Probabilistic structural analysis to evaluate the structural durability of SSME critical components

NASA Lewis Research Center is currently developing probabilistic structural analysis methods for select Space Shuttle Main Engine (SSME) structural components. Briefly, the deterministic, three-dimensional, inelastic analysis methodology developed under the Hot Section Technology (HOST) and R and T Base Programs is being augmented to accommodate the complex probabilistic loading spectra, the thermoviscoplastic material behavior, and the material degradation associated with the environment of space propulsion system structural components representative of the SSME such as turbine blades, transfer ducts, and liquid-oxygen posts. The development of probabilistic structural analysis methodology consists of the following program elements: (1) composite load spectra; (2) probabilistic structural analysis methods; (3) probabilistic finite element theory - new variational principles; and (4) probabilistic structural analysis application. In addition, the program includes deterministic analysis elements: (1) development of structural tailoring computer codes (SSME/STAEBL); (2) development of dynamic creep buckling/ratcheting theory; (3) evaluation of the dynamic characteristics of single-crystal SSME blades; (4) development of SSME blade damper technology; and (5) development of integrated boundary elements for hotfluid structure interaction

The Vibroacoustic Analysis of The Hydrocarbon Processing Plant Piping System Operating at Elevated Temperature.

In this paper it is presented the vibroacoustic analysis of the selected section of the hydrocarbon processing chemical plant piping system operating at elevated temperature and subjected to dynamic load exciting vibration of the structure. The pump suction and discharge piping system is a part of chemical plant for processing hydrocarbon mixture at 270° C. Elevated temperature is one of static loads that influences the boundary conditions of the piping structure thus generating pump nozzle loadings leading to possible pump body deflection. Deflected shape of the pump body results in generation of flow fluctuation, visible and measurable as a pressure pulsation. This kind of fluctutation has been assumed further to be one of the dynamic loading on piping system structure. The dynamic analysis was performed to quantify the loading effect of pressure pulsation excited in the pump discharge nozzles on the structure of pipelines and the connected pump nozzles. The simulation was based on the numerical analysis of the excitation by acoustic waves propagation in subjected piping system. Measured on–site pressure pulsation at pumps nozzles has been identified and assumed to be the source of the acoustic waves. In the simulation elastic features of the piping structure as well as the fluid, and pressure loses in pipes, taken into account. Final result of the acoustic part of the simulation was spectral characteristics of the acoustic shock forces, defined further as harmonic loads for the dynamic structural analysis. To observe an influence of the acoustic excitation on the piping there was performed structural analysis of the piping system and the combined results of static and dynamic loading influence determined. This part of the analysis has been perfomed by means of FEM computer software Bentley AutoPIPE as well as some use of ANSYS FEM program. Important step in this simulation there was the theoretical modal analysis. This analysis allows to predict possible vibroacoustic resonance in the structural system under specific conditions of the coincidence between acoustic excitation and modals. The results of the combined static and dynamic loadings analysis contain the information on the node displacements, internal forces, resulting stresses in the pipe walls and loads on the pump nozzles and piping supports

Analysis of flexible aircraft longitudinal dynamics and handling qualities. Volume 2: Data

Two analysis methods are applied to a family of flexible aircraft in order to investigate how and when structural (especially dynamic aeroelastic) effects affect the dynamic characteristics of aircraft. The first type of analysis is an open loop modal analysis technique. This method considers the effect of modal residue magnitudes on determining vehicle handling qualities. The second method is a pilot in the loop analysis procedure that considers several closed loop system characteristics. Both analyses indicated that dynamic aeroelastic effects caused a degradation in vehicle tracking performance, based on the evaluation of some simulation results. Volume 2 consists of the presentation of the state variable models of the flexible aircraft configurations used in the analysis applications mode shape plots for the structural modes, numerical results from the modal analysis frequency response plots from the pilot in the loop analysis and a listing of the modal analysis computer program

Research on the structural performance of large rocket booster subjected to longitudinal excitations

Dynamic structural behavior of large booster rocket subjected to longitudinal excitations - analysis of theoretical mode

