Search Results (614)

Background/Objectives: Blunt thoracic aortic injury (BTAI) is a rare, highly lethal trauma typically occurring at the aortic isthmus. Advanced BTAI is primarily treated with thoracic endovascular aortic repair (TEVAR). Because emergent surgical debranching is rarely feasible, management depends heavily on patient anatomy, especially regarding the left subclavian artery (LSA). Patient-specific computational fluid dynamics (CFD) models offer critical insights into periprocedural planning and outcome prediction. Methods: This study investigates hemodynamic changes in a patient-specific BTAI case following intentional LSA coverage by a stent graft. Three-dimensional patient-specific models were coupled with RCR-Windkessel boundary conditions for both pre- and post-procedural imaging data to simulate blood flow in each scenario. Results: Post-intervention, flow distribution improved significantly; relative perfusion to the brachiocephalic trunk and left common carotid artery increased by 3.51% and 4.02%, respectively, alongside an elevated overall pressure throughout the entire computational domain. However, regions with high oscillatory, low magnitude shear (HOLMES), specifically wall areas with values < 0.3 Pa, expanded post-stenting. This warrants careful monitoring during follow-ups, given the associated risk of thrombus formation. Furthermore, time-averaged swirling strength (TASS) variation along the aorta decreased (standard deviation dropped from 1.8610 to 1.3835), indicating stabilized flow within the stented region, while normalized swirling strength increased distally. Conclusions: This study establishes an effective, non-invasive framework for assessing pre- and post-TEVAR hemodynamics. It demonstrates that LSA coverage induces uniformly elevated pressure and alters wall shear stress and helicity indices, highlighting the need for future research into pharmacological management to optimize long-term outcomes. Full article

A prosthetic vascular graft is an important vascular conduit used for end-to-end anastomosis; however, optimizing pore morphology to improve local hemodynamic performance remains a significant challenge. The purpose of this study was to investigate the influence of regular and reconstructed irregular pore morphologies on local blood flow characteristics in prosthetic vascular grafts. Three graft models, including a non-porous model, a regular porous model with regular square-prism pores, and a reconstructed irregular porous model reconstructed from segmented scanning electron microscopy (SEM) images, were employed to simulate blood flow within virtual end-to-end anastomoses. To enable a direct comparison of pore morphology, the regular and irregular porous models were designed with the same porosity. Steady laminar blood flow through virtual end-to-end anastomoses was simulated using computational fluid dynamics (CFD) assuming Newtonian blood, rigid vessel walls, and a no-slip boundary condition. The non-porous model exhibited a flow pattern representative of a conventional graft and served as the baseline for comparison. Compared with the regular porous model, the reconstructed irregular porous model generated more irregular recirculation patterns, a non-uniform pressure distribution, and significantly greater spatial heterogeneity in wall shear stress (WSS). Although the irregular porous model exhibited the lowest mean and median WSS, it produced the highest localized WSS at sharp pore edges and the largest surface area exposed to low WSS. Quantitative analyses demonstrated that the irregular pore morphology increased the spatial variability in WSS and altered the distribution of low-WSS regions and local recirculation compared with the regular porous model under the same porosity conditions. The results demonstrate that pore morphology, rather than porosity alone, significantly influences local hemodynamic characteristics under identical porosity conditions. Furthermore, the SEM-based reconstruction approach captured realistic spatial variations in flow and WSS that could not be fully reproduced by an idealized regular porous model. These findings provide insights into the hemodynamic effects of porous graft architectures and may contribute to the design and optimization of prosthetic vascular grafts. Full article

Asphalt bridge deck pavements are highly susceptible to rutting, shoving, and interlayer slippage under high-temperature traffic conditions, where interlayer shear stress plays a decisive role. To clarify the coupled effects of thermal gradients and moving loads, this study developed a sequential three-dimensional thermo-mechanical finite element model for a double-layer pavement in Zhongshan, China. Field-recorded air temperature, solar radiation, sunshine duration, and wind speed were used to define transient thermal boundaries. The calculated temperature field was then transferred to a fully bonded moving-load model with dual rectangular contact areas and braking-induced longitudinal traction. Axle load, roadway slope, braking coefficient, and the thicknesses of the SMA-13 and AC-20 layers were varied. The predicted temperature fluctuation attenuated and the peak time was delayed with depth. The pavement surface reached 58.95 °C at 13:00, whereas the bottom of the asphalt overlay reached 46.99 °C at 17:00. Under the adopted 14:00 near-peak summer condition, increasing axle load amplified the overall response and raised the maximum asphalt-layer shear response from 0.172 to 0.223 Mpa. Roadway slope mainly affected traffic-direction stress transfer. Increasing the braking coefficient from 0 to 0.7 increased longitudinal shear response from 57.9 to 161.2 kPa in the asphalt layers and from 56.4 to 112.6 kPa near the AC-20/concrete interface. Increasing SMA-13 thickness reduced thermal and mechanical demand in the underlying layers, whereas increasing AC-20 thickness reduced the response near the concrete deck but shifted part of the tensile and shear demand toward the upper asphalt layer. Full article

