Search Results (82)

This study uses the CREATE^TM-AV/Kestrel simulation software to model a towed jumper scenario using standard aircraft settings to quantify paratrooper stability and risk of contact during static line airborne operations. The focus areas of this study include a review of the technical build-up, which includes aircraft, paratrooper and static line modeling, plus preliminary functional checkouts executed to verify simulation performance. This research and simulation development effort is driven by the need to meet the analysis demands required to support the US Army Personnel Airdrop with static line length studies and the North Atlantic Treaty Organization (NATO) Joint Airdrop Capability Syndicate (JACS) with airdrop interoperability assessments. Each project requires the use of various aircraft types, static line lengths and exit procedures. To help meet this need and establish a baseline proof of concept (POC) simulation, simulation setups were developed for a towed jumper from both the C-130J and C-17 using a 20-ft static line to support US Army Personnel Airdrop efforts. Concurrently, the JACS is requesting analysis to support interoperability testing to help qualify the T-11 parachute from an Airbus A400M Atlas aircraft, operated by NATO nations. Due to the lack of an available A400M geometry, the C-17 was used to demonstrate the POC, and plans to substitute the geometry are in order when it becomes available. The results of a nominal Computational Fluid Dynamics (CFD) simulation run using a C-17 and C-130J will be reviewed with a sample of the output to help characterize performance differences for the aircraft settings selected. The US Army Combat Capabilities Development Command Soldier Center (DEVCOM-SC) Aerial Delivery Division (ADD) has partnered with the US Air Force Academy (USAFA) High Performance Computing Research Center (HPCRC) to enable Modeling and Simulation (M&S) capabilities that support the Warfighter and NATO airdrop interoperability efforts. Full article

As an essential technology for precision airdrop missions, parafoil systems have gained widespread adoption in military and civilian applications due to their superior glide performance and maneuverability compared to conventional parachutes. Addressing the trajectory-tracking control challenges of the parafoil system under significant wind disturbances, characterized by wind uncertainty and system underactuation, this paper proposes a stochastic model predictive control (SMPC) framework based on Markov-based multi-scenario optimization. Traditional deterministic model predictive control (MPC) methods often exhibit excessive conservatism due to reliance on worst-case assumptions and fail to capture the time-varying nature of real-world wind fields. To address these limitations, a high-fidelity dynamic model is developed to accurately characterize aerodynamic coupling effects, overcoming the oversimplifications of conventional three-degree-of-freedom point-mass models. Leveraging Markov state transitions, multiple wind-disturbance scenarios are dynamically generated, effectively overcoming the limitations of independent and identically distributed hypotheses in modeling realistic wind variations. A probabilistic constraint-reconstruction strategy combined with a rolling time-domain covariance update mechanism mitigates uncertainties and enables cooperative optimization of inner-loop attitude stabilization and outer-loop trajectory tracking. The simulation results demonstrate that the SMPC framework achieves superior comprehensive performance compared to deterministic MPC, evidenced by significant reductions in maximum position error, average position error, and control effort variation rate, along with a 94% tracking success rate. By balancing robustness, tracking precision, and computational efficiency, the method provides a theoretical foundation and a promising simulation-validated solution for airdrop missions. Full article

With the wide application of airdrop technology in rescue activities in civil and aerospace fields, the importance of accurate airdrop is increasing. This work comprehensively analyzes the interactive mechanisms among multiple models affecting airdrops, including wind field distribution, drag force effect, and the parachute opening process. By integrating key parameters across various dimensions of these models, a multidimensional parameter dynamic evolution (MPDE) target prediction method for aerial delivery parachutes in radar-detected wind fields is proposed, and the Runge–Kutta method is applied to dynamically solve for the final landing point of the target. In order to verify the performance of the method, this work carries out field airdrop experiments based on the radar-measured meteorological data. To evaluate the impact of model input errors on prediction methods, this work analyzes the influence mechanism of the wind field detection error on the airdrop prediction method via the Relative Gain Array (RGA) and verifies the analytical results using the numerical simulation method. The experimental results indicate that the optimized MPDE method exhibits higher accuracy than the widely used linear airdrop target prediction method, with the accuracy improved by 52.03%. Additionally, under wind field detection errors, the linear prediction method demonstrates stronger robustness. The airdrop error shows a trigonometric relationship with the angle between the synthetic wind direction and the heading, and the phase of the function will shift according to the difference in errors. The sensitivity of the MPDE method to wind field errors is positively correlated with the size of its object parachute area. Full article

