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The multi-axis vibration environment and man
,4pplied Er,~,orTomics ?979, ".5, 25~-267
The multi-axis vibration environment and man E. J. Lovesey Royal Aircraft Establishment, Farnborough Many investigations into the effects of vibration on man have been performed since Mallock's first study of London Underground vibrations in 1902. The vibration research has tended to be confined to the vertical (heave) axis, yet recent experiments have indicated that low frequency vibration along the lateral (sway) axis has a greater adverse effect upon comfort and performance. Measurements of the vibration environments in current forms of transport including motor vehicles, hovercraft and aircraft etc have shown that appreciable quantities of vibration along all three axes exist. Further vibration research should consider the effects of mu Iti-axis vibrations upon man rather than limit tests to single axis vibration. Since early researchers (Mallock, 1902 and Melville, 1903) first became interested in the effects of vibration on man, most vibration experiments have been confined to the effects of heave vibration. There have been a few exceptions (Reiher and Meister, 193 l) and (Jacklin, 1933) who showed that sway and shunt vibrations were less tolerable than heave. Experiments involving combined heave and sway (Harwood, 1966) began when recent developments in large commercial transport aircraft (Zbrozek, 1965) drew attention to the adverse effects of multi-axis vibrations on crew and passengers. As these aircraft have increased in size the amplitudes of vibrations in both heave and sway have intensified while frequencies have decreased to those of the predominant body resonances. This has resulted in several experiments being performed (Harwood, 1966, Lovesey, 1968, Brumaghim, 1969, and Shurmer, 1967) in which aircrew subjects have been exposed to low frequency heave and sway vibrations simultaneously. These tests showed that whereas heave vibrations alone have little effect upon subjects, sway alone has a marked detrimental effect and heave combined with sway produces an even greater degradation in comfort and performance.
In 4 of these experiments, a jet transport aircraft take off and climb were simulated with various amounts of heave and sway vibration present. Performance under these conditions was assessed by the ability of the subject to follow a commercial flight director instrument situated on a panel 0.61 m (2 ft) in front of him. Tests showed that heave levels of up to 0"25 rms g had little detrimental effect and sometimes even improved performance. Sway levels of 0-15 rms g usually degraded performance, especially when combined with the 0.25 rms g heave vibration. The following table shows relative tracking errors using a head-down director during a 5 minute simulated climb, averaged for 6 subjects, with each pilot completing 36 tests. Heave vibrations consisted of 2-2 Hz at 0-25 rms g. Sway vibrations were of 3-5 Hz at O. 13 rms g. Subjects were seated in an ejection seat and wore a tight 3-point harness throughout each test. The Friedman test indicates that there is a significant difference between performance scores obtained under no vibration, heave vibration, and combined heave and sway vibration.
These results are not surprising, since man has evolved in a heave vibration environment caused by walking (Gunther, 1969) running etc and can tolerate quite large amplitude heave vibrations. Until relatively recently, on the evolutionary scale, man has had little experience of sway and shunt vibrations and has had little opportunity to adapt to them.
Table 1
Tracking dimension
No vibration
Further studies (Lovesey, 1970) of other forms of transport have shown that heave vibrations combined with appreciable quantities of sway and shunt vibrations are by no means uncommon.
Azimuth error
1"00
1-21
1-56
Pitch error
1"00
0"93
1.37
(Azimuth P = 0-05, Pitch P = 0-01).
Tracking errors during simulated climb Heave Heaveand sway
Combined heave and sway vibration tests Six separate experiments using low frequency combined heave and sway vibrations between 1½ to 4Hz, have been completed by the Engineering Physics Dept, Royal Aircraft Establishment, Farnborough.
258
Applied Ergonomics December 1970
Similar though not significantly different at P = 0-05, compensatory tracking error scores during a 5 minute cruise period, when a small randomly generated display perturbation had to be nulled, are shown in Table 2.
Table 2
Tracking errors during simulated cruise
Tracking dimension
Ig
No vibration
Heave
Heave and sway
2g
Og Ig
Azimuth error
1.00
0"93
1.15
Pitch error
1.00
0.97
1-13
HeQve
°' f
t
~
~
J
~
~
4
~
I second
j Sway
Fig 2 Heave and sway accelerations at the cockpit floor of a medium haul jet transport aircraft at touch-down.