Groundwater-related weakening and repeated low-strain-rate disturbances can jointly affect the long-term stability of soft surrounding rock. In this study, a PFC3D model was developed by combining a cumulative residual-strain damage variable with a Weibull statistical damage variable. Water effects were represented indirectly through water-content-dependent mesoscopic parameters and contact-strength degradation, thereby linking macroscopic irreversible deformation to progressive mesoscopic bond degradation. The cyclic responses of mudstone specimens with water contents of 0%, 3%, 5%, and 7.04% were simulated under a roadway-like three-directional, five-face boundary condition, consisting of axial loading, lateral pressure, one laterally constrained side, and one free face. The model reproduced the main stress–strain trends and failure characteristics. From the dry to saturated state, the experimental and simulated peak strengths decreased by 68.51% and 67.44%, respectively. Increasing water content also promoted earlier crack initiation, weakened strong force-chain continuity, and shifted failure from localized shear instability to distributed tensile–shear damage. Energy dissipation became increasingly important as water content increased. These findings clarify the mesoscopic damage mechanism of water-bearing mudstone under coupled water-induced softening and low-strain-rate cyclic loading, providing a reference for stability assessment and support design in underground soft-rock engineering. Full article

The nematic mesogens within dielectric liquid crystal elastomers (DLCEs) rotate in response to external electric fields, thereby driving macroscopic active shape morphing. This work establishes a rigorous theoretical framework to investigate the electro-mechanical bending mechanics of cantilevered DLCE sheets governed by this actuation mechanism. By theoretically formulating the electromechanical effect as a localized spontaneous strain field, we analytically correlate the stress-free deformation with the local nematic director alignment. We demonstrate that the macroscopic bending morphology of the DLCE sheet can be deterministically programmed by tailoring the principal bending directions via this microscopic director design. Our findings reveal that the synergistic interplay between the tailored spontaneous curvature and cantilever boundary constraints generates a rich variety of three-dimensional configurations, enabling active regulation of both deflection and out-of-plane tilting at the free edge. Furthermore, we explicitly highlight the critical, yet often overlooked, role of spontaneous shear strain, which significantly governs the bending response even within the thin-plate limit. These theoretical insights establish a robust foundation for the structural design of DLCE-based directional soft actuators and flexible devices. Full article

Cerebrovascular computational fluid dynamics (CFD) models often rely on generic boundary conditions, which may limit their ability to represent subject-specific hemodynamics and cerebral autoregulation (CA). We propose a multimodal data-driven boundary calibration (MDBC) framework integrating transcranial color-coded Doppler and continuous blood pressure monitoring to optimize individualized outlet resistances. As a proof-of-concept, we evaluated the MDBC framework in a single healthy volunteer at resting baseline and enhanced external counterpulsation (EECP)—a hemodynamic perturbation potentially triggering CA. Compared with conventional open boundary (OB) and static Murray allocation boundary (SMAB) strategies, MDBC achieved closer agreement with in vivo middle cerebral artery (MCA) velocity waveforms under both states. At rest, MDBC’s left MCA relative root mean square error (rRMSE) was 7.19%, versus 22.85% (OB) and 30.89% (SMAB). During EECP, conventional models yielded rRMSEs > 32%, whereas MDBC maintained 11.24%. Meanwhile, MDBC reproduced inter-hemispheric perfusion imbalance, an EECP-induced flow surge in the right MCA, and pronounced wall shear stress increases that were masked by generic boundary strategies. Moreover, MDBC estimated a 25.8% increase in global cerebrovascular resistance during EECP, suggesting the capability of the framework to characterize subject-specific impedance adaptations potentially associated with CA during intervention. These single-subject findings support the technical feasibility of integrating multimodal physiological measurements into cerebrovascular CFD boundary calibration and warrant further validation in larger cohorts and patient populations. Full article

