【発明の詳細な説明】[Detailed description of the invention]
本発明は例えば起振力の小さなプロペラや振動
の小さい船舶の開発に寄与できるプロペラ圧力変
動計測等に適用し得る圧力変動計測方法に関す
る。
従来、空洞水槽（Cavitation Tunnel）内のプ
ロペラに基因する水圧変動の計測等には、第１図
縦断面図に示すように、圧力計０３をプロペラ０
１の直上に設置された計測平板０２に取付け、計
測平板０２は空洞水槽外板０８に平板支持棒０
４、板バネ０６、板バネ支持機構０７、シール０
５を介してプロペラ０１との間の間隔を調節可能
に取付け、流速０９が存在する流れの場でプロペ
ラ０１を回転させて水圧変動を圧力計０３で計測
するようにしている。
しかしながら、このような手段では、圧力変動
自体は微小であるが、面積の広い計測平板０２全
体で圧力変動を受けるので、計測平板に対する起
振力は大となり計測平板が振動を生ずる。
圧力変動によつて計測平板が振動を始めると、
それによる２次的圧力変動が発生し、プロペラに
よる圧力変動だけを圧力計で計測することが困難
となる。そこで、計測平板の振動の発生を防ぐた
めに計測平板及びその支持部材をある程度剛性に
するとか、計測平板の重量を大にしなければなら
ないが、これらは実現困難な要素が多いので、現
在の計測手段では、やむを得ず、数10％の誤差を
許容しているのが実情である。
また、水圧変動が1g／cm2程度の微小圧力であ
るので計測精度を高めようとしてもこれが仲々に
困難であり、更に、圧力計が温度変化に敏感なた
めに、微小圧力の計測値がばらつくことが多い等
の不都合もある。
本発明はこのような事情に鑑み感度を良好なら
しめるとともに温度変化等に対しても安定な水圧
変動を計測することのできる圧力変動計測方法を
提供することを目的とするもので、試験水槽内の
供試物体に基因する水圧変動を計測部材に付設し
た振動計を用いて計測するに当り、上記振動計で
測定した上記計測部材の振動応答と、別途求めた
上記計測部材の振動特性とより水圧変動を逆解析
して求めることを特徴とし、例えばプロペラ圧力
変動は特定の周波数（例えば回転数×羽根数の周
波数成分）が問題となるが、本発明によれば圧力
変動に面積をかけた起振力を振動計測結果と平板
系の伝達関数から逆推定することにより、プロペ
ラが発生する圧力変動を推定することができる。
なお上記の振動応答とは、例えば計測平板に水圧
変動が作用すると、計測平板に振動が発生する
が、この振動は計測平板という振動系に水圧変動
という力が入力された場合の応答量を示してお
り、これを振動工学の分野では振動応答と称され
ているものである。
本発明を空洞水槽におけるプロペラの回転に基
因する水圧変動の計測に適用した一実施例を図面
について説明すると、第２図はその縦断面図、第
３図は第２図の計測平板の振動特性を求める要領
を示す説明図、第４図は第２図による本発明のブ
ロツク線図、第５図は第２図とは異なる他の実施
例を示す縦断面図である。
まず、第２図において、１は供試プロペラ、２
は計測平板、４，４はそれぞれ計測平板２の両端
附近を適宜間隔を存して水槽外板８に平行に固定
するための２本の平板支持棒、８は水槽外板、９
は水槽水の流速、１０は計測平板２上に適宜間隔
で付設された複数の振動計である。
このような計測手段において、流送９が存在す
る流れの場でプロペラ１を回転させ、振動計１０
にて計測平板２の振動応答の時刻歴波形を示す振
動応答ｘを計測する。
振動応答ｘと計測平板２に作用する圧力変動に
起因する起振力〓との間には、周波数領域で下記
力学的関係が成立する。
ｘ（ω）＝〓（ω）・〓 …(1)
ただし、
The present invention relates to a pressure fluctuation measurement method that can be applied to, for example, propeller pressure fluctuation measurement that can contribute to the development of propellers with small excitation force and ships with low vibration. Conventionally, when measuring water pressure fluctuations caused by propellers in a cavity tunnel, pressure gauge 03 was used to measure propeller 0 as shown in the vertical cross-sectional view of Figure 1.
1, and the measurement flat plate 02 is attached to the hollow water tank outer plate 08 with a flat plate support rod 0.