Two other experiments were performed using a 2 dimensional tracking task when subjected to heave and/or sway vibrations. Similar results were found again with heave vibrations causing the least change in performance, sway causing a marked change and combined 2Hz heave and 3½Hz sway causing the greatest degradation of all. Fig 1 shows the effects of 0-25 rms g heave, 0-2 rms g sway or combined heave and sway at 2 or 3½ Hz on compensatory pitch tracking performance, averaged for four subjects. The same vibration conditions produced similar effects upon the azimuth tracking scores. (Significantly different using the Friedman test at P = 1-01). In all experiments, subjective tolerance of the vibrations closely reflected the tracking performance scores. It should be noted that during the vibrational tests, the degree of tracking performance and comfort was reduced when a restraining harness was used.
~jL
I L
Fig 3 Morris 1300 saloon finer accelerations over roughly surfaced road at 15 km/h (10 mph).
Field measurements of multi-axis vibrations Vibration measurements of the ride in many types of vehicles have been recorded but very few published reports show accelerations other than those of heave (Kerr, 1963).
I00
An exception to this is shown in Fig 2 (Lovesey, 1970) where both cockpit floor heave and sway accelerations have been recorded at the touchdown of a medium haul jet transport aircraft. It is interesting to note that the sway vibrations are of slightly greater amplitude than those of the heave, resulting in an uncomfortable ride for the cockpit crew.
--1
i
In order to provide additional comprehensive 3 axis acceleration information about the low frequency (from approximately 1-40 Hz) vibration environments existing in present transport systems, a portable tape recorder system was assembled to record the output signals from 3 accelerometers mounted mutually perpendicular to each other. A series of measurements have been taken at the floors of different vehicles using this equipment.
50
O
~.
o .~ ,~,o . , o'~L~" o ~ . o po , ~~o
/
/
~ ~" o '~" o p o o
ff ~' ~,. ~,. o~'~v ~ , . % ,~,. ~,. , ~,~. ,~ ,_~ ~. ~'-40'~,. 4c ~" ~,~ ~,',_~
Fig 1 Compensatory tracking scores in pitch, averaged for 4 subjects wearing a 3-point harness and seated in an ejection seat.
A typical record of heave, sway and shunt accelerations taken by this equipment in a 1300 cc saloon car is shown in Figure 3, and Table 3 summarises the analysis of the records from several different types of transport. It can be seen that although heave is generally, ( though not always), the predominant vibration axis, appreciable quantities of sway and shunt are not uncommon. Care should be taken in the interpretation of the information given in Table 3. All vibration records are of the levels at the floor of the vehicles and may not be the same as the vibration levels at the input or inputs to the occupants of the vehicle. The present accelerometer pack is too bulky to be mounted on the seat cushion between the man and seat in order to record the primary vibration input to the man.
Applied Ergonomics December 1970
259
b
3
/ 1"8 ! 19"0
~ 0"8 i22"0
j' 1"2
Morris 1300
Hillman Minx Estate
DoubleDeck Bus
Single Deck 30Seat Bus
Hydrofoil 18m (60 ft) in 1
Launch 9 m
14.5.69
6.8.69
5.3.70
5.3.70
8.5.70
17.9.70
(28 ft) in length
~ 1'8 ~12"0
37"0
2"5 3"0 2"5 2"5
2'8 2"8 2'5 11"0 10'0
1"8 24"0 f 16 t19"0
+1"0 --0"4 + 0" 15
+-0"15 +-0'1
+-0"1 +-0'1 +-0"3 +-0"1
+-0"12 +-0"23 +-0'3 +-0"4 +-1"0
+-0"15 -+0"1 to 1'0 +-0"2 +-0"15 +-0'1 + 0"02
+-0"1 +-0'08
+- 0"25 +-0"12 +-0"14
