Search Results (76)

Polymer flooding is a well-established chemical enhanced oil recovery (EOR) method, primarily aimed at improving sweep efficiency. However, the interplay between polymer properties and porous media, particularly the influence on permeability reduction, remains poorly understood. In this study, we investigate how polymer molecular weight, chemistry, and mechanical pre-shearing influence residual resistance factor (RRF) and in situ rheology in Berea sandstone core floods. Post-polymer brine flow exhibits clear non-Darcy behavior, indicating that permeability becomes rate-dependent after polymer adsorption. Application of a Forchheimer-based approach demonstrates that inertial contributions become significant at reservoir-relevant velocities, suggesting enhanced microscopic inertia dissipation associated with interaction between flowing brine and the stationary adsorbed polymer layer. Applying conventional Darcy-based interpretation systematically overestimates RRF under these conditions. RRF increases with polymer molecular weight for polymers with similar bulk viscosities, suggesting that permeability reduction is primarily controlled by effective hydrodynamic size and pore-scale interactions rather than polymer concentration. Mechanical pre-shearing substantially reduces RRF and the non-linear flow contribution, suggesting that laboratory measurements performed on unsheared solutions may overestimate field-scale injectivity impairment. In contrast, an ATBS-containing polymer exhibits relatively low RRF but high apparent viscosity, indicating that alterations in polymer chemistry may override molecular weight as the main factor. The results demonstrate that polymer–surface interactions can induce rate-dependent permeability at reservoir-relevant velocities, and highlight the need for non-Darcy analysis when interpreting polymer core flood experiments for field application. Full article

This study investigates the mechanisms of nonlinear modal interactions in a circularly curved cantilever beam, utilizing the geometrically exact Timoshenko beam formulation. The governing equations take into account shear deformation, rotary inertia, and the geometric nonlinearities associated with significant deflections. A Chebyshev pseudospectral scheme is employed to achieve highly accurate linear eigenvalues, which are subsequently used in a nonlinear modal projection to develop a reduced-order model. Explicit expressions for the quadratic and cubic modal coupling coefficients are derived. The Harmonic Balance Method is then applied to explore internal resonance phenomena, frequency modulation behavior, and the transfer of energy between non-commensurate lateral and normal vibration modes. Full article

This study investigates the shear performance of high-strength concrete (HSC) beams reinforced with steel, fiber composite grids (CFRP and GFRP), and their hybrid configurations in the absence of transverse reinforcement. A total of six full-scale beams with varying reinforcement configuration and shear span-to-depth (a/d) ratios were experimentally tested under monotonic loading to evaluate their load capacity, cracking characteristics, failure modes, and serviceability behavior. The results revealed that beams reinforced solely with fiber grids exhibited significantly reduced strength and brittle shear failure. Hybrid systems incorporating both steel and fiber grids demonstrated improved strength and ductility, closely matching or surpassing control specimens with conventional steel reinforcement. Key structural parameters such as effective moment of inertia, cracking moment, shear strength, and midspan deflection were compared against analytical predictions based on ACI 318-16 and the Canadian Education Module code. While predictions generally aligned for hybrid beams, notable discrepancies were found for FRP-only systems, particularly in serviceability performance. The findings highlight the potential of hybrid reinforcement as a viable design strategy for HSC beams, offering a balance between strength, ductility, and service performance. Full article

The large-scale integration of wind power into the grid has led to a reduction in system inertia, threatening frequency stability. There is an urgent need to accurately assess the inertia support capability of wind turbines, providing a theoretical basis for grid inertia dispatch and supporting grid frequency stability. However, due to factors such as wake effects, time-delay effects, and wind shear effects, the rotational speeds of different wind turbines within a wind farm under certain wind speed conditions exhibit probabilistic distribution characteristics. Existing research on wind turbine inertia assessment rarely accounts for the rotational speed randomness. To address this, this paper proposes a probabilistic assessment method for the available inertia of wind turbines that considers rotational speed randomness, establishes a joint probability model for wind speed and rotational speed, deriving the conditional probability density function of rotational speed. By substituting this into the frequency-domain inertia model, we achieve probabilistic inertia assessment. Using operational data from a wind farm in China, a practical case study is constructed, verifying the accuracy of the proposed probabilistic assessment method. At a wind speed of 6 m/s, the proposed method accurately captures the actual system inertia within its 90% confidence interval, in contrast to a conventional approach which yielded a significant 6.5% error. Full article

