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• Staggered transient analysis procedures for coupled mechanical systems: Formulation

  C. Felippa, K. Park

  Computer Methods in Applied Mechanics and Engineering (1980). Vol. 24 (1), pp. 61-111

  
  

  Abstract

  Coupled-field dynamic problems in mechanics have been traditionally solved by treating the entire system as one computational entity. More recently, increasing attention has been directed to an alternative approach; partition the governing equations into subsystems, which are treated by subsystem analyzers. The selection of the subsystems may be based on weak-coupling considerations, widely different time response characteristics, isolation of nonlinear effects, or more pragmatic reasons such as the availability of analyzer software. In a staggered solution procedure the solution state of the coupled system is advanced by sequentially executing the subsystem analyzers. Subsystem coupling terms are accounted for by temporal extrapolation techniques.This paper focuses on the formulation and computer implementation of staggered solution procedures for two-field problems governed by semidiscrete second-order coupled differential equations. Such equations find application in the modeling of structure-fluid, structure-soil and structure-structure interaction. Following an introductory description of candidate problems and general solution strategies, direct time integration methods are formulated and applied to the coupled system. Staggered solution procedures are constructed through two alternative approaches which are based upon partitioning at the difference and differential equation level, respectively. Characteristic equations that govern the stability of the resulting implementations are derived, and the selection of stable extrapolators discussed. Finally, possible extensions of staggered solution procedures to coupled-field static and eigenvalue problems are suggested.

  Abstract
  Coupled-field dynamic problems in mechanics have been traditionally solved by treating the entire system as one computational entity. More recently, increasing attention has [...]

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• A Family of Early-Time Approximations for Fluid-Structure Interaction

  C. Felippa

  Journal of Applied Mechanics (1980). Vol. 47 (4), pp. 703-708

  
  

  Abstract

  A hierarchical family of early-time, high-frequency asymptotic, surface interaction approximations is derived for a structure submerged in an infinite acoustic fluid. Kirchhoff's retarded-potential integro-differential formulation is used as exact source formula. The well-known plane-wave and curved-wave approximations result as the first two members of the hierarchy. Acoustic impedance characteristics of the first four members are exhibited for several sample geometries.

  Abstract
  A hierarchical family of early-time, high-frequency asymptotic, surface interaction approximations is derived for a structure submerged in an infinite acoustic fluid. Kirchhoff's [...]

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• Partitioned Transient Analysis Procedures for Coupled-Field Problems: Accuracy Analysis

  K. Park, C. Felippa

  Journal of Applied Mechanics (1980). Vol. 47 (4), pp. 919-926

  
  

  Abstract

  Partitioned solution procedures for direct time integration of second-order coupled-field systems are studied from the standpoint of accuracy. These procedures are derived by three formulation steps: implicit integration of coupled governing equations, partitioning of resulting algebraic systems and extrapolation on the right-hand partition. It is shown that the combined effect of partition, extrapolation, and computational paths governs the choice of stable extrapolators and preservation of rigid-body motions. Stable extrapolators for various computational paths are derived and implementation-extrapolator combinations which preserve constant-velocity and constant-acceleration rigid-body motions are identified. A spectral analysis shows that the primary error source introduced by a stable partition is frequency distortion. Finally, as a guide to practical applications, the advantages and shortcomings of five specific partitions are discussed.

  Abstract
  Partitioned solution procedures for direct time integration of second-order coupled-field systems are studied from the standpoint of accuracy. These procedures are derived [...]

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• Nonlinear Static Analysis of Deep Ocean Mining Pipe—Part I: Modeling and Formulation

  C. Felippa, J. Chung

  Journal of Energy Resources Technology (1981). Vol. 103 (1), pp. 11-15

  
  

  Abstract

  A static analysis procedure is formulated and implemented for the numerical determination of nonlinear static equilibrium configurations of deep ocean risers or mining pipes. This implementation involves selection of a finite element model, modeling of structure, surface and subsurface environment and external forces, and solution of nonlinear equilibrium equations. The riser is modeled by three-dimensional beam finite elements which include axial, bending, and torsional deformations. These deformations are coupled through geometrically nonlinear effects. The resulting tangent-stiffness matrix includes three contributions identified as linear, geometric (initial-stress) and initial-displacement stiffness matrices. For the solution, a combination of load-parameter incrementation, state updating of fluid properties, and corrective Newton-Raphson iteration is used. The resulting riser configuration reflects the realistic modeling of environments and external forces. The static equilibrium solution can be used as initial condition for vibration or transient analysis. Numerical studies are presented in Part II of this paper.

  Abstract
  A static analysis procedure is formulated and implemented for the numerical determination of nonlinear static equilibrium configurations of deep ocean risers or mining pipes. [...]

