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The design of a helicopter is an intricate and challenging process. Decisions made during the preliminary design phase can significantly impact subsequent design stages, making it crucial to base these decisions on a solid foundation. A range of methods, including hand calculations, finite element analyses, and experimental tests, can be employed to establish the conceptual design parameters. However, these methods often come with the drawbacks of being time-intensive and costly, especially when testing various structures during the early design phase. To address this issue, this study introduces an artificial neural network-based design tool to evaluate the static structural characteristics of a helicopter's horizontal stabilizer. The tool was built in Python using the Keras library. The required database for the training of the artificial neural network model was established using finite element analyses of the horizontal stabilizer subjected to the aerodynamic load for diverse design variables. The model's performance was evaluated, and the model's outputs were compared to the results derived from the finite element analyses. Moreover, the Hammersley sampling methodology was employed to reduce the size of the database without compromising on accuracy. The study also assessed the impact of decreasing the amount of data fed into the network model. [ABSTRACT FROM AUTHOR]

The variable-sweep wing, as an important morphing wing technology, has received widespread attention because it can change the sweep angle according to different flight conditions. It has the advantage of simultaneously utilizing a large sweep angle to reduce shock wave drag at high speeds and improving lift characteristics at small sweep angles. However, it has always been the case that the variable-sweep wing will bring about a rearward shift of the center of gravity when the sweep angle increases, leading to a decrease in aircraft stability. This paper focuses on a structural design of a variable-sweep wing based on a four-bar planar linkage. The novel variable-sweep wing structure containing a four-bar planar linkage and an outer wing section is proposed, and key parameters are extracted to establish a mathematical model of the mechanism. Through parametric analysis, main parameters have been identified, and the structure is optimized: the longitudinal position (direction of the fuselage) of the wing's center of gravity is designed to maintain minimal change during the morphing process, but remain the same at both the beginning and ending states of the transformation. The structural design of the variable-sweep wing is carried out based on this. Then, the finite-element model is established to validate the load-bearing capacity of the variable-sweep wing and derive the driving force. Finally, as one of the main novelties, a full-size prototype is successfully manufactured for load testing. The results of finite-element simulation and load testing show that this variable-sweep wing structure can achieve movement from 30° to 70° under an aerodynamic load that is up to 460 kg/m2. The present study demonstrates the effectiveness and potential of the proposed morphing trailing edge concept for real application on aircraft. [ABSTRACT FROM AUTHOR]

In recent years, circulation control (CC) technology has garnered significant attention in the field of active flow control. However, the issue of significant premature stall angle of attack in circulation control airfoils is highly prominent. This study numerically simulates the high angle of attack stall process of a circulation control wing using the unsteady Reynolds-averaged Navier–Stokes (U-RANS) turbulent model. A circulation control airfoil is attained by modifying the trailing edge of the NACA-64A-010 airfoil. This modification results in a substantial increase in the lift coefficient, although advancing the stall angle by 5°. A comparative evaluation of aerodynamic characteristics and flow physics differences between the circulation control airfoil and the nonjet airfoil is conducted under poststall conditions. Large-scale long-period fluctuations in aerodynamic forces result from the complex interaction between the trailing edge jet and the vortex system on the leeward side. Effective control of these large fluctuations during stall can be achieved by superimposing a sinusoidal pulsed jet on the steady jet. Activating a sinusoidal pulse jet when the lift coefficient reaches its maximum or minimum value, and matching the excitation frequency with the fundamental frequency of the aerodynamic force fluctuations, yields effective control. Practical Applications: This paper unveils the influent of the CC, a kind of active flow control technology, on the airfoil stall characteristics. CC not only dramatically increases the lift coefficient of the airfoil but also leads to significant premature stall angle of attack. The CC airfoil stall is due to the complex interaction between the trailing edge jet and the vortex system on the leeward side. This results in large-scale, long-period fluctuations in aerodynamic forces. However, effective control of these large fluctuations during stall can be achieved by superimposing a sinusoidal pulsed jet on the steady jet under the guidance of this research. It ensures that lift is maintained even at high angles of attack, thus mitigating stall risk. This research promises substantial benefits for the aviation industry, enabling the development of planes that are more fuel-efficient and require shorter runways, while increasing safety. This advancement is expected to have a profound impact on commercial, cargo, and military aviation, leading to cost-effective operations and enhanced flight performance. [ABSTRACT FROM AUTHOR]

Satellites in very low Earth orbits can leverage the aerodynamics forces for control purposes. Three-axis attitude control can be achieved by adjusting the orientation of aerodynamic surfaces, benefiting from both drag and lift forces. However, complete control over the orbital motion of a satellite is unattainable using aerodynamic forces alone, as positive thrust cannot be generated. Nonetheless, this limitation does not apply when focusing on the control of a satellite formation. By properly modulating the orientation of panels, positive and negative relative forces can be generated. This paper shows that even in a formation of simple microsatellites, it is possible to achieve formation and attitude simultaneous control by using no other actuators than the aerodynamics surfaces. • Very Low Earth orbits are appealing but the large atmospheric density can be a problem. • The atmospheric forces can be used for control purposes. • Formation control and attitude control can be individually realized by using aerodynamic forces. • A GNC architecture is implemented to realized both goals with the same aerodynamic actuators. • Performance in keeping or acquiring a desired state (attitude and relative position) is promising. [ABSTRACT FROM AUTHOR]

Experimental investigations are carried out to explore the aerodynamic performance and vortex shedding characteristics of S5010 and E214 airfoil-based wings to provide guidance for the design of MAVs and other low-speed vehicles. Force and wake shedding frequency measurements are carried out in a subsonic wind tunnel in the Reynolds number (Re) range of 4 × 104 - 1 × 105. The measurements with increasing Re show that the slope of the lift curve in the linear region increases by 14% for S5010, while this increment is 11% for E214. The peak lift coefficient of both airfoils reduces with reducing Re. For lower pitch angles, the influence of Re on drag coefficients is less significant, but at higher angles, the drag increases as the Re drops. Unlike pre-stall mountings, the pitch-down propensity of the airfoil enhances in the post-stall region for high Re flows. Moreover, the frequency of shed vortices reduces with rising angle of attack at a given Re. In contrast, the Strouhal number almost remains constant with varying Re at a fixed angle of attack. For S5010 and E214 airfoils, the Strouhal number is noticed to vary between 0.68 - 0.36 and 0.58 - 0.36, respectively, for pitch angle variation of 12°- 28°. The airfoils show a higher Strouhal number than the bluff body wakes, but this difference decreases for high angles of attack mountings. This finding reveals that the wake structure of the airfoil at a high post-stall angle behaves as bluff body wakes. [ABSTRACT FROM AUTHOR]

