Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: General objective of the study This thesis aims to evaluate the hydraulics of an inflatable weir in its fully inflated position to the almost fully deflated position using different diameter circular weirs with varying discharges, by considering the change in the weir radius and the dynamic pressures on the weir. In the evaluation, three cylindrical weirs were installed in a 2m wide flume and tested over various discharges. Methodology The three weirs, one with a 300mm diameter, another with a 250mm diameter, and the last one with a 100mm diameter, were used to determine the effects of over flow water on the weir as seen in the different stages of the normal operation of an inflatable weir. Simulation involved measurement of the upstream and downstream water levels with the weir height involved at stable over flow conditions. Measurement of pressure variations was done on the weir faces with different water inflow rates to the test flume with three pressure sensors installed on each weir at 0°, 11.25° and 22.5° from the crest to the downstream. Additionally a single 0.15m radius weir was tested for pressures 67.5°, 78.75° and 90° from weir crest. Water level variation on the downstream of the weir was created by means of a variable tail gate to observe its effects. Results of the investigation The effects of upstream arches, stage, radius of curvature, discharge, pressure, energy losses over the weir and the downstream hydraulic jump were investigated in the inflation and deflation of the inflatable weir. The findings were as follows: ►Based on literature by Chanson and Montes (1998), Shabanlou et al. (2013), Schmockeret al. (2011) and Bahzad et al. (2010), upstream arches have insignificant influence onthe performance of the inflatable weir. There is rather reduced afflux due to the shape ofthe upstream of the weir from the Bernoulli’s equation. This shape of the upstream of theweir also contributes to the transport of sediments Gebhardt et al. (2012). ►Investigation of the discharge coefficient and factors influencing showed that: oAs the weir radius is reduced during the deflation, the unit discharge over each weirincreased with increase in head above the crest. oDischarge coefficient of the inflatable weir increases with the increase in head aboveweir crest, and the discharge coefficient is inversely proportional to the radius ofcurvature of the weir. ►Investigation of pressures on the downstream face of the weir models showed that: oThe negative (suction) pressure acting on the downstream face of the weir becomesincreasingly negative with increase in H/R values. oPoint of separation of nappe was seen with pulsations of pressure of the recordpressure. Generally, energy dissipation over the weir decreases with the decrease in the weir radius and the jump is more stable with the smallest circular weir and can be more accurately determined in the case of a small weir. Conclusions and Recommendations The inflatable weir has a high discharge at its fully inflated position. Its hydraulic performance is largely influenced by inflow head and is inversely proportional to the radius of curvature. Nappe pulsation as seen in the nappe vibrations can cause the vibration of weir. Future research on inflatable weirs should aim to monitor the negative pressure on measuring pressures further down the face of the weir because larger negative pressures are expected to develop after 90˚ as with this study.

The performance of a flexible structure as a breakwater is investigated numerically. The structure is a hemicylinder and is filled with water of uniform pressure. It is anchored along the sides. Only flexural modes are present. The structure is modeled as an elastic shell using the finite element program ABAQUS. The fluid is assumed to be inviscid and incompressible. The fluid flow is analyzed using a boundary integral method and the integral equation is solved numerically by a panel method. The vibration characteristics of the structure are analyzed both in the absence and presence of water. The hydrodynamic coefficients, forces, and the dynamic response of the structure in waves are obtained as a function of the wave number. Two different water depths of 5 m and 6 m are considered. For each water depth, normal and oblique incident waves are considered. The free surface elevation in front of and behind the structure is evaluated for different wave frequencies and directions. The results indicate that the flexible structure is effective in reducing the incident wave intensity over a wide range of frequencies. / Master of Science

High aspect-ratio, long-endurance aircraft require different design modeling from those with traditional moderate aspect ratios. High aspect-ratio, long endurance aircraft are generally more flexible structures than the traditional wing; therefore, they require modeling methods capable of handling a flexible structure even at the preliminary design stage. This work describes a design optimization method for combining rigid and inflatable wing design. The design will take advantage of the benefits of inflatable wing configurations for minimizing weight, while saving on design pressure requirements and allowing portability by using a rigid section at the root in which the inflatable section can be stowed. The multidisciplinary design optimization will determine minimum structural weight based on stress, divergence, and lift-to-drag ratio constraints. Because the goal of this design is to create an inflatable wing extension that can be packed into the rigid section, packing constraints are also applied to the design. / Master of Science

