Inflatable Membrane Structure Research Articles

Fluid-structure interaction in inflatable membrane structures: A featured study of mechanical behavior

This paper presents a comprehensive analysis of fluid-structure interaction (FSI) effects on the behavior of inflatable membrane structures under wind loads, aiming to enhance the understanding of the structural performance. We adopted a mixed-methods approach, incorporating a numerical simulation based on the RNG k-ε turbulence model. The work focused on a semi-cylindrical air-supported membrane structure examining the effects of varying wind directions, speeds, and internal pressures. Specifically, we investigated the displacement and stress on the inflatable membrane structure under wind velocities of 12, 15, and 18 m/s, taking into account the internal air pressure. Consequently, we determined the influence coefficients for displacement and stress, representing the ratio of FSI effects to those in a static case. Our findings indicate that the displacement coefficient is inversely related to internal pressure, whereas the stress coefficient directly correlates with wind speed. The maximum displacement and stress under FSI conditions can be calculated by applying an influence coefficient to the static case results. The findings from this study offer a convenient and reliable method for predicting the actual structural response. This paper provides valuable insights for the design and optimization of inflatable membrane structures to withstand wind loads, a topic that has been underexplored in previous studies. Future studies should investigate additional cases to further enhance the reliability of this method.

Blast mitigation effects of TPU polymers-based inflated membrane structures under external explosion

TPU polymers-based inflated membrane structures are a potential technology to protect pre-existing lightweight buildings, with the advantages of lightweight and simple building process. In this study, a series of field blast tests were performed for the structural response and blast load parameters to study the blast mitigation effect of the inflated membrane structures. The corresponding numerical models of the tests were then developed and validated to reproduce the fluid-structure interaction. Thin aluminum plates were used as the protected structure. Based on their maximum displacement, average plastic strain, depth of depression, and permanent deformation, damage factor was defined to evaluate their damage level. Both the experimental and numerical results show that inflated membrane structures can effectively mitigate blast loading and significantly reduce the permanent displacement of the aluminum plate by elastic compression deformation. The effects of the initial height and internal pressure of inflated membrane structures on the blast mitigation effectiveness were clarified by the parametric study. The overpressure-impulse equivalent damage curves were established by combining the damage factor and overpressure-impulse loads, which further confirmed the blast mitigation performance of inflated membrane structures. Our study has verified the blast mitigation effects of inflated membrane structures based on TPU polymers, which is potentially valuable in the field of protective engineering for lightweight construction.

Deflation analysis of an air cushion for underwater shaking tables

The deflation process of inflatable membrane structures has always been a topic worthy of in-depth research. Inflatable membrane structures are employed for waterproofing in underwater environments, and their deflation process often poses safety concerns, warranting increased attention. An air cushion, which is applied to waterproof the underwater shaking table, is researched. It is arranged between the shaking table and the cover plates and can provide waterproof protection for the driving equipment of the shaking table. This article mainly studies the complete process of deflation for the waterproof air cushion. Force analysis was conducted on the air cushion membrane at different stages of deflation, and the factors that affect force during the deflation process were determined. A simulation method that combines the CEL (Coupled Eulerian-Lagrangian) method and fluid cavity method was used to analyze the deflation process of the air cushion, taking into account the effects of different deflation speeds and initial inflation pressures on the process. Based on the analysis results of the pressure-air volume curve and the deformation of the air cushion, the deflation process can be divided into three stages: elastic shrinkage stage, extrusion deformation stage, and free deformation stage. Based on the analysis results of dynamic stability, the extrusion deformation stage is further divided into two sub-stages: the extrusion stable stage and the extrusion unstable stage. It was found that the air cushion can achieve stability during both the elastic shrinkage stage and the extrusion stable stage, leading to the proposal of an evaluation method for air cushion deflation. Finally, the instantaneous leakage process of different positions on the air cushion was analyzed, and engineering suggestions were provided based on the analysis results. The research results provide a reference for the application of underwater inflatable membrane structures.

Numerical Simulation of wind load on Inflated Membrane Structure

The fluid-structure interaction (FSI) program were used to simulate the condition that inflated membrane structure transport process in incoming flow. A comparison between the results from numerical simulation and from the ground simulation test was used to validate the computational method. Due to the analysis of flow field and membrane structure’s deformation, the law of force variation of inflated membrane structure during FSI was discussed, and the causes of deformation instability in FSI problems were preliminary discussed. Possible ways to reduce the sensitivity of envelope deformation caused by constraint position were explored, and the effect of this improved method on the surface stress of the envelope was investigated.

