Laboratorio Calcolo e Strutture - uniroma1.it stiffness particularly for membrane strain. ... Z1,Z2 (real, default Z1 = -0.5T, ... Laboratorio Calcolo e Strutture

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Università di Roma - Sapienza

Laboratorio Calcolo e Strutture

Esercitazione n. 2- Statica (Elementi 2D)

Laboratorio Calcolo e Strutture Esercitazione n. 2

“Strutture bidimensionali”

Ing. Mauro Linari

Pro ject Manager

MSC Software S.r. l .

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Schematizzazione delle strutture Esempi di strutture modellabili con elementi bidimensionali

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• Definition:

– A plate (or shell) is a structural element which

represents a component with one small

dimension and two large dimensions

• Plate and shell elements are used to model thin plates.

– A thin plate is one in which the thickness is

much less than the next larger dimension

(roughly 1/15).

• For linear analysis, MSC Nastran plate

elements assume classical engineering

assumptions of thin plate behavior

– The deflection of the mid-surface is small

compared with the thickness

– The mid-surface remains unstrained (neutral)

during bending (this applies to lateral loads,

not in-plane loads).

– The normal to the mid-surface remains normal

to the mid-surface during bending

Two-Dimensional Elements Plates and shells - Background

• An important fact about plate and shell

elements is that they have no stiffness

term for in-plane rotational dof.

‒ As such, if BAR or BEAM elements are

connected to a plate of shell, special modeling

effort is required.

• Some references on basic plate theory:

1. Theory of Plates and Shells, by S.

Timoshenko and S. Woinowsky-Krieger,

2nd ed., McGraw Hill, 1959

2. Stresses in Plates and Shells, by A. C.

Ugural, McGraw Hill, 1981

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• TRIA3

Three-noded isoparametric flat plate element.

– Commonly used for mesh transitions. May have excessive stiffness particularly for membrane strain.

• QUAD4

Four-noded isoparametric flat plate element.

– Behaves well when irregularly shaped, good results can be obtained with skew angles up to 45 degrees

• TRIA6

Isoparametric triangle element with three corner and three midside grid points.

– Used in regions with curvature.

• QUAD8

Isoparametric element with four corner and four edge grid points.

‒ Useful for modeling singly-curved shells (e.g. cylinder).

‒ QUAD4 performs better for doubly curved shells (e.g.

sphere).

• SHEAR

Four-noded, shear and extensional force only element. Used for analyzing thin reinforced plates and shells.

– Commonly used with rod elements to analyze thin-skinned aircraft structures (best if rectangular).

• TRIAR

Three-noded isoparametic flat element.

– Companion to the QUADR element.

– Has R3 stiffness.

• QUADR

Four-noded isoparametric flat plate element.

– Less sensitive to distortion and yields better results for in-plane bending. Has R3 stiffness.

Two-Dimensional Elements MSC Nastran 2D Elements

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• The QUAD4 element is the most commonly used plate element

• It is a 4-noded flat plate element

• It is capable of resisting both, in-plane and out-of-plane loads

• It is capable of modeling either plane strain or plane stress

• It has terms in its stiffness matrix to account for transverse shear

flexibility and also for membrane-bending coupling

• In-plane penalty bending stiffness term is added with a default

PARAM,K6ROT,100. (see section 5 for further details)

• PARAM,SNORM,20. is a default as well (see section 5)

Two-Dimensional Elements The QUAD4 Element – General Behaviors

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• Element force output includes:

– Fx,Fy : Membrane force per unit lenght

– Fxy : Membrane shear force per unit length

– Mx,My : Bending moments per unit length

– Mxy : Twisting moment per unit length

– Vx,Vy : Transverse shear forces per unit length

• Element Stress output includes:

– Stress components: sx, sy, txy,

(at center - optionally at corners)

• Element force and stress sign convention

Two-Dimensional Elements The QUAD4 Element – Output Data

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Two-Dimensional Elements QUAD4 Element definition

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• The element coordinate system

– Is defined based on the order and location of the connecting points

– Defines positive sense of normal pressures applied to the element

– Used to define layers of a composite material

– Used to interpret the element output forces and stresses (element output is in

the element coordinate system by default for these elements)

Element x-axis

It bisects the angle 2a. Positive direction is from G1

towards G2.

Element y-axis

It is perpendicular to the element x-axis and lies in the

plane defined by G1, G2, G3, and G4. Positive direction

is from G1 towards G4.

Element z-axis

It is normal to the x-y plane of the element. Positive

sense is defined by the right-hand rule and the ordering

of the connected grids.

Two-Dimensional Elements QUAD4 Element coordinate system

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• Are defined using either a PSHELL, PCOMP (composite), PCOMPG

(composite) or PLPLANE (nonlinear) entry.

Field Contents

PID Property identification number

MID1 Material identification number for membrane behavior (integer > 0 or blank)

T Plate or membrane thickness

MID2 Material identification number for bending behavior (integer > 0 or blank, MID2 = -1 represents plane strain) NOTE: THE DEFAULT FOR MID2 IS NOT TO INCLUDE THE BENDING STIFFNESS. FOR MOST MODELS, MID2 SHOULD NOT BE BLANK

12I/T3 Normalized bending inertia per unit length (real or blank, default = 1.0). The default value is correct for solid, homogeneous

plates.

