Model Airplane Engine Analysis

Chapter 28: Model Airplane Analysis

28

Model Airplane Engine Analysis 

Summary



Introduction



Required Solution



FEM Solution



Input File(s)



Video

485

475 476

476 484

476

CHAPTER 28 475 Model Airplane Engine Analysis

Summary Title

Chapter 28: Model Airplane Engine Analysis

Contact features

• Deformable-deformable contact - glue contact; Segment - Segment Contact • Gasket material • Bolt modeling with BOLT entry

Geometry 66

Units: mm 33

82

Eq. Stress At Pressure

Material properties

• Linear elastic material (Steel) for the engine block, plug, and bolts: E = 2.1  10 5 MPa ,  = 0.3

• Linear elastic material (aluminium) for the cylinder head: E = 7.0  10 4 MPa ,  = 0.3

• Isotropic in-plane behavior or the gasket body: E = 120MPa , G = 60MPs

• Isotropic in-plane behavior of the gasket body: E = 100MPa , G = 50MPa

• Out-of-plane pressure-over closure curves are used for the gasket body and gasket ring using loading and unloading curves. Analysis type

Quasi-static analysis

Boundary conditions

Some nodes on the outer boundaries on the engine block are constrained in all directions

Applied loads

Step 1: Enforces displacement of 0.25 mm on the bolts using BOLT. Step 2: Pressure load of 16 MPa

Element type

• 4-node tetrahedron elements • 8-node CHEXA to model the gasket

Contact properties

• Glue contact, segment to segment contact • Extended tangential contact tolerance at sharp corners

FE results

• Displacement of the engine model, Load history chart for bolt • Contact pressure and forces on the gasket

476 MD Demonstration Problems CHAPTER 28

Introduction The model airplane engine analysis consists of a cylinder head, a engine block, a gasket, bolts, and a plug. The gasket is assembled between the head and the block. The problems demonstrates how the solution sequence 400 of MD Nastran can be used for a typical analysis for engine involving the nonlinear pressure-over closure relationship of the gasket material and bolt pre-tension load. Glued contact is used to establish contact between the different parts of this engine model.

Required Solution The nonlinear analysis involving large displacement and gasket nonlinearity is carried for the model airplane engine to find the forces in the bolts and contact forces in the gasket.

FEM Solution MD Nastran’s nonlinear solution sequence SOL 400 is used to analyze the engine model under the bolt and pressure loads in two steps. The details of finite element models, contact simulations, material, load, boundary conditions, and solution procedure are discussed in the following sections.

Finite Element Model The finite element model used for the 3-D solid approach is shown in Figure 28-1. The model consists of 88293 CTETRA element and 468 CHEXA elements. MD Nastran’s 4-node tetrahedral elements are used for block using the following PSOLID and PSLDN1 options. Head, bolts, and plug are also models with 4-node tetrahedral elements. PSOLID PSLDN1

1 1

Figure 28-1

1 1

0

Finite Element Model for Model Airplane Engine

CHAPTER 28 477 Model Airplane Engine Analysis

Using the following PSOLID and PSLDN1 options, the gasket body is modeled using MD Nastran’s 8-node hexahedral gasket elements. Here, the gasket material is referred to by the material ID 5. PSOLID PSLDN1

5 5 C8

3 3 SLCOMP

0 1 L

The gasket ring is also modeled in a similar way using the different material ID 6. PSOLID PSLDN1

5 5 C8

6 6 SLCOMP

0 1 L

Contact Model For the contact definition, various parts of the model airplane engine are defined as deformable contact bodies. the following BCBODY and BSURF entries show the contact body definition for the gasket. BCBODY BSURF

1 4

3D 70172

DEFORM THRU

4 70639

0

0

The contact bodies for other parts of the model as also defined in a similar way. Figure 28-2 presents the details of different contact bodies defined for the model airplane engine.

