bluuebunny/crossref_metadata_2025 huggingface dataset:
Solar Receiver Experiment for the Space Station Freedom Brayton Engine
Authors: Strumpf Hal J. , Coombs Murray G.
Published: June 2008

An experimental investigation has been conducted to develop fabrication procedures and acquire test data for a heat receiver assembly (HRA) in support of the design and development effort for the Brayton engine solar receiver for the NASA Space Station Freedom solar dynamic option. The HRA configuration is a cylindrical receiver lined with tubes; each tube is surrounded by phase change material (PCM). The Brayton cycle working fluid flows inside the tubes. The PCM surrounding the tubes, a eutectic mixture of LiF and CaF2, is contained in a series of sealed metallic containment canisters. During periods of sunlight, heat is transferred through the PCM to the Brayton cycle working fluid; during periods of eclipse, the PCM gives up its heat to the working fluid. A section of a full-size receiver tube was fabricated, assembled, and tested. Performance of the receiver tube qualitatively validates the expected receiver performance. Over 4500 cycles (of approximately 91-min duration) had been completed as of June 15, 1989.
Integration and Optimization of the Gas Removal System for Hybrid-Cycle OTEC Power Plants
Authors: Rabas T. J. , Panchal C. B. , Stevens H. C.
Published: June 2008

A preliminary design of the noncondensible gas removal system for a 10 MWe, land-based hybrid-cycle OTEC power plant has been developed and is presented herein. This gas removal system is very different from that used for conventional power plants because of the substantially larger and continuous noncondensible gas flow rates and lower condenser pressure levels which predicate the need for higher-efficiency components. Previous OTEC studies discussed the need for multiple high-efficiency compressors with intercoolers; however, no previous design effort was devoted to (a) the details of the intercoolers, (b) integration and optimization of the intercoolers with the compressors, and (c) the practical design constraints and feasibility issues of these components. The resulting gas removal system design uses centrifugal (radial) compressors with matrix-type crossflow aluminum heat exchangers as intercoolers. Once-through boiling of ammonia is used as the heat sink for the cooling and condensing of the steam-gas mixture. A computerized calculation method was developed for the performance analysis and subsystem optimization. For a specific number of compressor units and the stream arrangement, the method is used to calculate the dimensions, speeds, power requirements, and costs of all the components.
Modeling of Arbitrary-Shaped Specific and Latent Heat Curves in Phase-Change Storage Simulation Routines
Authors: Bart G. C. J. , van der Laag P. C.
Published: June 2008

In solar heat storage, use is often made of the latent heat of phase-change materials (PCM) with a wide temperature transition range. In this paper the heat withdrawal of a slab of such a phase-change material after a step-wise change in wall temperature, and as a function of the shape of the specific and latent heat curve, has been studied with a computer simulation. It will be outlined that various shaped curves show the same heat withdrawal character as an equivalent rectangular-shaped specific heat curve. A procedure to obtain this equivalent curve will be given.
Solar Central Receiver Thermal Loss Test Method
Authors: Baker Alvin F.
Published: June 2008

This paper presents a test method for determining the thermal loss from a solar central receiver at normal operating conditions. The thermal loss determined by this test method is independent of knowing the incident solar power onto the receiver. Thermal loss includes losses from emitted radiation, convection, and conduction. Reflected radiation is accounted for by an effective solar absorptance. The paper describes the test method and derives the equations used to evaluate the receiver thermal loss from the test.
A Repetitive Day Method for Predicting the Long-Term Thermal Performance of Passive Solar Buildings
Authors: Feuermann D.
Published: June 2008

The long-term thermal performance of passively-heated solar buildings is predicted by a single repetitive meteorological day which contains judiciously chosen solar radiation and ambient temperature functions. These are used as the driving functions of the governing equations that describe the passive solar building under study. The solar radiation and ambient temperature functions are chosen such that they include, both qualitatively and quantitatively, the essential radiation and temperature statistics of the climate in which the building is to be located. The relevant statistics are determined from hourly meteorological data. When hourly meteorological data are not available for a given location, the solar radiation and ambient temperature functions can be constructed from the knowledge of only two climatic data, namely, the monthly average horizontal radiation and the ambient temperature. Model calculations compare favorably with experimental data from Los Alamos solar test cells and with computer simulations.
Two-Dimensional Heat Transfer From Earth-Sheltered Buildings
Authors: Krarti Moncef , Claridge David E.
Published: June 2008

