Ansys Mechanical APDL lecture 8 by Haydar Alsalami from IRAQ - Hilla, studied in JNTUH - INDIA .

1 | Haydar Alsalami \ JNTUH \ India mobile: 00919059070644 – Iraq mobile: 009647801518389 E-Mail: [email protected]

Building Analysis with Natural Frequency

according to self Mass and Weight:

Building Structure:

Roof color

Beam color

keypoint color


This is important thing we must

do, Changing Job Name is the

better way to save our work later

without any problems.

Enter the Job Name you want. And

Pick Yes for new Log error file this

is good for Session Editor.

Hint: Sometimes, some windows

disappear, so click on this icon


Preprocessor:

Choosing structural to

update all mechanical

and physical properties

such as Loads, stresses ..

etc.


In structure we have many Element

types, first we choose Structure Mass –

3D mass 21, this is because we want to

analysis the building according to its

Mass.

Then we choose Beam – 3D Finite

strain or 2 node 188, because the

Lines in the construction of this

building take the Beam Element.

Shell – 3D 4node 181, for Roofs


Combination – (Spring – Damper) we add

this Element Type to the building because

we want apply Natural Frequency

according to the Mass of building

(Spring – Damper) element type

makes Natural Frequency and

frequently motion like pull and

push without any external force.


Select for structural Mass element type,

from Options (3D w/o rot inertia) means

we don’t need any rotation in the mass,

just concentrate downward.


Add Real Constant for Mass : enter

the amount of mass for FLOOR let us

say (50 kg), then Apply.

Enter the amount of mass for

Beam because it is different from

Floor let us say (30 kg), then OK.


We must enter Spring Constant

according to any problem, we take it

here = 2500, also if there is Damping

Coefficient, this is OK, but here we

don’t have. Also we have to set the

Real Constant Set No. as we wish,

here we take it = 3, because this will

help us in Mesh Attribute.

Real Constant for

Combination

No Real Constants

for Beam and Shell

At last we get this


We will Add material properties

later, (this is up to you), but now

we will complete the modeling.


Change view and you

will get these Keypoints

These represent the

ground keypoints


Now make a Copy to the keypoints

Pick the four keypoints then Apply

No. of copies: includes No. of

original keypoints set + any No. as

you want, here we select 2 sets to

be easier to connect with Lines later

Enter 4 , distance on Y-axis


Pick OK

Click Fit to see the

keypoints


Connect the keypoints to get

the first Floor (Storey)

After you complete pick OK


Repeat same procedure, Copy the upper

keypoints and do as in the fig.


Click Fit again you will

see only keypoints.


Select Multi-Plots


You will get this


Repeat same procedure, Copy

keypoints and Connect with

Lines until you get this.


Make the Floor Area. By

Arbitrary – By Lines, select

only four Lines then Apply.


Repeat same procedure Floor

after Floor, until you get this.


Now we reach the IMPORTANT step, means adding other

keypoints for Spring Element represent the (Natural Frequency),

these keypoints must be drawn at the same height of top Floor, so

make Copy for any two keypoints on same side on the top Floor

at any span you want


Now connect these two points

with Lines


Enter two difference properties one

for the Beam another for Floor.


Choose any Section for Beam and

fill as in the Fig. remember ID = 2

because it is Carbon


Enter Shell thickness, means Floor

thickness. Remember ID = 1 ,

because it is Aluminum . OK.


Material No. = 1 (Aluminum)

Real Constant = 1 (Mass = 50kg for Floor)

For Picked Areas we choose Shell, and already it will take the Mass

Element Section for Shell, thickness = 0.25 called Floor

Apply Mesh Attributes, first

for Areas, but attention it is

very critical to select the

suitable properties and Real

constants as in the fig.


Material No. = 2 (Carbon)

Real Constant = 2 (Mass = 30kg for Beam)

For Picked Lines we choose BEAM, and already it will take the Mass

Element Section for Beam Dimension = 0.25 * 0.25 called Beam

Select All Lines except two

Lines for Spring as in the

fig.


No matter select 1 or 2 , this will not considered because of combination

Real Constant = 3 (K = 2500 for Spring)

For Picked Lines we choose COMBINATION

No matter select any thing , this will not considered because of combination

Select these two Lines


Now select All the keypoints that you want

to show the concentrated Mass on it, I picked

All keypoints at the corners except at the

ground and at the end of Spring as in the fig.

Material No. = 1 (Aluminum)

Real Constant = 1 (Mass = 50kg for Floor)

For Picked Keypoints we choose MASS


Select Manual Mesh and mesh the two Line for

Spring No. of Division = 1 this is to get Natural

Frequency as Dinesh said. (we can enter another

numbers but this won’t give us Natural Frequency)


Mesh remaining Lines No.

of Division = 10


Mesh – Keypoints : Select All keypoints except at

ground and at the end of spring. This is important

to make a relationship between analysis of Shell

(Floor) and Beam.


You will get this



Mesh – Lines : pick Line by

Line (each Line) but don’t

use the command (Pick All)



Apply Displacement

constraint on keypoints

at ground only, All DOF


Apply self-weight (depending on Mass) :

Structural – Inertia – Gravity – Global, then

enter (9.81) with Y-axis


Yes



Until now we complete first

stage of our work of drawing

Natural Frequency, we must

press Finish before we enter

the next stage.


In the previous examples we analyze as a Static (means

any geometry with static load), so when we want to post to

next stage such as Modal , we have to finish our work as a

Static (like we just done) then introduce to choosing the

Modal, (same procedure must done if we want another

types in the window below)

Static : Any shape with static loads.

Modal : Any shape with self-weight and natural frequency.

Harmonic : Any shape with external force.

Transient : Any shape analysis with respect to time.

Spectrum : Any shape with respect to crack propagation.


Analysis Options : this window for setup motion of frequency like

up and down (all these options for choosing the shape of

frequency) and where it should affect .. select (Block Lanczos) if

there is no solution select (PCG Lanczos) they give same work.

Enter 10 for example, means the No. of Nodes

that expose to the extraction of Frequency

Enter 10, means the No. of Nodes

that expose to the expansion of

Frequency

Pick Yes

Pick OK

Frequency start from 0 unit

Frequency end at 10 units

Select To unity for better frequency as Dinesh said

Pick OK



Pick (First Set)

nothing happen but

the Ansys

understands that we

want Read and Plot

the first set of

NODES in the

drawing, means

first motion how

it’s look like.


First Set give us the

following deformation


Pick (Next Set)

nothing happen but

the Ansys

understands that we

want Read and Plot

the next set of

NODES in the

drawing, means

next motion how

it’s look like.


And so-on, but for better

and real view activate the

Animation, and you will see

the real Natural Frequency.


TimeHist Postpro: from

appearing window we can

setup a graphs like between

Time and Distance.

Pick Add Data

For example select DOF

solution with X-axis


Drag this window and

select any keypoints or any

element in the drawing. I select this keypoint

Pick OK


Pick Graph Data, means

the change of Distance with

Time for this keypoint.

You can see here the Time

always appear, and below

is the chosen type for graph

Note: since we are in Modal study

then we can graph Time with

Deformation only (UX, UY and

UZ), when enter to Harmonic we

can graph with Stress, as Dinesh

said


This is like scientific calculator if

you need it to solve any equation

you can use it, and (maybe solved

equation can used in the graph) as

Dinesh said.

Ansys Mechanical APDL lecture 8 by Haydar Alsalami from IRAQ - Hilla, studied in JNTUH - INDIA .

Documents

iraq mobile

copy keypoints

d mass

ground keypoints

upper keypoints

structure mass

beam element

original keypoints set