The aim of this study was to assess the accuracy of predicting the aerodynamic loads and investigate the aerodynamic wake characteristics of a vertical axis wind turbine (VAWT) rotor using a simplified two-dimensional numerical rotor model and an advanced numerical approach – the Scale Adaptive Simulation (SAS) coupled with the four-equation γ – Reθ turbulence model. The challenge for this approach lies in the operating conditions of the rotor, the blade pitch angles, and the very small geometric dimensions of the rotor. The rotor, with a diameter of 0.3 m, operates at a low tip speed ratio of 2.5 and an extremely low blade Reynolds number of approximately 22.000, whereas the pitch angles, β, are: -10, 0, and 10 degrees. Validation was conducted based on high-fidelity measurements obtained using the PIV technique at TU Delft. The obtained results of rotor loads and velocity profiles are surprisingly reliable for cases of β = 0° and β = –10°. However, the 2-D model is too imprecise to estimate both aerodynamic loads and velocity fields accurately. [ABSTRACT FROM AUTHOR]

In response to the global shift toward renewable energy, wind energy is a pivotal player in sustainability. Floating offshore wind turbines (FOWTs) emerge as a promising solution for expanding wind energy into economically challenging deep waters. Despite their potential, challenges persist, necessitating a thorough understanding of the complex coupling effects between wind turbine aerodynamics and hydrodynamics, particularly during the design phase. This study highlights this critical need and extends its scope to review the relevant existing literature. The paper provides insights into the design considerations and assessment methodologies crucial for both new structures and the evaluation of existing ones. Through modeling in the Ashes wind turbine software, the study reveals that platform surge motion significantly impacts rotor performance, causing rotor power and thrust fluctuations. By comparing various wind and sea states with baseline testing, the study underscores the necessity of coupling aerodynamic and hydrodynamic forces for accurate performance predictions. Besides, the paper offers actionable recommendations for designing and optimizing FOWTs, and sheds light on the challenges and opportunities within offshore wind energy, offering valuable guidance for engineers working toward sustainable energy solutions. [ABSTRACT FROM AUTHOR]

The new‐generation manned spacecraft employs a new recovery system of parachutes and airbags. In order to realize the effective cushion of the return capsule airbag, the conversion of the single‐point hanging to the double points for the spacecraft is necessary. In the conversion process, the long hanging rope and the height of the return capsule will cause a large impact and disturbance to the cabin, but the traditional dynamic modeling method is not suitable for those with complex boundary conditions. In order to solve these problems, a finite element model is proposed to analyze the suspension conversion process and simplify the parachute model based on the aerodynamic load dynamic matching control method to analyze the dynamic response characteristics, such as overload, speed, and force of the cabin, quantifying the conditions of the rope in the process. Results are generally consistent with experimental data. This study provides guidance for future optimization work and will greatly support the safe‐return technology of the new‐generation manned spacecraft. [ABSTRACT FROM AUTHOR]

The transient processes of laminar separation bubble (LSB) formation and bursting on a rectangular NACA 0018 wing are studied experimentally. A two-dimensional airfoil model is used as a baseline for the assessment of finite wing effects. The models are subjected to ramp changes in free-stream velocity causing the flow to switch between a state where an LSB forms and a state without reattachment. Lift force and particle image velocimetry measurements are used to relate the flow development to the aerodynamic loading. The lift coefficient of the airfoil exhibits substantial hysteresis, and the duration of the lift transients range from $10$ to $22$ convective time scales for bubble formation and $22$ to $30$ convective time scales for bursting. In contrast, the transient lift coefficients of the wing change gradually, with less hysteresis. The wing tip causes greater three-dimensionality in the separation bubble, whose thickness increases near the midspan where bursting is initiated. During bubble formation, the region of separated flow contracts towards the midspan. The gradual change in lift of the wing is linked to slower spanwise expansion and contraction of the separated flow region relative to the airfoil. On both models, the wavenumbers and amplitudes of disturbances in the separated shear layer rapidly change when reattachment initiates or ceases. Applying the bursting criterion of Gaster (Tech. Rep. Reports and Memoranda 3595. Aeronautical Research Council, London, 1967) to the bubble on the wing shows that bursting of the bubble at a single spanwise location is insufficient to cause complete spanwise failure of reattachment, and that the relationship between bursting parameters depends on spanwise position. [ABSTRACT FROM AUTHOR]

The aeroelasticity of a panel in the presence of a shock is a fundamental issue of great significance in the development of hypersonic vehicles. In practical engineering, cavity pressure emerges as a crucial factor that influences the nonlinear dynamical characteristics of the panel. This study focuses on the aeroelastic bifurcation of a flexible panel subjected to both cavity pressure and oblique shock. To this end, a computational method is devised, coupling a high-fidelity reduced-order model for unsteady aerodynamic loads with nonlinear structural equations. The solution is meticulously tracked by continuous calculations. The obtained results indicate that cavity pressure plays a pivotal role in determining the bifurcation and stability characteristics of the system. First, the system exhibits hysteresis behaviour in response to the ascending and descending dynamic pressures. The evolution of hysteresis behaviour originates from the phenomenon of cusp catastrophe. Second, variations in cavity pressure induce three types of bifurcation phenomena, exhibiting characteristics akin to supercritical Hopf bifurcation, subcritical Hopf bifurcation and saddle-node bifurcation of cycles. The system's response at the critical points of these bifurcations manifests as long-period asymptotic flutter or explosive flutter. Lastly, the evolution of the dynamical system among these three types of bifurcations is an important factor contributing to the discrepancies observed in certain research results. This study enhances the understanding of the nonlinear dynamical behaviour of panel aeroelasticity in complex practical environments and provides new explanations for the discrepancies observed in certain research results. [ABSTRACT FROM AUTHOR]

The response of airfoils to unsteady disturbances is a classic problem in the aerodynamics field. Many theoretical models have been proposed in the past to predict the unsteady aerodynamic forces of airfoils. However, these theories focused on individual airfoil motions or incoming flow disturbances, while the theoretical models for multiple disturbances still need to be developed. In this study, a theoretical model to predict the aerodynamic force of an oscillating airfoil encountering vertical gust is derived from a linear combination of Theodorsen's and Sears' theories. Experimental investigations involving a two-dimensional pitching airfoil encountering a sinusoidal vertical gust are carried out to examine the proposed theory. It is found that the theory effectively captures the trends in the unsteady lift of airfoils subjected to dual disturbances. However, it tends to overestimate the lift amplitude. Notably, when a quasi-steady correction is applied to the theory, the prediction accuracy is greatly improved. The theory correction agrees well with experiment at small pitching frequencies, while deviations exist at higher pitching frequencies. The temporal evolution of the flow velocity reveals that the velocity disturbance induced by the coupled disturbance around the airfoil conforms to the linear superposition of the velocities induced by each individual disturbance, consistent with the prediction of the vortex sheet model. As the pitching frequency increases, significant nonlinear effects appear near the trailing edge of the airfoil, which may be one key factor for the disparities between the theoretical predictions and the experimental lift at higher pitching frequencies. [ABSTRACT FROM AUTHOR]

