning model can give a first estimate of the flutter critical wind velocity, based on flat-plate theory, from preliminary design parameters, for a family of bridges derived from one existing bridge. A finite element model of the Dakrong cable-stayed bridge in Vietnam is updated to match ten of the twelve natural frequencies measured on site (root-mean-square error 4.7%). Three hundred bridge configurations are generated from the updated model by Latin Hypercube Sampling of eleven variables within slenderness limits, and their critical velocity is estimated with the Selberg formula and checked with the Rocard formula. On a test set of 61 configurations, Gaussian process regression with automatic relevance determination, trained only on span, width, depth, mass and inertia, reproduces the Selberg estimate with R2 = 0.92 and a mean absolute percentage error of 6.4%, and 95.1% of the test values fall inside its 95% confidence intervals. These values measure agreement with the formula-based labels, not with the actual flutter speed. The labels assume flat-plate aerodynamics and a single pair of modes, and additional checks suggest that, for this open-girder deck, their uncertainty is larger than the prediction error. The model is therefore intended only for comparing deck alternatives within the sampled family and does not replace a flutter check.
Vibration dynamics of a dependent suspension system of half-car model with tire-road separation
Trang: 1198-1210 Nguyen Dang Quy, Do Van Tu, Le Van Trung, Lai Viet Anh, Nguyen Dinh Tung, Le Xuan Long, Le Van ManhTóm tắtThis paper presents a vibration analysis of a truck suspension system using a dependent vibrating half-car model to evaluate its dynamic behavior under tire-road contact and separation conditions. The proposed model consists of four degrees of freedom and considers the coupled motions between the front and rear wheels. A numerical approach is applied to calculate the vertical and roll responses of the suspension system under different road excitations. The equations of motion are formulated by incorporating the tire-road separation condition for both wheels, allowing the transition between contact and separation states to be examined. The effects of road profiles and suspension parameters on the dynamic responses are analyzed in both the time and frequency domains. The results show that considering tire-road separation provides a more realistic prediction of vehicle vibration behavior compared with the conventional assumption of continuous tire-road contact. The findings can be used as a reference for suspension design and for developing control methods aimed at improving vehicle stability and rollover resistance.
Trang: 1211-1225 Van Thao Le, Chi Tinh Phung, Manh Tung Do, Dinh Si Mai, Van Son Nguyen, Ba Tinh Do, Manh Cuong Bui, Tat Khoa DoanTóm tắtWire arc additive manufacturing (WAAM) of Inconel 718 thin walls requires careful parameter selection to balance geometric accuracy and surface quality. In this study, the effects of wire feed speed (wfs) and travel speed (v) on the effective width (EW), total height (TH), and surface roughness (Sa) of 20-layer walls fabricated by cold metal transfer (CMT)-WAAM process were first analyzed through a full factorial experiment design. To resolve the trade-off between productivity and surface integrity, a multi-criteria decision-making framework integrating Entropy weight method (EWM) with COPRAS and WASPAS methods was applied. The analysis of variance (ANOVA) results reveal that wfs primarily governs EW, while v dominates TH and Sa. Both COPRAS and WASPAS optimization techniques consistently identify wfs = 6 m/min and v = 40 cm/min as the optimal condition, achieving high deposition height with acceptable surface roughness. The proposed framework offers a robust strategy for optimization in CMT-WAAM of Inconel 718 superalloys.
Trang: 1226-1242 Van-Tham VuTóm tắtA semi-analytical model is developed for the electro-thermoelastic free vibration of functionally graded porous sandwich plates with orthogonal stiffeners. The plate comprises a PoFGPie top face sheet, a porous metal-foam core, and a fully dense stiffened FGM bottom face sheet. A four-variable shear deformation theory (HSDT4), the Lekhnitskii smeared-stiffener model, and the pb²-Ritz method are combined in a unified formulation. A cosine-linear electric potential and uniform (UTR), linear (LTR), and nonlinear (NLTR) temperature rises are considered. The model is validated against published 3D, finite-element, and coupled-field solutions. Parametric studies cover core porosity, material gradation, layer thickness, stiffeners, voltage, geometry, boundary conditions, and thermal loading. Within the investigated ranges, increasing core porosity raises the fundamental dimensionless frequency because mass reduction dominates stiffness loss. Greater stiffener height raises the frequency, but the best stiffener orientation depends on the boundary condition and two-directional stiffening is not always optimal. Negative voltage produces a stiffening effect, positive voltage a softening effect, and thermal loading reduces the frequency, with UTR causing the largest decrease.
