Airship Envelope Research Articles

Experimental study and refined numerical simulation of ultimate pressure-bearing performance of rope-reinforced airship envelope structures

Stratospheric airships require a lightweight envelope to contain lighter-than-air buoyancy gas, making the lightweight design and pressure-bearing performance of the envelope structure a key research issue. The stress state at different cross-sectional positions of the airship envelope structure is different, resulting in a low utilization rate of the overall material performance of the envelope structure. This paper proposes a design scheme for reinforcing envelope structures with sliding reinforcing cable to improve the bearing capacity of the composite fabric structure while reducing its weight, ultimately achieving the optimal strength-to-weight ratio. Two types of composite fabric structures (A-airship and B-airship) were subjected to inflatable burst tests, and the strain changes in the envelope gores were analyzed by digital image correlation. Through re-assembly of the broken composite fabric pieces and analysis of their tear textures, crack origination positions, failure causes, and the stress behavior and state at the failure position were identified. An envelope structural model with consideration of the cutting pattern effect was established, allowing the stress distribution of the envelope to be analyzed and the damage positions to be more accurately predicted. Based on the analysis of the ultimate pressure-bearing performance of an airship envelope structure, a novel idea of incorporating coupled tensile-shear stress into the strength criterion was proposed. Through the data in the study and existing references, it is verified that the strength criterion can accurately predict the ultimate pressure-bearing performance of the envelope structure.

Dynamic Characteristics of Airship Envelope Material with Concentrated Mass

Dynamic Characteristics of Airship Envelope Material with Concentrated Mass

Conceptual Design, Sizing and Thermal Analysis of An Alerting System for Manned Airships

This paper describes an automatic and self-contained electromechanical safety system for manned airships, which alerts the flight crew when the temperature at some point over the envelope exceeds a pre-determined safe limit. The system consists of a thin electrical wire that is looped over the airship envelope along its length, which melts at the location(s) at which the safe temperature is exceeded, and sounds an alarm in the crew cabin. A detailed technical description of the alerting system and all its elements is provided, and a methodology for carrying out sizing of the system, and to carry out thermal analysis is outlined. The methodology is used to size the system for an airship of 30 m envelope length cruising at a speed of 20 m/s at an altitude of 10,000 ft. Results indicate that the mass of the system is a small fraction of the force of buoyancy generated by the airship envelope. Thermal analysis indicates that the alerting system is thermally stable, and despite the fact that current is consistently and continuously flowing in the alarming circuit, the wires are not overheated. The system can be of great help in increasing operational safety levels of a manned airship.

Adjusting Accuracy of Digital Image Correlation Through Variable Subsets and Application in Airship Envelope

Adjusting Accuracy of Digital Image Correlation Through Variable Subsets and Application in Airship Envelope

Experimental Study on the Influence of Temperature on the Mechanical Properties of Near-Space Airship Envelopes

A biaxial tension test considering temperature is crucial to predict the mechanical properties of airship envelopes. However, there is a lack of biaxial tensile test equipment for high- and low-temperature correlation. In this study, a temperature control device suitable for biaxial tension was designed based on the traditional device, and the biaxial tension test of the UN-5100 material in high- and low-temperature environments was realized. In addition, a series of tests were carried out to verify the effectiveness and rationality of the temperature control device. Then, a biaxial tensile test of UN-5100 specimens between −33 °C and 80 °C were carried out and the stress–strain relationship of the UN-5100 specimens under high- and low-temperature environments was obtained. Based on the test data, the elastic modulus and Poisson’s ratio of the UN-5100 specimens at different temperatures were calculated. Finally, the test results showed that the elastic modulus and Poisson’s ratio of the airship envelope were larger at low temperatures, indicating that the capsule is relatively safe at such temperatures. The relationships between the temperature and the mechanical properties of the airship were also summarized.