Objective: To present an innovative endoscopic method, the “Parachute Technique,” for effectively closing recurrent oronasal fistulas in cleft palate patients using autologous tissue. Summary Background Data: Oronasal fistulas are common complications after cleft palate repair, often leading to impaired quality of life due to difficulties with speech, eating, and an increased risk of infections. Current surgical methods exhibit high recurrence rates, especially in cases involving significant scarring or large defects. Therefore, there is a need for new techniques that improve outcomes and reduce recurrence. Methods: The study introduced the “Parachute Technique,” which uses autologous tissue from the inferior nasal turbinate to create a mucosal flap. This flap is transposed through the fistula using a guidewire under endoscopic guidance. The endoscopic approach minimized trauma to the surrounding tissues and allowed for precise manipulation during the procedure. Results: The “Parachute Technique” successfully closed recurrent oronasal fistulas, particularly in cases where conventional surgical methods had failed. The use of autologous tissue reduced the immunological risks, while the minimally invasive nature of the endoscopic procedure decreased the postoperative morbidity and improved the healing outcomes. Conclusions: The “Parachute Technique” offers a promising alternative for the treatment of recurrent oronasal fistulas in cleft palate patients, providing a minimally invasive, effective solution that can be easily adopted by specialists across multiple surgical disciplines. Full article

Traditional aerostat deployment systems within the Earth’s atmosphere face various limitations, such as high risk and lengthy deployment times. In contrast, rapid-deployment aerostat systems have the advantage of high efficiency and flexibility. To improve the deceleration and stability performance, a dynamic model of the parachute and dynamic and thermodynamic models of the aerostat are established in this work. The impact of different parachute radii, rise–radius ratios (h_p/R_p), and filling-time coefficients during the deceleration and inflation process is investigated in detail. Additionally, the comparative analysis of different aerostats is discussed. The results show that the radius and h_p/R_p of the parachute mainly affect its deceleration ability, while the filling-time coefficient affects the dynamic load. For radii of balloons exceeding 8 m, increasing the parachute radius cannot enable deployment above 10,000 m. As the radius of the balloon increases, a larger filling-time coefficient is required. A parachute with h_p/R_p = 0.8 is recommended for a balloon with a radius below 6.5 m, and h_p/R_p = 0.6 is recommended for a radius over 6.5 m. These findings provide valuable references for rapid-deployment aerostat systems. Full article

This article presents a novel experimental method of calculation of kinematic viscosity parameter for rarefied/low-density air using the analysis of optically recorded oscillations of the stratospheric balloon mission parachute’s canopy. The parachute behavior was captured by a high-definition optical device in the stratosphere during the re-entry phase, giving the input data for the Roshko and Reynolds numbers, which were used in an adapted formula to determine the kinematic viscosity. The calculated parameter was compared with laboratory literature data, showing good alignment, with any sources of discrepancies indicated and discussed. The canopy-breathing method of determination of kinematic viscosity in rarefied air can be employed for the easy investigation of real atmospheric parameters, helpful in the analysis of atmospheric and ionospheric mass flows and the design and performance verification of various novel types of parachutes and re-entry devices. Full article

Weather balloons are a popular tool to obtain atmospheric data. One of the biggest advantages of using this type of vehicle for scientific research is their inexpensiveness, as they are only composed of an inflated envelope, a parachute, and a sonde. However, their flight is dependent on the atmospheric conditions, and their life cycle is short. Thus, altitude control for weather balloons, along with trajectory planning, is a major area of interest, as it would allow one to mitigate the disadvantages while maintaining the benefits. This article presents a novel, efficient, lightweight, and cost-effective framework for weather balloon control and path planning. The proposed solution integrates a P-D cascade controller for altitude control, adapted specifically to the dynamics and actuation constraints of weather balloons, with a wind-based trajectory planner built on the A* algorithm. To the best of the authors’ knowledge, this planner is the first to incorporate wind constraints in a grid-based search tailored for weather balloon navigation. By commanding the ballast release for ascent and helium venting for descent, the developed control solution proves efficient and robust in simulation, guiding the balloon to reach defined goals while traveling through predetermined waypoints. However, it demonstrates limitations in maintaining the balloon over a fixed area. Full article

This paper presents an offline optimal trajectory planning method for powered parachutes (PPCs) using dynamic model simulations, emphasizing their potential in applications such as remote sensing and aerial delivery systems. A six-degrees-of-freedom (6-DOF) dynamic model of the PPC is developed, complemented by a novel optimization technique called Incremented Genetic Algorithms (IGA). IGA improve the computational efficiency by dynamically increasing the number of variables only when optimization goals are unmet, eliminating the need to predefine input variable counts. This approach significantly reduces the computational time and CPU usage while maintaining cost-effectiveness for 3D trajectory planning. The proposed method was validated on three trajectories under diverse constraints, including the time, position, and predefined obstacles. The results demonstrate that IGA can effectively generate optimal trajectories using a single control parameter (the parachute steering angle) and a minimal number of control points, showcasing its practicality and efficiency. Full article

