Search Results (100)

Brush seals, as a fundamental dynamic sealing technology in the aerospace and energy propulsion industries, require performance enhancement through instantaneous adjustment of the friction coefficient and force analysis of brush filaments. This paper establishes an instantaneous friction coefficient correction method based on the open volume between bristles and the backing plate. The downstream section of the double-row brush wire (2.6 mm) was quantitatively identified as the maximum leakage point, and it was found that the vortex characteristic length in the downstream area is approximately 1–3 times the bristle gap, with an increasing pressure ratio enhancing downstream turbulence and reducing gas leakage. A cantilever beam structural model was developed to assess the motion, force, and hysteresis properties of a single filament. Additionally, a porous medium model was utilized to elucidate the flow field and temperature distribution within the seal. The results suggest that the lag angle increases linearly over the first one-third of the brush wire’s length from the free end to the fixed end and is directly proportional to the pressure difference ΔP, reaching a maximum of 10.18°. The viscous drag causes the radial force y-component F_xy to increase and then decrease near the free end. The rear baffle contact force, F_b, shows variable peaks at two-thirds of the filament length. The displacement at the brush filament’s free end, the deflection angle, and the bending moment are directly proportional to the pressure differential. As pressure increases, the deformed region propagates toward the fixed end, and the maximum displacement at the free end of the brush wire reaches 13.04 mm. The leakage rate increases nearly linearly with ΔP and its deformation, reaching a maximum of 0.00849 m²/s. The pressure gradient growth rates of 164%, 73%, and 29% at the front baffle corner demonstrate that adding pressure chambers on front and rear baffles is optimal for high-pressure scenarios (ΔP > 0.3 MPa), while the formation of vortices between bristles and rotor reduces tip friction force and front-row turbulent disturbance, providing design guidance for extending seal service life. Full article

In-flight propulsion system diagnosis in multirotor unmanned aerial vehicles (UAVs) remains a challenging problem due to closed-loop control interactions, strong environmental disturbances, and common-mode effects that obscure rotor-specific anomalies. Conventional passive monitoring approaches based solely on electrical or mechanical measurements are often insufficient for reliable fault localization and for distinguishing global degradations from nominal operation. This paper proposes an active diagnostic framework that exploits low-amplitude sinusoidal excitation injected into the control null space during hover operation. By employing lock-in detection, rotor responses are selectively extracted at the excitation frequency, enabling the derivation of robust amplitude-based sensitivity indicators from rotational speed, current, and electrical power signals. A pairwise signed diagnostic metric is formulated to achieve reliable localization of asymmetric rotor faults. In addition, an absolute indicator referenced to a baseline condition is introduced to capture symmetric degradations affecting all rotors through the combined use of current- and power-based sensitivities. The proposed method is validated in a high-fidelity quadrotor simulation environment incorporating viscous-friction and thrust-coefficient degradation faults. Extensive Monte Carlo analyses demonstrate robust fault-detection and localization performance, including scenarios that are indistinguishable using conventional pairwise normalization techniques. Full article

Reliable characterization of the wellbore temperature field is essential for ensuring drilling safety and optimizing operational parameters in shale oil horizontal wells. To address the limitations of conventional models that assume constant thermophysical properties and neglect interactions among multiple heat sources, a transient heat transfer model featuring one-dimensional heat transfer in the wellbore and two-dimensional heat transfer in the formation is developed. The model uniquely accounts for variable thermophysical properties along with three internal heat sources: bit–rock interaction heat (BRIH), viscous dissipation heat (VDH), and drillpipe–formation friction heat (DFFH). The governing equations are implemented numerically using a fully implicit finite-difference approach and verified against field measurements from 10 wells in the Shengli Oilfield. The model demonstrates high predictive accuracy, with an average relative error of 1.58%. VDH contributes significantly to wellbore temperature elevation (≈3.33 °C), whereas BRIH and DFFH exert comparatively minor effects (≈0.34 °C). Sensitivity analysis shows that geothermal gradient is the dominant factor controlling BHCT (correlation coefficients: 0.74 for OBDF; 0.65 for WBDF), followed by drilling fluid density, with all parameters exhibiting weak intercorrelations. Furthermore, a PSO-RBF optimization framework is developed, reducing computation time from 48.34 min per evaluation to an average of 9.0 min per well (81.4% efficiency improvement) while maintaining high prediction accuracy. Overall, this study contributes theoretical understanding and practical value to temperature prediction and parameter optimization in shale oil horizontal well drilling. Full article