Field Contents

MID3 Material identification number for transverse shear behavior (integer > 0 or

blank)

TS/T Transverse shear thickness divided by membrane thickness (default = .833333). The default value is correct for solid, homogeneous plates.

NSM Nonstructural mass per unit area (real)

Z1,Z2 Stress recovery distances for bending (real, default Z1 = -0.5T, Z2 = +0.5T)

MID4 Material identification number to define coupling between membrane and bending deformation

Two-Dimensional Elements QUAD4 Element properties

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• The QUAD4 element can have in-plane, bending, and transverse

shear behavior. The element mechanical behavior is specified by the

presence or absence of a material ID number in the appropriate

field(s) on the PSHELL entry.

• To model a membrane plate, use only MID1

• To model a plate with bending stiffness only, use only MID2

• For bending with transverse shear flexibility, use MID2 and MID3

• Note: Mass is not calculated if MID1 is blank.


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• Use MID3 to include an extra shear term in the element stiffness

calculations (i.e. includes transverse shear flexibility).


• For a solid homogeneous plate, MID1, MID2, and MID3 should reference

the same material ID

• MID4: The MID4 field (bending and membrane deformation coupling) should

be defined only if the element’s cross section is unsymmetric.

Default is blank = symmetric cross section.

MSC Software




Two-Dimensional Elements Patran - QUAD4 Element Definition: Thin and Thick Shell

Only one material can be selected

MID1 = MID2 = MID3

One material for each QUAD4 behavior

MID1 ≠ MID2 ≠ MID3

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Two-Dimensional Elements Patran - QUAD4 Element Definition: Bending/Membrane Panel


Only MID2 ≠ 0

Only One material can be selected

Only MID1 ≠ 0

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Two-Dimensional Elements Patran - QUAD4 Element Definition: Plane Strain/Plane Stress

MID1 ≠ 0 and MID2 = -1 A different property

card is generated


Only One material can be selected

MSC Software




Notice that

the in

-pla

ne r

ota

tion

is

constr

ain

ed

for

the m

odel

positio

ned in the x

-y p

lane.

Two-Dimensional Elements QUAD4 Example

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DISP = ALL Displacement for all Grid Points

FORCE = ALL Element forces at the center only (default)

Two-Dimensional Elements QUAD4 Example – Force Output

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Stress = ALL Element stress at center only (default)

STRESS(BILIN) = ALL Element stress at center plus extrapolated at the 4 nodal positions

Two-Dimensional Elements QUAD4 Example – STRESS Output

sHVM = [(3.024E6)2 – (3.024E6)(2.268E5) + (2.268E5)2] ½ = 2.917E6

STRAIN(BILIN,FIBER) = ALL element strain at the fiber distances at center plus extrapolated at the 4 nodal positions

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• The PCOMP property entry may be used when the element is a

composite consisting of layers of unidirectional fibers.

• The information on the PCOMP entry includes the thickness,

orientation, and material identification of each layer.

– This information is used within MSC Nastran to compute the entries of

a PSHELL entry, which should not be simultaneously entered by the

user for the same element(s).

• Special layer-by-layer output is provided when the PCOMP

option is used.

– Putting the NASTRAN PRTCOMP=1 system cell at the top of the .dat

file along with “echo=sort” will print the equivalent PSHELL and MAT2

entries.

Two-Dimensional Elements QUAD4 alternate property definition

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• Si considera una piastra (Lunghezza = 1m, Larghezza = 0.5 m) sottoposta

alle seguenti condizioni di carico

– Caso 1: Carico concentrato in uno degli angoli dell’estremo libero (F = 1000N)

– Caso 2: Carico di pressione uniforme (p =1000 Pa)

– Caso 3: Carico di pressione variabile sulla piastra (si consideri il valore di pressione

del caso precedente come riferimento

• Lato incastrato: pA=0.75, pB=1p

• Lato incastrato: pC=0.25, pD=0,5p

Esempio Applicativo Statico Lineare Piastra Incastrata soggetta a diverse condizioni di carico

A

B

C

D

Materiale: Acciaio E = 2.06e11 N/m2 V = 0.3 Ρ = 7800 K/m3

L1 = 2 m L2 = 3 m t= 4 mm

MSC Software




Esempio Applicativo Statico Lineare Costruzione della geometria e definizione dei vincoli

1 – GEOMETRIA (Item: Geometry)

2 – VINCOLI (Item: Load/BC)

I vincoli si applicano direttamente sulla geometria (edge)

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Esempio Applicativo Statico Lineare Definizione delle proprietà del materiale e della piastra

4 – PROPRIETA’ PIASTRA (Item: Properties) 3 – MATERIALE ISOTROPO (Item: Properties)

Il riferimento diretto alla entità geometrica consente di rendere quanto si sta definendo indipendente dalle entità FEM create

Cambiando Mesh quanto definito sulla goometria viene automaticamente riassegnato alle nuove entità FEM ad essa associate

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Esempio Applicativo Statico Lineare Costruzione della mesh

6 – Creazione della mesh (Item: Meshing) 5 – Definizione dei ‘mesh seed’ (Item: Meshing)

20

ele

me

nti

su

ed

ge 4

del

la S

urf

ace

1

30

ele

men

ti s

u e

dge

3 d

ella

Su

rfac

e 1

Proprietà, vincoli e carichi

precedentemente associati alla

superficie vengono associati agli

elementi su di essa costruiti

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Patran – Discretizzazione della struttura Verifica congruenza mesh su superfici adiacenti

Si ‘Meshano’ tutte le superfici Su ciascuna delle superfici vengono generati degli elementi ed in particolare per ciascun bordo vengono creati dei nodi sovrapposti La verifica dei bordi liberi evidenzia

chiaramente la non continuita della discretizzazione in corrispondenza di tutti i bordi comuni delle superfici

Si utilizza la funzione di ‘equivalenza’ dei nodi per connettere gli elementi adiacenti in corrispondenza dei bordi delle superfici

La verifica finale sui bordi evidenzia come l’operazione di equivalenza ristabilito la congruenza tra le mesh create sulle diverse superfici .

