搜档网
当前位置:搜档网 › Detection of cavitation in operation of kinetic pumps.

Detection of cavitation in operation of kinetic pumps.

Detection of cavitation in operation of kinetic pumps.
Detection of cavitation in operation of kinetic pumps.

Detection of cavitation in operation of kinetic https://www.sodocs.net/doc/2f7801063.html,e of discrete frequency tone in audible spectra

Mirko C

ˇudina *,Jurij Prezelj University of Ljubljana,Faculty of Mechanical Engineering,A?kerc

ˇeva 6,1000Ljubljana,Slovenia a r t i c l e i n f o Article history:

Received 30November 2007

Received in revised form 11July 2008Accepted 14July 2008

Available online 5September 2008PACS:43.30.Nb 47.55.dp 47.85.lf 47.85.Kn Keywords:

Kinetic pumps Cavitation Noise

Measurement Control

a b s t r a c t

Safe operation of kinetic pumps,as liquid movers,can be threatened by cavitation phenomenon in,

amongst others.Cavitation is the Achilles’heel of kinetic pumps.It can cause deterioration of the hydrau-lic performance,damage of the pump by pitting and material erosion,and structure vibration and noise.Cavitation can appear within the entire range of operating conditions,therefore it must by all means be prevented.To prevent cavitation in a pump we have to know the beginning and development of the cav-itation in the pump.For this purpose,the emitted noise in the audible range can be used,amongst other possibilities.Experiments have shown that there is a discrete frequency tone within the audible noise spectra,which is in strong correlation with development of the cavitation process in the pump.Therefore,the discrete frequency tone can be separated from the noise spectra of a cavitating pump and used to detect the incipient of cavitation and its development as well as to prevent the onset of the cavitation process in the pump,by means of initiating an alarm,shutdown,or control signal via an electrical control system.

ó2008Elsevier Ltd.All rights reserved.

1.Introduction

Cavitation in kinetic pumps occurs when the absolute static pressure at some point within a pump falls below the saturated va-pour pressure of the ?uid at the prevailing temperature conditions.In this case,the ?uid starts to ?ash and vaporization occurs.Vapor-ization of the ?owing ?uid is connected with the onset of bubbles.The bubbles are caught up by the ?owing liquid and collapse with-in the pump when they reach a region of higher pressure,where they condense.This process is accompanied by a violent collapse or implosion of the bubbles and a tremendous increase in pressure,which has the character of water hammer blows [1].The process of cavitation and bombardment of the pump surface by the bursting bubbles causes three different,undesirable effects:?rstly deterio-ration of the hydraulic performance of the pump (total delivery head,capacity and ef?ciency),secondly possible pitting and mate-rial erosion in the vicinity of the collapsing bubbles,and thirdly vibration of the pump walls excited by the pressure and ?ow pulsations,and resultant undesirable (crackling or hissing)noise.

In a case of fully developed cavitation within pump there is no ?ow and purpose of the pump is lost,pumping process is broken.Cav-itation is thus the Achilles’heel of kinetic pumps.

Cavitation can appear within the entire range of operating con-ditions,therefore to ensure pumping process undisturbed it must by all means be prevented.To prevent the onset of the cavitation we have to know the beginning of cavitation phenomenon in the pump and its full development.According to the available litera-ture,cavitation within the kinetic pumps (and water turbines)has been the subject of much research,numerous studies and al-most all books [1–7].But,due to the chaotic nature of the cavita-tion phenomenon,there is no possibility for a numerical prediction of an exact value of the emitted noise.Therefore,an ex-act value of cavitation noise can only be obtained by one of the available engineering methods.There are different engineering methods for detecting the beginning of the cavitation process and its full development.

1.Determination of the net positive suction head (NPSH)by a 3%drop in the total delivery head at the constant ?ow rate.The NPSH value so determined represents the required or critical value at which cavitation is fully developed.The method needs a special test stand according to the ISO 3555standards [8],and

0003-682X/$-see front matter ó2008Elsevier Ltd.All rights reserved.

doi:10.1016/j.apacoust.2008.07.005

*Corresponding author.Tel.:+38614771443;fax:+38612518567.

E-mail address:mirko.cudina@fs.uni-lj.si (M.C ˇudina).Applied Acoustics 70(2009)

540–546

Contents lists available at ScienceDirect

Applied Acoustics

journal homepage:w w w.e l s e v i e r.c o m /l oc a t e /a p a c o u s

t

a set of measurement results at different?ow rates.It is also

used to guarantee tests,but it is not suitable for cavitation mon-itoring in onsite operations.

2.Visualisation of the?ow through an impeller eye is the second

most popular engineering https://www.sodocs.net/doc/2f7801063.html,ing a transparent model casing and stroboscopic light,in which,calming down the cav-itating?ow,visualisation and photographic evidence of cavita-tion is possible.The procedure for testing is similar to the one before,but measuring is based on NPSH(4mm)data or4mm long vapour cavities,which correspond to the3%drop in total delivery head or the state of fully developed cavitation(NPSH required).The method is suitable for high-powered pumps and especially water turbine[3,6,7,9–11].However,it is less appropriate for small pumps and for the?ow rates far from the BEP,i.e.at partial?ow rates and towards the free delivery.

Instead of stroboscopic light,computer-aided camera visualisa-tion and digitalisation of the pictures can be used.It can also be used to guarantee tests.

3.Paint erosion testing is based on painting the impeller blades

and shrouds and observation of the cavitation erosion by evi-dent removal of the paint.Its application is good in combination with the NPSH(4mm)test,which shows if the cavitation pro-cess occurs within the pump or not.This method is complicated by dif?culties in choosing the proper paint adhesivity and sen-sitivity[6].The same method can be used for metal erosion after a long time of operation and for comparison with the painted erosion at the same percentage of design?ow rate. 4.A method that is based on measurement of the static pressure

within the?ow or on the volute-casing wall.With this method the onset of the cavitation cores is determined indirectly by comparison of the measured static pressure and the vapour pressure at the given temperature of the?ow or by the spectral analysis of the vortex patterns and pressure signal using the so-called wavelet analysis[12].The method is impractical since the local static pressure can be changed by the random chang-ing of the integral pump parameters caused by changing of the operation point,and by the?ow instability caused by the onset of stall and surge.

5.Measuring the vibration of the structure,by mounting a trans-

ducer in the pump inlet near the impeller blades,or as close as possible to the place of implosion bubbles.This method is sim-ilar to the previous one,but simpler and,unfortunately,less

accurate.The measured signal may be contaminated and cor-rupted by background noise,such as that of aero-dynamical, mechanical and electromagnetic origins,which attenuate or amplify the measured signal[4,5,12–16].According to the liter-ature used,the cavitation noise is broadband in nature and pro-nounced mainly in the high frequency range–in ultra sound.

Therefore,many researchers measured acoustic signal in fre-quency range up to1MHz.They used two different sensors: for low frequency noise,up to80kHz,an accelerometer was used,and for higher frequency range,up to1MHz,an acoustic emission(AE)sensor had to be used[5].Many of the authors excluded the low frequency range,up to10kHz,by using a high pass?lter[5],so that there is little data about cavitation noise from kinetic pumps in audible frequency range below20kHz.

6.A method based on ultra sound measurement.Relatively few

original studies have been published in which ultra sound is regarded as a source of information for monitoring the onset of cavitation and its development in centrifugal pumps[17–19].Common to all these studies are measurements of noise emission in ultra sound,up to1MHz.As a transducer,a hydro-phone or an AE sensor appropriate for high frequency range was used.All of them detected pronounced noise peaks at the high frequency range,above40kHz and up to500kHz.

7.A method based on measurement of sound pressure in audible

range.This is a rarely used engineering method,although it is simple and logical.The appearance of cavitation is clearly heard by normal listening;therefore,use of acoustic signals has been

a dream of many researchers.The signi?cance of sound in mon-

itoring of pump operations,as well as the cavitation phenome-non,its appearance and development,has been known for a long time.Nevertheless,according to authors knowledge there are no published studies in which sound waves in audible range are regarded as a source of information for monitoring the onset of cavitation and its development in kinetic pumps.

