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Ocean-surface stress is a critical driver of polar sea ice dynamics, air-sea interactions, and ocean circulation. This work provides a daily analysis of ocean-surface stress on 25-km Equal-Area Scalable Earth (EASE) Grids across the ice-free and ice-covered regions of the polar oceans (2011–2018 for Arctic, 2013–2018 for Antarctic), covering latitudes north of 60° N in the Arctic and south of 50° S in the Antarctic and Southern Ocean. Ocean-surface stress is calculated using a bulk parameterization approach that combines ocean-surface winds, ice motion vectors, and sea surface height (SSH) data from multiple satellite platforms. The analysis captures significant spatial and temporal variability in ocean-surface wind stress and the resultant wind-driven Ekman transport, while providing enhanced spatiotemporal resolution. Two sensitivity analyses are conducted to address key sources of uncertainty. The first addresses the fine-scale variability in SSH fields, which was mitigated using a 150-km Gaussian filter to smooth three-day SSH datasets and enhance compatibility with the other monthly product, followed by linear interpolation to achieve daily resolution. The second investigates uncertainty in the ice-water drag coefficient, which revealed that variations in the coefficient have a proportional influence on the computed ocean-surface stress under the tested conditions. These uncertainties are most pronounced during winter, with median values reaching 20 % in the Arctic and 40 % in the Southern Ocean. Validation efforts utilized Ice-Tethered Profiler velocity records, revealing moderate correlations (r = 0.6–0.8) at monthly timescales, effectively capturing low-frequency signals but with small northward biases. Satellite-derived velocity fields, including both Ekman and geostrophic components, explain 40–50 % of the total variance. The unexplained variance reflects unresolved processes, such as mesoscale dynamics and other unparameterized factors. This dataset is publicly available at https://doi.org/10.5281/zenodo.14750492 (Liu & Yu, 2024). [ABSTRACT FROM AUTHOR]

This study investigates the deceleration dynamics of projectiles during vertical penetration into silica sand targets up till the final depth of burial (DoB). Experiments were conducted with cone cylinder rods launched vertically into sand targets using a compressed air gun. Velocity–time records were obtained using a multichannel homodyne photon Doppler velocimeter (PDV) which tracked the back face of the penetrator as it decelerated, supplemented by high-speed video cameras from two views. A Poncelet framework was employed to describe the velocity–penetration relationship and drag and resistance coefficients were extracted by fitting the experimental measurements. Experiments were performed in dense and loose sand at a nominal impact velocity of 200 m/s, and experimental excursions were conducted with modified launch parameters. Mean drag and bearing resistance coefficients were found for sands under dry and wet pore saturation, as well as loose and dense packing. The work contributes essential insights for predicting the DoB of projectiles, particularly relevant for environmental remediation efforts in formerly used military sites. [ABSTRACT FROM AUTHOR]

The two-dimensional laminar flow over a simultaneously pitching-heaving teardrop airfoil is studied numerically. The influence of frequency and amplitude on the wake structure and aerodynamic performance is investigated at a constant Reynolds number, Re = 2 6 4 0. The computational modeling accurately depicts the changes in the wake structure that occur between the von Karman, reverse von Karman and deflected conditions. Investigations at low flapping frequencies and amplitudes identified the presence of additional wake structures that had not been reported previously. The interaction between the flapping frequency and vortex shedding frequency appears to govern the formation of such multiple vortex wakes. The wake structures identified are presented in the form of a wake map where the transitions between the wake structures are visible. This study correlates the wake arrangement with the variation in force coefficients and explains why the presence of a reverse von Karman street is necessary but not a sufficient condition for thrust production. The time history of the drag coefficient and the phase relation between lift and drag show the dynamics of the wake. The variation of force coefficients and efficiency at different flapping conditions is evaluated, and the influence of flapping parameters is assessed. The underlying vortex interactions that influence the aerodynamic performance are identified. The development and distribution of stress fields developed due to periodic fluctuations behind the flapping airfoil have not been discussed previously. The velocity fluctuations in the wake due to the periodic flapping are presented, and regions of maximum stress distribution are identified. [ABSTRACT FROM AUTHOR]