Trang: 1243-1258 Tuyet Thi Hoang, Tu Anh Do, Viet Hai Hoang, Duc Chinh NgoTóm tắtThis paper compares the effects of fly ash (FA) and silica fume (SF) replacement on the hydration heat characteristics and early-age thermal cracking potential of high-strength concrete in a single bridge-pier cross-section. Experimental data from two independent experimental programs comprising two mixture series (FA: 0-30%; SF: 0-15%) were evaluated using within-series control normalization. The eight mixtures were assessed for a common 2.0 m × 3.0 m section under the same seven-day thermal-mechanical analysis conditions. Maximum adiabatic temperature rise decreased by 17.6% for FA30 and 7.3% for SF15 relative to their respective controls; at 10% replacement, the reductions were 4.5% for FA and 5.2% for SF. Despite the greater heat reduction in the FA series, its maximum cracking index increased from 0.9793 (FA00) to 1.0241 (FA30), with FA30 alone exceeding the adopted stress-to-strength threshold of 1.0. In contrast, SF10 and SF15 reduced the maximum cracking index by 4.51% and 6.58%, respectively, relative to SF00; the corresponding indices were 0.8343 and 0.8162. These contrasting trends show that the benefits of reducing hydration heat cannot be assessed independently of early-age tensile strength development. For the investigated section and boundary conditions, SF at 10-15% provided the more favorable combined response, whereas increasing FA replacement reduced heat release without improving the calculated cracking index. The findings are comparative and specific to the studied series of mixtures and structural scenario.
Trang: 1259-1274 Tran Duc Cong, Le Khanh Giang, Ho Thi Lan HuongTóm tắtMonitoring the operational condition of cable-stayed bridges is essential for ensuring structural safety and long-term serviceability. GNSS-RTK technology has emerged as an effective solution for continuous, high-precision displacement measurement in structural health monitoring (SHM). However, high-frequency GNSS data are often noisy and unlabeled, posing significant challenges for traditional analysis methods. This study addresses the problem of identifying structural operational states from unlabeled GNSS-RTK data using an unsupervised learning framework. Displacement data collected from two GNSS stations installed symmetrically on a cable-stayed bridge were segmented into hourly windows and preprocessed using Hampel filtering and Kalman smoothing. Feature vectors were then standardized and reduced in dimensionality using Principal Component Analysis, while t-SNE was applied for visualization. Clustering algorithms, including K-Means, hierarchical agglomerative clustering, Gaussian mixture models, and DBSCAN, were implemented and evaluated using multiple internal validation indices and stability metrics. The results reveal a consistent two-state structure in the horizontal displacement component, with K-Means achieving the best performance (Silhouette score up to 0.7006) and perfect stability (ARI = 1.0). Importantly, the clustering results are highly consistent across both stations, indicating strong spatial reliability. These findings demonstrate that unsupervised learning can effectively extract meaningful operational states from GNSS-RTK data, providing a robust and scalable approach for structural health monitoring of large-scale bridges.
Trang: 1275-1290 Mai Quang Huy, Nguyen Dang PhongTóm tắtLocal scour around bridge piers is a major threat to foundation stability, and accurate prediction of its temporal development is important for bridge safety assessment. This study investigates clear-water local scour around a cylindrical bridge pier using an existing laboratory dataset and three-dimensional CFD-based morphodynamic simulation with REEF3D. The experimental dataset comprises 21 time-resolved scour-depth measurements collected over a 330-min test. The numerical model solves the incompressible RANS equations with the standard k- turbulence model and couples the hydrodynamic solution with the Engelund–Fredsøe bed-load formulation and movable-bed evolution. Mesh-resolution and critical Shields parameter sensitivity analyses were conducted to identify a suitable calibrated configuration. The selected configuration reproduced the measured temporal scour development with satisfactory agreement and captured the characteristic progression from rapid initial erosion through transitional scour growth to gradual stabilization toward quasi-equilibrium. The results indicate that a properly calibrated REEF3D framework can reproduce the temporal development of clear-water pier scour with reasonable accuracy, although broader independent validation is required before general engineering application.
Trang: 1291-1305 Nguyen Thi Thu Hao, Vo Le Ngoc Dien, Doan Dinh Thien VuongTóm tắtTile cut away at room edges wastes material and embodied carbon, yet layout optimizers treat one pattern in one room. This paper develops a two-dimensional layout and packing algorithm: four laying patterns obey a minimum-cut rule, off-cuts are reused across rooms only along precedence-feasible tiling orders searched by simulated annealing, and layouts are compared on waste, cutting effort and an embodied-carbon indicator. Geometry can be read one-way from an Industry Foundation Classes (IFC) model and the indicator covers the tile only, so the framework is neither a complete building information modelling workflow nor a life-cycle assessment. On five computational benchmarks with one tile product per dwelling, default setting-out, a 10 cm minimum cut and nominal joint-free dimensions, reuse lowers the waste of running bond by 53%, and schedule-constrained cross-room reuse lowers waste by 24% and 70% relative to within-room reuse in six- and eight-room apartments (median 37% over 60 random apartments); simulated annealing matched enumeration wherever possible (non-trivially only for six rooms). The eight-room value is a favourable case, because its spans let off-cuts fit later pieces exactly. With 2-3 mm joints and a 2.5 mm kerf the gains are 20-21% and 13-15% (median 28-29%); when as-built span deviations, separate wet-area tiles and one rejected off-cut in five are added, they average 16-17% and 10-18%. Reuse also assumes one production lot; site validation is future work.