2"0 2"5 8"5
BR Electric Train
+0-05
2.5.69
+-0"13
I 1"5
HM-2 Sidewall Hovercraft
2.5.69
+-0'3 +-0"16 +-0"14 +0"25 +- 0'3 +-0"25 -+0'1
+-0"18 +- 0"25 -0 +-0"25 +-0"12 +0.5 -0'25 +-0"2
+-0"01 + 0"05
+0-05 +-0"05
g
~ 1"3
SRN5 Hovercraft
15.4.69
1"5 2"0 4"7 0"93 1"3 1"5 5
0"5
3 0"9 0'25
2'1 1
SRN 5 Hovercraft
Dove Twin Engined Aircraft
27 27
12 11'5
Hz
Heave
14.5.69
2.3.70
Scout Helicopter
16.4.69
m
o
Sioux Helicopter
Vehicle
16.4.69
Date
+-0"05 +0"05
+-0"06 +-0'05 -+ 0"25 +0"08 +0-14
+-0'05 +- 0'05 +0'05 + 0"05 + 0"04 +-0"05 +-0"05
+0"03
-+0"03 -+0"05 -+0"03
+0-08 +- 0'04
+0"45 +- 0"6
+0"35 +-0"25
g
37
1"2
0"8 34
20"0 12'0 28"0 2"5
22'0 14"0 10"0 14"0 10"0
1"5 14"0 1-5 25"0
-+ 0 1
+-0"15
+-0"05 +-0'1
+-0"1 +0"1 +-0"12 +-0"1
+-0'11 +-0"12 +-0"2 -+0"2 "1-0"5
+-0"07 +-0"1 +-0"02 +- 0"01
. . . 19"0 +-0"2
1'8 12"0
26"0 43"0 44"0 44"0 44'0
125 12"5 12"5 12"5 2"6 13"5 12"5
1"2
1-0 0"9 -
21 1 "0
27 27
12 11"5
Hz
Sway
37
1"2
0"8 34
30"0 13-0 28"0 25'0
22'0 40"0 14"0 40"0 10'0
1"8 20"0 2"0 25"0
. 19"0
12'0
12"5 43"0 44"0 44"0 44"0
1'5 2'0 4"7 18"0 3"2 1"5 12"5
1-2
1"0 0"9 --
2"1 1 "0
27"0 27'0
24'0 24"0
Hz
g
+- 0"C7
+-0"1
+0'03 +-0"07
+0"1 +-0'1 +-0"1 +-0"06
+-0"1 +0"1 +-0"1 +-0"1 +-0'3
+-0"08 -+0"07 -+0"02 +- 0"01
+-0"25
+-0"02
+-0'04 +- 0"05 + 0'2 +0"05 +-0"06
+-0'07 + 0'07 +-0'06 +- 0"05 + 0"05 +-0'05 +0"05
+-0-03
+-0'03 +-0-05 +-0"03
+-0'06 +- 0'02
+- 0"15 -+ 0"2
+-0"2 +-0"1
Shunt
30s
60s
several mins 70s 50s
60s 3s 3s lOOs ½s
lOs 10s several rains
several rains
60s 60s
10 s 10s 3s
20s'
10s 20 s 60s several mins 60 s 60s 60s
60s
10s 60s 10s
8s 20 s
several mins
several rains
Duration of vibration Notes
ride ride ride ride ride
(NB Accelerometer pack on centre line 2"5 m (8 ft) from bows
28 K t over 304--457 mm (1--11/= ft) high waves
35 Kt over smooth sea
1 5 - 5 0 krn/h (10--30 mph) along minor road (NB Accelerometer pack on floor centreline behind driver) 15--50 km/h (10--30 mph) along minor road (NB Accelerometer pack on floor centreline at rear of bus)
bumpy bumpy bumpy bumpy
ride ride ride ride
Violent ride. Heave and sway are in phase
Smooth ride, but high frequency affecting head--teeth chatter
Slightly Slightly Slightly Slightly
ride ride ride ride ride
Slightly Slightly Slightly Slightly Slightly
15--50 km/h ( 1 0 - 3 0 mph) along urban roads (NB Accelerometer pack on floor centreline in front of bus behind driver)
bumpy bumpy bumpy bumpy bumpy
Rough anduncomfortable Rough and uncomfortable Slightly bumpy ride Slightly bumpy ride
Very smooth ride Very smooth ride
Bumpy ride Bumpy ride
Smooth Smooth Smooth Smooth Smooth
Slightly bumpy ride Slightly bumpy ride Slightly bumpy ride Very rough ride Very rough ride Very rough ride Very rough ride
Bumpy ride through mild turbulence
Generally a bumpy ride Heave, sway and shunt are in phase
Smooth ride but very noisy Slight visual interference Smooth ride Smooth ride with occasional mild turbulence
Subjective comments
15 km/h (10 mph) over pot holed gravel road producing an appreciable rolling motion 3 0 - 5 0 km/h (20--30 mph) over rough B class road 30--50 km/h ( 2 0 - 3 0 mph) over rough B class road
105 km/h (65 mph) over newly surfaced A class road between Odiham and Aldershot
50 to 60 km/h (30 to 40 mph) between Brookwood and Woking 50 to 60 km/h (30 to 40 mph) between Brookwood and Woking
Calm water with occasional light choppy waves Between Charing Cross Pier and Greenwich Between Charing Cross Pier and Greenwich Between Charing Cross Pier and Greenwich Induced by wash from tug and barges