Zoomed view of contact parts without head and block

Figure 28-2

Details of the Different Contact Bodies

The following BCTABLE entries identify how the contact bodies can touch each other. The BCTABLE with ID 1 is used to define contact conditions at the first step of the analysis. Since there is no difference in the contacts in Second Step the same BCTABLE with ID 1 is used to define the contact conditions for second step in the analysis, and it is flagged using the option BCONTACT = 2 in the case control section. Glued contact is used for all the six contact pairs defined

478 MD Demonstration Problems CHAPTER 28

in the BCTABLE option. Delayed sliding is enabled for the contact pairs involving gasket by choosing the value 2 for the field ICOORD. BCTABLE

1 SLAVE

6 1 1 4 1 1 5 2 1 4 2 1 5 3 1 4 4 1 5

MASTERS SLAVE MASTERS SLAVE MASTERS SLAVE MASTERS SLAVE MASTERS SLAVE MASTERS

0.0 2

0

0.0 2

0

0.0 0

0

0.0 0

0

0.0 0

0

0.0 0

0

0.0

0.0

1

0.0

0.0

1

0.0

0.0

1

0.0

0.0

1

0.0

0.0

1

0.0

0.0

1

Material The linear isotropic elastic properties of the steel and aluminium materials are defined using the following MAT entries. Steel properties are used for block, bolts and plug and aluminium properties are used for cylinder head. MAT1 MAT1

1 2

210000. 70000.

.3 .3

7.86-6 2.7-6

1.-5 2.4-5

The in-plane membrane properties of gasket body (ID 3) and gasket ring (ID 4) materials are defined using the following MAT1 entries. The nonlinear pressure-over closure relation for the gasket body (ID 3) and gasket ring (ID 5) are defined using the following MATG entries. MAT1 MAT1 MATG

3 4 5

120. 100. 3

MATG

35. 6

0.05 4

35.

0.0

60. 50. 0 0

9.99E-7 1.99E-6 1 2 3

5.E-5 0.0001 52.

72.

42.

64.

4

Figure 28-3 shows the pressure-over closure properties for the gasket materials. The following TABLES1 entries (referred in the MATG entries) are used to define these nonlinear gasket properties. $ Displacement Dependent TABLES1 1 + 0.0 0.0 + 0.108 33.28 $ Displacement Dependent TABLES1 2 + 0.1 0.0 + 0.16 35.84 $ Displacement Dependent TABLES1 3 + 0.0 0.0 + 0.104 26.88 $ Displacement Dependent TABLES1 4 + 0.12 0.0 + 0.168 30.72

Table : body_loading 0.027 2.08 0.054 0.135 52. 0.175 Table : body_unloading

8.32 56.

0.081 ENDT

0.1225 5.04 0.1375 0.1675 45.36 0.175 Table : ring_loading

14. 56.

0.1525 ENDT

0.026 1.68 0.052 0.13 42. 0.18 Table : ring_unloading

6.72 48.

0.078 ENDT

12. 48.

0.162 ENDT

0.138 0.174

4.32 38.88

0.15 0.18

+ 18.72+ + 27.44+ + 15.12+ + 23.52+

CHAPTER 28 479 Model Airplane Engine Analysis

Gasket Pressure (MPa) 60 Body

Loading Curve Body

50 40

Unloading Curve Body

Ring

Loading Curve Ring Unloading Curve Ring

30 20 10 0 0.00

0.05

0.10

0.15

0.20

Gasket Closure (mm) Figure 28-3

Pressure-over Closure Relations for Gasket Materials

Loading and Boundary Conditions The analysis for the model airplane engine is carried out in two steps. In the first step, a pre-tension load is applied on bolts. In the second step, a pressure load is applied in the part of head and gasket. Some nodes on the outer boundaries on the block are constrained in all directions. Figure 28-4 shows these boundary conditions applied in both Steps 1 and 2.