This paper describes use of the Interzone Temperature Profile Estimation (or ITPE) technique, an analytical calculation procedure to predict heat transfer within earth in contact with a structure. The solutions governing steady-state and steady-periodic heat conduction are derived for rectangular earth-sheltered buildings. The procedure accepts continuously variable values of geometric dimensions, insulation levels, and constant soil thermal characteristics and considers the presence of a finite water table level. Soil temperature profiles are shown for both steady-state and steady periodic conditions. The effects of insulation and water table depth on the heat losses from an earth-sheltered building envelope are discussed.
Evaporation Rate Model for a Natural Convection Glazed Collector/Regenerator
Authors: Nelson D. J. , Wood B. D.
Published: June 2008

In the present work, a numerical method has been applied to model the water evaporation rate of a glazed collector/regenerator component of an open-cycle absorption refrigeration system. This two-dimensional model calculates local heat and mass-transfer coefficients as part of the solution. The air flow in the glazed channel is driven by the combined buoyancy of both heat and mass transfer (water evaporation). Since the heat and mass-transfer coefficients each depend on both of the driving potentials determined by local conditions in the falling film, a solution of the conjugate problem is required. The resulting nonuniform air-film interface conditions cause the local heat and mass transfer to differ significantly from the uniform boundary condition case. The glazed collector/regenerator is much less sensitive to the ambient temperature and humidity than the unglazed collector. The addition of a glazing over the collector/regenerator provides a significant performance improvement and enhances solution regeneration in a windy humid climate. The glazed collector/regenerator water evaporation rate is higher relative to the unglazed case because the reduction in convective and radiative heat losses increases the absorbent temperature and vapor pressure sufficiently to overcome the concomitant reduction in the mass-transfer coefficient.
The Use of an Artificial Diffusion Term to Improve a Distributed-Parameter Model of a Flat-Plate Solar Collector
Authors: Siegler Miriam , Rorres Chris
Published: June 2008

Two models for the temperature distribution within a flat-plate solar collector are investigated. The simpler of the two (the one-temperature model) is a distributed-parameter model that determines the temperature of the collector fluid without reference to the temperature of the collector plate. The more accurate model of the two (the two-temperature model) takes into consideration the temperatures of both the collector plate and the fluid. In a previous work the authors showed how the solutions of the two-temperature model tend to the solutions of the one-temperature model as the thermal coupling between the fluid and the collector plate increases. In the present work we include an artificial diffusion term in the one-temperature model. We show that this diffusion term causes the solutions of the one-temperature model to better approximate those of the more accurate two-temperature model. In essence, the artificial diffusion term produces effects similar to those caused by the thermal coupling between the fluid and the collector plate, which is not accurately modeled in the original one-temperature model. In realistic collectors the value of the diffusivity associated with this artificial diffusion term is much larger than the diffusivity of the collector fluid, which we neglect in all models under consideration. Graphical results further demonstate the good agreement between the revised one-temperature model and the two-temperature model.
Techniques for Processing Experimental Data From a Solar Central Receiver to Evaluate the Receiver Steady-State Efficiency
Authors: Baker Alvin F.
Published: June 2008

This paper describes techniques for processing experimental data from a solar central receiver to evaluate the receiver steady-state efficiency. These techniques are applicable when the necessary experimental data is recorded on media that can be processed by a computer. The description includes how to select which measured value to use for the various parameters, how to determine a receiver steady-state condition, and how to evaluate the receiver efficiency. We compare the results from using these techniques for two different solar central receiver facilities using two different methods to evaluate the receiver steady-state efficiency.
Stress Intensity Factors and Crack Paths for Cracks in Photoelastic Motor Grain Models
Authors: Smith C. W. , Constantinescu D. M. , Liu C. T.
Published: June 2008

Computational analysis and two dimensional tensile tests on single motor grain fins suggest that cracks in fin tips are most likely to originate at the coalescence of the fin end tip radius with a small radius emanating from the side of the fin. Prior studies have indicated that under internal pressure, cracks on the fin axis are subject to similar stress peaks and may grow more readily than the former types due to an absence of shear modes. The present study focuses upon two types of cracks emanating from the former location called “off-axis” cracks and attempts to differentiate from the two types by their paths and SIF values, determined by the frozen stress photoelastic method.
Study of Microstructural Effect in Particulate Composites
Authors: Kwon Y. W. , Liu C. T.
Published: June 2008

The effects of random and non-uniform particle distribution on the damage initiation and growth leading to a crack were investigated for particulate composites using a multi-scale technique. Damage was described at the constituent material level (i.e. micro-level) and the results compared well qualitatively and quantitatively with experimental observation. Non-uniform, random particle distribution yielded sporadic crack initiation and growth within a uniform tensile specimen. No local crack propagated beyond a certain size. Breakage of the specimens was not caused by the continuous growth of a single critical crack. Instead, coalescence of neighboring sporadic short cracks resulted in breakage of the specimens. Computer simulation indicated that random particle distribution affected the strength of the composite significantly, but as expected, not its effective stiffness.
A General Numerical Procedure for Extracting Mixed-Mode Stress Intensity Factors Along the Fronts of Three-Dimensional Nonplanar Cracks
Authors: Gosz M. , Cammino R.
Published: June 2008