This paper proposes a force-sensing wing, Senswing, to enhance the intelligence of flapping-wing aerial vehicles (FWAVs). Force perception is a crucial capability for robots to interact safely and effectively in unknown environments. However, FWAVs perform flapping motions with significant acceleration and deceleration, which can cause the flexure element inside force sensors to deteriorate due to repeated loading or even fail due to impulsive forces. To address this, we constructed a force measurement system by attaching 16 strain gauges directly to the wing root while maintaining high rigidity. We confirmed that the external force measurement capability closely matched the values obtained by a six-axis force sensor, with almost no error. Additionally, when measuring aerodynamic forces during wing flapping, the sensor could detect differences in wind speed even during flapping. With this sensor, FWAVs can achieve in-flight measurement of thrust and lift through a force-sensing system. [ABSTRACT FROM AUTHOR]

The train operates in special environments such as large bridges and elevated viaducts. The fluctuations of the aerodynamic loads of the high-speed train (HST) are more intense and the possibility of the train derailment and overturning will increase when the train is running on the bridge under the crosswind. Thus, it is of utmost importance to study both the aerodynamic characteristics and the running safety of the train in this situation. This study uses the IDDES method to investigate the aerodynamic characteristics of the train running on the double track bridge in both up and down train directions at different speeds. The differences in the impact of aerodynamic loads on the train's dynamic response indicators are discussed using the wind-vehicle coupling dynamic response calculation method. Based on these researches, the operational safety of the train under different operating conditions is evaluated from both flow field and dynamic perspectives. The results show that large-scale vortices fall off from the nose of the train and form a larger vortex structure on the leeward side and when the train is running under the crosswind. Its aerodynamic loads fluctuate intensely with time due to the complex wake flow of the train. The dominant frequencies of the unsteady aerodynamic loads are mostly concentrated in the range of 0–5Hz, which is close to the natural modal frequencies of the train. This will lead to the overturning of the train due to vehicle resonance. The derailment coefficient and wheel load reduction rate of the train increase with the speed. Their peak values exceed the limit of 0.8 while the peak duration of the derailment coefficient is less than 0.05s, which means the state of the leeward wheel will recover from a short derailment. However, the duration of derailment increases with speed. Therefore, appropriate measures should be taken to prevent accidents when the train is running at higher speed on the bridge to guarantee the operational safety of the HST. [ABSTRACT FROM AUTHOR]

To address the challenges in predicting the aeroelastic phenomenon and the resulting wind-induced forces on slender bridges, a real-time aeroelastic hybrid simulation (RTAHS) system was developed. The RTAHS system directly measures the aerodynamic and aeroelastic forces through load cells. It controls the next step's position of the deck section model with linear motors by solving the governing equations of motion in real time. Given the complex shape of a bridge deck section geometry, load cells are chosen for force measurement instead of as pressure sensors. In the previous RTAHS system proposed by the authors, the inertial forces of a rectangular section model were eliminated from the measured forces under the assumption of the model's rigid-body motion. However, when conducting RTAHS experiments with a realistic bridge deck section model, increasing the mass ratio between the mass of the model and the target mass input to the hybrid system results in unstable vibrations. This instability is primarily attributed to forces generated by the model's flexibility. This study developed an improved RTAHS system, which took into account the inertial forces arising from the nonrigid motion of the flexible bridge deck section model. An accelerometer was additionally installed at the midpoint of the model, and the inertial forces caused by the nonrigid behavior were compensated using a calibration factor derived from impact hammer tests. This approach was validated by comparing the spring-supported experiments conducted on a realistic bridge deck section model. [ABSTRACT FROM AUTHOR]

• The aerodynamic effect of wind on QUAV is analyzed, and a dynamic model of QUAV with wind disturbance is established. • By using different weight functions, wind effect on multi-QUAVs is simplified and dynamic model is established. • A multi-QUAVs formation finite time consensus control with wind disturbance and time delay is proposed. Wind interference and time delay environment have great influence on the stable flight of a multi-quadrotor UAVs (QUAVs) formation, which has important study to achieve the consensus control of multi-QUAVs formation flying in these conditions. In this paper, through analyzing the aerodynamic force and moment caused by the wind effect on the quadrotor, a quadrotor dynamic model with wind disturbance is established. Considering that the multi-QUAVs formation flight will be affected by different degrees of wind effect, several different weighting functions are proposed to simplify this complicated problem, and multi-QUAVs dynamic model in wind disturbance environment is innovatively established. Based on the continuous time consensus algorithm, considering the influence of wind disturbance and time delay, using the graph theory and leader-follower formation idea, dynamic modeling of multi-QUAVs is proposed, and realize the finite time consensus control. The simulation and experiment results prove the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Aerodynamic breakup refers to the process where large droplets are fragmented into small droplets by the aerodynamic force in airflow, which plays a vital role in fluid atomization and spray applications. Previous research has primarily concentrated on the aerodynamic breakup of single‐component droplets, but investigations into the breakup of emulsion droplets are limited. This study experimentally investigated the aerodynamic breakup of water‐in‐oil emulsions in airflow, utilizing high‐speed photography to observe the breakup process and digital in‐line holography to measure fragment sizes. Comparative analyses between emulsion droplets and single‐component droplets are conducted to examine the breakup morphology, breakup regime, deformation characteristics, and fragment size distributions. The emulsion droplets exhibit higher apparent viscosity and shorter stretching lengths of the bag film and peripheral rim due to the presence of a dispersed phase. The breakup regime transitions of emulsions are modeled by integrating the viscosity model of emulsions and the transition model of the pure fluid. The fragment sizes of emulsion droplets are larger due to the shorter lengths of the bag film and peripheral rim. [ABSTRACT FROM AUTHOR]

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This study investigates the effects of positive horizontal acceleration of the freestream velocity on a pitch‐oscillating VR‐12 airfoil using computational fluid dynamics. The shear stress transport k–ω model, coupled with a low‐Reynolds number correction, was employed for Re <105 during dynamic stall. The flow equations were solved in two‐dimensional, incompressible form using the finite volume method. The study examined various parameters, including positive acceleration values of the inflow and the angle of attack of the airfoil, to determine their impact on lift and drag coefficients, as well as the C l / C d ${C}_{{\rm{l}}}/{C}_{{\rm{d}}}$ ratio. Additionally, the maximum lift coefficient was analyzed under different inflow and airfoil motion conditions. The results indicate that aerodynamic force coefficients and the C l / C d ${C}_{{\rm{l}}}/{C}_{{\rm{d}}}$ ratio are influenced by both the attack angle and the acceleration of the inflow. Furthermore, inflow acceleration affects the onset of dynamic stall conditions. Generally, inflow acceleration modifies the lift coefficient of the airfoil during the upstroke, while having minimal effect on the drag coefficient, except near dynamic stall points. The findings also suggest that, for a specific airfoil, the sequence of factors with the greatest influence on lift force generation before static stall occurs is as follows: asymmetric airfoil oscillation, symmetrical airfoil oscillation, accelerated inflow, constant velocity inflow, and static airfoil. [ABSTRACT FROM AUTHOR]

