Nonlinear Time-Domain Structure/Aerodynamics Coupling in Systems with Concentrated Structural Nonlinearities

This paper details a practical approach for predicting the aeroelastic response (structure/aerodynamics coupling) of flexible pod/missile-type configurations with freeplay/hysteresis concentrated structural nonlinearities. The nonlinear aeroelastic response of systems in the presence of these nonlinearities has been previously studied by different authors; this paper compiles methodologies and related airworthiness regulations. The aeroelastic equations of the pod/missile configuration are formulated in state-space form and time-domain integrated with Fortran/Matlab codes developed ad hoc for dealing with freeplay/hysteresis nonlinearities. Results show that structural nonlinearities change the classical aeroelastic behaviour with appearence of non-damped motion (LCOs and chaotic motion)

A vertical monolithic combination of an InGaAsP/InP laser and a heterojunction bipolar transistor

A DH InGaAsP/InP mesa laser and a DH InGaAsP/InP mass-transport laser were successfully put together with an InGaAsP/InP heterojunction bipolar transistor in a vertical configuration. A laser threshold current as low as 17 mA and an output laser power of over 30 mW were achieved. Base injection current-controlled optical bistability and optical switching were demonstrated

A Simple Multi-Directional Absorbing Layer Method to Simulate Elastic Wave Propagation in Unbounded Domains

The numerical analysis of elastic wave propagation in unbounded media may be difficult due to spurious waves reflected at the model artificial boundaries. This point is critical for the analysis of wave propagation in heterogeneous or layered solids. Various techniques such as Absorbing Boundary Conditions, infinite elements or Absorbing Boundary Layers (e.g. Perfectly Matched Layers) lead to an important reduction of such spurious reflections. In this paper, a simple absorbing layer method is proposed: it is based on a Rayleigh/Caughey damping formulation which is often already available in existing Finite Element softwares. The principle of the Caughey Absorbing Layer Method is first presented (including a rheological interpretation). The efficiency of the method is then shown through 1D Finite Element simulations considering homogeneous and heterogeneous damping in the absorbing layer. 2D models are considered afterwards to assess the efficiency of the absorbing layer method for various wave types and incidences. A comparison with the PML method is first performed for pure P-waves and the method is shown to be reliable in a more complex 2D case involving various wave types and incidences. It may thus be used for various types of problems involving elastic waves (e.g. machine vibrations, seismic waves, etc)

Cosmological Parameters from the 2003 flight of BOOMERANG

We present the cosmological parameters from the CMB intensity and polarization power spectra of the 2003 Antarctic flight of the BOOMERANG telescope. The BOOMERANG data alone constrains the parameters of the $\Lambda$CDM model remarkably well and is consistent with constraints from a multi-experiment combined CMB data set. We add LSS data from the 2dF and SDSS redshift surveys to the combined CMB data set and test several extensions to the standard model including: running of the spectral index, curvature, tensor modes, the effect of massive neutrinos, and an effective equation of state for dark energy. We also include an analysis of constraints to a model which allows a CDM isocurvature admixture.Comment: 18 pages, 10 figures, submitted to Ap

Impact of pier length and connection type in static and dynamic response of RC bridge structure

In this paper are presented analysis results of two bridges with similar geometry. The difference between them is in the length of piers. 3D (three-dimensional) mathematical model composed of RC piers (substructure) absolutely fixed at the base and RC deck (superstructure) are developed. Both bridges are analyzed as Bridge Type 1 (with hinge connection between superstructure and substructure) and Bridge Type 2 (with fixed connection between superstructure and substructure). Superstructure is the same for both bridges. Three analyses types are performed for both bridges: - Static analysis including computation of displacements and element forces due to specified static loads. - Analyses of structural dynamic characteristics including mode shapes and corresponding free-vibration periods. - Dynamic response analyses under real earthquake ground excitation specified by corresponding input acceleration history. Comparative analysis results of static and dynamic response for each Bridge Type, considering different connection between piers and superstructure are presented

Analyzing dynamic performance of power systems over parameter space using the method of normal forms of vector fields

Today\u27s power systems have become more and more stressed due to the high utilization of available facilities. The complex dynamic behavior of large stressed power systems following disturbances can not be fully explained with present tools, such as linear eigen-analysis tools and nonlinear time-domain simulation methods. This research work applies a nonlinear analytical tool, the method of normal forms of vector fields, to help understand the complex transient oscillations in stressed power systems;The method of normal forms is a well-known mathematical tool to study systems of differential equations. The basic idea is to simplify the dynamical system by a sequence of nonlinear coordinate transformations. If there is no resonance in the system, then the nonlinear vector field can be turned into a linear one by the transformations. Previous work applied the second-order normal form transformation under non-resonance condition to power system dynamical equations. The nonlinear interaction among the fundamental modes was investigated. Based on these efforts, this work extends the application of normal forms to evaluate the dynamic performance of power systems taking into account changing operation conditions;As the resonance and near-resonance could occur in parameter space, a new normal form transformation under second order resonance condition is derived. The analysis shows that the high nonlinearity resulting from the resonance and near-resonance among poorly damped oscillatory modes and control modes is detrimental to the system performance. An approach to determine the resonance and near-resonance regions in parameter space is developed. The modes contributing to the detrimental behavior associated with the near-resonance region are identified by a procedure based on certain modal interaction indices. The state variables showing detrimental behavior are then determined using nonlinear participation factors. The accuracy of the prediction is verified by conducting nonlinear time-domain simulation. In order to compare the effect of nonlinear modal interaction quantitatively under different operating conditions, a new index in the state space of machine variables is developed. The nonlinear modal interaction together with the linear modal characteristics accounts for the dynamic performance of the system over a range of operating conditions. The method and procedures are tested and validated on a sample test system

Characterisation of the low-frequency wake dynamics for a square-back vehicle equipped with side trailing edge tapers [Powerpoint]

Characterisation of the low-frequency wake dynamics for a square-back vehicle equipped with side trailing edge tapers [Powerpoint

Spitzer Space Telescope: Unprecedented Efficiency and Excellent Science on a Limited Budget

The Spitzer Space Telescope completed nearly six years of cryogenic operations in 2009 and in August 2011 began the third year of ‘warm’ science observations. Over 50,000 hours of science have been executed in the first 8 years of the mission. Nearly 40% of the cryogenic mission project budget was devoted to data analysis funding provided directly to the astronomical community. For the warm mission, the observatory was effectively reinvented as a new, scientifically productive mission operating at a substantially lower cost. In this paper we discuss how the design of the science operations, observing modes and observing program for the cryogenic mission led to very high observing efficiencies and maximized the observatory time devoted to science. The philosophy of maximizing science output per dollar has continued in the warm mission. The transition to warm operations has maintained an outstanding science program while reducing the project budget by nearly 70% from the cryogenic mission level

Shell forming mode effect on casting quality

The paper deals with the influence of shell forming modes on some parameters of castings: the surface and internal defects. The degree of roughness and stress concentration were determined on the castings obtained under production conditions. According to the result, it was found that the use of variable pressure in the formation of the shell ensures the purity of the casting and the reduction of the stress level in the casting