Hidrolika I (IL-2101) Slide 2

8/10/2019 Hidrolika I (IL-2101) Slide 2

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INTRODUCTION TOFLUID MECHANICS

Benno RahardyanMarisa HandajaniHaryo Satrio Tomo


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Fluids Properties Fluids vs. solids Density Compresibilty

Viscosity Surface Tension Pressure


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Motivasi

Pola, Perilaku, Interaksi?


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Definition of a Fluid

A fluid is a substance that flows under the action of shearingforces. If a fluid is at rest, we know that the forces on it are in

balance.

A gas is a fluid that is easily compressed. It fills any vessel inwhich it is contained.

A liquid is a fluid which is hard to compress. A given mass ofliquid will occupy a fixed volume, irrespective of the size ofthe container.

A free surface is formed as a boundary between a liquid and agas above it.


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Shear : A force acting in a direction parallel to a surface or to aplanar cross section of a body.


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Density

The density of a fluid is defined as its mass per unitvolume. It is denoted by the Greek symbol, .

=V m3 kgm -3

If the density is constant (most liquids), the flow is

incompressible .If the density varies significantly (eg some gasflows), the flow is compressible .

(Although gases are easy to compress, the flow may be treated as

incompressible if there are no large pressure fluctuations)

water = 998 kgm-3

air = 1.2kgm -3

kgm


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Exercise 1 The specific weight of water at ordinary pressure and

temperature is 9.81 kN/m3. The specific gravity of mercuryis 13.56. Compute the density of water and specific weightand density of mercury


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Compressibility

Compressibility :change in volume dueto change in pressure

For liquid is a functionof P, T

Liquid compressibility

is inverselyproportional to itsvolume modulus ofelasticity

dpd d

dp E


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Kompresibilitas


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Kompresibilitas


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Kompresibilitas


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Kompresibilitas Gas IdealE = np

Proses isotermal n = 1 E = p Proses isentropik n = k E = kp

Note: Gas ideal : gas yang memiliki panas spesifik yang konstan (Cp dan Cv) dan

mengikuti aturan:P/ = P = RT

=g = gP/RT R = 287 N.m/(kg.K) = 287 m 2/s 2.K

Gas real (non gas ideal): Panas spesifik bervariasi dalam perbedaan temperatur, sehingga:

P/ = P = zRTRo = zRM

z= faktor kemampuamampatan yang tergantung pada tekanan dan temperatur.


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Fluida Real

Memiliki gaya tangensial/geser pada saat ada gerakan relatifterhadap bidang FRIKSI

Gaya berlawanan dengan gerakan partikel

Gaya geser inilah yang menjadi prinsip sifat fluida :

viskositas/kekentalan


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Punya tegangan geser tertentu untuk dapat digerakan

berubah sejalan dengan laju deformasi

viskositas tidak berubah dengan laju deformasi


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Viskositas


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Viskositas


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Viskositas


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Viskositas


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Pressure

Pressure is the force per unit area, where the force is perpendicular to the area.

p= A m2

Nm -2

(Pa)

N F

This is the Absolute pressure , the pressure compared toa vacuum.

pa= 105

Nm-2

1psi = 6895Pa

The pressure measured in your tyres is the gauge pressure, p-p a.


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Measuring pressure (1)Manometers

h

p1 p2=p a

liquiddensity

x y

z

p1 = p x

px = p y

pz= p 2 = p a

(negligible pressurechange in a gas)

(since they are atthe same height)

py - p z = gh

p1 - p a = gh

So a manometer measures gauge pressure .


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Tegangan Permukaan


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Metode Pengukuran


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Metode Pengukuran


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Metode Pengukuran

Hidrolika I (IL-2101) Slide 2

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