Absorbed power distribution in the whole-body system of a tractor operator.
INTRODUCTION AND OBJECTIVE
Many people are exposed to vibration (WBV) in their occupational lives. The biodynamic responses of the human body in sitting conditions have been widely measured under whole-body vibration (WBV). The measures are most often expressed in terms of force-motion relations at the driving-point, namely, mechanical impedance, apparent mass and absorbed power, and flow of vibration through the body, such as seat-to-head and body segments vibration transmissibility. The absorbed power is a measure of the energy absorbed by the subject due to the external forces applied to the system.


MATERIALS AND METHODS
The body behaves like a vibrating physical system with distributed energy-storage elements (masses, springs) and energy-dissipation elements (dampers). The total quantity of power can be divided into 2 components - one real and one imaginary. The real component reflects the energy-absorbing part of the system, due to the transformation of friction into heat within the tissues. The imaginary component reflects the energy-storing part of the system which does not consume any vibration energy.


RESULTS
The seated human is modeled as a series 4-DOF dynamic models. After introduction of the excitation, the response in particular segments of the model can be analyzed. As an example, the vibration power dissipated in an operator's body segments has been determined as a function of the agricultural combination operating speed 1.4 - 2.75 ms(-1).


CONCLUSIONS
The concept of absorbed power as a measurement for evaluation of WBV exposure opens a new area for research. The important character of absorbed power is that it has physical significance and therefore can be measured as well as computed analytically. The absorbed power relates to dissipation of energy attributed to relative motions of the visco-elastic tissues, muscles and skeletal system, which under prolonged exposures could lead to physical damage in the musculoskeletal system. A structural model of the human operator allows determination of the dynamic characteristics of the model, and study of the energy flow between the elements of the model.
EVALUATION OF WHOLE-BODY-VIBRATION AMONG TRACTOR (41 KW) DRAWN SUBSOILERS
Whole-body-vibration can be say to that part of vibration which received by a person’s body, from the machine. Subsoiling is heavy draft farm operation so to know the effect of subsoiling on vibration, it needs documentation which helps to decide safe exposure limits in sense of duration of safe subsoilling hours. For study, three subsoilers as single tine straight shank subsoiler (S1), double tine straight shank subsoiler (S2), and double tine curved shank subsoiler (S3) at three different depths (20-25, 25-30, and 30-35 cm) performed subsoiling and evaluated the effect of subsoiling on different parameters as vibration, fuel consumption, wheel slip, draft, and soil disturbance area were observed and analyzed. The vibration was increased as operating depth was increased. It was recorded maximum at depth of 30-35 cm (d3) for “X” direction as 0.296 m/s2, for “Y” direction as 0.284 m/s2, for “Z” direction as 0.431 m/s2, and for total acceleration (Ahv) as 0.451 m/s 2. The vibration in “X” direction was increased 5.86 % and 11.64 %, in “Y” direction was increased 6.52 % and 12.42 %, in “Z” direction was increased 3.68 % and 8.11 %, and Ahv was increased 10.23 % and 13.59 %, for d2 and d3 depths compared to d1 depth. On the other hand, the fuel consumption, wheel slip, and draft were found maximum for S2 subsoiler and minimum for S1 subsoiler. Soil disturbance area was observed maximum for S2 subsoiler and minimum for S1 subsoiler. Also same effect as vibration, the increased subsoiling depth resulted increased in these parameters. The safe exposure working hours were calculated as work with S1 subsoiler at the depths of d1, d2, and d3 were 8 h, 6 h, and 4 h respectively. Same as for S2 subsoiler were 4 hours at all depths and for S3 subsoiler it was calculated 4 to 6 hours. In conclusion, single tine subsoiler can be a better option for subsoiling. Only the soil disturbance area and field capacity becomes half as compared to double tine subsoilers. keywords: whole-body-vibration, subsoiling, vibration database, safe exposure period.
A Preference for Forgetting: Some Reflections on Publishing Looking For Blackfellas' Point: An Australian History of Place
Blackfellas' Point lies on the Towamba River in south-eastern New South Wales. As the river descends rapidly from its source on the Monaro plains, it winds its way through state forest, national park and farming land. Around twenty-five kilometres before it reaches the sea, just south of Eden, it passes through Towamba, the small village in which Mark McKenna now owns eight acres of land. Mark's land looks across the river to 'Blackfellas' Point', once an Aboriginal camping ground and meeting place. Looking for Blackfellas' Point is a history that begins by looking across the river to the arc of bush that is 'Blackfellas' Point. From there, Mark McKenna's gaze pans out - from the history of one place he knows intimately, to the history of one region and, ultimately, to the history of Australia's quest for reconciliation between Indigenous and non-Indigenous Australians. Looking For Blackfellas' Point is a history for every Australian who is interested in the story of settler-Australia's relations with Indigenous people - what happened between us, how we learnt to forget and, finally, how we came to confront the truth about our past and build a movement for reconciliation.