Pectins are structurally complex plant polysaccharides whose functional properties strongly depend on molecular structure that may vary depending on the source of origin. The present study aimed to characterize and compare the hydrodynamic properties of pectins obtained from red and blackcurrants in semidilute and concentrated aqueous solutions. Pectins were extracted and analyzed using light scattering methods and rheology at 25 °C, 30 °C, 35 °C and 40 °C. The methodology used enabled the determination of the hydrodynamic properties of the pectins with changing temperature and concentration, and mathematical modeling was performed using the Kohlrausch–Williams–Watts model. The obtained samples differed in molecular structure, and these differences were reflected in the chain behavior in aqueous solution. The results indicate that even closely related botanical sources may yield pectins with significantly different functional properties. Hydrodynamic studies revealed that relaxation phenomena occurred in a similar manner for redcurrant pectin in the concentrated region and for blackcurrant pectin in the semidilute region (similar diffusion coefficients). Under shear flow conditions, blackcurrant pectin solutions behaved like Newtonian fluids, whereas redcurrant pectin exhibited complex, non-Newtonian behavior. Redcurrant pectin solutions also exhibited lower apparent viscosity values at concentrations comparable to those of blackcurrant pectin. The ability to scale apparent viscosity values indicated a unchanging friction mechanism in viscous flow, characteristic of semidilute and concentrated regions. Full article

This study introduces a modified computational scheme for handling linear and nonlinear fractal time-dependent partial differential equations. The method is constructed using three different stages that provide third-order accuracy in the fractal time variable. The stability of the approach is examined using scalar fractal models and Fourier analysis, while convergence is established for coupled convection–diffusion systems. The numerical algorithm is applied to analyze the mixed convective flow of a Carreau–Yasuda non-Newtonian fluid over stationary and oscillating plates under the influence of viscous dissipation and magnetic field effects. For spatial discretization, the incompressible continuity equation is handled by a first-order difference scheme, whereas higher-order compact schemes are implemented for the momentum, thermal, and concentration equations. The numerical findings show that increasing the Weissenberg number and magnetic field inclination reduces the velocity distribution. An accuracy assessment against existing numerical techniques demonstrates that the present method yields smaller computational errors, particularly when central difference schemes are used in space. In addition, a surrogate machine learning model is developed to predict the skin friction coefficient and local Nusselt number using Reynolds, Weissenberg, Prandtl, and Eckert numbers as input features. The predictive capability of the model is validated through Parity plots, bar charts for sensitivity analysis, scatter visualization, and Taylor Diagrams, confirming strong agreement with the numerical results. Full article

This study introduces an efficient and accurate two-stage explicit computational scheme for solving partial differential equations (PDEs) containing first-order time derivatives. The suggested method is a modification of the classical Runge–Kutta scheme that introduces a new first-stage formulation. This minimizes numerical error with moderate step sizes while preserving the stability region of the classical method. Spatial discretization is performed using a sixth-order compact finite-difference scheme to obtain high-resolution solutions. The analysis of stability and convergence is strictly determined for both scalar and system forms of convection–diffusion-type equations. To illustrate the suitability of the method, a dimensionless mathematical model of the unsteady, incompressible, laminar flow of a Prandtl-type non-Newtonian nanofluid over a Riga plate is considered, accounting for viscous dissipation, thermophoresis, Brownian motion, and a magnetic field. Here, the Prandtl ternary nanofluid is defined as a non-Newtonian nanofluid that follows the Prandtl rheological model, and it exhibits three critical transport phenomena: heat conduction, viscous dissipation, and nanoparticle diffusion. Representative values of the Prandtl number $P_r=3$ and Reynolds number $R_e=5$ are used to perform the simulation, and other parameters, including but not limited to the Hartmann number $H_a$, Williamson number $W_e$, thermophoresis $N_t$ and Brownian motion $N_b$, are varied to evaluate the flow behavior. Moreover, an artificial neural network (ANN)-developed surrogate model is used to calculate the skin friction coefficient and the local Sherwood number, using five input parameters: the Reynolds number, Prandtl number, Schmidt number, Brownian motion parameter, and thermophoresis parameter. The governing partial differential equations yield high-fidelity numerical data used to train the surrogate model. The data is split into 80% for training, 10% for validation, and 10% for testing. The ANN is tested using regression analysis and error histograms, which demonstrate high accuracy and generalization capacity. Numerical simulation combined with AI-based prediction is a cost-efficient method for real-time estimation of complex non-Newtonian nanofluid systems. Full article