Figure 28-4

Constraints used in Steps 1 and 2

480 MD Demonstration Problems CHAPTER 28

The following data in case control section of the input file defines the load and boundary conditions at the two different steps of the analysis. The bulk data entries SPCD, SPC1, and PLOAD4 are used to define the boundary condition and loads in these steps. Bolt pretension loading is simulated using BOLT. In order to define Pre-Stress in Bolts, Bolt modeling is carried out using BOLT entry. BOLT consists of combination of two pairs, TOP and BOTTOM nodes set. The key idea is to split the element mesh of the bolt across the shaft in two disjoint parts, such that duplicate grid points appear at the cut, and to create an overlap or gap between the two parts via multi-point constraints. If the motion of these parts is somehow constrained in the direction in which the gap or overlap is created, then an overlap (shortening) will introduce a tensile (pre-) stress in each of the parts and a gap (elongation) will result in a compressive stress. This technique is more elaborated in Chapter 23: Bolted Plates. However the internal MPC equations are generated between the TOP and BOTTOM nodes to a free node which is also called as Control node. The BOLT entry for Bolt_1 is defined as follows: BOLT

89847 TOP

+ + + + + BOTTOM + + + + +

38083 38271 38278 38285 38292 38299 38306 22467 22463 22341 22475 22482 21641

38272 38279 38286 38293 38300 38307 22459 22461 22816 22465 21643 21640

38273 38280 38287 38294 38301

38274 38281 38288 38295 38302

38275 38282 38289 38296 38303

38276 38283 38290 38297 38304

38277+ 38284+ 38291+ 38298+ 38305+

22466 22814 22480 22472 22469

22470 22813 22458 22471 22479

22481 22478 22477 22275 22468

22817 22474 22473 21642 21644

22460+ 22462+ 22464+ 22476+ 22815+

Here 89847 indicates the BOLT ID; 38083 indicates the Control node ID; TOP indicates the set of node IDs and BOTTOM indicates the bottom node IDs. Similarly the remaining 3 bolts are defined as follows: BOLT

89848 TOP

+ + + + + BOTTOM + + + + + BOLT

89849 TOP

+ + + + + BOTTOM + + +

38007 38308 38315 38322 38329 38336 38343 20192 21825 21826 20205 20193 19871

38309 38316 38323 38330 38337 38344 20191 21828 20185 19867 20190 20206

38310 38317 38324 38331 38338

38311 38318 38325 38332 38339

38312 38319 38326 38333 38340

38313 38320 38327 38334 38341

38314+ 38321+ 38328+ 38335+ 38342+

20194 20184 20196 20199 19868

21827 20186 20188 20197 20203

20202 20187 20189 20201 20198

22544 20838 20183 19870 20200

20195+ 20207+ 21829+ 19869+ 20204+

38084 38345 38352 38359 38366 38373 38380 20324 20322 20308 20327

38346 38353 38360 38367 38374 38381 20318 19721 20305 20317

38347 38354 38361 38368 38375

38348 38355 38362 38369 38376

38349 38356 38363 38370 38377

38350 38357 38364 38371 38378

38351+ 38358+ 38365+ 38372+ 38379+

20320 20311 20312 22008

20321 20325 20313 20328

20309 20304 20315 20326

20310 22009 20316 20306

20307+ 21808+ 20319+ 20323+

CHAPTER 28 481 Model Airplane Engine Analysis

+ + BOLT

89850 TOP

+ + + + + BOTTOM + + + + +

22451 20314

19722 19719

22007

19723

22006

22005

19720+

38085 38382 38389 38396 38403 38410 38417 21071 21089 21065 22539 22542 22543

38383 38390 38397 38404 38411 38418 21069 21074 21067 21070 21083 21397

38384 38391 38398 38405 38412

38385 38392 38399 38406 38413

38386 38393 38400 38407 38414

38387 38394 38401 38408 38415

38388+ 38395+ 38402+ 38409+ 38416+

21068 21066 21398 22541 21399

21080 21073 21075 21072 21081

21078 21086 21087 21395 21085

21076 21401 22540 21082 21084

21077+ 21400+ 21088+ 21079+ 21326+

The SPCD data is used for applying the imposed displacement of 0.25 mm in the vertical direction in Steps 1 and 2 at the controlled nodes for bolts. The lateral displacements at these four control nodes are constrained. STEP 1 $! Step name : Bolt_Preload SPC = 30 LOAD = 31 BCONTACT = 1 ANALYSIS = NLSTAT NLSTEP = 2 STEP 2 $! Step name : Static_Pressure SPC = 31 LOAD = 32 BCONTACT = 1 ANALYSIS = NLSTAT NLSTEP = 3 ... SPCD 31 38083 3 SPC1 31 3 38083 SPCD 31 38007 3 SPC1 31 3 38007 SPCD 31 38084 3 SPC1 31 3 38084 SPCD 31 38085 3 SPC1 31 3 38085 ... SPC1 9 123 987 SPC1 9 123 2453 ... PLOAD4 1 85127 16. ... PLOAD4 2 55616 16. ...