• The Bi-LSTM networks are used to explore the predictability of atmospheric drag coefficients (Cd). • The results of Cd prediction can be used for orbit prediction of LEOs and improve the accuracy of orbit prediction. • The predicted values of Cd are used as prior information in the process of short arc orbit determination. In the precise orbit determination (POD) of Low Earth Orbit (LEO) satellites with onboard Global Navigation Satellite System (GNSS) observations, atmospheric drag coefficients (Cd) are estimated piece-wise to absorb atmosphere density modeling errors, attitude modeling errors and windward area errors when the satellite physical metadata is not available. This study focuses on modeling and prediction of atmospheric drag coefficient in LEO satellite orbit determination and prediction. Orbit determination was conducted to determine atmospheric drag coefficients for eight LEO satellites with the orbital altitudes from 500 km to 1300 km. The Bidirectional Long Short-Term Memory (Bi-LSTM) neural network was used to model and predict the atmospheric drag coefficient estimations. The average Mean Absolute Percentage Error (MAPE) and average relative error between the predicted and estimated values of Cd for the eight satellites, were 0.09 and 0.11, respectively, indicating a satisfactory prediction performance of Cd. Prediction of the Cd is applied in orbit prediction and 30-minute short arc orbit determination (SOD). The results of the orbit prediction show that the modeling of Cd plays a key role in improving the accuracy of orbit prediction. The accuracy of the orbit prediction method based on the Cd prediction is better than that of the method without Cd prediction, and the average accuracy improves by 67.5 % and 73.7 % for the eight satellites in 2019 and 2023, respectively. The highest accuracy improvement rate is 94.5 % for GRACE-C satellite in 2019 and 86.6 % for Swarm-B satellite in 2023. Among them, the RMS of the average 3D error of the 3-day orbit prediction of the Swarm-B satellite is the lowest in both 2019 and 2023, at 2.11 m and 8.79 m, respectively. The results show that the SOD method with constrained Cd for eight satellites has different degrees of accuracy improvement in most arcs relative to the method without constrained Cd. The average orbital accuracy with constrained Cd improves by 14.8 % and 17.1 % for the eight satellites in 2019 and 2023, respectively, with the highest accuracy improvement of 24.7 % for GRACE-C satellite in 2019 and 24.2 % for GRACE-D satellite in 2023. The average orbit error of GRACE-C satellite is reduced from 9.23 cm to 5.95 cm, and the average orbit error of GRACE-D satellite is reduced from 13.45 cm to 8.22 cm. [ABSTRACT FROM AUTHOR]

Flow around two identical wall-mounted trapezoidal bluff bodies, arranged in tandem, is numerically investigated at a Reynolds number of 750,000. The investigation employs Reynolds-averaged Navier–Stokes (RANS) equations and the k–ω SST turbulence model. The effect due to the change of the angular orientation of the inclined faces (α) of this bluff body and the pitch distance (L/D) on hydrodynamic quantities and turbulence quantities is investigated. Furthermore, the drag coefficient and Strouhal number have also been evaluated to understand the vortex shedding and flow pattern-related phenomena. For d and intermediate types of bluff bodies, the streamwise mean velocity, cross-stream mean velocity, turbulence kinetic energy, and recirculation length decrease with the increase of α or L/D. Significant changes are also observed in the case of Strouhal number. Reduction in drag coefficient and recirculation length is observed with increased L/D at a constant α for d-type bluff bodies. The change of α and L/D also creates the formation of a periodic von Kármán vortex street at downstream of the second bluff body in the case of L/D = 7, making the flows more complex and unstable. The maximum size of the recirculation bubble occurs in the case of L/D = 10 at α = 30 deg. The investigation provides valuable insight into the complex dynamics of tandem configurations of wall-mounted bluff bodies. [ABSTRACT FROM AUTHOR]

This study simulates wind effects on a standard tall building model as specified by the Commonwealth Advisory Aeronautical Council (CAARC). We generated data to enhance living conditions through passive flow control, which mitigates building weathering, reduces wind loads, and improves energy efficiency and natural ventilation. The research also aids building designers with robust numerical predictions. The validity of these results was confirmed by comparing drag coefficient (C D) values with those from previous studies. The findings demonstrate that passive flow control significantly reduces wind-induced drag forces on the building at various angles of attack (α) by altering wind-induced pressures, reducing vorticity, and decreasing vortex shedding magnitudes. The objective was to identify the optimal placement of segmented cladding materials with desired gaps between segments to allow airflow to influence temperature variations when exposed to wind at 293 K and a heat flux of 500 W/m2 at wind speeds of 1, 2, and 4 m/s (Reynolds numbers of 5.2 × 10³, 10.4 × 10³, and 20.8 × 10³). Using 2D numerical analysis, twenty-four different facade and building model combinations were simulated. This study offers practical guidance on facade selection and positioning to optimize wind resistance and enhance the livability and functionality of building environments. [ABSTRACT FROM AUTHOR]

This study numerically investigates the three-dimensional flow characteristics around circular cylinders of finite- and infinite-lengths under subcritical Reynolds numbers using the SST κ–ω turbulence model within OpenFOAM. The simulations were conducted for aspect ratios (ARs) of 2, 5, and 10 and Reynolds numbers (Re) of 1 × 104, 3 × 104, 5 × 104, and 1 × 105. Under infinite conditions, the drag coefficient (Cd) and lift coefficient (Cl) exhibit Cl ear transitions from steady to unsteady flow regimes as Re increases, driven by organized vortex shedding. For finite conditions, the presence of a free end significantly alters the flow, inducing strong three-dimensional effects such as high-velocity regions near the end surface and complex vortex structures. The Cd and Cl trends for finite cylinders show reduced values and slower convergence compared to infinite cases due to free end interference. Additionally, the vortex density near the fixed boundary intensifies with increasing Re. These findings provide a comparative understanding of flow dynamics in finite and infinite cases, offering insights into the design of offshore structures. [ABSTRACT FROM AUTHOR]