4, leaf spring 06, leaf spring support mechanism 07, seal 0
The propeller 01 is attached so that the distance between the propeller 01 and the propeller 01 can be adjusted via a pressure gauge 03, and the propeller 01 is rotated in a flow field where a flow velocity 09 exists, and water pressure fluctuations are measured with a pressure gauge 03. However, in such a means, although the pressure fluctuation itself is minute, the entire measurement flat plate 02 having a large area receives the pressure fluctuation, so the vibrational force applied to the measurement flat plate becomes large, causing the measurement flat plate to vibrate. When the measurement plate begins to vibrate due to pressure fluctuations,
This causes secondary pressure fluctuations, making it difficult to measure only the pressure fluctuations caused by the propeller with a pressure gauge. Therefore, in order to prevent the generation of vibrations in the measurement plate, it is necessary to make the measurement plate and its supporting members to a certain degree of rigidity, or to increase the weight of the measurement plate, but there are many factors that are difficult to achieve, so current measurement methods The reality is that we have no choice but to allow an error of several 10%. In addition, since water pressure fluctuations are minute pressures of about 1 g/cm 2 , it is difficult to improve measurement accuracy.Furthermore, since pressure gauges are sensitive to temperature changes, the measured values of minute pressures vary. There are also some inconveniences, such as frequent occurrences. In view of these circumstances, it is an object of the present invention to provide a pressure fluctuation measurement method that has good sensitivity and is capable of measuring stable water pressure fluctuations even with temperature changes. When measuring water pressure fluctuations caused by the test object using a vibration meter attached to the measurement member, the vibration response of the measurement member measured by the vibration meter and the separately determined vibration characteristics of the measurement member were used. It is characterized by determining water pressure fluctuations by inverse analysis. For example, propeller pressure fluctuations are a problem with a specific frequency (for example, the frequency component of rotation speed x number of blades), but according to the present invention, pressure fluctuations are multiplied by area. By inversely estimating the excitation force from the vibration measurement results and the transfer function of the flat plate system, it is possible to estimate the pressure fluctuations generated by the propeller.
The above-mentioned vibration response refers to the amount of response when the force of water pressure fluctuation is input to the vibration system of the measurement plate, for example, when a water pressure fluctuation acts on the measurement plate, vibration occurs in the measurement plate. This is called vibration response in the field of vibration engineering. An embodiment in which the present invention is applied to the measurement of water pressure fluctuations caused by the rotation of a propeller in a hollow water tank will be explained with reference to the drawings. Fig. 2 is a longitudinal cross-sectional view thereof, and Fig. 3 is the vibration characteristics of the measurement flat plate shown in Fig. 2. FIG. 4 is a block diagram of the present invention according to FIG. 2, and FIG. 5 is a longitudinal sectional view showing another embodiment different from FIG. 2. First, in Figure 2, 1 is the test propeller, 2
denotes a measurement flat plate, 4 and 4 are two flat plate support rods for fixing the measurement flat plate 2 near both ends parallel to the aquarium outer plate 8 with an appropriate interval, 8 is an aquarium outer plate, and 9
is the flow rate of water in the aquarium, and 10 is a plurality of vibration meters attached at appropriate intervals on the measurement flat plate 2. In such a measuring means, the propeller 1 is rotated in a flow field where the flow 9 exists, and the vibration meter 10 is
A vibration response x indicating a time history waveform of the vibration response of the measurement flat plate 2 is measured. The following mechanical relationship holds true in the frequency domain between the vibration response x and the vibrational force caused by pressure fluctuations acting on the measurement flat plate 2. x(ω)=〓(ω)・〓…(1) However,
【表】
ω…角周波数（円振動数）
(1)を変形して(2)を得る。
〓（ω）＝H-1（ω）・ｘ（ω） …(2)
すなわち、(2)の関係を用いて前記成分ｘ（ω）
と別途求めることのできる計測平板の伝達関数〓
（ω）とより、第４図ブロツク線図に示すよう
に、計測平板の前記成分〓（ω）を求めることが
できるのである。
すなわち、第４図ブロツク線図において、各振
動計１０で計測された出力信号ｘ（ｔ）はデータ
レコード１１に記録された後、周波数分析器１２
により分析されて各周波数に対応する前記成分ｘ
（ω）を出力する。
この計測平板２の振動応答ｘを、後記する要領
で別途求めておいた計測平板２の伝達関数〓
（ω）を用いて計算器１３による(2)式の演算を行
なうことにより〓（ω）＝〓（ω）・ｘ（ω）を算
出し、これを適当なデイスプレイ装置１４上にデ
イスプレイすることができる。
伝達関数〓（ω）の求め方の一例を挙げれば、
第３図に示すように、各振動計１０の下部からフ
オースハンマ２０（ハンマに打撃力を測定できる
素子２１をつけたもの）で叩き、各振動計１０が
キヤツチした振動と打撃力との間の相関関係を求
めておけばよい。
なお、加振点（打撃点）の数と応答すべき振動
計の数は等しくする必要があるが、加振点と振動
計測点の数を増せば、加振力の分布や位相をも詳
細に知ることができる。
計測平板２が振動することによつて生起する２
次的圧力変動は付加質量の効果として伝達関数の
中に含まれるので２次的圧力変動に基因する誤差
は発生しない。
振動計が速度型、加速度型の場合には、圧力計
に比べて、振動数が高い領域では、相対的に感度
が良く、更に温度変化に対しても安定した高精度
の計測が可能となる。
第５図に示す第２実施例は、計測平板２′をコ
字状支持棒４′，４′を介して水槽外板８と同一平
面上に取付けた点で、第２図に示した第１実施例
と構造を異にするが、作用効果の点は第１実施例
と実質的に異なるところはない。なお上記各実施
例においては、計測部材として平板を使用するも
のについて説明したが、必ずしも平板である必要
はなく、受圧面を広くとれる形状であればよい。
要するに、本発明によれば、試験水槽内の供試
物体に基因する水圧変動を計測部材に付設した振
動計を用いて計測するに当り、上記振動計で測定
した上記計測部材の振動応答と、別途求めた上記
計測部材の振動特性とより水圧変動を逆解析して
求めることにより、高精度かつ温度変化に対して
も安定な圧力変動測定方法を得るから、本発明は
産業上極めて有益なものである。[Table] ω…Angular frequency (circular frequency)
Transform (1) to obtain (2). 〓(ω)=H -1 (ω)・x(ω) …(2) In other words, using the relationship (2), the above component x(ω)
The transfer function of the measurement plate that can be obtained separately is
(ω), the component 〓(ω) of the measurement plate can be obtained as shown in the block diagram of FIG. That is, in the block diagram of FIG.
