Chained Analysis: Fan Blade Out with Rotor Dynamics

Chapter 53: Chained Analysis: Fan Blade Out with Rotor Dynamics

53 Chained Analysis: Fan Blade Out with Rotor Dynamics

Summary 1068

Introduction 1069

Modeling Details 1073

Results 1081

Input File(s) 1086

Video 1087

MD Demonstration Problems

CHAPTER 531068

SummaryTitle Chapter 53: Chained Analysis - Fan Blade Out to Rotor Dynamics

Features • Chained implicit -> explicit -> implicit analyses• Generation of FBO contact forces for loading on blade tips and case• Transferring the unbalanced geometry of explicit FBO to implicit RD analysis• Fusing the bearing using a force failure criterion

Geometry

Material properties • Blade & Rotor (Titanium): Elastic- Plastic Material

= 4.466 g/cm3, = 0.35, Yield Stress = 1009 MPaTangent modulus = 731 MPa, Young’s modulus = 117 GPaPlastic strain failure limit 0.2

• Case (various materials): Elastic-Plastic Material

Analysis characteristics Nonlinear implicit static, Transient explicit dynamic, and nonlinear implicit transient analyses

Boundary conditions • Prestress Implicit: Fixed at the bearing locations• FBO Explicit & RD Implicit: Fixed boundary at the mount

Applied loads Prestress Fan at 4500 rpm, Release blade, Rotor dynamics unbalance

Element types 1-node concentrated mass, 2-node beam, 4-node shell, and 8-node solid elements

FE results Unbalanced loading due to blade out

Implicit Prestess Explicit FBOFixedMount

Bearings

Implicit RD

-0.0008

-0.0006

-0.0004

-0.0002

0

0.0002

0.0004

0.0006

0.0008

-0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006 0.0008

Y-location

Z-lo

catio

n

1069CHAPTER 53

Chained Analysis: Fan Blade Out with Rotor Dynamics

IntroductionThis example presents a multi-disciplinary, integrated implicit-explicit-implicit analysis process tailored for more accurate and efficient simulations of aero engine fan blade-out events using MD Nastran. A Fan Blade Out (FBO) event can be extremely nonlinear because of the heavy wide chord fan blades incorporated in the new generation of high by-pass ratio jet engines. These new wide chord blades are used to meet airframe manufacturers’ demand for higher thrust engines with improved performance and optimum weight. Airframe and engine manufacturers use computerized analysis procedures to support the design of both the propulsion system and adjacent wing structures.

However, manufacturers, typically, do not share finite element models and, traditionally, construct a new model to suit their analysis objective. For example, typical FBO models are very detailed and can exceed two or three million elements whereby a rotor dynamics models is much coarser and can be under 50,000 elements. So the challenge becomes how to transfer the FBO loads computed by the SOL 700 explicit solver (based on a very fine meshed model) to a coarse model for rotor dynamics simulation in the SOL 400, all within one common modeling environment.

This example demonstrates the automated, multi-disciplinary simulation capability in MD Nastran to streamline the FBO event simulation facilitated by SOL 700 and SOL 400 which normally consists of the following separate steps:

1. Pre-stress fan blade using conditions at the maximum rotating speed and including static loads such as gravity with an implicit solution (SOL 700 implicit solver or SOL 400).

2. An explicit solution for few cycles with release of a fan blade to simulate: damage to the trailing fan blade(s); fan rubs with the engine case; breakage or damage to the inlet or engine containment case; twisting and bending of the FAN shaft and/or other rotating shafts.

3. An implicit solution to continue the analysis more rapidly and reach the steady state “windmilling” speed. This is done by including realistic input forcing functions and damage incurred during the explicit solution. Techniques to reduce the loads for application to a coarser model are introduced to preserve the solution integrity.

4. This integrated MD Nastran SOL 700 explicit and SOL 400 implicit solution with the Nastran rotor dynamics capability is used to predict the engine unbalance and to extract the whirling diagrams and critical tolerances (Figure 53-1). This allows the engine manufacturers to share results of the explicit phase with other manufacturers of modern airframe/propulsion system components seamlessly and without compromising design secrets, thus achieving higher accuracy and improved productivity with fewer bottlenecks.