Since the structure of a particular noise spectrum as well as the total noise level depends on the operation conditions and on the stage of cavitation phenomenon within the pump,detailed analysis of noise spectra of the pumping process was performed to detect the onset and development of the cavitation phenomenon.During analyses we tried to?nd the characteristic frequency within noise spectra,which magnitude is changing by the cavitation process

Nomenclature

BEP best ef?ciency point

BPF(Hz)blade passage frequency

c(m sà1)speed of sound

c s(m sà1)?ow velocity in suction pipe f(Hz)frequency

H(m)total delivery head

H geo,s(m)geodetic suction head

i(–)number of harmonics

I A(Pa s)acoustical impulse

k(rad mà1)wave number

Lp(dB)sound pressure level

Lp tot(dB)total sound pressure level

n(sà1)speed of rotation

NPSH(m)net positive suction head

p a(Pa)acoustic pressure

p b(Pa)barometric pressure

p L(Pa)liquid pressure

p st(Pa)local static pressure

p v(Pa)vapour pressure

D p loss,s(Pa)pressure loss

Q(m3sà1)?ow rate

Q des(m3sà1)design?ow rate

SPL(dB)sound pressure level

r(m)distance from the centre of bubble

r b(m)radius of the bubble

t(s)time

t1(s)initial time of acoustic impulse

t2(s)time of duration impulse due to collapsing cavitation

bubble

T(K)temperature of the pumping liquid

V(m3)volume of the bubble

w(m sà1)local?ow velocity within pump

z f(–)number of impeller blades

q(kg mà3)density

q L(kg mà3)liquid density

x(sà1)angular frequency(2p f)

r Thomas’cavitation coef?cient

M.Cˇudina,J.Prezelj/Applied Acoustics70(2009)540–546541

and at the same time is in correlation with the corresponding NPSH required value at different?ow rates.The total sound pressure le-vel(SPL)was also observed.In our earlier research work[20–22] and in the present study only audible sound,between20and 20,000Hz,was measured and discussed,with a goal to obtain an experimental base to implement acoustic monitoring of the cavita-tion process to operation also in industrial environments.Acoustic monitoring,by measurement of sound signals,is easy and simple, we just need a microphone and a computer equipped with a sound card.The drawback of the method is possible appearing of back-ground noise,which can disturb sound signal at the characteristic discrete frequency,although this effect can be overcome by shield-ing the microphone.

2.Test procedure

Three different pumping sets with kinetic pumps were used in the experiments.Amongst them one(No.1)was,centrifugal pump used in nuclear power plants with6semi-open impeller blades, one(No.2)was chemical centrifugal pump with6normal(closed) impeller blades,and the third(No.3)was water mixed-?ow pump with5semi-open rotor blades(see Table1).Material of the pump No.1was KOTERM-HDPE,No.2stainless steel and No.3brass (impeller)and glass(casing).The performance and cavitation char-acteristics,as well as the noise characteristics were measured on a special test stand in a closed loop,according to the valid ISO3555 standard[8,22].The pump took?uid from a closed vessel in which the pressure level was varied by changing the air pressure above the liquid level using a vacuum pump in case of the pumps Nos. 1and2,or by throttling in the suction pipe in case of the pump No.3.To detect the onset of the cavitation of the pump,the total delivery head is measured at a constant constant?ow rate,with available varying NPSH conditions.At the same time,the spectra and total emitted level of noise were measured by a microphone placed at a distance of0.5m from the pump casing in case of pump Nos.1and3,and0.1m in case of the pump No.2,and perpendic-ular to the pump-motor axis.A B&K FFT analyser,Type2032,was used for the spectral analysis.Since the NPSH values vary with?ow rates,the procedure was repeated for different?ow rates.

3.Experimental results and discussion

A pump set consists of two main parts,a pump and a driving electric motor having a cooling fan.The total emitted noise of the pumping set is generated partially by the pump and partially by the electric motor and consists of hydrodynamic,aerodynamic, mechanical and electromagnetic noise origins.The contribution of the particular noise source and particular noise generating mecha-nism to the total sound pressure level(SPL)depends on the geom-etry of the pumping set and on the operating conditions.

The noise spectra are broadband in nature with pronounced dis-crete frequency tones.The pronounced discrete frequency tones are mainly created by unbalanced rotating masses,by friction in the bearings,packings and electric motor and by interaction of the rotor blades with nearby stationary objects(e.g.,volute tongue or guide vanes).These noise-generating mechanisms create dis-crete frequency tones at the rotational frequency(RF)and/or blade passage frequency(BPF)of the pump,the cooling fan,and the elec-tric motor rotor teeth when passing the stationary part of stator or electric motor channels,and their higher harmonics,BPF=inz f,(i is the number of harmonics,n is the revolutions per second and z f is the number of impeller blades of the pump or number of rotor blades of the fan,or the number of the rotor teeth or slots of the electric motor).The tonal noise level is independent of the load of the pumping set and has theoretically a constant value within entire operating regimes[21].

The turbulent noise of the pumping set is provoked by pressure ?uctuations caused by turbulence and?ow friction,by internal recirculation,by laminar and turbulent boundary layer vortex shedding,by?ow separation and vortices produced by boundary layer interaction between a high-velocity and low-velocity region in the main?uid?eld,by vortices in the radial and axial clearances especially between the semi-open rotor of the pump and cooling fan,respectively,and the adjacent stationary part of the casing. Turbulent noise is strongly dependent on the operating point;at the design point of operation it has its minimum value.At the off-design operation,an additional turbulent noise within the pump is created;so that the total emitted noise of the pumping set steadily increases towards a zero?ow rate and towards free delivery.When the pump operates at higher?ow rates(Q>Q des), the pump is subject to the effect of laminar and turbulent bound-ary layer vortex shedding on the pressure side of the blade that in-crease towards the free delivery.At partial?ow rates(Q

When cavitation within the pump occurs,an additional noise generation mechanism appears–the so-called cavitation noise having a characteristic crackling or hissing noise.Cavita-tion noise is produced by the pulsation waves of bubbles(mono-pole noise source)and by the collapse(implosion)of the vapour bubbles at the moment when they enter the region of high pres-sure.Bubbles appear when the static pressure decreases below va-pour pressure,p st

p

a

er;tT?

q

L

4p r

d2V

d t

;e1Twhere p a is the acoustic pressure propagation versus time t and dis-tance r from the centre of the bubble,q L is the density of the liquid, V is the volume of the bubble.The emitted noise is thus propor-tional to the second derivation of the bubble volume in time,there-fore it increases by implosion of the bubble,i.e.,by decreasing volume of the bubble,and reach its maximum value at a minimum volume of the bubble,i.e.,at a maximum value of the d2V/d t2.

An example of acoustic pressure generated by collapsing of a particular cavitation bubble is presented in Fig.1b[23].We can see one pronounced impulse response,which corresponds to the

Table1

Characteristics of pumps used in the experiments

Pump Type of pump Impeller blades Diameter D2(mm)Flow rate Q(m3/s)Head H(m)Speed n(minà1)

No.1Centrifugal,n q=186Semi-open1600.007322900

No.2Centrifugal,n q=206Closed1690.0085312900

No.3Mixed-?ow,n q=805Semi-open362.50.24010914–941

542M.Cˇudina,J.Prezelj/Applied Acoustics70(2009)540–546

bubble collapse,and later another smaller peak,which is result of the reverberation of the primary pulse.Acoustical impulse,I A,is de?ned by area below acoustical impulse in Fig.1b

I A?

Z t2

t1p

a

d tePa sT;e2T

where p a is the acoustic pressure in(Pa),t1is the initial time of acoustic impulse in(s)and t2is the time of the impulse duration due to collapsing of cavitation bubble in(s).

At the fully developed cavitation radius of the bubble is approx-imately100times greater than at the beginning of cavitation.The peak of the sound pressure generated by implosion of the bubble can reach value of approximately1014MPa and more.This peak can also be calculated by next approximation formula[23]:

p peak %100

r b p

L

r

;e3T

where r b is the radius of the bubble,p L is the pressure in the liquid around bubble and r is the distance from the centre of the bubble.

In reality we have enormous number of bubbles different in size and time of appearing and collapsing within pump.The implosion of the bubbles appears thus randomly and chaotically,therefore they cause a great increase in pressure pulsation and a turbulent noise in a wide frequency range.At fully developed cavitation,bub-bles collapse in close proximity to impeller walls(blades,shrouds) acting like impulses(impact waves)to the metal itself and eroding it.

According to Karasik[1]cavitation increases approximately lin-early with the?ow rate(or?ow velocity with nearly power two), the number of bubbles,the maximum equivalent volume of the cavitation bubbles and their concentration per unit volume.But, due to the chaotic rise of the bubbles in number and size(volume), there is no possibility for a numerical prediction of an exact value of the emitted noise.Therefore,an exact value of cavitation noise can only be obtained by measurements of the SPL at the particular ?ow rate.

The cavitation is associated with insuf?cient suction head or NPSH required value of the pump.The NPSH required value is a head that is required above the liquid vapour pressure at the place of the lowest static pressure,e.g.,at the suction nozzle.The NPSH is de?ned by the well-known formula:

NPSH?p

b

àp veTTàD p loss;s

q gàH geo;sà

c2

s

2g

?ráH;e4T

where p b is the barometric pressure,p v is the saturated vapour pres-sure corresponding to the local temperature T of the pumping li-quid,D p loss,s is the pressure loss due to?ow friction in the suction pipe,q is the liquid density,g=9.81m/s2,H geo,s is the geo-detic suction head of the pump,c s is the?ow velocity in the suction pipe,r is Thomas’cavitation coef?cient representing measure of the resistance of the?ow to cavitation and H is the total delivery head.The lower the coef?cient r is,the more likely cavitation is to occur. r is de?ned by quotient of the static pressure and the?ow speed w or corresponding dynamic pressure:

r?p stàp veTT

0:5áqáw2

;e5T

where p st is the local static pressure–usually ambient static pres-sure,and w is the local?ow(usually relative)velocity in the pump.