In recent years there has been a growing demand for reduced mass, small launch volume, and, at the same time, high-gain large-aperture antenna systems in modern space-borne applications. This dissertation introduces new techniques for dual-band reflectarray antennas to meet these requirements. A series of developments is presented to show the dual-band capability of the reflectarray. A novel microstrip ring structure has been developed to achieve circular polarization (CP). A C/Ka dual-band front-fed reflectarray antenna has been designed to demonstrate the dual-band circular polarized operation. The proposed ring structure provides many advantages of compact size, more freedom in the selection of element spacing, less blockage between circuit layers, and broader CP bandwidth as compared to the patches. An X/Ka dual-band offset-fed reflectarray is made of thin membranes, with their thickness equal to 0.0508 mm in both layers. Several degrading effects of thin substrates are discussed. To overcome these problems, a new configuration is developed by inserting empty spaces of the proper thickness below both the X and Ka band membranes. More than 50 % efficiencies are achieved at both frequency ranges, and the proposed scheme is expected to be a good candidate to meet the demand for future inflatable antenna systems. An X/Ka dual-band microstrip reflectarray with circular polarization has also been constructed using thin membranes and a Cassegrain offset-fed configuration. It is believed that this is the first Cassegrain reflectarray ever developed. This antenna has a 0.75-meter-diameter aperture and uses a metallic sub-reflector and angular-rotated annular ring elements. It achieved a measured 3 dB gain bandwidth of 700 MHz at Xband and 1.5 GHz at Ka-band, as well as a CP bandwidth (3 dB axial ratio) of more than 700 MHz at X-band and more than 2 GHz at Ka-band. The measured peak efficiencies are 49.8 % at X-band and 48. 2 % at Ka-band. In summary, this dissertation presents a series of new research developments to support the dual-band operation of the reflectarray antenna. The results of this work are currently being implemented onto a 3-meter reflectarray with inflatable structures at the Jet Propulsion Laboratory and are planned for other applications such as an 8-meter inflatable reflectarray in the near future.

Satellite-based communication system can provide access to voice, data, video and internet transmission that is independent of terrestrial infrastructure. This is particularly important in disaster response situations and military maneuvers where mobile personnel need to maintain direct contact with each other and the central control. One of the factors that currently limits the effectiveness and practicality of these systems is portability. These systems require lightweight equipment that can be quickly and easily deployed and operated in a variety of environments. Parabolic dish antennas are the only antennas capable of providing the high gain required for direct satellite communication but their size and weight severely limit their portability and hence their use for portable direct satellite communication. Inflatable structures have been used in the space environment to overcome the limitations of launch vehicle size and weight restrictions. They are constru cted from thin film, or gossamer materials, and use internal pressure to maintain their shape. Inflatable structures are lightweight, have a low stowed volume and a high packing efficiency. It is proposed that this type of structure can be used to produce an inflatable parabolic dish antenna that can operate under terrestrial conditions to overcome the limits on portability for land-based communication. This thesis presents a design for a parabolic dish antenna and conical feed horn constructed entirely from polyester thin film. To further reduce the weight and stowed volume of the antenna the conical horn is fed by a microstrip patch. The performance of the components and their ability to operate under terrestrial conditions are assessed by comparing the results to those of an identical rigid system.

<p> Inflatable structures have attracted much interest in space applications. The three main components of inflatable satellites are inflatable struts, an inflatable torus as the structural support component, and some sort of lens, aperture, or array housed inside the boundary of the torus. This project is devoted towards understanding the dynamic characteristics of an inflated torus with a focus on the self-rigidizing torus, SRT, developed by United Applied Technologies.</p> <p> The self-rigidizing torus is manufactured from flat sheets of Kapton® that are formed into curved films with the regular pattern of hexagonal domes. The inflated torus can support its structural shape even when there is no internal pressure.</p> <p> Modal testing is used to determine the dynamic properties of the structure for comparison with the numerical model. The feasibility of using a non-contact in-house fabricated electromagnetic excitation is investigated. The first four, in-plane and out-of-plane, damped natural frequencies and their corresponding damping ratios and modes shapes are extracted and compared with prior experimental studies. A preliminary finite element modal analysis is carried out for a torus made of flat film and the results are compared with prior studies. Kapton 300JP®'s frequency-dependent modulus of elasticity is determined.</p> <p> Owing to the large number of hexagonal domes in the self-rigidizing torus, a simplified sub-structuring technique is used. Each hexagonal dome is replaced with a statically equivalent flat hexagon with the same mass and stiffness as the hexagonal dome. Then the finite element modal analysis of the self-rigidizing torus is carried out for an equivalent torus made of flat film. The geometric nonlinearity and the effect of the follower load on the stiffness are included in this analysis. The methodology is verified through the correlation between the analytical and modal test results of the self-rigidizing torus.</p> / Thesis / Doctor of Philosophy (PhD)