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• Nonlinear Static Analysis of Deep Ocean Mining Pipe—Part II: Numerical Studies

  J. Chung, C. Felippa

  J. Energy Resour. Technol. (1981). Vol. 103 (1), pp. 16-25

  
  

  Abstract

  This part applies the modeling and solution techniques discussed in Part I to the computerized steady-state deflection analysis of deep ocean mining pipe systems. For accurate analysis, a realistic representation of drag forces along the pipe is required. This is affected by three major factors. First, in a temperature-stratified ocean, the viscosity and consequently the Reynolds number (Re) and drag coefficient vary significantly along the depth. Second, three-dimensional subsea current velocity distribution must be combined with ship velocity data and pipe configuration in the calculation of relative pipe-fluid velolcities. Finally, the drag coefficient versus Re, which varies between experiments and becomes very sensitive in the transition region, has to be properly characterized. Several cases that illustrate these parametric effects are presented for an 18,000-ft pipe modeled by three-dimensional beam elements which include coupled axial, bending and torsional deformations. The sensitivity of the results to environment characterization suggests that, for deep-ocean applications, a review of many current modeling and analysis practices is necessary.

  Abstract
  This part applies the modeling and solution techniques discussed in Part I to the computerized steady-state deflection analysis of deep ocean mining pipe systems. For [...]

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• Trends in computational engineering

  C. Felippa

  Advances in Engineering Software (1981). Vol. 3 (2), pp. 50-54

  
  

  Abstract

  This article presents the author's views on computational engineering. This is an emerging branch of the applied sciences shaped by the interaction of engineering, mathematics, and computer sciences, and paced by present advances in software technology and computer hardware. Impact of these advances on various aspects of engineering software are discussed, and predictions as to future effects are ventured. An annotated multidisciplinary reference list is provided for curious readers.

  Abstract
  This article presents the author's views on computational engineering. This is an emerging branch of the applied sciences shaped by the interaction of engineering, mathematics, [...]

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• Architecture of a distributed analysis network for computational mechanics

  C. Felippa

  Computers and Structures (1981). Vol. 13 (1), pp. 405-413

  
  

  Abstract

  An integrated software system called NICE (Network of Interactive Computational Elements) is presently under development at the Applied Mechanics Laboratory. The overall purpose of this development is to further the formulation, implementation and application of advanced computational methods in fluid and solid mechanics. From a software engineering standpoint, system design stresses functional modularity, decentralization, adaptability to interactive computing environments, and ability to accommodate research, development, analysis and testing activities. A clear separation is established between architectural elements such as analysis control and data management, and result-productive computational components called processors. This paper gives a functional overview of the NICE architecture, for which the author is responsible. Control functions that shape the user's perception of the system are emphasized.

  Abstract
  An integrated software system called NICE (Network of Interactive Computational Elements) is presently under development at the Applied Mechanics Laboratory. The overall purpose [...]

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• Interfacing Finite Element and Boundary Element Discretizations

  C. Felippa

  Applied Mathematical and Mechanics (1981). Vol. 5 (5), pp. 383-386

  
  

  Abstract

  A review is provided of various methods for coupling a mechanical finite element model to an infinite external acoustic domain. The associated physical problem involves a three-dimensional structure, submerged in an acoustic fluid, and a pressure shock impinging on the structure. Of primary concern is the structural response and, in particular, the structure's survivability. The governing matrix equation of motion for the dynamic response of a discrete structure is considered along with the fluid equations of the interaction equations. Three approaches for solving the obtained coupled finite element/boundary element system are reported, giving attention to the 'field elimination' method, the procedure of simultaneous integration, and a partitioned integration process.

  Abstract
  A review is provided of various methods for coupling a mechanical finite element model to an infinite external acoustic domain. The associated physical problem involves a [...]

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• Software for testing stability polynomials

  C. Felippa

  Applied Mathematical Modelling (1982). Vol. 6 (3), pp. 209-215

  
  

  Abstract

  Fortran 77 routines for testing root-locus stability conditions on real polynomials with the Routh and Schur-Cohn algorithms are presented. The use of the routines is illustrated by two case studies.

  Abstract
  Fortran 77 routines for testing root-locus stability conditions on real polynomials with the Routh and Schur-Cohn algorithms are presented. The use of the routines is illustrated [...]

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• Partitioned Analysis of Coupled Systems

  K. Park, C. Felippa

  (1983). Computational Methods for Transient Analysis

  
  

  Abstract

  This paper reviews partitioned analysis procedures for the analysis of coupled-field dynamical problems. These problems involve two or more distinctive subsystems that are tightly coupled. Examples are provided by fluid-structure, soil-structure, thermal-structure and structure-magnetodynamic interactions. The computer analysis of such systems depends on the integration of analysis capabilities for the separate components. Partitioned analysis procedures provide an efficient and modular way of achieving that integration. These procedures advance the solution of the coupled problem in a staged fashion.

  Abstract
  This paper reviews partitioned analysis procedures for the analysis of coupled-field dynamical problems. These problems involve two or more distinctive subsystems that are [...]

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