Bab 10 Dynamic Capability

7/27/2019 Bab 10 Dynamic Capability

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Chapter X Dynamic Input and Analysis

Training on Caesar II1

BAB X

DYNAMIC INPUT &ANALYSIS


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10.1. The Dynamic Capability :

1. Natural Frequency Calculation

2. Harmonic Analysis

3. Response Spectrum Analysis

4. Time History Analysis


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1. Natural Frequency Calculation

1. Natural Frequency Information can

indicate the tendency of the piping system

to response the dynamic loads2.A systems modal natural frequency

should not to be close to the equipment

operating frequency

3. Higher natural frequency usually cause

less trouble than low natural frequency


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Basic DynamicEquation

Eigensolver

- Natural Frequency

- Modes of Vibration

MODAL ANALYSIS


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If Sturm Sequence Check is failed, the user may

either return to the dynamic input or continue with

the spectral analysis

Sturm Sequence Check

used to confirm no mode

were skipped


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2. Harmonic Analysis

1. Fluid pulsating in reciprocating pump line or

vibration due to rotating equipment

2. The loads are modeled as concentrated force ordisplacement at one or more points in the system

3. Harmonic response represent the maximum

dynamic amplitude the piping system


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For each forcing frequency listed in the dynamic input,

CAESAR II performs a separate analysis. These analysis

are similar to static analysis and take the same amountof time to complete.

At the completion of each solution the forcing frequency,

its largest calculate deflection, and the phase angle

associated with it are listed on the screen. The rootresults for each frequency, and the system deflection, are

saved for further processing.

When all frequencies are analysis, CAESAR II presents

the frequencies on the screen and allow the user toselect those whose needs for further analysis. This

choice can be made after checking deflection at pertinent

node for those frequency


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Selection of Phase Angles

- For all phased harmonic analysis, the user is given the choice ofselecting from 18 separate phase angles solution for each

excitation frequency. Each separate phase angle solution

represents a point in time during one complete cycle of the

system response.

- The primary difference between the solution with and without

phase angle is when the phase angles are entered, there is no

way of knowing beforehand just when the maximum stress, force,

and displacement are going to occur during the cycles.

- For these reason, the displacements and stresses are oftenchecked for a number of points during the cycles for each

excitation frequency.


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3. Response Spectrum Analysis

1. The response spectrum method allows an impulse type

transient event to be characterized by response vs.

frequency spectra

2. Each mode of vibrating of the piping system is related toone response on the spectrum

3. The modal are summed together to produce the total

system response

4. The stresses for these analysis, summed with the

sustained stresses, should be compare to the occasional

stress allowable defined by the piping code


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The spectrum analysis procedure can be broken

down into three tasks :

1. Calculate the systems natural frequencies, modeshapes, and mass participation factors.

2. Using the system frequencies, pull thecorresponding response amplitude from the

spectrum table, and calculate the system responsefor each mode of vibration.

3. Combine the modal responses and directionalcomponents of the shock.

After the natural frequencies are calculated, systems

displacement, forces, moments, and stresses are

calculate on the modal level and combined


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4. Time History Analysis Is used to solve (by numeric integration) the dynamic equation of

motion to simulate the system response throughout the load

duration

It can solve any type of dynamic loading.

The modal time history analysis follows steps similar to aspectrum analysis.

The modes of vibration of the system are computed, the equation

of motion is solved through numerical integration techniques for

each mode, at a number of successive time steps, with the modal

results being summed, yielding system response at each time

steps.

The output processor displays one load cases with the maximum

loads developed throughout the load application.


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10.2. Model Modification for Dynamic Analysis

The dynamic technique employ by CAESAR

II require strict linearity in the piping and

structural system

Dynamic response associated with nonlinear

effect are not addressed

Non-linear problem (ex: slapping and friction

problem) must be linearized for use in

dynamic analysis


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If requested,

CAESAR II

canapproximate

the friction

resistance to

movement in

the dynamic

model by

including

spring

stiffnessnormal to the

restrain line

action.


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10.3. Major Steps in Dynamic Input

Developing dynamic input for CAESAR II

comprises four basic steps :

1. Specifying the loads

2. Modifying the mass and stiffness model

3. Setting the parameters that control the analysis4. Starting and errors checking the analysis


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Entering the Dynamic

Analysis Input Menu

10.4. Overview The Dynamic Input Processor


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Available Commands During Dynamic Input


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10.5. Input Overview Based on

Analysis Input ProcessorLump Mass

Snubbers


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Control Parameter


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Advanced


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10.6. H a r m o n i c

1. Specifying The Loads

Excitation Frequency


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Harmonic Forces

Harmonic Displacements


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2. Modifying Mass and Stiffness Model

Lumped mass and snubbers are modified in the same way

as described formodal analysis

3. Control ParameterThese parameter described how the analysis will be conducted.

Undamped harmonic analysis may be done by setting damping to 0.0


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10.7. Earthquake loads

Define by defining one or more response spectra and applyingthem in a specified direction over part or all of the pipingsystem.

Spectrum Definition Command

Describe the type of data in the spectrum

- period/frequency vs. force multiplier- period/frequency vs. acceleration

- period/frequency vs. velocity or

- period/frequency vs. displacement

as well as the interpolation method for each axis.

