SHIPBU tIDING R[SEARCH INSTITUTE ZAGRER
New Electric Self-Propulsion Dynamometers
by
Kaname Taniguchi
Chief of Mitsubishi Nagasaki Experimental Tank
and
Kyoji Watanabe
Assistant to Chief of Mitsubishi Nagasaki Experimental Tank
?APER No 10
?aper to be presented at the Symposium on the
Towing Tank Facilities, lastrumentation and
Measuring Technique Zagreb
22-25
September 1959.K. Taniguchi and K. Watanabe
The so-called ebers" type dinainometer has commonly been used for many years for the measurement of torque and thrust in self-propulsion test, but is now unable to meet the recent increase in requirements completely with respect to accuracy and reliability and is of no use at all for self-propulsion test in waves which has now gained much importance. In order to solve this problem, studies have been made for a new and superb self-propulsion d.ynaniorneter, and. as a result, the following two types are now coinpleted
/A/ Inductance type self-propulsion dynamometer /I.S.D.-I/
/ß/ Wire strain gauge type self-propulsion dynamometer /S.S.D.-II/
t
The dynamometer /A/ is intended chiefly for the test of large models of 7 meters in length and the dynamometer
¡BI
for small models of small craft. The former has a high accuracy /max. error 0.2 %/ and reliability and the latter is light /1.0 HP,7.3
kg/ and very small in size and of high speed /4,000 r.p.m.! yet with sufficient accuracy.1/ Preface:
The so-called &ebers type1 /Fig. 1/ self-propulsion dynainometer has commonly been used in the world and in our experimental tank too, but has following defects.
/1/ As reversible motor is used for the on-off control, it is difficult to design and regulate the control mechanism.
/2/ It is hard to design the electric contact for the reversible motor and is often necessary to repair the contact on account of fouling and burning. The accuracy of measurement decreases by these troubles.
/3/
This dynarnometer does not suit the measurement for small high speed craft because o± its considerably heavy weight and large size./1-i-/ On account of its complicated mechanism, high
relia-bility can not be expected and considerably high skill is neeessary for handling.
/5/
The most important defect of this dynamometeristhat it cannot be used for tests in waves.
After World War II, we set forth the study of
self-propulsion dynainometer in order to improve the above-mentioned defects as far as possible and completed the Mitsubishi
Nagasaki Self-Propulsion Dynainometer /called MSD type here-after! for the reconstructed Experimental Tank which had been destroyed by an Atomic Bomb. This equipment was also of Gebers Type in principle and. the above defect
/5/
was not yet corrected.drive motor
(J
o
o
coupling
(free uiom axial force)
-3-record of T C,, C2 base line TB thrust bearing differential gear sup por t thrust balanceFig. 1. Gebers' Type Self-Propulsion Dynamometer /Explanation of ruechanisrri/
Fig. 2. MSD-Type Self-Propulsion Dynamometer
thrust of propel/er I., L o L V, L o w (J o o travelling weight
Moreover, on account of its complicated mechanism, it was difficult to judge the extent of reliability and the equip-ment could not be so improved as to guarantee an accuracy of 0.2 to 0.3 % always.
Just then, requirement for studies on problems in waves was increasing, so it became desirable to have a handy
self-propulsion dynamometer usable both in smooth water and. in waves which has a simple mechanism and. high
reliabi-lity. F' this purpose,studies were made for an electric
self-propulsion dyiiamometer and the following two types were completed. These new electric self-propulsion dynamo-meters have satisfactory properties and are now in general use in our experimental tank. The following chapters are devoted to the explanations about these dynamometers.
2/ The reasonswhy the electric self-propulsion dynamometers were adopted:
The accuracy desired for our self-propulsion dynamometers are as follows;
For self-propulsion test in smooth water:
The maximum error is smaller than + 0.2 % of the rated value.
For self-propulsion test in waves:
The maximum error is smaller than ± i to 2 % of the rated value.
