Search Results (253)

To address the neglect of real-time mass transfer effects by traditional analysis methods during the side-by-side offloading process of Floating Production Storage and Offloading (FPSO) and shuttle tankers, a numerical model incorporating the variable mass effect is established to enable the simulation of dynamic offloading processes. Using this model, the dynamic response characteristics under different offloading rates and sea conditions are systematically investigated and validated against towing tank tests. Based on the previously optimized benchmark configuration, which includes 16 side-by-side mooring lines, six floating fenders, and an anchor line angle of 60° for the FPSO, the evolution laws of mooring line tension and fender pressure under different offloading rates were systematically investigated under normal and extreme sea conditions. The results show that an increase in offloading rate significantly amplifies the system’s fender load; when the offloading rate reaches approximately 1.4 t/s, the system transitions from the quasi-static response region to a significant nonlinear coupling region, demonstrating obvious sea condition–rate coupling characteristics. Under the combined action of high offloading rates and severe sea conditions, fender pressure rapidly approaches the design limit, becoming the primary safety bottleneck for the system. Model test results indicate that the numerical model can well predict mechanical responses under low and medium offloading rate conditions. The research results can provide a reference for offloading rate control, safety assessment, and operational window determination during FPSO side-by-side dynamic offloading operations. Full article

As oil and gas development increasingly targets low and ultra-low permeability reservoirs, conventional recovery techniques often prove insufficient for mobilizing residual oil. Surfactant flooding, a key chemical enhanced oil recovery (EOR) technology, thus requires careful system optimization and mechanistic investigation. This study focuses on low-permeability reservoirs in the Changqing Oilfield, evaluating three surfactant systems—YHS-Z1 (a 7:3 mass ratio blend of hydroxypropyl sulfobetaine and cocamide), YHS-Z2 (a polyether carboxylate, a nonionic-anionic composite) and a middle-phase microemulsion system (Heavy alkylbenzene sulfonate and hydroxysulfobetaine were combined with a mass ratio of 7:3)—through a series of experiments including interfacial tension measurement, contact angle analysis, static and dynamic oil displacement tests, as well as emulsion transport/retention index assessments, to comprehensively characterize their oil displacement properties. Based on the experimental data, this study constructed four classical regression models: Ridge Regression, Random Forest (RF), Gradient Boosting Regression (GBR), and Support Vector Regression (SVR), and conducted a comparative analysis of their predictive performance. The results demonstrate that the Random Forest (RF) model achieved the optimal prediction performance, with a Mean Absolute Error (MAE) of 1.8245, a Mean Absolute Percentage Error (MAPE) of 4.78%, and a coefficient of determination (R²) of 0.9428 on the training set. Further analysis using the SHapley Additive exPlanations (SHAP) algorithm revealed that the retention index is the primary global factor (accounting for 49.79% of the variance), while significant intergroup differences exist in the primary factors across different surfactant systems. Concurrently, single-factor and multi-factor sensitivity analyses were conducted to elucidate synergistic effects and threshold behaviors among parameters. The optimal parameter combination, identified via a random search method, achieved a predicted recovery factor of 45.61%, representing a 6.57% improvement over the highest experimental value. This study demonstrates that machine learning methods can effectively identify the dominant factors in oil displacement and enable synergistic parameter optimization, thereby providing a theoretical foundation for the efficient development of surfactant flooding in low-permeability reservoirs. Full article

