Engineering topics

Childs, D.

Publications and source records attributed to Childs, D..

5 records

NASA NTRS2003

Information technology security system engineering methodology

A methodology is described for system engineering security into large information technology systems under development. The methodology is an integration of a risk management process and a generic system development life cycle process. The methodology is to be used by Security System Engineers to effectively engineer and integrate information technology security into a target system as it progresses through the development life cycle. The methodology can also be used to re-engineer security into a legacy system.

Security risk analysis system engineering↗

NASA NTRS1989

Annular honeycomb seals: Test results for leakage and rotordynamic coefficients - Comparisons to labyrinth and smooth configurations

Test results are presented for leakage and rotordynamic coefficients for seven honeycomb seals. All seals have the same radius, length, and clearance; however, the cell depths and diameters are varied. Rotordynamic data, which are presented, consist of the direct and cross-coupled stiffness coefficients and the direct damping coefficients. The rotordynamic-coefficient data show a considerable sensitivity to changes in cell dimensions; however, no clear trends are identifiable. Comparisons of test data for the honeycomb seals with labyrinth and smooth annular seals shows the honeycomb seal had the best sealing (minimum leakage) performance, followed in order by the labyrinth and smooth seals. For prerotated fluids entering the seal, in the direction of shaft rotation, the honeycomb seal has the best rotordynamic stability followed in order by the labyrinth and smooth. For no prerotation, or fluid prerotation against shaft rotation, the labyrinth seal has the best rotordynamic stability followed in order by the smooth and honeycomb seals.

Childs, D.↗

NASA NTRS1989

An entrance region friction factor model applied to annular seal analysis - Theory versus experiment for smooth and honeycomb seals

A friction factor model is developed for the entrance-region of a duct. The model is used in an annular gas seal analysis similar to Nelson's (1984). Predictions of the analysis are compared to experimental results for a smooth-stator/smooth-rotor seal and three honeycomb-stator/smooth-rotor seals. The model predicts a leakage and direct damping well. The model overpredicts the dependence of cross-coupled stiffness on fluid prerotation. The model predicts direct stiffness poorly.

Elrod, D.↗

NASA NTRS1986

Test results for sawtooth-pattern damper seals - Leakage and rotordynamic coefficients

Test results consisting of direct and transverse force coefficients are presented for eleven sawtooth-pattern damper-seal configurations. The designation 'damper' seal refers to a seal which uses a deliberately roughened stator and smooth rotor to increase the net seal damping force. The designation 'sawtooth-pattern' refers to a stator-roughness pattern whose cross section normal to the axis of the seal resembles saw teeth with the teeth direction opposing fluid motion in the direction of shaft rotation. The sawtooth pattern yields axial grooves in the stator which are interrupted by spacer elements which act as flow constrictions or 'dams'. Sawtooth-pattern seals had more damping than smooth seals but less than the round-hole-pattern seals tested previously. If damping is sacrificed, sawtooth-pattern seals can be designed to leak less than round-hole-pattern seals.

Childs, D.↗

NASA NTRS1976

Journal bearing impedance descriptions for rotordynamic applications

The paper deals with the development of analytic descriptions for plain circumferentially-symmetric fluid journal bearings, which are suitable for use in rotor dynamic analysis. The bearing impedance vector is introduced, which defines the bearing reaction force components as a function of the bearing motion. Impedances are derived directly for the Ocvirk (short) and Sommerfeld (long) bearings, and the relationships between the impedance vector and the more familiar mobility vector are developed and used to derive analytic impedance for finite-length bearings. The static correctness of the finite-length cavitating impedance is verified. Analytic stiffness and damping coefficient definitions are derived in terms of an impedance vector for small motion around an equilibrium position and demonstrated for the finite-length cavitating impedance. Nonlinear transient rotordynamic simulations are presented for the short pi and 2-pi impedances and the finite-length cavitating impedance. It is shown that finite-length impedance yields more accurate results for substantially less computer time than the short-bearing numerical-pressure-integration approach.

Childs, D.↗