Inflatable Membrane Structure Research Articles

Computational method for in-situ finite element modeling of inflatable membrane structures based on geometrical shape measurement using photogrammetry

Inflatable membrane structures with the advantages of light weight, large span, long duration and aesthetical appearance have gained considerable attentions from buildings, super-pressure balloons, airships and deployable antennas. This paper presents a novel computational method for in-situ finite element modeling of inflatable membrane structures based on geometrical shape measurement using photogrammetry for further structural analysis. Firstly, kinematic equations of membrane link structure simplified from the measured inflatable membrane structure are established on force equilibrium between membrane internal and external forces to calculate the tensile forces. Then, computational method for solving zero-stress state is proposed through unloading internal pressure based on equilibrium matrix theory. Finally, true finite element model is established through numerical simulation of reloading internal pressure with considering the zero-stress state as initial model. For verifying purpose, inflated forming and normal working tests of an ethylene-tetrafluoroethylene (ETFE) air-inflated cushion structure were carried out. By comparing geometrical shapes and stress distributions of ETFE cushion between numerical and experimental results, good agreements with 0.72% and 4.76% maximum errors are acquired. These findings strongly confirm the need of in-situ finite element modeling of inflatable membrane structures undergoing long-term service and provide an effective computational method for further structural analysis.

Dynamic geometrical shape measurement and structural analysis of inflatable membrane structures using a low-cost three-camera system

Abstract Inflatable membrane structures have gained considerable popularity in recent years owing to the advantages of light weight, beautiful surface and durability. This paper concerns the dynamic geometrical shape in-situ measurement and structural analysis of inflatable membrane structures using a low-cost three-camera system. The measurement system was developed based on three-dimensional (3D) digital photogrammetry. In order to acquire the high-quality measurement results, accuracy influence factors of the system were evaluated. Based on these considerations, dynamic geometrical shapes of inflatable membrane structures can be real-timely measured through the data processing which is used to determine the 3D coordinates of the target points pasted on membrane surfaces from the two-dimensional (2D) photographs captured by three cameras. Following the in-situ measurement of geometrical shape, the stress distributions of inflatable membrane structures can be determined based on the force equilibriums of membrane surfaces between the in-plane forces and out-of-plane loads. For verifying the proposed method, a selected ethylene-tetrafluoroethylene (ETFE) inflated cushion structure model was manufactured and employed for the experimental study of pre-inflated forming and normal working. By carefully analyzing and comparing the experimental results, it is observed that the measurement accuracy was better than 1/11000. More importantly, the geometrical shape of ETFE cushion still deformed with +5.81% difference during the normal working process of 6 months, resulting in that the maximum stress decreased with −3.49% difference. In general, this paper could provide an efficient and accurate method to measure the dynamic geometrical shapes of inflatable membrane structures, which is the basic information for the further structural analysis.

An automatic system for pressure control and load simulation of inflatable membrane structure

Abstract Inflatable membrane structure employs flexible membranes as main constructive materials, as well as pressurized gas in the membrane envelope aiming to provide the bearing capacity and structural integrity. Therefore, the internal pressure control and load simulation method are very significant to estimate the structural behavior of inflatable membrane structure. This paper presents an automatic system for pressure control and load simulation of inflatable membrane structure, including a pressure control subsystem and a load simulation subsystem. For pressure control, internal pressure of inflatable membrane structure is controlled by switching the high-speed on/off valves which connect air compressor to the structure. For load simulation, wind pressure and wind suck loads, acting on membrane surface in the normal direction, are simulated by controlling the solenoid valves to allow the vacuum pumps to inflate air into or pump air out from the load simulation chamber which is closely connected to inflatable membrane structure with an airtight space. More importantly, the coupling control of two subsystems can be automatically carried out to simulate the inflatable membrane structure under resisting the varied wind loads. These above actions are automatically performed based on the control logic coded in software module. In order to estimate the proposed automatic system, the internal pressure control, load simulation and coupling control tests were performed on a square double-layer ETFE (ethylene tetrafluoroethylene) cushion model. Control performance and accuracy of the proposed system are proved by analyzing the measured pressures. It is thus demonstrated that the proposed automatic system is considerably automatic, accurate, efficient and reliable for pressure control and load simulation of inflatable membrane structures.