The use of polyester and polyamide fabrics for parachute constructions has a great advantage because, in comparison with classical silk-based parachutes, they are more durable and suitable for absorbing higher mechanical shocks. Because polyester and polyamides are thermoplastics, they are sensitive to sudden increases in temperature due to mechanical shocks and high-speed friction. It is known that the local surface temperature of these parachute fabrics may exceed the melting point of the canopy for a short time period during parachute opening, which would have irreversible effects on parachute functionality and could lead to catastrophic parachute rupture. The main aim of this article is to enhance the surface heat resistance of the parachute fabrics from polyamide and polyester filaments through surface coating combined with super-fine TiO₂ particles and silanization. This coating is also selected to increase the frictional heat loss and enhance the mechanical stability of parachute fabrics constructed from polyamide and polyester filaments. The changes in air permeability, bending rigidity, and friction of surface-coated parachute fabrics are evaluated as well. The new method based on laser irradiation by a pulsed laser is used for the prediction of these fabrics’ short-time surface thermal resistance. Full article

During clathrin-mediated endocytosis in yeast cells, a small patch of flat membrane is deformed into a tubular shape. It is generally believed that the tubulation is powered by actin polymerization. However, studies based on quantitative measurement of the actin molecules suggest that they are not sufficient to produce the forces to overcome the high turgor pressure inside of the cell. In this paper, we model the membrane as a viscous 2D fluid with elasticity and study the dynamic membrane deformation powered by a boundary lipid flow under osmotic pressure. We find that in the absence pressure, the lipid flow drives the membrane into a spherical shape or a parachute shape. The shapes over time exhibit self-similarity. The presence of pressure transforms the membrane into a tubular shape that elongates almost linearly with time and the self-similarity between shapes at different times is lost. Furthermore, the width of the tube is found to scale inversely to the cubic root of the pressure, and the tension across the membrane is negative and scales to the cubic root squared of the pressure. Our results demonstrate that boundary flow powered by myosin motors, as a new way to deform the membrane, could be a supplementary mechanism to actin polymerization to drive endocytosis in yeast cells. Full article

The study of vibration equations of large membranes is crucial in various scientific and engineering fields. Analyzing the vibration equations of bridges, roofs, and spacecraft structures helps in designing structures that resist excessive oscillations and potential failures. Aircraft wings, parachutes, and satellite components often behave like large membranes. Understanding their vibration characteristics is essential for stability, efficiency, and durability. Studying large membrane vibration involves solving partial differential equations and eigenvalue problems, contributing to advancements in numerical methods and computational physics. In this paper, the Elzaki transformation decomposition method and the Shehu transformation decomposition method, along with inverse Elzaki and inverse Shehu transformations, are used to investigate the fractional vibration equation of a large membrane. The solutions are obtained in terms of Mittag–Leffler functions. Full article

Parachute suspension lines shed vortices during descent, and these vortices develop oscillating aerodynamic forces that can induce forced parasitic vibrations of the lines, which can have an adverse impact on the parachute system. Understanding the line’s mechanical behavior can assist in studying the vibrations experienced by the suspension lines. A well-calibrated structural model of the suspension line could be used to help to identify how the braid’s architecture contributes to its mechanical behavior and to explore if and how a suspension line can be designed to mitigate these parasitic vibrations. In the current study, a mesomechanical finite element model of a polyester braided parachute suspension line was constructed. The line geometry was built in the Virtual Textile Morphology Suite (VTMS), and a user material model (UMAT) was implemented in LS-DYNA^® release 14 to describe the material behavior of the individual tows. The material properties were initially calibrated using experimental tension tests on individual tows, which exhibited an initial modulus of ~4100 MPa before transitioning to ~3200 MPa at a stress of 30 MPa. When these properties were applied to the full braid model, slight adjustments were made to account for geometric complexities in the braid structure, improving the correlation between the model and experimental tensile tests. The final calibrated model captured the bilinear tensile behavior of the braid, with an initial modulus of 2219 MPa and a secondary modulus of 1350 MPa, compared to experimental values of 2253 MPa and 1420 MPa, respectively, showing 2% and 5% differences. The calibrated model of the braided cord was then subjected to torsion, and the results showed good agreement with dynamic and static experimental torsion tests, with a difference of 8–19% for dynamic tests and 13–27% for static tests when compared to experimental values. The availability of virtual models of suspension lines can ultimately assist in the design of suspension lines that mitigate flow-induced vibration. Full article