110 K(IAS) cruise at 1 50Oft Crossing Solent at 45 Kt(IAS) Over calm water (Sea State 1) Crossing Solent at approximately 15 Kt ground speed Over 0"9-1 "2 m ( 3 - 4 ft) high steep choppy waves with white horses in gale force winds
Cruise at 500 ft Cruise at 500 ft 110 K(IAS) cruise at 1 50Oft
Ground roll Initial climb
100 Kt(IAS) cruise at 1 000 ft 100 Kt(IAS) cruise at 50 ft
Low speed taxi at 10 ft A G L Cruise at 70 Kt(IAS) and 1 000 ft A G L
Predominant vibration frequencies and levels of different vehicles' floors near centre of gravity
"O
o
Table 3
Seat structure and cushion dynamics invariably modify the vibration input to the man. For example, the seat dynamics in the electric train almost certainly amplified the low amplitude heave and sway vibrations to uncomfortable levels. The Morris 1300 seat, on the other hand, definitely attenuated the vibrations to give, subjectively, a very smooth ride. However, these measurements do give an indication of the order of frequency, amplitude and axis of vibrations to be found in existing transport systems. Bracketed figures in Table 3, as in the case of the electric train, show where two predominant frequencies exist concurrently. In other vehicles the frequency may change with the surface over which the vehicle is travelling. This is so with the SRN5 hovercraft, where the low frequency vibration is largely dependent upon wave encounter rate. In helicopters, the complex fluctuating loading of the main rotor blades is thought to produce sway vibrations which predominate over shunt and heave vibrations. Much of the vibration is attenuated by the seat cushion before it reaches the man. However, complaints of degraded vision are not common from helicopter aircrew. Some of the vibrations listed in Table 3 are of appreciable amplitude. For example, both single and double deck buses produce floor accelerations which are accepted by the travelling public, but which are rated as unacceptable when reproduced in an experiment using a vibration test rig.
Fig 4
This aerial example is not typical of vehicle
motion, but illustrates one way in which large transient accelerations may be induced. The photograph was taken after the hovercraft had negotiated 2-metre-high surf in gale force winds. Most of the hovercraft vibrations are confined to the vertical axis to which the human body is, fortunately, the least sensitive.
Conclusions and recommendations
Recent investigations have shown that although heave vibration may be the predominant in existing vehicles, sway and shunt vibrations are often present in appreciable quantities and contribute significantly to ride discomfort and performance decrement. Future tests of human response to vibration should not be confined to single axis heave but should include both sway and shunt vibrations in combination with the heave to represent the real life situation. Further measurements of the vibrations within existing types of transport should be repeated with accelerometers small enough to be placed at the seat/man interface in order to determine the actual vibration input to the man. Much more work must be done before the effects of vibration and its interactions with other stresses upon man, can be really understood.
References
Brumaghim, S. H. 1969 Subjective response to commercial aircraft ride. International symposium on man-machine systems. Cambridge. Gunther, R. 1969 Impact vibrations in human walking. RAE Translation 1388. Harwood, K. G. and Lovesey, E. J. 1966 Preliminary tests on the effects of low frequency, whole body vibration on aircrew performance. Unpublished Ministry of Technology Report.