CHAPTER 531070

Figure 53-1 Chained FBO-RD Analysis

The MD Nastran MASTER database is tailored to include only the FBO loads and other relevant information required for rotor dynamic simulation without compromising the confidentiality of model geometry and modeling details. The MASTER database can be shared between MD Nastran users from different companies and organizations for follow-up analysis. For example, after the FBO analysis simulated by SOL 700, the MASTER database can be sent to airframe manufacturers to use the loads in their rotor dynamics analysis facilitated by SOL 400. The following steps are completely automated in SOL 400 rotor dynamics simulation:

1. Read the MASTER database generated by SOL 700 to use the FBO loads as a pre-condition to RD analysis.

2. Map the loads onto the coarse finite element model in RD simulation. An advanced search technology is implemented in SOL 400 to identify the closest element to a given load. The load is then distributed over the corner nodes of the element.

3. Synchronization of the explicit and implicit timesteps, The explicit timestep is much smaller than the implicit timestep, so the timesteps need to be “synched up” when the analysis is switched from FBO analysis to RD simulation. The synchronization is based on Fast Fourier Transformation (see Timestep Control on SOL 400 for details)

Prestress – Implicit simulation Choice of MD Nastran SOL 106/400 or 700 (Implicit)

Initial Condition for explicit run

MD Nastran SOL400 RD (Unbalance loading)

Extract final displacement after stabilization

FBO/FOD – Explicit simulation MD Nastran SOL 700 (bird strike)

Simulate damage and extract mass, inertia and center of gravity for rotordynamics unbalance

-0.0008

-0.0006

-0.0004

-0.0002

0

0.0002

0.0004

0.0006

0.0008

-0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006 0.0008

Y-location

Z-lo

catio

n

1071CHAPTER 53


It is believed that this process can result in much higher levels of accuracy and dramatically reduce the cost of analysis and design of the propulsion system and wing. The example problem that is used in this example is a representative finite element model of an engine mounted on a wing.

SOL 700 Entries IncludedSOL 700TSTEPNLDYPARAM,LSDYNA,DATABASE,SSSTATMDBEXSSSDYPARAM,LSDYNA,DATABASE,NCFORCCSPOTBLDOUTSOL400ANALYSIS=NLTRANROTORGRSPINTCONM2UNBALNCCBUSHPBUSHPBUSHT

Loadings Types

The dynamic loads on the engine after the FBO can be classified under two categories:

a. Large amplitude transient impact loads generated inside the engine due to the released blade hitting the containment and contact with the trailing blade(s).

b. The so-called “Seizure Torque” being applied on the fan rotor due to unbalance caused by the missing blade. The seizure torque is a result of contact between the tip of the blades and the fan case (rubbing). If the torque is large enough it could stall the engine causing a “seizure” (see below for more details).

The transient impact loadings are calculated and stored by SOL 700. Only three types of loadings are taken into account.

1. Impact loads between the broken blade and the case

2. Rubbing loads on fan case

3. Rubbing loads on blade tips

Additionally, this release (MDR3) is limited to the analysis of only one released blade and assumes that there are no other failed trailing blades. In other words, only the released blade is considered for unbalance. The other types of loads and unbalances, such as impact loads between the broken blade and remaining blades unbalance generated by breaking some of the remaining blades due to the impact between the broken and remaining blades and so on, will be considered in future releases of MD Nastran.

The impact forces contain both a normal component (to the fan case) and tangential components which change with time as the blade hits various parts of the containment ring. The released blade, pre-determined in the analysis and in testing, is the only blade which is actually released at the hub and impacts the fan case. In many cases, the trailing blade will impact the root of the released blade, causing the trailing blade to fail and break at a different location. As


CHAPTER 531072

a result, one or more trailing blades will behave like shrapnel and will contribute significantly to the impact loads. These forces and their contact locations are stored in SOL 700 “binout” as well as the MD Nastran database MASTER file in the Nastran basic coordinate system. The entry BLDOUT in MD Nastran defines blade out force output information and mapping criteria for a combined SOL 700 – SOL 400 Blade-out analysis (used both in the SOL 700 and subsequent SOL 400 analyses).