The NPSH required is determined by a test in which the total head is measured at a constant?ow rate and test water tempera-ture,under varying NPSH conditions(according to the ISO3555 standard[8]).Lowering the NPSH value to the point where the available NPSH is insuf?cient causes a cavitation suf?cient to de-grade the performance of the pump and the total delivery head deteriorates.In practice,it is dif?cult to determine the exact value of the NPSH required and incipient of cavitation for a kinetic pump. Therefore,for a particular?ow rate being tested,the NPSH that produces an approximately3%drop in total delivery head is stated to be the NPSH required at which cavitation is fully developed.

In this study,the NPSH available value was used as a basis for determination of the signi?cant noise signal,which could be used for detection of the beginning of the cavitation phenomenon and its development.In order to?nd the correlation between the char-acteristic frequency within the noise spectra,which the best repre-senting cavitation process and its development,and the NPSH available values,the total noise levels,corresponding noise spectra, the total delivery head and the NPSH available values were mea-sured simultaneously at the design and off-design operation.

The total noise levels of the pumping set with cavitation in the pump are for approximately3and up to10dB(A)higher than the total noise level before cavitation inception within almost entire operating regimes[21,22,25].These differences are great enough to use the total level of noise as a signal to detect the onset of the cavitation,to remove and to prevent further process of cavita-tion in the pump.Nevertheless,changing the operating point of the pump or sudden increase of background noise can diminish this difference or even abolish it,especially at the smaller differences in the total noise levels;therefore,it cannot be used to prevent the onset of cavitation within the pump by changeable operating conditions.Because of this,we prefer to use a discrete frequency tone to monitor cavitation process in a pump.Experimental results have shown that there is a discrete frequency or a group of discrete frequencies,which are in strong correlation with the cavitation process and its development.Fig.2a shows spectrogram measured by a sound card and Fig.2b noise spectra of pumping set No.1mea-sured by FFT analyser(B&K,Type2032)at the design operation; both before incipient cavitation in the pump(thick curve)and after cavitation was fully developed(thin curve).From Fig.2b,we can see that mainly broadband turbulent noise is increased,especially within the high frequency range.

M.Cˇudina,J.Prezelj/Applied Acoustics70(2009)540–546543

But,from detailed comparison of the noise spectra in Fig.2b,be-fore cavitation inception and after it was fully developed,we can see a great difference in noise peak at the discrete frequency of 147Hz within the low frequency range,which was not noticed in case without cavitation[20–22].To check,if the discrete frequency at147Hz is in close correlation with the development of cavitation phenomenon,noise spectra were measured at constant?ow rate and different NPSH available values.The measured values are transferred to Excel?le and level of the observed discrete fre-quency tone(147Hz)is depicted versus NPSH available value and in comparison with the fall of the total delivery head,accord-ing to Fig.3a.As we can see from Fig.2,there are more discrete fre-quencies,which could be used to monitor cavitation processes in a pump,but in choosing a proper discrete frequency for monitoring cavitation process we are looking for that which shows the greatest difference in the noise level before cavitation inception and after it was fully developed at all?ow rates for the particular pump observed.

The discrete frequency at the147Hz is at the half of the BPF (BPF/2)of the impeller blades for pump No.1,but as we will see below it is not signi?cant for all pumping set observed.In some cases,the most signi?cant discrete frequency can be at an arbitrary frequency or frequency range,which is in close correlation with the vibration frequency(mode)of the pump casing excited by bombardment of the pump inner surface by the bursting bubbles. Detailed analyses have shown that this discrete frequency could well be used for detection of the cavitation process in the pump.

Fig.3a shows comparison between the total noise level(Lp tot), the noise level of the discrete frequency147Hz(Lp147Hz)and the total delivery head(H)for particular?ow rate(Q=8l/s)versus NPSH available values,measured on a microphone distance of 0.5m.Fig.3b shows noise level of discrete frequency147Hz ver-sus NPSH available values for different?ow rates.In Fig.3the empty squares indicate the points of beginning of the total delivery head drop or noticeable cavitation phenomenon,and the black dots indicate the beginning of instability known as auto-oscillation and the points at which the NPSH required or critical value is de?ned. The black points,thus,indicate the state of fully developed state of cavitation in the pump corresponding to the3%drop in the total delivery head.

From Fig.3we can also see that noise level of the peak at147Hz increases by decreasing the NPSH available value and by increasing the?ow rate.The level of the peak starts steeply to increase by development of the cavitation process until it reaches around a maximum or critical value(black dots in Fig.3),when the cavita-tion process is fully developed,and then it starts to decrease rap-idly.The reason can be ascribed to the increase of the number and volume of cavitation bubbles,which causes lesser bombard-ment of the pump inner surfaces and consequently their smaller vibration and emitted noise.When the number and volume of bub-bles are high enough then a two-phase?ow within the impeller in-let(nozzle)causes reduction of sound transmission to the surroundings on one side,and reduction of the impulse strength when collapsing bubbles on the other side.

Fig.3a shows that the incipience of cavitation appears much sooner than it is re?ected in the curve of total noise level(Lp tot) or in total delivery head(H).According to[5],cavitation noise ap-pears sooner than the drop of total delivery head due to the addi-tional‘‘thermodynamic”effect causing an additional adiabatic evaporation of liquid and unsteady cavitation oscillations and noise.

Fig.3b shows that differences between the noise levels of the discrete frequency(147Hz)before cavitation inception(the mini-mum value)and after it was fully developed(the maximum value denoted by black dots)are between12and20dB for different?ow rates[25].These differences are high enough to use this character-istic discrete frequency for monitor cavitating process in a pump and its development in presence of a background noise.

147Hz

544M.Cˇudina,J.Prezelj/Applied Acoustics70(2009)540–546

Similar results were obtained at the two other pumps observed [26].Fig.4shows corresponding results for pump No.2and Fig.5 for pump No.3.We can see that the characteristic discrete fre-quency tones,with the highest changing in noise level,are at a 2176Hz for the pump No.2(see Fig.4c)and at a760Hz for the pump No.3(see Fig.5c).The?rst with2176Hz corresponds to the7th harmonic of the BPF and the second with760Hz corre-sponds to the10th harmonic of the BPF.This means that the char-acteristic discrete frequency tone depends on the pump design,i.e., on its geometry(with semi-open or closed impeller)and material they were produced.

The differences in peak noise level at the characteristic discrete frequencies2176Hz(Fig.4)for pump No.2,measured on a dis-tance of0.1m,are between10and14dB.The corresponding dif-ferences for the pump No.3at characteristic discrete frequency 760Hz(Fig.5),measured on a distance of0.5m,are between12 and20dB(on a higher distance these differences are smaller and opposite in a near?eld these differences are much greater).The pump No.2causes thus smaller differences in noise level at the characteristic discrete frequency than the other two pumps, although on smaller microphone distance and although otherwise generates higher total noise level than the pump No.1.This is a re-sult of closed impeller representing an acoustical shield for trans-mission of cavitation noise and stainless steel casing of the pump with smaller response to vibration.Nevertheless,these differences are still great enough to use the noise signal to detect the onset of

M.Cˇudina,J.Prezelj/Applied Acoustics70(2009)540–546545

cavitation process in the pump and its development at a particular ?ow rate,also in situ operation.

The discrete frequency tone can,thus,be separated from the noise spectra of a cavitating pump,and used for determination of the NPSH-required value,as an alternative method,by determina-tion of the?rst positive slope on the noise level curve situated in the black dots in Figs.3–5.This type of noise signal can also be used to control the operation of the pump and to prevent the onset of the cavitation process in the pump,by means of initiating an alarm,shutdown,or control signal via an electrical control system.

4.Conclusions

Cavitation within a kinetic pump causes deterioration of the hydraulic performance,damage of the pump by pitting and mate-rial erosion,structure vibration and noise.Therefore,cavitation must by all means be prevented.To prevent cavitation in a pump we have to know the beginning and development of the cavitation process in the pump.For this purpose,the total emitted noise in the audible range can be used,among other possibilities.Instead of this, noise of a discrete frequency tone can be used.Experimental results have shown that there is a discrete frequency tone or a group of dis-crete frequencies within the audible noise spectra,which is in strong correlation with the cavitation process and its development. The difference in noise level of the discrete frequency tone before the incipient of cavitation and after it was fully developed is great enough,between12and20dB on a distance of below0.5m for pumps No.1and3,and between10and14dB on a distance of be-low0.1m for pump No.2.In addition maximum of the discrete fre-quency peak coincides with the net positive suction head critical value(NPSH cr).Therefore,the discrete frequency tone within spec-tra of cavitating pumps can be used for determination of the NPSH required or critical value,which corresponds to the3%drop in the total delivery head.It can also be used to detect the incipient of cav-itation in the pump and its development also in onsite operation.In comparison with the other methods,this method is cheap,easy and user-friendly.We do not need a special test stand or bore a hole in the pump wall to mount a sensor,but only a microphone placed nearby and a computer with a sound card.