Jacklin, H. M. and Liddell, G. J. 1933 Riding comfort analysis. Perdue University Bulletin 44. Kerr, T. H., Nethaway, J. E. and Chinn, H. W. 1963 Aircraft tests in high-speed, low-level flight, including impressions of a spring-mounted seat. Nato Report 442. Lovesey, E. J. 1968 The influence of a restraining harness upon human comfort and tracking performance under single and multi-axis heave and sway vibration. Unpublished Ministry of Technology ReporL Lovesey, E. J. 1970 3 axis vibrations of hovercraft and other vehicles. RAE Report in preparation. Mallock, H. R. A. 1902 Vibrations produced by the working of traffic on the central London Railway. Board of Trade Report Command Papers No 951. Melville, G. W. 1903 Engineering 75. The vibration of steamships. Reiher, H. and Meister, F. J. 1931 The influence of vibration on human beings. Translation: Air Material Command Report No. F-TS-616RE. Wright Field, Ohio. Shurmer, C. R. and Silverthorn, D. 1967 Effects of tracking performance of vibration in each and in combinations of the heave, sway and roll axes. BAC GW Human Factors Study Note 4 No 12. Zbrozek, J. K. 1965 The need for research on the cockpit vibrational environment of the Concorde. Unpublished Ministry of Technology Report. Applied Ergonomics December 1970
261
The multi-axis vibration environment and man E. J. Lovesey Royal Aircraft Establishment, Farnborough Many investigations into the effects of vibration on man have been performed since Mallock's first study of London Underground vibrations in 1902. The vibration research has tended to be confined to the vertical (heave) axis, yet recent experiments have indicated that low frequency vibration along the lateral (sway) axis has a greater adverse effect upon comfort and performance. Measurements of the vibration environments in current forms of transport including motor vehicles, hovercraft and aircraft etc have shown that appreciable quantities of vibration along all three axes exist. Further vibration research should consider the effects of mu Iti-axis vibrations upon man rather than limit tests to single axis vibration. Since early researchers (Mallock, 1902 and Melville, 1903) first became interested in the effects of vibration on man, most vibration experiments have been confined to the effects of heave vibration. There have been a few exceptions (Reiher and Meister, 193 l) and (Jacklin, 1933) who showed that sway and shunt vibrations were less tolerable than heave. Experiments involving combined heave and sway (Harwood, 1966) began when recent developments in large commercial transport aircraft (Zbrozek, 1965) drew attention to the adverse effects of multi-axis vibrations on crew and passengers. As these aircraft have increased in size the amplitudes of vibrations in both heave and sway have intensified while frequencies have decreased to those of the predominant body resonances. This has resulted in several experiments being performed (Harwood, 1966, Lovesey, 1968, Brumaghim, 1969, and Shurmer, 1967) in which aircrew subjects have been exposed to low frequency heave and sway vibrations simultaneously. These tests showed that whereas heave vibrations alone have little effect upon subjects, sway alone has a marked detrimental effect and heave combined with sway produces an even greater degradation in comfort and performance.
In 4 of these experiments, a jet transport aircraft take off and climb were simulated with various amounts of heave and sway vibration present. Performance under these conditions was assessed by the ability of the subject to follow a commercial flight director instrument situated on a panel 0.61 m (2 ft) in front of him. Tests showed that heave levels of up to 0"25 rms g had little detrimental effect and sometimes even improved performance. Sway levels of 0-15 rms g usually degraded performance, especially when combined with the 0.25 rms g heave vibration. The following table shows relative tracking errors using a head-down director during a 5 minute simulated climb, averaged for 6 subjects, with each pilot completing 36 tests. Heave vibrations consisted of 2-2 Hz at 0-25 rms g. Sway vibrations were of 3-5 Hz at O. 13 rms g. Subjects were seated in an ejection seat and wore a tight 3-point harness throughout each test. The Friedman test indicates that there is a significant difference between performance scores obtained under no vibration, heave vibration, and combined heave and sway vibration.
These results are not surprising, since man has evolved in a heave vibration environment caused by walking (Gunther, 1969) running etc and can tolerate quite large amplitude heave vibrations. Until relatively recently, on the evolutionary scale, man has had little experience of sway and shunt vibrations and has had little opportunity to adapt to them.
Table 1
Tracking dimension
No vibration
Further studies (Lovesey, 1970) of other forms of transport have shown that heave vibrations combined with appreciable quantities of sway and shunt vibrations are by no means uncommon.
Azimuth error
1"00
1-21
1-56
Pitch error
1"00
0"93
1.37
(Azimuth P = 0-05, Pitch P = 0-01).
Tracking errors during simulated climb Heave Heaveand sway
Combined heave and sway vibration tests Six separate experiments using low frequency combined heave and sway vibrations between 1½ to 4Hz, have been completed by the Engineering Physics Dept, Royal Aircraft Establishment, Farnborough.
258
Applied Ergonomics December 1970
Similar though not significantly different at P = 0-05, compensatory tracking error scores during a 5 minute cruise period, when a small randomly generated display perturbation had to be nulled, are shown in Table 2.
Table 2
Tracking errors during simulated cruise
Tracking dimension
Ig
No vibration
Heave
Heave and sway
2g
Og Ig
Azimuth error
1.00
0"93
1.15
Pitch error
1.00
0.97
1-13
HeQve
°' f
t
~
~
J
~
~
4
~
I second
j Sway
Fig 2 Heave and sway accelerations at the cockpit floor of a medium haul jet transport aircraft at touch-down.