The objective of this study was to measure the aerodynamic characteristics of the NACA 0018 airfoil across a range of low Reynolds numbers, with a particular focus on the unique behaviours observed in this regime. The experiments were conducted primarily in a low-turbulence wind tunnel using wall pressure taps, a pressure rake, and a force gauge. The Reynolds numbers investigated ranged from 30.000 to 160.000, with angles of attack spanning from -190 to +20 degrees. A major achievement of this research was the successful acquisition of data at Re = 30.000, where the lift behaviour significantly deviated from that observed at higher Reynolds numbers. The results demonstrated a strong dependency of aerodynamic characteristics on Reynolds number, with the drag coefficient at zero angle of attack decreasing by over 700 percent when Re increased from 30.000 to 160.000. Additionally, two independent techniques for measuring lift force were employed, both yielding consistent results despite the low Reynolds number. The experimental results were also compared with XFOIL and 2-D CFD simulations, which, although not perfectly accurate, provided reasonably good predictions. [ABSTRACT FROM AUTHOR]

This study evaluates the unsteady laminar flow and heat and mass transfer of a nanofluid in the appearance of gyrotactic microorganisms. In this analysis, using the Darcy–Forchheimer flow inside the vicinity of a nonlinearly stretched surface with Brownian motion and thermophoresis impacts. Similarity conversion is familiar with reduced governing models into dimensionless variables, and "bvp4c," a MATLAB solver, is employed to find the computational outputs of this analysis. This analysis reports that the use of nanofluids provides better thermal characteristics which are helpful to enhance the heat transfer coefficient. Graphs for this analysis are created for distinct values of non-dimensionless parameters, whereas the coefficient of surface drag, heat flux, mass flux, and rate of microorganism density are all interpreted numerically and graphically. The high level of resistance provided by velocity slip and Forchheimer parameters leads to a decrease in velocity curves while an increment is seen in the temperature profile. It is also remarked that bioconvection Peclet number induces a decrement in the density distribution of motile microorganisms. In addition, it has been observed that the Nusselt number for a nonlinear stretching sheet is better as compared to a linear stretching sheet. [ABSTRACT FROM AUTHOR]

This study investigates the dynamics of two oscillating rigid spheres moving through an infinite porous medium saturated with Stokes fluid flow, addressing the problem of how fluid properties, permeability, frequency, and slip length influence the system. The objective is to model the interactions between the spheres, which differ in size and velocity as they move along the axis connecting their centers while applying slip boundary conditions to their surfaces. We derive the governing field equations using a semi-analytical method and solve the resulting system of equations numerically through a collocation technique. Our novel quantitative results include insights into the drag force coefficients for both in-phase and out-of-phase oscillations of each hydrophobic sphere, considering parameters such as diameter ratio, permeability, frequency, velocity ratios, slip lengths, and the distances between the spheres. Notably, when the spheres are sufficiently far apart, the normalized drag force coefficients behave as if each sphere is moving independently. Additionally, we present streamlines that illustrate the interactions between the spheres across a range of parameters, highlighting the novelty of our findings. A purely viscous medium and no-slip conditions are used to validate the numerical approach and results. [ABSTRACT FROM AUTHOR]

With the growing need for sustainable transportation solutions, understanding the relationship between driving characteristic parameters, vehicle type, and their impact on emissions and fuel consumption over real driving scenarios is becoming increasingly important. In this paper, four conventional vehicles and one hybrid vehicle with different technologies were compared in four distinct routes in Tehran city. Nineteen real driving cycles were generated using widely employed K-means and PCA algorithms. The vehicles were simulated on MATLAB/Simulink according to their specifications. Twelve driving characteristic parameters, fuel consumption, CO, NOx, HC, and CO2 of vehicles with different powertrains, engines, and body styles were calculated over real and standard driving cycles. Notable findings show that driving characteristic parameters exhibit distinct influences on fuel consumption and emissions, depending on the specific driving conditions and vehicle type. Additionally, the hybrid vehicle achieved 39% and 26% fuel savings compared to gasoline and dual fuel vehicles, respectively. However, it emitted significantly higher levels of CO and HC. In contrast, the turbocharged vehicle increased CO and HC emissions compared to the naturally aspirated vehicle, but consumed less fuel (approximately 6%) and emitted lower amounts of CO2 (approximately 19%). In real driving cycles, the sedan vehicle generally exhibited slightly lower values compared to petrol SUV due to lower weight and drag coefficient. [ABSTRACT FROM AUTHOR]