In micro-extrusion and direct ink writing, the nozzle outlet diameter is often used to estimate the deposited line width or free-filament diameter. However, highly loaded conductive silver pastes may exhibit pronounced extrusion swell after leaving the nozzle, resulting in a filament diameter larger than the nozzle inner diameter. To quantify this deviation, this study proposes a single-parameter semi-theoretical correction model based on radial force balance at the nozzle exit, integrating Herschel–Bulkley yield stress–shear-thinning rheology with a finite-deformation description. The exit radial stress is derived from pressure-driven circular tube flow, while the post-exit radial expansion is balanced against atmospheric constraint. A comprehensive correction force constant, C, is introduced to account for wall-induced energy dissipation, particle-structure rearrangement, residual elastic recovery, and model simplifications. After calibration using a transition-swelling nozzle, C was determined as 1.03 × 10⁻² N. The model was applied to six nozzle diameters and four nozzle length–pressure conditions. For Nozzles 1–4 with significant swelling, the mean absolute percentage error was 5.31%, while the overall error for all six nozzles was 11.84%, mainly due to overestimation for the nearly non-swelling Nozzle 6. For varying nozzle lengths, the error was 5.20%, and both experimental and predicted swell ratios decreased with increasing effective nozzle length. The model provides a semi-theoretical tool for estimating free-filament dimensions and analyzing nozzle-length effects, primarily under pronounced-swell conditions. Its predictive capability becomes limited as the swell ratio approaches unity, where additional corrections for wall slip, relaxation, and the zero-swell boundary are required. Full article

To achieve high interconnect density in 2.5D packages, various microscale structures such as through-silicon vias (TSVs), microbumps, and redistribution layers (RDLs) are employed. These features typically exist at the micron scale, whereas other package components span millimeter to centimeter scales, resulting in a wide range of physical dimensions within the package. Although finite element analysis (FEA) has proven effective for evaluating the mechanical and thermal characteristics of 2.5D packages, the inherent multi-scale nature poses significant computational challenges and numerical convergence issues, severely hindering the design and analysis of increasingly dense packages. To address this problem, this paper proposes an efficient numerical homogenization method for the mechanical and thermal analysis of 2.5D packages. The method employs periodic boundary conditions (PBCs) based on the concept of referential statistical volume elements (rSVEs). In this approach, typical microstructures—including TSVs, microbumps, and RDL traces together with the surrounding matrix material—are treated as a homogeneous medium, and the equivalent material properties of the multi-scale structures are evaluated. These properties include the stiffness matrices (from which the equivalent Young’s modulus, shear modulus, and Poisson’s ratio can be derived), coefficients of thermal expansion, and thermal conductivity. Validation results demonstrate that the proposed method ensures continuity of displacement, stress, strain, and heat flux across opposite surface pairs of the rSVEs. Compared with experimental measurements and other existing homogenization techniques, the method accurately determines the equivalent material properties of complex multi-scale structures without being restricted to specific geometries, while significantly improving computational efficiency. Finally, the proposed numerical homogenization method is successfully applied to wafer warpage analysis during the manufacturing process and to thermal analysis under operating conditions. The results indicate that the method achieves high computational efficiency while maintaining accuracy in both mechanical and thermal analyses of 2.5D packages, thereby laying a solid foundation for the development of next-generation 2.5D package structures. Full article

Currently, Computational Solid Mechanics (CSM) and Computational Fluid Dynamics (CFD) simulations are not enough to correctly estimate the different physical characteristics found in the human cardiovascular system. As an alternative to individual simulations, Fluid Structure Interaction (FSI) simulations can yield more accurate physical quantities. In this study a comparison between rigid-wall CFD of a thoracic aorta affected by an aneurysm and the FSI of the Descending Thoracic Aortic Aneurysm (DTAA) itself was performed. The 18-year-old patient-specific geometry of the aorta and its branches was based on the National Institutes of Health public database. A patient-specific pulsatile blood flow waveform and a pressure three-element Windkessel model were set for boundary conditions. Parameters such as wall pressure, velocity distribution, Wall Shear Stress (WSS), Time-averaged Wall Shear Stress (TAWSS), Oscillatory Shear Index (OSI), wall displacement and Von Mises Stress (VMS) were investigated. The research shown that blood flow in the aorta is strongly affected by the onset of the aneurysm, which causes recirculation and uneven flow within the aneurysmal bulge. The results highlight that rigid-wall CFD, which cannot capture wall deformation and aneurysm compliance, leads to an overestimation of velocity, WSS, and TAWSS by 15, 21, and $32\%$ respectively, compared to FSI during the systolic peak; furthermore, a key novelty is represented by the slight underestimation of pressure during the systolic peak, an aspect not previously detailed in the DTAA literature. Full article

