Hybrid analytical technique for nonlinear analysis of structures
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Noor, A. K.↗
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Nonlinear structural dynamic analysis using a modified modal method
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Knight, N. F., Jr.↗
DYCAST: A finite element program for the crash analysis of structures
DYCAST is a nonlinear structural dynamic finite element computer code developed for crash simulation. The element library contains stringers, beams, membrane skin triangles, plate bending triangles and spring elements. Changing stiffnesses in the structure are accounted for by plasticity and very large deflections. Material nonlinearities are accommodated by one of three options: elastic-perfectly plastic, elastic-linear hardening plastic, or elastic-nonlinear hardening plastic of the Ramberg-Osgood type. Geometric nonlinearities are handled in an updated Lagrangian formulation by reforming the structure into its deformed shape after small time increments while accumulating deformations, strains, and forces. The nonlinearities due to combined loadings are maintained, and stiffness variation due to structural failures are computed. Numerical time integrators available are fixed-step central difference, modified Adams, Newmark-beta, and Wilson-theta. The last three have a variable time step capability, which is controlled internally by a solution convergence error measure. Other features include: multiple time-load history tables to subject the structure to time dependent loading; gravity loading; initial pitch, roll, yaw, and translation of the structural model with respect to the global system; a bandwidth optimizer as a pre-processor; and deformed plots and graphics as post-processors.
Pifko, A. B.↗
Three parallel computation methods for structural vibration analysis
The Lanczos (1950), multisectioning, and subspace iteration sequential methods for vibration analysis presently used as bases for three parallel algorithms are noted, in the aftermath of three example problems, to maintain reasonable accuracy in the computation of vibration frequencies. Significant computation time reductions are obtained as the number of processors increases. An analysis is made of the performance of each method, in order to characterize relative strengths and weaknesses as well as to identify those parameters that most strongly affect computation efficiency.
Storaasli, Olaf↗
Analysis of structures with rotating, flexible substructures applied to rotorcraft aeroelasticity
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Hodges, Dewey H.↗
Stability and implementation of partitioned CSI solution procedures
A partitioned procedure developed for the efficient solution of control-structure interaction (CSI) problems is presented with emphasis on its computational stability, implementation aspects, and accuracy characteristics. The partitioned CSI procedure proposed here can facilitate the use of large-scale structural analysis for control-structure interaction problems. It is anticipated that real-time CSI simulations will become routine if adequate advances are made in the construction of reduced-order observers and, for some time variant problems, if substantially faster parallel solution procedures for the Riccati equations become available.
Park, K. C.↗
Finite element analysis of structural components using viscoplastic models with application to a cowl lip problem
The viability of advanced viscoplastic models for nonlinear finite element analyses of structural components is investigated. Several uniaxial and a multiaxial problem are analyzed using the finite element implementation of Freed's viscoplastic model. Good agreement between the experimental and calculated uniaxial results validates the finite element implementation and gives confidence to apply it to more complex multiaxial problems. A comparison of results for a sample structural component (the cowl lip of a hypersonic engine inlet) with the earlier elastic, elastic-plastic, and elastic-plastic-creep analyses available in the literature shows that the elastic-viscoplastic analyses yield more reasonable stress and strain distributions. Finally, the versatility of the finite-element-based solution technology presented herein is demonstrated by applying it to another viscoplastic model.
Arya, V. K.↗
The structural dynamics analysis of the main injector LOX inlet tee and its redesign
A ground test of a specially instrumented Space Shuttle Main Engine (SSME) revealed excessively high strains in the high pressure Liquid Oxygen (LOX) inlet line which carries LOX to the Main Injector. The inlet tee acts as a manifold which utilizes two splitter vanes to direct the flow of LOX into the main injector. When the high strains were discovered, it was thought that these splitter vanes, coupled with high energy flow was the source. This resulted not only in high strains in the LOX inlet tee, but excessive vibration at a frequency of 4000 Hz located at the gimbal bearing, and at the main injector. This was later to be known as The 4kHz Phenomenon. The dynamic analysis which was used to predict the response due to the 4kHz phenomenon and the analysis used to aid in the design modification required to the hardware to reduce or eliminate the phenomenon is examined.
Romano, E.↗
Three parallel computation methods for structural vibration analysis
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Storaasli, Olaf↗
Reliability analysis of structural ceramics subjected to biaxial flexure
The reliability of alumina disks subjected to biaxial flexure is predicted on the basis of statistical fracture theory using a critical strain energy release rate fracture criterion. Results on a sintered silicon nitride are consistent with reliability predictions based on pore-initiated penny-shaped cracks with preferred orientation normal to the maximum principal stress. Assumptions with regard to flaw types and their orientations in each ceramic can be justified by fractography. It is shown that there are no universal guidelines for selecting fracture criteria or assuming flaw orientations in reliability analyses.