During the fan blade out event, as the unbalance forces on the rotor make it to go off-center and the running

tip-clearance between the rotating blades and the stator structure is eliminated, the tips of the blades will rub against the enclosure. The rubbing loads are distinguished between those that are applied on the fan case and those that are located on the blade tips. There are equal and opposite sets of forces on the containment ring and on the blade tips. The primary difference is that the rubbing loads on the containment ring can be stationary whereas the rubbing loads on the blade tips are varying as the blades rotate and at any given instant, different blades on the rotor continue to

contact the stator structure in the same location. The rub loads have radial and tangential components, with

radial component acting along the span of the blade and tangential component opposite to the direction of

motion of the rotor. Using the relationships for tip Coulomb damping with the coefficient of friction , the magnitude

of the tangential component is computed as: . Since the torque on the rotor produced by the frictional force

always opposes the motion, its tendency would invariably be to slow-down the spin of the rotor-shaft. These

loads, if severe enough, may even stop it, a phenomenon called “seizure torque”. Thus, rubbing forces have normal

and tangential components and , respectively at the points of contact. Similar to impact forces, SOL 700

will compute the contact location and magnitude of the rubbing loads and store them into “binout” as well as the “MASTER” file. The loads that have zero magnitude are filtered out and are not written to the database to save time and disk space.

The unbalance force , which results from the mass of the missing blade material, occurs whether the

remaining unbroken blades contact the containment ring or not. This force is output by SOL 700 in the Nastran basic coordinate system and saved in the SOL 700 “binout” file. In addition, the mass of the broken blade will be saved for use in the subsequent creation of UNBALNC entries for the SOL 400 rotor dynamics analysis.

Time Step Control in SOL 400

The contact forces computed by SOL 700 are stored and transferred to SOL 400. These forcing functions have very small time intervals and they may unnecessarily increase the analysis time. In order to increase the timestep and synchronize the explicit and implicit timesteps, a technique based on Fast Fourier Transformation (FFT) and Inverse Fast Fourier Transformation (IFFT) is used to eliminate the high frequencies of the data.

First, the time histories from SOL 700 are changed by FFT from time domain to frequency domain. Next, the frequency domain histories are processed by a low pass filter in which the low pass frequency can be selected by the user. Finally, the histories are changed by Inverse FFT from frequency domain back to time domain.

Mur2

Frub

Fr Ft

Ft Fr=

Ft

Fr Ft

Mur2 Mu

1073CHAPTER 53


Load Mapping Scheme

Modeling DetailsA simplified generic engine model was provided by Boeing for the purpose of this study (Figure 53-2). The engine model was modified and enhanced by MSC to include realistic fan blades, rotor, three bearings (Figures 53-3 and 53-4)and other components. Typically, full FBO models can easily have millions of elements and degrees of freedom to represent a realistic jet engine. However, for the purpose of this study, even though the FBO model was constructed with a much finer mesh density than the rotor dynamics model, it is not as elaborate as the full engine models that are used by manufacturers in their explicit simulation. The FBO model has 8864 nodes and 8256 shell elements and is deemed to be sufficiently detailed to capture the physics of the problem and compute the impact and rubbing loads. The fan blades were constructed by shell elements with various thicknesses across their width and length. The rotor was made of a hollow rod with varied cross sections across its length and a rotational velocity of 4500 rpm. The material for both rotor and fan blades is titanium grade with the following properties:

= 4.466 g/cm3 Poisson’s ratio = 0.35

y = 1009 MPa Tangent modulus = 731 MPa

Young’s modulus = 117 GPa Plastic strain failure limit 0.2

Distinguishing Rubbing & Impact using different contac t definitions

Results are stored in binary output file (binout) and MASTER

Generate Rubbing force & impact force entries in the different files

Pass to SOL 400 via “MASTER”

Requirement in SOL 700

Read loads in SOL 400 by DBLOCATE = *MASTER


CHAPTER 531074

Figure 53-2 Rotor Dynamics Model

Figure 53-3 Implicit Prestress Blade and Rotor Model and Location of Bearings on the Rotor

fixed in y and z translational directions

fixed in x, y and z translational directions fixed in x rotational direction

1075CHAPTER 53


Figure 53-4 Explicit FBO Engine Model and Location of Bearings on the Rotor

The bearings were modeled by constructing two concentric rings with pre-determined stiffness properties that can contact each other. The flange on the bearings prevents the axial movement of the rotor during the fan blade out. The bearing models and their properties are important design considerations to simulate the “fusing” during the FBO and rotor dynamics analysis. Fusing is an event where a bearing or other support structure fails as a result of high loads beyond the design strength of the fusing structure, and its stiffness is reduced to zero.