GLI UNICI BORDI LIBERI SONO CORRETTAMENTE QUELLI NON IN CONTATTO CON ALCUNA DELLE SUPERFICI

Meshing/Create/Mesh

Meshing/Verify/Boundaries

Meshing/Equivalence

Meshing/Verify/Boundaries

• Si ricorda che ….

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Esempio Applicativo Statico Lineare Definizione dei carichi – Verifica direzione normali elementi 2D

• Dovendo definire dei carichi di pressione è consigliabile eseguire

preliminarmente una verifica della direzione delle normali degli elementi

‒ La conoscenza della normale all’elemento consente di definirne il top (lato elemento

nella direzione della normale) ed conseguentemente il bottom

‒ Corretta applicazione del carico di pressione

TOP

BOTTOM

Si c

on

sigl

ia d

i eff

ett

uar

e q

ue

sta

veri

fica

dir

ett

ame

nte

sulla

en

tità

ge

om

etr

ica

in q

uan

to p

iù f

acilm

en

te

con

tro

llab

ile e

d e

ven

tual

me

nte

mo

dif

icab

ile

Step 7

Item: Meshing

Item: Geometry

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Esempio Applicativo Statico Lineare Definizione dei carichi – Carico Concentrato

• Carico concentrato in nodo d’angolo del lato corto ‘libero’ della piastra

Il carico verrà automaticamente

assegnato al ‘Load Case’ Corrente.

Opportune operazioni di creazione o modifica di ‘Load

Case ‘ consentiranno eventualmente di definire

correttamente le condizioni di carico e vincolo desiderate

Item: Load/BC

Step 8

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Esempio Applicativo Statico Lineare Definizione dei carichi – Carico di pressione uniforme

Da notare come convenzionalmente

negli elementi 2D la pressione è positiva

se è diretta verso l’interno dell’elemento

considerandola definita nel lato (TOP o

BOTTOM) di applicazione

Zel

p

BOTTOM

TOP (p > 0)

(p < 0)

Item: Load/BC

Step 9

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Esempio Applicativo Statico Lineare Definizione dei carichi – Carico di pressione non costante

• La definizione di un carico di pressione applicato

in modo non uniforme sulla struttura comporta la

definizione di un FIELD di tipo spaziale.

• I ‘FIELDS’ in PATRAN sono delle funzioni

utilizzate per definire la variabilità di:

‒ Carichi

‒ Condizioni di vincolo

‒ Proprietà del materiale

‒ Proprietà degli elementi

• Ci sono tre tipi di FIELDS

‒ Spaziali

‒ Non Spaziali

‒ Proprietà del materiale

Il concetto di ‘FIELD’

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• In particolare il metodo da usare nel caso in

esame è quello che sfrutta la definizione del

FIELD in forma tabellare

‒ Il pannello si sviluppa nel piano XY per cui i valori di

pressione si definiscono sulla base delle coordinate

X ed Y dei punti di angolo del pannello stesso

Analisi al Transitorio di un cassone alare PATRAN – Definizione del carico: Il FIELD spaziale

P1 ≡ (0., 0., 0.)

P2 ≡ (2., 0., 0.)

P4 ≡ (0., 3., 0.)

P3 ≡ 2., 3., 0.)

• FIELD Name = Pressure_Distribution

2.0 3.0

0.0 0.0

Step 10

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Esempio Applicativo Statico Lineare Definizione dei carichi – Carico di pressione non costante

Step 11

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Esempio Applicativo Statico Lineare Patran – Definizione delle condizioni di carico

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Esempio Applicativo Statico Lineare Impostazione dell’analisi

Selezione del tipo di analisi Definizione delle caratteristiche della singola condizione di carico

Definizione dell’output Selezione delle condizioni di carico da analizzare

Creazione input file

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File di input MSC Nastran Executive e Case Control Deck

EXECUTIVE CONTROL DECK

SUB

CA

SE ≡

Co

nd

izio

ne

di c

aric

o

1

2

3

C a r i c h i

O u t p u t

V i n c o l i

CA

SE C

ON

TRO

L D

ECK

I comandi comuni ai vari sottocasi potrebbero essere posizionati al di sopra del primo sottocaso Quanto definito al di sopra del primo

sottocaso vale come default per tutti I sottocasi

Quanto dichiarato all’interno del singolo sottocaso vale solamente all’interno di esso

Relativamente all’identificativo del singolo sottocaso: Non deve essere necessariamente

definito come il successivo di quello del precedente

La sequenza degli identificativi dei sottocasi deve rispettare la sola condizione di essere creascente

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File di input MSC Nastran Bulk Data Deck - Rappresentazione del modello ad elementi finiti

(G1)

(G2)

(G3)

(G4)

D e f i n i z i on e d e l l a n or m a l e a l l ’ e l e m e n t o

Note that there are two coordinate systems on the GRID entry:

