Simple and efficient numerical tools for the analysis of parachutes

Abstract

Purpose -The purpose of this paper is to describe a set of simple yet effective, numerical method for the design and evaluation of parachute-payload system. The developments include a coupled fluidstructural solver for unsteady simulations of ram-air type parachutes. The main features of the computational tools are described and several numerical examples are provided to illustrate the performance and capabilities of the technique. Design/methodology/approach -For an efficient solution of the aerodynamic problem, an unsteady panel method has been chosen exploiting the fact that large areas of separated flow are not expected under nominal flight conditions of ram-air parachutes. A dynamic explicit finite element solver is used for the structure. This approach yields a robust solution even when highly nonlinear effects due to large displacements and material response are present. The numerical results show considerable accuracy and robustness. Findings -A simple and effective numerical tool for the analysis of parachutes has been developed. Originality/value -An analysis code has been developed which addresses the needs of ram-air parachute designers. The software delivers reasonably accurate results in a short time using modest hardware. It can therefore assist the design process, which nowadays relies on empirical methods. IntroductionThe numerical simulation of parachutes is a challenging coupled problem. From the structural point of view, parachutes are complex in design and behaviour. Braced membranes, such as parachute canopies, cannot equilibrate an arbitrary set of loads unless drastic geometrical changes take place; thus, the structural response is extremely nonlinear. The lack of bending stiffness of the structural components makes them buckle (wrinkle) under compressive loads, exhibiting an asymmetric behaviour. Moreover, the interaction and contact between the different structural elements often has to be accounted for in order to properly model the problem. The flow surrounding the parachute is also complex and highly unsteady in some flight stages of the parachutes (e.g. deployment and inflation). The aerodynamic model adopted should also account for massive flow separation, the presence of large unsteady wakes and aerodynamic interactions between the structural components. The nature of the applied forces, which depend heavily on the structural response of the parachute, adds an extra layer of complexity to the analysis. As the magnitude and direction of the aerodynamic forces (mainly follower pressure loads) are not known in advance but

Aeroelastic analysis of parachute deceleration systems with empirical aerodynamics

“…Rayleigh damping factor (user input) and b1  0.06 [33]. The low-frequency mas damping term is calculated at each node by…”

“…The FE model employed in this work is described in detail in [33]. The formulation derives from the principle of virtual work.…”

“…The matrix C includes Rayleigh damping (which is a linear combination of the mass and stiffness matrices CRay = αM+βK) and bulk viscosity to control high-frequency noise in the solution. Further details of the FE model can be found in [33,34].…”

“…For the undamped case and ignoring the effect of Poisson's ratio, ∆t min l /c , where l is the edge length and c the material's dilatational wave speed. More details on the effects of damping and material properties are available in [33,34].…”

Ram-Air Parachute Simulation with Panel Methods and Staggered Coupling

“…T computational cost in many practical parachute problems; recent applications can be found in [9][10][11]. A step forward in fidelity and scope has been achieved with methods involving the solution of the Navier-Stokes equations with full discretization of the surrounding flow.…”