Proximity of seabed complicates vortex-induced vibrations of submarine pipelines. Empirical models are better in engineering problem than high fidelity simulations and experiments to some extent. Present paper aims to propose a model consisting of structure and wake oscillators to predict in-line and cross-flow coupling vibration of a near-wall cylinder. Based on phenomena, mechanisms, and data analysis, some hydrodynamics, namely vortex shedding frequency and time-varying/time-averaged lift/drag coefficients, are modeled by Reynolds number, thickness of boundary layer, and gap (G) between cylinder and wall. Model responses reflect effects of the wall on the cylinder's vibration successfully. When G/D drops from 2 to 1 (D is diameter of the cylinder), amplitudes decrease monotonously, and the maximum amplitude shifts to a smaller reduced velocity (Ur). Vibrations and resonant tend to start/end at a larger/smaller Ur, leading to narrowing lock-in regions. Time-averaged transverse displacements increase monotonously in whole, while streamwise displacements drop in the resonance regime. Trajectories are shapes of symmetric "8," being similar to that of an isolated cylinder in free stream. There are some unique features when G/D decreases from 1 to 0.35. First peak of in-line vibration tends to disappear. Trajectories become asymmetric shape of "8" or oval because the cylinder tends to vibrate in approximating frequencies in 2 directions. With further researches on effects of wall proximity, improvements of hydrodynamics can be better to enhance model's rationality and accuracy. An accurate model is essential to analyze the safety and reliability of submarine pipelines suffering vibration. [ABSTRACT FROM AUTHOR]

Control of noise generated by flow around cylinders is of significant importance in various engineering applications. This paper analyzes the flow and acoustic fields of cylinders with square-wave profiles based on computational fluid dynamics, acoustic analogy, and vortex dynamics theory. To address noise reduction for cylinders, a hybrid aerodynamic noise numerical simulation method combining improved delayed detached eddy simulation with the Ffowcs Williams–Hawkings integral equation is employed. Refined numerical simulations of the flow characteristics, near-field sound sources, and far-field noise radiation characteristics of square-wave cylinders are conducted, elucidating the noise reduction mechanisms. The results indicate that square-wave cylinders contribute to reducing drag coefficient and effectively suppressing fluctuating lift coefficient, thereby significantly reducing overall noise. The optimal noise reduction performance for square-wave cylinders occurs at a crest-to-trough length ratio of 50%, achieving approximately 22 dB suppression of tonal noise at low frequencies and around 15 dB suppression of broad-spectrum noise at mid-to-high frequencies. Tonal noise is markedly suppressed or even eliminated. To explore potential noise suppression mechanisms, the study meticulously examines the deformation process of near-field vorticity around square-wave cylinders. The presence of square wave elongates vortex structures in the wake, suppressing the periodic shedding of cylinder vortices, altering lift coefficient fluctuation, pressure fluctuation fields, and changing the directivity of far-field noise radiation. [ABSTRACT FROM AUTHOR]

The bogie is a unique component exclusive to railway locomotives and rolling stock, and the simplified level of the bogie model directly influences the distortion and accuracy of the experimental results obtained. In this study, the effects of bogie simplified thresholds (T) are numerically investigated employing the improved delayed detached eddy simulation method. Three bogie configurations, comprising complex, moderate, and simple setups, were proposed for a 1/8th scale train model, each featuring different thresholds. The numerical algorithm was validated through a wind tunnel test, with a focus on aerodynamic loads and pressure distribution. The results indicate that as the bogie simplified threshold T increases, the drag and lift forces of each car increase. The head car exhibits a reduction in both lateral force and rolling moment coefficients, whereas the middle car sees a marginal increase, and the tail car maintains unchanged coefficients. As the bogie simplified threshold T increases, the blockage effects of the bogie cavity diminish under crosswinds, leading to decreased airflow impact on the bogie. However, the airflow impact on the vehicle bottom and the bogie cavity's end faces intensifies. The simple setup (T = 200 mm), due to neglecting significant geometric features, exhibits poorer agreement in surface and surrounding flow fields around the train, compared to the other two configurations. Therefore, to guarantee precise predictions accounting for both drag coefficients and detailed bottom flows, it is recommended to maintain the bogie simplified threshold at T = 100 mm at minimum. This study offers prospective insights into modeling detailed components for rail vehicles during wind tunnel experiments. [ABSTRACT FROM AUTHOR]