Acknowledgements

The authors gratefully acknowledge the support of the Slove-nian Ministry of Education,Science and Sport.

Appendix A.Supplementary data

Supplementary data associated with this article can be found,in the online version,at doi:10.1016/j.apacoust.2008.07.005.References

[1]Karassik I,McGuire T.Centrifugal pumps.2nd ed.New York:Pergamon Press;

1997.

[2]Leighton TG.The acoustic bubble.London:Academic Press Limited;1994.

[3]Japikse D,Marscher DW,Furst RB.Centrifugal pump,design and

performance.Vermont,USA:Concepts ETI,Inc.;1997.

[4]Nelik L.Centrifugal and rotary pumps:fundamentals with

applications.Florida:CRC Press LLC;1999.

[5]Li SC.Cavitation of hydraulic machinery.London:Imperial College Press;2000.

[6]Grist E.Cavitation and the centrifugal pump:a guide for pump

users.Philadelphia,PA:Taylor&Francis;1999.

[7]Young FR.Cavitation.London:McGraw-Hill Company;1989.

[8]ISO3555.Centrifugal,mixed?ow and axial pumps–code for acceptance tests

–class B;1977(E).

[9]Nakayama Y,Aoki K,Ohta H.Visualization of pressure distribution due to

impact accompanying collapse of cavity on the vanes of mixed?ow pump-turbine.International symposium on physical and numerical?ow visualization,vol.22.ASME;1985.p.101–8.

[10]Ohki H,Yoshinaga Y,Tsutsumi Y.Visualization of relative?ow patterns in

centrifugal impellers.The3rd international symposium on?ow visualization.

Michigen,USA:Ann Arbor;1983.

[11]Palgrave R,Cooper P.Visual studies of cavitation in pumping machinery.In:

Proceedings of the third international pump symposium.Texas A&M University,Texas:Turbomachinery Laboratory;1986.

[12]Newland DE.Random vibrations,spectral and wavelet

analysis.Harlow:Addison Wesley Longman Ltd.;1993.

[13]Escaler X,Egusquiza E,Farhat M,Avellan F,Coussirat M.Detection of

cavitation in hydraulic turbines.Mech Syst Signal Process2006;20:983–1007.

[14]Kaye M.Cavitation monitoring of hydraulic machines by vibration analysis,

Doctor https://www.sodocs.net/doc/2f7801063.html,usanne:2000.

[15]Escaler X,Egusquiza E,Farhat M,Avellan F.Vibration cavitation detection

using onboard measurements.Fifth international symposium on cavitation (cav2003).Osaka,Japan:2003.p.7.

[16]Sinha JK,Rao AR.Vibration based diagnosis of a centrifugal pump.Technical

note,structural health monitoring,vol.5.SAGE Publications;2006.p.325–32.

[17]McNulty PJ,Pearsall IS.Cavitation inception in pumps.J Fluids Eng

1982;104(3):99–104.

[18]McNulty PJ.Measurement techniques and analysis of?uid-borne noise in

pumps.Glasgow:National Engineering Laboratory;1981.[NTIS:N82-22504].

[19]Gopalakrishnan S.Modern cavitation criteria for centrifugal pumps.2nd

International pump symposium.College Station:Turbomachinery Laboratory, Texas A&M University;1985.

[20]Cˇudina M.Noise as an indicator of cavitation and instability in centrifugal

pumps.J Mech Eng–Ljubljana1999;45(4):134–46.

[21]Cˇudina M.Noise as an indicator of cavitation in a centrifugal pump.In:

Proceedings of the ICSV7.Garmishpartenkirchen:2000.p.543–50.

[22]Cˇudina M.Noise as an indicator of cavitation and instability in centrifugal

pumps.In:Proceedings of the?rst congress of Slovenian acoustical society.

Portorozˇ:1998.p.125–46.

[23]Hickling R,Plesset MS.Phys Fluids1964;7:7.

[24]Cˇudina M.Technical acoustics.Faculty of Mechanical Engineer-

ing.Ljubljana:University of Ljubljana;2001.

[25]Cˇudina M.Detection of cavitation phenomenon in a centrifugal pump using

audible sound.Mech Syst Signal Process2003;17(6):1335–47.

[26]Cˇudina M,Prezelj https://www.sodocs.net/doc/2f7801063.html,e of audible sound for determination of the NPSH in

centrifugal pumps.In:Proceedings of the14th internationales seminar,vol.

22–24.Wasserkraftanlagen:Technische Universit?t Wien;2006.p.327–36.

546M.Cˇudina,J.Prezelj/Applied Acoustics70(2009)540–546

英语中的比较级与最高级 详解

比较级与最高级 1.as...as 与(not) as(so)...as as...as...句型中,as的词性 第一个as是副词,用在形容词和副词的原级前,常译为“同样地”。第二个as是连词,连接与前面句子结构相同的一个句子(相同部分常省略),可译为“同..... He is as tall as his brother is (tall) . (后面的as 为连词) 只有在否定句中,第一个as才可换为so 改错: He is so tall as his brother.(X) 2.在比较状语从句中,主句和从句的句式结构一般是相同的 与as...as 句式中第二个as一样,than 也是连词。as和than这两个连词后面的从句的结构与前面的句子大部分情况下结构是相同的,相同部分可以省略。 He picked more apples than she did. 完整的表达为: He picked more apples than she picked apples. 后而的picked apples和前面相同,用did 替代。 He walked as slowly as she did.完整表达为: He walked as slowly as she walked slowly. she后面walked slowly与前面相同,用did替代。

3.谓语的替代 在as和than 引导的比较状语从句中,由于句式同前面 主句相同,为避免重复,常把主句中出现而从句中又出现的动词用do的适当形式来代替。 John speaks German as fluently as Mary does. 4.前后的比较对象应一致 不管后面连词是than 还是as,前后的比较对象应一致。The weather of Beijing is colder than Guangzhou. x than前面比较对象是“天气”,than 后面比较对象是“广州”,不能相比较。应改为: The weather of Bejing is colder than that of Guangzhou. 再如: His handwriting is as good as me. 应改为: His handwriting is as good as mine. 5.可以修饰比较级的词 常用来修饰比较级的词或短语有: Much,even,far,a little,a lot,a bit,by far,rather,any,still,a great deal等。 by far的用法: 用于强调,意为“...得多”“最最...”“显然”等,可修饰形容词或副词的比较级和最高级,通常置于其后,但是若比较级或最高级前有冠词,则可置于其前或其后。

常用兽药原粉汇总

常用兽药原粉汇总 原粉名称 适应症 安乃近临床上常用于猪附红细胞体、链球菌、弓形体、圆环病毒、 蓝耳病、猪瘟、猪丹毒等病引起的体温升高,有明显的解 热镇痛作用。鸡的禽流行性感冒、新城疫、法氏囊等引起 的体温升高,能迅速解除症状。 地美硝唑主要用于禽弧菌性肝炎、坏死性组织、火鸡组织滴虫病、 禽的毛滴虫病等,对牛的毛滴虫病也有很好的疗效。 氟苯尼考主要用于治疗: 1:猪:猪传染性萎缩性鼻炎、猪呼吸疲乏综合症(PRDC)、 传染性胸膜肺炎、气喘病、肺疫、仔猪黄白痢、副伤寒; 猪瘟、蓝耳病、乙型脑炎等引起的继发感染; 2:禽:慢性呼吸道病、气囊炎、鸭传染性浆膜炎、霍乱、 大肠杆菌病、沙门氏菌病;鸡新城疫、禽流感等引起的 继发; 3:水产类:由弧菌,链球菌,假单胞菌,爱德华氏菌, 产气单胞菌引起的虾的红腿病,幼体菌血症,甲壳溃疡病, 黑鳃和烂鳃病,丝状细菌病,河蟹的烂肢病,水霉病,颤 抖病,鱼的弧菌病,出血病、肠炎、赤皮、烂尾、腐皮等 细菌性爆发病。 黄芪多糖主要用于抗病毒,提高机体免疫力,如新城疫、法氏囊、 喉气管炎等疾病;对猪圆环病毒、蓝耳病、传染性胃肠炎、 肝炎等疾病有防治作用 磺胺间甲氧嘧啶钠主要用于治疗和预防各种敏感菌引起的呼吸道、消化道、 泌尿道感染及球虫病、猪弓形虫病、猪水肿病、鸡住白细 胞虫病、猪萎缩性鼻炎。局部灌注可治疗乳腺炎和子宫内 膜炎;水产类敏感菌所致的肺炎,出血性败血症。 磺胺氯吡嗪钠本品属磺胺类药物,具有性质稳定,抗菌谱较广,水溶性 好等优点。口服有效,并能很快分布至其它器官。主要用 于抗球虫病。 甲磺酸左旋氧氟沙 星本品主要用于治疗由敏感菌引起的畜禽呼吸系统、泌尿生殖系统、皮肤软组织、消化系统疾病。如禽的大肠杆菌病、沙门氏菌病、传染性鼻炎、鸡奇异变形杆菌病、葡萄球菌病、鸭疫巴氏杆菌病、禽霍乱、慢性呼吸道病、仔猪的喘气病、仔猪黄、白痢、仔猪副伤寒、牛传染性胸膜肺炎、牛出败、牛弧菌性疾病、牛流行性腹泻、羔羊疾病、传染 性胃肠炎等 甲硝唑主要用于禽弧菌性肝炎、坏死性肠炎、火鸡组织滴虫病、禽的毛滴虫病等,对牛的毛滴虫病也有很好的疗效。