A numerical procedure is described for extracting mixed-mode stress intensity factors along the fronts of three-dimensional, nonplanar cracks embedded in solids. The mixed-mode stress intensity factors at points along the crack front are obtained by evaluating interaction energy integrals for three-dimensional, non-planar cracks. To assess the validity of the numerical procedure, two numerical examples are considered. First, we consider the problem of a non-planar, lens-shaped crack in an infinite solid subjected to hydrostatic tension. The numerical results are shown to be in excellent agreement with available analytical results. We then consider the case of a non-planar, warped elliptical crack surface, where to our knowledge no analytical solution exists, and the results are discussed.
Identification of Critical Surface Displacement Parameters for Characterization of Subsurface Flaws
Authors: Herrington Paul D. , Schilling Paul J. , Verges Melody A. , Durgam Prashanth K.
Published: June 2008

Several NDE methods provide accurate techniques for measuring surface displacements. While these techniques have been successful in identification of near-surface embedded flaws, they generally offer little in terms of characterization of the flaws. The ability to characterize embedded flaws from measurements of surface displacements would offer substantial benefits, especially in terms of remaining life predictions. This paper focuses on the identification of critical out-of-plane surface displacement parameters, and assessment of the potential to characterize subsurface flaw geometry based on these parameters. Finite element models of a homogeneous material have been created that vary the embedded flaw size and edge distance. The results suggest that there is potential to characterize the subsurface geometry from the surface displacement parameters.
Break Up Patterns of a Linear String of Balls Hit by a Cue Ball
Authors: Vinogradov Oleg
Published: June 2008

The timing and the sequence of break ups of a string of balls hit by a cue ball reflect the properties of both the system and the balls. If the system is kept the same then different ball’s models may lead to different break up patterns and thus allow assessment of the validity of various models. The latter is important in predicting the outcome of dynamic simulations in granular mechanics, especially when in dense systems clusters of balls are formed. Two ball’s models, with equivalent linear and nonlinear (Hertz) stiffness, are tested numerically for different strings of balls: from 5 to 30. The collisions are assumed to be central. It is shown that the equivalent stiffness model is more computationally efficient while preserving the accuracy of the break up phenomenon.
Computational Methods for the Design of Deformation Processes of Porous Materials
Authors: Zabaras Nicholas , Ganapathysubramanian Shankar
Published: June 2008

An updated Lagrangian framework of the continuum sensitivity method (CSM) is presented to address important computational design problems in the deformation processing of porous materials. Weak sensitivity equations are developed that are consistent with the kinematic, constitutive, contact and thermal analyses used in the solution of the direct thermomechanical problem. The CSM is here used to analyze die and preform computational design problems in industrial metal forming processes wherein temperature and the accumulated damage play an important role in influencing the deformation mechanism, material state and shape of the deformed workpiece.
Computational Nanomechanics
Authors: Kwon Y. W. , Jung S.
Published: June 2008

A computational technique for nanomechanics was presented for static equilibrium problems. The approach was based on atomic force equilibrium that was computed from energy potential function. This atomic model was coupled with the conventional finite element analysis model. Furthermore, a multi-scale approach relating the nano-scale behavior to the macro-scale mechanical properties was provided with an example of composite materials. Various examples were provided to demonstrate the presently developed technique.
Nonlinear 3D Finite Element Formulation for the Analysis of Submarine Pipelines During Laying Operations
Authors: Ciaccia Marco , Marti´nez Cora , Goncalves Raul
Published: June 2008

A new three-dimensional formulation using the finite element method is presented in this paper to analyze stresses and displacements of submarine pipelines during laying operations. The method is based on the Corotational formulation using Bernoulli nonlinear beam elements of constant cross-section. The problem is modeled in such a way that the actual boundary conditions are all taken into account. The pipe rolls over the barge ramp, passes through a tensioner and slides over the stinger before reaching the sea floor. The stinger is modeled introducing gap elements into the analysis, which makes possible to model exactly the actual boundary conditions, since these elements allow the pipeline to separate from the stinger naturally as required. This fact improves noticeably the calculation of the internal forces in the supported length of the pipe as well as in the region close to the lift off point. Additionally, using gap elements allows the pipe to reach the sea floor in all that points that naturally require this condition; therefore it is possible to drive the pipeline to reach the sea floor without imposing any displacement during the convergence process, which can generate instability problems. In addition to the applied tension at the barge, the buoyancy and the weight of the pipe, lateral forces induced by marine currents are also considered in the analysis. Numerical examples are provided in order to verify the accuracy and computational effectiveness of the developed method in comparison with the finite element formulation developed by the authors in previous works.
Buckling of Cracked Cylindrical Shells With Internal Pressure Subjected to an Axial Load
Authors: Vaziri A. , Estekanchi H. E. , Nayeb-Hashemi H.
Published: June 2008