This paper investigates the effects of shear deformation on the flutter and divergence instabilities of a cantilever beam subjected to a concentrated mass and applied dynamic couple. The beam is modeled using classical and truncated Timoshenko beam theory, accounting for both shear deformation and rotary inertia. The inclusion of rotary inertia is shown to significantly influence the dynamic response, particularly for beams with greater thickness. According to Hamilton’s principle, the equations of motion for the cantilevered beam are derived, applying both classical and truncated Timoshenko beam theories. Auxiliary functions are utilized to solve the resulting system analytically. Various numerical examples are presented, illustrating typical results to demonstrate the effectiveness of the proposed approach. The numerical findings show significant convergence and computational effectiveness. The effect of the location of a concentrated mass and the dynamic couple applied at the free end is analyzed for various beam slenderness ratios and curvature positions, emphasizing their impact on modifying the critical instability limits. To highlight the significance of shear effects, a comparison is made between the outcomes of the Timoshenko model and those of the Euler-Bernoulli beam model, showing notable variations in the anticipated divergence and flutter stability characteristics. All the examples were executed using both classical theory and the truncated Timoshenko theory, and the findings indicated a remarkable level of convergence. Finally, a numerical comparisons with literature papers was performed. The results achieved showed strong alignment. Full article

Vibration energy harvesting from ambient mechanical sources offers a sustainable alternative to batteries for powering low-power electronics in remote environments, yet challenges persist in achieving broadband efficiency, low-frequency operation, and concurrent vibration suppression. Here, we introduce a pyramidal piezoelectric sandwich beam (PPSB) with periodic elastic constraints, leveraging homogenized lattice truss cores for enhanced electromechanical coupling. Using Lagrange equations, we derive the coupled dynamics, validated against finite element simulations with resonant frequency errors below 3%. Compared to equivalent-stiffness uniform beams, the PPSB exhibits 3.42-fold higher voltage and 11.68-fold greater power output, attributed to optimized strain distribution and resonance amplification. Parametric analyses reveal trade-offs: increasing core thickness or spring stiffness elevates resonant frequencies but reduces voltage peaks due to stiffness–strain imbalances; conversely, a larger beam length, truss radius or tilt angle will reduce the natural frequency while increasing the output through inertia and shear enhancement. Piezoelectric constants and load resistance minimally affect mechanics but optimize electrical impedance matching. This single-phase, geometrically tunable design bridges gaps in multifunctional metamaterials, enabling self-powered sensors with vibration attenuation for aerospace, civil infrastructure, and biomedical applications, paving the way for energy-autonomous systems. Full article

Wood-based materials in the form of wood veneer composites (WVCs) possess a high lightweight construction potential for load-bearing applications in mechanical engineering due to their high strength properties combined with low density. However, in order to substitute energy-intensive metallic construction materials (such as steel or aluminum), additional structural space is required to compensate for the comparatively low stiffness by means of the area moment of inertia. Under bending loads, an increase in cross-sectional height at a constant span length leads to elevated shear stresses. Owing to the low shear strength and stiffness of wood-based materials, the influence of shear stresses must be considered in both the design of wooden components and in material testing. Current standards for determining the bending properties of wood-based materials only describe methods for assessing pure bending behavior, without accounting for shear effects. The present contribution introduces a method for determining both bending and shear properties of WVC using the three-point bending test. This approach allows for the derivation of bending and shear modulus values through an analytical model based on Timoshenko beam theory by testing various span-to-height ratios. These modulus values represent material constants and enable the numerical design of wooden components for arbitrary geometric parameters. Full article

The effect of third-order shear deformation theory (TSDT) on thick functionally graded material (FGM) spherical shells under sinusoidal thermal vibration is investigated by using the generalized differential quadrature (GDQ) numerical method. The TSDT displacement field and an advanced nonlinear shear correction coefficient are used to derive the equations of motion for FGM spherical shells. The simple stiffness of FGM spherical shells under a temperature difference along the linear vs. z-axis direction is considered in the heat conduction equation. The dynamic GDQ discrete equations of motion subjected to thermal load and inertia terms can be expressed in matrix form. A parametric study of environmental temperature, FGM power-law index, and advanced nonlinear shear correction on thermal stress and displacement is conducted under the vibration frequency of a simply homogeneous equation and applied heat flux frequency. This is a novel method for obtaining the numerical GDQ results, comparing cases with linear and advanced nonlinear shear correction. The novelty of the present work is that an advanced varied-value type of shear correction coefficient can be successfully used in the thick-walled structure of FGM spherical shells subject to thermal vibration while considering the nonlinear term of TSDT displacements. The purpose of the present work is to investigate the numerical thermal vibration data for a two-material thick FGM spherical shell. Full article

