Engineering topics

Raefsky, Arthur

Publications and source records attributed to Raefsky, Arthur.

4 records

NASA NTRS1991

Models of recurrent strike-slip earthquake cycles and the state of crustal stress

Numerical models of the strike-slip earthquake cycle, assuming a viscoelastic asthenosphere coupling model, are examined. The time-dependent simulations incorporate a stress-driven fault, which leads to tectonic stress fields and earthquake recurrence histories that are mutually consistent. Single-fault simulations with constant far-field plate motion lead to a nearly periodic earthquake cycle and a distinctive spatial distribution of crustal shear stress. The predicted stress distribution includes a local minimum in stress at depths less than typical seismogenic depths. The width of this stress 'trough' depends on the magnitude of crustal stress relative to asthenospheric drag stresses. The models further predict a local near-fault stress maximum at greater depths, sustained by the cyclic transfer of strain from the elastic crust to the ductile asthenosphere. Models incorporating both low-stress and high-stress fault strength assumptions are examined, under Newtonian and non-Newtonian rheology assumptions. Model results suggest a preference for low-stress (a shear stress level of about 10 MPa) fault models, in agreement with previous estimates based on heat flow measurements and other stress indicators.

Lyzenga, Gregory A.↗

NASA NTRS1990

Using a multifrontal sparse solver in a high performance, finite element code

We consider the performance of the finite element method on a vector supercomputer. The computationally intensive parts of the finite element method are typically the individual element forms and the solution of the global stiffness matrix both of which are vectorized in high performance codes. To further increase throughput, new algorithms are needed. We compare a multifrontal sparse solver to a traditional skyline solver in a finite element code on a vector supercomputer. The multifrontal solver uses the Multiple-Minimum Degree reordering heuristic to reduce the number of operations required to factor a sparse matrix and full matrix computational kernels (e.g., BLAS3) to enhance vector performance. The net result in an order-of-magnitude reduction in run time for a finite element application on one processor of a Cray X-MP.

King, Scott D.↗

NASA NTRS1987

An improved method of Nusselt number calculation

A novel method for calculating the Nusselt number, Nu, in a steady-state Rayleigh-Benard convection problem is presented, in which calculations are done for a square box with constant temperature, free-slip boundary conditions at the top and bottom, and a reflection symmetry along the side walls. The element heat flux is obtained by averaging over the entire element; element heat fluxes are then projected to the adjacent nodes. Compared with previous methods, the approach reduces the calculated depth variation in horizontally averaged flux by more than a factor of 10 and shows more rapid convergence of Nu as a function of grid size.

Ho-Liu, Phyllis↗

NASA NTRS1986

Tectonic motions in California inferred from very long baseline interferometry observations, 1980-1984

Using VLBI, three baselines of 150-300 km length within California, and three baselines of 1500 km length between California and Texas, measured between 1980 and 1984, have been fitted to a steady plane/strain rotation model. The observed rate of displacement across the southern San Andreas fault is in agreement with other contemporary rate estimates near 3 cm/yr. Discrepancies between these rates and indicators of relative plate motion near 6 cm/yr seem to be related to local departures of the San Andreas system from the expected strike of the plate boundary. Results support a regional distribution of elastic strain that is offset in about the same sense and amount as the Big Bend of the San Andreas fault, and finite element simulations suggest that tractions on the base of the crust that accompany mantle downswelling beneath the Transverse Ranges could contribute to these strain inhomogeneities.

Lyzenga, Gregory A.↗