Non-uniqueness of deep parameters and shocks in estimated DSGE models: a health warning

Estimation of dynamic stochastic general equilibrium (DSGE)models using state space methods implies vector autoregressive moving average (VARMA)representations of the observables. Following Lippi and Reichlin’s (1994)analysis of nonfundamentalness, this note highlights the potential dangers of end of non-uniqueness, both of estimates of deep parameters and of structural innovations

Introducing Adaptive Incremental Dynamic Analysis: A New Tool for Linking Ground Motion Selection and Structural Response Assessment

Adaptive Incremental Dynamic Analysis (AIDA) is a novel ground motion selection scheme that adaptively changes the ground motion suites at different ground motion intensity levels to match hazardconsistent properties for structural response assessment. Incremental DynamicAnalysis (IDA), a current dynamic response history analysis practice in Performance-Based Earthquake Engineering (PBEE), uses the same suite of ground motions at all Intensity Measure (IM) levels to estimate structural response. Probabilistic Seismic Hazard Analysis (PSHA) deaggregation tells us, however, that the target distributions of important ground motion properties change as the IM levels change. To match hazard-consistent ground motion properties, ground motions can be re-selected at each IM level, but ground motion continuity is lost when using such “stripes” (i.e., individual analysis points at each IM level). Alternatively, the data from the same ground motions in IDA can be re-weighted at various IM levels to match their respective target distributions of properties, but this implies potential omission of data and curse of dimensionality. Adaptive Incremental Dynamic Analysis, in contrast, gradually changes ground motion records to match ground motion properties as the IM level changes, while also partially maintaining ground motion continuity without the omission of useful data. AIDA requires careful record selection across IM levels. Potential record selection criteria include ground motion properties from deaggregation, or target spectrum such as the Conditional Spectrum. Steps to perform AIDA are listed as follows: (1) obtain target ground motion properties for each IM level; (2) determine “bin sizes” (i.e., tolerance for acceptable ground motion properties) and identify all candidate ground motions that fall within target bins; (3) keep ground motions that are usable at multiple IM levels, to maintain continuity; (4) use each ground motion for IDA within its allowable IM range. As a result, if we keep increasing the “bin sizes”, AIDA will approach IDA asymptotically; on the other hand, if we decrease the “bin sizes”, AIDA will approach the other end of “stripes”. This paper addresses the challenges of changing records across various IM levels. Different ground motion selection schemes are compared with AIDA to demonstrate the advantages of using AIDA. Example structural analyses are used to illustrate the impact of AIDA on the estimation of structural response in PBEE. By combining the benefits of IDA and PSHA without the omission of useful data, AIDA is a promising new tool for linking ground motion selection and structural response assessment

Behaviour of traditional Portuguese timber roof structures

The aim of this paper is to present the results of a structural analysis of common trusses traditionally used in roof construction in Portugal. The study includes the results of a preliminary survey intending to assess the geometry, materials and on site pathologies, as well as a twodimensional linear elastic static and dynamic analysis. The trusses behaviour under symmetric and non-symmetric loads, the king post/tie-beam connection, the stiffness of the joints and the incorrect positioning of the purlins, were some of the structural aspects that have been investigated

MOD-1 WTG dynamic analysis

An analysis of the MOD-1 2000 kW horizontal axis wind turbine was given. The MOD-1 design was briefly described, and the analysis used to evaluate the dynamic loads and structural interactions is discussed. The resonant frequency placement, the treatment of unsteady wind loading, and the dynamic load sensitivity to frequency shifts were reviewed for the design

From coupled elementary units to the complexity of the glass transition

Supercooled liquids display fascinating properties upon cooling such as the emergence of dynamic length scales. Different models strongly vary with respect to the choice of the elementary subsystems (CRR) as well as their mutual coupling. Here we show via computer simulations of a glass former that both ingredients can be identified via analysis of finite-size effects within the continuous-time random walk framework. The CRR already contain complete information about thermodynamics and diffusivity whereas the coupling determines structural relaxation and the emergence of dynamic length scales