Passive solar array orientation system /thermal heliotrope/ Final report, 23 Dec. 1968 - 23 Sep. 1969

Tracking requirement, design, and fabrication of passive solar array orientation system using bimetal element

Ultra-thin film tribology of elastomeric seals in pressurised metered dose inhalers

Within pressurised Metered Dose Inhalers (pMDIs) the contact between the valve components and elastomeric seals is of major significance, representing the main contributory factor to the overall system frictional characteristics. Therefore, the seal performance is extremely important and must be optimised to meet the contradictory requirements of preventing leakage and allowing smooth actuation. The environmentally driven trend to HFA formulations as opposed to CFC based ones has deteriorated this problem due to poor lubrication conditions and it has, consequently, increased the frictional losses during the pMDI actuation (hysteresis cycle). Research has been conducted into the key areas of the inhaler mechanism. As such, the contact pressure distribution and resulting reactions have been investigated, with emphasis on the correct treatment of the elastomer (seal) characteristics. The modelling of the device has been conducted within the environment of the multibody dynamics commercial software ADAMS, where a virtual prototype has been built using solid CAD geometries of the valve components. An equation was extrapolated to describe the relation between the characteristics of the ultra thin film contact conditions (sliding velocity, surface geometry, film thickness and reaction force) encountered within the inhaler valve and integrated into the virtual prototype allowing the calculation of friction within the conjuncture (due to viscous shear and adhesion). The latter allowed the analysis and optimisation of key device parameters, such as seal geometry, lubricant properties etc. It has been concluded that the dominant mechanism of friction is adhesion, while boundary lubrication is the prevailing lubrication regime due to the poor surface roughness to film thickness ratio. The multibody dynamics model represents a novel multi physics approach to study the behaviour of pMDIs, including rigid body inertial dynamics, general elasticity, surface interactions (such as adhesion), hydrodynamics and intermolecular surface interactions (such as Van der Waals forces). Good agreement has been obtained against experimental results at component and device level

Development of compressor end seals stator interstage seals, and stator pivot seals in air breathing propulsion systems Semiannual report no. 1, 29 Jun. - 31 Dec. 1965

Seal concepts evaluation for compressor end seals, stator interchange seals, and stator pivot seals in air breathing propulsion syste

Experimental and advanced computational modelling study of downhole elastomer seal assemblies

Elastomers seals are widely used in various drilling, completion, and production equipment. One such equipment is liner hanger which has become integral part of modern well designs. Failure of liner hanger seal assembly can compromise well integrity, and lead to severe health, safety, and environmental consequences. Concerns regarding reliability of elastomer seals in liner hanger assemblies have been raised by the regulators as well as industry. This dissertation work provides detailed investigation of design, and failure of downhole elastomer seal assemblies using experimentally supported advanced computational modeling techniques. This work is partially supported by Bureau of Safety and Environmental Enforcement (BSEE) and it is set in the context of liner hanger assemblies. However, major outcomes of this research also applies to other downhole seal assemblies. Specific objectives of this dissertation are - (i) investigate performance of liner hanger seal assembly under various design, operational, and failure scenarios, (ii) develop operating envelops and identify critical parameters influencing performance of the elastomer seal assembly, (iii) develop a modelling tool for predicting leakage through elastomer seal interface considering surface characteristics, (iv) generate guidelines for design and qualification of elastomer seals and provide regulatory recommendations. Novel technical aspects of this research work are – (i) studying material behavior of different elastomer material (NBR, EPDM, FKM, FEPM, FFKM, PTFE) under normal and downhole conditions, (ii) using the elastomer material data in true-scale finite element (FEA) models to evaluate equipment level performance of seal, (iii) scaled laboratory tests and analytical calculations to validate FEA models, and (iv) development of a leakage modelling tool that can predict leakage rates as a function of surface topography of seal interface and operating conditions. Results from this dissertation indicate that type and design of seal equipment determines which elastomer properties need to be qualified. Hardness and elastic modulus alone may not be good predictors of fitness-for-service of seal assembly. For example, performance of expandable liner hanger seal assembly primarily depends on seal dimensions and elastomer shear modulus while performance of conventional liner hanger seal assembly mainly depends on elastomer bulk modulus. Selection of appropriate elastomer material for a certain application depends not only on chemical environment and temperature but also on assembly design, operational constraints, and thermal changes. Comparative evaluation demonstrated that conventional liner hanger seal assembly outperforms expandable liner hanger seal assembly in terms of contact pressure generated per unit energization but it is more prone to failure than expandable assembly. Contact pressure at seal-pipe interface, as predicted by macro-scale FEA models, does not accurately indicate fluid pressure that can be effectively sealed. Leakage modelling studies demonstrated that surface characteristics of elastomer and fluid properties determines the contact pressure needed to achieve complete sealability. Leakage modelling approach developed in this work can be an invaluable tool in seal design workflow for determining target seal energization needed for complete sealability