To address the limitations regarding poor adaptability to complex forest environments as well as high installation and operational costs in existing mountain transportation equipment, a modular cable-type equipment for moso bamboo transportation was designed based on the terrain characteristics of steep bamboo forests and specific transportation requirements. This study first presents the overall structure and working principle of the transportation equipment. Next, a theoretical analysis and component selection were conducted for critical parts such as the wire rope, supporting components, wire-rope-driven devices, and hydraulic systems. Then, the static characteristics of the supporting components and the vibration characteristics of the wire rope were simulated and analyzed. Finally, performance testing of the equipment was conducted, focusing on transportation productivity and machine utilization. The results showed that the maximum deformation of the supporting components was 1.75 mm, occurring at the lower roller–rail contact region. During unloading, the first-order principal vibration amplitude of the wire rope had the greatest impact at the mid-span position, with a value of 0.27 m. The vibration frequency of the wire rope during operation is influenced by the its initial tension, load mass, and attachment distance, with the first-order frequency range approximately between 0.85 and 3.90 Hz. Within this frequency range, the bouncing excitation caused by moso bamboo does not induce resonance in the wire rope. The transportation productivity of the equipment was 2.61 tons per hour, with the machine utilization rate exceeding 95%. This study indicates that the designed cable-type equipment effectively meets the requirements for moso bamboo transportation in complex forest environments. Full article

The structural segmentation of wind turbine blades offers advantages in transportation, manufacturing, and maintenance; however, it introduces interfaces that may compromise load transfer and fatigue performance. This study presents the experimental and numerical validation of a composite coupling system designed for small wind turbine blades compliant with IEC 61400-2 requirements. A 2 m representative section extracted from the mid-span region of a 9 m blade was manufactured using vacuum-assisted resin infusion and tested under static loading conditions. A detailed finite element model based on classical laminate theory and orthotropic material properties was developed to predict structural response. Experimental measurements showed a maximum tip deflection of 15 mm under the applied load, compared to 13.76 mm predicted numerically, corresponding to a deviation of 8.9%. Surface strain measurements obtained from eight strain gauges installed across the blade–coupling interface indicated maximum mean values of +632.4 με in tension and −664.2 με in compression, with no evidence of localized strain amplification at the instrumented locations. These findings demonstrate that fully composite permanent segmentation can preserve stiffness continuity while maintaining strain levels below reported fatigue initiation thresholds, supporting the structural feasibility of segmented blade architectures for small wind turbine applications. Full article

Fatigue properties remain a key challenge for aluminum–steel self-piercing riveted (SPR) joints in lightweight structures. This study evaluates shot peening as a pretreatment for the AA5052 sheet to improve the fatigue behavior of AA5052/SPFC440 dissimilar joints and to clarify the underlying mechanisms. Shot-peened and conventional SPR joints were prepared for comparison. Quasi-static tensile tests were conducted, and tension–tension fatigue tests were performed at high and low load levels. After shot peening, multiple factors with residual compressive stress, subsurface hardening, and surface roughness influenced the fatigue performance of the SPR joints. This led to a load-level-dependent fatigue behavior, with improved fatigue performance at low load levels and reduced performance at high load levels. At high load conditions, the increased surface roughness played a more significant role, with more crack initiation sites observed, resulting in fatigue lives comparable to or slightly lower than those of conventional joints. In contrast, at low load levels in the long-life regime, surface tensile stress was effectively reduced, crack initiation at surface defects was suppressed, and crack initiation shifted from the surface to subsurface regions, resulting in an 11.3% improvement in fatigue strength. These findings provide practical guidance for improving the fatigue performance of dissimilar-material SPR joints through material surface pretreatment. Full article