Inflatable dams are flexible, cylindrical structures anchored to a foundation. They are used for a variety of purposes, e.g. diverting water for irrigation or groundwater recharging, impounding water for recreational purposes, and raising the height of existing dams or spillways. The vibration behavior of such dams is analyzed. Single-anchor inflatable dams with fins are considered. First, a static analysis is performed which yields the equilibrium shapes of the dam, both in the presence and absence of water. Then, a dynamic analysis is undertaken which analyzes the small vibrations of the inflatable dam about the equilibrium configuration, both in the presence of water (hydrostatic water as well as parallel flowing water) and absence of water. The dam is modeled as an elastic shell. It is assumed to be air-inflated and resting on a rigid foundation. The cross-sectional perimeter, material thickness, modulus of elasticity, and Poisson's ratio are given. The analysis is performed for different values of internal pressure and external water heads. Initially, the dam is assumed to lie flat. The internal pressure is then increased slowly until it reaches the desired value. Then the external water is applied and the equilibrium configuration is obtained. Small vibrations about this configuration are considered. The water is assumed to be inviscid and incompressible, and potential theory is used. The infinite-frequency limit is assumed on the free surface. A boundary element technique is utilized to determine the behavior of the water, and the finite element program ABAQUS is used to analyze the structural behavior. Both the cases of fluid at rest and flowing parallel to the dam are considered. The vibration frequencies and mode shapes are computed. The effect of the internal pressure of the dam is investigated, and the results are compared to those for the dam in the absence of external water. / Master of Science

Inflatable space-based devices have become popular over the past three decades, as they offer minimized launch-mass and launch-volume. Since some satellites have mirror sections over fifty feet in diameter and struts with lengths over ninety feet, inflation while in orbit has become a necessary procedure. Once inflated, these space structures are subject to two types of vibrations: those induced mechanically by guidance systems and space debris and those induced thermally from variable amounts of direct sunlight as they orbit about earth. Controlling vibrations of spaced-based structures is critical to ensuring optimal performance. The focus of this research is derived from an Air Force program to develop and model an active control system using smart materials to suppress the vibrations of inflatable communication satellites. When small piezoceramic devices are attached to an aluminum or steel structure, the effects of the piezo on the dynamic properties of the host are typically ignored. However, the inflatable satellites of interest to this project are manufactured from Kapton®, a thin, light polyimide film. Therefore, even a piezopolymer film actuator, such as PVDF, could greatly change the mass and stiffness values in the area under and around the patch, altering the dynamic behavior of the satellite. Thin-walled pressure vessel theory was employed to assess the state of stress at any location on an inflated torus. A flat, rectangular coupon was selected at a general point on the structure and modeled as a membrane. The equation of motion for this membrane with clamped edges was derived and a closed-form solution for the natural frequencies and mode shapes was presented. The Rayleigh-Ritz and finite element methods were then seen to numerically approximate the natural frequencies and mode shapes for the bare membrane with a high degree of accuracy. A passive PVDF patch was then attached to the base membrane and the equation of motion derived using an energy approach. Since a closed-form solution was not readily available, the Rayleigh-Ritz and finite element methods were again employed to obtain approximate results that agreed remarkably well. Trends in natural frequencies for various patch areas and thicknesses were explored. It was shown, that membrane theory represented the added mass of the patch but was unable to account for the added stiffness of the PVDF attachment. Traditional membrane theory was also unable to model an active PVDF patch as a sensor for out of plane vibrations, but the ability of the patch to alter the tension in the base layer was predicted. / Master of Science