二年级语文的、地、得用法教案

二年级语文的、地、得用法教案 一、“的、地、得”的用法 “白勺的、提土地、双人得”是我们在语文学习中经常 使用的三个词,它们都起着连接作用;它们在普通话中都各 自有着不同的读音,但当他们附在词,短语,句子的前面或 后面,表示结构关系或某些附加意义的时候都读轻声“de”,没有语音上的区别。但在书面语中有必要写成三个不同的字,这样可以区分他们在书面语用法上的不同。这样做的好处, 就是可使书面语言精确化。 (一)首先我们来看白勺“的”的用法。通常白勺“的”的后面往往跟名词,我们用算式表示就是“的+名词”。名 词包括哪些呢?人物,如:妈妈、老师、校长。动植物,如:小鸟、小草、苹果。景物,如风景、西湖、运河。事物,衣服、头发、球赛,等等。它们都属于名词。 现在我们来举一些例子,比如:亲切的妈妈、大大的窗户、红红的花朵、优美的风景、精彩的球赛、机灵的小鸟、 漂亮的衣服、黑黑的头发、雄伟的长城……。 通过这些短语,我们不难发现白勺“的”前面的词语一 般用来说明白勺“的”后面事物怎么样。 白勺“的”除了可以用在名词前外,句子的末尾也用白 勺“的”。比如:我们是知道的。我们是一起来的。你是数 不清的。

(二)其次,我们来看提土“地”的用法。通常提土“地”的后面往往跟的是表示动作的词,也就是动词,我们 用算式表示就是“地+动词”。 比如:仔细地看,大声地说,慢慢地走。看,提土地后 面的看、说、走都是表示动作的词。 现在我们再来举几个例子:快速地跑,用力地抓,认真 地读,快活地游着,积极地参加,早早地离开,自由自在地 飞翔,一次又一次地握手、迅速地包围、沙沙地直响、斩钉 截铁地说、用力地踢、仔细地看……。也就是说,提土“地”前面的词语一般用来说明提土“地”后面的动作怎么样。 (三)最后,我们来看双人“得”的用法。双人“得” 前面多数是表示动作的词或词语,少数是形容词,我们用算 式表示就是“动词(形容词)+得”。比如:玩得开心,红得发紫,吃得好,大得很,跳得高,急得满头大汗,“玩、吃、跳”这些是动词,“大、红、急”这些是形容词,后面都得 用双人“得”。 现在我们再来举几个例子:玩得刺激,看得仔细,唱得 好听,写得端正,举得高高的,说得真精彩,气得双脚直跳、理解得十分深刻、乐得合不拢嘴、惊讶得目瞪口呆……。也 就是说,双人“得”后面的词语一般用来补充说明双人“得”前面的动作怎么样。 二、“的、地、得”用法补充说明:

感官动词和使役动词

感官动词和使役动词 默认分类2010-05-28 23:14:26 阅读46 评论0 字号:大中小订阅 使役动词,比如let make have就是3个比较重要的 have sb to do 没有这个用法的 只有have sb doing.听凭某人做某事 have sb do 让某人做某事 have sth done 让某事被完成(就是让别人做) 另外: 使役动词 1.使役动词是表示使、令、让、帮、叫等意义的不完全及物动词,主要有make(使,令), let(让), help(帮助), have(叫)等。 2.使役动词后接受词,再接原形不定词作受词补语。 He made me laugh. 他使我发笑。 I let him go. 我让他走开。 I helped him repair the car. 我帮他修理汽车。 Please have him come here. 请叫他到这里来。 3.使役动词还可以接过去分词作受词补语。 I have my hair cut every month. 我每个月理发。 4.使役动词的被动语态的受词补语用不定词,不用原形不定词。 (主)He made me laugh. 他使我笑了。 (被)I was made to laugh by him. 我被他逗笑了。 使役动词有以下用法: a. have somebody do sth让某人去做某事 ??i had him arrange for a car. b. have somebody doing sth.让某人持续做某事。 ??he had us laughing all through lunch. 注意:用于否定名时,表示“允许” i won't have you running around in the house. 我不允许你在家里到处乱跑。 ******** 小议“使役动词”的用法 1. have sb do 让某人干某事 e.g:What would you have me do? have sb/sth doing 让某人或某事处于某种状态,听任 e.g: I won't have women working in our company. The two cheats had the light burning all night long. have sth done 让别人干某事,遭受到 e.g:you 'd better have your teeth pulled out. He had his pocket picked. notes: "done"这个动作不是主语发出来的。 2.make sb do sth 让某人干某事 e.g:They made me repeat the story. What makes the grass grow?

英语中的比较级和最高级

大多数形容词有三种形式,原级,比较级和最高级, 以表示形容词说明的性质在程度上的不同。 形容词的原级: 形容词的原级形式就是词典中出现的形容词的原形。例如: poor tall great glad bad 形容词的比较级和最高级: 形容词的比较级和最高级形式是在形容词的原级形式的基础上变化的。分为规则变化和不规则变化。 规则变化如下: 1) 单音节形容词的比较级和最高级形式是在词尾加 -er 和 -est 构成。 great (原级) (比较级) (最高级) 2) 以 -e 结尾的单音节形容词的比较级和最高级是在词尾加 -r 和 -st 构成。wide (原级) (比较级) (最高级) 3)少数以-y, -er, -ow, -ble结尾的双音节形容词的比较级和最高级是在词尾加 -er 和 -est 构成。 clever(原级) (比较级) (最高级) 4) 以 -y 结尾,但 -y 前是辅音字母的形容词的比较级和最高级是把 -y 去掉,加上 -ier 和-est 构成. happy (原形) (比较级) (最高级) 5) 以一个辅音字母结尾其前面的元音字母发短元音的形容词的比较级和最高级是双写该辅音字母然后再加 -er和-est。 big (原级) (比较级) (最高级) 6) 双音节和多音节形容词的比较级和最高级需用more 和 most 加在形容词前面来构成。 beautiful (原级) (比较级) (比较级) difficult (原级) (最高级) (最高级) 常用的不规则变化的形容词的比较级和最高级: 原级------比较级------最高级 good------better------best many------more------most much------more------most bad------worse------worst far------farther, further------farthest, furthest 形容词前如加 less 和 least 则表示"较不"和"最不 形容词比较级的用法: 形容词的比较级用于两个人或事物的比较,其结构形式如下: 主语+谓语(系动词)+ 形容词比较级+than+ 对比成分。也就是, 含有形容词比较级的主句+than+从句。注意从句常常省去意义上和主句相同的部分, 而只剩下对比的成分。