Coastal erosion is increasingly influenced by anthropogenic alterations to the sediment cycle and morphological transformations. Traditional shallow water models often neglect the mechanical behavior of the seabed and its rheological response to hydrodynamic forcing, limiting their accuracy in forecasting erosion patterns. To address these limitations, this study extends the classical one-dimensional Saint-Venant (shallow water) model by incorporating effects of viscosity, frictional effects, sediment transport and viscoelasticity. The seabed is treated as a Kelvin–Voigt material, characterized by an elastic modulus and a viscous damping coefficient, to account for both immediate and time-dependent mechanical responses. Using the COMSOL Multiphysics platform, the evolution of the water column and seabed was simulated in six idealized case studies under various conditions, including changes in seabed topography and different frictional and dispersive regimes. The results demonstrate the influence of seabed topography, friction $S_f$, diffusion/dispersion regularization term $E$, and viscoelastic properties on wave seabed interactions and morphodynamic bed evolution (Exner-type). The inclusion of viscoelastic damping contributes to the stabilization of morphological evolution, mitigating abrupt changes in bathymetry and enhancing the physical realism of the simulations. The whole research aims to improve the prediction capabilities of erosion processes and advance the current modeling tools. Full article

This study numerically investigates the hydrothermal behaviour of a Jeffrey nanofluid with relevance to maritime thermal systems. The coupled nonlinear governing equations for momentum, heat, and mass transport are solved using a shooting technique that accounts for magnetohydrodynamic effects, Darcy porous-media resistance, viscous dissipation, and spatially varying internal heat generation. Variable thermophysical properties, including temperature-dependent viscosity and density, are also considered. The results reveal that porous resistance, fluid elasticity, and thermophysical variations significantly influence velocity, temperature, and concentration fields. The combined effects of porous drag and variable properties markedly alter the characteristics of heat and mass transfer. These findings provide insights into thermal and mass-transport performance, including skin friction, heat transfer, and concentration distributions, which are critical metrics for porous heat exchangers and nanofluid-based maritime coatings. Here, maritime relevance is represented via a generalised porous nanofluid model rather than a specific material. Among the key findings, increasing the slip velocity factor can reduce the surface skin-friction coefficient by approximately 48.7%, while the heat-transfer rate increases by nearly 27.1%, accompanied by a decrease of about 18.9% in the Sherwood number. Conversely, raising the density factor enhances the skin friction coefficient by roughly 103.8% and also augments the heat and mass transfer rates by about 61.3% and 106.1%, respectively. Likewise, at zero relaxation–retardation ratio, the flow reduces to the Newtonian case. Increasing this factor reduces the local Nusselt number by about 1.45%, indicating a slight weakening of heat transfer due to elastic effects. Furthermore, the reliability of the current numerical framework is established through a dual-validation approach, including an analytical assessment of limiting cases and a rigorous comparison with established data from the literature. Full article