Cylindrical shells constitute the main structural component in pressure vessels and pipelines. Buckling is one of the main failure considerations when designing these cylindrical shells. Defects such as cracks may develop during manufacturing or service life of these structures. These defects can severely affect their buckling behavior due to high stress field generated around these defects. Finite Element Analyses are performed to study the buckling behavior of cylindrical shells with and without a crack, under various internal pressures. Effects of crack length and its orientation on the buckling loads of cylindrical shells having a through or a thumbnail crack are studied. The results show that the buckling loads are not significantly affected for cylindrical shells with a crack less than a critical length. However, longer cracks cause local buckling of the cracked shells and can severely affect their buckling loads. This critical crack length depends on the crack orientation and the shell internal pressure. The results indicate that the buckling loads of cracked shells with internal pressure are quite sensitive to the crack angle. For cylindrical shells with an axial crack, the first buckling load drastically reduces with increasing the shell internal pressure. In contrast, the buckling load increases with the shell internal pressure for circumferentially cracked shells. The buckling loads of cracked shells with internal pressure are quite sensitive to crack angle. However, the bucking loads are little dependent to the crack angle for shells with no internal pressure.
Comparison of Vibration Characteristics of Stiffened Composite Shallow Circular Cylindrical Shell Panels
Authors: O¨zerciyes V. , Yuceoglu U.
Published: June 2008

The problem of “Free Vibrations Centrally and Non Centrally Stiffened Composite Shallow Cylindrical Shell Panels” are briefly considered and their vibration characteristics are compared, in detail, in terms of their natural frequencies and the corresponding mode shapes. First, the complete set of composite shallow cylindrical shell equations are reduced to a system of first order ordinary differential equations in “state-vector” form. Then, by making use of the “Modified Transfer Matrix Method”, the effects of the position and the width of the stiffening shell strip in the natural frequencies and the mode shapes of the panel system are plotted and compared. Some significant results of parametric studies and also the possibility of some kind of hit-and-run type of optimization are presented.
Comparison of Different Shell Theories for Large-Amplitude Vibrations of Circular Cylindrical Shells
Authors: Amabili M.
Published: June 2008

Large-amplitude (geometrically nonlinear) vibrations of circular cylindrical shells subjected to radial harmonic excitation in the spectral neighbourhood of the lowest resonances are investigated. The Lagrange equations of motion are obtained by an energy approach, retaining damping through Rayleigh’s dissipation function. Four different nonlinear shell theories, namely Donnell’s, Sanders-Koiter, Flu¨gge-Lur’e-Byrne and Novozhilov’s theories, are used to calculate the elastic strain energy. The formulation is also valid for orthotropic and symmetric cross-ply laminated composite shells. The large-amplitude response of perfect and imperfect, simply supported circular cylindrical shells to harmonic excitation in the spectral neighbourhood of the lowest natural frequency is computed for all these shell theories. Numerical responses obtained by using these four nonlinear shell theories are also compared to results obtained by Galerkin approach, used to discretise Donnell’s nonlinear shallow-shell equation of motion. A validation of calculations by comparison to experimental results is also performed. Boundary conditions for simply supported shells are exactly satisfied. Different expansions involving from 14 to 48 generalized coordinates, associated to natural modes of simply supported shells, are used. The nonlinear equations of motion are studied by using a code based on arclength continuation method that allows bifurcation analysis.
Effects of Local Energy Loss on the Dynamic Response of a Cylindrical Bar With a Penny Shape Crack
Authors: Vaziri A. , Nayeb-Hashemi H.
Published: June 2008

The effects of a penny shape in a cylindrical bar on its axial dynamic response are obtained, considering the local energy loss at the crack tip. The crack is taken to be normal to the bar axis and the bar is subjected to a harmonic axial load. The bar material is assumed to be viscoelastic perfectly plastic. The penny shape crack is assumed an open crack, for simplicity of calculations. The local flexibility is calculated by using the strain energy release rate. The local damping due to the crack presence is related to the plastic zone and the crack opening displacement. The results show that the bar material damping does not affect the lower resonant frequencies significantly, however, it decreases the amplitude of response. It is observed that for the range of crack length studied here, the system resonant frequencies and the system amplitude are little affected by considering the local energy loss at the crack tip. Furthermore, the results show that that the system resonant frequencies are not sensitive to the presence of a small penny shape crack. However, with increasing radius of the penny shape crack, resonant frequencies of the system decrease drastically. The results also indicate that the resonant frequencies are more sensitive to the crack location than its size.
Fatigue Analysis of a Welded Lap Joint Under Bending Load
Authors: Koay Kenny , Bracht Brad , Browne Vance
Published: June 2008