常用兽药原粉药使用说明

常用兽药原粉药使用说明 抗生素类药物的选用 1、由革兰氏阳性菌引起的疾病,如猪丹毒、破伤风、炭疽、马腺疫、气肿疽、牛放线菌病、葡萄球菌性和链球菌性炎症、败血症等,可选用青霉素类、头孢菌素类、四环素类和大环内酯类、林可霉素等。 2、由革兰氏阴性菌引起疾病,如巴氏杆菌病、大肠杆菌病、沙门氏菌病、肠炎、泌尿道炎症,选用氨基糖苷类、氟喹诺酮类等。 3、由耐青霉素G 金黄色葡萄球菌所致呼吸道感染、败血症等,可选用耐青霉素酶的半合成青霉素,如苯唑西林、氯唑西林,也可选用大环内酯类和头孢菌素类抗生素。 4、由绿脓杆菌引起的创面及尿路感染、败血症、肺炎等,选用庆大霉素、多黏菌素等。 5、由支原体引起的猪喘气病和鸡慢性呼吸道病,则应首选氟喹诺酮类药,如恩诺沙星、红霉素、泰乐菌素、泰妙菌素等。 一.喹诺酮类: 1、氧氟沙星(纯粉): (作用与用途)本品对多数革兰氏阴性、阳性菌、霉形体和某些厌氧菌有较强杀灭作用,主要用于治疗大肠杆菌病,霍乱、沙门氏菌病、慢性呼吸道病、鸭巴氏杆菌病等;(用法与用量)预防10g兑水200kg,冶疗100kg 1日2次,连用3-5天。 2、盐酸环丙沙星(纯粉) (作用与用途)本品是一种新型喹喏酮类、广谱、高效抗菌药。对各种细菌和霉形体均有强大的杀灭作用,尤其适用于细菌混合感染,主要用于鸡慢性呼吸道病、大肠杆菌、沙门氏菌、葡萄球菌、绿脓杆菌、霉形体及嗜血杆菌等细菌感染引起的消化道、呼吸道、肺部及全身炎症,临床上常作为消化道疾病用药。 (用法与用量)预防10克兑水100公斤,治疗50公斤,混料加倍,连用3-5天

3、乳酸环丙沙星(纯粉) 作用与用途)作用与用途同盐酸环丙沙星,其不同之处在于乳酸环丙沙星水溶性大大增强,吸收率高且吸收迅速,血药浓度高,因而治疗效果大大增强。 (用法与用量)同盐酸环丙沙星 4、氟哌酸(盐酸诺氟沙星)(纯粉) (作用与用途)本品属第三代喹诺酮类广谱抗菌药,高效,安全。主要用于大肠 杆菌、沙门氏菌、葡萄球菌、绿脓杆菌、霉形体及嗜血杆菌等细菌感染引起的消化道、呼吸道、肺部及全身炎症,临床上常作为消化道疾病用药。 (用法与用量)预防10克兑水100公斤,治疗50 公斤,混料加倍,连用3-5天 5、盐酸蒽诺沙星(纯粉) (作用与用途)本品为最新开发出的喹诺酮类药物之一,对各种细菌和霉形体有特效,本品的特点是广谱、高效、见效极快、杀菌彻底,有克菌王之称,是目前防治各种细菌病及霉形体病的特效药物。 (用法与用量)预防10克兑水100公斤,治疗50 公斤,混料加倍,连用3-5天 6、盐酸洛美沙星(纯粉) (作用与用途)本品是第三代喹诺酮类最新抗菌药,对各种细菌和霉形体有特效,口服吸收完全,用药后一小时就可达到有效杀菌浓度,见效极快,作用时间长达8小时,是目前治疗各种细菌病及鸡慢性呼吸道病的特效药物。 (用法与用量)预防10 克兑水200公斤,治疗兑水100公斤,连用3-5 天。 二、大环内脂类: 1、替米考星(纯品) 编辑版word

《“的、地、得”的用法》语文微课教案

《“的、地、得”的用法》语文微课教案 《“的、地、得”的用法》语文微课教案 一、教学背景 在语言文字规范化大背景下,帮助学生解决应用“的地得”的疑惑与困难。 二、设计思路 针对学生对于“的地得”的误用与忽视展开教学,规范结构助词“的地得”的使用。按照“问题的提出、问题的分析、问题的解决”的思路展开教学,总结归纳优化的方式方法。 三、教学目标 1、知道“怎么样的什么、怎么样地干什么、干得怎么样”三种固定搭配。 2、掌握“的、地、得”的区别与联系。 3、运用小儿歌“动前土、名前白、行动后面双人来”的口诀帮助正确使用“的、地、得”。 四、教学重难点 1、知道“的、地、得”的区别。 2、在实际情境中正确运用“的、地、得”。 五、教学时间 8分钟微课堂 六、教学适用对象 义务教育九年制内的学生 七、教学准备 多媒体课件、录屏软件 八、教学设计与过程 开场白: 同学们好!今天我们一起来学习“的、地、得”的正确用法。首先我们来了解一下它们的区别。 1、相同之处:原来它们都是念轻声“de”,都是结构助词,起连接作用。 2、不同之处:在书面语中要写成三个不同的字,而且它们的搭配及用法也各不相同。(1)怎么样的什么 (2)怎样样地干什么 (3)干得怎么样 下面我们就来学习一下它们的正确用法。 白勺“的”的结构是用“形容词或名词或代词+的+名词”来表示,而我们最常见,用得最多的还是“形容词+的+名词”的结构。 而土也“地”的用法可以用“形容词+地+动词”的结构来表示。 双人“得”是用“动词+得+形容词”的结构来表示 3、练习巩固 (1)形近区分 静静(的)河面静静(地)写字欢乐(的)山谷 欢乐(地)歌唱满意(地)点头满意(的)作品 (2)类别区分

感官动词的用法

感官动词 1.see, hear, listen to, watch, notice等词,后接宾语,再接省略to的动词不定式或ing形式。前者表全过程,后者表正在进行。句中有频率词时,以上的词也常跟动词原形。 注释:省略to的动词不定式--to do是动词不定式,省略了to,剩下do,其形式和动词原形是一样的,但说法不同。 see sb do sth 看到某人做了某事 see sb doing sth 看到某人在做某事 hear sb do sth 听到某人做了某事 hear sb doing sth 听到某人在做某事 以此类推... I heard someone knocking at the door when I fell asleep. (我入睡时有人正敲门,强调当时正在敲门) I heard someone knock at the door three times. (听到有人敲门的全过程) I often watch my classmates play volleyball after school. (此处有频率词often) (了解)若以上词用于被动语态,须将省略的to还原: see sb do sth----sb be seen to do sth hear sb do sth----sb be seen to do sth 以此类推... We saw him go into the restaurant. → He was seen to go into the restaurant. I hear the boy cry every day. → The boy is heard to cry every day. 2.感官动词look, sound, smell, taste, feel可当系动词,后接形容词。 He looks angry. His explanation sounds reasonable. The cakes smell nice.

英语比较级和最高级的用法归纳

英语比较级和最高级的用法归纳 在学习英语过程中,会遇到很多的语法问题,比如比较级和最高级的用法,对于 这些语法你能够掌握吗?下面是小编整理的英语比较级和最高级的用法,欢迎阅读! 英语比较级和最高级的用法 一、形容词、副词的比较级和最高级的构成规则 1.一般单音节词和少数以-er,-ow结尾的双音节词,比较级在后面加-er,最高级 在后面加-est; (1)单音节词 如:small→smaller→smallest short→shorter→shortest tall→taller→tallest great→greater→greatest (2)双音节词 如:clever→cleverer→cleverest narrow→narrower→narrowest 2.以不发音e结尾的单音节词,比较在原级后加-r,最高级在原级后加-st; 如:large→larger→largest nice→nicer→nicest able→abler→ablest 3.在重读闭音节(即:辅音+元音+辅音)中,先双写末尾的辅音字母,比较级加-er,最高级加-est; 如:big→bigger→biggest hot→hotter→hottest fat→fatter→fattest 4.以“辅音字母+y”结尾的双音节词,把y改为i,比较级加-er,最高级加-est; 如:easy→easier→easiest heavy→heavier→heaviest busy→busier→busiest happy→happier→happiest 5.其他双音节词和多音节词,比较级在前面加more,最高级在前面加most; 如:bea utiful→more beautiful→most beautiful different→more different→most different easily→more easily→most easily 注意:(1)形容词最高级前通常必须用定冠词 the,副词最高级前可不用。 例句: The Sahara is the biggest desert in the world. (2) 形容词most前面没有the,不表示最高级的含义,只表示"非常"。 It is a most important problem. =It is a very important problem.