Prediction of tear propagation path of stratospheric airship envelope material based on deep learning

Tear propagation of the envelope material could cause fatal damage to the stratospheric airship (SSA) and it is very important to detect the crack and predict its tear propagation path. A hybrid deep neural network (DNN) model is proposed in this paper to predict tear propagation of the SSA envelope material mainly including stress field predictor and crack map predictor by considering the time and spatial characteristics. The Gated Recurrent Unit (GRU) is applied by using the gating network signaling that control how the present input and previous memory for the stress field predictor. A Feature Pyramid Network (FPN)-based faster region-based Convolutional Neural Network (CNN) is proposed to predict the crack location by declaring the crack propagation direction and velocity of the envelope material. Furthermore, two deformable operation modules are embedded into the crack detector to achieve better identification of out-of-plane cracks of the envelope material for a real airship with curvature. The dataset is obtained by extended finite element method (XFEM) analysis. The proposed approach has potential applications in the field of envelope material design and structural health monitoring of the SSA.

Theoretical analysis and experimental study on physical explosion of stratospheric airship envelope

The shock wave released from physical explosion of a pressurized stratospheric airship can produce serious damage to the environment. Shock wave overpressure can measure the degree of damage that an explosion can cause to such things as buildings and the human body. To obtain the overpressure from an airship envelope explosion, explosion energy must first be conducted. Explosion energy is derived based on Brode’s equation, Brown’s equation, and Crowl’s equation. An equivalent TNT computational model is then applied to calculate the overpressure of the explosion energy. In order to verify the accuracy of the computational model, a ground test must be conducted. The experimental result shows that a computational model based on Crowl’s equation is more accurate than the other two. Finally, the effect of geometric scale ratio, pressure difference, and the gas of the explosion overpressure is discussed. This paper can provide a relatively effective calculation method for shock wave overpressure for an airship envelope explosion.

Temperature-compensated fiber-optic online monitoring methodology for 3D shape and strain of near-space airship envelope.

Near-space airships are high-end airships that are being vigorously developed in the aerospace industry. It has important application value in the telecommunication, surveillance, monitoring, remote sensing, and exploration fields. The envelope is the key component that provides lift to the airship. Online monitoring of envelope status is critical to ensuring airship performance, safety, and reliability. However, online monitoring of the 3D shape and strain of the airship envelope is still a challenging task. A hybrid multi-core and single-core fiber-optic monitoring method with a temperature self-compensation function is proposed to address this issue. The method uses multi-core fiber optic sensors, 3D curves, and a surface reconstruction algorithm to obtain the 3D shape of the envelope. Temperature decoupling of the sensing signal is carried out via sensors on the central core of the multi-core fibers that are only sensitive to temperature, thereby eliminating the influence of temperature changes on the measurement accuracy. The strain field of the envelope skin is measured by single-core fiber optic sensors and a strain interpolation algorithm. The accuracy of the proposed method is experimentally validated. The results show that the 3D shape measurement error of the envelope skin is 4.82% when the skin is bent in the range of 10m -1-15.38m -1. When the ambient temperature changes in the range of -50∘ C-150∘ C, the position measurement error caused by the temperature change is only 1.2% of the effective measurement length (160mm) of the multi-core fiber optic sensor. When the skin is stretched in the range of 500-5000µε, the measurement error of the average value of the skin strain field is only 0.75%. This proves that the proposed method can simultaneously measure the 3D shape and strain field of the envelope skin and also effectively suppress the influence of ambient temperature changes on the measurement accuracy. The proposed method has application prospects in the online monitoring of airship envelopes.