Recently, the phenomenon of tail-sustained swaying of the 160 km/h EMU in single-track tunnels has gained much attention, especially for the rear-powered vehicle. This phenomenon is investigated from the perspective of aerodynamic fluid–structure coupling vibration in this study. The aerodynamics simulation model of the train in tunnels and the multi-body dynamics model of the rear-powered vehicle were respectively established through the software of XFlow and Simpack, and then the fluid–structure coupling vibration was simulated by using real-time data dynamic exchange between the two models. Moreover, the carbody's vibration acceleration and the aerodynamic loads acting on the carbody under various wheel–rail contact geometrical conditions were discussed. Finally, the train tail swaying in field was tested, and the dominant frequencies were analyzed. The results show that the periodic aerodynamic loads and the frequency locking effect caused by the coupled vibration are the main factors for ride comfort deterioration. The violent vibration caused by fluid–structure coupling is named vortex-induced vibration (VIV) in some industries such as bridge and submarine pipeline. For the vehicle in this work, with the decrease of equivalent conicity in wheel–rail contact, the amplitude of carbody swaying increases owing to the carbody hunting, which enhances the fluid–structure coupling vibration, and further deteriorates the ride comfort. The swaying of the carbody is dominated by the vehicle hunting frequency, and the improvement of vehicle lateral stability can weaken this phenomenon. [ABSTRACT FROM AUTHOR]

In this study, we conducted an aeroelastic stability analysis of a laminated composite magnetorheological fluid (MRF) sandwich panel in supersonic airflow for varying yawed angles. The aeroelastic equations for a rectangular sandwich panel (MRF core layer and composite cross‐ply laminate constraining and host layers) were established using a MIN3 plate element. Aerodynamic forces for different yawed angles would result in different coupled flutter boundaries of the panel. The first‐order piston theory with a flow‐yawed angle was employed. The flutter dynamic pressure was obtained through eigenvalue analysis. The effects of various parameters such as the magnetic field intensity, MRF core and constraining layer thicknesses, ply orientation, and yawed flow angle on the flutter dynamic pressure were studied for the simple‐ and fixed‐support boundary conditions. Our results demonstrated that the flutter dynamic pressure of the laminated composite MRF sandwich panel (i) increased for increasing magnetic field intensity and constraining layer thickness; (ii) initially decreased and then increased with the increasing MRF core thickness; and (iii) was strongly influenced by the ply orientation and yawed flow angle. [ABSTRACT FROM AUTHOR]

Developing offshore wind power can effectively reduce carbon emissions, and adopting large‐capacity wind turbines is an important way to achieve cost reduction and efficiency increase. With increasing power capacity, the hub height and rotor‐nacelle assemblies (RNA) load will increase significantly. Ultra‐high performance concrete (UHPC) possesses ultra‐high compressive performance, good tensile, fatigue, and corrosion resistance, and thus is an effective way to further improve the mechanical performance and economic efficiency of tall offshore wind turbine (OWT) towers. Evaluation of ultimate strength is an essential aspect of design for OWT towers, and the tower structure is mainly under the combined action of axial compression from the self‐weight and RNA loads and bending from the eccentricities of RNA and aerodynamic loads from the rotor on the tower top. In this work, the mechanical behavior of prestressed UHPC wind turbine tower columns under combined axial compression and bending was numerically investigated. The finite element (FE) analyses were carried out using ABAQUS, and the material and geometric nonlinearity were considered in the model, as well as the tensile strain hardening properties of UHPC. The FE models were firstly verified by the typical experimental results of UHPC hollow columns, reinforced UHPC beams, prestressed UHPC beams, and prestressed concrete‐steel hybrid wind turbine tower model. Then the parametric study was carried out, and the parameters included the control stress and number of prestressing tendons, rib number, diameter‐to‐thickness ratio of the UHPC column, steel ratio of longitudinal reinforcement, axial load ratio, and UHPC strength. The calculation methods for flexural capacity of prestressed UHPC wind turbine tower columns were finally proposed, and were found to agree well with the modeling results. [ABSTRACT FROM AUTHOR]

AbstractRail models may be simplified at different levels in wind tunnel tests and numerical simulations. This work used delayed detached eddy simulations to analyze and compare the aerodynamic loads (drag, side force, lift, and rolling moment), surface pressure, and flow characteristics around a train model placed on subgrades with three different rail models: no-rail, simplified rail, and realistic rail. The simulations were conducted at a large yaw angle of 60°. The mean aerodynamic characteristics of the car bodies and bogies were similar with the simplified rail model and realistic rail model, while those were completely different without the rail model. The difference in aerodynamic loads between the no-rail model and the realistic rail model was as high as 53.1%, whereas the difference between the simplified and realistic rail models was only 7.7%. And for fluctuating aerodynamic characteristics of the train, there was still differences between the cases with the simplified and realistic models. Further, the rail model significantly impacted the flow (such as the velocity, turbulent kinetic energy, and vorticity) around the train, especially under the train, resulting in significant differences in the aerodynamic loads in time and frequency domains. For accurate and precise measurements of mean aerodynamic loads, incorporating a rail model (with the simplified model being sufficient) can improve accuracy by 48.0% and precision by 66.9%. When focusing on fluctuating aerodynamic loads, using a realistic rail model is essential to accurately capture amplitude-frequency characteristics. The rail model setup recommendations outlined in this work aim to enhance the accuracy and reliability of various wind tunnel tests and numerical simulations related to train aerodynamics. [ABSTRACT FROM AUTHOR]

The present study is aimed at reducing the drag loads on cylinders by using a passive control technique which consists in shape modification for streamlined and bluff bodies, particularly those used in aeronautics. Various shapes of elliptic and ovate-elliptic cross sections were tested with studying the effect of geometric parameters, namely, the radius ratio and axial ratio. The flow around the proposed geometries was studied numerically using k–ε, k–ω, and Spalart–Allmaras turbulence models at the Reynolds numbers from 104 to 2.4·104. The results obtained were compared with those for a circular cylinder of constant radius, showing a significant weakening of aerodynamic forces acting on the cylinder with modified shapes, especially at high Reynolds numbers, for both elliptic and ovate-elliptic geometries with a better performance for the latter. [ABSTRACT FROM AUTHOR]

Dragonflies can independently control the movement of their forewing and hindwing to achieve the desired flight. In comparison with previous studies that mostly considered the same kinematics of the fore- and hindwings, this paper focuses on the aerodynamic interference of three-dimensional tandem flapping wings when the forewing kinematics is different from that of the hindwing. The effects of flapping amplitude (Φ1), flapping mean angle ( ϕ 1 ¯ ), and pitch rotation duration (Δtr1) of the forewing, together with wing spacing (L) are examined numerically. The results show that Φ1 and ϕ 1 ¯ have a significant effect on the aerodynamic forces of the individual and tandem systems, but Δtr1 has little effect. At a small L, a smaller Φ1, or larger ϕ 1 ¯ of the forewing can increase the overall aerodynamic force, but at a large L, smaller Φ1 or larger ϕ 1 ¯ can actually decrease the force. The flow field analysis shows that Φ1 and ϕ 1 ¯ primarily alter the extent of the impact of the previously revealed narrow channel effect, downwash effect, and wake capture effect, thereby affecting force generation. These findings may provide a direction for designing the performance of tandem flapping wing micro-air vehicles by controlling forewing kinematics. [ABSTRACT FROM AUTHOR]