Generally in the case of purely electric measurement, it may be safe to consider the accuracy within i - 2 % errors, taking the fluctuation of the electric source, the accuracy of the transducer itself and of indicators all
into consideration. It seems, therefore, to be impossible to obtain sufficient accuracy for our purpose by the purely electric method of measurement. But when a mechanical
balan-ce is used together and almost all the forbalan-ces and the moments to be measured are balanced by weights, the errors can be smaller than + 0.2 % with such an electric instrument. Besides, in self-propulsion test in smooth water, it is not so difficult to estimate the values of the thrust and. the torque and to balance about 90 % of them previously by
weights. As the dynamometer of this type has not the recor-ding mechanism with itself, the mechanism of operation becomes simpler, lighter and smaller in size. On the other hand, in the self-propulsion test in waves, non-stationary forces can be measured, if the dynamometer is devised to measure the whole quantities electrically by removing the mechanical
balances, which are available for calibration of the electric transducer. By such an appropriate combination of mechanical balance and electric transducer, namely by so-called compen-sation method, electric self-propulsion dynamometers with such high accuracy as we require can be manufactured. The foregoing are reasons why we designed electric self-propulsion dynamometers.
3/ Types of electric transducer:
From the viewpoint of the above-mentioned purposes and reasons, the conditions required for the electric transducer of this dynaniometer are as follows:
/1/ The mechanism is simple and. accurate, and the trans-formation between forces and electrical quantities is in linear relation.
/2/ It should be easy to treat and. have simple recording apparatus.
/3/
Its characteristics are constant for a long timeand
it has high reliability.The following types of transducers are generally in use:
/1/ Inductance type
/2/ Wire strain gauge type
/3/ Capacity type
/'+/ Maeto-strictjon gauge type
Of these, the inductance type and
the wire strain gauge
type
were adopted from the standpoint that the perfoiiaance isstable and
reliable for a long time and the operation iseasy.
3-1/ Inductance type transducer:
The transducer adopted is of such a well-known type as shown
in Fig.
3.
As for the carrier wave,taking the electric source, stray capacity, frequency of measured quantities and others into
conside-ration, sine wave of 1 ICC in frequency and 100 V in voltage was selected and a motor-generator was adopted as the electric source. The capacity of this MG is large enough to supply with a few self-propulsion dynamometers at the same time, but in addition to this a portable source of electricity of vacuum tube oscillator type is also prepared for each self-propulsion dynamometer. Investigations were made for the size of the
pick-up and the relation between the displacement of moving iron and. the gaps between iron pieces, taking the availability of core into account. In the first place, pen-writing milliam-meter of moving coil type ¡Yokokawa KR-type 5inA/ was
chosen from the viewpoint of the simplicity for use. This
6
Symbols
T, T2
2 1
step down transformer1 52 rectifier R, variable resistor (0- adjuster) R2 R3 resisfor R4 resis for 300Q dummy load)
J1 plug & jack for pen writing
mill/ammeter
J2 plug & jock for electromagnetic os cilla graph L C
filter
1,000C/s 100 V 7 l JJJ T, OOOOOOOOQQFig. . ISD-I Type Self-Propulsion. Dynamorneter
¡Principie Diagram of Inductance Type Transd.ucer/
pen-writing milliammeter was designed to operate without amplifier. It was desirable that the displacement of the moving iron should be pretty large considering the relation to the mechanical balance. As a result of investigations in-to this point, the maximum designed displacement of the moving
iron and the gap between the irons were selected + 2 mm and
5 mm respectively, and the size of the E-type iron piece was determined 4-O mm x 30 mm. Using this pick-up, we succee-ded in obtaining the sufficient output to operate the auto-matic recording milliainmeter without amplifier. As the pen-writing milliamnieter, however, cannot trace the quantity
varying with high frequency, an electromagnetic oscillograph
was used together to record the fluctuating quantities as is the case with tests in waves. Pig. 14 shows the schematic plan of this transducer.
3-2/ Strain gauge type transducer:
If strain gauge is used for pick-up, strain meter avai-lable in market can be used as amplifying and recording appa-ratus, and a dynamometer of this type can be made rather
easily and. light in weight and small in size. Por this reason, self-propulsion dynamometer of this type was chosen as the second type. On each side of spring steel equi-stress beam at the pick-up, two strain gauges were affixed, i.e. four gauge method, in order to reduce the influences due to the difference of.the positions of the strain gauges and to increase the sensitivity. The spring of the pick-up was
de-signed to be exchangeable according to whether all or a part of the quantities are measured by the strain gauge pick-up and also to be used for both torque and thrust balance. Besides, reading apparatus of zero-method type was attached in order that comparatively constant forces may be measured with high accuracy. As mentioned above, this self-propulsion dynamoiueter can measure various values by choosing the proper one of the three methods - electro-magnetic oscillograph /for fluctuation with high frequency!, pen-writing oscil-lograph /f or measuring 15-30 c/s variation/ and measurement of mean values by zero-method.