The integration of axial flux motors into canned motor pumps offers a promising approach to overcome the efficiency and size limitations of traditional designs, particularly in critical sectors like aerospace. However, the hydrodynamics in magnetic gap between the stator and rotor are poorly understood. This study investigates the effect of magnetic gap on performance and internal flow. Six magnetic gap schemes are developed, ranging from 0.2 to 1.2 mm. Numerical simulations are conducted, and simulation results showed good agreement with experimental data. The magnetic gap exhibits a non-linear effect on performance. The peak head coefficient occurs at a 0.4 mm gap and maximum efficiency at 1.0 mm. At a 0.2 mm gap, strong viscous shear forces increase disk friction loss and create high-vorticity flow. As the gap widens, flow transitions from viscosity-dominated to inertia-dominated, leading to a more ordered flow structure. The blade passing frequency is the dominant frequency. For a gap of 0.8 mm, the pressure fluctuation intensity is lowest. By analyzing performance, head coefficient, velocity, vorticity, entropy production, and pressure fluctuations, a gap of 0.8 mm is identified as the optimal design. This study provides critical guidance for optimizing the design of axial flux canned motor pumps. Full article

Due to the structural aspects of the wind turbine, such as wind shear and tower shadow effects, the output power of the wind turbine has periodic fluctuations, known as 3P fluctuations. These fluctuations can reduce overall power generation and deteriorate power quality. In this context, this paper proposes a power smoothing control method that utilizes rotor inertia and a DC-link capacitor as small-scale energy storage devices. First, the typical energy storage capacities of the rotor’s rotational kinetic energy and the DC-link capacitor’s electrostatic energy are analyzed to assess their smoothing potential. Secondly, a control method is presented to apply the rotor and the DC-link capacitor as small-scale energy storage, with the smoothing frequency range allocated according to their respective storage capacities. Finally, the proposed method is compared with the conventional maximum power point tracking (MPPT) method and the 3P-notch filter method. The effectiveness of the proposed algorithm is verified through MATLAB/Simulink simulations, demonstrating its capability to mitigate periodic power fluctuations. The results showed that the proposed control method is applicable, reliable, and effective in mitigating periodic power fluctuations. Full article

Coarse-grained beaches consisting of gravel, pebbles, and cobbles play a crucial role in coastal protection. On the Croatian Adriatic coast, there are artificial gravel pocket beaches created for recreational and protective purposes. However, these beaches are subject to constant morphological changes due to natural forces and human intervention. This study investigates the morphodynamics of artificial gravel pocket beaches, focusing on berm formation and crest build-up processes characteristic for low to moderate wave conditions. Despite mimicking natural formations, artificial beaches require regular maintenance due to sediment shifts dominantly caused by wave action and storm surges. Structure-from-Motion (SfM) photogrammetry and UAV-based surveys were used to monitor morphological changes on the artificial gravel pocket beach Ploče (City of Rijeka). The XBeach-Gravel model, originally adapted to simulate the effects of high-energy waves, was calibrated and validated to analyze low to moderate wave dynamics on gravel pocket beaches. The calibration includes adjustments to the inertia coefficient (ci), which influences sediment transport by shear stress at the bottom; the angle of repose (ϕ), which controls avalanching and influences sediment transport on sloping beds; and the bedload transport calibration coefficient (γ), which scales the transport rates linearly. By calibrating XBeach-G for low to moderate wave conditions, this research improves the accuracy of the model for the cases of morphological responses “berm formation” and “crest build-up”. Full article