Based on experimental studies, a model of the control effect on the plastic deformation process under boundary asymmetric loading conditions has been developed. The regulating factor of plastic deformation unevenness δ, which determines the stress–strain state of the entire deformation zone and the boundary conditions, is presented. The boundary conditions, determined by additional compressive and tensile stresses along the height, generate shear stresses and specific loading regimes at the edges and within the deformation zone itself. The confirmed reduction in interaction, which coincides with the effect of plastic deformation occurring under conditions of force unevenness, is one of the criteria for the controlling effect. A distinctive feature of this approach is the recognition and proof of the existence of a controlling additional effect under conditions of complex force and deformation loading. Theoretical and experimental studies have revealed such effects under various loading conditions. Based on a closed-form problem in plasticity theory and the method of argument functions of a complex variable, a mathematical model of the control process exerted by the metal’s plastic flow zone has been developed. A key feature of the solution to this theoretical problem was the consideration of the interaction between zones under different force loads, represented by a finite-difference scheme in the mathematical model. The decisive influence of deformation unevenness from the working rolls on the force and deformation parameters of the process was demonstrated, with the deformation unevenness factor δ serving as a quantitative measure of this influence. The result obtained through theoretical justification was confirmed by numerical simulation and a comparison of calculated data with experimental data, ensuring the reliability of the result. Full article

As a commonly used component in robot joints, helical planetary gear system is restricted from further application in the robotics industry due to excessive maximum subsurface shear stress and vibration amplitude during their meshing motion. Tooth modification can effectively reduce the maximum subsurface shear stress and vibration amplitude of gears, making it particularly important to conduct research on the modification of helical planetary gear trains. In this study, a lumped mass method is first adopted to establish a bending to rsionaxial coupling dynamic model of the helical planetary gear train. Subsequently, multi-objective optimization modification research on the left tooth flank of the planetary gear is carried out using both traditional empirical formulas and an improved Multi-Objective Particle Swarm Optimization (MOPSO) algorithm featuring physics-informed search boundaries and an automated optimal selection mechanism, respectively. Then, the finite element method is employed to analyze the maximum subsurface shear stress of planetary gears under three scenarios: unmodified, traditionally modified, and modified with the improved MOPSO. Finally, the 4th-order Runge Kutta method is used to solve the bending to rsionaxial coupling dynamic model of the helical planetary gear train system, thereby obtaining the vibration amplitude of the sun gear under the three scenarios. The research results show that the empirical formula method and the improved MOPSO reduce the maximum subsurface shear stress of the planetary gear by 12.629% and 30.107%, respectively, and decrease the vibration amplitude of the sun gear by 10.26% and 19.29%, respectively. This study provides theoretical and data support for the development of helical planetary gear modification and promotes its further application in the robotics industry. Full article

Ensuring the long-term serviceability of nearshore breakwaters constructed on weak seabeds is important for sustainable port infrastructure. This study investigates the wave-induced dynamic response of a vibro-compaction sand-pile composite foundation used in the Jinpai Port breakwater project in Lingao, Hainan, China. A coupled wave–structure–seabed numerical model was established using FssiCAS. Four representative monitoring points were selected inside and outside the structural influence zone and at different burial depths. The displacement, effective stress, shear stress, and pore water pressure responses were analyzed by combining full-field contour distributions with local time-history results. The results show that the foundation response is strongly location-dependent. The maximum horizontal displacement follows the order D > C > A > B, with values of approximately 10.8, 7.6, 0.5, and 0.3 mm, respectively. The final settlement follows the order A > B > C > D, with values of approximately 84, 43, 31, and 19 mm, respectively. Residual pore pressure is more significant beneath the breakwater, especially at Point B. The breakwater toes, structural boundaries, shallow seabed, and improved–natural foundation transition zones are identified as stability-sensitive zones, providing guidance for targeted monitoring, local reinforcement, drainage improvement, and maintenance planning. Full article

