C. F. Abrams

APPLICATION OF A DAMPED SPRING-MASS HUMAN VIBRATION SIMULATOR IN VIBRATION TESTING OF VEHICLE SEATS

Abstract There is a need for standardized methods for testing vehicle seats. Such methods would allow for the direct comparison of the merits of seats of diverse types and designs. At the present time standardized testing procedures are not possible because the dynamic characteristics of the human subjects occupying the seat during testing vary widely from man to man and affect the seat response. Testing with dead weight loading does not accurately portray the dynamic characteristics of the seat. A damped spring-mass system closely approximating to the dynamic characteristics of a seated man to vertical modes of vibration has been developed as the basis on which a standardized vehicle seat testing procedure can be built. Analysis of the problem by means of mechanical impedance techniques indicated that a two-degree-of-freedom system was sufficient to simulate the major dynamic characteristics of man in the frequencies below 10 Hz where seat vibration is most severe. Test procedures have been developed whi...

Hand-arm vibration part III: A distributed parameter dynamic model of the human hand-arm system

Abstract An anatomically analogous distributed parameter dynamic model of the human arm is proposed and quantitatively validated. Distributed mass and stiffness parameters have been obtained by representing each long bone of the arm as a flexural beam. A distributed damping parameter was introduced by allowing the beam stiffness to be a complex quantity. Hand properties were modelled as a lumped parameter damped spring-mass system. Mechanical driving point impedance techniques were used to verify the model. A dual beam model of the forearm was first proposed, and its frequency response was compared with impedance data collected on the forearm. After having established the validity of the forearm model, it was then extended to include the upper arm. The frequency response of the whole-arm model was then compared with impedance data on the whole arm collected by a previous investigator. It is concluded that the beam model of the human arm adequately represented its dynamic behavior as measured by mechanical driving point impedance techniques. The amount of information concerning the dynamic behavior of the arm yielded by the distributed parameter model is found to be vastly greater than that yielded by lumped parameter models.

Development of a simulator for use in the measurement of chain saw vibration.

The measurement of vibration production of light, hand held power tools is important in the assessment of the potential for elicitation of vibration injury to the operators of these tools. The manner in which these measurements are made can greatly affect the results. The measured vibration production of the tool becomes a function of the operator holding the saw during the measurement and his physical characteristics. The objective of the work reported here was to develop a simulator of the operator which might be used in the vibration production analysis of chain saws. The operator was modelled in terms of the driving point mechanical impedance characteristics of humans for input to the hands. A simulator was developed based on the driving point impedance characterization of the operator and evaluated with chain saw vibration measurements.

Air Flow Resistance Characteristics of Bulk Piled Sweet Potatoes

ABSTRACT THE air flow resistance characteristics of bulk piled sweet potatoes were estimated in a laboratory test. Sweet potatoes exhibit air flow resistance properties similar to ear corn, bell peppers, and potatoes. The results presented are sufficient for conservative design of pilot scale bulk curing and storage facilities.

Mechanical impedance techniques for evaluating the dynamic characteristics of biological materials

Driving point mechanical impedance, which is the complex ratio of force to velocity at the driving point, is a useful tool for characterizing the dynamic response of a non-rigid distributed system. Being a complex quantity it has a magnitude and a phase angle for each frequency of excitation. The necessary apparatus includes a shaker, force and acceleration transducers and means for recording the transducer outputs. To simplify analysis of results the shaker should have a sinusoidal output which is variable over the frequency range of interest. Although vibrational intensity is usually detected as acceleration and integrated to get velocity it could be sensed directly. In order to eliminate manual treatment of the transducer outputs to get the magnitude and phase angle there are instruments available which compute these values automatically as excitation frequency is scanned. Observing the dynamic characterization of biological system by means of mechanical impedance techniques is particularly appropriate because the parameters of these systems are usually distributed. The method has the advantage of not requiring that transducers be attached to the material being tested; that is, the technique is an input-output measurement. The method is analogous to impedance evaluation of electrical circuits in alternating current theory. The method has been successfully used in the mathematical modelling and subsequent construction of a dynamic stimulator describing the responses of a seated subject to low frequency whole-body vibration. Work is underway on the medium to high frequency responses of the hand-arm system. Potential applications range from evaluation of structures to testing of fruits, vegetables, eggs and other animal products as well as intact plant systems.

