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It is well known that the dynamic performance of a rocket or launch vehicle is enhanced when the length of the divergent section of its nozzle is reduced or the nozzle exit area ratio is increased. However, there exists a significant performance trade-off in such rocket nozzle designs due to the presence of random side loads under overexpanded nozzle operating conditions. Flow separation and the associated side-load phenomena have been extensively investigated over the past five decades; however, not much has been reported on the effect of side loads on the attitude dynamics of rocket or launch vehicle. This paper presents a quantitative investigation on the influence of in-nozzle random side loads on the attitude dynamics of a launch vehicle. The attitude dynamics of launch vehicle motion is captured using variable-mass control-volume formulation on a cylindrical rigid sounding rocket model. A novel physics-based stochastic model of nozzle side-load force is developed and embedded in the rigid-body model of rocket. The mathematical model, computational scheme, and results corresponding to side loading scenario are subsequently discussed. The results highlight the influence of in-nozzle random side loads on the roll, pitch, yaw, and translational dynamics of a rigid-body rocket model. [ABSTRACT FROM AUTHOR]

The analysis of a precision method for attenuating temperature variation in a high-throughput control fluid stream is discussed. The study emphasizes heat transfer analysis of the constituent control device and derives theoretical descriptions of system responses to time-varying fluid temperature.

This article theoretically and experimentally characterizes direct contact, packed bed thermal gradient attenuators in which a fluid control stream, subject to broadband thermal disturbances, flows through a thermally attenuating packed bed medium. The theoretical model decomposes the device into three subsystems: an upper mixing volume, the packed bed, and a lower mixing volume. Analysis of the packed bed subsystem leads to a coupled system of equations that describe local heat transfer within the control stream and within individual spherical elements comprising the packed bed; the system of equations obtained has the same general form as that derived in an earlier investigation of tube-in-shell, noncontact thermal gradient attenuators [J. Heat Transfer 123, 796 (2001)]. Associated subsystem transfer functions are derived, and in analogy with observations reported in the earlier investigation, are shown to provide simple, unambiguous criteria for designing and optimizing packed bed attenuators. It is found that, for 52 different sets of experimental conditions, theoretical performance of the device matches experimental performance to within 2.5 dB root mean square, and that the device provides several orders of magnitude attenuation for flow rates on the order of 1 l/min and disturbance frequencies higher than approximately 10 mHz. The results of the present study and the earlier investigation together provide a useful basis for analyzing and designing large and small, contacting and noncontacting, thermal gradient attenuators. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A simple device for simultaneously measuring two spatially separated contact forces is described. The device uses a monolithic dual-cantilever touch sensor driven by a piezoelectric PZT actuator. A phase-locking method allows measurement of resonant frequency shifts at constant phase, based on the strain response of a second attached PZT. Calibration and force measurement procedures are developed to extract applied contact forces from the dual-cantilever's coupled, nonlinear response. Based on a preliminary calibration, the present device exhibits maximum relative measurement error on the order of 6%. Procedures for reducing this error are described. [ABSTRACT FROM AUTHOR]

An analog, macroscopic method for studying molecular-scale hydrodynamic processes in dense gases and liquids is described. The technique applies a standard fluid dynamic diagnostic, particle image velocimetry (PIV), to measure: i) velocities of individual particles (grains), extant on short, grain-collision time-scales, ii) velocities of systems of particles, on both short collision-time- and long, continuum-flow-time-scales, iii) collective hydrodynamic modes known to exist in dense molecular fluids, and iv) short- and long-time-scale velocity autocorrelation functions, central to understanding particle-scale dynamics in strongly interacting, dense fluid systems. The basic system is composed of an imaging system, light source, vibrational sensors, vibrational system with a known media, and PIV and analysis software. Required experimental measurements and an outline of the theoretical tools needed when using the analog technique to study molecular-scale hydrodynamic processes are highlighted. The proposed technique provides a relatively straightforward alternative to photonic and neutron beam scattering methods traditionally used in molecular hydrodynamic studies.