The 1999 Center for Simulation of Dynamic Response in Materials Annual Technical Report

Introduction: This annual report describes research accomplishments for FY 99 of the Center for Simulation of Dynamic Response of Materials. The Center is constructing a virtual shock physics facility in which the full three dimensional response of a variety of target materials can be computed for a wide range of compressive, ten- sional, and shear loadings, including those produced by detonation of energetic materials. The goals are to facilitate computation of a variety of experiments in which strong shock and detonation waves are made to impinge on targets consisting of various combinations of materials, compute the subsequent dy- namic response of the target materials, and validate these computations against experimental data

Über die GPS-basierte Bestimmung troposphärischer Laufzeitverzögerungen

One major problem of precise GPS data analysis is that of modeling wetdelays with high precision. All conventional models have to fail in this task due to the impossibility of modeling wet delays solely from surface measurements like temperature and relative humidity. Actually, the non-hydrostatic component of the tropospheric propagation delay is highly influenced by the distribution of water vapor in the lower troposphere which cannot be sufficiently predicted with sole help of surface measurements. A work-around is to include atmospheric parameters as additional unknowns in the analysis of GPS data from permanent monitor stations that turns out to improve the quality of position estimates. Moreover, knowledge of zenith wet delays allows to obtain a highly interesting value for climatology and meteorology: integrated or precipitable water vapor being important for the energy balance of the atmosphere and holds share of more than 60% of the natural greenhouse effect. GPS can thereby contribute to the improvement of climate models and weather forecasting. This work outlines the application of ground-based GPS to climate research and meteorology without omitting the fact that precise GPS positioning can also highly benefit from using numerical weather models for tropospheric delay determination for applications where GPS troposphere estimation is not possible, for example kinematic and rapid static surveys. In this sense, the technique of GPS-derived tropospheric delays is seen as mutually improving both disciplines, precise positioning as well as meteorology and climatology

[Research activities in applied mathematics, fluid mechanics, and computer science]

This report summarizes research conducted at the Institute for Computer Applications in Science and Engineering in applied mathematics, fluid mechanics, and computer science during the period April 1, 1995 through September 30, 1995

Structural optimization of steel jackets for offshore wind turbines considering dynamic response and fatigue constraints

Programa Oficial de Doutoramento en Enxeñaría Civil . 5011V01[Abstract] It takes time for society to digest changes, but we are changing. We can not deny climate change anymore and, as a species, we have come to realize there is an urgent need to change our energy generation habits. They have changed indeed and, in the last decades, renewable energies have clearly colored the picture of energy sources. Particularly, wind energy is called to be one of the most valuable cards in the hand of renewable energies in the near future. However, the current trend, and target of this thesis, are not the typical wind turbines installed inland. In the last years, the preferred location for the placement of wind farms has traveled, or we better say sailed from land to the seas, seeking for higher efficiency and exploitation of wind’s potential. Even though there are reasons to carry wind turbines offshore, the trip is neither easy nor low-cost and implies the analysis and design of new substructures to bear the weight of the turbines. Those substructures are called jackets. This thesis defines a procedure of analysis of the dynamic behavior of offshore wind turbines supported by jackets. Upon that analysis, a structural optimization problem is defined and solved using mathematical and numerical optimization techniques. The goal is to reduce the amount of material needed to manufacture the jackets and therefore reduce the investment of offshore wind turbine structures and consequently the indirect cost of energy production. The structural model is based on a non-linear dynamic analysis of three dimensional framed structures for fully coupled offshore wind turbines considering the rotation of the blades. Special care is taken in the description of the environmental loading conditions. Wind and wave actions and forces on the elements of the structure are thoroughly modeled. One of the most decisive aspects in the design of offshore structures is fatigue in steel elements arising from cyclic loads. In this thesis fatigue damage is assessed in terms of S-N curves by means of the Palmgren-Miner rule and using the Rainflow algorithm for counting stress cycles. Long-term fatigue damage in the joints of the jackets is accurately estimated from the damage computed for short-term computational simulations. Since the analysis of the jackets is addressed in the time domain, the problem is faced as a dynamic response optimization. Although there are a few methodologies to handle time-dependent constraints, none is able to accomplish the task efficiently and still retaining all the valuable information about the structural status. A novel methodology is introduced to efficiently deal with the time-dependent structural constraints imposed to the dynamic response of the structure. The optimization model is presented as a weight minimization of the steel jacket under Ultimate Limit Stress, Fatigue Limit State and frequency constraints. Crosssections of the tubular elements and bottom and top widths of the jacket are chosen as design variables to perform a simultaneous shape and size optimization while preserving the straight alignment of the legs. The optimization is addressed using Sequential Linear Programming which requires a first order sensitivity analysis. The sensitivities are obtained through Direct Differentiation and analytic derivatives except for the fatigue damage constraint since it lacks analytic derivative. The sensitivity core of the computational code constitutes an extremely expensive part in terms of CPU time and storage. The optimization methodology developed is applied to real jacket structures bearing fully coupled rotating wind turbines. The optimization results show fair robustness of the algorithm when facing different problems and substantial reductions in the weight of the steel jackets are obtained while guarantying the fulfillment of the conditions imposed by the structural standards