The aerodynamic interference effects between tandem structures are significant and can adversely affect both the wind-induced vibration characteristics and the aerodynamic performance. To investigate these effects, wind tunnel tests and numerical analyses were performed on chamfered and non-chamfered rectangular sections. Different spacings 2.9B–5.0B (B represents section width) were considered. Wind tunnel tests evaluated the vortex-induced vibrations (VIV) amplitude and wind speed range. Numerical analyses examined the aerodynamic characteristics and flow structure. It indicates that chamfered corners can enhance the VIV performance of a single structure. While the maximum VIV amplitude in the upstream column with chamfered corners, at spacing of 2.9B, increases by 288% than that of a single section, and gradually decreases as the spacing increases. The maximum VIV amplitudes of upstream rectangular section are slightly increased. For downstream section, the maximum VIV amplitude is much smaller than that of a single section. The mean drag coefficient of downstream cylinder consistently remains lower than that of upstream section, although it slightly increases with larger spacing. Chamfered corners cause upstream wake vortices to contract and downstream wake vortices to elongate along the flow direction. At spacing 2.9B, vortices shed from the upstream section just impact the windward side of downstream section. Compared to the upstream section, the vortex core center of the downstream column section is closer to its leeward surface, and the recirculation length is shorter than that of the upstream section. The research findings can serve as a reference for wind-resistant design of similar structures. [ABSTRACT FROM AUTHOR]

Externally mounted sensors on autonomous vehicles can introduce interference effects, altering the aerodynamic characteristics compared with those of conventional vehicles and significantly increasing aerodynamic drag. In this study, the structure of the external flow field around an autonomous vehicle and the constitutive law of its aerodynamic drag were revealed through computational fluid dynamics simulations. A wind tunnel experiment was conducted to validate the reliability of the numerical method. To minimize the aerodynamic drag of the autonomous vehicle, the shapes of the externally mounted sensors were parameterized. The design of experiments, the Kriging surrogate model, and the optimization algorithm were then used to optimize these shapes. Finally, the improvements in the steady and unsteady aerodynamic performance of the autonomous vehicle were analyzed, and the mechanisms and effects of the drag reduction were explored in detail. The results indicate that, compared with the baseline model, the optimized model significantly reduces the proportion of interference drag within the total aerodynamic drag, along with a marked decrease in the interference effects of the externally mounted sensors. Furthermore, compared with the baseline model, the optimized model reduces the aerodynamic drag coefficient by 5.99% under steady-state simulation and significantly improves aerodynamic performance under unsteady simulation. These findings demonstrate the high effectiveness of the optimization design for autonomous vehicles. [ABSTRACT FROM AUTHOR]

The external flow around deformable or flexible thin-walled square and circular rings is investigated. Although numerous studies have focused on analyzing the characteristics of the flow over solid cylinders, investigations into the flow passing over a deformable ring are limited. This study comprehensively investigates the dynamic responses of very thin elastic cylindrical shells with square and circular cross sections in a laminar flow at Re = 200. An identical hydraulic diameter (Dh = 2 R o = 10 mm) and an equal thickness (tc = 0.1 mm) were set for both shells. The cylinder height varies from LZ = 5 to 20 (mm). The relative fluidic and structural deformation equations are presented, and then the deformations or vibrations of the rings due to hydrodynamic forces are studied. A comprehensive modal analysis is performed. Furthermore, the lift and drag coefficients of the rings are analyzed and the vibration of the shells in x- and y-directions are investigated. The results show that as the height of the ring increases, a phase lag occurs between the drag and x-direction vibration of the shell; however, the phase lag between lift and y-direction vibration is almost negligible. It is demonstrated that the alignment or misalignment of vibrational responses with applied forces causes localized stress concentrations on the ring's surface in which the location of these stresses is influenced by the geometry and length of the cylinders. [ABSTRACT FROM AUTHOR]

Heat transfer enhancement is always pursued in the industry to achieve high-performance and low-energy-consumption heat exchange devices and systems. For decades, various types of heat transfer-enhancing tubes with differing geometries and wall configurations have been developed. In this paper, the heat transfer and pressure drop characteristics of air inside an innovative heat transfer tube with regular wall dimples, namely a vortex-enhanced tube, which has a great application prospect in the gas–gas heat exchanger, are numerically studied with an experimentally validated model. The effects of the depth, axial pitch, and radial rotation angle of the dimple in the tube wall on the convective heat transfer coefficient and friction drag coefficient are comprehensively analyzed. Based on the Performance Evaluation Criteria (PEC) of the tubes, the optimal parameters of the vortex-enhanced tube are obtained. When Re ranges from 10,000 to 40,000, the comprehensive evaluation factor of the vortex-enhanced tube is 1.29 times higher than the smooth tube. Dimple pacing, dimple depth, and dimple helical angle of the optimal tube type are 8 mm, 6 mm, and 83°, respectively. [ABSTRACT FROM AUTHOR]