DETAILED SPACIAL AND TIME RESOLVED STUDIES OF LUBRICANT DEGRADATION IN MULTI-CYLINDER DIESEL ENGINES

This work formed part of the North American Space Agency /US Department of Energy project to produce a 55% thermodynamic efficient diesel engine, which required the construction of a "low heat rejection" engine. Work was carried out on a Caterpillar 3406B, a commercial, multi-cylinder, 'low emission' diesel engine. The work evaluated oil mass and gas flow, the chemical and physical degradation of commercial and experimental lubricants, the effects the sulphur content in diesel fuels had on the particulate size in lubricants, lubricant transport through the piston ring pack of the Caterpillar 3406B, and the effects different piston ring packs had on both lubricant degradation and lubricant transport. Piston ring zone sampling was used throughout this work. Lubricant samples were taken from four positions on the Caterpillar 3406B piston, namely the 2nd compression ring, accumulator groove, 1 st compression ring and base of the crown land. A duel sampling system was developed which enabled lubricant samples to be taken from two sampling positions on the piston simultaneously. This sampling system proved to be reliable with over 650 hours of operation, at various engine speeds and loads. Oil mass and gas flow experiments showed complex behaviour. Oil mass and gas flow generally increased as engine speed and load increased, however 'peaks' of oil mass and gas flow were observed at various engine speed and load combinations, which may be a reflection of the piston ring pack design. Examination of oil mass obtained from 1991 and 1994 US Emission control piston ring packs, under conditions of low engine speed and low load, demonstrated that the 1994 piston rings allowed more lubricant to enter the ring pack. Significantly less oil was obtained from the base of the crown land with the 1994 piston ring pack, highlighting their superiority with regards to reducing lubricant related emissions. Measurement of the chemical and physical degradation of various lubricants demonstrated that degradation increased as the sampling position moved closer to the piston crown. Different degradation levels were noted whether the sampling position was on the piston face or behind the piston rings. Analysis of lubricant degradation using statistical techniques demonstrated that lubricant type, sampling position, fuel sulphur content and piston ring pack significantly affected lubricant degradation The work showed that engine speed and load did not effect lubricant degradation The use of statistical analysis demonstrated that lubricant samples could be graded according to their level of degradation, which highlights the potential use of piston ring zone sampling as a quick screening method for evaluating experimental lubricants. Lowering the sulphur content in diesel fuels had the effect of increasing the size of particulates in the lubricant. This questions the effectiveness of the dispersant additives in the lubricant formulation, and highlights the need for more effective dispersant additives to be used with lower sulphur diesel fuel Lubricant transport to the 1!1t compression ring was found to be considerably slower in a modem engine, when compared to older engines. This demonstrates that there may be a need for engine manufacturers to recommend the use of synthetic lubricants over the use of mineral based lubricants. A lubricant flow model was developed which showed that the piston rings act as secondary oil control rings and that 19«110 of the lubricant that reaches the 2nd compression ring would be transported to the base of the crown land. Comparison of lubricant degradation in the 1991 and 1994 US Emission control piston ring packs demonstrated that the 1994 piston ring pack degraded lubricants to a lesser extent, which is thought to be due to there being more oil present in this piston ring pack. The lubricant transport measurements showed that the transport time to the 191 compression ring was less for the 1994 piston rings than the 1991 piston rings, and that the 1994 rings allowed more lubricant to be passed from the 2nd compression ring to the 191 compression ring.North American Space Agency)/US Department of Energy, through Caterpillar INC, BP Amoc