Marine midges, tiny insects with a body size of 2 mm and a weight of 0.07 dyn, provide valuable insights into advanced locomotion techniques. Found in shallow reefs at Wanlitong, Kenting National Park, Taiwan, these midges can continuously traverse seawater surfaces for over 90 min at speeds around 340 body-lengths per second. Their flight relies on two primary mechanisms: wing sculling to utilize surface tension for thrust and wing retraction to generate aerodynamic lift. This study addresses the gap in understanding how marine midges generate the lift and thrust needed for prolonged flight. We investigated their unique locomotion by conducting experiments to measure their weight, speed, and wing frequency. These measurements informed 3D computational fluid dynamics (CFD) simulations to analyze the aerodynamic forces involved. The results highlight the critical role of the ground effect, where maintaining minimal gaps of 0.08 mm between the midge trunk and 0.055 mm at the wing tips is essential for lift. Additionally, a high wing-beat frequency exceeding 300 Hz is crucial for generating sufficient lift during wing retraction. Our findings emphasize that ground effect, forward speed (>60 cm/s), and wing-beat frequency are key factors enabling marine midges to sustain flight above the sea surface. This unique adaptation for water surface locomotion not only showcases the midge's remarkable flight capabilities but also offers valuable insights for the design of micro-air vehicles (MAVs). [ABSTRACT FROM AUTHOR]

Shock–shock interactions (SSIs) are widespread in hypersonic vehicles. The mutual interaction between multiple shock waves can result in severe pressure loads and increase the thermal load. The SSI induced by a double wedge configuration is a classical problem. This paper describes a novel U-electrode surface arc actuator that produces a supermultichannel array surface arc discharge under hypersonic conditions. High-speed schlieren measurements are used to investigate the SSI induced by the hypersonic double wedge and plasma control under Mach 8 flow conditions. The results show that the shock wave array induced by the plasma forms a virtual compression surface. This surface deforms the shock wave induced by the first wedge, and the oblique shock wave in front of the secondary wedge and the SSI region disappear due to the uplift and hot gas mass disturbance from the impact. Because the applied actuation frequency is higher than the characteristic frequency of the base flow field, the high-frequency pulsations of the shock wave are controlled by the plasma actuation. Additionally, the low-frequency instability is suppressed. Thus, the aerodynamic load and low-frequency instability of the double wedge configuration under high-Mach-number conditions are effectively regulated. [ABSTRACT FROM AUTHOR]

The design speed of high-speed maglev trains is much higher than that of wheel-rail trains, and they will be subject to more operational safety threats under complex wind conditions. The present study uses the improved delayed detached eddy simulation method based on the shear stress transfer k–ω turbulence model to explore the effect of active flow control on the aerodynamic lateral force of a maglev train and examines the main aerodynamic performance differences caused by two active control forms (suction and blowing airflow), involving multiple active flow speeds. In the current scenario, blowing can reduce the lateral force coefficient of the head car by up to 15% while greatly increasing its transient instability, which can be attributed to direct and indirect changes in pressure distribution near the air slots and a larger range of the leeward surface. The suction is believed to suppress the downstream motion of the main vortex on the leeward side of the maglev train and weaken the turbulent kinetic energy of the wake, while the blowing effect reduces the dominance of the main vortex. The application of blowing is proved as an effective means of reducing the risk of operating a maglev train in a crosswind environment, while it requires a careful consideration of both train safety and energy efficiency. [ABSTRACT FROM AUTHOR]

This paper numerically investigates the aerodynamic forces and the three-dimensional wake characteristics of wall-mounted circular cylinders with and without porous media coatings using large eddy simulation at a Reynolds number of 3.2 × 10 4 . Short cylinders with aspect ratios of 0.5, 1.0, and 3.0 are considered, with one end fixed to a bottom wall in the current work. The study focuses on aerodynamic coefficients, flow characteristics, and wake structures for cylinders both with and without porous coatings. The statistical results indicate that porous media significantly alter flow patterns behind the cylinders, suppress downwash flow from the free end, and reduce velocity fluctuations and turbulent kinetic energy within the wake. The porous coating enhances the leeward side's base pressure, leading to a reduction in drag on the cylinder surface. The analysis of flow structures reveals that the topology of the arch vortex behind solid cylinders is significantly dependent on the aspect ratio, whereas this dependency is negligible for porous cylinders. Porous coatings diminish the intensity of the tip and trailing vortices behind the cylinder. Finally, based on the time-averaged flow field, we proposed two conceptual models of topological correlation for wall-mounted short cylinders, both with and without porous coatings, which contributes to describing the geometric characteristics and interactions of vortex structures. [ABSTRACT FROM AUTHOR]

In practical optimization design, an excessive number of design variables have a highly detrimental influence on the efficiency and accuracy of the final design scheme and expose the optimization problem to the curse of dimensionality. Therefore, incorporating only the most essential variables into an optimization design problem facilitates obtaining accurate and cost-efficient solutions. Reported here is an optimization design method based on parameter reduction and active subspaces, and it is used to redistribute the tip load in a transonic fan. Specifically, a coupled design strategy is developed to reduce the number of parameters needed to describe the three-dimensional blade shape, which leads to far fewer design variables being involved in the optimization design. Moreover, active subspaces are used to perform sensitivity analysis and establish low-dimensional surrogate models. After the coupled design, a blade is represented effectively by only three parameters, each of which has a significant influence on the fan performance. Three one-dimensional active subspaces are established for maximum mass flow rate, maximum total pressure ratio, and maximum efficiency, based on which the linear surrogate models are obtained. Next, the chordwise tip blade loading is optimized, after which the rotor efficiency at the design point is increased by 1.1%, while the total pressure ratio remains nearly unchanged. Finally, the flow field is analyzed to understand the mechanism for this performance improvement, and the results show that the optimized blade loading reduces the aerodynamic losses caused by shock-induced flow separation and the interaction between shocks and tip leakage flows. [ABSTRACT FROM AUTHOR]

Research on aerodynamic loads and flow field characteristics of trains under real wind gust is limited. Most studies focus on train's dynamics under wind gust. By using numerical simulation methods to model the spatiotemporal evolution of the flow field around the train under real wind gust, the aerodynamic load and flow field characteristics of the train were studied. The one-minus-cosine wind gust model was adopted to achieve the real wind gust and the improved delayed detached eddy simulation based on shear stress transport k–ω turbulence model was used to perform numerical simulations of train operation under wind gust by applying the specified wind gust model function to the velocity inlet boundary. During the wind gust, the peak values for most of the aerodynamic loads of the train cannot reach the levels corresponding to those under constant crosswind, since the flow field around the train cannot fully develop into a stable flow field akin to that under constant crosswind. Compared to the wind gust without zero-crossing, the differences between unsteady and quasi-steady peaks are greater for side force, rolling moment, and yaw moment under wind gust with zero-crossing. This study addresses the gap in research on train aerodynamics under real wind gust conditions, providing essential data for train dynamics and a theoretical foundation for the safe operation of the train. [ABSTRACT FROM AUTHOR]

