Computational Structural Mechanics Engine Structures

NASA Technical Memorandum 1021 19

Computational Structural Mechanics for Engine Structures

-~

[NASA-TM- 1021 19) C O f l P U T A T I O N A L S T E U C T U B A L N89-26259

L e w i s Research Center ) 12 p CSCL 20K HECHANICS FOR ENGINE S T R U C T U R E S {NASA.

Unclas G3/39 0 2 1 9 6 0 4

C.C. Chamis Lewis Research Center Cleveland, Ohio

Prepared for the 30th Structures, Structural Dynamics and Materials (SDM) Conference cosponsored by AIAA, ASME, ASCE, AHS, and ACS Mobile, Alabama, April 3-5, 1989

https://ntrs.nasa.gov/search.jsp?R=19890016888 2020-03-20T01:30:12+00:00Z

COMPUTATIONAL STRUCTURAL MECHANICS FOR ENGINE STRUCTURES

C.C. Chamis* National Aeronautics and Space Administration

Lewis Research Center Cleveland, Ohio 44135

SUMMARY

The computational structural mechanics (CSM) program at NASA Lewis Research Center encompasses: (1) fundamental aspects for formulating and solving structural mechanics problems and ( 2 ) development of integrated software systems to computationally simulate the performance/durability/life of engine structures. It is structured to mainly supplement, complement, and whenever possible replace, costly experimental efforts which are unavoidable during engineering research and development programs. Specific objectives include:

reformulating/solving structural mechanics problems and formulating/solving

system computational simulators for: Predicting structural performances, evaluating newly developed methods, and for identifying and prioritizing improved/missing methods needed. Herein the CSM program is summarized with emphasis on the engine structures computational simulator (ESCS). Typical results obtained using ESCS are described to illustrate its versatility.

co QI (1) investigate unique advantages of parallel and multiprocesses for: co d I

W multidisciplinary mechanics problems and (2 ) develop "integrated" structural

INTRODUCTION

NASA Lewis Research Center is conducting extensive research for engine structures with emphasis on advanced structural analysis, structural dynamics, structural aspects of aeroelasticity, and life prediction of turbine engine structures and structural components. These components can be made from con- ventional materials (used as bill of materials), advanced materials (utectics, directional solidified) and fiber composites. The general objective is to develop the methodology to permit the rational structural design and analysis of components for advanced gas turbine engines as well as the overall engine system. Structural models are developed to provide analysis capability which will assure the structural integrity of the part and to provide the designer with a method of optimizing component designs for maximum performance at mini- mum weight and cost. Engine system structural models are also developed to analyze the behavior of the entire engine as a complex, interacting dynamic system. The models incorporate overall displacements and distortions as well as component-to-component interactions due to steady-state and transient thermal and mechanical loads. The combined rotating engine structural components under various operating conditions such as takeoff, cruise, maneuver, and land- ing need t o be determined. Fracture mechanics methods specifically related to engines, such as elevated temperature, nonlinear crack growth, and failure prediction methods, are also developed (ref. 1). Fundamental and common to all these developments is the precise geometric and analytical model description of engine structures at several assembly levels from individual parts, through the component, the substructure, and the entire engine.

*Senior Aerospace Scientist, Structures Division, AIAA Associate Fellow.

Both the precise geometric modeling and the analytical models at the several different levels of the engine structure have resulted in integrated computer programs (refs. 2 and 3). These integrated computer programs are independent, stand along, codes, each with its own input/output formats. A recent research activity identified as Computational Structural Mechanics (CSM) has an objective of integrating these individually integrated multidiscipline codes into one software system (engine structures computational simulator, ESCS) where each discipline-specific code will be a module. The objective o f the present paper is to describe the CSM program in general and ESCS in some detai 1 .

COMPUTATIONAL STRUCTURAL MECHANICS

The general content of the CSM NASA Lewis program plan is summarized in figure 1. The long-range objective of the program is the full engine structural simulation. opment and HOST programs over a 10 year period (prior to FY86) . methodology is multidiscipline and includes: (1) high temperature structures specialty analysis methods, ( 2 ) rotating system dynamics, (3) advanced components, and (4) durability and life.

It draws on methodology developed under research and devel- This

The present emphasis is in: ( 1 ) integrating these codes to computationally simulate the interdisciplinary performance of propulsion structural systems, (2 ) exploiting new computer hardware systems, and (3) adapting these analyses methods to multiparallel processors.