A Numerical Analysis Model of Composite Pneumatic Formwork Considering the Stiffness Contribution of Polyurethane Layer

Pneumatic formwork is a kind of inflated fabric-polyurethane composite formwork formed by spraying polyurethane on the interior surface of the membrane. A numerical analysis model of composite pneumatic formwork considering the stiffness contribution of polyurethane is proposed to predict the structural response. The analysis model simulates the component of fabric and polyurethane with membrane elements and shell elements respectively, and Tie constraint of surface to surface is defined at the interface. A nonlinear material model for fabric is adopted considering the influence of stress ratio and loading history, and the constitutive relation of polyurethane is described in the foaming plane with different properties for tension and compression. Newton-Raphson incremental iterative method is used to solve the involved nonlinear problems. The simulation accuracy of the proposed analysis model is verified by comparing its predictions with test results about the loaddeformation response of an inflated membrane structure and the corresponding composite pneumatic formwork under horizontal loading. The numerical model is further used to investigate the influence of the thickness of polyurethane layer on the improvement of overall structural stiffness of a larger pneumatic formwork under horizontal fresh gale, and the polyurethane is proved to be beneficial for the shape-control of pneumatic formwork.

Analysis of Mechanical Properties of Air-Ribbed Skeleton Membrane Structure

The existing large inflatable membrane structure is complex in structure and takes a long time to be extended. In this paper, an air-ribbed skeleton membrane structure is proposed to meet the requirement of camp and emergency tents needing to be set up quickly and easily. Ten single-arch air ribs are arranged side by side to support the tarpaulin, and wind ropes are added to the end and side faces of the tarpaulin to remain stable. The finite element model of the air-ribbed skeleton membrane structure is established to analyze the stress and the displacement of the membrane structure under combined wind and snow loads. The maximum displacement (439.4 mm) and maximum stress (29.94 MPa) are both within the safe standard. The stress and the displacement of the membrane structure in the wind load case is affected by the angle of the wind. The value of maximum stress and displacement at the wind angle of 90° are both lower than those at 0° and 45° in the wind load case. It is advisable to align the site layout of the membrane structure at the wind angle of 90°. The effect of the angle of wind ropes on the stress and displacement of the membrane structure is also studied. The maximum stress and displacement in the case when the angle of wind rope is 30° is smaller than those in the case when the angle of wind ropes is 45°. It is recommended that the wind rope should be laid at 30° to reinforce the membrane structure.

Dynamic and simulation of inflatable multilayer membrane structure under hypervelocity impact

The dynamic of hypervelocity projectile impacting inflatable multilayer flexible membrane structure is studied in this paper. The velocity increment of the inflatable multilayer flexible membrane structure under hypervelocity impact comes from two parts. One is the acceleration caused by the pulling of the membrane when the hypervelocity projectile is in direct contact with the membrane, and the other is the acceleration provided by the reverse impulse caused by the gas leakage in the inflatable structure. The hypervelocity projectile will be decelerated in the impact process, and finally fly with the accelerated multilayer flexible membrane structure at the same velocity, which means that the projectile is captured by the membrane structure. According to the above process, the influence of the mechanical property parameters of the flexible membrane on the structural parameters of the multi-layer flexible membrane can be calculated, which can be used to guide the engineering design. Finally, the hypervelocity impact process is verified by the numerical simulation.

Experimental and Numerical Studies on Bending and Failure Behaviour of Inflated Composite Fabric Membranes for Marine Applications

Owing to their excellent physical characteristics of lightweightiness, compactness and rapid deployment, the inflated membrane structures satisfy the demands of maritime salvage and military transportation for long-distance delivery and rapid response. Exploring the failure behaviour of inflated membrane structures can greatly contribute to their widespread applications in ocean engineering. In this research, the main objective is to comprehensively investigate the bending and failure behaviour of inflated membrane structures. Thus, the Surface-Based Fluid Cavity method is employed to set up the finite element model (FEM) which is compared to the experimental results to verify its reliability. In parallel, the effects of internal pressure and wrinkles are discussed. An empirical expression of the ultimate bending loading was fitted by face-centred composite designs of the Response Surface Methodology. The results of experiments and FEM show that the bearing capacity of the inflated membrane structure is positively correlated with the internal pressure but decreased obviously with the occurrence and propagation of wrinkles. The deformation behaviour and the stress distribution are similar to those of the traditional four-point bending beam, and the local instability induced by wrinkles will cause structural failure. In addition, the numerical model and the proposed expression showed deviations below 5% in relation to the experimental measures. Therefore, the FEM and proposed expression are high of reliability and have important engineering guiding significance for the application of inflated membrane structures in ocean engineering.