Response Spectrum Table Value

- can be entered directly

- built and store as a file for use by CAESAR II


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If not read in from a file, the data points for a user enter spectrum

may be entered by using the Tools-Spectrum Data Points

command, selecting the spectrum name and entering the data


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1. Spectrum Load Cases

Used to modify

the magnitude of

the shock

Define the

orientation of the

uniform inertialloading (X,Y,Z)


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2. Static/Dynamic Combination

Each shock case produce output report listing :

- displacements,

- forces,

- moments, and

- stresses

Most piping code combine the occasionaldynamic stresses with sustained staticstresses

It is the sustained plus occasional stresssum that is compared to the occasionalallowable stress


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Static

Load Case

Dynamic

Load Case


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3. Modifying Mass and Stiffness ModelLumped Mass and Snubers are modified in the same way as described

forModal Analysis

Theseparameter

described how

the analysis is

to be

conducted

4. Control Parameter


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10.8. Relief Loads

1. Specifying Loads

This method is set up to solve a relief valve loadingthrough Force Spectrum Methodology.

In other to analyze a piping system for a relief valveloading, its necessary to estimate the force-timeprofile for the loading

This must then be converted to a Force Multiplier(Dynamic Load Factor) spectrum

The applied force then must be applied in conjunctionwith this spectrum

C


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2. Relief Loads Synthesis

If the user does not know the characteristic of the relief valveload, the Relief Load Synthesis Command provided a

calculation scratch based upon a model of a relief valve

venting steam or liquid to atmosphere .

This utility can be used to estimate : relief valve thrust loads,

exits velocity, and

pressure

which can in turn be used to estimate the force vs. time profile

of the applied load.

Ch t X D i I t d A l i


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3. Pulse Table/ DLF Spectrum Generation

Allow user to convert known Force-Time profile into

a Dynamic Load Factor Spectrum in order to solve

problem using spectrum methodology.

The user must designate a file name to which the

DLF spectrum is to be written, as well as the

maximum frequency to use, and the number data

point to generate.



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4. Spectrum Definition

Response spectrum

table value can be

entered directly or built

and store as a file for

use by CAESAR II

such as those generated

through the DLF

Spectrum Generator



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5. Force Sets

Forces are

grouped into

numbered

forced setswhen :

- these forces

occur together,

or

- need to be

manipulated in

the analysis

together



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6. Spectrum/Load Cases

The Spectrum Load Cases for force spectrum runs must

ling a Force Multiplier spectrum to a force set

The Load CaseDefinition consists

of one or morelines on which :

- Spectrum

- Factor

(usually = 1)- Direction

- Force Set



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7. Control Parameter

- These parameter

described how the

analysis is to be

conducted- Particular

attention should

be paid to the

modal summationmethodology



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10.9. Water Hammer/ Slug Flow

1. Specifying The Load

This method of solving water hammer or slug

problem is the force spectrum method as used for

relieve valve loading, except the relieve loadsynthesizer is not necessary. The user estimates a

Force-Time profile, then turns it into a Force

Multiplier Spectrum, which is then linked to Force Set

in the load cases.



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This method is set up to solve a relief valveloading through Force Spectrum Methodology.

In other to analyze a piping system for a reliefvalve loading, its necessary to estimate the

force-time profile for the loading

This must then be converted to a ForceMultiplier (Dynamic Load Factor) spectrum

The applied force then must be applied inconjunction with this spectrum



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2. Pulse Table/DLF Spectrum Generation

Allow user to convert known Force-Time profileinto a Dynamic Load Factor Spectrum in order tosolve problem using spectrum methodology.

The user must designate a file name to which theDLF spectrum is to be written, as well as themaximum frequency to use, and the number data

point to generate.



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3. Spectrum Definitions

Response spectrum

table value can be

entered directly or

built and store as afile for use by

CAESAR II such as

those generated

through the DLFSpectrum Generator



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p y p y


4. Force Sets

Forces are grouped

into numberedforced sets when :

- these forces occur

together, or

- need to be

manipulated in the

analysis together



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p y p y


5. Spectrum Load Cases

The Spectrum Load Cases for force spectrum runs must ling aForce Multiplier spectrum to a force set

The Load Case

Definition consists ofone or more lines onwhich :

- Spectrum

- Factor (usually = 1)- Direction

- Force Set



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p y p y


6. Static/Dynamic Combinations

Each shock case produce output report listing :- displacements,

- forces,

- moments, and- stresses

- Most piping code combine the occasional

dynamic stresses with sustained static stresses- It is the sustained plus occasional stress sumthat is compared to the occasional allowablestress



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p y p y


Static LoadCase

Dynamic Load

Case



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10.10. Time History

1. Specifying The Loads

Loading are specified in term of :

- Force-time profile

Used to specified the load timing

- Forces sets

Used to define the load direction and location

Either the force profile and force set can be used

to define the magnitude



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2. Time History Profile Definition

Time history profilemust be given :

- a name

- data definition(which must beForce vs. Time)

- interpolation

method



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3. Force Sets

Forces are groupedinto numbered

forced sets when :- these forces occur

together, or

- need to bemanipulated in theanalysis together



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4.Control Parameter

These parameter

described how theanalysis is to be

conducted

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Bab 10 Dynamic Capability