This study examines the mechanical response of medium-manganese TRIP steels under different stress states, focusing on deformation-induced austenite-to-martensite transformation and ageing phenomena. Two steels with distinctly different ferrite–austenite morphologies and retained austenite (RA) fractions were analysed: a globular microstructure with 18% RA and a lamellar microstructure with 14% RA, produced by single (SA) and double annealing (DA), respectively. Continuous and interrupted tests were performed under in-plane shear, uniaxial tension, and plane strain stress states. Strain fields were analysed using high-resolution digital image correlation, while RA fractions were quantified as a function of strain by ex situ X-ray diffraction. The results demonstrate a pronounced stress-state dependence. SA samples exhibit discontinuous yielding, with uniaxial tests showing clear Lüders band formation. Both steels exhibit dynamic strain ageing manifested by Portevin–Le Chatelier (PLC) serrations and associated strain bands, which are most pronounced under uniaxial tension, weaker in plane strain, and barely detectable in in-plane shear. Static strain ageing is also evidenced by a strengthened yield response upon unloading–reloading in all samples. The SA globular microstructure exhibits higher PLC band inclination angles than the lamellar DA microstructure, consistent with its more pronounced anisotropy. The propagation velocity in uniaxial tensile samples decreases with increasing strain following the work-hardening response. For both steels, the austenite-to-martensite transformation rate is highest in uniaxial tension, slightly reduced in plane strain, and strongly suppressed under in-plane shear. A Beese–Mohr/Johnson–Mehl–Avrami–Kolmogorov formulation incorporating stress triaxiality and Lode angle captures these trends for both steels. For the stress states considered, the DA condition exhibits a consistently higher transformation rate than the SA condition, accompanied by a higher work-hardening rate. These findings highlight the coupled role of stress state and microstructural morphology in governing localisation behaviour and strain-induced transformation in medium-manganese steels. Full article

This paper introduces a compact pneumatic artificial muscle (CPAM) that integrates a coaxial rod and an internal helical compression spring (stiffness 9750 N/m) into a McKibben-type outer muscle and compares it to a commercial DMSP-20-200N from FESTO Budapest, Hungary, with identical outer geometry and materials. Both actuators were mounted in a force-controlled test rig, pre-tensioned, and then cycled quasi-statically between their stretched and maximally contracted states at 13 internal pressures. For each pressure, median loading and unloading force–contraction curves were obtained from five repeats measuring both the cylinder excitation force and a load cell, and hysteresis was quantified by a normalized loop area based on peak force and common contraction range. Under the rated load of 2000 N at 0.6 MPa, the CPAM elongates less (−1.5% vs. −3%) and generates higher forces over most of the contraction range. The normalized hysteresis index of the CPAM is markedly lower at low pressures (≈0.05–0.25 MPa, reductions of about 10–25%), similar near 0.30 MPa, and slightly higher at 0.35–0.60 MPa (≈6–14%). Full article

Construction on soft, highly compressible soils increasingly requires reliable ground improvement solutions. Among these, Rigid Inclusions (RIs) have emerged as one of the most efficient soil-reinforcement techniques. This paper synthesizes evidence from over 180 studies to provide a comprehensive state-of-the-art review of RI technology encompassing its governing mechanisms, design methodologies, and field performance. While the static behavior of RI systems has now been extensively studied and is supported by international design guidelines, the response under cyclic and seismic loading, particularly in liquefiable soils, remains less documented and subject to significant uncertainty. This review critically analyzes the degradation of key load-transfer mechanisms including soil arching, membrane tension, and interface shear transfer under repeated loading conditions. It further emphasizes the distinct role of RIs in liquefiable soils, where mitigation relies primarily on reinforcement and confinement rather than on drainage-driven mechanisms typical of granular columns. The evolution of design practice is traced from analytical formulations validated under static conditions toward advanced numerical and physical modeling frameworks suitable for dynamic loading. The lack of validated seismic design guidelines is high-lighted, and critical knowledge gaps are identified, underscoring the need for advanced numerical simulations and large-scale physical testing to support the future development of performance-based seismic design (PBSD) approaches for RI-improved ground. Full article

This study systematically investigates the kinematic characteristics and static stability of a spatial under-constrained four-cable-driven parallel mechanism, specifically designed for supporting aircraft models in wind tunnel tests. Addressing the inherent strong coupling between kinematics and statics in such systems, an integrated solution framework is proposed. Firstly, a hybrid intelligent algorithm integrating genetic algorithm, chaos optimization, and particle swarm optimization is introduced to efficiently solve the direct and inverse geometric-statics problems, ensuring the identification of physically feasible equilibrium configurations under constraints such as cable tension limits and mechanical interference. Subsequently, a stability evaluation method based on the eigenvalue analysis of the system’s total stiffness matrix is employed, establishing a criterion (minimum eigenvalue λ_min > 0) to identify statically stable equilibrium points. Finally, the static feasible workspace and the static stable workspace are systematically analyzed and quantified, providing practical operational limits for mechanism design and trajectory planning. The effectiveness of the proposed solution framework is validated through numerical computations, simulations, and experimental tests, demonstrating its superiority over benchmark methods. This study provides theoretical support for the design, analysis, and control of under-constrained four-cable-driven parallel mechanisms. Full article