Proximal tibiotarsal cancellous bone mechanical properties in broilers

Broiler leg abnormalities cause significant economic losses through decreased body weight gains and increased mortalities. The mechanical properties of poultry cancellous bone could be contributory factors in lameness caused by these abnormalities. For example, a decreased elastic modulus indicates that the bone is less resistant to deformation. In the subchondral growth plate area, decreased deformation resistance could lead to greater incidences of damage to the growth plate, resulting in morphologic changes causing lameness. The objective of this study was to examine the effects of age and of altering protein and amino acid nutrition on body weight, bone ash content, and cancellous bone compressive strength characteristics (strength, elastic modulus, and resilience). Body weights increased as age increased, regardless of other factors. Bone ash content typically declined by nine weeks of age. A reduction in strength, elastic modulus, and resilience was seen at nine weeks of age with elastic modulus in the lateral region of proximal tibiotarsal cancellous bone being the exception. In general, bone ash content directly affected the measured bone strength parameters, i.e., a decrease in bone strength parameters occurred when bone ash content decreased.

A Proposed Phenomenological Model to Characterize Mechanical Properties of Flue-cured Tobacco Leaves

It was determined that the visco-elastic behavior of four flue-cured tobacco leaves could be modeled by the equation; sI = EIe + CIe1+b + sd; where sI = stress index (N/mm), EI = elastic index coefficient (N/mm), cI = non-linear elastic index parameter (N/mm), b = elastic exponent, m = damping coefficient dependent on strain rate (N/mm) and d = damping exponent. The relationship between m and strain rate was determined to be m = Ge. b where G = viscous constant (Nsb/mm), b = constant, and e. = strain rate (L/s). In all cases, the coefficient of determination (R2) was above 95% thereby indicating that this phenomenological model can be used to describe the non-linear loading curve of these tobacco leaves. Results indicated the non-linear elastic parameter (cI) influenced the response of the tissue more than the linear elastic coefficient (EI). Viscous behavior was non-linear and resembled the characteristics of pseudoplastic flow.

Depth Limitations on Bulk Piling of Sweet Potatoes

ABSTRACT LABORATORY tests were conducted to estimate the maximum allowable depth of piling sweet potatoes in large, continuous volume piles for curing and long-term storage. Based on published and measured physical properties, the maximum allowable depth was estimated to be 5.000 m. Comparison of experimental weight loss data obtained in simulated deep piling tests with accepted norms resulted in an estimate of 5.400 m.

Vibration Isolation of Power Tool Operators

Vibration measurements on a selection of powered hand tools revealed that many exceeded recommended handle vibration levels. Handles attached to the tool bodies with isolating mounts generally vibrated less than non-isolated handles. Resilient (foam rubber) handgrips, placed between the tool handles and the operators hand provided good isolation at higher frequencies. Reasonable thicknesses of foam soft enough to reduce the lower frequencies were not strong enough to withstand the high handgrip and other forces required to operate the tools without complete compression of the cells. The resulting configuration caused increased stiffness and loss of low frequency attenuation.

Simulation of Bulk Harvest and Handling of Sweet Potatoes

ABSTRACT BULK handling is being studied to determine if sweet potatoes can be mechanically harvested and handled in bulk form without excessive deterioration in quality due to injuries. This basic harvesting approach is used with other crops; but, the operational aspects of its use in sweet potato harvesting and handling have not been thoroughly studied. Furthermore, there exist no suffi-ciently general simulators developed for other crops with parameters which can be modified for use in this connec-tion. It was desired to develop a simulator which could be used to appropriately size the components of bulk harvesting and handling systems envisioned for sweet potatoes. Incorporation of as much generality as possible was also desirable so that the utility of the simulator could be extended to other crops. HARVSIM was developed using the SIMSCRIPT programming language. The primary use of the simulator is as a research tool with which the operational aspects of a proposed system can be studied prior to its existence. It can be eventually used to assist commercial growers in selecting new equip-ment as it becomes available for bulk harvesting and handling. The utility of HARVSIM in studying the various features of bulk harvest and handling of sweet potatoes is demonstrated with an example.