Input

The simulation consists of three runs. The first run is a prestress analysis that computes the deformations and stresses due to rotational velocities. This computation is essentially linear static and an implicit solver is selected for the purpose of computational efficiency. Boundary and initial conditions of the prestress run differ from the FBO run. In the prestress run the three bearing points are fixed and a force in the circumferential direction is applied to the rotor and fan blades.

Implicit Prestress Run

Since the entries and details of the prestress input file are quite similar to that of “Bird Strike on rotating fan blades with prestress” example, explanation of the prestress input will be skipped.

Explicit FBO Run

Since the explicit FBO input is also similar to of the explicit input of “Bird Strike on rotating fan blades with prestress” example, only additional or different entries will be explained.

BLADEOUT option activates the chaining simulation. All FBO forces assigned in BLDOUT entry will be stored in “MASTER” file after the simulation.

SOL 700,NLTRAN STOP=1 PATH=3 BLADEOUT

TSTEPNL 1 300 .1e-3 1 ADAPT 2 10


CHAPTER 531076

TSTEPNL entry describes the number of Time Steps (300) and Time Increment (1.e-4 seconds) of the simulation. End time is the product of the two entries (30 ms).

DBEXSSS entry requests the statistics of subsystems. The subsystems are defined by BCPROP entries.

DYPARAM, LSDYNA,DATABASE,SSSTATM parameter requests to store the mass, mass center and mass inertia tensor of the subsystems which are assigned by DBEXSSS entry. All information will be stored to jid.dytr.ssstat ascii file at every 0.000008 seconds and will be used for unbalance input in the rotor dynamic simulation.

BCPROP 101 includes the properties of all blades and BCPROP 21 includes only the broken blade properties. These two subsystem information will be used in UNBALANC and CONM2 entries of SOL 400 rotor dynamics simulation.

In the example, 9 contacts are defined. In order to reduce the size of binout file which includes the contact forces, only the fan case is considered to capture the FBO loads. Only the contact forces between the remaining blades and the fan case (contact 01) and the broken blade and the fan case (contact 02) are stored in the binout file. To store contact forces in binout files, two options in BCTABLE and one parameter are required. SPR and MPR options can store the contact forces on SLAVE and MASTER parts respectively. DYPARAM*,LSDYNA,DATABASE,NCFORC parameter controls the timestep of contact forces output which are defined in BCTABLE.

DBEXSSS 111 21 2 3 4 5 6 7 ++ 8 9 10 11 12 13 14 15 ++ 16 17 18 19 20 101DYPARAM LSDYNA DATABASESSSTATM .00008

$$ ALL BLADES$BCPROP,101,1011106,1011107,1011108,1011109,1011110,1011111,1011112,+

$$ CONTACT ID SLAVE BODY MASTER BODY DESCRIPTION$ 01 1 22 remaining all blades to direct contact case (recording)$ 02 21 22 broken blade to direct contact case (recording)$ 03 21 1 broken blade to remaining all blades$ 04 1 remaining all blades (self contact)$ 05 21 23 broken blade to non-direct contact case$ 06 22 direct contact case (self contact)$ 07 1001 1004 bearing point 1 : fuse at 6.0E-3 seconds$ 08 1002 1005 bearing point 2$ 09 1003 1006 bearing point 3$BCTABLE 1 9 SLAVE 1 0. 0. 0.1 0. 0 0 0 0 0.1 SS1WAY+++ 1 1

1077CHAPTER 53


To define the release mechanism, breakable joints (CSPOT) are used (53-5). These are elements that have coincident nodes on the hub and the blade roots but are distinct.

Figure 53-5 Adding Breakable Joints

The breakable joints between the hub and the release blade are added using CSPOT. The joints will be released at 0.00001 seconds after the start of FBO simulation.

CSPOT entry defines the complex or combined welds. This is used to connect two nodes which are defined by BCGRID entry and are released (broken) at 0.00001 seconds.