Fig.
5.
shows the schematic plan of this transducer.pick up gauges G. 3 G pen writing oscillo graph
--measuring circuit for zero-method Sealed Sealed wire wire DC-amplifierS6-P-A
f//f low im.edonce gauge Volt {osciilaforhiqh irrioe dance output ,),../
G, G G5 G4 pick up gauges
R2 . . variable resistor for null balance method
(measurment extent can be shifted by changing the position of
R1 ...resistor. (sensitivity are, variable, by changing the
resilor R,)
C-Bal. R-Bal. bridge balance
ATT attenuator 4 steps ( 1,
Gain . . . . gain control
Re.! rectifier
Re.2 rectifier
Fig.
5.
SSD-II Type Self-Propulsion Dynamometer /Schematic diagram of T. & Q. measurement by strain gauge type transducer/ -9-sfra in meter C-Bol R-Bal R5 Ca/ibm (/01, ¡Ite Type - DS 6-R4/ Inductance-type self-propulsion dynamoineter /ISD-I type/:
This dynamorneter was designed, chiefly aiming at acòuracy and. reliability, for exclusive use for self-propulsion test
of 7 meter models /for large tank/ both in smooth water and. in waves.
The capacity and main particulars are as follows:
Thrust .. Capacity 20 kg Maximum error is smaller than
f
% of the rated valuesin smooth water and 1 - 2 % in waves.
Torque .... Capacity 70 kg-cm Maximum error is the same as that of the thrust.
Number of revolutions Max. 30 rps
Weight 27 kg
Size 600 mm x 250 inn x 600 mm/lengthxbreadthxheight/
Pick-up Inductance-type tansducer, whose carrier wave is a sine-wave of 1000 c/s and 100 V.
Recording apparatus Pen-writing D.C. ammeter,
Yokokawa KR type.
Por self-propulsion tests in smooth water, forces are most-ly balanced. by weights and onmost-ly the rest are automaticalmost-ly recorded, and for tests in waves total forces are measured electrically and the mean values or the variations slower than i c/s are recorded. by pen-writing ammeter, or if neces-sary, true variation by electro-magnetic oscillograph. The balance for tests in smooth water is removed for tests in waves and is used for calibration only.
The pick-ups for the thrust and the torque are of all the same type and size. Fig. 6. is the drawing and Fig.
7.
is the photograph of this self-propulsion dynanionieter.-s'
a'
r
11L...J
I-::1.
ti, d,i'e I! I li -iMani typ, tinrr ¿*kaee
2P/iJ aaj axial .owint
,ear box direttic« of ,eiotio,t is roytrid
Fig. 6.
Adjusting box
/containing the measu-ring circuit shown in Fig.
L./
KR-Type pen-writing inilliamineter I-Control box for 100 c/s motor-generator ISD-I Type self-propulsion dyiamometer Thrust Torque balance balanceFig. 7 ISD-I Type Self-Propulsion Dynamometer
The torque is taken out of torque balance by combining the three belev gears as shown in Fig. 6., and measuring the moment around the axis which acts on the centre. bevel gear.
As shown in Fig. 6., a special coupling is provided bet-ween torque balance and thrust balance, so that it may absorb
-slight movement of shaft due to thrust while delivering tor-que only to tortor-que balance. This construction was the result of strenuous efforts and is believed to be the most reliable design considering the ease of manufacturing.
This dynamometer displayed an excellent performance and was put into operation with modification after trial manufac-ture. And it has been utilized for many years without any trouble since its completion. In addition, as this dynamometer
is easy to use, the time taken to carry out a self-propulsion test was reduced to half. As a result of this reduction, it became a practice at our tank to make a resistance test and a self-propulsion test on one condition on the same day. Furthermore, various influences on the result of these tests due to the difference of the surface conditions, deformation, and ballasting of ship models disappeared naturally and the reliability of the results became higher.
When we take the errors of the calibration of transducer for the last month for example, the probable errors for thrust and torque are 0.1 % and 0. 15 % of the capacities respecti-vely, and it is confirmed that the initially designed accuracy
is maintained.
5/
Wire strain gauge type self-propulsion dynamometer /SSD-II/: /See Fig. 8/As stated above, ISD-I type dynamorneter was completed with success, but this is not available for small ship models /including models of high speed boats, submarine etc./ on account of comparatively large weight and volume, as it was originally designed for large ship models of 7 meters long. It is often required, however, for tests on warships to mount a self-propulsion motor of 2 - 3 HP and a self-propulsion dynamometer for 2 or 3 shafts on a small ship model of.4-6 meters in length and 150-400 kg in displacement.