Two other experiments were performed using a 2 dimensional tracking task when subjected to heave and/or sway vibrations. Similar results were found again with heave vibrations causing the least change in performance, sway causing a marked change and combined 2Hz heave and 3½Hz sway causing the greatest degradation of all. Fig 1 shows the effects of 0-25 rms g heave, 0-2 rms g sway or combined heave and sway at 2 or 3½ Hz on compensatory pitch tracking performance, averaged for four subjects. The same vibration conditions produced similar effects upon the azimuth tracking scores. (Significantly different using the Friedman test at P = 1-01). In all experiments, subjective tolerance of the vibrations closely reflected the tracking performance scores. It should be noted that during the vibrational tests, the degree of tracking performance and comfort was reduced when a restraining harness was used.
~jL
I L
Fig 3 Morris 1300 saloon finer accelerations over roughly surfaced road at 15 km/h (10 mph).
Field measurements of multi-axis vibrations Vibration measurements of the ride in many types of vehicles have been recorded but very few published reports show accelerations other than those of heave (Kerr, 1963).
I00
An exception to this is shown in Fig 2 (Lovesey, 1970) where both cockpit floor heave and sway accelerations have been recorded at the touchdown of a medium haul jet transport aircraft. It is interesting to note that the sway vibrations are of slightly greater amplitude than those of the heave, resulting in an uncomfortable ride for the cockpit crew.
--1
i
In order to provide additional comprehensive 3 axis acceleration information about the low frequency (from approximately 1-40 Hz) vibration environments existing in present transport systems, a portable tape recorder system was assembled to record the output signals from 3 accelerometers mounted mutually perpendicular to each other. A series of measurements have been taken at the floors of different vehicles using this equipment.
50
O
~.
o .~ ,~,o . , o'~L~" o ~ . o po , ~~o
/
/
~ ~" o '~" o p o o
ff ~' ~,. ~,. o~'~v ~ , . % ,~,. ~,. , ~,~. ,~ ,_~ ~. ~'-40'~,. 4c ~" ~,~ ~,',_~
Fig 1 Compensatory tracking scores in pitch, averaged for 4 subjects wearing a 3-point harness and seated in an ejection seat.
A typical record of heave, sway and shunt accelerations taken by this equipment in a 1300 cc saloon car is shown in Figure 3, and Table 3 summarises the analysis of the records from several different types of transport. It can be seen that although heave is generally, ( though not always), the predominant vibration axis, appreciable quantities of sway and shunt are not uncommon. Care should be taken in the interpretation of the information given in Table 3. All vibration records are of the levels at the floor of the vehicles and may not be the same as the vibration levels at the input or inputs to the occupants of the vehicle. The present accelerometer pack is too bulky to be mounted on the seat cushion between the man and seat in order to record the primary vibration input to the man.
Applied Ergonomics December 1970
259
b
3
/ 1"8 ! 19"0
~ 0"8 i22"0
j' 1"2
Morris 1300
Hillman Minx Estate
DoubleDeck Bus
Single Deck 30Seat Bus
Hydrofoil 18m (60 ft) in 1
Launch 9 m
14.5.69
6.8.69
5.3.70
5.3.70
8.5.70
17.9.70
(28 ft) in length
~ 1'8 ~12"0
37"0
2"5 3"0 2"5 2"5
2'8 2"8 2'5 11"0 10'0
1"8 24"0 f 16 t19"0
+1"0 --0"4 + 0" 15
+-0"15 +-0'1
+-0"1 +-0'1 +-0"3 +-0"1
+-0"12 +-0"23 +-0'3 +-0"4 +-1"0
+-0"15 -+0"1 to 1'0 +-0"2 +-0"15 +-0'1 + 0"02
+-0"1 +-0'08
+- 0"25 +-0"12 +-0"14
2"0 2"5 8"5
BR Electric Train
+0-05
2.5.69
+-0"13
I 1"5
HM-2 Sidewall Hovercraft
2.5.69
+-0'3 +-0"16 +-0"14 +0"25 +- 0'3 +-0"25 -+0'1
+-0"18 +- 0"25 -0 +-0"25 +-0"12 +0.5 -0'25 +-0"2
+-0"01 + 0"05
+0-05 +-0"05
g
~ 1"3
SRN5 Hovercraft
15.4.69
1"5 2"0 4"7 0"93 1"3 1"5 5
0"5
3 0"9 0'25
2'1 1
SRN 5 Hovercraft
Dove Twin Engined Aircraft
27 27
12 11'5
Hz
Heave
14.5.69
2.3.70
Scout Helicopter
16.4.69
m
o
Sioux Helicopter
Vehicle
16.4.69
Date