Nonlinear two-dimensional analysis of manifold marine inflated membrane structures using vector form intrinsic finite element method

This study aims to investigate the two-dimensional nonlinear deformation of manifold marine inflatable membrane structures. The vector form intrinsic finite element method is adopted and the pseudo-dynamic stiffness damping is introduced to better get a steady-state solution for quasi-static problems. Three typical marine membrane structures, including the partially submerged pontoon, water-filled dam and finger-bag skirt of a hovercraft, are simulated with rod elements, the spatial varied fluid loads and interaction with deformed structures are considered via user-defined functions. Satisfactory deformation results can be obtained with a simplified two-dimensional profile model. Furthermore, a preliminary analysis of the effects of internal and external pressure on the dam is performed, more accurate hovercraft skirt tension can be obtained than traditional analytical method and the hazardous tuck-under behavior of the skirt is simulated. The models and simulations using vector form intrinsic finite element method are beneficial for understanding the deformation behavior and providing a reference for the design of marine membrane structures.

Finite elements and finite volumes methods in wind engineering applications

In view of the importance of understanding and predicting the effects of wind on wide-span membranes and inflatable structures, a complementary experimental-numerical campaign was conducted to demonstrate the physical importance of numerical simulations in this field and to discuss relevant modeling aspects. This work aims, on the one hand, to examine the effects of some main CFD modeling decisions, such as mesh resolution, turbulence modeling, wall functions, etc., on the accuracy of simulation results. On the other hand, to compare the two most popular CFD numerical technologies (Finite Volumes and Finite Elements Methods), using the open-source frameworks OpenFOAM and Kratos Multiphysics, respectively. This parametric study and cross-validation will contribute to the ultimate goal of obtaining practical and reliable predictive numerical simulations in the field of wind engineering. This paper discusses the numerical modeling approaches of the first and fundamental step of a systematic chain of test cases, performed experimentally. It focuses on the case where a constant uniform flow and a rigid inflatable membrane structure are considered. Further extensions will include ABL flow scenarios and fluid-structure interaction.

Numerical Simulation of Atmospheric Boundary Layer Turbulence in a Wind Tunnel Based on a Hybrid Method

In the Computational Fluid Dynamics (CFD) simulation for building structures, it is important to generate a stable atmospheric boundary layer (ABL) flow field that meets the standards. In this paper, the wind profile, turbulence intensity, and wind velocity power spectrum in the target region of a numerical wind tunnel were accurately simulated by a hybrid method. With the numerical simulation software FLUENT, the hybrid simulation method was implemented. In the hybrid simulation method, the wind field was simulated by setting the roughness element in the upstream of the model, adding random disturbance, and setting the circulation surface. The influences of simulation parameters (such as roughness element and random number parameters) and FLUENT solution methods on the flow field results were studied. The results show that the influence range of the roughness element on turbulence intensity is approximately 6 times its physical height. The turbulence intensity is positively correlated with the standard deviation of random numbers and negatively correlated with the assignment height. Finally, the wind fields for different terrains satisfying the standards were obtained in numerical wind tunnels. A simulation of the wind pressure on an inflatable membrane structure was illustrated. The comparison between numerical and experimental results shows a good accordance, which indicates a desirable potential in practical application.

Wind-Induced Response Characteristics and Equivalent Static Wind-Resistant Design Method of Spherical Inflatable Membrane Structures

The wind-induced responses and wind-resistant design method of spherical inflatable membrane structures are presented in this paper. Based on the wind pressure data obtained from wind tunnel experiments, the characteristics of wind-induced responses are studied via nonlinear dynamic time–history analysis, considering the influences of spans, rise–span ratios, internal pressures, wind velocities, and cable configurations. The results show that with the increment of wind velocity, the position of the maximum displacement changes from the top to the windward region, which usually leads to the exceedance of the displacement limitation. Under high wind velocity, enhancing the internal pressure can effectively reduce deflection. However, the membrane stress will also increase. Particular attention should be paid to checking the strength. The restraint effect of cross cables on wind-induced response is better than radial cables. Furthermore, an equivalent static analysis method for the wind-resistant design of spherical inflatable membrane structures is developed. The empirical formulas and recommendation values of gust response factors and nonlinear adjustment factors are provided for engineering reference.

