Development and realization of a method for real time data aquisition of slamming pressure signals

SCIENT1HC AND METHODOLOGICAL

SEMINAR ON SHIP

HYDRODYNAMICS

15m

JUBILEE

SESSION

PROCEEDINGS,

VOLUME

2

VARNA,

6-11 OCTOBER

k: :NIScE W1IVERSITE3T

ScheepshydmhMj

ABSTRACT

ì method for real time data acquisition of sianols with slamming pressure is developed. The realized soft-ware system based on the special hardsoft-ware contributed for carrying out slamming test on the new quality levol.

The method developed is universal and con be used for investigation of signals with limited informativeness.

1. INTRODUCTION

The slamming phenomenon is a complex, 000stationary

one, both in theoretical and in experimental aspect, characterized by a sharp change in the bow ship

sec-tion bottom pressure being investigated for a very

short period of time 1,!). The obtaining of sufficiently

good and reliable results in the experimental

investi-gation without specialized computer and program means

is connected with a high labour consumption. The paper

discusses the creation of a specialized program system

including also nonconventional computer technique with

which the problem under discussion of determining the

slamming pressure ir real time is solved sufficiently

operatively and completely on a high scientific level.

The computer and program means ensuring the slamming

experiment must realize the acquisition of dato from the so called "fast" channels containing the peak pressure,

whose scanning frequency reaches up to 50 CNr, as well

as slow values as relative motion and speed of the

mo-del ship or body being investigated relative to the

water surface, waves, etc., whose scanning frequency is

reaching 50 Hz, For measuring channels with entering frequency up to 2KHz the dota can be acquired with an

universal minicomputer equipped with standard

periphe-rals,real time operating system and input/output devices for connection with the object (2) , The use of

conven-tional measuring and computer means is practically

im-possible for registration of the peak pressure with

high frequency of discretization due to the following reasons:

- a huge operating memory is necessary for recording of the entering information with frequency 25-50 KHz,since practically no recording can be performed on an external memory in the course of data entering;

- the reaching of the desired frequency of acquisition is impossible;

- excess information is available in the data acquisi-tion from the channels containing the peak pressure be-ing measured in the record parts without impact, The

processing of the useful information is impeded.

i - Research Scientist

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JUBILEE

SESSION

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D. Radevt, A. Stephanov1

05MG, Seakeeping and Manoeuvrabïlit Department 05MG, Computer Technique and Automated Measuring System

Yama, Bulgaria

29

-The conclusion imposes itself of the need lot

ape-cialized methods, hardware and program meens for

dis-tributed processing by means of which the

information-significant data could be "picked out" still during the

scanning .

2. ESSENCE OF THE pRoPoSED DATA ACQUISITION THOD

The method proposed for overcoming of the

above-men-tioned problems consists in the following (3)

- Separate scanning is performed of the "slow"and"fast" channels, the scanning being controlled by two indepen-dent real time clocks,

- The channels are scanned only in the peak area am

the scanning starts at overflow of a particular signai

level. It is advisable to control the "fast"

by a dedicated computer, in order to guoranteo the

ne-cessary quick action and operating memory for informa-'

tion buffering.

- The readings' absolute time reale is connected to the

real time clock used for the "slow" channels.

- The relative times of the readings from the "fase'

channels are connected to the absolute time scale (Fig.

1), using the following relation:

TIIIEABS=ITINE1 *FREQ+(DEL-ITIl'1E2) *FREQ/ DEL +RELTIME,

where:

1TIME - absolute peak timo

ITIME4' - contents of the program counter of the

in-terruptions of the real time clock for the

"slow channels

ITIME2 - contents of the internal counter of the

real time clock for the"slow'channels

DEL - dimension of the internal counter of the

real time clock for the slow channels

FREQ - clock frequency

RELTIME - relative time of the peak in the buffer.