的地得的用法和区分

《“的、地、得”的用法》语文微课教案 一、教学背景 在语言文字规范化大背景下,帮助学生解决应用“的地得”的疑惑与困难。 二、设计思路 针对学生对于“的地得”的误用与忽视展开教学,规范结构助词“的地得”的使用。按照“问题的提出、问题的分析、问题的解决”的思路展开教学,总结归纳优化的方式方法。 三、教学目标 1、知道“怎么样的什么、怎么样地干什么、干得怎么样”三种固定搭配。 2、掌握“的、地、得”的区别与联系。 3、运用小儿歌“动前土、名前白、行动后面双人来”的口诀帮助正确使用“的、地、得”。 四、教学重难点 1、知道“的、地、得”的区别。 2、在实际情境中正确运用“的、地、得”。 五、教学时间 8分钟微课堂 六、教学适用对象 义务教育九年制内的学生 七、教学准备

多媒体课件、录屏软件 八、教学设计与过程 开场白: 同学们好!今天我们一起来学习“的、地、得”的正确用法。首先我们来了解一下它们的区别。 1、相同之处:原来它们都是念轻声“de”,都是结构助词,起连接作用。 2、不同之处:在书面语中要写成三个不同的字,而且它们的搭配及用法也各不相同。 (1)怎么样的什么 (2)怎样样地干什么 (3)干得怎么样 下面我们就来学习一下它们的正确用法。 白勺“的”的结构是用“形容词或名词或代词+的+名词”来表示,而我们最常见,用得最多的还是“形容词+的+名词”的结构。 而土也“地”的用法可以用“形容词+地+动词”的结构来表示。 双人“得”是用“动词+得+形容词”的结构来表示 3、练习巩固 (1)形近区分 静静(的)河面静静(地)写字欢乐(的)山谷

欢乐(地)歌唱满意(地)点头满意(的)作品 (2)类别区分 1)跑(得)飞快飞快(地)跑 2)愉快(的)旅行旅行(得)愉快 3)强烈(的)渴望强烈(地)渴望 (3)综合杂糅 小雏鹰飞到大树的上方,高兴地喊起来:“我真的会飞啦!而且飞(得)很高呢!” 小结:能填对这个句子的你肯定就已经学会它们的用法了! 4、特殊情况 质疑:假如遇到特殊情况怎么办呢? 我从书包里拿出书交给她们,她们高兴得.围着我跳起舞来。(出自二年级上册《日记两则》) (1)质疑:为什么这里要使用“得”呢? (2)释疑:原来这里强调的是心情,动词在后,形容词在前,相当于后置,“得”修饰“跳舞”而非“围”。现在你明白了吧? 5、小结归纳: 怎么样,你们学会了吗?为了让同学们能够更快的记住它们的用法,老师送给大家一首口诀来帮助你们熟记三个“的”的正确使用方法:动前土、名前白、行动后面双人来。

英语中感官动词的用法

英语中感官动词的用法 一、感官动词 1、感官动词(及物动词)有:see/notice/look at/watch/observe/listen to/hear/feel(Vt)/taste(Vt)/smell(Vt) 2、连缀动词(含感官不及物动词) be/get/become/feel/look/sound/smell/taste/keep/stay/seem/ appear/grow/turn/prove/remain/go/run 二、具体用法: 1、see, hear, smell, taste, feel,这五个动词均可作连系动词,后面接形容词作表语,说明主语所处的状态。其意思分别为"看/听/闻/尝/摸起来……"。除look之外,其它几个动词的主语往往是物,而不是人。 例如:These flowers smell very sweet.这些花闻起来很香。 The tomatoes feel very soft.这些西红柿摸起来很软。 2、这些动词后面也可接介词like短语,like后面常用名词。 例如:Her idea sounds like fun.她的主意听起来很有趣。 3、这五个感官动词也可作实义动词,除look(当"看起来……"讲时)只能作不及物动词外,其余四个既可作及物动词也可作不及物动词,此时作为实义动词讲时其主语一般为人。 例如:She smelt the meat.她闻了闻那块肉。 I felt in my pocket for cigarettes.我用手在口袋里摸香烟。 4、taste, smell作不及物动词时,可用于"t aste / smell + of +名词"结构,意为"有……味道/气味"。 例如:The air in the room smells of earth.房间里的空气有股泥土味。 5、它们(sound除外)可以直接作名词,与have或take构成短语。 例如:May I have a taste of the mooncakes?我可以尝一口这月饼吗?taste有品位、味道的意思。 例如:I don’t like the taste of the garlic.我不喜欢大蒜的味道。 She dresses in poor taste.她穿着没有品位。 look有外观,特色的意思,例:The place has a European look.此地具有欧洲特色。 feel有感觉,感受的意思,watch有手表,观察的意思。例:My watch is expensive.我的手表很贵。 6、其中look, sound, feel还能构成"look / sound / feel + as if +从句"结构,意为"看起来/听起来/感觉好像……"。 例如:It looks as if our class is going to win.看来我们班好像要获胜了。 7、感官动词+do与+doing的区别: see, watch, observe, notice, look at, hear, listen to, smell, taste, feel + do表示动作的完整性,真实性;+doing 表示动作的连续性,进行性。 I saw him work in the garden yesterday.昨天我看见他在花园里干活了。(强调"我看见了"

英语比较级和最高级的用法

More than的用法 A. “More than+名词”表示“不仅仅是” 1)Modern science is more than a large amount of information. 2)Jason is more than a lecturer; he is a writer, too. 3) We need more than material wealth to build our country.建设我们国家,不仅仅需要物质财富. B. “More than+数词”含“以上”或“不止”之意,如: 4)I have known David for more than 20 years. 5)Let's carry out the test with more than the sample copy. 6) More than one person has made this suggestion. 不止一人提过这个建议. C. “More than+形容词”等于“很”或“非常”的意思,如: 7)In doing scientific experiments, one must be more than careful with the instruments. 8)I assure you I am more than glad to help you. D. more than + (that)从句,其基本意义是“超过(=over)”,但可译成“简直不”“远非”.难以,完全不能(其后通常连用情态动词can) 9) That is more than I can understand . 那非我所能懂的. 10) That is more than I can tell. 那事我实在不明白。 11) The heat there was more than he could stand. 那儿的炎热程度是他所不能忍受的 此外,“more than”也在一些惯用语中出现,如: more...than 的用法 1. 比……多,比……更 He has more books than me. 他的书比我多。 He is more careful than the others. 他比其他人更仔细。 2. 与其……不如 He is more lucky than clever. 与其说他聪明,不如说他幸运。 He is more (a)scholar than (a)teacher. 与其说他是位教师,不如说他是位学者。 注:该句型主要用于同一个人或物在两个不同性质或特征等方面的比较,其中的比较级必须用加more 的形式,不能用加词尾-er 的形式。 No more than/not more than 1. no more than 的意思是“仅仅”“只有”“最多不超过”,强调少。如: --This test takes no more than thirty minutes. 这个测验只要30分钟。 --The pub was no more than half full. 该酒吧的上座率最多不超过五成。-For thirty years,he had done no more than he (had)needed to. 30年来,他只干了他需要干的工作。 2. not more than 为more than (多于)的否定式,其意为“不多于”“不超过”。如:Not more than 10 guests came to her birthday party. 来参加她的生日宴会的客人不超过十人。 比较: She has no more than three hats. 她只有3顶帽子。(太少了) She has not more than three hats. 她至多有3顶帽子。(也许不到3顶帽子) I have no more than five yuan in my pocket. 我口袋里的钱最多不过5元。(言其少) I have not more than five yuan in my pocket. 我口袋里的钱不多于5元。(也许不到5元) more than, less than 的用法 1. (指数量)不到,不足 It’s less than half an hour’s drive from here. 开车到那里不到半个钟头。 In less than an hour he finished the work. 没要上一个小时,他就完成了工作。 2. 比……(小)少 She eats less than she should. 她吃得比她应该吃的少。 Half the group felt they spent less than average. 半数人觉得他们的花费低于平均水平。 more…than,/no more than/not more than (1)Mr.Li is ________ a professor; he is also a famous scientist. (2)As I had ________ five dollars with me, I couldn’t afford the new jacket then. (3)He had to work at the age of ________ twelve. (4)There were ________ ten chairs in the room.However, the number of the children is twelve. (5)If you tel l your father what you’ve done, he’ll be ________ angry. (6)-What did you think of this novel? -I was disappointed to find it ________ interesting ________ that one. 倍数表达法 1. “倍数+形容词(或副词)的比较级+than+从句”表示“A比B大(长、高、宽等)多少倍” This rope is twice longer than that one.这根绳是那根绳的三倍(比那根绳长两倍)。The car runs twice faster than that truck.这辆小车的速度比那辆卡车快两倍(是那辆卡车的三倍)。 2. “倍数+as+形容词或副词的原级+as+从句”表示“A正好是B的多少倍”。