Cavity structures on hypersonic vehicle surfaces alter aerodynamic heat flux and force (pressure) compared to flat surfaces. In this study, an investigation explores the aerodynamic effects of multiple cavities on rarefied hypersonic flows, utilizing the Direct Simulation Monte Carlo method to assess the impact on hypersonic vehicle surfaces. While previous research predominantly concentrated on the implications of a single cavity, this study extends the investigation to multiple cavity configurations under rarefied flow conditions, which are less understood but critical due to the potential for significant impacts on vehicle performance and structural integrity. The research examines how variations in the number of cavities, as well as their geometric arrangement (distance and length-to-depth ratio), influence key aerodynamic parameters, including pressure, skin friction, and heat transfer coefficients. The study's findings reveal that in the rarefied hypersonic flow at Mach 25 at 70 km, each cavity independently influences the flow field and the aerodynamic surface properties, largely determined by its geometric characteristics, irrespective of adjacent cavity presence. The study underscores that the macroscopic aerodynamic force escalates with an increase in the number of cavities and their length-to-depth ratio, while it diminishes with inter-cavity distance. These insights are crucial to optimizing the design of hypersonic vehicles, contributing to improved performance and stability by managing aerodynamic forces more effectively. The comprehensive data and analyses provided support the development of more accurate models to predict and control the behavior of hypersonic vehicles with multiple cavities. [ABSTRACT FROM AUTHOR]

Droplet transport is very essential in many industrial applications. This article proposed the concept of employing dual synthetic jets in conjunction with superhydrophobic materials to facilitate the long-distance directional transport of water droplets. Experiments showed that the droplet transport speed could reach approximately 90 mm/s. In addition to linear transport, dual synthetic jets were also capable of achieving curved transport of droplets on superhydrophobic surfaces. High-speed photography captured the details of the droplet transport process. Additionally, simulations analyzed the water droplet's aerodynamic forces and the deformation and breakup mechanisms at the actuator's outlet. The research in this paper was anticipated to contribute to new methods for directed droplet transport on superhydrophobic surfaces. It is eliminated the need for pre-processing the surface to create a path, and there was also no need to incorporate conductive or magnetic substances within the droplets. [ABSTRACT FROM AUTHOR]

Aerodynamic interference occurs at the wingtips when flying organisms fly in a V formation. In this paper, the wingtip aerodynamic interference of two flapping wings on opposite sides at low Reynolds numbers (Re) is numerically investigated. The effects of streamwise spacing (L1), spanwise spacing (L2), and phase angle (γ) on aerodynamic performance are considered. The results show that, compared to a single wing, a favorable combination of L1 and L2 can improve the overall thrust by 24% while keeping the overall lift essentially unchanged. In an unfavorable case, overall lift and thrust decrease by 18% and 20%, respectively. The overall aerodynamic forces are dominated by the rear wing. Analyzing the essential flow characteristics reveals the double-edged role of downwash and upwash in force generation. Moreover, it is found that the rear wing can realize the upwash/downwash exploitation by flap phasing, turning an unfavorable situation into a favorable one. The key flow physics behind this transformation lies in the relationship between the direction of wing motion and the direction of fluid velocity induced by vortices. These findings provide valuable insights into the understanding of biological phenomena and the design of new flapping wing vehicles. [ABSTRACT FROM AUTHOR]

Mathematical models based on inviscid flow theory are effective at predicting the aerodynamic forces on large-scale aircraft. Avian flight, however, is characterized by smaller sizes, slower speeds, and increased influence of viscous effects associated with lower Reynolds numbers. Therefore, inviscid mathematical models of avian flight should be used with caution. The assumptions used in such models, such as thin wings and streamlined bodies, may be violated by birds, potentially introducing additional error. To investigate the applicability of the existing models to calculate the aerodynamic performance of bird flight, we compared predictions using simulated wakes with those calculated directly from forces on the bird surface, both derived from computational fluid dynamics of a high-fidelity barn owl geometry in free gliding flight. Two lift models and two drag models are assessed. We show that the generalized Kutta–Joukowski model, corrected by the streamwise velocity, can predict not only the lift but also span loading well. Drag was predicted best by a drag model based on the conservation of fluid momentum in a control volume. Finally, we estimated force production for three raptor species across nine gliding flights by applying the best lift model to wake flow fields measured with particle tracking velocimetry. [ABSTRACT FROM AUTHOR]

This study employs a high-fidelity numerical approach to simulate fluid–structure interaction phenomena for the dynamic response of flexible hyperelastic morphing wing structures under low aerodynamic loads. The computations are performed using the open-source solids4Foam toolbox, employing a partitioned two-way fluid–structure interaction approach with a finite volume solver for both fluid and solid. The considered morphing wing is divided into a flexible and a rigid segment, with the flexible segment featuring a 60% chord length and being made of a hyperelastic rubber-like material. The concept of damping is incorporated into the solid momentum balance equation as a virtual force that opposes the velocity of the structure. Damping is employed to disperse energy from the system, hence mitigating the oscillations and reducing computational time. To understand morphing wing aerodynamics and aeroelasticity behavior, a series of tests are conducted at low and medium Reynolds numbers, specifically 2 × 10 5 and 5 × 10 5 . The results show that, for low Reynolds number, the morphing structure has a negligible impact on aerodynamic behavior. However, at higher Reynolds numbers, morphing results in improved aerodynamic efficiency at low angles of attack. Overall, the study highlights the aero-structural behavior of hyperelastic morphing wings and their potential for developing efficient and adaptive wing structures, highlighting their promise for future aircraft design innovations. [ABSTRACT FROM AUTHOR]

Cable-stayed bridges with box girders are essential innovations in civil engineering, especially for long-span structures. These bridges, reinforced with prestressed cables and box girders, are designed to handle significant loads but remain vulnerable to aerodynamic forces, particularly wind. The vulnerability is measured using the Pb parameter, as defined by the Ministry of Public Works (2015), which helps determine the windbreak structures needed for stability. This study analyzes the aerodynamic stability of bridge decks with widths of 8 m, 13 m, and 19 m on a 420 m bridge, featuring a 220 m main span and two 100 m side spans. The results reveal that the larger the deck width-to-span ratio, the higher the structure's natural frequency, which improves stability. The natural frequency values were recorded at 0.3 Hz for a 7 m deck (3.2%), 0.43 Hz for a 12 m deck (5.48%), and 0.53 Hz for an 18 m deck (8.2%). The most stable span ratio was found with the 18 m deck, with a Pb value of 0.04, showing minimal wind load effects. Moreover, a larger deck width enhances aerodynamic stability and extends the bridge's service life by reducing damage risk from wind loads. [ABSTRACT FROM AUTHOR]