The effect of transient dynamics of the internal combustion compression ring upon its tribological performance

The losses in an internal combustion engine are dominated by thermal and parasitic sources. The latter arises from mechanical inefficiencies inherent within the system, particularly friction in load bearing conjunctions such as the piston assembly. During idle and at low engine speeds, frictional losses are the major contributor to the overall engine losses as opposed to the dominant contribution of thermal losses under other driving conditions. Given the relatively small size and simple structure of the top compression ring, it has a disproportionate contribution to the total frictional losses. This suggests further analysis would be required to understand the underlying causes of compression ring behaviour throughout the engine cycle. The available literature on tribological analyses of compression rings does not account for the transient ring elastodynamics. They usually assume a rigid ring for film thickness and power loss predictions, which is not representative of the ring’s dynamic response. A combined study of ring elastodynamic behaviour and its tribological conjunction is a comprehensive approach. [Continues.

A numerical and experimental study on cavitation in positive displacement pumps and its application in valve design optimization

Appendix of "Technical sheets and drawings" appears in the online version only.This thesis was previously held under moratorium from 26/11/2015 to 15/06/2021.A comprehensive and transient Computational Fluid Dynamic model of a Positive Displacement reciprocating pump in cavitating condition was developed in order to study the main features and the causes of cavitation in this kind of device. Several sensitivity analyses were also carried out in order to identify the most influential parameters on cavitation; the design of the inlet valve as well as the operating conditions were found to be the main parameters playing an important role in cavitation. To complete the numerical study, a sensitivity analysis on the air content in the water was carried out.;This highlighted the importance of the physical properties of the working liquid in influencing the vapour generation during cavitation. The second part of the project was dedicated to the experimental analysis; a test rig replicating the numerical model was designed and built. The experimental tests were carried out and the results were compared to the numerical data obtained in the previous part. The comparison revealed a reasonable accuracy as well as good consistency although numerical problems were found in the way the cavitation model accounted for the influence of the air dissolved in the water which was overestimated. The validated numerical model was utilised to modify the design of the inlet valve.;A new model of the valve was presented and described, it was demonstrated capable of minimising the vapour generation under the same operating condition with respect to the initial valve design. The modification proposed was implemented in the design of new valves which are already being manufactured and tested in the field, they will be introduced into the market afterwards. The project is the demonstration that numerical tools based on CFD are nowadays ready to effectively support designers and industries in bringing down the cost of the engineering process of new and more efficient products.A comprehensive and transient Computational Fluid Dynamic model of a Positive Displacement reciprocating pump in cavitating condition was developed in order to study the main features and the causes of cavitation in this kind of device. Several sensitivity analyses were also carried out in order to identify the most influential parameters on cavitation; the design of the inlet valve as well as the operating conditions were found to be the main parameters playing an important role in cavitation. To complete the numerical study, a sensitivity analysis on the air content in the water was carried out.;This highlighted the importance of the physical properties of the working liquid in influencing the vapour generation during cavitation. The second part of the project was dedicated to the experimental analysis; a test rig replicating the numerical model was designed and built. The experimental tests were carried out and the results were compared to the numerical data obtained in the previous part. The comparison revealed a reasonable accuracy as well as good consistency although numerical problems were found in the way the cavitation model accounted for the influence of the air dissolved in the water which was overestimated. The validated numerical model was utilised to modify the design of the inlet valve.;A new model of the valve was presented and described, it was demonstrated capable of minimising the vapour generation under the same operating condition with respect to the initial valve design. The modification proposed was implemented in the design of new valves which are already being manufactured and tested in the field, they will be introduced into the market afterwards. The project is the demonstration that numerical tools based on CFD are nowadays ready to effectively support designers and industries in bringing down the cost of the engineering process of new and more efficient products

