Edward A. Rodriguez

A PROBABILISTIC ANALYSIS OF A NONLINEAR STRUCTURE USING RANDOM FIELDS TO QUANTIFY GEOMETRIC SHAPE UNCERTAINTIES

Sσ sensitivity with respect to standard deviation COV Coefficient of Variation (= µ/σ) Engineers at Los Alamos National Laboratory (LANL) are currently developing the capability to provide a reliability-based structural evaluation technique for performing weapon reliability assessments. To enhance the analysts confidence with these new methods, an integrated experiment and analysis project has been developed. The uncertainty associated with the collapse response of commercially available spherical marine float is evaluated with the aid of the non-linear explicit dynamics code DYNA3D coupled with the probabilistic code NESSUS. Variations in geometric shape parameters and uncertainties in material parameters are characterized and included in the probabilistic model. Inherent anomalies and variations in geometry and material properties, which were collected from the set of test specimen, are included in the numerical model in the form of random fields and probability density functions (PDF’s). A comprehensive analysis of the parameter correlations is performed to determine appropriate correlation functions to use for the geometric random fields. E Youngs modulus

APPLICATION OF PROBABILISTIC METHODS TO WEAPON RELIABILITY ASSESSMENT

Southwest Research Institute in collaboration with engineers at Los Alamos National Laboratory (LANL) are currently developing capabilities to provide reliability-based structural evaluation techniques for performing weapon component and system reliability assessments in support of eventual weapon certification by analysis. Focus herein is placed on two problems recently studied: 1) The uncertain structural response of an explosive actuated valve-piston assembly, and 2) the quasi-static collapse response of a spherical shell. The probabilistic dynamic response of the piston is evaluated through the coupling of the probabilistic software NESSUS (Numerical Evaluation of Stochastic Structures Under Stress) 2 with the non-linear structural dynamics code, ABAQUS/Explicit 3 . The probabilistic model includes variations in piston mass and geometry, and mechanical properties, such as Youngs Modulus, yield strength, and flow characteristics. The probabilistic response of the shell is evaluated through the coupling of the NESSUS software and the explicit dynamic code DYNA3D 5 . Variations in geometric shape parameters and material properties are considered. Nomenclature

The role of nondeterminism in model verification and validation

Model verification and validation (V&V) is an enabling methodology for the development of computational models that can be used to make engineering predictions with quantified confidence. Model V&V procedures are needed to reduce the time, cost and risk associated with component and full-scale testing of products, materials, and engineered systems. Quantifying the confidence and predictive accuracy of model calculations provides the decision-maker with the information necessary for making high-consequence decisions. Development of guidelines and procedures for conducting a V&V programme are currently being defined by a broad spectrum of researchers. This paper briefly reviews the main concepts involved in model V&V and then focuses on the critical role that nondeterministic analysis plays in the V&V process.

ASME code ductile failure criteria for impulsively loaded pressure vessels

Ductile failure criteria suitable for application to impulsively loaded high pressure vessels that are designed to the rules of the ASME Code Section VI11 Division 3 are described and justified. The criteria are based upon prevention of load instability and the associated global failure mechanisms, and on protection against progressive distortion for multiple-use vessels. The criteria are demonstrated by the design and analysis of vessels that contain high explosive charges.

Verification and validation of a penetration model for the design of a blast containment vessel part I: Validation experiments

Model verification and validation (V&V) provides a mechanism to develop computational models that can be used to make engineering predictions and decisions with quantified confidence. Model V&V procedures are needed to reduce the time, cost and risk associated with component and full-scale testing of products, materials and engineered systems. The Los Alamos National Laboratory Dynamic Experimentation (DynEx) program is designing and validating steel blast containment vessels using limited experiments coupled with computational models. This paper describes the testing program for the validation experiments in support of a verification and validation process for an analytical and computational model used to predict the penetration depth of explosively released fragments into the containment vessel structure. The V&V process is described as well as pre-test analytic modeling and validation experiments. Uncertainties in the experiments that may influence model validation are discussed from an uncertainty quantification perspective since there are inherent and subjective uncertainties in the model that must be correlated with the uncertainties from the experiments.