Interest in the exploration of other planets has led to the success of Ingenuity (Mars helicopter)'s first flight in the Martian atmosphere. Despite this achievement, the flight of aircraft under ultra-low air density, such as Mars, is still limited. A flapping-wing aircraft that mimics nature's flyers can provide an alternative solution to conventional aircraft. Successful flapping flight on Mars, where the air density is very thin, requires an understanding of aerodynamics, and prediction of the dynamic changes of the flapping wing under very-low air density. In this paper, we constructed a simple dynamic model that can predict the changes in aerodynamics and dynamic behavior under various low air densities. The predicted changes were compared with the measured ones in a chamber that could simulate the low air density with a modified flapping-wing system based on our flapping-wing micro-air-vehicle (FW−MAV) models, the KUBeetle. Both prediction and measurement showed that when the air density decreased, the flapping frequency tended to increase due to drag reduction, even without consuming additional power. The model reasonably predicted a large decrease in the lift for the 10 % air density, where the flapping frequency increased by 10 %. Under the 50 % and 25 % low air densities, the measured lift coefficients did not change much. However, under the 10 % air density, the lift coefficient decreased by about 16 % due to less wing rotation and wing twist. While the aerodynamic power was predicted to decrease significantly due to the large decrease in aerodynamic forces under low air density, an increase in the angular velocity and peak angular acceleration caused an increase in the inertial power. Therefore, the amount of reduction in the measured mechanical power consumption under the 10 % air density was relatively small, compared to that under the 100 % air density. This work may provide insights into the design of an FW−MAV for the ultra-thin air density, such as Mars. • The proposed dynamic model reasonably predicted the flapping motion under low air density. • The measured flapping frequency increased by about 15 % under the 10 % air density, consuming about 9 % less power. • The reduction in measured power consumption under low air density was small, due to the large inertial power. • The measured lift coefficient decreased by about 16 % under the 10 % air density, due to less wing Q4 rotation and wing twist. [ABSTRACT FROM AUTHOR]

Understanding particle ejection behaviours in plume-regolith interaction is important for a safe soft-landing system and landing manoeuvre in planetary missions. In this study, a Mach 5.8 hypersonic jet at the different Reynolds numbers of 2.58 × 104 and 9.35 × 102 impinges on the deposited glass particles of 80 μm diameter in a vacuum chamber, and the particle and gas motions at the nozzle pressure ratios (NPR) of 95, 950, and 1900 are investigated using the time-resolved PIV and high-speed Schlieren techniques. A narrow hypersonic jet consisting of several shock cells forms at the lower NPR of 95 and causes a deeply narrow crater due to its jet penetration into the deposited particles. The deeply narrow crater makes a particle ejection angle increase upwardly. On the other hand, a relatively wide crater forms due to the jet impingement at the other NPR conditions which a widely long shock cell is generated. Based on the present experimental results, a dominant factor in particle ejection angle is the crater size and depth, whereas a particle diffusion velocity is dominated by surrounding pressure. The diffused particles move faster in a low surrounding pressure because of a low aerodynamic drag force acting on the diffused particles. • A dominant factor in particle ejection angle is the crater size and depth. • The diffused particles move faster in a low surrounding pressure. • The particle and gas motions at several NPRs are investigated in a vacuum chamber. [ABSTRACT FROM AUTHOR]

Rapid launching is a crucial technology for the digitalization and regularization of space transportation systems. This paper focuses on the fast trajectory prediction of the launch-vehicle boost phase. A high-precision and high-efficiency analytical solution of the whole boost phase dynamics model of the rocket is obtained by adopting one of the regular perturbation methods called the state-space perturbation method in the launch rotated coordinate system. An analytical framework known as the perturbation expansion framework is proposed by first figuring out the correlation with the state variables/independent variables and then performing the approximate expansion. This framework can successfully address the issue of analytically solving the transfer matrix and integral term caused by the coupling and time-varying properties among state variables of the affine equations of the boost phase. The analytical solution developed in this paper has great fidelity and takes into account the combined effects of various factors, including thrust, aerodynamic force, Earth's gravity, oblateness, and rotation. It can serve as a theoretical guide for the rapid launch requirements and iterative design processes for early rocket demonstrations in engineering. [ABSTRACT FROM AUTHOR]

Accurate numerical values of aerodynamic parameters are important in aircraft design. The knowledge of stability and control aerodynamic parameters is essential to postulate high-fidelity control laws. The aerodynamic forces and moments are strong functions of the angle of attack (AOA), Reynolds number, and control surface deflections. Typically, conventional estimation techniques such as maximum likelihood (MLE) and least-squares (LS) principles facilitate the determination of these parameters. Unsteady aerodynamics may complicate the estimation of aerodynamic parameters at high AOA. Data-driven techniques employing neural networks provide an alternative for modeling the system behavior based on its observed state and control input variables. Nonlinearity increases because of flow separation at high AOA, which is close to stall. This paper explores the feasibility of employing a machine learning approach using neural networks to predict aircraft dynamics in a limited sense to identify aerodynamic characteristics. Integrating a neural network with the artificial bee colony (ABC) method facilitated the optimization of unknowns of the proposed aerodynamic model (AM). The proposed neural artificial bee colony (NABC) optimization approach estimated the longitudinal dynamics and stall properties for two experimental aircraft. Comparison of the estimates provided by the NABC approach with those of the standard MLE and neural Gauss–Newton (NGN) techniques established its efficacy. Furthermore, robust statistical analysis indicated that the proposed method provides a viable alternative for parameter estimation in nonlinear applications. [ABSTRACT FROM AUTHOR]

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Cyber–physical testing has been applied for a decade in hydrodynamic laboratories to assess the dynamic performance of floating wind turbines (FWTs) in realistic wind and wave conditions. Aerodynamic loads, computed by a numerical simulator fed with model test measurements, are applied in real time on the physical model using actuators. The present paper proposes a set of short and targeted benchmark tests that aim to quantify the performance of actuators used in cyber–physical FWT testing. They aim at ensuring good load tracking over all frequencies of interest and satisfactory disturbance rejection for large motions to provide a realistic test setup. These benchmark tests are exemplified on two radically different 15 MW FWT models tested at SINTEF Ocean using a cable-driven robot. [ABSTRACT FROM AUTHOR]

The pitch bearings of wind turbines are slowly oscillating, grease-lubricated slewing bearings. They facilitate the pitching movements of blades which control aerodynamic loads. These bearings have diameters of several meters, their blade-side sealings can face the environment, bending moment loads can cause radial deformation of the bearing rings, and their highly variable operating temperatures can facilitate condensation of water inside them. All of this makes water ingress into the lubricant possible. There is limited public knowledge with regards to the maximum water content for safe operation in this application. This work presents the results of a series of scaled wind turbine time series tests with both 'dry' (no water contamination) and 'wet' (10 mass % demineralized water added) greases. A set of four commercially available greases were tested. The time series were scaled from wind turbine operation and represented a 13.7 h worst-case scenario of operation with small oscillation amplitudes and no longer lubrication runs in between. Three of the greases showed reduced friction and no or limited raceway damage in the wet condition, whereas one showed increased friction and raceway damages. [ABSTRACT FROM AUTHOR]