Experimental and numerical analysis of tensile membrane action in reinforced concrete slabs in the framework of structural robustness

As a consequence of several structural failures in the last decades, the European Standard EN 1990 (2002) ‘Basis of structural design’ incorporated the following requirement with respect to robustness: “A structure shall be designed and executed in such a way that it will not be damaged by events such as explosion, impact and the consequence of human errors to an extent disproportionate to the original cause”. In addition, the European Standard EN 1991-1-7 (2006) ‘Actions on structures – Part 1-7: Accidental actions’ points to strategies to enhance structural robustness, emphasising amongst others the favourable contribution of developing alternate load paths in case of abnormal loading events. The investigations reported in the present thesis aim for a better understanding of the alternate load path provided by the transition from a flexural to a tensile load transfer. In particular, the load transfer provided by tensile membrane action developing at very large displacements after a support removal scenario and, subsequently, excessive loading is investigated. It is widely appreciated that this tensile membrane behaviour has a positive effect on the structural behaviour. The ultimate limit state behaviour for tensile membrane action developing in slabs, however, is largely unknown due to the limited amount of experimental largescale investigations. Based on an extensive literature review, an experimental program has been elaborated in order to investigate tensile membrane action developing in a restrained one-way concrete slab. A unique test set-up has been developed allowing a loading test on a four-span reinforced concrete slab strip under longitudinal elongation restraint into the region of large deflections. The tested slabs were 140 mm or 160 mm thick and 1800 mm wide with a geometric reinforcement ratio of about 0.5 %. The total length of each specimen was 14.3 m, whereas the distance between the inner supports and the central support was 4 m. These spans changed to one span of 8 m between the inner supports after the controlled removal of the central support, thus simulating an accidental event.Further, also a testing procedure was elaborated, consisting of 3 phases (i.e. loading until an arbitrary preloading level, removal of the central support and loading until failure). During the first phase, the load was gradually increased up to the preloading level for the situation where the central support was still present. Subsequently, the slab was unloaded. In a second phase, the central support of the specimens was gradually removed in order to simulate a failure of the support and to obtain valuable data regarding the robustness of the specimens. Accordingly, the two inner spans of 4 m each, changed to a single span of 8 m. The specimens were allowed to bend progressively in the central span of the slab, resulting in a redistribution of stresses and the development of an alternate load path distributing the emerging forces to the remaining supports. Finally, in the third phase, the load was applied again by two line loads in a displacement controlled manner until failure. With increasing vertical deflections of the specimens the slabs’ ends started to move inwards provoking a significant increase in the loadcarrying capacity due to emerging tensile membrane forces established by a horizontal restraining system. In total three different tests on slab strips with horizontal restraint were performed. In case of slab 1, the longitudinal top and bottom flexural reinforcement was continuous over the entire length of the specimen. Hence, no reinforcement curtailing was applied. Further, a second specimen featuring a realistic reinforcement curtailment was tested. In case of slab 3 the longitudinal flexural reinforcement was curtailed similar to slab 2, but the thickness of the slab was reduced from 160 mm to 140 mm. In all three tests, tensile membrane action was activated during the third phase of testing, significantly increasing the load carrying capacity of the specimen under investigation. During the tests, manual measurements were executed after each successive increase of the load or displacement, comprising dial gauges, crack widths measurements and DEMEC measurements. Further, around 60 digital channels were recording the digital measurements comprising displacements, horizontal (membrane) and vertical (reaction) load cell forces and strain measurements with stirrups. Each tested slab strip was exposed to three distinct stages: an elastic, plastic and tensile membrane stage. The development of displacements, strain measurements as well as the horizontal forces within this investigation confirmed a load transfer process from an elastic bending mechanism, over a plastic stage towards a tensile membrane mechanism controlled by tension. As tensile membrane forces developed, the load bearing capacity was able to increase until approximately 3 times the service load for slab 1 and 2.6 times for slab 2 (despite the removal of the central support). For slab 3 the ultimate collapse load even amounted to about 3.6 times the service load. Hence, the importance of quantifying this additional bearing capacity became clear, especially in robustness analysis, as otherwise one disregards an inherently available and very large additional safety. The test results provide a unique set of detailed experimental data (crack widths, deformations, rotation angles, displacements, etc.) allowing for a detailed analysis and refined comparisons with respect to the structural response under tensile membrane action as well as regarding the failure criteria.Finite element modelling was used to simulate the structural behaviour of oneway slabs under large deformations and tensile membrane actions. On the basis of the experimental findings, the numerical model was validated with special attention to material models, mesh definition and boundary conditions accounting for highly non-linear material performances as well as geometrical non-linear behaviour. In summary, the load-displacement curves until the failure of the top reinforcement bars, displacements, rotation angles, the development of strains and tensile membrane forces were calculated within a reasonable tolerance and showed good agreement with the laboratory tests. As such, it is demonstrated that the developed finite element model is a suitable tool being capable to predict the structural response under tensile membrane forces. By means of this developed finite element model, a parametric study was conducted. In this study the influence of several geometries (various span lengths, thicknesses and reinforcement ratios), material assumptions (various steel qualities and ultimate reinforcement strains) and boundary conditions are investigated and discussed. A literature study with respect to analytical models for tensile membrane action was performed serving as a starting point for the analytical investigation. On the basis of the standard plastic theory an analytical model is proposed firstly considering perfectly restrained edges. The loading response, the formation of tensile membrane action and the failure load is accounted for. Further, the proposed method was applied and refined in order to simulate the structural behaviour of the conducted slab experiments by incorporating non-linear horizontal movements of the restraining system. The calculation results were compared with numerical and experimental findings and the analysis results show good agreement. In the presented PhD thesis it is demonstrated by means of experimental, numerical as well as analytical investigations that the development of tensile membrane behaviour as a result of horizontal edge restraint is capable of generating a considerable strength reserve significantly increasing the loading response of one-way reinforced concrete slabs when very large deformations occur. The insights gained from these investigations give strong evidence of the beneficial contribution of tensile membrane action to the loading capacity and robustness of concrete structures in accidental load situations. The developed numerical and analytical calculation techniques are shown to be feasible tools not only to quantify the loading response corresponding to the experimentally observed ultimate limit state behaviour but also to predict the structural response under tensile membrane action for other boundary conditions and material characteristics serving as a general calculation framework to include tensile membrane action in conventional design when robustness is considered

