Dinamika Teknik

cuckootrainMechanics

Oct 31, 2013 (3 years and 9 months ago)

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SISTEM PENILAIAN


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Penilaian

:


Absensi

(10 %)


Tugas
/
Quis

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Ujian

I (mid semester) (40 %)


Ujian

II (
akhir

semester) (40 %)



Quis

dapat

dilakukan

setiap

saat
,
tanpa

pemberitahuan

sebelumnya
,
dapat

dilakukan

pada

awal

atau

akhir

setiap

perkuliahan


Sehingga

persiapkan

diri

anda

setiap

saat


Setiap

quis

digunakan

kertas

ukuran

A4 (
setiap

mahasiswa

harus

membawa

sendiri
)

Dynamics
, in physics,
dynamics refers to the
effects of forces on the
motion of objects

Kinematics

is a branch of physics which describes
the motion of objects without consideration of the
circumstances leading to the motion. An example is
the prediction of
centripetal force

in
uniform circular
motion
, regardless of whether the circular path is
due to
gravitational attraction
, a
banked curve

on a
highway, or an attached string.

Kinetics

a branch of
dynamics
, concerned
with what motions of
bodies are produced
under the action of
particular forces (or affect
the motion). Not to be
confused with
kinematics
, the study of
what forces are implied
by selected motions.


Dynamics


Study of Forces and machine behaviour under forces
and how to use them in the design of mechanisms.

You need to know “Statics” and “Dynamics”
!


Kinematics


Study of Motion and how to achieve a desired motion.


kinematics also deals with velocities, size, shape, weight, etc.
These parameters might be the inputs to the mechanism design
process (
which will affect the final outcome of the mechanism design: type,
configuration, etc.
)

A

B

Translation

Rotation


In order to design a mechanism and its components we need to
understand how the mechanism transfers energy.


We need to identify the forces to be able to determine the proper
dimensions of the components (i.e.,
design
).


We need to know how the input forces flow through the
mechanism (power flow or power transmission) to the output link.



The objective of the force analysis of mechanisms is to find the
transformation of forces from the input link to the output link



This transformation depends on the position of the mechanism
(i.e.,
it is a function of time
)


It is important to find out how these forces change “during one
cycle” to find their maxima (for example)

Analytical Methods



this
approach is suitable for automatic
computation. Once a solutions if
obtained the solution for the entire
motion range is obtained.

Graphical Methods



provide the
designers with a quick straightforward
method but parameters cannot easily
be manipulated to create the solution
for the entire range of motions.

Free Body Diagram(s)


In force analysis two type of forces must be
considered:


External:

Forces applied to the links from
external sources w.r.t. the mechanism (e.g.,
motors, pistons, etc.).


Internal:

Forces acting between the joints
(constraint of reaction forces).


Solutions to Force Analysis:


Direct Dynamics:

The motion is caused by known external forces, and can be
found by formulating and solving differential equations describing the dynamic
equilibrium of the mechanism at any moment in time.


Inverse Dynamics:

When the motion is known (motion of the input link is
known), then from the kinematic
analysis, the
accelerations of all links are
known (thus, the inertial forces associated to all links can be obtained). The
known inertial forces (considered as external forces) and force analysis is
reduced to solving equilibrium equations for the mechanism at any given
position.

9


First steps in problem solving similar for both
Statics/Dynamics and Mechanics of Materials:


Draw a
FREE BODY DIAGRAM






Solve for unknown external forces and moments


F
x

= 0,

Fy = 0,

M
A

= 0


Tiga buah gaya dalam keseimbangan


Tiga buah gaya yang bekerja (gambar a) akan berada
dalam keseimbangan jika gaya


gaya tersebut
membentuk
sistem poligon tertutup
(gambar b)


Kasus pertama


Empat buah gaya F1, F2, F3, dan F4 dimana gaya F1
diketahui arah dan besarnya , sedangkan yang lainya
hanya diketahui arahnya


Kasus kedua


Empat buah gaya F1, F2, F3, dan F4 dimana gaya F1
dan F2 diketahui arah dan besarnya , sedangkan F3
hanya diketahui arahnya dan F4 diketaui titik garis
kerja


Gaya P diketahui arah dan besarnya,
sedangkan F1 dan F2 hanya diketahui arah
gayanya.