The expanding use of civilian unmanned aerial vehicles (UAVs) has brought forth a crucial need to address the safety risks they pose in the event of failure, especially when flying in populated areas. This paper reviews recent advancements in recovery systems designed for the emergency landing of civilian UAVs. It covers a wide range of recovery methods, categorizing them based on different recovery approaches and UAV types, including multirotor and fixed-wing. The study highlights the diversity of recovery strategies, ranging from parachute and airbag systems to software-based methods and hybrid solutions. It emphasizes the importance of considering UAV-specific characteristics and operational environments when selecting appropriate safety systems. Furthermore, by comparing various emergency landing systems, this study reveals that integrating multiple approaches based on the UAV type and mission requirements can achieve broader cover of emergency situations compared to using a single system for a specific scenario. Examples of UAVs that utilize emergency landing systems are also provided. For each recovery system, three key parameters of operating altitude, flight speed and added weight are presented. Researchers and UAV developers can utilize this information to identify a suitable emergency landing method tailored to their mission requirements and available UAVs. Based on the key trends and challenges found in the literature, this review concludes by proposing specific, actionable recommendations. These recommendations are directed towards researchers, UAV developers, and regulatory bodies, and focus on enhancing the safety of civilian UAV operations through the improvement of emergency landing systems. Full article

Background and Objectives: The elbow joint, essential for daily activities, often requires soft tissue reconstruction following trauma, infection, or tumor excision. Free flap surgery using the brachial artery (BA) as the recipient vessel offers stable vascular support, but preserving distal blood flow is crucial. Due to vessel diameter differences, end-to-side (ETS) anastomosis is usually necessary, as flow-through anastomosis can be challenging. Although reports exist on soft tissue reconstruction using the BA as the recipient vessel, complications and outcomes related to using the sole main artery as the recipient remain unclear. We developed the microscopic parachute end-to-side (MPETS) technique, adapted from ETS, to more easily address vessel size discrepancies. This study evaluates the effectiveness and safety of MPETS in BA-based elbow reconstruction, alongside a review of outcomes in other cases. Materials and Methods: We retrospectively analyzed seven cases of elbow reconstruction from April 2018 to September 2023, focusing on patients with BA recipient vessels and a minimum 12-month follow-up. Variables included patient demographics, etiologies, flap types, and postoperative outcomes measured by Jupiter’s Criteria. Following PRISMA 2020 guidelines, a systematic literature review identified similar cases using the BA in free flap reconstruction for comparison. Results: In all our cases, flap survival was 100%, with no distal ischemia observed, and the average range of motion was 119°. Complications were limited, with one reoperation due to venous thrombosis. The MPETS technique minimized blood flow issues and accommodated the BA’s diameter. The literature review included 77 cases, confirming the BA’s viability and stability as a recipient vessel. Conclusions: Using the BA as a recipient vessel with MPETS demonstrates high effectiveness and safety in elbow soft tissue reconstruction. Our results support the BA’s suitability for complex reconstructions, with MPETS enhancing vessel compatibility and reducing complications. Full article

High-fidelity simulations are used to study the stability of a coupled parachute–payload system in different configurations. A 8.53 m ring–slot canopy is attached to two separate International Organization for Standardization (ISO) container payloads representing a Twenty Foot Equivalent (TEU). To minimize risk and as an alternative to a relatively expensive traditional test program, a multi-phase design and evaluation program using computational tools validated for uncoupled parachute system components was completed. The interaction of the payload wake suspended at different locations and orientations below the parachute were investigated to determine stability characteristics for both subsonic and supersonic freestream conditions. The DoD High-Performance Computing Modernization Program CREATE^TM-AV Kestrel suite was used to perform CFD and fluid–structure interaction (FSI) simulations using both delayed detached-eddy simulations (DDES) and implicit Large Eddy Simulations (iLES). After analyzing the subsonic test cases, the simulations were used to predict the coupled system’s response to the supersonic flow field during descent from a high-altitude deployment, with specific focus on the effect of the payload wake on the parachute bow shock. The FSI simulations included structural cable element modeling but did not include aerodynamic modeling of the suspension lines or suspension harness. The simulations accurately captured the turbulent wake of the payload, its coupling to the parachute, and the shock interactions. Findings from these simulations are presented in terms of code validation, system stability, and drag performance during descent. Full article