http://yetl.yabesh.ir/yetl1/handle/yetl/19054 2026-06-11T05:29:09Z 2026-06-11T05:29:09Z Kim, Namhee Reddy, J. N. http://yetl.yabesh.ir/yetl1/handle/yetl/4310716 2026-02-17T21:50:24Z 2025-01-01T00:00:00Z

Method of Manufactured Solutions to Verify Three-Dimensional Least-Squares Finite Element Model of Generalized Newtonian Fluids Kim, Namhee; Reddy, J. N. A mixed least-squares finite element model (LSFEM) with spectral/hp approximations was developed for three-dimensional (3D) nonisothermal flows of a generalized Newtonian fluid, which obeys the power-law constitutive model. The finite element model consists of velocity, pressure, viscous stress, temperature, and heat flux as the field variables. A least-squares formulation provides a variational framework for the Navier–Stokes equations and does not require compatibility of the approximation spaces for field variables. Also, using spectral/hp elements in conjunction with the least-squares formulation, various forms of locking can be avoided, which often appear in low-order least-squares finite element models for incompressible viscous flows; thus, accurate results are obtained with exponential convergence in least-squares functionals. The method of manufactured solutions (MMS) is used to verify the present code.

2025-01-01T00:00:00Z Park, Joel T. McCoy, Andrew M. http://yetl.yabesh.ir/yetl1/handle/yetl/4310668 2026-02-17T21:48:30Z 2025-01-01T00:00:00Z

100-Year Analysis of Roll Decay for Surface-Ship Models Park, Joel T.; McCoy, Andrew M. A history is described on roll decay analysis for experiments with surface-ship scale models at the Naval Warfare Center Carderock Division (NSWCCD), a naval hydrodynamic facility known as David Taylor Model Basin (DTMB). The earliest roll decay analysis for a model test is from a report in 1923 that compares roll decay analysis for bilge keels off and on. A time history plot provides a measurement of roll period. The roll damping is indicated graphically by a curve fit of the peaks. With modern methods, the damping coefficient is computed with a curve fit of exponential damping. An early example of the estimate of roll damping is by log decrement of the ratio of successive roll peak pairs in 1976. More recently, both damping coefficient and period are computed from a curve fit of exponentially decaying cosine function, which is the solution of a second-order ordinary differential equation with constant coefficients. The largest uncertainty in damping coefficient is by log decrement, and lowest by the exponential cosine with the exponential fit of peaks in between. For the log decrement method, roll period must be computed independently. The roll period is calculated from the time between zero crossings in the time series, the time between peaks, or the peak in the power spectrum of the roll angle.

2025-01-01T00:00:00Z Jayasankar, Akhil Ollivier-Gooch, Carl http://yetl.yabesh.ir/yetl1/handle/yetl/4310450 2026-02-17T21:39:54Z 2025-01-01T00:00:00Z

On Order Elevation for Unstructured Finite Volume Solvers Using Defect Correction Jayasankar, Akhil; Ollivier-Gooch, Carl Much of the effort in improving the accuracy of computational fluid dynamics (CFD) simulations is focused on mesh refinement and adaptation although studies have shown that the use of high-order methods are more efficient in improving accuracy. Stability issues, complexity of implementation, and demand of computational resources are some of the key factors hindering the use of high-order methods in commercial CFD solvers. This paper demonstrates an improvement in the order of accuracy of finite volume solutions on unstructured meshes without using a high-order solver. Defect correction and the error transport equation method are the techniques discussed, along with the method for obtaining an appropriate estimate of the truncation error, which is crucial in both these techniques. Methods to obtain high-order interpolation of the control volume averages and high-order integral functionals along curved boundaries are also discussed. Third-order accurate results are obtained for a variety of problems, including the 2D Euler equations, without using a third-order discretization scheme.

2025-01-01T00:00:00Z Jayasankar, Akhil Ollivier-Gooch, Carl http://yetl.yabesh.ir/yetl1/handle/yetl/4310440 2026-02-17T21:39:36Z 2025-01-01T00:00:00Z

Adjoint Error Correction on Unstructured Finite Volume Solvers Jayasankar, Akhil; Ollivier-Gooch, Carl One of the major applications of the adjoint method is the improvement in the order of accuracy of integral quantities obtained from CFD simulations. Although the theory requires the use of a smooth interpolation of the solution, this has seldom been used with unstructured finite volume solvers. In this paper, the adjoint based correction is applied to output functionals obtained using finite volume method on unstructured meshes. A smoothing spline based on a C1 continuous representation of the discrete solution is employed to reduce the random noise in the solution and to improve the rate of convergence of the derivatives. Tests performed on randomly perturbed meshes in 1-D showed fourth-order convergence of output functionals obtained from second-order solution, corrected using the truncation error obtained using the smoothing spline and second-order accurate adjoint solution. The extension of this method to 2-D problems showed superconvergence for output functionals and improvements over existing results.

2025-01-01T00:00:00Z