Beam-Induced Damage Mechanisms and their Calculation

The rapid interaction of highly energetic particle beams with matter induces dynamic responses in the impacted component. If the beam pulse is sufficiently intense, extreme conditions can be reached, such as very high pressures, changes of material density, phase transitions, intense stress waves, material fragmentation and explosions. Even at lower intensities and longer time-scales, significant effects may be induced, such as vibrations, large oscillations, and permanent deformation of the impacted components. These lectures provide an introduction to the mechanisms that govern the thermomechanical phenomena induced by the interaction between particle beams and solids and to the analytical and numerical methods that are available for assessing the response of impacted components. An overview of the design principles of such devices is also provided, along with descriptions of material selection guidelines and the experimental tests that are required to validate materials and components exposed to interactions with energetic particle beams.Comment: 69 pages, contribution to the 2014 Joint International Accelerator School: Beam Loss and Accelerator Protection, Newport Beach, CA, USA , 5-14 Nov 201

Collisions Between Gravity-Dominated Bodies: 1. Outcome Regimes and Scaling Laws

Collisions are the core agent of planet formation. In this work, we derive an analytic description of the dynamical outcome for any collision between gravity-dominated bodies. We conduct high-resolution simulations of collisions between planetesimals; the results are used to isolate the effects of different impact parameters on collision outcome. During growth from planetesimals to planets, collision outcomes span multiple regimes: cratering, merging, disruption, super-catastrophic disruption, and hit-and-run events. We derive equations (scaling laws) to demarcate the transition between collision regimes and to describe the size and velocity distributions of the post-collision bodies. The scaling laws are used to calculate maps of collision outcomes as a function of mass ratio, impact angle, and impact velocity, and we discuss the implications of the probability of each collision regime during planet formation. The analytic collision model presented in this work will significantly improve the physics of collisions in numerical simulations of planet formation and collisional evolution. (abstract abridged)Comment: Version 3, accepted to ApJ in Nov. 2011 published online Dec. 2011. Abstract abridge

A holistic framework for designing for structural robustness in tall timber buildings

With the ever-increasing popularity of engineered wood products, larger and more complex structures made of timber have been built, such as new tall timber buildings of unprecedented height. Designing for structural robustness in tall timber buildings is still not well understood due the complex properties of timber and the difficulty in testing large assemblies, making the prediction of tall timber building behaviour under damage very difficult. This paper discusses briefly the existing state-of-the-art and suggests the next step in considering robustness holistically. Qualitatively, this is done by introducing the concept of scale, that is to consider robustness at multiple levels within a structure: in the whole structure, compartments, components, connections, connectors, and material. Additionally, considering both local and global exposures is key in coming up with a sound conceptual design. Quantitatively, the method to calculate the robustness index in a building is presented. A novel framework to quantify robustness and find the optimal structural solution is presented, based on the calculation of the scenario probability-weighted average robustness indices of various design options of a building. A case study example is also presented in the end

Elevated Temperature Progressive Damage and Failure of Duplex Stainless Steel

Ductile failure of metals has been the focus of research efforts within academia and industry for many years since it is tremendously important for understanding the failure of structures under extreme loading conditions. However, limited research has been dedicated to elevated temperature ductile failure, which is critical for evaluating catastrophic events such as industrial, structural or shipping vessel fires. A detailed investigation was conducted on the structural response of Duplex Stainless Steel at elevated temperatures. The temperature dependence of elastic modulus, yield strength, ultimate strength, and ductility was measured up to 1000°C and a continuum damage plasticity model was developed. Experiments were conducted to validate the model for predicting the failure of loaded structures subjected to transient heating. The model captured crack initiation locations, failure times and temperatures within 5% for panel specimens in tension. The continuum damage plasticity model was then validated for predicting the critical heated zone size which results in catastrophic failure of pressure vessels, providing insight into the criticality analysis of thermal protection systems. Catastrophic failure during fully engulfing fuel fires can be very destructive when a boiling liquid expanding vapor explosion occurs. The predictive capability developed during this research enables the design of hazard mitigation solutions and damage inspection requirements for industrial fires. This is the first known capability presented in the literature for predicting the transition from local to catastrophic failure in un-cracked pressure vessels and pipelines due to localized heating, which has historically focused on the criticality of existing cracks under ambient conditions