-Drive motor /0.6 HP/ 1 Self-propulsion dynamoine te r Torque Thrust balance balance
Pig. 8. SSD-II Type Self-Propulsion Dynamometer
Por this purpose, a self-propulsion dynamometer with small weight and volume and large number of revolutions is indispen-sable at the expense of accuracy to some extent. As the wire strain gauge type transducer seemed to be suitable for this dynamometer, a self-propulsion dynauiometer of this type was
- l'rni-
-Control unit
Strain meter for null-balance Power unit
manufactured for trial. The capacities and rarticulars re-quired for this self-propulsion dynamonieter are as follows:
Capacities thrust 15 kg
torque 50 kg-cm
/The maximum error is smaller than ± 0.5 % of the rated value./
Maximum number of revolution L1,00O rpm
Maximum delivered power 1
f
Weight
7.3
kgVolume max. breadth 16o mm
As this dynamometer is mounted on small ship models, the weights of the balance were fixed to the dynamometer and so the displacement of center of gravity of the dynamometer due to the displacement of the weights was restricted as small as possible.
A speed reduction device by combining spur gears instead of bevel gears was applied for taking out the torque at the torque balance, for the gears with high accuracy are neces-sary for such a dynamometer with large number ol' revolutions and high accuracy is obtained more easily by using spur gears.
Mechanical parts of the balances have such construction as shown in Fig.
9.
and weights of-f
and 1 kg are used. The notches are used for moving weights for the sake of sim-plicity for measurement.The transducer of strain meter type was so designed with a view to simple structure that all or a part of the quanti-ties may be measured by exchanging only the pick-up spring.
SK-4 ¡a sort of special steel! was adopted for the pick-up spring. The spring was designed to be an equi-stress one, the stress of which was 4 kg/mm2.
-'win leverai tnrg..e &21a,,ve 3'Q I-'o t 4&ne Ml,,a an
rinn.iw, ,id*.» ,tA,v,
reUJhLt,Ofl cianfre 14. L.1ction peor a-'Ii oIloiiifl Lb twnn, tear ntho i SO) antozstqd'os ttQxwii ntoveriient -6(eeiin9 v.ei9ht i ke fAwit
haul lever of ti Ply) t1V,CC
cnnt,iiwr )pn to.5oe jievooc
fe p.efiv suivit
aaxu/lar
¿soja Ste Joy com/sen3atv)n nu etliod (fo,q(Le I
X-X section
Pig.
9.
Fig. 10-A. 2 Sets of SSD-II Dynaiuometer and Drive Motor arranged for under water test.
Fig. 10-B. SSD-II Dynamometers with Water-tight Box mounted on the Submarine Model.
-As this self-propulsion dynaniometer is often used in large number of revolutions, a frame was provided so that it may be directly connected to the high speed self-propulsion
motor of 0.6 HP /100 % overload drive is permissi'ble/ x 6000 rpm to avoid troubles due to misalignment.
This dynamometer weighs
7.3
kg and if connected directly to the self-propulsion motor of 0.6 HP /including the tachometer-generator/, 21.5 kg. So it became possible to carry outmeasurement as far as about 3-6 HP with the weight of 65 kg in case of three shaft ship, and self-propulsion tests on special crafts which had hitherto been impossible became practicable with satisfactory results.
Fig. 10 shows this self-propulsion dynainometer applied to the self-propulsion test on a submarine model underwater.
In this case, the dynaniometer is contained in the compact water-tight box as illustrated.
5/
Conclusions:Studies, designing and manufacturing for trial have been made for self-propulsion dynamometers of a new type which make use of inductance type and strain meter type transducers together with compensation method, and the following two are now completed.
¡AI
ISD-I self propulsion dynamoineter¡BI
SSD-II self propulsion dynamometerThe d.ynamometer
¡AI
is intended chiefly for the testof large models of 7 meters long and the dynainometer ¡B/ for small models of small craft. The former has a high accuracy and reliability and the latter is light and small in size and of high speed yet with sufficient accuracy.
-Owing to the conipletion of these dynamometers, not only the accuracy of measurement has risen to a great extent, but
also the testing capacity of the experimental tank doubly
increased by /A/ because of the reductìon of the time for tests to half, and the self-propulsion tests on small crafts which has been regarded as impossible became possible by