A linear stability analysis is performed for a power-law liquid film flowing down an inclined rigid plane over a deformable solid layer. The deformable solid is modeled using a neo-Hookean constitutive equation, characterized by a constant shear modulus and a nonzero first normal stress difference in the base state at the fluid–solid interface. To solve the linearized eigenvalue problem, the Riccati transformation method, which offers advantages over traditional techniques by avoiding the parasitic growth seen in the shooting method and eliminating the need for large-scale matrix eigenvalue computations, was used. This method enhances both analytical clarity and computational efficiency. Results show that increasing solid deformability destabilizes the flow at low Reynolds numbers by promoting short-wave modes, while its effect becomes negligible at high Reynolds numbers where inertia dominates. The fluid’s rheology also plays a key role: at low Reynolds numbers, shear-thinning fluids ($n<1$) are more prone to instability, whereas at high Reynolds numbers, shear-thickening fluids ($n>1$) exhibit a broader unstable regime. Full article

This study examines the flow dynamics of synovial fluid within a lubricated knee joint during movement, incorporating the effect of inertia and linear re-absorption at the synovial membrane. The fluid behavior is modeled using a couple-stress fluid framework, which accounts for mechanical phenomena and employs a lubricated membrane. synovial membrane plays a crucial role in reducing drag and enhancing joint lubrication for the formation of a uniform lubrication layer over the cartilage surfaces. The mathematical model of synovial fluid flow through the knee joint presents a set of non-linear partial differential equations solved by a recursive approach and inverse method through the software Mathematica 11. The results indicate that synovial fluid flow generates high pressure and shear stress away from the entry point due to the combined effects of inertial forces, linear re-absorption, and micro-rotation within the couple-stress fluid. Axial flow intensifies at the center of the knee joint during activity in the presence of linear re-absorption and molecular rotation, while transverse flow increases away from the center and near to synovium due to its permeability. These findings provide critical insights for biomedical engineers to quantify pressure and stress distributions in synovial fluid to design artificial joints. Full article

Lattice materials demonstrate exceptional advantages in lightweight design applications due to their low mass density, high specific strength, and customizable topology. Inspired by the hollow vascular bundle structure of bamboo, this study develops four bio-inspired lattice configurations through two key modifications to conventional body-centered cubic (BCC) structures: Z-axis (loading direction) strut reinforcement and strut hollowing. The specimens were fabricated using AlSi10Mg powder via selective laser melting (SLM) technology, followed by the systematic evaluation of the compressive properties and the energy absorption characteristics. The experimental results reveal that the synergistic combination of Z-strut reinforcement and hollow design significantly enhances both the compressive resistance and the energy absorption capacity. The optimized BCC-5ZH configuration (5 Z-struts with full hollowing) achieves remarkable performance metrics at 0.5 g/cm³ density: yield strength (16.78 MPa), compressive strength (27.91 MPa), and volumetric energy absorption (10.4 MJ/m³). These values represent 236.9%, 283.4%, and 239.3% enhancements, respectively, compared to the reference BCC lattices with an equivalent density. Z-strut integration induces homogeneous stiffness distribution throughout the lattice architecture, while strut hollowing increases the effective moment of inertia. This structural evolution induces a failure mode transition from single shear band deformation to dual X-shaped shear band propagation, resulting in enhanced deformation sequence regulation within the lattice system. Full article

Power generation is an important part of air vehicle energy management when developing long-endurance and reusable hypersonic aircraft. In order to utilize an air turbine power generation system on board, fuel-based rotating cooling has been researched to cool the turbine’s rotor blades. For fuel-cooling air turbines, each blade corresponds to a separate cooling channel. All the separate cooling channels cross together and form a distributary cavity and a confluence cavity in the center of the disk. In order to determine the flow characteristics in the distributary and confluence cavities, computational fluid dynamics (CFD) simulations using the shear–stress–transport turbulence model were carried out under the conditions of different rotating speeds and different mass flow rates. The results showed great differences between non-rotating flow and rotating flow conditions in the distributary and confluence cavities. The flow in the distributary and confluence cavities has rotational velocity, with obvious layering distribution regularity. Moreover, a high-speed rotational flow surface is formed in the confluence cavity of the original structure, due to the combined functions of centrifugal force, inertia, and the Coriolis force. Great pressure loss occurs when fluid passes through the high-speed rotational flow surface. This pressure loss increases with the increase in rotating speed and mass flow rate. Finally, four structures were compared, and an optimal structure with a separated outlet channel was identified as the best structure to eliminate this great pressure loss. Full article