Active Control of Fan Noise-Feasibility Study. Volume 2: Canceling Noise Source-Design of an Acoustic Plate Radiator Using Piezoceramic Actuators

The feasibility of using acoustic plate radiators powered by piezoceramic thin sheets as canceling sources for active control of aircraft engine fan noise is demonstrated. Analytical and numerical models of actuated beams and plates are developed and validated. An optimization study is performed to identify the optimum combination of design parameters that maximizes the plate volume velocity for a given resonance frequency. Fifteen plates with various plate and actuator sizes, thicknesses, and bonding layers were fabricated and tested using results from the optimization study. A maximum equivalent piston displacement of 0.39 mm was achieved with the optimized plate samples tested with only one actuator powered, corresponding to a plate deflection at the center of over 1 millimeter. This is very close to the deflection required for a full size engine application and represents a 160-fold improvement over previous work. Experimental results further show that performance is limited by the critical stress of the piezoceramic actuator and bonding layer rather than by the maximum moment available from the actuator. Design enhancements are described in detail that will lead to a flight-worthy acoustic plate radiator by minimizing actuator tensile stresses and reducing nonlinear effects. Finally, several adaptive tuning methods designed to increase the bandwidth of acoustic plate radiators are analyzed including passive, active, and semi-active approaches. The back chamber pressurization and volume variation methods are investigated experimentally and shown to be simple and effective ways to obtain substantial control over the resonance frequency of a plate radiator. This study shows that piezoceramic-based plate radiators can be a viable acoustic source for active control of aircraft engine fan noise

The structural behaviour of concrete at elevated temperatures

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