Accurate, Meshless Methods for Magneto-Hydrodynamics

Recently, we developed a pair of meshless finite-volume Lagrangian methods for hydrodynamics: the 'meshless finite mass' (MFM) and 'meshless finite volume' (MFV) methods. These capture advantages of both smoothed-particle hydrodynamics (SPH) and adaptive mesh-refinement (AMR) schemes. Here, we extend these to include ideal magneto-hydrodynamics (MHD). The MHD equations are second-order consistent and conservative. We augment these with a divergence-cleaning scheme, which maintains div*B~0 to high accuracy. We implement these in the code GIZMO, together with a state-of-the-art implementation of SPH MHD. In every one of a large suite of test problems, the new methods are competitive with moving-mesh and AMR schemes using constrained transport (CT) to ensure div*B=0. They are able to correctly capture the growth and structure of the magneto-rotational instability (MRI), MHD turbulence, and the launching of magnetic jets, in some cases converging more rapidly than AMR codes. Compared to SPH, the MFM/MFV methods exhibit proper convergence at fixed neighbor number, sharper shock capturing, and dramatically reduced noise, div*B errors, and diffusion. Still, 'modern' SPH is able to handle most of our tests, at the cost of much larger kernels and 'by hand' adjustment of artificial diffusion parameters. Compared to AMR, the new meshless methods exhibit enhanced 'grid noise' but reduced advection errors and numerical diffusion, velocity-independent errors, and superior angular momentum conservation and coupling to N-body gravity solvers. As a result they converge more slowly on some problems (involving smooth, slowly-moving flows) but more rapidly on others (involving advection or rotation). In all cases, divergence-control beyond the popular Powell 8-wave approach is necessary, or else all methods we consider will systematically converge to unphysical solutions.Comment: 35 pages, 39 figures. MNRAS. Updated with published version. A public version of the GIZMO MHD code, user's guide, test problem setups, and movies are available at http://www.tapir.caltech.edu/~phopkins/Site/GIZMO.htm

Numerical Assessment of Friction Dampers Under Quasi-Static and Impact Loading

Steel structures are being the most widely used form of construction in various types of applications around the globe in recent years. To make the built environment sustainable, steel construction is considered as the nodal intervention in the construction industry. Whereas, in steel frame structures joints are considered to play the most significant role in providing ductility, sufficient rotational capacity and adequate dissipation under extreme conditions. However, the accidental loadings such as blast, fire and impact, may instantaneously causes rupture of the elements that are located within the vicinity of the impact, in some situation leading to a disproportionate failure of structural components or even to the failure of complete structure. Therefore, to make the built environment safe and to ensure that buildings remain operational and more importantly do not collapse under extreme loading conditions, this work aims at investigating a new innovative design strategy of ?FREEDAM?(Free from Damage Connections) connection under accidental conditions. This connection was initially design as a sustainable connection, able to withstand without any damage in the rotation demands due to seismic events. The response of this type of connections subject to transient dynamic loads is uncertain and yet absent in current design guidelines. Such innovative beam-to-column connections are equipped with friction dampers which are located at the bottom flange level of the connected beam to dissipate the input energy. Therefore, the study addresses the issues by developing a validated three-dimensional finite element model of such a connection under impact and quasi-static conditions. Exploring numerical procedures to simulate non-linear behaviour of friction damper subjected to impact loads, the friction resistance is calibrated by accounting the number of bolts, their diameter and tightening torque governing the preloading. The flexural resistance results from the product between the damper friction resistance and the lever arm. The friction damper numerical model is used to describe the behaviour of joint; i) ?under quasi-static loading? and ii) ?under impact conditions? presented in a beam-to-column moment resistant connection. The components of the friction damper are responsible in facilitating the dissipation of induced energy in joints and being able to provide sufficient ductility to a joint. Although, the friction damper model is a less intricate model, compared to the complete joint, yet its frictional behaviour incorporation to a joint?s dissipation capacity is quite arduous. Equipped with a failure criterion describing the softening phase of the materials, the FE model describes the failure modes observed experimentally in the displacing plate of the friction damper. Results exhibited that the transient loads application, induced elevated strain rate in the material, which enhanced the constitutive mechanical properties. Therefore, enabling the friction damper to resist the maximum load observed in quasi-static cases with reduced displacements. Parametric studies show that stiffer friction dampers are less prone to develop elevated strain rates and therefore, less keen to strength enhancement; on the other hand, the ductility capacity is reduced for rather flexible dampers comparing the quasi-static with the impact response.Steel structures are being the most widely used form of construction in various types of applications around the globe in recent years. To make the built environment sustainable, steel construction is considered as the nodal intervention in the construction industry. Whereas, in steel frame structures joints are considered to play the most significant role in providing ductility, sufficient rotational capacity and adequate dissipation under extreme conditions. However, the accidental loadings such as blast, fire and impact, may instantaneously causes rupture of the elements that are located within the vicinity of the impact, in some situation leading to a disproportionate failure of structural components or even to the failure of complete structure. Therefore, to make the built environment safe and to ensure that buildings remain operational and more importantly do not collapse under extreme loading conditions, this work aims at investigating a new innovative design strategy of ?FREEDAM?(Free from Damage Connections) connection under accidental conditions. This connection was initially design as a sustainable connection, able to withstand without any damage in the rotation demands due to seismic events. The response of this type of connections subject to transient dynamic loads is uncertain and yet absent in current design guidelines. Such innovative beam-to-column connections are equipped with friction dampers which are located at the bottom flange level of the connected beam to dissipate the input energy. Therefore, the study addresses the issues by developing a validated three-dimensional finite element model of such a connection under impact and quasi-static conditions. Exploring numerical procedures to simulate non-linear behaviour of friction damper subjected to impact loads, the friction resistance is calibrated by accounting the number of bolts, their diameter and tightening torque governing the preloading. The flexural resistance results from the product between the damper friction resistance and the lever arm. The friction damper numerical model is used to describe the behaviour of joint; i) ?under quasi-static loading? and ii) ?under impact conditions? presented in a beam-to-column moment resistant connection. The components of the friction damper are responsible in facilitating the dissipation of induced energy in joints and being able to provide sufficient ductility to a joint. Although, the friction damper model is a less intricate model, compared to the complete joint, yet its frictional behaviour incorporation to a joint?s dissipation capacity is quite arduous. Equipped with a failure criterion describing the softening phase of the materials, the FE model describes the failure modes observed experimentally in the displacing plate of the friction damper. Results exhibited that the transient loads application, induced elevated strain rate in the material, which enhanced the constitutive mechanical properties. Therefore, enabling the friction damper to resist the maximum load observed in quasi-static cases with reduced displacements. Parametric studies show that stiffer friction dampers are less prone to develop elevated strain rates and therefore, less keen to strength enhancement; on the other hand, the ductility capacity is reduced for rather flexible dampers comparing the quasi-static with the impact response