CSPOT 1111 101 10 1111 0.00001..CSPOT 1126 116 10 1126

BLDOUT 1 0 1.0E-6 0.0 0.09204 2.90E+1 0.244 12 0 0. 1. 0. 2 4 1 3 1 2 2 2 1 99 3 3 99 99 99 99

Add breakable joints between the hub and the released blade


CHAPTER 531078

BLDOUT entry defines the contact force output information and mapping criteria for a sequential SOL 700 FBO and SOL 400 RD analyses. Using this entry, the all forces can be categorized and stored to MASTER file in the SOL 700 run. All slaves and masters in the BCTABLE must be assigned to BLDOUT entry using six different types of flags in ISLVi’s and IMASTi’s. In the example, nine ISLVi’s and nine IMASTi’s are required because there are nine contact definitions in BCTABLE. See MD Nastran Quick Reference Guide for other fields.

The spin down event after the blade out can be defined by using a time-dependent pre-determined rotational speed of the turbine using SPCD2, BCGRID, and TABLED1 entries.

Rotor Dynamics Run (SOL 400)

The FBO loads computed in SOL 700 are read by SOL 400 by assigning the _FBO.MASTER file to DBSET in the File Management Section (FMS) of SOL 400 run.

SOL 400 executive control entry activates nonlinear static and transient analysis.

Case control commands are defined in the following box.

ANALYSIS=NLTRAN actives “nonlinear transient analysis”.

SPCD2 1 GRID 123 5 80 -1.$BCGRID 123 20003787THRU 2000386220003867THRU 2000394220003947++ THRU 20004022

nastran buffsize=65536nastran dbcfact=4nastran system(151)=1init scratch logi=(scratch(9999000))assign dbloc1='impact_FBO.MASTER'dblocate datablk=(GEOM3K) logical=dbloc1 , where(projno>0 and version=* and wildcard)

SOL 400

analysis=nltranrigid=linearRGYRO= 100DISPLACEMENT(print,plot,SORT1,REAL)=ALLSTRESS(plot,SORT1,REAL)=ALLSTRAIN(plot,SORT1,REAL)=ALL

1079CHAPTER 53


Bulk data starts with BEGIN BULK.

In order to use equivalent material properties in SOL 400, all MATD024 materials models used in SOL 700 are translated to MAT1 and MATEP with slope option.

TSTEPNL entry of SOL 400 controls the convergence criteria and data for nonlinear transient analysis.

ROTORG entry defines the rotor which consists of GRID IDs from 10 to 21. RSPINT entry indicates the rotational direction which is assigned to the rotational axis from GRID 11 to GRID 10. The rotational speed is defined in TABLED1, 10 for describing the speed down at various time steps. Note that the magnitude of the rotational velocities defined in SOL 400 differ from SOL 700. This is because the unit of rotational velocity used in SOL 400 is RPM and is different to that used by SOL 700 (radian/seconds)

$ impact_FBO.dytr.ssstatsubsystem: 1

total mass of subsystem = 0.91899477E-01 x-coordinate of mass center = 0.16037865E+03 y-coordinate of mass center =-0.28772884E+02 z-coordinate of mass center = 0.10338639E+03.... subsystem: 21

total mass of subsystem = 0.59591613E+01 x-coordinate of mass center = 0.16148860E+03 y-coordinate of mass center = 0.41383951E-05 z-coordinate of mass center = 0.10000020E+03

inertia tensor in global coordinates

BEGIN BULK..$MATD024 403153 4.14E-4 1.60E+7 0.35000 2.5E5 1.38E5 0.25000$MAT1 101 1.60E+7 0.35000 4.14E-4MATEP 101 SLOPE 2.5E5 1.38E5

TSTEPNL 100 4000 1.0E-4 2 1.0E-2 1.0E-2 0

ROTORG 10 10 THRU 21$RSPINT 10 11 10 RPM 1000$TABLED1 1000 ++ 0.0 4500.0 0.012 4255.0 0.016 4096.6 0.028 3834.2 ++ 0.042 3689.1 0.055 3605.1 0.25 2915.7 0.5 2250.0 ++ 100. 2250.0 ENDT


CHAPTER 531080

row1= 0.2385E+04 -0.5329E-03 -0.2139E+01 row2= -0.5329E-03 0.1748E+04 -0.1921E-02 row3= -0.2139E+01 -0.1921E-02 0.1748E+04

-> translate

UNBALNC,100,0.0919,12,0.,1.,0.,,++,29.00,180.0,1.10995$$ blade + hub$CONM2, 2001,12, ,5.959,,,,,++, 0.2385E+04,0,0.1748E+04,0,0,0.1748E+04$GRID 12 161.488 0. 100.