A triaxial tensile machine for three-dimensional membrane components: Experimental investigations and numerical simulations

The use of fabric materials for inflated membrane structures has attracted considerable attention in recent decades due to light weight, high strength-to-weight ratio and excellent environmental stability. The load curtain of the catenary system for stratospheric membrane structures is a typical three-dimensional component with complex stress state, meaning that existing uniaxial and biaxial machines are not suitable to identify essential mechanical properties of this component. This paper focuses on the development of a new triaxial tensile machine and evaluation of mechanical properties of a three-dimensional load curtain component. The triaxial tensile machine with specific configurations could independently control five loads (X+/X-, Y+/Y- and Z). A series of cyclic experiments are carried out in terms of in-plane and out-of-plane angle combination.It is found that experimental observations in the first cycle and subsequent cycles are distinctly different for three-dimensional membrane components. The force reduction in the first cycle is caused by plastic deformation during loading-unloading process. The stress state in subsequent cycles is approximately elastic due to the elimination of plastic deformation in the first cycle, indicating that cyclic experiments are suitable for identifying stable mechanical properties. The force differences between X+ and X- directions are related to stiffness difference between warp and weft directions. Moreover, the effects of Z force could result in asymmetrical X and Y forces, especially for small out-of-plane angle. Furthermore, a numerical model is developed for comparing with experimental results. The X and Y forces in terms of loading and unloading are in good agreement with experimental results, which could justify numerical methods.

In Situ Determination of Stress Distribution of Inflatable Membrane Structure Using Force Finding Method

AbstractStress distribution on a membrane surface plays a key role in the structural safety and bearing capacity of an inflatable membrane structure, especially for the state under service conditio...

Effects of on-axis and off-axis tension on uniaxial mechanical properties of plain woven fabrics for inflated structures

The use of enhanced plain woven fabrics for aerospace engineering needs essential and accurate mechanical parameters for analyzing structural behavior and performing numerical simulations. The uniaxial tensile tests are direct and effective approaches to investigate these mechanical properties. This study focused on uniaxial monotonic and cyclic mechanical properties of an enhanced plain woven fabrics URETEK 5893 in on-axis and off-axis tension. For uniaxial monotonic mechanical properties, an improved method to determine yield stress was proposed and digital image correlation (DIC) technique was utilized to investigate detailed breaking mechanism. It is found that yield stresses were stable in each loading direction and typical yield stresses in the warp, weft and 45° directions were 5.56MPa, 8.84MPa and 1.96MPa, respectively. Moreover, the breaking mechanism in terms of strain propagation process was identified. For cyclic mechanical properties, approximate stable ratcheting strain and elastic modulus were investigated. Nonlinear ratcheting strain was more sensitive near 45° than other directions. Moreover, Poisson ratios in three directions were obtained with DIC technique and the maximum Poisson ratio existed in the 45° direction. The comparisons between experimental and theoretical elastic moduli showed that the best agreement existed in the warp and weft directions and the accuracy of using the theoretical equation to calculate elastic modulus was dependent on material linearity.In general, this study could provide basic observations and useful values for understanding mechanical properties of plain woven fabrics in use for inflated membrane structures.

Modal behaviors and influencing factors analysis of inflated membrane structures

Accurate modal analysis is the basis to evaluate the dynamic performance of inflated membrane structures, however, it is still a challenge to analyze and testify due to strong nonlinearity of geometry deformation, initial stress and the air-elastic effects. This paper presents modal characteristics of inflated beam and flexible airship envelope. Firstly, an approach to numerically simulate modal behaviors of a plane membrane in the air was validated by testing natural vibration behaviors of plane membranes. This was followed with modal analysis of inflated tube in experimental and numerical methods. The influencing factors for the modal performance of the inflated tube were estimated in terms of boundary condition, internal pressure, elastic modulus and air. Based on this outcome, the verified simulation method was employed to investigate the natural vibration behaviors of flexible airship including dry and wet modal analysis. Thirdly, pressure difference, geometric dimension, welding seam were considered as influencing factors to study their effects on modal characteristics of non-rigid airship hull. Lastly, modal analysis of airship with suspended curtain in self-equilibrium configuration and self-weight and buoyancy was to investigate close practical engineering structural behavior of large airship.