– CP = “position” coordinate system - used to define the location in space

– CD = “displacement” coordinate system - used to measure the motion of the point and to define constraints at the point

These may be rectangular, cylindrical, or spherical systems

O u t p u t i n f i l e X D B

Ele

me

nti

2D

co

n

rela

tiv

e p

rop

rie

tà

CP CD

M a t e r i a l e

Da notare come nella scheda proprietà (PSHELL) siano stati attivati tutti i tipi di comportamenti dell’elemento 2D (compresa la flessibilità a taglio)

MSC Software




File di input MSC Nastran Bulk Data Deck - Rappresentazione del modello ad elementi finiti

V i n c o l o

La scheda PLOAD4

consente di descrivere

sull’elemento sia carichi

uniformi che variabili

Va

ria

bile

sull’elem

ento

Uniforme sull’elemento

1

2

3 S c h e d e d i c o m b i n a z i o n e c a r i c h i

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Analisi dei risultati MSC Nastran – Soluzione del problema

• La soluzione del problema si ha bloccando il gradi di libertà R1 di uno dei

due nodi di estremità (ad esempio la condizione di vincolo ‘Appoggio_DX’)

T1”

T2”

T3”

R1 $ Displacement Constraints of Load Set : Appoggio_DX

SPC1 10 123 101

$ Displacement Constraints of Load Set : Appoggio_DX

SPC1 10 1234 101

Sottocaso 1 OK

Sottocaso 2 OK

Sottocaso 3 OK

MSC Software




Analisi dei risultati MSC Nastran – Lettura file di input per importazione modello

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Analisi dei risultati MSC Nastran – Lettura file di output per importazione risultati

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Analisi dei risultati Deformate della struttura

Deformed Plots

Fri

ng

e P

lots

1

2

3

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Analisi dei risultati Stato tensionale nella struttura

• Lo stato tensionale viene calcolato nei due punti Z1 e Z2 definiti nella

scheda PSHELL

– Per default:

Z1 = BOTTOM FIBER = -T/2

Z2 = TOP FIBER = T/2

• Se ‘STRESS = ALL stato tensionale calcolato solo al centroide

Tensore delle tensioni Invarianti

Centroide

Corner point

Corner points

Centroide

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Analisi dei risultati ‘Fringe Plot’ dello stato tensionale - VonMises

1

3

2

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Analisi dei risultati ‘Vector Plot’ dello stato tensionale – Tensioni Principali

1

2

3

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ANALYSIS HEALTH CHECKS

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• Consistent Units

• Check with Force = Mass * Acceleration

• Element Distortion

• Use your pre-processor to visually check distortion

• Use WARNING messages in .f06 to confirm

Analysis Health Checks Essential ‘Quality Assurance (QA) checks –Pre Analysis

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• MSC.Nastran non conosce il concetto di unita’ di misura

• In sostanza opera con i numeri che vengono forniti

• Utilizzare unita’ di misura consistenti

• Attenzione al caso in cui pur operando nell’ambito del S.I. le

lunghezze vengono fornite in mm

• Fornire la densità di massa, altrimenti utilizzare uno dei metodi

suggeriti

Esempio 1: Analisi statica [E]=N/mm2 [L]=mm [P]=N Ku = P [K]=N/mm [u]=mm [Ku]=N

Primo e secondo membro sono in N

Esempio 2: Analisi Dinamica [E]=N/mm2 [L]=mm []=Kg/mm3 [P]=N Ku + Ma = P [K]=N/mm [u]=mm [Ku] = N

[M]=Kg [a]=mm/s2 [P]=N [Ma] = Kg•mm/s2=mN

Numericamente il termine di massa e’ 1000 volte piu’ grande

Soluzione 1: densita’ in [t •mm3] Soluzione 2: PARAM,WTMASS,0.001

Analysis Health Checks Consistent Units - Considerazioni sulle unità di misura

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• Element Distortions (cont.)

– Aspect ratio

• Aspect ratio should be less than about 4:1 (much less in regions where

stress levels change rapidly). In cases of nearly-uniaxial stress fields, larger

aspect ratios are acceptable.

– Skew Check

• Quadrilateral elements should be kept as square as possible

a b

a

b

Analysis Health Checks Essential Quality Assurance (QA) checks

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• Element Distortions

– Taper Check

– Warp

• Up to ~ 5% is normally acceptable. No real limit, but the element does not

include warpage.

h

ha

WARP = h / [0.5*(D1+D2)]

MSC Software




• Element Distortions checks into Patran

Analysis Health Checks Essential Quality Assurance (QA) checks

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• Pre-processors are notorious for generating elements with bad

geometry (aspect ratio, taper, warp, skew, etc)

• In the past, there was a separate message for each element

which did not satisfy the recommendations for MSC Nastran

(this often resulted in pages upon pages of messages which

most users ignored)

• There is now an option (V2001+) which provides user-control of

these messages (so if you want to ignore them, you can disable

their printout – NOT RECOMMENDED)

• This is done by the GEOMCHECK executive control statement

Analysis Health Checks Essential QA checks – Element Geometry checks into MSC Nastran

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GEOMCHECK

• Geomcheck specifies geometry check options

– Specifies tolerance values and options for optional finite element

geometry test

Format

test_keyword A keyword associated with the particular element geometry test

tol_value Tolerance value to be used for the specified test

n The minimum number of messages that will produced. The default is 100 messages for each element type.