Welded lap joints subject to cyclic loading are used in industrial vehicles and equipment. Cyclic bending loads can result in fatigue failure of these joints. It is desirable to predict the expected life of the joint as a function of a load-stress parameter. To predict the life of a typical welded structure, additional types of weld joints and loads must also be considered. The lap joint work covered here provides a building block for the structure life prediction. For the work reported here, lap joints were formed by an industrial manufacturing wire feed weld process by certified welders. Strain gages were applied to one of the joint members. A fixture was designed and built to apply a pure bending load to the welded members at the joints, and this was installed in a fatigue test machine. A number of fully reversed tests were run to failure at various loads and some were run to effective infinite life. A resulting set of stress life curves was generated based on mean life and mean life less one and two standard deviations as a function of the “hot spot” stress. This hot spot is the region near the weld toe where the stress distribution starts to deviate from linearity due to the geometric stress riser of the weld fillet and joint geometry. Measurements show that this stress can be approximated by the calculated beam bending stress for the specimens and loads used in the tests. The results of this work provide guidelines for design of welded lap joints for a desired cycle life and for predicting the expected cycle life of an existing joint including uncertainties in life due to weld and test variables. The stress needed to predict the life of a joint is obtained by strain measurements on the actual structure. For design, the stress may be approximated by calculated stresses.
Fatigue Assessment for Combined HCF/LCF Loading
Authors: Jelaska Damir T.
Published: June 2008

The closed form expression for estimation of the crack initiation life at combined HCF/LCF loading is derived, and the way of reshaping the crack growth rate formulae in the form enabling their use in fatigue design at non-stationary loading is demonstrated. This new derived formula suggests an additional damage increase when crossing from one stress block to another. It is proposed to call this effect as “block crossing effect”. Herein, the reshaped crack growth rate formula is applied for the fatigue design of structures and components made of titanium alloy Ti-6Al-4V and subjected to combined HCF/LCF loading. For the stress history simplified in the way that it consists of one LCF stress block with number of cycles equal to number of start-up in-service operations, at load ratio r = 0, followed by one HCF stress block at load ratio r > 0 with summed-up all HCF cycles, the closed form expression is derived for estimating the crack propagation life at combined HCF/LCF loading. Smith and Haigh diagrams as design tool for estimating the fatigue strengths for designed fatigue life, known load ratio and various number of HCF cycles per one combined stress block, are obtained for same material and same loading.
Behavior of Thin, Moderately Thick and Thick Woven Composites Subjected to Low Velocity Impact Loads
Authors: Kelkar Ajit D.
Published: June 2008

The effects of low velocity impact on woven composite panels are presented in this study. In the experimental program, 8 ply, 16 ply and 24 ply VARTM manufactured woven composite panels were subjected to low velocity impact loads. The laminates were held in a special fixture, which was designed to simulate simply supported boundaries. Impact experiments were conducted using a Dynatup low velocity impact testing machine where a drop-weight system was used to strike each panel at 90° incidence under controlled conditions of impact velocity. The impactor used was of a constant weight and tip diameter. The impact height and hence the velocity and energy were used as variables in the study. Preliminary impact tests were performed to establish the incipient damage (lower bound) and visible back face damage and spalling (upper bound) energy for each of the 8 ply (thin), 16 ply (moderately thick) and 24 ply (thick) woven graphite/epoxy laminates. Seven energy levels were selected to study the progressive deformation and damage mechanics. It is shown that threshold damage criteria can be established by using a simple FFT smoothening of impact load-time history data.
Mechanical Modeling of Fabrics in Bending
Authors: Lahey T. J. , Heppler G. R.
Published: June 2008

A model of fabric bending that includes a nonlinear elastic contribution, a viscous friction contribution, a Coulomb friction contribution, and a hysteretic contribution is presented. These are combined to recover the loading, unloading and hysteresis behaviors observed in the bending tests performed under the Kawabata Evaluation System. Results of the model and its components are compared and contrasted with experimental results. It is found that inertial effects dominate the behavior of the model in the early stages of the KES test and that, once the static friction threshold is overcome, friction arises from the slipping of the yarns with respect to each other. The results show that nonlinear elastic behavior arises from jamming of the yarns and their subsequent compression.
Modeling and Analysis of 1-3 Piezoelectric Composites
Authors: Nakhwa Sanjay , Saigal Anil
Published: June 2008