The combination of an universal minicomputer and a

dedicated microprocessor system (Fig,2) is the most

suitable computer system to ensure the slamming

tests,

The tasks of experiment preparation, data acquisition from the "slow" channels and their further processing

are solved on the universal minicomputer, The dedicated microprocessor system solves the problems of data

acqui-sition from the "fast" channels The universal

mini-computer is equipped with analog-digital convertor(ADC)

with average characteristics and a real timo clock. The

microprocessor has a fast ADCs for each channe] .The con-nection between these ADC5 and the mcroprocessor la

realized by a direct access channel

The problems with the operating memory and the data

reduction are solved by means of placing a trigger on

the ABC input, which starts only at availability of a particular level in the entering signal. After the

starting, only points of the time series containing

in-formation for a particular peak pressure are entered

the reaching of the specified level is waited for,

re-gistration is performed again, etc,, until the end of

the experiment

A basic problem in the procedure being proposed is

the connection of the "fast' channels' readings to real

time clock connected to the minicomputer (Fig.1).Adigi-,

tal interface is envisaged for this purpose, which

re-ceives the pulses from the triggers starting the

acqui-sition of a tine series from the "fast" channels. These

pulses interrupt the minicomputer and as a result the

absolute times of the readings' starts are recorded, A

parallel digital interface is also envisaged by which

the data are transferred to the minicomputer after the

test termination.

3, TECHNICAL REALIZATION

For the particular realization of the above method,

a minicomputer from the POP 11 series was selected,

equipped with an analog subsystem AR 11 containing a

real time clock (A), digital interface with interrupt logic DR1 IC () , digital interface IEEE88 for transfer

of numerical values and a fast ADC (6), with

possibil-ity of operation of up to 4 channels.

The general structure of the software operating on

the basis of the elaborated conceptional and technical

condition is presented in Fig.3. All programs are

real-ized on FORTRAN and ASSEMBLER for minicomputer PUP 11 with operating system RSX11M4,1. The programs are

not bound with the operating system generation but are

generated additionally after that. As seen from Fig. 3

there are three programs ensuring data acquisition

du-ring slamming tests.

The first of them (RESLEM) ensures the scanning of

the "slow" channels, the entering of the absolute times

of the initial points of the buffers containing the

peaks and the registration of information. After its

ire-G)

on a

o

29 - 2

plementation the file TIMER1 .DAT containing the absolute times, and the files RECOXX.DAT, with channels data are

created.

The program REGRAD transfers the peak values from the

"fast" ADC and determines their relative times in the

data buffer. It creates the file RELTIM.DAT containing

these times. This file, together with the file TIMER1.

DAT, are the inputs for the CONVT program It converts

the relative times to the absolute time scale relative

to the real time clock on the minicomputer POP 11/34.

The converted times together with the respective peak

value are output in the file FINT1M,DAT,

4. CONCLUSION

A method for real time data acquisition of signals with slamming pressure, based on specialized hardware,

is realized. Compared to the alternativeariant for

en-tering of such signals by analog tape-recorders,

con-siderable economy of labour and experimental time is reached. The respective software, implemented in real time is developed as well. This method is universal and

can be used for investigation of signals with limited informativeness.

5. REFERNCES

Radev D.," Slamming Investigation of Cylindrical Bow Ship Sectionsjoint Sulgarrian-Russian Seminar on

Behaviour of Ships and Narine Structures in Waves,Le-ningrad, 1984 (R)

Stephanov A,, "Design and Investigation of Software by the Simulation Modelling Method", Proc, of Confr. on

Computer Technique and Advanced Scientific Instrumenta-tion Ship Hydrodynamics, Varna, 1984, vol.3, 109-113.

Radev D., Stephanov A,, Report (TP-81-05.03107),

BSHC, Varna, 1986.

4, Aril User's Manual, Dec., 1975.

5. Drue User's Manual, Dec., 1976.

6. W + W Signal Memory Recorder, Service Manual, As

Basel, 1983.

I0

Ti J2 Ti absolute time scale

Fig. 1. Relation Between Absolute and Relative Tine Scales

ADC F ADC REAL TIME CLOCK

HARDWARE

V

DIGITAL INPUT MODULE

MINI COMPUTER 16 bits MULTI -C HANN E L ADC ADC

Fig.. Computer Measuring System fer Slemmin Tests

SOFTWARE

l'i

V

DATA

BASE

PEAK VALUES AND THEIR RELATIVE TIMES ( t.) TIME SERIES FROM SLOW CHANNELS PEAKS ABSCLUTE/ TIMES (T1)

/