Concrete linings containing cold joint defects may crack or detach under the aerodynamic fatigue loading generated by high-speed train operation, which posing a serious threat to the normal operation of high-speed trains. However, there is currently no simulation method specifically for fatigue damage of concrete linings containing cold joints. Based on the Roe-Siegmund cycle cohesive force model, a cohesive force fatigue damage elements were developed. A large dataset was constructed through numerical simulation software to build a BP neural network for back-calculated parameter of cohesive force fatigue damage elements. By combining experimental data, fatigue damage parameters corresponding to different pouring interval cold joints were back-calculated. These back-calculated parameters were then incorporated into the numerical model to compare simulation results with experimental results to validate the applicability of cohesive force fatigue damage elements and back propagation neural networks (BP neural network). The research results show that the difference between the fatigue life and fracture process calculated by numerical simulation and experimental data is small, verifying the applicability of the method proposed in this paper. The pouring interval directly affects the initial strength of the cold joint interface and the starting conditions of fatigue damage. The possibility of fatigue damage and fracture of concrete components containing cold joints increases with the increase of pouring interval, while the variability of fatigue life decreases with the increase of pouring interval. Interface strength and thickness are the main factors affecting the possibility of fatigue damage occurrence and the variability of fatigue life. The research results can be used to analyze the damage and cracking status of concrete linings containing cold joints under aerodynamic fatigue loading. [ABSTRACT FROM AUTHOR]

Unmanned Aerial Vehicle (UAV) aerial recovery is a challenging task due to the limited maneuverability of both the transport aircraft and the UAV, making it difficult to establish an effective capture connection in the airflow field. In previous studies, we proposed using a Cable-Driven Parallel Robot (CDPR) for active interception and recovery of UAVs. However, during the aerial recovery process, the CDPR is continuously subjected to aerodynamic loads, which significantly affect the stiffness characteristics of the CDPR. This paper conducts a stiffness analysis of a single cable and a CDPR in a flow field environment. Firstly, we derive the stiffness matrix of a single cable based on a model that considers aerodynamic loads. The CDPR is then divided into elements using the finite element method (FEM), and the stiffness matrix for each element is obtained. These element stiffness matrices are assembled to form the stiffness matrix of the CDPR system. Secondly, we analyze the stiffness distribution of a single cable at various equilibrium positions within a flow field environment. Aerodynamic loads were observed to alter the equilibrium position of the cable, thereby impacting its stiffness. The more the cable bends, the greater the reduction in its stiffness. We examine the stiffness distribution characteristics of the CDPR's end-effector within its workspace and analyze the impact of varying flow velocities and different cable materials on the system's stiffness. This research offers a methodology for analyzing the stiffness of CDPR systems operating in a flow field environment. [ABSTRACT FROM AUTHOR]

This study investigated the aerodynamic behavior and structural responses of prismatic and tapered high-rise buildings under extreme wind conditions, focusing on peak wind-induced forces and moments. Using Computational Fluid Dynamics (CFD) simulations with a hybrid RANS/LES approach, the analysis explored the effects of turbulent inflow on the mean pressure coefficients, vortex dynamics, and force coefficients at different wind incidence angles (0°, 30°, and 60°). The results revealed significant differences in peak aerodynamic loads between prismatic and tapered building shapes. The tapered models experienced larger vortex formations and greater suction effects, particularly at two-thirds of the building height, with peak across-wind forces occurring at a 30° wind incidence angle. In contrast, the prismatic model showed the highest peak in along-wind forces and base overturning moments at a 60° wind incidence angle, with Karman vortex shedding and horseshoe vortices prominently captured. The study also highlighted the importance of unsteady inflow conditions in accurately predicting peak dynamic responses, particularly in the wake flow, where vortices significantly influence aerodynamic loads. [ABSTRACT FROM AUTHOR]

In this paper, the numerical approach for the structural assessment of tall ship rigs is presented. It allows investigating complex sailing vessel structural rig layouts, composed of different types of masts (armed with both square and Lateen sails), yards, stays and spreaders. For these types of vessels, Classification Societies do not provide any direct calculation approaches, but only a mere comparison between cross sections and thicknesses with reference values as a function of the mast length. The provided approach can overcome this lack and it is based on considerations and calculations of real aerodynamic forces and the experimental evaluation of the pretension load of stays and shrouds. The herein proposed approach is very practical and can be adopted as a reference for this type of vessel, also with different mast configurations. [ABSTRACT FROM AUTHOR]

This paper focuses on the active removal of spent upper stages from LEO using de-orbiting devices. It proposes a method of regulating aerodynamic loads on the target during its re-entry by utilizing the features of spatial attitude motion. A mathematical model of the re-entry process is developed, and numerical simulations are conducted, demonstrating that the nature of the attitude motion during the descent influences the load factors and, thus, the breakup altitude. It is shown that the respective de-orbiting devices should control both the initial tumbling and spin of the target to achieve different mission outcomes, such as minimizing the debris footprint size or maximizing the breakup altitude. [ABSTRACT FROM AUTHOR]

A time-stepping, lifting-line solution algorithm for the prediction of the unsteady aerodynamics of morphing wings is presented. The velocity induced by the wake vorticity is determined through a free-wake vortex-lattice model, whereas the Küssner and Schwarz's unsteady airfoil theory is used to evaluate the sectional loads, and the generalized aerodynamic loads related to body deformation including camber morphing. The wake vorticity released at the trailing edge derives from the bound circulation and is convected downstream as a vortex ring to form the vortex-lattice wake structure. The local bound circulation is obtained by the application of the Kutta–Joukowski theorem extended to unsteady flows. The accuracy of the loads predicted by the proposed solver is assessed by comparison with the predictions obtained by a three-dimensional boundary-element-method solver for potential flows. The two sets of results agree very well for a wide range of reduced frequencies. [ABSTRACT FROM AUTHOR]

The coupling between a transonic buffeting flow and a supercritical airfoil with harmonic heave motion was studied. A parametric space of the heave frequency and amplitude was investigated using a verified fluid–structural interaction framework. The spatial-temporal flow pattern around the transonic airfoil was studied using dynamic mode decomposition (DMD) to unveil the physical coupling mechanism. The results show three types of flow responses under the heave motion: (I) A buffet frequency response with a λ -shape shock wave structure and recirculation zone at the shock foot. The aerodynamic performance was alike the scenario in the flow past the stationary airfoil. (II) A transitional response with a weakened shock and enhanced boundary layer. The aerodynamic performance deteriorated sharply at f = f buffet and recovered after the frequency was past the buffet frequency. The flow pattern was characterized by a double-shock structure that interacted with the enhanced boundary layer. (III) A heave frequency response with the dominant heave motion. The variance in the aerodynamic loading increased significantly at f > f buffet and there were higher heave amplitudes in this stage. The driving motion of the airfoil transferred the energy of the buffet mode to the boundary layer with a more even energy balance according to the energy contribution analysis of the DMD modes. [ABSTRACT FROM AUTHOR]