An innovative methodology for measurement of stress distribution of inflatable membrane structures

The inflatable membrane structure has been widely used in the fields of civil building, industrial building, airship, super pressure balloon and spacecraft. It is important to measure the stress distribution of the inflatable membrane structure because it influences the safety of the structural design. This paper presents an innovative methodology for the measurement and determination of the stress distribution of the inflatable membrane structure under different internal pressures, combining photogrammetry and the force-finding method. The shape of the inflatable membrane structure is maintained by the use of pressurized air, and the internal pressure is controlled and measured by means of an automatic pressure control system. The 3D coordinates of the marking points pasted on the membrane surface are acquired by three photographs captured from three cameras based on photogrammetry. After digitizing the markings on the photographs, the 3D curved surfaces are rebuilt. The continuous membrane surfaces are discretized into quadrilateral mesh and simulated by membrane links to calculate the stress distributions using the force-finding method. The internal pressure is simplified to the external node forces in the normal direction according to the contributory area of the node. Once the geometry x, the external force r and the topology C are obtained, the unknown force densities q in each link can be determined. Therefore, the stress distributions of the inflatable membrane structure can be calculated, combining the linear adjustment theory and the force density method based on the force equilibrium of inflated internal pressure and membrane internal force without considering the mechanical properties of the constitutive material. As the use of the inflatable membrane structure is attractive in the field of civil building, an ethylene-tetrafluoroethylene (ETFE) cushion is used with the measurement model to validate the proposed methodology. The comparisons between the obtained results and numerical simulation for the inflation process of the ETFE cushion are performed, and the strong agreements demonstrate that the proposed methodology is feasible and accurate.

On the Static and Dynamic Contact Problem of an Inflated Spherical Viscoelastic Membrane

Inflated membrane structures, useful in vibration/shock isolation devices, terrestrial and space structures, etc., rely on the internal dissipation in the membrane for vibration attenuation. In this work, using the Christensen viscoelastic material model, we study the contact mechanics, displacement-controlled relaxation response, force-controlled creep response, dynamic contact, and energy dissipation due to oscillatory contact in an inflated spherical nonlinear viscoelastic membrane. We consider an inflated spherical membrane squeezed between two large rigid, frictionless, parallel plates. The effective stiffness and damping in the membrane–plate assembly are determined, and a phenomenological model is developed. Under oscillatory contact condition, the energy dissipation per cycle is determined. Further, using the free-vibration test, the damped natural frequency of the membrane–plate system is calculated.

Analysis of joint peeling in an inflated flat toroidal membrane

An inflatable membrane structure with a flat toroidal geometry is formed from a stack of two identical flat annular membranes bonded together at the inner and outer boundaries (equators). The analysis of peeling/debonding at the joints of such a membrane structure subjected to finite inflation under a uniform internal pressure is considered. Homogeneous and isotropic Mooney–Rivlin and Gent solid models are used for the membrane material. Two different peeling conditions are considered, namely constant pressure peeling and constant amount of gas peeling. It is observed that the inner equator of the torus is more likely to debond than the outer equator for both the peeling conditions. The geometry of the torus in terms of the ratio of the undeformed inner and outer equatorial radii is found to influence the energy release rate. The stability of the debonding process is also checked by calculating the rate of change of the energy release rate during peeling.

Dynamic deflation assessment of an air inflated membrane structure

As a critical safety performance index, the emergency evacuation capacity of air inflated membrane structures subjected to accidental deflation deserves in-depth study. Although conventional static analysis can be applied to predict its potential collapsed shapes, it cannot provide details of collapse behavior and the internal air state variation. Dynamic analysis is recommended. The focus of this paper is to apply the Control Volume method to deflation simulation of a large-scale air inflated arch frame, which is designed for a temporary pavilion, and to validate numerical analysis results by full-scale testing. Through a series of preliminary studies on air inflated single arches, practical analytical parameters and solutions are concluded regarding proper numerical modeling, pre-stressing, and precision controlling. A full-scale frame is then modeled and simulated. Results appear to agree with experimental tests of the corresponding real-life structure with minor differences in collapse behavior and deflation duration time. Several general guidelines for design and deflation simulation analysis are proposed as a result of research. Feasible measures to ensure emergency evacuation capacity of the air inflated arch frame are adopted in the design based on results of this dynamic assessment.

Vibration characteristic analysis and experiment of non-rigid airship with suspended curtain

In order to evaluate the vibration characteristics of non-rigid airship with suspended curtain, we introduce vibration characteristic analysis method of the inflatable membrane structure. Modal numerical method of the inflatable membrane structure under the pressure difference is validated by the model testing of the inflatable cantilever tube. The finite element model of 75m airships is established to simulate the vibration characteristics subjected to only pressure difference and the resultant force of weight and buoyancy. The nonlinear static deformation and stress analysis are investigated for two kinds of equilibrated configurations with various pressure differences, as well as the vibration characteristics. The structural efficiency of the suspended curtain is investigated through the force transfer ratio at the assumed equilibrated point. The effects of manufacture error of the suspended cable length on the structural behavior are analyzed. The results indicate that the local area of airship envelope connected to the suspended cable is a weak part. Various pressures and pressure gradients have significant effects on the global airship structure and the suspended curtain. The suspended curtain is effective to transfer the equilibrated force from the bottom to the top of airship envelope. Manufacture error of the suspended cable length could result in obvious deformation of local airship envelope. The presented work is valuable to the structural engineering design of stratospheric airship.