IDENTIFIED METHODOLOGY-IMPROVED/MISSING

An important part of the CSM for engine structures program is the identi- fication of methodology which needs improvement and/or is missing. This methodology includes the following key elements: (1) boundary elements for three-dimensional inelastic analysis, ( 2 ) boundary elements for hot fluid/ structure interaction, (31, efficient hybrid elements, (4) adapting transitional finite elements, (5) computational composite mechanics, (6) computational contact mechanics, and (7 ) couple computational simulation with optimization. For example, a missing technology item is boundary elements for hot fluid/structure interaction is natural, since the boundary elements are formulated to match specified surface conditions and satisfy the interior field equations exactly.

Another missing technology item identified is adaptive transitional finite elements. These types of finite elements are useful in transitioning meshes from three-dimensional to two-dimensional, from a dense local mesh to progres- sively coarser with distance, or from a higher DOF element to lower.

IDENTIFIED METHODOLOGY - ALTERNATE Another important part of the CSM program is to identify methodology for

the computational simulation such as: ( 1 ) probabilistic simulation for quanti- fying the uncertainties in structural response associated with all variables/ parameters of structural analysisldesign and (2 ) alternate methods/approaches for formulating structural mechanics problems. Those identified to date are:

2

(1) probabilistic/stochastic: variational principles for probabilistic finite element, probabilistic structural analysis methods, and probabilistic fracture mechanics; and ( 2 ) alternate formulations: multiparallel processors for multidiscipline mechanics problems, specialty functions for singular mechanics problems, coupled constitutive relationships, and dedicated expert systems.

The development of probabilistic structural analysis methods constitute an extensive multi-institute program (ref. 4). This extensive program also includes the development of dedicated expert systems. Multifactor coupled constitutive relationships are a part of another recently initiated program because these relationships are essential in the computational simulation of high temperature composites and composites for superconductors.

ENGINE STRUCTURES COMPUTATIONAL SIMULATOR

A major part of the NASA Lewis CSM program is the development of engine structures computational simulator (ESCS). ESCS integrates discipline specific methodology and computer codes developed under research and technology programs indicated in the periphery blocks in figure 2. ESCS predicted results are post processed to make assessment of engine structural performance in terms of the requirements listed in the block at the right in the figure.

As already mentioned, each computer code identified in the periphery blocks was developed to be stand-alone and transportable. These codes, in essence, are the discipline modules required to perform the requisite multidiscipline analyses within the framework of the simulator. these types of codes require an especially coded executive module and interfacing modules. The executive module controls the program execution and the communication between the different discipline modules.

The integration of

ESCS SOFTWARE SYSTEM ARCHITECTURE

ESCS is modular with an expert system driven executive module. includes interfacing modules, a database and its manager. A schematic of the ESCS present status configuration is shown in figure 3. The interfacing modules provide the logic t o merge different discipline analysis models as well as loading conditions for the system analysis models. The analysis modules include advanced analysis methods such as specialty finite elements (three- dimensional inelastic analysis), mixed elements (MHOST) (ref. 5), and boundary elements (BEST3D) (ref. 5) as well as thermal and gas dynamic analyses. They also include NASTRAN and structures optimization (STAEBL) (ref. 6). The dedicated database has a permanent and a temporary record part. part is designed to handle proprietary data that the user can erase after he completed his analysis.

It

The temporary

ESCS is configured to computationally simulate the structural performance of engine structures: ( 1 1 subcomponents, ( 2 ) components, ( 3 ) subassembl ies, (4) assemblies, and (5) integrated systems for mission specified requirements. These are shown in figure 4 from bottom left to top right, respectively.

An important part o f current research activities, deals with the logistics and solution algorithms for handling large problems. For example: how do we

3

simulate the whole engine and still have a manageable model with respect to: (1) size, (2 ) global response, and (3) local detail? New methods of substruc- turing, superelement, and telescoping finite elements are attractive a1 ternati ves.

of for

ti 1

It is worthy of note that undertaking the development of a software system he magnitude of ESCS provides opportunities to identify research activities the solution of large multidiscipline, dynamically interacting problems.

SOME TYPICAL RESULTS

Typical results obtained using ESCS are described to illustrate its versa- the intearation and interac- ty-and potential to computational ly simulate

tion of the participating multidisciplines. The ( 1 ) loads simulation, ( 2 ) the structural dynamic (3) blade tip displacements at three different f tip displacements throughout a mission.

Loads Simulation

results Gescribed include: response of a bladed rotor ight conditions, and ( 4 ) b

The loads on the blades (temperatures, pressures, and rotating speeds) determined b y an engine loads module (COSMO (ref. 7) in the ESCS schematic,

ade

are

fig. 3). pressures are predicted on the surface at user selected span stations. cal example for temperatures is illustrated in figure 5. The blade surface temperatures have been unfolded for three-dimensional plotting presentation. Pressures and other local loads can be similarly represented.