International GPS Service for Geodynamics

This 1995 annual report of the IGS International GPS (Global Positioning System) Service for Geodynamics - describes the second operational year of the service. It provides the many IGS contributing agencies and the rapidly growing user community with essential information on current organizational and technical matters promoting the IGS standards and products (including organizational framework, data processing strategies, and statistics showing the remarkable expansion of the GPS monitoring network, the improvement of IGS performance, and product quality). It also introduces important practical concepts for network densification by integration of regional stations and the combination of station coordinate solutions. There are groups of articles describing general aspects of the IGS, the Associate Analysis Centers (AACs), Data Centers, and IGS stations

Goddard Conference on Mass Storage Systems and Technologies, Volume 1

Copies of nearly all of the technical papers and viewgraphs presented at the Goddard Conference on Mass Storage Systems and Technologies held in Sep. 1992 are included. The conference served as an informational exchange forum for topics primarily relating to the ingestion and management of massive amounts of data and the attendant problems (data ingestion rates now approach the order of terabytes per day). Discussion topics include the IEEE Mass Storage System Reference Model, data archiving standards, high-performance storage devices, magnetic and magneto-optic storage systems, magnetic and optical recording technologies, high-performance helical scan recording systems, and low end helical scan tape drives. Additional topics addressed the evolution of the identifiable unit for processing purposes as data ingestion rates increase dramatically, and the present state of the art in mass storage technology

Fire performance of residential shipping containers designed with a shaft wall system

seven story building made of shipping containers is planned to be built in Barcelona, Spain. This study mainly aimed to evaluate the fire performance of one of these residential shipping containers whose walls and ceiling will have a shaft wall system installed. The default assembly consisted of three fire resistant gypsum boards for vertical panels and a mineral wool layer within the framing system. This work aimed to assess if system variants (e.g. less gypsum boards, no mineral wool layer) could still be adequate considering fire resistance purposes. To determine if steel temperatures would attain a predetermined temperature of 300-350ºC (a temperature value above which mechanical properties of steel start to change significantly) the temperature evolution within the shaft wall system and the corrugated steel profile of the container was analysed under different fire conditions. Diamonds simulator (v. 2020; Buildsoft) was used to perform the heat transfer analysis from the inside surface of the container (where the fire source was present) and within the shaft wall and the corrugated profile. To do so gas temperatures near the walls and the ceiling were required, so these temperatures were obtained from two sources: (1) The standard fire curve ISO834; (2) CFD simulations performed using the Fire Dynamics Simulator (FDS). Post-flashover fire scenarios were modelled in FDS taking into account the type of fuel present in residential buildings according to international standards. The results obtained indicate that temperatures lower than 350ºC were attained on the ribbed steel sheet under all the tested heat exposure conditions. When changing the assembly by removing the mineral wool layer, fire resistance was found to still be adequate. Therefore, under the tested conditions, the structural response of the containers would comply with fire protection standards, even in the case where insulation was reduced.Postprint (published version