To address severe stress concentration, excessive convergence, and instability of the roadside backfill body (RBB) in gob-side entry retaining (GER) under thick and hard roof conditions, this study investigates the control mechanism of main roof fracture position on surrounding rock stability, using the 3⁻¹01 working face of Huoluowan Coal Mine as a case study. A combined approach integrating theoretical analysis, numerical simulation, and field investigation is adopted. A statically indeterminate mechanical model based on masonry beam theory is established to characterize the lateral roof fracture behavior. The deflection and bending moment distributions are derived, and a criterion for fracture position determination is developed based on the maximum bending moment condition. The theoretical results indicate that the natural fracture position is located approximately 9.4–11.2 m inside the gob boundary. Numerical simulations using UDEC Trigon under different fracture positions (−2 m, 1 m, 5 m, and 9 m) show that fracture location significantly affects the mechanical response of GER. Fractures occurring above the roadway or RBB induce large deformation levels and more extensive plastic zones, while gob-side fracture conditions correspond to relatively lower disturbance levels and improved structural stability. The RBB exhibits shear-dominated failure characteristics, and the displacement distribution is non-uniform along height, with larger deformation in the middle-to-upper region. To improve stability, a coordinated control strategy combining anchor cable reinforcement and directional long-distance hydraulic fracturing (HF) is proposed to regulate the main roof fracture position through the formation of artificial weak planes. Field monitoring results show that the maximum displacements of the roof, floor, and ribs are 558 mm, 233.5 mm, and 71.3 mm, respectively, with a convergence ratio of 19.8%. Borehole imaging confirms the development of hydraulic fractures within the designed roof stratum, supporting the effectiveness of the proposed control approach. These results demonstrate that the fracture position of the main roof plays a key role in controlling GER stability, and its regulation provides an effective means for improving roadway performance under complex geological conditions. Full article

The design of intravascular ultrasound (IVUS) catheters involves inherently coupled acoustic, hemodynamic, and structural requirements. Existing design strategies, which often rely on empirical geometric refinement or single-physics optimization, are limited in their ability to simultaneously ensure acoustic transmission efficiency, flow compatibility, and mechanical reliability. A multiphysics topology optimization method for the integrated design of IVUS catheters under acoustic–fluid–structure interactions is proposed in this paper. A density-based design variable is introduced to characterize the material distribution within the design domain, and consistent interpolation schemes are employed to relate this variable to the effective acoustic properties in the Helmholtz equation, the Brinkman penalization coefficient in the incompressible Navier–Stokes equations, and the elastic stiffness tensor in the structural equilibrium equation. The optimization problem is formulated as a normalized multi-objective minimization of acoustic transmission loss, flow resistance, and structural compliance, subject to constraints on material volume, received acoustic energy, wall shear stress, and structural displacement. Density filtering and smooth Heaviside projection are incorporated to regularize the design field and promote well-defined material boundaries. An adjoint sensitivity formulation is further developed to enable efficient gradient evaluation for the coupled system. Compared with the initial design, the average acoustic transmission efficiency has increased by 59.01%, the shear stress has decreased by 53.87%, and the stiffness matching rate has reached 98.27%. The objective function converged after 35 iterations, demonstrating the numerical stability of the proposed acoustic–fluid–structure topology optimization framework. Full article

Dense granular materials under low confining stress and low shear velocity—conditions relevant to low-pressure powder handling, near-surface transport, and the upper layers of stored bulk solids—remain insufficiently characterized at the microstructural level. We perform three-dimensional discrete element method (DEM) simulations of annular shear of monodisperse glass spheres at σ = 1 kPa and v = 0.01 m/s, corresponding to an inertial number I ≈ 1.06 × 10⁻³ at the quasi-static limit of the dense flow regime. The steady-state friction coefficient stabilizes at μ_ss ≈ 0.78, consistent with the quasi-static limit of the μ(I) framework. The solid volume fraction decreases monotonically from φ ≈ 0.50 at the base to φ ≈ 0.35 near the top, while the tangential velocity decays exponentially with depth (decay length δ_s ≈ 10 mm). Particle trajectory tracking reveals a sharp kinematic transition near z ≈ 5–6 mm separating a quasi-rigid basal layer (z ≲ 5 mm) from an upper shear-active zone (z ≳ 6 mm). The contact force distribution follows an exponential decay P($f$/$⟨f⟩$) ∝ exp(−β·$f$/$⟨f⟩$) with β ≈ 0.45, with strong force chains selectively concentrated in the upper zone. Together, these four microstructural descriptors co-locate within a single transition band, providing quantitative benchmarks for material characterization and constitutive modelling at the lower boundary of dense flow. Full article