The generation and stability of foam are critical attributes influencing the perceived efficacy and sensory experience of cleansing products like face cleansers and hair shampoos. This study rigorously investigated the influence of water hardness on the foam characteristics of a face cleanser and hair shampoo through integrated macroscopic, microscopic, and rheological analyses. Hard water consistently induced severe foam destabilization, evidenced by significantly increased foam decay and shortened drainage half-lives. Microstructural analysis revealed pronounced bubble coalescence, manifested as reduced bubble counts and elevated mean bubble areas. Rheologically, hard water compromised foam viscoelasticity, leading to diminished complex moduli (G*), earlier G″/G′ crossovers, and heightened phase angles (δ), signifying a rapid transition to a predominantly viscous, unstable state. Conversely, soft water consistently yielded highly elastic foams with robust G* values, maintained G′ dominance, and low δ, indicative of superior structural integrity and temporal stability. Notably, controlled rate viscosity profiles remained unaffected by water hardness. These findings collectively demonstrate that divalent cations fundamentally undermine foam lamellar film stability, inducing profound structural and mechanical degradation. Concurrently, tribological measurements revealed that the face cleanser consistently exhibited higher coefficients of friction in hard water across varying sliding speeds, whereas the hair shampoo displayed a more complex, speed-dependent frictional profile that was comparatively less sensitive to water hardness. This underscores the critical necessity for formulation chemists to mitigate water hardness effects to ensure consistent product performance and sensory attributes. Full article

This work presents an experimental and theoretical study of a pitching point-absorber wave energy converter (WEC) equipped with a nonlinear stiffness mechanism (NSM) based on a pre-compressed spring. The mechanism is designed to reduce the equivalent restoring stiffness and enhance the device response without external control. A 1:13 scale prototype of the Lafkenewen WEC, deployed off Lebu (Chile), was tested in regular waves within a wave tank for two configurations: with and without the NSM. The rotational response amplitude operator (RAO) was obtained from experiments and compared against a linear hydrodynamic model formulated via Newtonian mechanics and frequency domain radiation/excitation coefficients. Dry friction at the hinge was represented as an equivalent viscous damping term identified iteratively. Unlike narrow-resonance WECs, both configurations exhibited a broadband response without a sharp resonance peak in the $0.7$–$1.2$ Hz range, due to significant radiation damping and hinge friction. The NSM produced a moderate amplification of the rotational RAO (up to ∼32%) while preserving the broadband character. Theoretical predictions agreed with the measurements when dry friction was included. These results demonstrate that passive stiffness reduction via an NSM enhances wave–structure energy transfer even in systems dominated by effective damping and provides a consistent basis for future nonlinear time domain modeling and control-oriented studies. Full article

This study experimentally investigates single-phase forced convection heat transfer and flow characteristics of Al₂O₃-water nanofluids under rotating hypergravity conditions ranging from 1 g to 5.1 g. While nanofluids offer enhanced thermal properties for advanced cooling applications in aerospace and rotating machinery, their performance under hypergravity remains poorly understood. Experiments employed a custom centrifugal test rig with a horizontal test section (D = 2 mm, L = 200 mm) operating at constant heat flux. Alumina nanoparticles (20–30 nm) were dispersed in deionized water at mass fractions of 0.02–0.5 wt%, with stability validated through transmittance measurements over 72 h. Heat transfer coefficients (HTC), Nusselt numbers (Nu), friction factors (f), and pressure drops were measured across Reynolds numbers from 500 to 30,000. Results demonstrate that hypergravity significantly enhances heat transfer, with HTC increasing by up to 40% at 5.1 g compared to 1 g, most pronounced at the transition from 1 g to 1.41 g. This enhancement is attributed to intensified buoyancy-driven secondary flows quantified by increased Grashof numbers and modified particle distribution. Friction factors increased moderately (15–25%) due to Coriolis effects and enhanced viscous dissipation. Optimal performance occurred at 0.5 wt% concentration, effectively balancing thermal enhancement against pumping penalties. Random forest (RF) and eXtreme gradient boosting (XGBoost) achieved R² = 0.9486 and 0.9625 in predicting HTC, respectively, outperforming traditional correlations (Gnielinski: R² = 0.9124). These findings provide crucial design guidelines for thermal management systems in hypergravity environments, particularly for aerospace propulsion and centrifugal heat exchangers, where gravitational variations significantly impact cooling performance. 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