0.25 0.25 0.25 0.25

THRU

2465 24238

23579

15870

15071

Solution Procedure The nonlinear procedure for the Step 1 is defined through the following NLSTEP entry with ID 2. NLSTEP specifies the convergence criteria, step size control between coupled loops and step/iteration control for each physics loop in MD Nastran SOL 400. NLSTEP entry is represented as follows: NLSTEP

2 GENERAL 50 FIXED 10 MECH P

1. 1 0.01

PFNT

482 MD Demonstration Problems CHAPTER 28

Here, 1. Indicate the total Time for the Load case; GENERAL indicates the keyword for parameters used for overall analysis; 50 indicates the maximum number of iterations per increment; FIXED indicates the fixed stepping is to be used; 10 indicate the number of increments for fixed stepping; 1 indicates interval for output. Every increment will be saved for output; MECH indicate the keyword for parameters for mechanical analysis; P indicates the load convergence criteria; 0.01 indicates convergence tolerance for load; PFNT indicates the Modified Full Newton Raphson Technique for updating stiffness matrix. The fields MAXQN, MAXLS, and MAXBIS are set to zero to disable the Quasi Newton, line search, and bisection techniques in the iterative process. Similar NLSTEP option with ID 3 is used for Step 2. NLSTEP 3 1. GENERAL 50 FIXED 10 1 MECH P 0.01 PFNT

Segment to Segment Contact method is activated using BCPARA. Here METHOD indicates the Global Contact type; SEGSMALL indicates the Small Segment-to-Segment Contact. If, in BCTABLE, there are multiple GLUE with different “SLAVE” entries, then NLGLUE, 1 must be used. BCPARA

0 METHOD

SEGSMALL NLGLUE

1

Results The variation of the bolt forces at grid points 38007,38083,38084 and 38085 as a function of the bolt shortening is shown in Figure 28-5. This clearly shows a nonlinear response. The normal contact forces in gasket are shown in Figure 28-6.

Figure 28-5

Bolt Force as a Function of Bolt Shortening

CHAPTER 28 483 Model Airplane Engine Analysis

Figure 28-6

Normal Contact Forces in Gasket

The displacement contours of the engine model in y-direction at Steps 1 and 2 are shown in Figure 28-7 and Figure 28-8. The pressure-closure output for the gasket element 70582 is presented here from the f06 output file at the end of Step 2. It is observed that the pressure for this gasket element exceeded the yield pressure of 52 MPa and this result in a plastic closure of 0.12 mm. ELEMENT ID 70582

Figure 28-7

PLY ID 1

INT. PT. ID 1 2 3 4

PRESSURE 7.805712E+01 8.207688E+01 7.722001E+01 8.107123E+01

CLOSURE 1.997745E-01 2.024191E-01 1.992237E-01 2.017574E-01

Displacement Contours in y-direction at Step 1

PLASTIC CLOSURE 1.200000E-01 1.200000E-01 1.200000E-01 1.200000E-01

484 MD Demonstration Problems CHAPTER 28

Figure 28-8

Displacement Contours in y-direction at Step 2

Figure 28-9

Von Mises Stress Contours for Node-Segment and Seg-Seg method

Input File(s) File nug_28m.bdf

Description MD Nastran SOL 400 input for model airplane engine

CHAPTER 28 485 Model Airplane Engine Analysis

Video Click on the image or caption below to view a streaming video of this problem; it lasts approximately 44 minutes and explains how the steps are performed.

66

Units: mm 33

82

Eq. Stress At Pressure

Figure 28-10

Video of the Above Steps