FATAL Geometry tests that exceed tolerance values produce fatal messages

INFORM Geometry tests that exceed tolerance values produce informative messages (default)

WARN Geometry tests that exceed tolerance values produce warning messages

SUMMARY A summary table of the geometry tests performed is produced. No individual element information messages are output.

NONE None of the optional element geometry tests will be performed

Analysis Health Checks Essential QA checks – GEOMCHECK

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• Controls are currently available for following elements only:

Element type Test_keyword: Number of tests

CQUAD4, CQUADR Q4_... 5

CTRIA3, CTRIAR T3_… 2

CTETRA TET_... 4

CHEXA HEX_... 4

CPENTA PEN_... 4

CBEAM BEAM_... 1

CBAR BAR_... 1

Total: 21

• Multiple GEOMCHECK directives may be present.

– Continuations are acceptable.

Analysis Health Checks Essential QA checks – GEOMCHECK (Cont.)

MSC Software




Keyword Value Type Default Comment Q4_SKEW Real ≥ 0.0 30.0 Skew angle in degrees

Q4_TAPER Real ≥ 0.0 0.50 Taper Ratio

Q4_WARP Real ≥ 0.0 0.05 Surface warping factor

Q4_IAMIN Real ≥ 0.0 30.0 Minimum Interior Angle in degrees

Q4_IAMAX Real ≥ 0.0 150.0 Maximum Interior Angle in degrees

T3_SKEW Real ≥ 0.0 10.0 Skew angles in degrees

T3_IAMAX Real ≥ 0.0 160.0 Maximum Interior Angle in degrees

TET_AR Real ≥ 0.0 100.0 Longest edge to shortest edge aspect ratio

TET_EPLR Real ≥ 0.0 0.50 Edge point length ratio

TET_DETJ Real 0.0 | J | minimum value

TET_DETG Real 0.0 | J | minimum value at vertex point

HEX_AR Real ≥ 0.0 100.0 Longest edge to shortest edge aspect ratio

HEX_EPLR Real ≥ 0.0 0.50 Edge point length ratio HEX_DETJ Real 0.0 | J | minimum value

HEX_WARP Real ≥ 0.0 0.707 Face warp coefficient

PEN_AR Real ≥ 0.0 100.0 Longest edge to shortest edge aspect ratio

PEN_EPLR Real ≥ 0.0 0.50 Edge point length ratio

PEN_DETJ Real 0.0 | J | minimum value

PEN_WARP Real ≥ 0.0 0.707 Quadrilateral face warp coefficient

BEAM_OFF Real ≥ 0.0 0.15 CBEAM element offset length ratio

BAR_OFF Real ≥ 0.0 0.15 CBEAM element offset length ratio


MSC Software




• Examples: 1. Set the tolerance for the CQUAD4 element skew angle test to

15.0 degrees and limit the messages to 50.

GEOMCHECK Q4_SKEW=15.0,MSGLIMIT=50

2. Limit messages to 500 for each element type

GEOMCHECK MSGLIMIT = 500

3. Set the message type to fatal for CQUAD4 element taper tests.

GEOMCHECK Q4_TAPER,MSGTYPE=FATAL

4. Request summary table output only using default tolerance values.

GEOMCHECK SUMMARY


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MSC Software




• Q4_Skew Check

Skew test: Skew angle for the

quadrilateral element is defined

to be the angle between the lines

that joins midpoints of opposite

sides of the quadrilateral.

Quadrilateral elements should

be kept as square as possible.

This angle is not 90 degrees

for any skew.

Desired value : α ≥ 60.


(default value)

• Q4_Taper Check

Taper test: Taper ratio for the

quadrilateral element is defined to

be the ratio of the area of the

triangle formed at each corner grid

point to one half the area of the

quadrilateral. The largest of the four

ratios is compared against the

tolerance value.

= A/4

MSC Software




• Q4_WARP Check

Warp test: Surface warping factor

for quadrilateral is defined to be the

distance of the corner points of the

element to the mean plane of the

grid points divided by the average

of the element diagonal lengths. Up to ~ 5% is normally acceptable. No

real limit, but the element does not

include warpage. For flat elements (all

grid point lie in a plane), this factor is

zero. Q4_WARP = H / [ (D1+D2)/2 ]

H D1

D2

Default value: Q4_WARP = 0.05

• Q4_IAMIN and Q4_IAMA

T3_SKEW and T3_IAMAX

Interior Angle test: Interior angles

are defined to be the angles formed

by the edges that meet at the

corner node on an element. There

are four for quadrilateral shapes

and three for triangular shapes. Skew angle for the triangular element is

defined to be the smallest angle at any

of the three vertices. T3_SKEW will be

changed to T3_IAMIN

Q4_IAMIN

Q4_IAMAX

T3_SKEW

T3_IAMAX

Default values:

Q4_IAMIN = 30o

Q4_IAMAX= 150o

Default values:

T3_SKEW = 10o

T3_IAMAX= 160o


MSC Software




● BEAM_OFF and BAR_OFF Check

Offset test: This test is applicable to CBEAM and CBAR elements.

The length of the element offset is compared to the original length of the

element.

If the ratio of these lengths is greater than the tolerance, an informational

message is issued identifying the element and its length with and without

the effects of offset.