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Dunnage bags are an inflatable dunnage variant, positioned and inflated between goods in multi-modal containers to restrain and protect the goods while in transit. This project endeavours to develop a simple method of generating new numerical prototypes for dunnage bags suitable for simulating operational loading of the bags. Previous research has produced a model that simulates the inflation of a paper dunnage bag using a simple pressure load. A dunnage bag reinforced with plain-woven polypropylene was chosen as the test case. Woven polypropylene is a highly non-linear, non-continuous, non-homogeneous material that requires specialised material models to simulate. A key aspect of this project was to develop a simple method for characterising woven-polypropylene and replicating it's response with material models native to LS-DYNA. The mechanical response of the plain-woven polypropylene was tested using a bi-axial tensile test device. The material response from physical testing was then mapped to two material models using the numerical optimiser LS-OPT. The response of the calibrated material models was found to correlate well with the measured response of the woven material. Dunnage bags are subjected to cyclic loading in operation. In order to capture the effects of compressing the contained gas, a gas inflation model was added to the model that calculates the pressure in the bag based on the Ideal Gas Law. A full bag model making use of the calibrated material models and the inflation model was subjected to a cycled boundary condition simulating loading and unloading of an inflated dunnage bag. The two prototype models captured the pressure drop in the bag due to material plastic deformation and the restraining force produced by the bag to within 10 %. The prototype models were also found suitable for predicting burst pressure in voids of arbitrary size and shape. / AFRIKAANSE OPSOMMING: Stusakke is 'n opblaasbare soort stumateriaal wat tussen goedere in multimodale vraghouers geposisioneer en opgeblaas word om sodoende die goedere vas te druk en te beskerm tydens vervoer. Hierdie projek poog om 'n eenvoudige manier te ontwikkel om nuwe numeriese prototipes vir stusakke, geskik om operasionele lading van die sakke te simuleer, te ontwikkel. Vorige navorsing het 'n model ontwikkel wat die opblaas van 'n papier stusak met eenvoudige drukkrag simlueer. 'n Hoë-vlak stusak versterk met plein-geweefde polipropileen, is gekies om getoets te word. Geweefde polipropoleen is 'n hoogs nie-lineêre, onderbroke, nie-homogene materiaal wat gespesialiseerde materiaalmodelle nodig het vir simulasie. Een van die fokuspunte van hierdie projek is om 'n eenvoudige metode te ontwikkel om die karaktereienskappe van polipropoleen te identifiseer en die gedrag daarvan na te maak met die materiaalmodelle van LSDYNA. Die meganiese reaksie van die plein-geweefde polipropoleen is getoets met 'n biaksiale/tweeassige trektoets-toestel. Die materiaal se reaksie op die fisiese toets is ingevoer op 'n numeriese optimiseerder, LS-OPT, om op die materiaalmodelle te toets. Die reaksie van die gekalibreerde materiaalmodelle het goed gekorelleer met die gemete reaksie van die geweefde materiaal. Stusakke word tydens diens onderwerp aan sikliese lading. Om die effek van die saamgepersde gas vas te stel is 'n gas-opblaasbare model bygevoeg by die model wat die druk in die sak bereken, soos gebaseer op die Ideale Gas Wet. 'n Volskaalse sakmodel wat gebruik maak van die gekalibreerde materiaalmodelle en die opblaas-model is onderwerp aan sikliese grensvoorwaardes wat die lading en ontlading van 'n opblaasbare stusak simuleer. Die twee prototipe modelle het die drukverlies in die sak a.g.v. die materiaal-plastiek vervorming en die bedwingingskrag van die sak beperk tot 10 %. Die protoyipe modelle is ook geskik bevind om barsdruk in arbitrêre leemtes te voorspel.

Performance of inflatable wings was investigated through laboratory, wind tunnel and flight-testing. Three airfoils were investigated, an inflatable-rigidazable wing, an inflatable polyurethane wing and a fabric wing restraint with a polyurethane bladder. The inflatable wings developed and used within this research had a unique outer airfoil profile. The airfoil surface consisted of a series of chord-wise \bumps.andamp;quot; The effect of the bumps or \surface perturbationsandamp;quot; on the performance of the wings was of concern and was investigated through smoke-wire flow visualization. Aerodynamic measurements and predictions were made to determine the performance of the wings at varying chord based Reynolds Numbers and angles of attack. The inflatable baffes were found to introduce turbulence into the free-stream boundary layer, which delayed separation and improved performance. Another area of concern was aeroelasticity. The wings contain no solid structural members and thus rely exclusively on inflation pressure for stiffness. Inflation pressure was varied below the design pressure in order to examine the effect on wingtip twist and bending. This lead to investigations into wing deformation due to aerodynamic loading and an investigation of wing flutter. Photogrammetry and laser displacement sensors were used to determine the wing deflections. The inflatable wings exhibited wash-in deformation behavior. Alternately, as the wings do not contain structural members, the relationship between stiffness and inflation pressure was exploited to actively manipulate wing through wing warping. Several warping techniques were developed and employed within this re-search. The goal was to actively influence the shape of the inflatable wings to affect the flight dynamics of the vehicle employing them. Researchers have developed inflatable beam theory and models to analyze torsion and bending of inflatable beams and other inflatable structures. This research was used to model the inflatable wings to predict the performance of the inflatable wings during flight. Design elements of inflatable wings incorporated on the UAVs used within this research are also discussed. Finally, damage resistance of the inflatable wings is shown from results of flight tests.