Theoretical results of the material properties of piezoelectric composites are generally limited to the transversely isotropic composites and are usually given in the form of upper and lower bounds. In most of these analyses all the material constants cannot be determined. However, the method of effective field has been used on a transversely isotropic piezoelectric composite to theoretically calculate all the ten material properties. In this work an alternative method to determine all the elastic, dielectric and piezoelectric coupling constants of 1-3 piezoelectric composite with periodic arrangement of fibers are investigated by using finite element analysis on a unit cell model. FEA of unit cell models for hexagonal, square with diagonal and square with edge orientation topologies are performed. Different mechanical and electrical loading patterns and their corresponding boundary conditions are formulated and simulated to get data necessary for deriving the various anisotropic material constants. FEA results are compared with those of the theoretical work. Effect of different parameters e.g. volume fraction, topology and electrical boundary conditions on the different material constants are discussed.
Optimization of Machine Tool Structures Based on Static and Dynamic Criteria
Authors: Kushnir Emmanuil , Newton Robert , Tuccio Mark
Published: June 2008

The process of designing any new machine tool consists of several stages during its prototype development. Once the cutting envelope and power requirements have been defined, the major structural components are usually designed simultaneously by several different designers, as a result of project time constraints. Because designers may sometimes have a difficult time knowing what impact their changes might have on the completed machine, they need to optimize each of their components separately. In theory, this approach should lead to a possibility of only minor component changes at the point when the complete machine is structurally analyzed. The optimization of each major component is a function of several defined sets of criteria, such as total weight and stiffness (both static and dynamic) under different types of load and boundary conditions. By establishing these criteria, the effectiveness of changes can be evaluated at different times of the machine’s development and optimization. When taking this design approach, it is safe to assume that complete machine tool structures, composed of optimized components, will not only have good static and dynamic characteristics, but also should be cost effective, as the total iron mass will be at a minimum for each component. Results of this process will be shown thru described component optimization changes of an actual new machine design from it’s concept, assembly and final testing.
Constitutive Modeling of Controllable Electrostrictive Structronic Thin Shells
Authors: Tzou H. S. , Chai W. K.
Published: June 2008

Electrostrictive material is one of the key smart materials, with tremendous potentials in many engineering applications, e.g., sonar, actuators, artificial muscles, etc. The (direct) electrostrictive effect of electrostrictive materials is a quadratic dependence of stress or strain on applied electric field and this nonlinear electromechanical effect contributes significant actuation performance as compared with that of conventional piezoelectric materials. A generic electrostrictive thin shell theory and its dynamic electro-mechanical system equations are derived based on a generic double-curvature thin shell defined in the paraelectric phase. Generic mathematical models and permissible boundary conditions of electrostrictive thin shells are defined based on Hamilton’s principle, elasticity theory, Kirchhoff-Love thin shell theory and Gibbs elastic free energy function. Electro-mechanical behaviors and dynamic characteristics of electrostrictive shells are evaluated. Simplifications of the generic electrostrictive shell theory to other common geometries are demonstrated, electrostrictive/dynamic coupling equations derived, and their electromechanical characteristics discussed.
Control of Largely-Deformed Nonlinear Electro/Elastic Beam and Plate Systems: Finite Element Formulation and Analysis
Authors: Wang D. W. , Tzou H. S. , Lee H.-J.
Published: June 2008

Adaptive structures involving large imposed deformation often go beyond the boundary of linear theory and they should be treated as “nonlinear” structures. A generalized nonlinear finite element formulation for vibration sensing and control analysis of laminated electro/elastic nonlinear shell structures is derived based on the virtual work principle. A generic curved triangular piezoelectric shell element is proposed based on the layerwise constant shear angle theory. The dynamic system equations, equations of electric potential output and feedback control force defined in a matrix form are derived. The modified Newton-Raphson method is adopted for nonlinear dynamic analysis of large and complex piezoelectric/elastic/control structures. The developed piezoelectric shell element and finite element code are validated and then applied to control analysis of flexible electro-elastic (piezoelectric/elastic) structural systems. Vibration control of constant-curvature electro/elastic beam and plate systems is studied. Time-history responses of free and controlled nonlinear electro/elastic beam and plate systems are presented and nonlinear effects discussed.
The Application of Probabilistic Risk Assessment to Habitable Payloads: Utilization of Risk-Based and Traditional Rule-Based Methodologies: A “First” for NASA
Authors: Flippen A. A. , Navarro R. J. , Larsen A. M. , Stamatelatos M.
Published: June 2008