Thjs moduie is based on engine thermodynamics. The temperatures and A typi-

Blade Tip Displacements

As was previously mentioned, the structural response can be predicted throughout the mission. Representative results for blade-tip radial displacement are shown in figure 6 at identifiable stages during the flight mission due to corresponding pressures, temperatures, and centrifugal loadings. These types of results can be obtained for any point in the component included in the simulation. The significance of having integrated, interdisciplinary structural response throughout the mission is that: (1) all dynamic interactions are properly accounted for; (2) results for stress/strain are suitable for durabilityllife assessments; and ( 3 ) results for global displacements, frequencies and/or instabilities can be used to design active controls.

Structural Dynamic Response

The structural dynamic response o f blades assembled in a bladed rotor is different than that of an individually simulated blade. The dynamics motion of a bladed rotor determined using ESCS is shown in figure 7 at take-off conditions. mine frequencies and compared with those obtained using single blades at unloaded and loaded conditions. A similar model was used t o determine the dynamic response under bird impact loading conditions.

Although results are not shown here, the same model was used to deter-

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Blade T i p Displacement a t Three F l i g h t C o n d i t i o n s

As was a l r e a d y ment ioned t h e ESCS e x e c u t i v e module couples t h e loads mod- u l e w i t h t h e ana lys i s -mode l i ng module and w i t h t h e a n a l y s i s module th rough module-communication l i n k s and proceeds t o determine the component s t r u c t u r a l response a t t h e p r e s e l e c t e d t i m e s d u r i n g the m iss ion . R e s u l t s from such an a n a l y s i s for t h e d isp lacements o f a t u r b i n e b lade a re shown i n f i g u r e 8 for t h r e e m i s s i o n c o n d i t i o n s .

The i m p o r t a n t p o i n t t o be made i s t h a t o n l y one user used t h e s i m u l a t o r ; he i n i t i a t e d t h e a n a l y s i s w i t h i n p u t i n f o r m a t i o n t y p i c a l f o r p r e l i m i n a r y des igns , and o b t a i n e d t h e d e t a i l e d r e s u l t s shown i n t h e f i g u r e . The t o t a l con- t i n u o u s connect t i m e was about 3 h r w i t h a CPU of about 1 h r . T h i s compares t o about 2 man-months by u s i n g t h e t r a d i t i o n a l approach and i l l u s t r a t e s t h e e f f e c - t i v e n e s s o f t h e s i m u l a t o r i n t h e usage of p r o f e s s i o n a l t i m e .

ESCS LONG RANGE OBJECTIVE AND A N T I C I P A T E D BENEFITS

The l o n g range o b j e c t i v e of ESCS i s t o p r o v i d e a computat ional s i m u l a t i o n t h a t p a r a l l e l s and r e p l a c e s , i n p a r t , t h e c u r r e n t development methods which make e x t e n s i v e use of exper imen ta l procedures. The p a r a l l e l between ESCS and t h e c u r r e n t development procedures a r e d e p i c t e d i n f i g u r e 9. ESCS w i l l m i n i - mize t h e e f f o r t expanded from i n i t i a l des ign t o engine b u i l d s and w i l l o f t e n r e s u l t i n more c o s t e f f e c t i v e engine b u i l d s for t h e same engine performance.

A n t i c i p a t e d b e n e f i t s i n c l u d e : ( 1 ) reduced t i m e development and c o s t , ( 2 ) f e w e r development engine b u i l d s , ( 3 ) l onger l i f e components, (4) reduced l i f e cyc e c o s t s on components, ( 5 ) reduced component and engine we igh t , (6) improved e n g i n e e r i n g p r o d u c t i v i t y , (7) increased performance, and ( 8 ) i nc reased r e l i a b i l t y . Engine manufacturers have c o s t es t ima tes f o r each of these i tems based on t h e i r own exper ience. S u f f i c e i t t o say t h a t each i t e m runs i n t o m u l t i m i l i o n d o l l a r s and takes seve ra l years to a s c e r t a i n i t s r e l i a b i l i t y i n o r d e r t o meet q u a l i f i c a t i o n and c e r t i f i c a t i o n requi rements.