Given the importance of drag model in solving fluid–particle interactions in unresolved numerical methods, this study proposed a machine learning (ML)-based drag model for irregular sand particles in transition flow, aided by spherical harmonic (SH) analysis and a resolved computational fluid dynamics-discrete element method (CFD-DEM). Initially, realistic particle shapes were reconstructed by the SH function, and their multi-scale shape features were quantified by the energy spectrums of SH frequencies. A developed fictitious domain method, particularly for irregularly shaped clumps, was proposed to solve fluid–solid interactions within resolved CFD-DEM. Subsequently, the fluid flow past a fixed particle test was repetitively simulated by the resolved CFD-DEM for 270 realistic sand particles, and a dataset consisting of 4220 drag coefficients was finally established. A classic ML algorithm, namely the multi-layer perceptron (MLP) neural network, was then utilized to train a drag model associated with the multi-scale shape features, particle orientations, and flow conditions. Compared with the results from the resolved CFD-DEM, the trained MLP model demonstrates both efficiency and accuracy in predicting the drag coefficients of natural sand particles with irregular shapes. This work provides a more reliable drag model for granular soils and shows its potential for application in large-scale modeling using the unresolved CFD-DEM framework. [ABSTRACT FROM AUTHOR]

Debris damming forces of 1∶20 -scale shipping containers freely accumulated against elevated coastal structure columns were experimentally determined to evaluate ASCE 7-22 tsunami-resilient design standards. Three inundation conditions were generated to represent Froude regimes estimated in posttsunami field studies. Three different column array densities and two different shipping container sizes were evaluated. A photogrammetric method was employed to estimate the submerged projected area of in situ transient debris dams from two synchronized camera perspectives. Relative to this experimental data, it was found that the ASCE 7-22 equation for simplified equivalent uniform lateral static pressure is conservative by a mean factor of safety of 14.6 and performs as intended given the prescribed scope. Similarly, the ASCE 7-22 equation for detailed hydrodynamic lateral forces yielded a lower mean factor of safety of 2.4 but maintained design conservatism across all tested experimental conditions, also performing as intended. Minimum closure ratios and overall structure drag coefficients serve as input values for these detailed hydrodynamic lateral design loads. The proportion of closure coefficients prescribed by ASCE 7-22 tend to be reasonably conservative in general, and any instances of experimental exceedance of these design values did not appear to affect the design conservatism of Eq. (3). Finally, drag coefficients for rectilinear structures prescribed by ASCE 7-22 appear unrepresentative of coastal structures, which tend to generate column-flow interactions and unbalanced hydrostatic conditions. It is therefore suggested that the flow resistance of such structures be quantified via a bulk resistance coefficient, indicated by recent literature as a more appropriate measure applicable to surface-piercing flow obstructions. Practical Applications: Since the 2016 adoption of tsunami-resilient design standards in ASCE 7-16, debris damming design loads have yet to be thoroughly examined. The results of this experiment indicate that the application of hydrodynamic loading equations in ASCE 7-22 Section 6.10 is conservative across all tested experimental conditions. Debris accumulation on the seaward face of the modeled structure is generally conservative relative to the design proportion of closure coefficients, and instances of exceedance do not result in unconservative load prediction. Finally, drag coefficients for rectilinear structures may not capture phenomena associated with surface-piercing flow obstructions such as column-flow interactions and unbalanced hydrostatic forces. It is suggested that a bulk resistance coefficient be adopted to account for both form drag and surface effects of flow around elevated coastal structure columns. Accurate quantification of tsunami-induced loads is crucial to the design of critical and essential infrastructure located within tsunami inundation zones, especially vertical evacuation refuge structures. [ABSTRACT FROM AUTHOR]

Introduction: Active drag in swimming is a critical variable that affects swimmers' performance, as well as the physiological load, but it is challenging for practitioners to assess this variable. This study aimed to assess if the load–velocity profiling method can be used as an indicator of active drag. Methods: A total of 419 swimmers performed three semitethered swimming trials in their speciality among the four competitive strokes with different external loads. Linear regression between external load and swimming velocity, as well as the external load relative to the body mass and swimming velocity, were established. The active drag and drag coefficient of each swimmer were calculated using a velocity perturbation method. Results: There were significant correlations of the active drag with the absolute slope (correlation coefficient ≥ 0.696, P < 0.001) and relative slope (correlation coefficient ≥ 0.538, P < 0.001) in all four strokes and both sexes. A multiple regression analysis exhibited that the primary determinant of these relationships was the drag coefficient (semipartial correlation ≥0.422, P < 0.001). The effects of the height and body mass index (BMI) on the relationship between the drag and the absolute slope were small (0.195 ≤ semipartial correlation ≤0.249, P < 0.001), which became either nonsignificant (height: P ≥ 0.282) or trivial (BMI: −0.099 ≤ semipartial correlation ≤ −0.081, P ≤ 0.011) when focusing on the relative slope. Conclusions: These results indicate that the absolute load–velocity slope is a strong indicator of the active drag, and the relative slope is useful when indirectly assessing the drag coefficient. [ABSTRACT FROM AUTHOR]

