Design Spectrum Analysis in NASTRAN

The utility of Design Spectrum Analysis is to give a mode by mode characterization of the behavior of a design under a given loading. The theory of design spectrum is discussed after operations are explained. User instructions are taken up here in three parts: Transient Preface, Maximum Envelope Spectrum, and RMS Average Spectrum followed by a Summary Table. A single DMAP ALTER packet will provide for all parts of the design spectrum operations. The starting point for getting a modal break-down of the response to acceleration loading is the Modal Transient rigid format. After eigenvalue extraction, modal vectors need to be isolated in the full set of physical coordinates (P-sized as opposed to the D-sized vectors in RF 12). After integration for transient response the results are scanned over the solution time interval for the peak values and for the times that they occur. A module called SCAN was written to do this job, that organizes these maxima into a diagonal output matrix. The maximum amplifier in each mode is applied to the eigenvector of each mode which then reveals the maximum displacements, stresses, forces and boundary reactions that the structure will experience for a load history, mode by mode. The standard NASTRAN output processors have been modified for this task. It is required that modes be normalized to mass

Modeling a ball screw/ball nut in substructuring

In the particular NASTRAN application discussed here, a nut was attached to a stationary structure. The object of the analysis was to determine the vibration characteristics of the whole structure for various configurations; i.e., the evaluation of the mode shapes and frequencies when parts were moved to different mating positions. Details of the analysis are given

Mass modeling for bars

Methods of modeling mass for bars are surveyed. A method for extending John Archer's concept of consistent mass beyond just translational inertia effects is included. Recommendations are given for various types of modeling situations

Skylab

The Skylab program is presented to show the construction of the space vehicle and the facilities provided. The projects to be conducted during Skylab missions are described. The cost of the program is discussed and plans for future Skylab vehicles and missions are analyzed. Photographs of the interior of Skylab simulators are included to clarify the report

Condensing loaded points for transients by substructuring

A technique for condensing dynamic loading points is described. The method was applied to substructure transient solutions and was found to be very effective

Experience with Free Bodies

Some of the problems that confront an analyst in free body modeling, to satisfy rigid body conditions are discussed and with some remedies for these problems are presented. The problems of detecting these culprits at various levels within the analysis are examined. A new method within NASTRAN for checking the model for defects very early in the analysis without requiring the analyst to bear the expense of an eigenvalue analysis before discovering these defects is outlined

Bubble vector in automatic merging

It is shown that it is within the capability of the DMAP language to build a set of vectors that can grow incrementally to be applied automatically and economically within a DMAP loop that serves to append sub-matrices that are generated within a loop to a core matrix. The method of constructing such vectors is explained

Diversity and Security in UK Electricity Generation: The Influence of Low Carbon Objectives

We explore the relationship between low carbon objectives and the strategic security of electricity in the context of the UK Electricity System. We consider diversity of fuel source mix to represent one dimension of security - robustness against interruptions of any one source - and apply two different diversity indices to the range of electricity system scenarios produced by the UK government and independent researchers. Using data on wind generation we also consider whether a second dimension of security - the reliability of generation availability - is compromised by intermittency of renewable generation. Our results show that low carbon objectives are uniformly associated with greater long-term diversity in UK electricity. We discuss reasons for this result, explore sensitivities, and briefly discuss possible policy instruments associated with diversity and their limitations.Diversity, Security, Low Carbon, Wind Generation, Electricity

Transients by substructuring with DMAP

Automated substructuring in level 16 of NASTRAN was employed as a preface to the solution of a direct transient analysis. The DMAP ALTER statements written to adapt the substructuring for transient purposes are explained. Data recovery was accomplished with transfer functions. Proof of the success of the method is presented with an application to a missile structure