The safety of the public, the astronaut crew, Agency assets, other payloads, and the environment are NASA’s priorities when assessing the adequacy of space flight designs. While Probabilistic Risk Assessment (PRA) has been successfully applied to Space Shuttle and Space Station vehicle risk decision-making, the mandated use of a non-probabilistic rule-based approach is unique to the safety certification of NASA’s habitable payloads. A 1997 survey of historical safety policies with NASA’s Payload Safety Review Panel (PSRP) revealed that the non-probabilistic approach for habitable payloads was not arbitrary but founded on informed risk decisions from 20 years ago by then NASA Headquarters policy makers. Based on a sound payload safety track record, there has been no compelling reason, until recently, to consider expanding from the present NSTS 1700.7B rule-based approach to include risk-based PRA as a viable alternative. However, with the Agency’s increased focus on structured risk management, the establishment of a Risk Assessment Program at NASA Headquarters, and refined PRA guidelines and techniques, PRA is now formally recognized as an essential method for evaluating complex and high risk systems. The PSRP recognizes a growing need and an opportunity for evaluating the efficacy of risk-based PRA methods for application to increasingly complex next generation payload technologies. Therefore, it is timely to revisit the potential application of PRA to habitable payloads. This paper discusses PRA as a risk-based method that, when properly implemented, will result in equivalent or improed safety compared with the rule-based failure tolerance requirements for achieving the Agency’s “Safety First” core value. The benefits and cautions associated with infusing PRA methodology into the PSRP safety certification process are also discussed, as well as a proposed deployment strategy of how PRA might be prudently tailored and applied to habitable payloads. The use of PRA for assessing payload reliability is unrestricted at NASA but this is beyond the scope of the present discussion of payload safety applications.
Alternative Techniques for Modeling Accident Progression in Aerospace Applications
Authors: Everline C. J. , Paulos Todd
Published: June 2008

A prerequisite for continuous risk management is a comprehensive risk assessment upon which decisions are predicated. Although advanced risk assessment techniques have been developed for numerous industries, they do not always have direct aerospace applicability. One particularly important issue pertains to modeling accident progression. This paper examines two techniques for accident progression modeling, evaluates their relative utility with respect to aerospace applications, and furnishes some sample illustrations of the methodologies.
A Method for the Evaluation of the Direct Failure Causes and Lines of Defense of Installations With Dangerous Substances
Authors: Laheij G. M. H. , Uijt de Haag P. A. M. , Ale B. J. M. , Post J. G.
Published: June 2008

According to the Hazards of Major Accidents Decree, the operator of an establishment should demonstrate in a safety report the risks of an operation and that these risks are adequately reduced. For each installation the most important failure causes should be described together with the effectiveness of the lines of defense installed. For this, a method is developed where in the first step a default is defined for each type of installation together with the default lines of defense related to this installation. A default system is defined as a system containing an inert substance and situated in surroundings not leading to any external causes of failure. The most important failure causes for a default installation are determined using historical data for the different parts of an installation, where also the stage of an installation (design, construction, operation and maintenance) is taken into account. Also a method is used that identifies failure causes based on the process phenomena. After this step it is investigated whether the substances used in the installation or the surroundings of an installation give rise to additional failure causes to be taken into account and subsequent the need for additional lines of defense. Guidelines are given to estimate the effectiveness of additional lines of defense.
Post-Incident Safety Analysis of an Automatic Train Protection System
Authors: Katsumata Peter T.
Published: June 2008

Rail is used as a form of transportation by millions of people each day. Many of these rail transit systems utilize automatic operation. Automatic operation of rail transit vehicles is provided by an Automatic Train Control (ATC) system, which is typically partitioned into three subsystems: Automatic Train Protection (ATP), Automatic Train Operation (ATO), and Automatic Train Supervision (ATS). This paper discusses the results of a post-incident safety analysis performed on an ATP system. A Fault Tree Analysis (FTA) was performed on a vehicle ATP subsystem following several incidents involving a compromise in system safety. The results of the FTA showed that the vehicle ATP subsystem did not meet the “fail safe” design criteria. This paper uses the results of the FTA to identify possible safety improvements.
Stochastic Theory of Human Slipping
Authors: Barnett Ralph L. , Glowiak Susanne A. , Poczynok Peter J.
Published: June 2008

The conventional approach to human slipping is essentially deterministic; it states that no slipping will occur when the average friction coefficient is greater than some critical friction criterion. Under this condition, pedestrians will not slip when they encounter the average friction coefficient. On the other hand, to successfully negotiate a walk of n-steps they must not slip when they encounter the smallest of the n friction coefficients. Consequently, a new slip theory has been formulated as a problem in extreme value statistics. An elegant relationship is obtained among the probability of slipping, the critical friction criterion, the number of steps taken by the walker, and the central measure, scatter, and asymmetry of the distribution of friction coefficients. The new theory reveals the structure of human slipping in a startling way that introduces completely new concepts: the go/no go nature of classical slip predictions is replaced by a probability of slipping; low friction floor/footwear couples may lead to fewer slips than high friction ones; slipping can occur in any case where conventional theory predicts “no slip”; and the number of slips depends on the distance traveled by a pedestrian. Finally, this paper develops the idea that the slipperiness of a real floor must be evaluated for a duty-cycle. Duty-cycles can be represented as frequency histograms when a floor is homogeneous and isotropic.
The Top Down Risk Management System of the Offshore Operations of the Ekofisk Protective Barrier
Authors: de Ridder Hennes A. J.
Published: June 2008