Compared with conventional aircraft, distributed electric propulsion (DEP) aircraft are recognized for their potential to enhance aerodynamic performance and propulsive efficiency, positioning them as one of the most promising advancements in future aviation. This paper explores the aeropropulsive coupling effects in boundary layer–ingesting DEP aircraft through numerical simulation and ground mobile testing. It employs two computational techniques, i.e., the actuator disk boundary condition and the full blade model, to assess the DEP's impact on wing aerodynamics and to evaluate the influence of the propulsors' shroud and design parameters. Ground mobile testing and numerical simulations are conducted on a DEP aircraft. The findings indicate that, with DEP thrust, the wing reduces the drag coefficient by 16% compared with a conventional wing, over a range of small-to-medium angles of attack. This reduction is attributed to the DEP's enhancement of the suction peak at the wing's leading edge and the extension of the plateau in pressure distribution. Additionally, incorporating a shroud around the distributed propulsors leads to a 17% increase in mass flow and a 40% rise in net thrust. However, as fan speed increases, while lift and net thrust on the DEP wing increase, the lift-to-drag ratio and overall propulsive efficiency of the system diminish. [ABSTRACT FROM AUTHOR]

In this paper, the numerical simulation of the swept strut ramjet combustor was carried out under wide-range conditions (Ma 3 = 1.8 ∼ 5.0), and the pressure drag characteristics of the swept strut were discussed. The results show that the pressure drag characteristics of the swept strut are related to the Mach number of the combustor inlet and the swept angle of the strut. The decreased boundary of the strut pressure drag coefficient gradually advances with the decrease of the Mach number of the combustor inlet. When Ma 3 = 1.8 ∼ 2.0, the pressure drag reduction boundary is α = 15°. When Ma 3 = 2.2 ∼ 2.8, the pressure drag reduction boundary is α = 45°. When Ma 3 = 3.0 ∼ 4.0, the pressure drag reduction boundary is α = 60°. When Ma 3 = 5.0, the pressure drag reduction boundary is α = 65°. In addition, with the decrease of the Mach number of the combustor inlet, the pressure drag reduction performance benefit brought by increasing the swept angle of the strut will gradually increase. Furthermore, a pressure drag coefficient prediction model suitable for wide-range conditions and multiple configurations of swept struts was proposed based on deep learning. The prediction model consists of two parts in series, which includes the prediction model of the surface pressure coefficient of the swept strut based on multilayer perceptron (MLP) and the prediction model of the pressure drag coefficient of the swept strut based on convolutional neural network (CNN). To improve the prediction accuracy of the MLP model, new training samples were added based on the ensemble-based uncertainty quantification, and the improved MLP model was obtained by retraining. The results show that both the two prediction models have high prediction accuracy under the effect of multiple complex flow characteristics on the strut. The results of this study are helpful to provide a reference for the aerodynamic drag reduction design of the strut in the wide-speed supersonic combustor. • The pressure drag characteristics of the swept strut under supersonic wide-range conditions were studied. • The pressure drag decreased boundary of the swept strut under supersonic wide-range conditions was obtained. • The prediction model for the surface pressure field of swept struts based on MLP was proposed. • The prediction model for the pressure drag coefficient of swept struts based on CNN was proposed. [ABSTRACT FROM AUTHOR]

The high-speed movement of trains generates train-induced wind, commonly referred to as slipstream, which presents a specific safety concern for passengers and personnel. Yet, the fastening system employed to secure ballastless tracks, characterised by its complex shape, substantial quantity, and dense arrangement, remains inadequately investigated regarding its influence on train aerodynamics. In the present study, a sliding mesh technique was employed to comparatively examine the impact of different track configurations--trackless, track-only, and track with a fastening system--on the aerodynamic characteristics, slipstream formation, and wake turbulence induced by trains. The results indicate that the tracks and the fastening system increased the drag force coefficient by 0.73% and 2.05%, respectively, compared with no track. Additionally, tracks and the fastening system had a significant impact on the slipstream velocity near the train and ground. Tracks notably altered the shape of the wake near the ground, and the fastening system exacerbated this phenomenon. Further, the fastening system further intensified the generation of secondary vortices at track and footstep locations. [ABSTRACT FROM AUTHOR]