Study of the Mechanical Properties of Near-Space Airship Envelope Material Based on an Optimization Method

An optimal calculation method for the mechanical properties of near-space capsule materials was proposed. First, biaxial tensile tests under low tensile ratios were carried out on the envelope materials of a near-space airship. The experimental results showed that the values of the elastic modulus and Poisson’s ratio, which are significantly affected by the warp and weft stresses, were not constant. Second, the elastic modulus and Poisson’s ratio of the near-space airship were obtained by using the traditional calculation method, and the limitations of this method were discussed. Third, an optimal calculation model for the elastic modulus and Poisson’s ratio of airship envelopes was proposed. The strain calculated by the proposed optimization model could be effectively correlated to the strain measured by the experiment. Then, through the user-defined subroutine of the finite element method and the elastic modulus and Poisson’s ratio calculated by the proposed optimization, the strain of the finite element simulation was obtained. The average error between the simulation results and the experimental values was approximately 8.21% (warp) and 8.41% (weft). The proposed method can consider the nonlinear changes of the elastic modulus and Poisson’s ratio of membrane material under different stress ratios and predict the force and deformation of the airship’s capsule more accurately, which is adaptable to engineering applications.

Preparation of PCU/PPy composites with self-healing and UV shielding properties

Polycarbonate-based polyurethanes (PCU) are frequently used in airship envelope materials because of its outstanding mechanical performances and aging resistance. However, the surface of PCU is likely damaged during processing and operating and the emerged minuscule cracks will lead to deterioration of perfomances for airship’s envelope materials. Herein, self-healing PCU/polypyrrole nanoparticles (PPy) composites were prepared by solution blending and quick healing of specific area for PCU was realized due to the high photo-thermal conversion merit of PPy. The results show that, the mechanical properties of PCU/PPy composites can be restored to more than 80% and the gas barrier properties can also be basically repaired when irradiating the destroyed surface using near-infrared light for only 60s. In addition, the ultraviolet visible (UV-vis) shielding performance of the PCU/PPy composites was enhanced significantly and the UV-vis transmittance was less than 14% and 2% with 0.25wt% and 0.5wt% PPy, respectively. Meanwhile when 0.25wt% PPy was added, the tensile strength increased from 17.9MPa to 21.7 MPa and the elongation at break increased from 647% to 829%. Besides, the thermal decomposition temperature at 5wt% loss increased from 277.8°C to 300.7°C and 304.88°C with 0.25 wt% and 0.5 wt% PPy, respectively. The prepared composites show promising application in aerospace domain.

Simulation and Analysis of Fluid–Solid–Thermal Unidirectional Coupling of Near-Space Airship

Based on the biaxial experiment data of the membrane material under hot and cold conditions, the mechanical properties calculation model of envelope material was established with consideration of the effects of varying stress ratios, stress magnitudes and temperatures on the mechanical properties of near-space airship material. Using the heat source model, Computational Fluid Dynamics (CFD) simulation, User-Defined Function (UDF), structural finite element analysis software and the user subroutine of an airship to define the behaviour of fabric material, the fluid–structure–thermal coupling model of airship envelopes was established. In addition, a near-space airship was selected as the research subject to calculate the diurnal temperature differences during the summer solstice and analyse the diurnal temperature distribution of the envelope. Under controlled environmental conditions, the deformation law of the near-space airship under the influence of fluid–structure–thermal coupling was calculated and summarised. The present fluid–solid–thermal coupling model takes into account the anisotropy of materials, temperature, stress magnitude, stress ratio and other influencing factors, which can more accurately reflect and predict the stress–strain distribution and the deformation law of near-space airships.

Mechanical Properties Evolution and Damage Mechanism of Kevlar Fiber under Ozone Exposure in Near-Space Simulation

The stratospheric airship, a long-term floating vehicle in near-space, has become a new hotspot in aerospace exploration. The airship’s envelope material is vulnerable to ozone exposure in near-space and degrades. This paper used typical Kevlar fiber as the research material for an ozone exposure experiment in a near-space simulated environment. The results showed that the elongation of the Kevlar fiber decreased and the elastic modulus increased after ozone exposure. The tensile strength of fiber decreased gradually with an increase in ozone concentration and exposure time. When ozone concentration increased from 0 pphm to 1000 pphm, the tensile strength of fiber decreased from 2397 MPa to 2059 MPa. With increasing ozone exposure time from 0 h to 1000 h under ozone concentration 1000 pphm, the tensile strength of fiber decreased from 2332 MPa to 1954 MPa. The hydrogen bonds and partial amide groups in the fiber structure were damaged, and the surface chemical functional groups of the Kevlar fiber were reassembled under ozone exposure. Low molecular weight oxidation products, including -COO- structures, formed on the surface of the Kevlar fiber. This work explores the ground simulation method in a near-space environment and enriches the service data of airship envelope materials.