To characterize a phenomenological model of a mechanical oscillator, it is important to know the properties of the envelope of the three main physical motion variables: deviation from equilibrium, velocity, and acceleration. Experimental data show that friction forces restrict the shape of these functions. A linear, exponential, or more abrupt decay can be observed depending on the different physical systems and conditions. This paper aimed to contribute to clarifying the role that some types of friction forces play in these shapes. Three types of friction—constant sliding friction, pressure drag proportional to the square of velocity, and friction drag proportional to velocity—were considered to characterize the line connecting the maxima and minima of displacement for a generic mechanical harmonic oscillator. The ordinary differential equation (ODE), describing the harmonic oscillator simultaneously containing the three types of dissipative forces (constant, viscous, and quadratic), was numerically solved to obtain energy dissipation, and the extrema of both displacement and velocity. The differential equation ruling the behavior of the amplitude, as a function of the friction force coefficients, was obtained from energy considerations. Solving this equation, we obtained analytical functions, parametrized by the force coefficients that describe the oscillator tail. A comparison between these functions and the predicted oscillator ODE extrema was made, and the results were in agreement for all the situations tested. Information from the velocity extrema and nulls was enough to obtain a second function that rules completely the ODE solution. The correlations obtained allow for the reverse operation: from the identified extremum data, it was possible to identify univocally the three friction coefficients fitting used in the model. Motion equations were solved, and some physical properties, namely energy conservation and work of friction forces, were revisited. Full article

This study addresses the question: “Does the towing tank water temperature affect the result of model-ship extrapolation?” While it is well-established that temperature variations affect Reynolds numbers and consequently frictional and viscous resistance, this study examines whether the ITTC 1978 extrapolation method properly compensates for these effects. Although current procedures consider temperature indirectly through the Reynolds number, they assume that the form factor depends solely on the Froude number and is insensitive to viscosity changes. Our analysis reveals that the form factor is also temperature-sensitive, indicating a fundamental limitation in the conventional approach. This sensitivity arises from the limitations of the ITTC 1957 friction curve and the method’s neglect of temperature-induced variations in the form factor. To quantify the effect of temperature, model-scale CFD simulations were conducted for two ship models (KCS and KVLCC2) at different water temperatures using the ITTC 1978 procedure with Prohaska’s method. The results show that the ship-scale total resistance coefficient ($C_T$) can vary by up to 2.8% depending on the water temperature and friction line selection. This demonstrates that the ITTC 1978 performance prediction method fails to adequately compensate for the temperature-induced changes in resistance, which leads to systematic errors in the extrapolated results. Full article

The accurate, robust, and efficient prediction of transition in viscous flows is a significant challenge in computational fluid dynamics. We present a coupled high-fidelity iterative approach that leverages the FUN3D flow solver and the LASTRAC stability code to predict transition in low-disturbance environments, initiated by the linear growth of boundary-layer instability modes. Our method integrates the ability of FUN3D to compute mixed laminar–transitional–turbulent mean flows via transition-sensitized Reynolds-Averaged Navier–Stokes equations with the ability of LASTRAC to perform linear stability analysis, all within an automated framework that requires no intermediate user involvement. Unlike conventional frameworks that rely on classical stability theory or reduced-order metamodels, our approach employs parabolized stability equations to provide more accurate and reliable estimates of disturbance growth for multiple instability mechanisms, including Tollmien–Schlichting, Kelvin–Helmholtz, and crossflow modes. By accounting for the effects of mean-flow nonparallelism as well as the surface curvature, this approach lays the foundation for improved N-factor correlations for transition onset prediction in a broad class of flows. We apply this method to three distinct flow configurations: (1) flow over a zero-pressure-gradient flat plate, (2) the NLF-0416 airfoil with both natural and separation-induced transition, and (3) a 6:1 prolate spheroid, where transition is primarily driven by crossflow instability. For two-dimensional cases, a formulated intermittency distribution is used to model the transition zone between the laminar and fully turbulent flows. The results include comparisons with experimental measurements, similar numerical approaches, and transport-equation-based models, demonstrating good agreement in surface pressure coefficients, transition onset locations, and skin-friction coefficients for all three configurations. In addition to contributing a couple of new insights into boundary-layer transition in these canonical cases, this study presents a powerful tool for transition modeling in both research and design applications in aerodynamics. Full article