Experimental Study on Aeroelastic Instability of Spherical Inflatable Membrane Structures with a Large Rise–Span Ratio

Spherical inflatable membrane structures are extremely prone to suffer aeroelastic instability under strong winds, which requires detailed investigation. In this paper, based on the digital image correlation technology (DIC), the displacement and strain response characteristics under wind loads are investigated. Furthermore, the aeroelastic instability characteristics and the criteria for determining the occurrence of this phenomenon are defined. The results show that the top, windward, and side parts of the structure deform upward, inward, and outward. The extreme value of the total displacement occurs at approximately 1/2 of the windward region. Maximum principal strains occur at the windward and leeward centers together with the top region. After the wind speed exceeds the critical value (the dimensionless critical wind speed is observed at 1.37), the structure undergoes a sudden change of dominant vibration mode, the damping ratio decreases dramatically and reaches nearly zero. It can be concluded that the aeroelastic instability of the spherical inflatable membrane structure is caused by vortex-induced resonance and is characterized by a sudden increase in deformation and amplitude, a sudden change of the dominant vibration mode, and a rapid decay of the damping ratio. The Reynolds number after reaching the instability critical wind speed is Re > 3.1 × 105.

Numerical and experimental study on novel tensioning method for the inflatable paraboloid reflector antenna

Inflatable membrane structures are the state-of-the-art fast evolving space structures owing to its inherent advantages such as lightweight, higher packaging efficiency along with ease of deployment. The membrane reflectors need to be actuated by adequate tension forces to get the required surface accuracy. The design of tensioning device has certain challenges, such as mass penalty, low packaging efficiency and power source dependency. The present study demonstrates the novel design methodology for the tensioning system for the inflatable paraboloid membrane reflector antenna using the wave springs. The loading analysis of the inflatable paraboloid reflector is carried out for adequate inflation pressure and tension forces maintaining the surface error within the tolerance limit. The numerical results of the loading analysis are compared and found to be consistent with the experimental findings. The relation between the displacement of tensioning spring and the dimensions of supporting inflatable torus is established. The results show that wave springs can successfully transfer the required tension forces to the reflector with required surface accuracy. The findings of this research provide insights for simple, lightweight, packaging efficient and cost-effective design solution to the tensioning system for inflatable paraboloid reflector antenna.

Experimental study on bearing capacity of a Tensairity arch

Based on the advantages of tension-string structures and inflatable membrane structures, this paper proposes a Tensairity arch and designs and builds a model for the structure. The mechanical response of the structure under a concentrated load is studied by carrying out static tests. From three aspects of the midspan deflection deformation, the strain of upper chord member and the tension of steel cable, this paper studies the influence of the internal inflation pressure, the tension of the lower chord steel cable, and the combinations of the steel cable on the bearing capacity of the structure. The results show that increasing the inflated air pressure to a certain extent can significantly improve structural stiffness, but compared with traditional spindle-shaped Tensairity, the prestress applied during the inflation process is not conducive to enhancing the structural load-bearing capacity. Changing the stress distribution of the upper chord member by tensioning the lower chord cable is beneficial to achieve a better material performance and weaken the adverse effects caused by the inflation of the airbag. The supplementary tension of the horizontal steel cable can improve the ultimate bearing capacity of the structure, thus contributing to the safety of the structure.

Bending and wrinkling behaviours of polyester fabric membrane structures under inflation

Membrane structures made of high-strength polyester fabrics are deployable and lightweight, which can be utilized in architecture, aerospace and marine structures. The design and optimization of an inflated structure depends on a thorough understanding of polyester fabric mechanics. In this work, firstly, the material properties of the polyester fabric membrane were analyzed by a tensile test. The bending and wrinkling behaviours of the inflated polyester fabric membrane were investigated by experimental, analytical and numerical methods. Specimens of varying internal pressures and diameters were subjected to bending tests with highly controlled loading and boundary conditions. It was found that the flexural capacity of the inflated membrane structure was positively correlated with the diameter and the internal pressure but decreased obviously with the occurrence and propagation of wrinkles. Based on the energy principle, the prediction formula of mid-span deflection was developed with the consideration of shear stiffness. Furthermore, the surface-based fluid cavity method was employed to set up a finite element model (FE model). The flexural behaviour of inflated membrane structure can be predicted by both the analytical and the numerical method, and the reliability was verified by comparing with the experiment

Wind tunnel tests of an inflated membrane structure. Two study cases: with and without end-walls