Chao, Luen-Yuan↗
Structural response analysis of unlatched shuttle payloads during reentry and landing
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Kos, Lawrence D.↗
Iterative methods for large scale static analysis of structures on a scalable multiprocessor supercomputer
A parallel Preconditioned Conjugate Gradient (PCG) iterative solver has been developed and implemented on the iPSC-860 scalable hypercube. This new implementation makes use of the Parallel Automated Runtime Toolkit at ICASE (PARTI) primitives to efficiently program irregular communications patterns that exist in general sparse matrices and in particular in the finite element sparse stiffness matrices. The iterative PCG has been used to solve the finite element equations that result from discretizing large scale aerospace structures. In particular, the static response of the High Speed Civil Transport (HSCT) finite element model is solved on the iPSC-860.
Sobh, Nahil Atef↗
Orbiter lessons learned: A guide to future vehicle development
Topics addressed are: (1) wind persistence loads methodology; (2) emphasize supportability in design of reusable vehicles; (3) design for robustness; (4) improved aerodynamic environment prediction methods for complex vehicles; (5) automated integration of aerothermal, manufacturing, and structures analysis; (6) continued electronic documentation of structural design and analysis; and (7) landing gear rollout load simulations.
Greenberg, Harry Stan↗
Parallel-vector design sensitivity analysis in structural dynamics
This paper presents a parallel-vector algorithm for sensitivity calculations in linear structural dynamics. The proposed alternative formulation works efficiently with the reduced system of dynamic equations, since it eliminates the need for expensive and complicated based-vector derivatives, which are required in the conventional reduced system formulation. The relationship between the alternative formulation and the conventional reduced system formulation has been established, and it has been proven analytically that the two approaches are identical when all the mode shapes are included. This paper validates the proposed alternative algorithm through numerical experiments, where only a small number of mode shapes are used. In addition, a modified mode acceleration method is presented, thus not only the displacements but also the velocities and accelerations are shown to be improved.
Zhang, Y.↗
A new sensitivity analysis for structural optimization of composite rotor blades
This paper presents a detailed mathematical derivation of the sensitivity derivatives for the structural dynamic, aeroelastic stability and response characteristics of a rotor blade in hover and forward flight. The formulation is denoted by the term semianalytical approach, because certain derivatives have to be evaluated by a finite difference scheme. Using the present formulation, sensitivity derivatives for the structural dynamic and aeroelastic stability characteristics, were evaluated for both isotropic and composite rotor blades. Based on the results, useful conclusions are obtained regarding the relative merits of the semi-analytical approach, for calculating sensitivity derivatives, when compared to a pure finite difference approach.
Venkatesan, C.↗
Semi-analytical static nonlinear structural sensitivity analysis
The paper discusses two uses of the semianalytical methods for nonlinear sensitivity analysis. First, the application to noncritical response is analyzed. It is shown that the semianalytical method is equivalent to a particular form of the overall finite difference approach. It is concluded that the difference between overall finite differences and the semianalytical approach is blurred for the case of nonlinear static response. Next, the application of the semianalytical method to calculating sensitivities of limit loads is discussed. A formulation that is easy to implement in general purpose finite element programs is derived. Three examples are used to demonstrate the application of the formulation and to explore its accuracy.
Haftka, Raphael T.↗
Finite element analysis of structural engineering problems using a viscoplastic model incorporating two back stresses
The feasibility of a viscoplastic model incorporating two back stresses and a drag strength is investigated for performing nonlinear finite element analyses of structural engineering problems. To demonstrate suitability for nonlinear structural analyses, the model is implemented into a finite element program and analyses for several uniaxial and multiaxial problems are performed. Good agreement is shown between the results obtained using the finite element implementation and those obtained experimentally. The advantages of using advanced viscoplastic models for performing nonlinear finite element analyses of structural components are indicated.
Arya, Vinod K.↗
Statistically generated weighted curve fit of residual functions for modal analysis of structures
A statistically generated weighting function for a second-order polynomial curve fit of residual functions has been developed. The residual flexibility test method, from which a residual function is generated, is a procedure for modal testing large structures in an external constraint-free environment to measure the effects of higher order modes and interface stiffness. This test method is applicable to structures with distinct degree-of-freedom interfaces to other system components. A theoretical residual function in the displacement/force domain has the characteristics of a relatively flat line in the lower frequencies and a slight upward curvature in the higher frequency range. In the test residual function, the above-mentioned characteristics can be seen in the data, but due to the present limitations in the modal parameter evaluation (natural frequencies and mode shapes) of test data, the residual function has regions of ragged data. A second order polynomial curve fit is required to obtain the residual flexibility term. A weighting function of the data is generated by examining the variances between neighboring data points. From a weighted second-order polynomial curve fit, an accurate residual flexibility value can be obtained. The residual flexibility value and free-free modes from testing are used to improve a mathematical model of the structure. The residual flexibility modal test method is applied to a straight beam with a trunnion appendage and a space shuttle payload pallet simulator.
Bookout, P. S.↗