The component x corresponding to each frequency is analyzed by
(ω) is output. The vibration response x of the measurement flat plate 2 was determined separately in the manner described later, and the transfer function of the measurement flat plate 2 was
Calculate 〓(ω)=〓(ω)・x(ω) by calculating equation (2) using the calculator 13 using (ω), and display this on an appropriate display device 14. I can do it. To give an example of how to find the transfer function 〓(ω),
As shown in FIG. 3, each vibration meter 10 is hit from the bottom with a force hammer 20 (a hammer equipped with an element 21 that can measure the impact force), and the difference between the vibrations caught by each vibration meter 10 and the impact force is measured. All you have to do is find a correlation. Note that the number of excitation points (impact points) and the number of vibration meters that should respond need to be equal, but if the number of excitation points and vibration measurement points is increased, the distribution and phase of the excitation force can be determined in more detail. can be known. 2 caused by the vibration of the measurement plate 2
Since the secondary pressure fluctuations are included in the transfer function as an effect of the added mass, errors due to secondary pressure fluctuations do not occur. If the vibration meter is a velocity type or an acceleration type, it is relatively sensitive in the high frequency range compared to a pressure gauge, and it is also possible to perform stable and highly accurate measurements against temperature changes. . The second embodiment shown in FIG. 5 differs from the one shown in FIG. Although the structure is different from that of the first embodiment, there is no substantial difference in function and effect from the first embodiment. In each of the above embodiments, a flat plate is used as the measurement member, but it does not necessarily have to be a flat plate, and any shape that allows for a wide pressure receiving surface may be used. In short, according to the present invention, when measuring water pressure fluctuations caused by a test object in a test water tank using a vibration meter attached to a measurement member, the vibration response of the measurement member measured by the vibration meter, The present invention is industrially extremely useful because it obtains a highly accurate pressure fluctuation measurement method that is stable against temperature changes by inversely analyzing the vibration characteristics of the measurement member and the water pressure fluctuations, which are determined separately. It is.
【図面の簡単な説明】[Brief explanation of the drawing]
第１図は公知の空洞試験水槽の水圧変動測定要
領を示す縦断面図、第２図は本発明の第１実施例
を示す縦断面図、第３図は第２図の計測平板の伝
達関数を求める要領を示す説明図、第４図は第２
図のブロツク線図、第５図は本発明の第２実施例
を示す縦断面図である。
１……プロペラ、２，２′……計測平板、４，
４′……平板支持棒、５……シール、８……水槽
外板、９……水槽水流速、１０……振動計、１１
……データレコーダ、１２……周波数分析器、１
３……計算器、１４……デイスプレイ装置、２０
……フオースハンマ、２１……打撃力測定素子。
FIG. 1 is a vertical cross-sectional view showing a procedure for measuring water pressure fluctuations in a known cavity test tank, FIG. 2 is a vertical cross-sectional view showing a first embodiment of the present invention, and FIG. 3 is a transfer function of the measurement flat plate shown in FIG. An explanatory diagram showing the procedure for determining the
FIG. 5 is a longitudinal sectional view showing a second embodiment of the present invention. 1...Propeller, 2,2'...Measuring plate, 4,
4'...Flat support rod, 5...Seal, 8...Aquarium outer plate, 9...Aquarium water flow rate, 10...Vibration meter, 11
...Data recorder, 12 ...Frequency analyzer, 1
3...Calculator, 14...Display device, 20
... force hammer, 21 ... impact force measuring element.