The mass, mass center and mass inertia tensors computed in SOL 700 are stored in the impact_FBO.dytr.ssstat file. These values are then used in SOL 400 to define mass unbalance by UNBALNC and CONM2 entries. As shown in the box above, the order of the subsystem id numbers in ssstat file is determined by the order of DBEXSSS as defined in SOL 700. For example, subsystem 1 represents the released blade while subsystem 21 represents all blades and hub information. The unbalance mass in the UNBALNC entry is the same value of total mass as defined in subsystem 1. ROFFSET and ZOFFSET of UNBALNC entry are calculated by the difference of the mass locations between subsystem 1 and 21. In the example, the x-direction in SOL 700 FBO simulation is coincident with the z-direction of the rotor in SOL 400 RD simulation. In addition, the mass inertia tensor of subsystem 21 is recorded to Iij fields of CONM2 entry. GRID 12 which describes the mass location of hub and blades is also set to the same center

location of subsystem 21.

In the gyroscopic nonlinear transient analysis, only the additional unbalance mass is considered as opposed to FBO simulation, where the unbalance mass results from losing mass due to blade out. Therefore, the additional mass must be added to the opposite side of the location where blade-out occurred. To add the mass to the opposite side of the blade out, the unbalance is assigned at the location which is measured 180 degrees in the positive direction of the local unbalance coordinate system.

BLDOUT entry is also used in SOL400. BLDOUT entry in SOL 400 can control and apply the FBO forces to the nonlinear transient analysis using different time steps.

Bearings in SOL 400 are modeled using CBUSH elements. PBUSHT controls the failure criteria. The CBUSH element is defined to fail at 1.65E5 lbf in radial (y-z) direction.

BLDOUT,1, 1, 1.0E-6, 0.0, 0, 0, 1.0E-3, 1+,0.0919,2.9000E+1, 1.10995, 12, 0, 0.,1.,0.

CBUSH 101 101 1002 1012 0PBUSH 101 K 1.0E7 1.0E7

1081CHAPTER 53


ResultsThe stress and deformation results between SOL 400 and SOL 700 are within 2% of each other, which is quite acceptable (see Table 53-1). However, for this particular analysis, which took a few minutes to complete, SOL 400 ran the same model three times faster than the SOL 700 implicit solver.

Results of Prestress Implicit Simulation

Figure 53-6 Displacement Contours on Fan Blades and Rotor – SOL 400 vs. SOL 700

SOL 400 SOL 700


CHAPTER 531082

Figure 53-7 Stress Contours on Fan Blades and Rotor – SOL 400 vs. SOL 700

The results and typical loads from the FBO analysis are demonstrated in Figures 53-8 to 53-12. The total simulation time was 30 ms which is about three complete revolutions of the rotor. As explained in Loading Types section of Introduction, only one blade was released and no trailing blades were broken. The simulation showed that even though there is an impact between the trailing and the released blade (see Figures 53-8 and 53-9), no other blades are actually broken. The plastic strains and stresses at t = 3 ms on the fan case are also shown in Figure 53-10.

Table 53-1 Comparison of SOL 400 vs. SOL 700 Pre-stress Results

SOL400 SOL 700Difference

(refer to SOL 400 results)

Analysis Time 135 seconds 398 seconds 300%

Maximum Resultant Displacement 24.66 mm(0.971 inch)

24.13 mm(0.950 inch)

2.2%

Maximum Equivalent Stress 710.2 MPa(103 ksi)

696.4 MPa(101 ksi)

2.0%

SOL 400 SOL 700

1083CHAPTER 53


Results of Fan Blade Out (FBO) Explicit Simulation

Figure 53-8 Effective Stress Contour

Figure 53-9 Snapshot of Contact Between Released Blade and Containment

0.0015 seconds 0.0037 seconds

0.0037 seconds at a different angle


CHAPTER 531084

Figure 53-10 Fan Case t = 3ms

The upper plot in Figure 53-11 shows the impact load and rubbing forces (magnitudes) on the fan case while the lower plot shows the rubbing forces on the blade tip at a typical location. It is noteworthy to mention that total resultant tangential rub loads on the case and blade tips should be equal and in opposite directions. However, as shown in Figure 53-12, these loads are extracted at different locations and are meant as representative loads only. All load components and their locations (in x, y and z coordinates) are recorded in the database for subsequent search and mapping to the new rotor dynamics model, with its coarser mesh.