The use of textile membranes in architecture and civil engineering has increased rapidly in the last decades. Membrane structures are lightweight, economic structures with unique shapes. At the same time, their structural analysis is particular compared to the analysis of conventional structures. The form-finding procedure, the large displacements of the structures, and the special properties of the composite material all require unique tools. The wind analysis of membrane structures is one of the most challenging parts of the design because the design codes do not provide the pressure coefficients of the doubly curved shapes of membrane structures. The main scope of the present research was to determine the mean pressure coefficient fields over an inflated membrane structure by wind tunnel experiments. The structure, composed of six inflated circular arches, was analyzed with and without end-walls for three wind directions. The equilibrium shape of the inflated structure was determined with the Dynamic Relaxation Method. During the numerical form-finding procedure, the orthotropic behavior of the membrane material and the warp and fill directions of the textile fibers were also considered. Based on the numerically determined equilibrium shape of the inflated structure, a model was made using a 3D printer. The flow around the model according to three wind directions was analyzed in an open-circuit wind tunnel. The pressures were measured in 102 external and 102 internal points of the inflated arches and 27 points on each end-wall. In this paper, the experimentally determined pressure coefficient fields for different wind directions are presented and compared for the open (without end-walls) and closed (with endwalls) cases. The thoroughly introduced experimental results can be used during the structural analysis of future inflated structures with similar shapes.

Form finding analysis of air cushion of underwater shaking tables

An air cushion, in the context of this study, is an inflatable membrane structure made of rubber-coated woven fabric reinforced composites. Inflatable membrane structures have wide application prospects in the waterproofing of underwater moving machineries, such as underwater shaking tables. A refining form finding analysis of a waterproof air cushion was carried out, and the mechanical characteristics in the process of form finding were studied. The air cushion had two layers. The lower layer is acted upon by air pressure, and the upper layer is acted upon by air and water pressure, both of which were theoretically analyzed. The dynamic equilibrium process of the air cushion was simulated by combining the Coupled Eulerian-Lagrangian(CEL) method with the fluid cavity analysis technology. The accuracy of the simulated results was verified by the theoretical analysis results. The dynamic equilibrium process of the air cushion with different initial inflation pressures was analyzed. The results show that the air cushion is most favorable when the initial inflatable pressure is slightly higher than the theoretical analysis result. Higher air pressure leads to higher stress of the air cushion, while lower air pressure will lead to slow stability during form finding. These results will provide a basis for engineering applications of air cushions in underwater shaking tables and in other fields.

Optimization Analysis of Stratospheric Airship Suspended Curtains

ABSTRACTThere has been considerable interest in stratospheric airships as a cost-effective alternative to earth orbit satellites for sightseeing, aerial photography, communication and carrying weapons, etc. Many countries have plans to develop the airship owing to its greatly expected usage. The suspended curtain plays a vital role in force transmission in stratospheric airships but lacks attention. In this paper, the relationship between the optimal shape of suspended curtain and load conditions was studied through CAE Abaqus and Isight. Firstly, by using secondary development function of Abaqus, parametric FEA models of suspended curtains and envelopes have been established, several parameters were used to describe the shape of suspended curtains. Secondly, parameters of the suspended curtain shape were optimized under different loading conditions by means of the genetic algorithm. Lastly, through the analysis of the results, some conclusions are summarized: The relationship between n1(n2) and nb was found to be linear when the suspended curtain is subjected to vertical load. The stress transfer law of suspended curtain and inflatable membrane structure under the inclined load were also obtained, which are valuable for the structural engineering design of stratospheric airships..

Wind-Load Response and Evacuation Efficiency Analysis of Marine Evacuation Inflatable Slide

Flexible inflatable membrane structure has the characteristics of light weight, large span, and small stiffness, and it is very sensitive to wind load. Aiming at the dynamic response of marine evacuation inflatable slides under complex and changeable wind loads at sea, the response law of the inflatable slide under different wind directions, wind speeds, and internal pressure conditions is studied by using fluid–solid coupling theory. The most dangerous conditions of evacuation system installation and the ideal internal pressure of the inflatable slide meeting the stability requirements are deduced. The LS-DYNA module is used to simulate the inflation process of the slide. The evacuation sliding is rationally simplified. By changing the inflatable internal pressure of the slide, the variation law of displacement, deformation, and sliding speed of the slide is obtained, and the optimal inflation internal pressure satisfying the evacuation efficiency requirement is obtained. The results show that the inflow wind direction angle of 30° is the most dangerous condition for slideway installation, and the internal pressure of 4000 Pa is the ideal internal pressure to meet the double standards of stability and evacuation efficiency. The numerical results obtained are valuable for analyzing wind resistance of offshore inflatable membrane structures and their practical design and application in evacuation systems.