兽药 原粉 治疗

香港正大生物制药 一.喹诺酮类: 氧氟沙星(纯粉): (作用与用途)本品对多数革兰氏阴性、阳性菌、霉形体和某些厌氧菌有较强杀灭作用,主要用于治疗大肠杆菌病,霍乱、沙门氏菌病、慢性呼吸道病、鸭巴氏杆菌病等; (用法与用量)预防10g兑水200kg,冶疗100kg,1日2次,连用3-5天。 盐酸环丙沙星(纯粉) (作用与用途)本品是一种新型喹喏酮类、广谱、高效抗菌药。对各种细菌和霉形体均有强大的杀灭作用,尤其适用于细菌混合感染,主要用于鸡慢性呼吸道病、大肠杆菌、沙门氏菌、葡萄球菌、绿脓杆菌、霉形体及嗜血杆菌等细菌感染引起的消化道、呼吸道、肺部及全身炎症,临床上常作为消化道疾病用药。 (用法与用量)预防10克兑水100公斤,治疗50公斤,混料加倍,连用3-5天。 乳酸环丙沙星(纯粉) (作用与用途)作用与用途同盐酸环丙沙星,其不同之处在于乳酸环丙沙星水溶性大大增强,吸收率高且吸收迅速,血药浓度高,因而治疗效果大大增强。(用法与用量)同盐酸环丙沙星 氟哌酸(盐酸诺氟沙星)(纯粉) (作用与用途)本品属第三代喹诺酮类广谱抗菌药,高效,安全。主要用于大肠杆菌、沙门氏菌、葡萄球菌、绿脓杆菌、霉形体及嗜血杆菌等细菌感染引起的消化道、呼吸道、肺部及全身炎症,临床上常作为消化道疾病用药。 (用法与用量)预防10克兑水100公斤,治疗50公斤,混料加倍,连用3-5天。 盐酸蒽诺沙星(纯粉) (作用与用途)本品为最新开发出的喹诺酮类药物之一,对各种细菌和霉形体有特效,本品的特点是广谱、高效、见效极快、杀菌彻底,有克菌王之称,是目前防治各种细菌病及霉形体病的特效药物。 (用法与用量)预防10克兑水100公斤,治疗50公斤,混料加倍,连用3-5天。 盐酸洛美沙星(纯粉) (作用与用途)本品是第三代喹诺酮类最新抗菌药,对各种细菌和霉形体有特效,口服吸收完全,用药后一小时就可达到有效杀菌浓度,见效极快,作用时间长达8小时,是目前治疗各种细菌病及鸡慢性呼吸道病的特效药物。 (用法与用量)预防10克兑水200公斤,治疗兑水100公斤,连用3-5天。二、大环内脂类: 替米考星(纯品) (作用与用途)本品为泰乐菌素的高科技替代产品,对革兰氏阳性菌和支原体有很强的抗菌活性,临床主要用于畜禽呼吸道及猪的支原体肺炎(尤其是对鸡的败

二年级语文的地得用法教案

二年级语文的、地、得用法教案一、“的、地、得”的用法 “白勺的、提土地、双人得”是我们在语文学习中经常 使用的三个词,它们都起着连接作用;它们在普通话中都各 自有着不同的读音,但当他们附在词,短语,句子的前面或 后面,表示结构关系或某些附加意义的时候都读轻声“de”,没有语音上的区别。但在书面语中有必要写成三个不同的字,这样可以区分他们在书面语用法上的不同。这样做的好处, 就是可使书面语言精确化。 (一)首先我们来看白勺“的”的用法。通常白勺“的”的后面往往跟名词,我们用算式表示就是“的+名词”。名 词包括哪些呢?人物,如:妈妈、老师、校长。动植物,如:小鸟、小草、苹果。景物,如风景、西湖、运河。事物,衣服、头发、球赛,等等。它们都属于名词。 现在我们来举一些例子,比如:亲切的妈妈、大大的窗户、红红的花朵、优美的风景、精彩的球赛、机灵的小鸟、 漂亮的衣服、黑黑的头发、雄伟的长城……。 通过这些短语,我们不难发现白勺“的”前面的词语一 般用来说明白勺“的”后面事物怎么样。 白勺“的”除了可以用在名词前外,句子的末尾也用白 勺“的”。比如:我们是知道的。我们是一起来的。你是数 不清的。

(二)其次,我们来看提土“地”的用法。通常提土“地”的后面往往跟的是表示动作的词,也就是动词,我们 用算式表示就是“地+动词”。 比如:仔细地看,大声地说,慢慢地走。看,提土地后 面的看、说、走都是表示动作的词。 现在我们再来举几个例子:快速地跑,用力地抓,认真 地读,快活地游着,积极地参加,早早地离开,自由自在地 飞翔,一次又一次地握手、迅速地包围、沙沙地直响、斩钉 截铁地说、用力地踢、仔细地看……。也就是说,提土“地”前面的词语一般用来说明提土“地”后面的动作怎么样。 (三)最后,我们来看双人“得”的用法。双人“得” 前面多数是表示动作的词或词语,少数是形容词,我们用算 式表示就是“动词(形容词)+得”。比如:玩得开心,红得发紫,吃得好,大得很,跳得高,急得满头大汗,“玩、吃、跳”这些是动词,“大、红、急”这些是形容词,后面都得 用双人“得”。 现在我们再来举几个例子:玩得刺激,看得仔细,唱得 好听,写得端正,举得高高的,说得真精彩,气得双脚直跳、理解得十分深刻、乐得合不拢嘴、惊讶得目瞪口呆……。也 就是说,双人“得”后面的词语一般用来补充说明双人“得”前面的动作怎么样。 二、“的、地、得”用法补充说明:

感官动词的用法

1.感官动词用法之一:see, hear, listen to, watch, notice等词,后接宾语,再接动词原形或ing形式。前者表全过程,后者表正在进行。句中有频率词时,以上的词也常跟动词原形。 I heard someone knocking at the door when I fell asleep. (我入睡时有人正敲门) I heard someone knock at the door three times. (听的是全过程) I often watch my classmates play volleyball after school.(此处有频率词often) 若以上词用于被动语态,后面原有动词原形改为带to不定式: We saw him go into the restaurant. →He was seen to go into the restaurant. I hear the boy cry every day. →The boy is heard to cry every day. 2.感官动词用法之二:look, sound, smell, taste, feel可当系动词,后接形容词: He looks angry. It sounds good. The flowers smell beautiful. The sweets taste sweet. The silk feels soft. I felt tired. They all looked tired. 这些动词都不用于被动语态。如:The sweets are tasted sweet.是个病句。注意:如果加介词like,则后不可接形容词,而接名词或代词:

常用兽药原粉药使用说明

常用兽药原粉药使用说明

常用兽药原粉药使用说明 抗生素类药物的选用 1、由革兰氏阳性菌引起的疾病,如猪丹毒、破伤风、炭疽、马腺疫、气肿疽、牛放线菌病、葡萄球菌性和链球菌性炎症、败血症等,可选用青霉素类、头孢菌素类、四环素类和大环内酯类、林可霉素等。 2、由革兰氏阴性菌引起疾病,如巴氏杆菌病、大肠杆菌病、沙门氏菌病、肠炎、泌尿道炎症,选用氨基糖苷类、氟喹诺酮类等。 3、由耐青霉素G金黄色葡萄球菌所致呼吸道感染、败血症等,可选用耐青霉素酶的半合成青霉素,如苯唑西林、氯唑西林,也可选用大环内酯类和头孢菌素类抗生素。 4、由绿脓杆菌引起的创面及尿路感染、败血症、肺炎等,选用庆大霉素、多黏菌素等。 5、由支原体引起的猪喘气病和鸡慢性呼吸道病,则应首选氟喹诺酮类药,如恩诺沙星、红霉素、泰乐菌素、泰妙菌素等。

一.喹诺酮类: 1、氧氟沙星(纯粉): (作用与用途)本品对多数革兰氏阴性、阳性菌、霉形体和某些厌氧菌有较强杀灭作用,主要用于治疗大肠杆菌病,霍乱、沙门氏菌病、慢性呼吸道病、鸭巴氏杆菌病等; (用法与用量)预防10g兑水200kg,冶疗100kg,1日2次,连用3-5天。2、盐酸环丙沙星(纯粉) (作用与用途)本品是一种新型喹喏酮类、广谱、高效抗菌药。对各种细菌和霉形体均有强大的杀灭作用,尤其适用于细菌混合感染,主要用于鸡慢性呼吸道病、大肠杆菌、沙门氏菌、葡萄球菌、绿脓杆菌、霉形体及嗜血杆菌等细菌感染引起的消化道、呼吸道、肺部及全身炎症,临床上常作为消化道疾病用药。(用法与用量)预防10克兑水100公斤,治疗50公斤,混料加倍,连用3-5天。 3、乳酸环丙沙星(纯粉) (作用与用途)作用与用途同盐酸环丙沙星,其不同之处在于乳酸环丙沙星水溶性大大增强,吸收率高且吸收迅速,血药浓度高,因而治疗效果大大增强。(用法与用量)同盐酸环丙沙星 4、氟哌酸(盐酸诺氟沙星)(纯粉) (作用与用途)本品属第三代喹诺酮类广谱抗菌药,高效,安全。主要用于大肠杆菌、沙门氏菌、葡萄球菌、绿脓杆菌、霉形体及嗜血杆菌等细菌感染引起的消化道、呼吸道、肺部及全身炎症,临床上常作为消化道疾病用药。 (用法与用量)预防10克兑水100公斤,治疗50公斤,混料加倍,连用3-5天。 5、盐酸蒽诺沙星(纯粉) (作用与用途)本品为最新开发出的喹诺酮类药物之一,对各种细菌和霉形体有特效,本品的特点是广谱、高效、见效极快、杀菌彻底,有克菌王之称,是目前防治各种细菌病及霉形体病的特效药物。 (用法与用量)预防10克兑水100公斤,治疗50公斤,混料加倍,连用3-5天。

相关主题