CONCLUSIONS

The computat ional s t r u c t u r a l mechanics program a t NASA Lewis Research Center i s d e s c r i b e d i n g e n e r a l . The development o f the engine s t r u c t u r e s com- p u t a t i o n a l s i m u l a t o r ( E S C S ) , a major p a r t o f t h e computat ional s t r u c t u r a l mechanics program, i s desc r ibed i n some d e t a i l . The d e t a i l s were l i m i t e d to: ( 1 ) o b j e c t i v e s , ( 2 ) i n t e g r a t e d , i n t e r d i s c i p l i n a r y con ten t , and ( 3 ) t y p i c a l r e s u l t s o b t a i n e d . These r e s u l t s show promise t h a t an ESCS so f tware sys tem i s a t t a i n a b l e and l e n d credence t o p r o j e c t i o n s on p o t e n t i a l long-range s i m u l a t i o n capabi 1 i t i e s and a n t i c i p a t e d b e n e f i t s .

REFERENCES

1 . "Engine S t r u c t u r e s - A B i b l i o g r a p h y of Lewis Research C e n t e r ' s Research f o r 1980-1 987, NASA TM-100842, 1988.

2. Chamis, C.C., " I n t e g r a t e d A n a l y s i s of Engine S t r u c t u r e s , " NASA TM-82713, 1981.

5

3. Chamis, C.C. and Johns, R.H., "Computa t iona l Engine S t r u c t u r a l A n a l y s i s , "

4. Chamis, C.C., " P r o b a b i l i s t i c S t r u c t u r a l A n a l y s i s Methods f o r Space P r o p u l s i o n System Components," NASA TM-88861, 1986.

5. Wi lson , R.B., Bak, J . J . , Nakazawa, S . , and Baner jee , P.K., "On 3-0 I n e l a s t i c A n a l y s i s Methods for Hot S e c t i o n Components," PWA-5940-36, P r a t t and Whitney A i r c r a f t , Eas t H a r t f o r d , CT, 1986, NASA CR-175060.

6. Brown, K.W., " A e r o / S t r u c t u r a l T a i l o r i n g o f Engine Blades (Aero/STAEBL) , I '

PWA-5774-82, P r a t t and Whitney A i r c r a f t , Eas t H a r t f o r d , CT, 1988, NASA

NASA TM-87231, 1986.

CR-180805.

7. McKnight, R.L., "Component S p e c i f i c Mode l ing , " NASA CR-174925, 1985.

FY 86 FY88 FY 90-92

COMPUTATIONAL ENGINE STRUCTURES TEMPERATURE SIMULATOR PERFORMANCEANTEGRI STRUCTURES SIMULATOR (ESCS)

dn

ITY

FULL ENGINE STRUCTURAL

SYSTEM STRUCTURAL Ii&fk:s"ZED MISSION DYNAMICS ANALYSIS ANALYSIS

COMPUTER TECHNOLOGY

FULL ENGINE STRUCTURAL

SYSTEM STRUCTURAL Ii&fk:s"ZED MISSION DYNAMICS ANALYSIS ANALYSIS

L

KEY PROGRAM ELEMENTS STRUCTURAL ANALYSIS METHODS ADVANCED COMPUTER TECHNOLOGY COMPUTATIONAL ESCS

LIFE PREDICTION, STRUCTURAL INTEGRITY, COMPOSITE MECHANICS, CONTACT MECHANICS,

FIGURE 1. - COMPUTATIONAL STRUCTURAL RCHANICS.

6

7 - ESCS

THERMAL LOADS

F.E.M. TRANSLATOR' COSMO TRANSLATOR' ESMOSS TRANSLATOR'

OURABILITY INTEGRITY STABILITY PERFORMANCE ECONOMY RETIREMENT FOR CAUSE OlSTORTlON CONTROL INSPECTION INTERVAL

LOADING MODULE I COSMO' ESMOSS'

GSM PLOT* GRAPH30.

I STRUCTURAL ANALYSIS I MODULE 3-0 INELASTIC ANALYSIS' NASTRAN'

STAEBL" BESTJO"

EXECUTIVE MODULE COMMUNICATIONS (REXX)' INTERFACE LINK

I

(REMFORTRAN)

PERMANENT RECORDS' TEMPORARY RECORDS' GEOMETRY-% GEOMETRY-DISCRETE MISSION MATERIAL PROPERTIES MISSION TEMPERATURES MISSION PRESSURES OTHER THERMAL PARAMETERS OEFAULT MISSION FILES OPERATING SYSTEM UTILITY FILES MISC. (MISSION CRAY JCL ... )

1 ARCHIVE" 1 *-PRELIMINARY VERSION AVAILABLE

"-TO BE INSTALLED

FIGURE 3. - SIMULATOR ARCHITECTURE OF THE SOFTWARE SYSTEM.

