Apparent mass of small children: Experimental measurements

A test facility and protocol were developed for measuring the seated, vertical, whole-body vibration response of small children of less than 18 kg in mass over the frequency range from 1 to 45 Hz. The facility and protocol adhered to the human vibration testing guidelines of BS7085 and to current codes of ethics for research involving children. Additional procedures were also developed which are not currently defined in the guidelines, including the integral involvement of the parents and steps taken to maximize child happiness. Eight children were tested at amplitudes of 0.8 and 1.2 m/s2 using band-limited, Gaussian, white noise acceleration signals defined over the frequency interval from 1 to 50 Hz. Driving point apparent mass modulus and phase curves were determined for all eight children at both test amplitudes. All results presented a single, principal, anti-resonance, and were similar to data reported for primates and for adult humans seated in an automotive posture which provided backrest support. The mean frequency of the apparent mass peak was 6.25 Hz for the small children, as compared to values between 6.5 - 8.5 Hz for small primates and values between 6.5 - 8.6 Hz for adults seated with backrest support. The peak value of the mean, normalized, apparent mass was 1.54 for the children, which compares to values from 1.19 to 1.45 reported in the literature for small primates and 1.28 for adults seated with backrest support. ISO standard 5982, which specifies a mean, normalized, apparent mass modulus peak of 1.50 at a frequency of 4.0 Hz for adults seated without backrest support, provides significant differences

Suspension system for a wheel rolling on a flat track

An improved suspension system for an uncrowned wheel rolling on a flat track is presented. It is characterized by a wheel frame assembly including a wheel frame and at least one uncrowned wheel connected in supporting relation with the frame. It is adapted to be seated in rolling engagement with a flat track, a load supporting bed, and a plurality of flexural struts interconnecting the bed in supported relation with the frame. Each of said struts is disposed in a plane passing through the center of the uncrowned wheel surface along a line substantially bisecting the line of contact established between the wheel surface and the flat surface of the truck and characterized by a modulus of elasticity sufficient for maintaining the axis of rotation for the wheel in substantial parallelism with the line of contact established between the surfaces of the wheel and track

Quasilocal Conservation Laws: Why We Need Them

We argue that conservation laws based on the local matter-only stress-energy-momentum tensor (characterized by energy and momentum per unit volume) cannot adequately explain a wide variety of even very simple physical phenomena because they fail to properly account for gravitational effects. We construct a general quasi}local conservation law based on the Brown and York total (matter plus gravity) stress-energy-momentum tensor (characterized by energy and momentum per unit area), and argue that it does properly account for gravitational effects. As a simple example of the explanatory power of this quasilocal approach, consider that, when we accelerate toward a freely-floating massive object, the kinetic energy of that object increases (relative to our frame). But how, exactly, does the object acquire this increasing kinetic energy? Using the energy form of our quasilocal conservation law, we can see precisely the actual mechanism by which the kinetic energy increases: It is due to a bona fide gravitational energy flux that is exactly analogous to the electromagnetic Poynting flux, and involves the general relativistic effect of frame dragging caused by the object's motion relative to us.Comment: 20 pages, 1 figur

Modifications Of Fluid Flow About Bodies And Surfaces With Synthetic Jet Actuators

The present invention involves a system for altering the aerodynamic shape and/or fluid flow field about a solid body. The preferred embodiment comprises a synthetic jet actuator embedded in a solid body, with the jet orifice built into the body surface. The synthetic jet actuator generates a series of fluid vortices emanating from the orifice so as to entrain fluid external to the actuator chamber and form a synthetic jet stream. A recirculating flow region is formed along the solid body surface about the synthetic jet orifice. As a result the apparent aerodynamic shape of the body is altered. Consequently, if the solid body is placed in a fluid flow field, the entire fluid flow field is altered by the operation of the synthetic jet actuator.Georgia Tech Research Corporatio