Floating photovoltaic (FPV) systems are increasingly deployed in offshore environments. Among various FPV concepts, membrane-type platforms offer distinct advantages, including reduced weight, lower material consumption, and cost-effectiveness. This study investigates the hydrodynamic response of a membrane-type offshore FPV system through a 1:40 scale physical model test based on the Ocean Sun prototype. Static-water free-decay tests were first conducted to determine the natural periods and damping characteristics in heave, surge, and pitch motions. Subsequently, irregular-wave tests were performed under seven sea states representative of an offshore demonstration site. Free-decay results show model-scale natural periods of approximately 1.0 s for heave, 0.8 s for pitch, and 15 s for surge. The long surge natural period avoids resonance with short-period waves, while the high damping in heave and pitch effectively limit dynamic amplification. Under irregular waves, heave and pitch motions remain small, whereas surge motion exhibits pronounced long-frequency excursions. Spectral analysis reveals a dominant low-frequency surge peak at f ≈ 0.067 Hz (corresponding to the natural period of 15 s), superimposed with higher-frequency components associated with wave-induced motions. A strong correlation is observed between low-frequency surge and mooring tensions. Across Sea States 1–6, the motion responses increase gradually, while a marked rise in the exceedance probability of mooring forces occurs only in the most severe sea state. Weibull extreme-value fits show good linearity, indicating that the measured extremes are statistically consistent. The results provide experimental data and design insights for membrane-type FPV systems, establishing a foundation for future hydroelastic studies. Full article

The paper presents the results of numerical simulation of the dynamic behaviour of the post-tensioned beams subjected to a constant force impulse load over time and a short-term force impulse load varying over time. Abaqus programme was used for numerical analysis, introducing necessary and detailed modifications to the modelling and calibration parameters. The numerical dynamics models were calibrated using results previously obtained from our own experimental and numerical static analysis. To estimate the dynamic strength of structural materials, the dynamic strength coefficient was applied in the concrete damage plasticity model, and the Johnson–Cook model was used to describe the evolution of the dynamic yield strength of steel elements. An explicit procedure was used to solve the dynamic equilibrium equations. The selection of the Rayleigh damping parameter and the methodology for determining the external load in a dynamic problem are discussed. The study presents new results on the influence of the type of force impulse loading and variable prestressing eccentricity in numerical simulations of post-tensioned beams. The results of the simulation show that the post-tensioned beams achieved a lower dynamic load capacity under a constant force impulse load of approximately 5% compared to the static load capacity achieved in the experimental static tests, regardless of the assumed prestressing eccentricity. A dynamic load capacity significantly exceeded the static load capacity under short-term time-varying force impulse loading. The beam with the larger prestressing eccentricity achieved a dynamic load capacity of 211% of the static load capacity, while the beam with the smaller prestressing eccentricity achieved a dynamic load capacity of 198% of the static load capacity. Full article

This study examines the mechanical performance of small-sized glued-laminated timber (GLT) produced from low-quality oak (Quercus spp.) lamellae and veneer arranged in 2–5 layers. After both non-destructive and bending tests, density, modulus of rupture, deflection and modulus of elasticity by static and dynamic methods were evaluated. Average densities ranged from 747 to 777 kg/m³. The two- and three-layer GLTs exhibited modulus of rupture values of 59.0 MPa and 63.7 MPa, while the four- and five-layer specimens reached 80.4 MPa and 80.0 MPa, respectively—up to 36% higher due to veneer reinforcement on the tension side. Static modulus of elasticity ranged between 11.2 and 12.1 GPa, and dynamic modulus of elasticity reached 13.0 GPa. The findings demonstrate that multi-layer configurations with veneer reinforcement effectively enhance bending performance and reliability, promoting the structural application potential of low-grade hardwood in accordance with EN 14080. Full article