Uncertainty quantification of a containment vessel dynamic response subjected to high-explosive detonation impulse loading

Los Alamos National Laboratory (LANL), in cooperation with Southwest Research Institute, has been developing capabilities to provide reliability-based structural evaluation techniques for performing weapon component and system reliability assessments. The development and applications of Probabilistic Structural Analysis Methods (PSAM) is an important ingredient in the overall weapon reliability assessments. Focus, herein, is placed on the uncertainty quantification associated with the structural response of a containment vessel for high-explosive (HE) experiments. The probabilistic dynamic response of the vessel is evaluated through the coupling of the probabilistic code NESSUS with the non-linear structural dynamics code, DYNA-3D. The probabilistic model includes variations in geometry and mechanical properties, such as Youngs Modulus, yield strength, and material flow characteristics. Finally, the probability of exceeding a specified strain limit, which is related to vessel failure, is determined.

Russian TOPAZ II System Test Program (1970–1989)

The Russian Topaz II system is a space nuclear power system capable of producing 4.5 to 5.5 kWe for three years of continuous autonomous operation. To qualify the system for flight, the Russian Topaz II program extensively tested their systems over a 20‐year period. Approximately 28 systems were fabricated for testing. During this time, two primary reasons necessitated system changes: the evolution of the military user requirements, and failures during testing that resulted in modifications and follow‐on systems testing. For these reasons the design, the technology, and the materials used for the system were modified and improved. The Russian Topaz II systems test program was sub‐divided into four major categories: nonnuclear thermophysical testing; mechanical testing, which included static load testing, dynamic testing, and impact/shock testing; nuclear ground testing; and cold temperature testing (CTT) to simulate prelaunch and launch temperature conditions. The testing was performed in a systematic man...

VERIFICATION AND VALIDATION OF A PENETRATION MODEL FOR THE DESIGN OF A BLAST CONTAINMENT VESSEL Part II: Model Validation

The use of computational simulation is increasingly relied upon as performance requirements for engineered systems increase and as a means of reducing testing. Model verification and validation (V&V) provides a mechanism to develop computational models that are utilized for engineering predictions and ensure decisions with quantified confidence. The Los Alamos National Laboratory Dynamic Experimentation (DynEx) program is designing and validating steel blast containment vessels using limited experiments coupled with computational models. This paper describes the verification and validation of an analytical and computational model used to predict the penetration depth of explosively released fragments into the containment vessel structure. A systematic approach of model V&V is used to compare model predictions and experiments and establish metrics to quantify confidence. The use of uncertainty quantification is an essential part of V&V as there are inherent and subjective uncertainties in the model that must be correlated with the uncertainties from the experiments.

Current LANL SCE 3-ft Vessel Inspection Discussion

On going discussions with NSTec and Newport news Industrial regarding SCE 3-ft vessel fabrication and inspection.

Long-Term, High-Throughput Operation of a Controlled Detonation Chamber Based on Shakedown Under Initial Overload in the Plastic Range

Hydrostatic or pneumatic overpressure testing prior to actual service provides a number of purposes related to structural integrity of pressure vessels, including some degree of confirmation of both the design and fabrication processes. For detonation chambers designed to control impulsive pressure loadings, preservice hydrostatic testing at impulses greater than those expected during normal operation can provide an added benefit—the ability to reduce cyclic fatigue damage caused by long-term, high-throughput operation, where the chamber may be use to control hundreds or even thousands of detonations without compromising structural integrity through excessive fatigue crack initiation and growth. This paper illustrates the favorable characteristics of controlled detonation chamber operation following an initial preservice impulsive over-testing program that demonstrates shakedown and satisfaction of strain ratcheting criteria, leading to favorable cyclic fatigue behavior during subsequent long-term, high-throughput operation.