+-0"05 +0"05
+-0"06 +-0'05 -+ 0"25 +0"08 +0-14
+-0'05 +- 0'05 +0'05 + 0"05 + 0"04 +-0"05 +-0"05
+0"03
-+0"03 -+0"05 -+0"03
+0-08 +- 0'04
+0"45 +- 0"6
+0"35 +-0"25
g
37
1"2
0"8 34
20"0 12'0 28"0 2"5
22'0 14"0 10"0 14"0 10"0
1"5 14"0 1-5 25"0
-+ 0 1
+-0"15
+-0"05 +-0'1
+-0"1 +0"1 +-0"12 +-0"1
+-0'11 +-0"12 +-0"2 -+0"2 "1-0"5
+-0"07 +-0"1 +-0"02 +- 0"01
. . . 19"0 +-0"2
1'8 12"0
26"0 43"0 44"0 44"0 44'0
125 12"5 12"5 12"5 2"6 13"5 12"5
1"2
1-0 0"9 -
21 1 "0
27 27
12 11"5
Hz
Sway
37
1"2
0"8 34
30"0 13-0 28"0 25'0
22'0 40"0 14"0 40"0 10'0
1"8 20"0 2"0 25"0
. 19"0
12'0
12"5 43"0 44"0 44"0 44"0
1'5 2'0 4"7 18"0 3"2 1"5 12"5
1-2
1"0 0"9 --
2"1 1 "0
27"0 27'0
24'0 24"0
Hz
g
+- 0"C7
+-0"1
+0'03 +-0"07
+0"1 +-0'1 +-0"1 +-0"06
+-0"1 +0"1 +-0"1 +-0"1 +-0'3
+-0"08 -+0"07 -+0"02 +- 0"01
+-0"25
+-0"02
+-0'04 +- 0"05 + 0'2 +0"05 +-0"06
+-0'07 + 0'07 +-0'06 +- 0"05 + 0"05 +-0'05 +0"05
+-0-03
+-0'03 +-0-05 +-0"03
+-0'06 +- 0'02
+- 0"15 -+ 0"2
+-0"2 +-0"1
Shunt
30s
60s
several mins 70s 50s
60s 3s 3s lOOs ½s
lOs 10s several rains
several rains
60s 60s
10 s 10s 3s
20s'
10s 20 s 60s several mins 60 s 60s 60s
60s
10s 60s 10s
8s 20 s
several mins
several rains
Duration of vibration Notes
ride ride ride ride ride
(NB Accelerometer pack on centre line 2"5 m (8 ft) from bows
28 K t over 304--457 mm (1--11/= ft) high waves
35 Kt over smooth sea
1 5 - 5 0 krn/h (10--30 mph) along minor road (NB Accelerometer pack on floor centreline behind driver) 15--50 km/h (10--30 mph) along minor road (NB Accelerometer pack on floor centreline at rear of bus)
bumpy bumpy bumpy bumpy
ride ride ride ride
Violent ride. Heave and sway are in phase
Smooth ride, but high frequency affecting head--teeth chatter
Slightly Slightly Slightly Slightly
ride ride ride ride ride
Slightly Slightly Slightly Slightly Slightly
15--50 km/h ( 1 0 - 3 0 mph) along urban roads (NB Accelerometer pack on floor centreline in front of bus behind driver)
bumpy bumpy bumpy bumpy bumpy
Rough anduncomfortable Rough and uncomfortable Slightly bumpy ride Slightly bumpy ride
Very smooth ride Very smooth ride
Bumpy ride Bumpy ride
Smooth Smooth Smooth Smooth Smooth
Slightly bumpy ride Slightly bumpy ride Slightly bumpy ride Very rough ride Very rough ride Very rough ride Very rough ride
Bumpy ride through mild turbulence
Generally a bumpy ride Heave, sway and shunt are in phase
Smooth ride but very noisy Slight visual interference Smooth ride Smooth ride with occasional mild turbulence
Subjective comments
15 km/h (10 mph) over pot holed gravel road producing an appreciable rolling motion 3 0 - 5 0 km/h (20--30 mph) over rough B class road 30--50 km/h ( 2 0 - 3 0 mph) over rough B class road
105 km/h (65 mph) over newly surfaced A class road between Odiham and Aldershot
50 to 60 km/h (30 to 40 mph) between Brookwood and Woking 50 to 60 km/h (30 to 40 mph) between Brookwood and Woking
Calm water with occasional light choppy waves Between Charing Cross Pier and Greenwich Between Charing Cross Pier and Greenwich Between Charing Cross Pier and Greenwich Induced by wash from tug and barges
110 K(IAS) cruise at 1 50Oft Crossing Solent at 45 Kt(IAS) Over calm water (Sea State 1) Crossing Solent at approximately 15 Kt ground speed Over 0"9-1 "2 m ( 3 - 4 ft) high steep choppy waves with white horses in gale force winds
Cruise at 500 ft Cruise at 500 ft 110 K(IAS) cruise at 1 50Oft
Ground roll Initial climb
100 Kt(IAS) cruise at 1 000 ft 100 Kt(IAS) cruise at 50 ft
Low speed taxi at 10 ft A G L Cruise at 70 Kt(IAS) and 1 000 ft A G L
Predominant vibration frequencies and levels of different vehicles' floors near centre of gravity
"O
o
Table 3