Enhanced coding, clock recovery and detection for a magnetic credit card

Merged with duplicate record 10026.1/2299 on 03.04.2017 by CS (TIS)This thesis describes the background, investigation and construction of a system for storing data on the magnetic stripe of a standard three-inch plastic credit in: inch card. Investigation shows that the information storage limit within a 3.375 in by 0.11 in rectangle of the stripe is bounded to about 20 kBytes. Practical issues limit the data storage to around 300 Bytes with a low raw error rate: a four-fold density increase over the standard. Removal of the timing jitter (that is prob-' ably caused by the magnetic medium particle size) would increase the limit to 1500 Bytes with no other system changes. This is enough capacity for either a small digital passport photograph or a digitized signature: making it possible to remove printed versions from the surface of the card. To achieve even these modest gains has required the development of a new variable rate code that is more resilient to timing errors than other codes in its efficiency class. The tabulation of the effects of timing errors required the construction of a new code metric and self-recovering decoders. In addition, a new method of timing recovery, based on the signal 'snatches' has been invented to increase the rapidity with which a Bayesian decoder can track the changing velocity of a hand-swiped card. The timing recovery and Bayesian detector have been integrated into one computation (software) unit that is self-contained and can decode a general class of (d, k) constrained codes. Additionally, the unit has a signal truncation mechanism to alleviate some of the effects of non-linear distortion that are present when a magnetic card is read with a magneto-resistive magnetic sensor that has been driven beyond its bias magnetization. While the storage density is low and the total storage capacity is meagre in comparison with contemporary storage devices, the high density card may still have a niche role to play in society. Nevertheless, in the face of the Smart card its long term outlook is uncertain. However, several areas of coding and detection under short-duration extreme conditions have brought new decoding methods to light. The scope of these methods is not limited just to the credit card

Research and Technology

Langley Research Center is engaged in the basic an applied research necessary for the advancement of aeronautics and space flight, generating advanced concepts for the accomplishment of related national goals, and provding research advice, technological support, and assistance to other NASA installations, other government agencies, and industry. Highlights of major accomplishments and applications are presented

Localist representation can improve efficiency for detection and counting

Almost all representations have both distributed and localist aspects, depending upon what properties of the data are being considered. With noisy data, features represented in a localist way can be detected very efficiently, and in binary representations they can be counted more efficiently than those represented in a distributed way. Brains operate in noisy environments, so the localist representation of behaviourally important events is advantageous, and fits what has been found experimentally. Distributed representations require more neurons to perform as efficiently, but they do have greater versatility