Default values: BEAM_OFF = BAR_OFF = 0.15 OFF = | L1-L2 | / L1

L1

L2

● ●


S5-56 NAS101A, Section 5, March 2012

Copyright 2012 MSC.Software Corporation

45o

80 QUAD elements

• Example:

GEOMCHECK Q4_SKEW=60., MSGLIMIT=5

• A SKEW angle of 90. degree is the ideal

value.

• The test will generate a message for any

value smaller than 60. degree.

• A Maximum of only 5 messages will be

generated.

• The default MSGTYPE is

MSGTYPE=INFORM,

• xxxx is the indicator for this type.

• The run will not be terminated

independently if this test fails.

Analysis Health Checks Essential QA checks – Element geometry check example



M O D E L S U M M A R Y

NUMBER OF GRID POINTS = 102

NUMBER OF CQUAD4 ELEMENTS = 80

*** USER INFORMATION MESSAGE 7555 (GMTSTD)

FINITE ELEMENT GEOMETRY CHECK RESULTS EXCEED TOLERANCE LEVELS FOR THE FOLLOWING ELEMENTS. METRIC VALUES THAT EXCEED

TEST TOLERANCE LIMITS ARE IDENTIFIED BY ONE OF THE FOLLOWING FLAGS PLACED TO THE RIGHT OF THE METRIC VALUE.

"xxxx" FOR TEST RESULTS EXCEEDING TOLERANCES. INFORMATIONAL ONLY. PROBLEM SOLUTION CONTINUES. (DEFAULT FLAG)

"xxxx" FOR TEST RESULTS EXCEEDING TOLERANCES. INFORMATIONAL ONLY. PROBLEM SOLUTION CONTINUES.

"WARN" FOR TEST RESULTS EXCEEDING TOLERANCES. INFORMATIONAL ONLY. PROBLEM SOLUTION CONTINUES.

"FAIL" FOR TEST RESULTS EXCEEDING TOLERANCES. SEVERE ERROR. PROBLEM SOLUTION TERMINATES.

USER ACTION: USE THE GEOMCHECK (EXECUTIVE CONTROL STATEMENT) KEYWORD=VALUE TO CHANGE TOLERANCE VALUES IF DESIRED.

A MAXIMUM OF 5 SKEW ANGLE (SA) TOLERANCE LIMIT VIOLATIONS WILL BE IDENTIFIED BY THE FLAG "xxxx"

PLACED AFTER THE VALUE METRIC FOR THE TEST.

A MAXIMUM OF 100 MIN INT. ANGLE (IA) TOLERANCE LIMIT VIOLATIONS WILL BE IDENTIFIED BY THE FLAG "xxxx"


A MAXIMUM OF 100 MAX INT. ANGLE (IA) TOLERANCE LIMIT VIOLATIONS WILL BE IDENTIFIED BY THE FLAG "xxxx"


A MAXIMUM OF 100 WARPING FACTOR (WF) TOLERANCE LIMIT VIOLATIONS WILL BE IDENTIFIED BY THE FLAG "xxxx"


A MAXIMUM OF 100 TAPER RATIO (TR) TOLERANCE LIMIT VIOLATIONS WILL BE IDENTIFIED BY THE FLAG "xxxx"


USER INFORMATION: THE MAXIMUM MESSAGE COUNT FOR ANY ONE ELEMENT ERROR TEST COULD BE EXCEEDED BY THE

CUMULATIVE EFFECT OF ALL THE MESSAGES GENERATED FOR ALL OF THE DIFFERENT TESTS PERFORMED.

GEOMCHECK Q4_SKEW=60.,MSGLIMIT=5

Maximum 5 message for the Q4_SKEW test only.

Maximum 100 messages (default

number) for the other QUAD tests.

Explanation of possible message flags.

The user specifies which type of flag will

be used with MSCTYPE option.




1 MSC.NASTRAN JOB CREATED ON 28-JUL-05 AT 11:18:00 JULY 28, 2005 MSC.NASTRAN 9/23/04 PAGE 4

0

TOLERANCE LIMITS ARE: SA = 60.00, IA(MIN) = 30.00, IA(MAX) = 150.00, WF = 0.05, TR = 0.50 (FLAG = LIMIT VIOLATED)

ELEMENT TYPE ID SKEW ANGLE MIN INT. ANGLE MAX INT. ANGLE WARPING FACTOR TAPER RATIO

QUAD4 1 45.00 xxxx 45.00 135.00 0.00 0.00

QUAD4 2 45.00 xxxx 45.00 135.00 0.00 0.00

QUAD4 3 45.00 xxxx 45.00 135.00 0.00 0.00

QUAD4 4 45.00 xxxx 45.00 135.00 0.00 0.00

QUAD4 5 45.00 xxxx 45.00 135.00 0.00 0.00


0

E L E M E N T G E O M E T R Y T E S T R E S U L T S S U M M A R Y

TOTAL NUMBER OF TIMES TOLERANCES WERE EXCEEDED

ASPECT/ MINIMUM MAXIMUM SURFACE/FACE EDGE POINT JACOBIAN

ELEMENT TYPE SKEW ANGLE TAPER RATIO INTER. ANGLE INTER. ANGLE WARP FACTOR OFFSET RATIO LENGTH RATIO DETERMINANT

QUAD4 80 0 0 0 0 N/A N/A N/A

N/A IN THE ABOVE TABLE INDICATES TESTS THAT ARE NOT APPLICABLE TO THE ELEMENT TYPE AND WERE NOT PERFORMED.