Effective Coulomb force modeling for spacecraft in Earth orbit plasmas

Coulomb formation flight is a concept that utilizes electrostatic forces to control the separations of close proximity spacecraft. The Coulomb force between charged bodies is a product of their size, separation, potential and interaction with the local plasma environment. A fast and accurate analytic method of capturing the interaction of a charged body in a plasma is shown. The Debye–Hückel analytic model of the electrostatic field about a charged sphere in a plasma is expanded to analytically compute the forces. This model is fitted to numerical simulations with representative geosynchronous and low Earth orbit (GEO and LEO) plasma environments using an effective Debye length. This effective Debye length, which more accurately captures the charge partial shielding, can be up to 7 times larger at GEO, and as great as 100 times larger at LEO. The force between a sphere and point charge is accurately captured with the effective Debye length, as opposed to the electron Debye length solutions that have errors exceeding 50%. One notable finding is that the effective Debye lengths in LEO plasmas about a charged body are increased from centimeters to meters. This is a promising outcome, as the reduced shielding at increased potentials provides sufficient force levels for operating the electrostatically inflated membrane structures concept at these dense plasma altitudes.

Finite element analysis of deployable space structures

This paper presents the stress analysis for predicating the behavior of flat thin inflatable membrane structure in MATLAB. This is having square shaped with a thickness in millimeter fabricated using the various smart materials. Within structural member, it is subjected to pre-stress rather than bending or moments. The deployable structure has the low weight (minimal mass to achieve high acceleration); large area & durable (easily withstand the temperature changes, micrometeoroid hazards in outer space). The objective of this paper is to optimize the smart material for the space satellite technology so that the light weight inflatable structure attracts in satellite application. The observations show the good agreement of finite element results.

Free Vibration Analysis of Inflatable Space Structure

This paper present the modal analysis for the predicating the behavior of inflatable membrane structure of general square shape with a thickness in millimeter using the various smart material which optimally within structural member subjected to edge- constrained rather than applying bending or moments. A numerical solution for membranes may also be found using the finite element method. In this paper flat thin membrane choose to analysis the behavioral effect of the multi-layered membranes using the properties of different smart material and compare their results in terms of frequency and out plane deflection with mode shape. This analysis makes more effective to select the smart materials in the space technology. Vibration analysis of arbitrary square shape membrane is also done using a finite element package, ANSYS APDL. The analysis shows good agreement in finite element solutions. Keywords: Boundary condition, finite element, material property, membrane, mode shape, natural frequency, out plane displacement. I. Introduction In the field of Engineering and Architecture, membrane structures play a vital role in many ways. Examples include textile covers and roofs, aircraft and space structures, parachutes, automobile airbags, sails, windmills, human tissues and long span structures. They are typically built with very light materials which are optimally used. These structures are characterized because they are only subjected to in-plane axial forces. Even in the field of architectures and civil engineering, both pre-stressed membranes and cable networks constitute a very remarkable group. A membrane is essentially a thin shell with no flexural stiffness. Consequently a membrane cannot resist any compression at all. However, membrane theory accounts for tension and compression stresses, and the need for a computational procedure that takes into account tension stresses only is needed. In membrane theory only the in-plane stress resultants are taken into account. A numerical solution for membranes may be found using the finite element method (1-3). The deployable space structures consist of thin polymer films that offer a wider range of packaging configurations than structures with traditional deployment mechanisms. Due to the flexibility of such deployable structure like shell or membrane shows greater importance for space application and hold great promise. The material constitutive behavior and the analytical tools to analyze them are required to make advances in building cheaper, lighter and more reliable structures. Many structures are in the developing stage and the materials that are meant to serve to make these applications possible are not yet within reach. Future missions depend much on new discoveries, mainly in material manufacturing. There are several different space applications in which the use of thin membrane structures are used or being considered. Due to their light weight, high strength-to-weight ratio and ease of stowing and deploying, membranes are especially attractive for space applications. Inflatable reflectors, space-based radar, space based communication systems such as antennae and solar power collection panels on spacecraft, etc are the examples included. (4-5). The membrane material used in the numerical analysis was assumed inextensible and its weight was neglected in the determination of the equilibrium shape. They found that the membrane's mass density is of little influence on the computed natural frequencies. Other researchers used finite elements and boundary elements to model and compute natural frequencies and mode shapes of a single-anchor inflatable dam (6). This study makes impact on finding the vibration aspect on the flat membrane using the various smart materials. The pressure in an inflatable structure can also play a critical role in the suppression of vibration (7). Literature that exists on pure structural membrane components has concentrated mostly on inflated components such as beams (8), torus (Main), and inflated lenticular concentrators (9). The dynamics of the membrane themselves are of great interest though, as it is the membrane itself that is performing the useful work, and in some applications they could be attached to more traditional aerospace structures. Therefore improving understanding the behavior of the membranes appears to be important. A membrane is essentially a thin shell with no flexural stiffness. Consequently a membrane cannot resist any Compression at all. However, membrane theory accounts for tension and compression stresses. In membrane theory only the in-plane stress resultants are taken into account (10). This paper present the modal analysis for the predicating the behavior of various inflatable membrane structure of general square shape with a thickness in millimeter using the various smart materials. A numerical solution for membranes may be found using the finite element method. Finite element analysis of membrane structures for small deformations can be found in (11) but