Design and analysis of hybrid electric multi-lobed airship for cargo transportation

Though a lot of curiosity has been developed towards a sustainable mode of cargo transportation, multi-lobed hybrid airships are touted to be a viable alternative to the conventional aircraft. The advantages of these Lighter Than Air (LTA) vehicles can further be boosted by incorporating a renewable source of energy. The requirements of high power in cargo airships and the current technological barriers call for the development of a hybrid propulsion system that can couple the best of both conventional and electric propulsion. The electric propulsion system is established by integrating solar arrays with fuel cells, which is then combined with conventional engines in a parallel power train architecture ensuring minimum transfer of energy and compact size. A solar irradiance model is adopted, to evaluate the amount of energy generated by the solar arrays installed over the airship envelope. A multi-lobed hybrid airship model is presented whose aerodynamic characteristics are obtained using computational fluid dynamic tools, which are then utilized to evaluate the power requirements through flight performance analysis. The hybrid propulsion system is then modified in accord with the power needs of the hybrid airship. Finally, detailed weight distribution between hybrid-powered and conventional hybrid-airship is presented displaying significant reduction in fuel weight of ∼350 kg due to the hybrid propulsion system.

Stochastic optimization of high-altitude airship envelopes based on kriging method

High-altitude airships can be used to transport substantial payloads to the stratosphere and remain there over long periods of time. In this paper, an algorithm for the design of high-altitude airship envelopes, accounting for uncertainties, is developed and applied. The algorithm is based on the non-intrusive polynomial chaos expansion scheme, which is employed to build a stochastic kriging metamodel. Two uncertainties are examined and characterized: 1) the stratospheric wind fluctuations using reanalysis datasets and 2) the variability in the turbulence levels. The method results are discussed to address the relevancy of the uncertainties. It is found that the drag coefficient of stratospheric envelopes can vary by as much as 30 percent. As a case of study, an ideal stratospheric airship is considered, operating at an altitude of 20 km, at a latitude of 30cN and carrying a payload of 250 kg. The baseline design follows the shape of the ZHIYUAN-1 envelope and the cost function to be minimized is the average mission drag coefficient. Due to the new method, a significant reduction (4%) of the average drag of the aircraft is achieved.

Effects of Short-Term Aging and Creasing Damage on Air Leakage Properties of Airship Envelope Materials

Effects of Short-Term Aging and Creasing Damage on Air Leakage Properties of Airship Envelope Materials

Light weight optimization of stratospheric airship envelope based on reliability analysis

A stratospheric airship is an essential flight vehicle in the aviation field. In this paper, optimal design approach of stratospheric airships is developed to optimize envelope shape considering three failure modes and multidisciplinary analysis models, and could also reduce the mass of a stratospheric airship to be deployed at a specific location. Based on a theoretical analysis, three failure modes of airships including bending wrinkling failure, hoop tearing failure and bending kink failure, are given to describe and illustrate the failure mechanism of stratospheric airships. The results show that the location, length and size of the local uniform load and the large fineness ratio are easier to lead to bending wrinkling failure and bending kink failure. The small fineness ratio and the increasing differential pressure are more prone to cause hoop tearing failure for an airship hull. The failure probability is sensitive to the wind field. From an optimization design, the reliability analysis is essential to be carried out based on the safety of the airship. The solution in this study can provide economical design recommendations.