The Ekofisk Field in the centre of the North Sea is a very important junction in the oil producing and transporting North Sea network. In 1987, the wave loads on the Ekofisk Installations had become unacceptable, due to a significant seabed subsidence. In order to cope with the increased wave loads, it was decided to build a Protective Barrier around the central Ekofisk Storage Tank. This barrier was to be installed in two separate half units, which were to be brought to the Ekofisk Field in floating condition. After installation, the two halves were to be structurally connected. The paper deals with the overall risk management of the total offshore operations, including tow-out, installation, coupling and completion. The operations were governed by conflicting requirements with respect to relevant aspects like stability, strength, stiffness, weight, geometry and were perceived to be extremely risky due to the marginal resistance against the expected load cases. The operations were weather dependent, thus dominated by changing stochastic boundary conditions. Most of the processes were irreversible, non-linear, and determined by a large number of variables. A top down risk management system was developed for control purposes. The system provided a continuous insight right from the very start of the project till the end of the project in the percentage of failure in the most relevant failure modes as a function of tow out date. The system allowed for strategic, tactical and operational interventions in case critical criteria were exceeded. This in particular makes that the approach—even 10 years after completion of the project—is still a new development in risk management and an interesting basis of further research on control of the design, construction and installation of complex Civil Engineering and other Systems.
The Use of Stochastic Safety Analysis Methods to Establish Control Strategies and Estimate Future Risk
Authors: Ryan Grant W. , Young Jonathan , Grisgby Mike
Published: June 2008

Stochastic safety analysis methods have been used at the Hanford Site in Washington State to establish control strategies and to estimate the future risk of waste transfer leak accidents. The Hanford Site tank farms currently store approximately 208 ML (55 Mgal) of radioactive/hazardous waste in 177 underground storage tanks. To move this waste a complex network of transfer piping and equipment is used. Each waste transfer carries a potential risk that a waste leak may occur. Waste transfer leaks into waste transfer structures, the soil (above ground and below ground), and into actively ventilated facilities due to a variety of causes were analyzed. A number of parameters (e.g., leak size, radiological composition of the leaked waste, wind speed and atmospheric dispersion) were treated as probability density functions (pdfs) in the safety analysis to determine the full range of potential consequences of waste transfer leaks. Each pdf was sampled in a Monte Carlo simulation model to determine the distribution of potential consequences from the various leak events. The resulting consequence distributions were evaluated with respect to risk guidelines to determine the appropriate control sets for daily operations to ensure that the risk from waste leak events could be minimized. The results were also used in the development of a probabilistic risk assessment to estimate accident risks to the public and co-located workers for both the tank farms and the future Hanford Site Waste Treatment Plant.
Use of Failure Modes Effects and Criticality Analysis to Improve Patient Safety
Authors: Coles Garill A. , Young Jonathan
Published: June 2008

The Joint Commission for Accreditation of Healthcare Organizations recently approved revisions to their accreditation standards that are intended to support improvements in patient safety and reduce medical errors. Key among these is the requirement to perform a Failure Modes, Effects, and Criticality Analysis (FMECA) on one high-risk process each year and propose measures to address the most critical failures. Because FMECA was developed for other industries such as nuclear, aerospace, and chemical, some adaptation of its form and use is needed. The FMECA process is normally performed by analyzing each element of an engineered system as represented on a process flow diagram. Medical processes, in contrast, are usually defined procedurally. The key elements of a medical process are more likely to be actions than equipment and components. A community project was put together to develop and test the FMECA adaptation and had good results. This collaboration consisted of safety analysts at Pacific Northwest National Laboratory in Richland, Washington and the Quality and Performance Improvement managers of the three local hospitals. This paper describes this adaptation.
A Comparison of European and North American Safety Requirements for Industrial Machinery
Authors: Lueck Tim , Vertechy Giovanni
Published: June 2008

This paper provides an introduction to various safety requirements for the design, manufacture and use of industrial machinery systems. To be successful, manufacturers must be aware of the different safety requirements that exist in North America and Europe with respect to electrical, mechanical and electromagnetic compatibility. With this knowledge, manufacturers can reduce the overall time to market and curb potential lawsuits. Users will also benefit from the safer equipment with a reduction of work-related accidents, injuries and down-time.