Karla Morris

Formal constraints on memory management for composite overloaded operations

The memory management rules for abstract data type calculus presented by Rouson, Morris & Xu [15] are recast as formal statements in the Object Constraint Language (OCL) and applied to the design of a thermal energy equation solver. One set of constraints eliminates memory leaks observed in composite overloaded expressions with three current Fortran 95/2003 compilers. A second set of constraints ensures economical memory recycling. The constraints are preconditions, postconditions and invariants on overloaded operators and the objects they receive and return. It is demonstrated that systematic run-time assertion checking inspired by the formal constraints facilitated the pinpointing of an exceptionally hard-to-reproduce compiler bug. It is further demonstrated that the interplay between OCLs modeling capabilities and Fortrans programming capabilities led to a conceptual breakthrough that greatly improved the readability of our code by facilitating operator overloading. The advantages and disadvantages of our memory management rules are discussed in light of other published solutions [11,19]. Finally, it is demonstrated that the run-time assertion checking has a negligible impact on performance.

Intermittency in the turbulent Ekman layer

The structure of the turbulent Ekman layer is explored by examining the three-dimensional velocity fields generated by means of direct numerical simulation (DNS). Emphasis is placed on determining the relation between the instantaneous structure of the velocity field and the turbulent dissipation. The results of our simulation show the following: (1) The pseudo-dissipation exhibits lognormal behavior, with a magnitude range spanning many orders of magnitude, (2) in horizontal planes within the Ekman layer, spatially localized regions of high and low pseudo-dissipation are found, with a magnitude ratio of about 104 between low and high regions, (3) the Ekman layer is found to be composed of a series of quasi-periodic plume-like structures, and (4) the pseudo-dissipation is found to be large at the outer edge of a typical plume, with much lower levels in the plume interior. Conjectures are put forth regarding the relevance of this work to known observations of clear air radar scattering, and suggestions are made for possible future efforts.