A01 気体内圧を受けるインフレータブル膜構造の三次元形状計測(宇宙構造物(1))

This report deals with deflection measurement of a inflatable membrane structure subjected to internal pressure loading. Conventionally, we have performed deflection measurement of the structure using laser displacement sensor. Lately, we introduced Kuraves which is a three-dimensional photo-grammetric system. To show the effect of the photo-grammetric system, the results is compared with using laser displacement sensor.

Panel method predictions of added mass for flexible airship

AbstractBecause of the huge volume and inflated membrane structure of stratosphere airship, the deformation of stratosphere airship is very sensitive to the change of environment conditions such as wind, temperature and so on. The influence of deformation on manipulation and control is very remarkable. So, during the course of building flight dynamic model of the flexible airship, the added-mass matrix of deformation is very important part in the state equations of dynamic models. For obtaining the accurate added-mass matrix of different flexible airship, we proposed an approach that can calculate the added-mass matrix of a flexible airship with arbitrary geometry shape by the panel method. Through the comparison of results of computation and theory for ellipsoid of revolution and the flexible Skyship-500 airship, the proposed method can calculate the added-mass matrix for arbitrary geometric shape very accurately.

Electrostatically inflated gossamer space structure voltage requirements due to orbital perturbations

This paper explores the concept of using electrostatic forces for deployment of gossamer space structures. The Electrostatically Inflated Membrane Structure (EIMS) uses two conducting membranes that are interconnected through membrane ribs. An absolute electrostatic charge is applied to the structure through active charge emission. This causes repulsion between layers of lightweight membranes that inflates the EIMS system and tensions the membranes. Assuming positive tensions, the EIMS system is modeled as a rigid system. Typical orbital perturbations are considered such as solar radiation pressure, differential gravity, and atmospheric drag which may compress the structure leading to shape destabilization. Restricting the analysis in this paper to flat membranes, the minimum potentials required to exactly compensate for the worst case scenario of differential solar radiation pressure at geostationary altitudes are estimated to be on the order of hundreds of volts. In low Earth orbit, voltage magnitudes of several kilovolts are required to reach an inflation pressure to offset the normal compressive drag pressure.

Instability of hyper-elastic balloon-shaped space membranes under pressure loads

This paper discusses the evaluation of quasi-static equilibrium solutions for inflatable space membrane structures. A Mooney–Rivlin hyper-elastic material model, with variable constitutive constants, is considered. A compressible weightless medium is used to introduce within the membrane a one-parametric over-pressure loading compared to an ambient pressure. Analytical instability results are shown for a spherical and derived for a cylindrical case. These are compared to numerical simulations based on a flat linearly interpolated triangular space membrane element. Path-following procedures are used to find generalized equilibrium paths, with different parameterizations. Numerical examples show that the methods developed can give information on the stability of the membranes, but that the medium and means for introducing the internal pressure are of importance for the interpretation of stability.

Development of Energy Saving Greenhouse by Air Inflated Membrane Structure

Development of Energy Saving Greenhouse by Air Inflated Membrane Structure