This study investigates the shear behavior of horizontal joints in prefabricated monolithic short-limb shear walls under static and low-cycle reversed cyclic loading, supported by finite-element simulations. Four specimens were tested to evaluate the influence of the bundled shear reinforcement ratio, initial reinforcement stress level, and loading protocol on shear capacity. The results show that increasing the bundled shear reinforcement ratio significantly enhanced both the yield and peak loads, with increases observed in the yield, peak, and failure loads. Conversely, a higher initial stress level in the reinforcement weakened the shear-friction mechanism, leading to a reduction in the load-carrying capacity. Compared to monotonic loading, low-cycle reversed cyclic loading accelerated crack propagation and cumulative damage, leading to a significant reduction in load-carrying and deformation capacities. Finite-element simulations, using the Concrete Damaged Plasticity (CDP) model, were in good agreement with experimental results, although the simulations slightly overestimated the ultimate capacity, confirming the model’s validity. Parametric analysis indicated that increasing axial tension progressively reduced the yield and peak loads, with the reduction in peak load being more pronounced, while the cracking load remained unchanged. These findings provide a theoretical foundation for the shear design and seismic performance evaluation of horizontal joints in prefabricated shear walls, offering valuable insights for future design improvements and modeling strategies. Full article

This study investigates the structural performance of TL-5 concrete bridge barriers reinforced with glass fiber-reinforced polymer (GFRP) bars at the critical deck–wall interface. Five full-scale barrier models were subjected to static load testing until failure. The wall reinforcement included four barriers with high- and standard-modulus GFRP bars using headed-end, bent, and hooked anchorage, and one with conventional steel reinforcement. The objective was to assess the load-bearing capacity, failure modes, and deformation behavior of GFRP-reinforced barriers with respect to the Canadian Highway Bridge Design Code (CHBDC) requirements. Results revealed that all GFRP-reinforced models achieved ultimate flexural capacities surpassing CHBDC design limits, with diagonal tension cracking at the corner joint emerging as the predominant failure mode. A set of new equations was developed to predict diagonal tension failure and determine minimum reinforcement ratios to mitigate such failure. Comparisons with experimental findings validated the proposed analytical approach. Among the configurations tested, barriers with headed-end high-modulus GFRP bars offered the most cost-effective and structurally sound solution. These findings support the incorporation of GFRP bars in bridge barrier design and establish a framework for future code development regarding GFRP-reinforced barrier systems. Full article

This paper presents a 16 MW typhoon-resistant Tension Leg Platform floating offshore wind turbine (TLP FOWT) designed for the South China Sea. The survivability of the TLP FOWT under extreme environmental conditions is investigated through an integrated time-domain coupled analysis numerical model. The accuracy of the numerical model is calibrated by comparing its results with experimental data. In comparisons of mooring system static stiffness tests and white noise tests, the results from the calibrated numerical model show good agreement with the experimental data. Regarding the free decay tests and the statistical time-domain response results, the most significant discrepancies are only 1.17% and 6.91%, respectively. Subsequently, the time-domain response of the numerical model was investigated under extreme South China Sea conditions, configured according to the IEC 61400-3-2 design load conditions. The safety of the design was then evaluated against ABS specifications. The analysis yielded maximum platform motion amplitudes and inclinations of 34.99 m (less than 30% of water depth) and below 1°, respectively. Under both 50-year and 500-year return period conditions, the platform maintained stable TLP motion characteristics with no tendon slackness, evidenced by a minimum tendon tension of 107.23 kN. All motion responses and tendon tensions complied with the ABS safety factors, confirming the design’s capability to ensure safe operation throughout its service life. The present work provides valuable insights for the design and risk assessment of future large-scale TLP FOWTs. Full article