FOR ALL ELEMENTS WHERE GEOMETRY TEST RESULTS HAVE EXCEEDED TOLERANCES,

QUAD4 ELEMENT ID 1 PRODUCED SMALLEST SKEW ANGLE OF 45.00 (TOLERANCE = 60.00).

GEOMCHECK Q4_SKEW=60.,MSGLIMIT=5,MSGTYPE=INFORM

The run will not be terminated if this test fails.





0



QUAD4 1 45.00 WARN 45.00 135.00 0.00 0.00

QUAD4 2 45.00 WARN 45.00 135.00 0.00 0.00

QUAD4 3 45.00 WARN 45.00 135.00 0.00 0.00

QUAD4 4 45.00 WARN 45.00 135.00 0.00 0.00

QUAD4 5 45.00 WARN 45.00 135.00 0.00 0.00


0





QUAD4 80 0 0 0 0 N/A N/A N/A




GEOMCHECK Q4_SKEW=60.,MSGLIMIT=5,MSGTYPE=WARN

The run will not be terminated if this test fails.





0



QUAD4 1 45.00 FAIL 45.00 135.00 0.00 0.00

QUAD4 2 45.00 FAIL 45.00 135.00 0.00 0.00

QUAD4 3 45.00 FAIL 45.00 135.00 0.00 0.00

QUAD4 4 45.00 FAIL 45.00 135.00 0.00 0.00

QUAD4 5 45.00 FAIL 45.00 135.00 0.00 0.00


0





QUAD4 80 0 0 0 0 N/A N/A N/A





0

*** USER FATAL MESSAGE 7555 (EMGPRO)

EMG MODULE TERMINATING DUE TO SEVERE FAILURE OF ELEMENT GEOMETRY CHECK TESTS. THE ELEMENT TYPES, ELEMENT IDS AND FAILING

TESTS ARE IDENTIFIED ON PREVIOUS PAGES WITH THE FLAG "FAIL" PLACED AFTER THE VALUE METRIC OF THE TEST THAT FAILED.

^^^ USER WARNING MESSAGE 9031 (ERRPH1)

^^^ NOGO ENCOUNTERED IN SUBDMAP SEMG

GEOMCHECK Q4_SKEW=60.,MSGLIMIT=5,MSGTYPE=FATAL

The run will be terminated if this test fails.


MSC Software




• Epsilon Value

• Applied Load Summation

• Reaction Summation

• Strain Energy Values

• Peak Deflections

Analysis Health Checks Essential QA checks – Post Analysis

MSC Software




Analysis Health Checks Essential QA checks – Post Analysis: Epsilon Value

• If 10-6 , or greater, it could be a

sign of ill-conditioning.

• For your type of Structure,

Idealization and Analysis

– Establish typical values for Epsilon

– Establish an agreed threshold

*** USER INFORMATION MESSAGE 5293 (SSG3A)

FOR DATA BLOCK KLL

LOAD SEQ. NO. EPSILON EXTERNAL WORK EPSILONS LARGER THAN 0.001 ARE FLAGGED WITH ASTERISKS

1 -1.3760919E-13 3.6560133E+04

MSC Software




• Particularly Important for:

– Inertia Loading

– Complex Pressure Loading

– Complex Distributed Loading

Analysis Health Checks Essential QA checks – Post Analysis: Applied Load Summation

0 RESULTANTS ABOUT ORIGIN OF SUPERELEMENT BASIC COORDINATE SYSTEM IN SUPERELEMENT BASIC SYSTEM COORDINATES.

0 OLOAD RESULTANT

SUBCASE/ LOAD

DAREA ID TYPE T1 T2 T3 R1 R2 R3

0 1 FX -3.900000E+03 ---- ---- ---- 0.000000E+00 3.744000E+05

FY ---- -4.500000E+03 ---- 0.000000E+00 ---- -1.296000E+06

FZ ---- ---- 0.000000E+00 0.000000E+00 0.000000E+00 ----

MX ---- ---- ---- 0.000000E+00 ---- ----

MY ---- ---- ---- ---- 0.000000E+00 ----

MZ ---- ---- ---- ---- ---- 0.000000E+00

TOTALS -3.900000E+03 -4.500000E+03 0.000000E+00 0.000000E+00 0.000000E+00 -9.216000E+05

0 20 FX 0.000000E+00 ---- ---- ---- 0.000000E+00 0.000000E+00

FY ---- -1.818989E-12 ---- 0.000000E+00 ---- 9.313226E-10

FZ ---- ---- 0.000000E+00 0.000000E+00 0.000000E+00 ----

MX ---- ---- ---- 0.000000E+00 ---- ----

MY ---- ---- ---- ---- 0.000000E+00 ----

MZ ---- ---- ---- ---- ---- 0.000000E+00

TOTALS 0.000000E+00 -1.818989E-12 0.000000E+00 0.000000E+00 0.000000E+00 9.313226E-10

0 30 FX 0.000000E+00 ---- ---- ---- 0.000000E+00 0.000000E+00

FY ---- -2.123938E+03 ---- 0.000000E+00 ---- -6.116941E+05

FZ ---- ---- 0.000000E+00 0.000000E+00 0.000000E+00 ----

MX ---- ---- ---- 0.000000E+00 ---- ----

MY ---- ---- ---- ---- 0.000000E+00 ----

MZ ---- ---- ---- ---- ---- 0.000000E+00

TOTALS 0.000000E+00 -2.123938E+03 0.000000E+00 0.000000E+00 0.000000E+00 -6.116941E+05

MSC Software




• Check that direction opposes and balances OLOAD summary

• SPCFORCE Resultant output is printed only if SPCFORCE

request has been included in Case Control Deck

Analysis Health Checks Essential QA checks – Post Analysis: Reaction Summation

RESULTANTS ABOUT ORIGIN OF SUPERELEMENT BASIC COORDINATE SYSTEM IN SUPERELEMENT BASIC SYSTEM COORDINATES.

