Experiments have been undertaken to investigate dam-break flows where a thin plate separating water at different levels is withdrawn impulsively in a vertically upwards direction. Depth ratios of 0, 0.1 and 0.45 were investigated for two larger depth values of 10 cm and 36 cm. The resulting sequence of surface profiles is shown to satisfy approximately Froude scaling. For the dry-bed case a horizontal jet forms at small times and for the other cases a vertical, mushroom-like jet occurs, none of which have been observed previously. We analyse the initial-release problem in which the plate is instantaneously removed or dissolved. Although this shows singular behaviour, jet-like formations are predicted. Artificially smoothing out the singularity enables a fully nonlinear, potential-flow computation to follow the jet formation for small times. There is qualitative agreement between theory and experiment.In the experiments, after a bore has developed downstream as a result of highly complex flow interactions, the surface profiles agree remarkably well with exact solutions of the shallow-water equations which assume hydrostatic pressure and uniform velocity over depth.

Experiments have been undertaken to investigate dam-break flows where a thin plate separating water at different levels is withdrawn impulsively in a vertically upwards direction. Depth ratios of 0, 0.1 and 0.45 were investigated for two larger depth values of 10 cm and 36 cm. The resulting sequence of surface profiles is shown to satisfy approximately Froude scaling. For the dry-bed case a horizontal jet forms at small times and for the other cases a vertical, mushroom-like jet occurs, none of which have been observed previously. We analyse the initial-release problem in which the plate is instantaneously removed or dissolved. Although this shows singular behaviour, jet-like formations are predicted. Artificially smoothing out the singularity enables a fully nonlinear, potential-flow computation to follow the jet formation for small times. There is qualitative agreement between theory and experiment.In the experiments, after a bore has developed downstream as a result of highly complex flow interactions, the surface profiles agree remarkably well with exact solutions of the shallow-water equations which assume hydrostatic pressure and uniform velocity over depth.

The generation of a single low-frequency wave (LFW) pulse by a single group of waves incident on a beach is investigated by means of laboratory experiments and a numerical model. This simplified case allows the LFW to be measured in isolation, after the incident group has passed and before there is any reflection from the wavemaker. A beach consisting of two different slopes (1:100 and 1:20) was used, and runs were made with the water level on each slope. The results were simulated using a composite numerical model, with Boussinesq equations in the deeper water and nonlinear shallow water equations in the surf zone. For some calculations, a friction term was included. For the 1:20 slope, the outgoing LFW is well predicted even without the friction term. With a 1:100 slope, a friction factor of 0.01 gave a good result, in this case reducing the amplitude of the outgoing LFW by a factor of about 2 compared with the frictionless result. The nondimensional equations show that the friction term is insignificant if the beach slope is large compared with the friction factor. Runs of the surf zone part of the model show the outgoing LFW to be correlated with the swash motion. Its amplitude is largest if the duration of the wave group is similar to the swash period of the largest wave in the group. The model also showed a slightly stronger than linear dependence of LFW amplitude on incident wave amplitude.

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S)USAF, AFRL AFOSR / PKC SPONSOR/MONITOR'S REPORT875 Randolph St. Room 3112 NUMBER(S)Arlington, VA 22203 DISTRIBUTION / AVAILABILITY STATEMENT SUPPLEMENTARY NOTES ABSTRACTThe project explores application of magneto-elastic active sensors (MEAS) for structural health monitoring (SHM) of responsive space satellite systems. Design, development and fabrication procedures for MEAS are presented and associated electrical and mechanical characteristics are discussed. MEAS miniaturization efforts are highlighted. Examples of MEAS-enabled SHM testing in aerospace structures of simple and complex geometry, such a honeycomb and realistic satellite panels, are provided. Nonlinear SHM methodologies using MEAS are considered and its use for acousto-elastic assessment of bolted joints is recommended. A new SHM methodology -magneto-mechanical impedance (MMI) testing is suggested and explored from both theoretical and practical perspectives. The MMI measurement technique demonstrates ability for non-contact structural dynamic measurements and effectiveness in detection of fatigue damage at early stage, well before onset of fracture and crack development. Analytical and numerical models of MEAS and MMI are suggested. Finally, MEAS capability for recording dynamics of payload during sub-orbital space flight is validated. The results of the sub-orbital flight measurements suggest feasibility of using MEAS in space environment although characterization of dynamic events was not possible due to limitation of the on-board data acquisition system. It is advocated that MEAS could find its own niche in traditional and innovative SHM methodologies. SUBJECT TERMSStructural health monitoring, magnetic, magneto-elastic, embedded ultrasonics, nonlinear diagnostics, space structures, structural joints, sub-orbital. ABSTRACTThe project explores application of magneto-elastic active sensors (MEAS) for structural health monitoring (SHM) of responsive space satellite systems. Design, development and fabrication procedures for MEAS are presented and associated electrical and mechanical characteristics are discussed. MEAS miniaturization efforts are highlighted. Examples of MEAS-enabled SHM testing in aerospace structures of simple and complex geometry, such a honeycomb and realistic satellite panels, are provided. Nonlinear SHM methodologies using MEAS are considered and its use for acousto-elastic assessment of bolted joints is recommended. A new S...