7

ENGINE

BLADE ROTOR SECTOR

FINITE ELEMENT MODEL

ROTORSTAGE

FIGURE 4. - ENGINE STRUCTURES COMPUTATIONAL SIMULATOR.

r PRESSURE SUCTION I SURFACE SURFACE7

'\ LEAD"G 1 110 r- PERCENT SPAN \, EDGE;

\ 1.1

PERCENT CHORD

25.00 SURFACE TEMPERATURE, O F

FIGURE 5. - SURFACE TEMPERATURE PROFILE FOR TURBINE BLADE.

8

,-TAKEOFF

X Ly

/ /_,-GROUND IDLE

-‘---STATIONARY (PRE-TAKEOFF)

IDLE

FIGURE 6. - DEFORNATION OF TURBINE BLADE UNDER FLIGHT CONDITIONS.

FIGURE 7. - STRUCTURAL DYNAMIC RESPONSE OF A BLADED ROTOR.

9

LEADING EDGE TIP -*'

.07

.06

.05 G- L

% .04 u 4 2 a

2 .03 2 4 d .02

DESIGN

-01

0

1 - ENGINE START 2.3 - GROUND IDLE 4,5 - TAKE OFF 6,-9 - CLIMB 10.11 - CRUISE 12-15 - DESCEND

!2,3 16 - APPROACH 17 - LAND 18,19 - FLIGHT IDLE 20,21 - THRUST REVEdSE

II 22.23 - GROUND IDLE 24 - ENGINE TURN-OFF F

2 '-23

124 ELAPSED FLIGHT TIME. SEC

FIGURE 8. - ESCS SAMPLE RESULTS FOR FLIGHT MISSION SIMULATION.

CERTIFICATION TEST

BUILDS

PERCENT COST , , , ELAPSED TIME NUMBER OF CONFIGURATIONS

INTEGRATED DESIGN

I

NET SAVINGS TIME + $

(B) COMPUTATIONAL SIMULATION METHOD.

FIGURE 9. - PARALLEL BETWEEN CURRENT DEVELOPMENT AND COMPUTATIONAL SIMULATION METHODS.

10

Natlonal Aeronautics and Space Administration

1. Report No.

NASA TM-102119

Report Documentation Page 2. Government Accession No.

7. Key Words (Suggested by Author(@)

Structural analysis; Stress analysis; Multidiscipline; Finite elements; Mixed elements; Boundary elements; Computer codes; 3-D analysis; Nonlinear analysis; Transient analysis

7. Author(s)

C.C. Chamis

18. Distribution Statement

Unclassified - Unlimited Subject Category 39

9. Performing Organization Name and Address

National Aeronautics and Space Administration Lewis Research Center Cleveland, Ohio 44135-3191

3. Security Classif. (of this report)

Unclassified

2. Sponsoring Agency Name and Address

National Aeronautics and Space Administration Washington, D.C. 20546-0001

20. Security Classif. (of this page) 21. No of pages 22. Price’

Unclassified 12 A03

5. Supplementary Notes

3. Recipient’s Catalog No.

5. Report Date

6. Performing Organization Code

8. Performing Organization Report No.

E-4898

10. Work Unit No.

505-63-1 1

11. Contract or Grant No.

13. Type of Report and Period Covered

Technical Memorandum

14. Sponsoring Agency Code

Prepared for the 30th Structures, Structural Dynamics and Materials (SDM) Conference cosponsored by AIAA, ASME, ASCE, AHS, and ACS, Mobile, Alabama, April 3-5, 1989.

6. Abstract

The computational structural mechanics (CSM) program at Lewis encompasses (1) fundamental aspects for formulating and solving structural mechanics problems and (2) development of integrated software systems to computationally simulate the performance/durability/life of engine structures. It is structured to mainly supplement, complement, and whenever possible replace, costly experimental efforts which are unavoidable during engineering research and development programs. Specific objectives include: (1) investigate unique advantages of parallel and multiprocesses for: reformulating/solving structural mechanics and formulating/solving multidisciplinary mechanics and (2) develop “integrated” structural system computational simulators for: predicting structural performances, evaluating newly developed methods, and for identifying and prioritizing improved/missing methods needed. Herein the CSM program is summarized with emphasis on the Engine Structures Computational Simulator (ESCS). Typical results obtained using ESCS are described to illustrate its versatility.

*For sale by the National Technical Information Service, Springfield, Virginia 221 61 NASA FORM 1626 OCT 88

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Computational Structural Mechanics Engine Structures