Seat structure and cushion dynamics invariably modify the vibration input to the man. For example, the seat dynamics in the electric train almost certainly amplified the low amplitude heave and sway vibrations to uncomfortable levels. The Morris 1300 seat, on the other hand, definitely attenuated the vibrations to give, subjectively, a very smooth ride. However, these measurements do give an indication of the order of frequency, amplitude and axis of vibrations to be found in existing transport systems. Bracketed figures in Table 3, as in the case of the electric train, show where two predominant frequencies exist concurrently. In other vehicles the frequency may change with the surface over which the vehicle is travelling. This is so with the SRN5 hovercraft, where the low frequency vibration is largely dependent upon wave encounter rate. In helicopters, the complex fluctuating loading of the main rotor blades is thought to produce sway vibrations which predominate over shunt and heave vibrations. Much of the vibration is attenuated by the seat cushion before it reaches the man. However, complaints of degraded vision are not common from helicopter aircrew. Some of the vibrations listed in Table 3 are of appreciable amplitude. For example, both single and double deck buses produce floor accelerations which are accepted by the travelling public, but which are rated as unacceptable when reproduced in an experiment using a vibration test rig.
Fig 4
This aerial example is not typical of vehicle
motion, but illustrates one way in which large transient accelerations may be induced. The photograph was taken after the hovercraft had negotiated 2-metre-high surf in gale force winds. Most of the hovercraft vibrations are confined to the vertical axis to which the human body is, fortunately, the least sensitive.
Conclusions and recommendations
Recent investigations have shown that although heave vibration may be the predominant in existing vehicles, sway and shunt vibrations are often present in appreciable quantities and contribute significantly to ride discomfort and performance decrement. Future tests of human response to vibration should not be confined to single axis heave but should include both sway and shunt vibrations in combination with the heave to represent the real life situation. Further measurements of the vibrations within existing types of transport should be repeated with accelerometers small enough to be placed at the seat/man interface in order to determine the actual vibration input to the man. Much more work must be done before the effects of vibration and its interactions with other stresses upon man, can be really understood.
References
Brumaghim, S. H. 1969 Subjective response to commercial aircraft ride. International symposium on man-machine systems. Cambridge. Gunther, R. 1969 Impact vibrations in human walking. RAE Translation 1388. Harwood, K. G. and Lovesey, E. J. 1966 Preliminary tests on the effects of low frequency, whole body vibration on aircrew performance. Unpublished Ministry of Technology Report.
Jacklin, H. M. and Liddell, G. J. 1933 Riding comfort analysis. Perdue University Bulletin 44. Kerr, T. H., Nethaway, J. E. and Chinn, H. W. 1963 Aircraft tests in high-speed, low-level flight, including impressions of a spring-mounted seat. Nato Report 442. Lovesey, E. J. 1968 The influence of a restraining harness upon human comfort and tracking performance under single and multi-axis heave and sway vibration. Unpublished Ministry of Technology ReporL Lovesey, E. J. 1970 3 axis vibrations of hovercraft and other vehicles. RAE Report in preparation. Mallock, H. R. A. 1902 Vibrations produced by the working of traffic on the central London Railway. Board of Trade Report Command Papers No 951. Melville, G. W. 1903 Engineering 75. The vibration of steamships. Reiher, H. and Meister, F. J. 1931 The influence of vibration on human beings. Translation: Air Material Command Report No. F-TS-616RE. Wright Field, Ohio. Shurmer, C. R. and Silverthorn, D. 1967 Effects of tracking performance of vibration in each and in combinations of the heave, sway and roll axes. BAC GW Human Factors Study Note 4 No 12. Zbrozek, J. K. 1965 The need for research on the cockpit vibrational environment of the Concorde. Unpublished Ministry of Technology Report. Applied Ergonomics December 1970
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