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This study introduces a decentralized control framework designed to improve energy efficiency in vehicle platooning by optimizing inter-vehicle gaps to minimize aerodynamic drag, a significant factor in energy consumption. The proposed framework integrates extremum seeking control (ESC), a proportional integral derivative controller with feedforward compensation (PIDFC), and an extended state observer for estimating aerodynamic drag coefficients. Through this integration, the ESC dynamically adjusts inter-vehicle gaps to minimize the drag force based on the estimated aerodynamic drag coefficients, while the PIDFC ensures precise tracking of the optimized gaps and effectively addresses disturbances arising from aerodynamic variations. The results show that the proposed ESC with PIDFC converged to the optimal distance gaps 37.14% faster than the ESC with PPC, within a steady-state error of ± 1 % . Additionally, it improved the computational efficiency by 70.6%, compared to the ESC with PPC. Furthermore, it reduced the energy consumption by 15.3%, compared to the fixed-gap approach. These findings demonstrate the framework's potential to enhance the energy efficiency, scalability, and practicality, advancing sustainable and autonomous transportation systems. [ABSTRACT FROM AUTHOR]

Based on field observation at the north coast of the Zhanjiang Bay in southern China, the characteristics of wave attenuation due to the drag force of one mangrove species, Avicennia marina (Forsk.) Viern., were quantitatively analyzed. The results demonstrated that the mean significant wave height decreased by ~62% within a forest belt up to 80 m due to various bio-physical interactions. Affected by the unique vertical configuration of vegetation, the wave attenuation rate is positively correlated with water depth. The drag force within the forest can be approximated by the function C d = 0.7344 e 0.1409 A m , where Am is the projected area of the submerged obstacle at a certain water depth. The wave attenuation rate and the vegetation density (ρveg) in volume (‰) satisfy the fitting relationship of r = 5 × 10 − 4 · ρ v e g − 3.6 × 10 − 3 . These findings can accumulate quantitative information for studying the influence of mangrove vegetation on wave attenuation characteristics and provide necessary basic data for modeling studies to investigate the processes contributing to the attenuation capacity of mangroves. [ABSTRACT FROM AUTHOR]

A numerical investigation is conducted on the two-dimensional corrugated wing section of the dragonfly Aeshna cyanea in forward flapping flight mode. The analysis aimed to determine the impact of various kinematic parameters on the aerodynamic performance and to identify the optimal kinematic conditions for achieving maximum mean lift ( C ¯ L m a x ) and minimum mean drag coefficient ( C ¯ D m i n ). In forward flapping flight mode, the insect moves forward by flapping its wings, and the forward velocity is not zero. The study used the QUICK (Quadratic Upstream Interpolation for Convective Kinetics) scheme for spatial discretization of convective terms and first-order accurate implicit for temporal discretization. The dynamic mesh method following the Arbitrary Lagrangian Eulerian (ALE) formulation is used to track the moving interface of rigid wing section in the fluid domain. It has been observed that the maximum of lift and drag occur during the downstroke of flight. The vortical structures are larger in size at the leading and trailing edges when the peak of lift occurs. The larger leading-edge vortex on the lower surface of the airfoil creates a low-pressure region, thus increasing the peak drag. The kinematic parameters of best performance varied depending on the performance parameter being considered. The Pareto optimal front (POF) is obtained using multi-objective optimization method using surrogate models, which is a set of various design points obtained considering the maximum mean lift and lowest mean drag as objectives. From the POF, one can obtain the corresponding drag and optimum kinematic parameters for a particular lift, and vice versa, for an optimum design. [ABSTRACT FROM AUTHOR]

The aerodynamic performance of a high-speed train is intimately linked to its head shape. In order to reduce the aerodynamic drag during the operation of high-speed trains, five distinct head types with varying parameters are developed for double-arch trains and numerical calculation models for high-speed trains are established by modifying the cab height and front window transition shape of the double-arch high-speed train. The three-dimensional, steady, incompressible N-S equation and RNS method are used to simulate the flow field of five models running at a constant speed in open air, the influence of train cab height and front window transition shape on resistance characteristics of the double-arch train in the stable operation of the open air is comparatively analyzed. The following conclusions are drawn: under the same running conditions, the pressure difference in the flow field around the train mainly occurs in the transition area at the front window of the driver's cab and above, and the external geometric parameters of the driver significantly affect the aerodynamic drag of double-arch high-speed trains. The aerodynamic drag coefficient decreases as the height of the design position of the curvature transition of the front window of the train head increases, the maximum difference is 14.5%, and the distribution range of high pressure in the head car is reduced. The design inclination of the front window of the cab is reduced and the maximum pressure on the front window of the cab is lowered, resulting in a 13.4% decrease in the train's aerodynamic drag coefficient. When the plane is chosen to replace the curved surface as the transition surface of the train cab's front window, the positive pressure at the front window of the cab can be reduced, but the negative pressure above the cab will be intensified, and the aerodynamic drag coefficient of the train is decreased by only 3%. To achieve optimal drag reduction, it is recommended to raise the driver's cab height within a reasonable range and decrease the inclination of the front window surface on double-arch high-speed trains. [ABSTRACT FROM AUTHOR]