Finite Element Simulation of the Microstructure of Stratospheric Airship Envelopes

There has been considerable interest in stratospheric airships that have their unique role in environmental monitoring and surveillance, communication transmission, and carrying weapons, among other uses. The problem presented in this paper is that the test values of pressure resistance are far from the theoretical values of spherical balls, which are made up of plain-weave fabrics. In this paper, the uniaxial tension in structural layers has been tested to certify the validity of the finite element analysis (FEA) models. A boundary condition that is suitable for airship envelope simulation analysis is also proposed here. Using the secondary development function of Abaqus, an FEA model of three-dimensional plain-weave fabric is then established to simulate the envelope inflation experiments. Finally, the stress behavior of the microstructure of plain-weave fabric is summarized, and several conclusions are obtained.

Investigation on influence of time on tear behaviour of airship envelope

An experimental investigation on tearing behaviour of a coated fabric used in aerostat/airship has been undertaken. The tear tests have been conducted on bi-axial set up and pressurised cylinder. Tear propagation was studied by inducing dynamic tear on a bi-axially stressed coated fabric through a falling dagger. The influence of traverse rates, 1–500 mm/min, on tear strength under uniaxial loading was also studied. Thiele’s empirical equation has been found to fit the data of bi-axial tests and cylinder tests. The instantaneous tear on a bi-axially stressed fabric when left under constant stress for some duration lead to failure of fabric at even 15% lesser than critical tear slit length in about 15 min. The tear strength of the coated fabric was found to be less at 1 mm/min traverse rate while remaining nearly constant for higher rates of traverse. The critical tear length not only depends upon inherent tear strength of material, diameter and pressure of envelope but also on the time for which the tear remains under creep.

No second-in-command: human fatigue and the crash of the airship Italia revisited

The dirigible Italia crashed onto the Arctic sea ice north-east of the Svalbard archipelago on 25 May 1928 at 10:33 GMT while travelling back to her base from the North Pole. Only eight of the 16 crew members survived: one was killed upon impact, one did not survive the post-crash ordeal and six were trapped in the airship envelope (i.e., the balloon), which floated away and disappeared. No definite conclusions have ever been reached about the causes of the crash. The judgements of the Commission of Inquiry instituted by the Italian government and published in 1929 are carefully examined. Recent analysis has presented evidence that the mishap may have been fatigue-related. In this paper, the pivotal question of why General Nobile was so sleep-deprived at the time of the accident is addressed, specifically with reference to the lack of a second-in-command (i.e., a deputy commander) during the flight. Such a position was a standard practice for airships at the time, and General Nobile himself described this position as one necessary for an airship. Nevertheless, for a variety of reasons he proceeded on the Italia expedition without an official crew member responsible for this role. The lack of a second-in-command is proposed as a possible major contributing factor in the overall sequence of events leading to the crash of the Italia, although other possible causes and contributing factors for the crash are also considered, including structural failures, crew selection and political obstacles.

Influence of Strengthening Material Behavior and Geometry Parameters on Mechanical Behavior of Biaxial Cruciform Specimen for Envelope Material.

The stratospheric airship envelope material is operated in biaxial stress, so it is necessary to study the in-plane biaxial tensile strength. In this paper, a theoretical model is developed to evaluate the mechanical properties of in-plane biaxial specimens. Being applied to the finite element analysis, the theoretical model is employed to evaluate the influence of strengthening material behavior (E*) and geometry parameters on the mechanical behavior in the central. The follows results are drawn: (i) smaller the length of the central region (Lcen), E* and larger the central region corner radius (r) contribute to smaller coefficient of variation (CV); (ii) smaller Lcen and larger E* contribute to smaller stress concentration factor (k), k in the limit state of r is larger than that in other conditions. (iii) The CV and k under stress ratio of 1:1 are smaller than those under other stress ratios. The study can provide a useful reference for the design of biaxial specimens.