Figure 53-11 Loads

Plastic Strain Effective Stresses

0 5 10 15 20 25 30

10-1

1

101

102

103

104

105

106

Tangential (Max = 15,767 N)Radial (Max = 78,842 N)

Impact (Max = 423,418 N)

Rubbing Loads

Rubbing Loads

Time (ms)

Ti ( )

Force Magnitude (N) Node 31795 (case)

Force Magnitude (N) Node 1405440 (blade)

31795

1405440

31795

1405440

0 5 10 15 20 25 301

101

102

103

104

105

106

Tangential (Max = 12,024 N)Radial (Max = 75,578 N)

1085CHAPTER 53


Figure 53-12 Node 31795 and 1405440 Locations on Case and Blade Tip

Results of Rotor Dynamics Implicit Simulation

In this analysis, the orbit diagrams between SOL 400 and SOL 700 (see Figure 53-13) demonstrate that the whirling characteristics are similar and deformation magnitudes of the whirl are very close in the z-direction but differ in the y-direction. The difference could be due to two contributing factors. The first is that the contact forces between the trailing and released blades were not taken into consideration in the rotor dynamics simulation, but only the impact and rubbing loads. The contact forces between the blades will have some contribution to the magnitude of the whirling deformation in the y-direction. The second reason is because the sectional properties of the rotor at the center where hub is located are approximated in the stick model for the rotor dynamics simulation. Figure 53-13 shows the orbit diagram of the tip node of the rotor due to mass unbalance and predicts the maximum “whirl” deformations in each direction.

Figure 53-13 Comparison of Orbit at the Tip of Rotor

-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Sol 700

Sol 400

Z-Displacement (inch)

Y-Displacement (inch)


CHAPTER 531086

In the implicit rotor dynamic analysis, the failure load for bearing 1 is set to 734 kN (1.6E5 lbf). A radial dependence is specified for the fuse option. Figure 53-14 shows the time history for the force in this bearing. The bearing is found to fuse in less than a revolution after the FBO event. The time-to-fuse is then used to modify the explicit FBO analysis. In the FBO analysis, fusing is modeled by deactivating contact between the two rings of the bearing at the analysis time recorded in the implicit rotor dynamic analysis.

Figure 53-14 Loadings on the First Bearing and Fusing After 0.004 Seconds

Input File(s)

The end time and the time history output interval in the fan blade out simulation were modified in the input deck, nug_53b.dat, to speed up the calculation. To get the same results as this document, please use the original end time and time history interval which is suppressed in the input deck.

$ original$TSTEPNL 1 300 .1e-3 1 ADAPT 2 10$DYPARAM*,LSDYNA,DATABASE,NCFORC,.1e-5,3$ modifiedTSTEPNL 1 100 .1e-3 1 ADAPT 2 10DYPARAM*,LSDYNA,DATABASE,NCFORC,.1e-4,3

File Description

nug_53a.dat MD Nastran Input file for prestress implicit analysis.

nug_53b.dat MD Nastran input file for fan blade out explicit analysis.

nug_53d.dat MD Nastran input file for rotor dynamics implicit analysis.

-150000

-100000

-50000

0

50000

100000

150000

0 0.002 0.004 0.006 0.008 0.01

Force-YForce-ZForce-magn

http://www.mscsoftware.com/doc/nastran/mdug/input_files/ch053/nug_53a.dat

http://www.mscsoftware.com/doc/nastran/mdug/input_files/ch053/nug_53b.dat

http://www.mscsoftware.com/doc/nastran/mdug/input_files/ch053/nug_53d.dat

1087CHAPTER 53


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

Figure 53-15 Video of the Above Steps

-0.0008

-0.0006

-0.0004

-0.0002

0

0.0002

0.0004

0.0006

0.0008

-0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006 0.0008

Y-location

Z-lo

catio

n

http://www.mscsoftware.com/training_videos/mdug/ch053/2010/ch053.swf

http://www.mscsoftware.com/training_videos/mdug/ch053/2010/ch053.swf

Chained Analysis: Fan Blade Out with Rotor Dynamics

Documents

Transcript of Chained Analysis: Fan Blade Out with Rotor Dynamics