0 SPCFORCE RESULTANT

SUBCASE/ LOAD

DAREA ID TYPE T1 T2 T3 R1 R2 R3

0 1 FX 3.900000E+03 ---- ---- ---- 0.000000E+00 0.000000E+00

FY ---- 4.500000E+03 ---- 0.000000E+00 ---- 9.216000E+05

FZ ---- ---- 0.000000E+00 0.000000E+00 0.000000E+00 ----

MX ---- ---- ---- 0.000000E+00 ---- ----

MY ---- ---- ---- ---- 0.000000E+00 ----

MZ ---- ---- ---- ---- ---- 0.000000E+00

TOTALS 3.900000E+03 4.500000E+03 0.000000E+00 0.000000E+00 0.000000E+00 9.216000E+05

0 20 FX 0.000000E+00 ---- ---- ---- 0.000000E+00 0.000000E+00

FY ---- 7.275958E-12 ---- 0.000000E+00 ---- 2.095476E-09

FZ ---- ---- 0.000000E+00 0.000000E+00 0.000000E+00 ----

MX ---- ---- ---- 0.000000E+00 ---- ----

MY ---- ---- ---- ---- 0.000000E+00 ----

MZ ---- ---- ---- ---- ---- 0.000000E+00

TOTALS 0.000000E+00 7.275958E-12 0.000000E+00 0.000000E+00 0.000000E+00 2.095476E-09

0 30 FX -3.410605E-12 ---- ---- ---- 0.000000E+00 0.000000E+00

FY ---- 2.123938E+03 ---- 0.000000E+00 ---- 6.116941E+05

FZ ---- ---- 0.000000E+00 0.000000E+00 0.000000E+00 ----

MX ---- ---- ---- 0.000000E+00 ---- ----

MY ---- ---- ---- ---- 0.000000E+00 ----

MZ ---- ---- ---- ---- ---- 0.000000E+00

TOTALS -3.410605E-12 2.123938E+03 0.000000E+00 0.000000E+00 0.000000E+00 6.116941E+05

MSC Software




• Equilibrium check is probably one of

the most important checks in static

analysis

S F = 0 S M = 0

– Previously, one can obtain OLOAD,

SPCFORCE, and MPCFORCE resultants

and manually add them up for equilibrium

check

– New EQUILIBRIUM Case Control command

available to request equilibrium output

• Available only for static analysis

Analysis Health Checks Essential QA checks – Post Analysis: Equilibrium Ckecks

MSC Software




• Set PARAM,PRTMAXIM,YES to output this

• The GRID ID is not included and can be different for each DOF

0

0 MAXIMUM DISPLACEMENTS

0 T1 T2 T3 R1 R2 R3

0 1 3.0938861E-07 4.1483727E-08 3.6560131E+01 7.2180829E+00 5.6827263E+01 0.0000000E+00

Value !!!

Work = ( approx) ½ OLOAD * Peak Deflection = ( 2e3 * 36.5 *.5 = 36.5e3 )

Analysis Health Checks Essential QA checks – Post Analysis: Peak Deflections & Strain Energy

*** USER INFORMATION MESSAGE 5293 (SSG3A)

FOR DATA BLOCK KLL

LOAD SEQ. NO. EPSILON EXTERNAL WORK EPSILONS LARGER THAN 0.001 ARE FLAGGED WITH ASTERISKS

1 -1.3760919E-13 3.6560133E+04

Work = ½ Total Force * Total Deflection

= ( approx) ½ OLOAD * Peak Deflection

( if peak deflection is near mean line of loading action)

MSC Software




GOOD MODELING PRACTICE

MSC Software




• Mesh Density – fit for purpose

• Mesh Quality – fit for purpose

• Loading Boundary Conditions

• Displacement Boundary Conditions

Good Modeling Practice Essentials

MSC Software




• Fit for purpose

– Consider the stress gradient as parameter

Good Modeling Practice Essentials – Mesh Density

MSC Software




• Fit for purpose

– Generate mesh where elements are as regular as possible

Good Modeling Practice Essentials – Mesh Quality

MSC Software




Poor stress distribution locally Good stress distribution locally

Good Modeling Practice Essentials – Loading Boundary Conditions

• Single Boundary Conditions?

• Single Boundary Conditions?

MSC Software




• Wrongly defining Output Coordinate Systems at SPCs, MPCs,

RIGID Elements, etc. can wreck a model.

• Over-constraining a model can give rise to Poisson contraction

stresses that distort the true stress field.

• A single nodal constraint (or force) produces a singularity in the

stress field - stress results at this point are likely to be erroneous.

• A special technique called inertia relief is available to perform

quasi-static analysis on unconstrained (free) structures under

uniform (i.e. zero or constant) acceleration.

Good Modeling Practice Essentials – Displacement Constraint Considerations

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