Bird Strike - Project - 2

AIM:-

In this project, we have performed the bird strike analysis using the Lagrange formulation. The bird is simplified in this case because the shell element is used and the material used for the bird is elastic material. Except that everything is kept quite similar to the actual bird strike simulation.

OBJECTIVE:-

1. Simulate a bird strike situation using given models with appropriate material models as required.
2. Establish a numbering system for the Ids of all the keywords with proper ranges for multiple cards.
3. Distribute the given model in individual keyword files for various components as well as analysis sub-components.
4. Use the ‘Include’ keyword to put these keyword files together and run the analysis such that moving the folder with these files won’t cause a problem with the analysis.
5. Use mass scaling to minimize the analysis time and its effect on the outputs.

INTRODUCTION:-

A bird strike is strictly defined as a collision between a bird and an aircraft that is in flight or on a takeoff or landing roll.

Bird Strike is common and can be a significant threat to aircraft safety. For smaller aircraft, significant damage may be caused to the aircraft structure and all aircraft, especially jet-engined ones, are vulnerable to the loss of thrust which can follow the ingestion of birds into engine air intakes. This has resulted in a number of fatal accidents.

Bird strikes may occur during any phase of flight but are most likely during the take-off, initial climb, approach and landing phases due to the greater numbers of birds in flight at lower levels. Since most birds fly mainly during the day, most bird strikes occur in the daytime. Most fatal are the ones in which birds get ingested into the engines and damage the rotors and cause explosions.

Problem statement:-

This is a classic nonlinear transient dynamics problem similar to car crashes and mobile drops. While accurate modeling of the problem requires advanced techniques such as SPH (Smooth Particle Hydrodynamics), this problem can be solved using a generic explicit solver. Here is the information required to model the phenomenon.

1. The blades should rotate at a constant velocity but the casing should remain stationary.
2. The cylindrical bird model should travel along its own axis and hit the blades.
3. Use elastic material for the bird (2000MPa) and the casing (200GPa). The material model for the blades is attached.
4. The velocity of the engine blades and the birds can be chosen so that blade failure can be seen within a short span of time.

Apart from this, a meshed file of the model was provided and it was asked to keep all the parts, keywords like contacts, boundary conditions, material data and control files into separate key files and unite them together in the main file.

PROCEDURE:-

1) Part Creation -

Open the BIRD_STRIKE.k file in LSPP. Here we see that there are four parts available(Hub, casing, blades and bird). New .k files are created individually for each part. For that go to PART and select one part, remaining parts are deleted and saved as a particular file name.

2) Material and Section Creation -

First of all, open all the part files created in LSPP one by one.Then create the material and section card. Here we use the unit system is Kg, mm, ms.

Bird , Blade, Casing are SHELL element. Hub is SOLID element.

Element formulation for shell is 16(fully integration) and for solid is 10(1 point tetrahedron)

thickness for

• bird = 2.0 mm
• blade = 2.0 mm
• casing = 2.5 mm

Casing: For casing ELASTIC steel material is defined.

A)Material Card:-

B)Section Card:-

Blades: In this model, elasto plastic material (MAT_24 LINEAR PIECEWISE PLASTICITY) card has choosen. ALUMINIUM is selected.

For blades material data curve is available in the question. So we use that data for creation of material.

A)Material Card:-

B)Load Curve Card:-

C)Section Card:-

Hub: We use steel data for creating the hub material card. In this model we only focus on the blade so defined the rigid material for hub because it provide addition benifit of constraining part in required degree of freedom otherwise we have to define the cylindrical joint between casing and the hub so that hub must be maintained in position. For the hub we create a SECTION_SOLID card.

A)Material Card:-

B)Section Card:-

Bird: Generally in bird strike modelling bird is challenging task because it consist bones blood and organ ,so for simplicity , In Aerospace industry bird is modelled as 90% water and 10% air like gelatin material.

In our case, bird is modelled with lower density and higher poisson ratio and lower young modulus.

A)Material Card:-

B)Section Card:-

3) Include -

One of the main goals is to develop the understanding of the INCLUDE keyword so that we can work with multiple files simultaneously and use them for our simulation so a separate keyword file is generated for each part and included in one keyword file named as the main .k file.

4) Creating Entities -

A)SPC:-

Go to Create Entity > Boundary > Spc > Create. Here 1 SPC is created with casing.

fixing the degrees of freedom for the engine casing as a single point constrains.

6) Initial Velocity -

An initial velocity of 50mm/ms is given for the bird in X-direction and rotational velocity of 0.523rad/ms is given for the hub and blade as a part set using *INITIAL_VELOCITY_GENERATION card.

7) Contacts -

In this model, a contact card is required to identify contact between parts. Here 3 contacts are generated,

a. Contact between Hub and Blade

Here give the slave as blades and master as hub.

b. Contact between Blade and bird

Here give the slave as blades and master as bird.

c. Contact between blade and casing

Here give the slave as blades and master as casing.

d. Contact for blade ie, self contact

Here take the slave as blade.

8) Renumbering -

Renumbering of nodes, elements and parts is very useful when we work on the very complex model.

-In our question we provide the number start from:-

i) nodes:- Start from 1,00,000

ii) Elements:- Start from 5,00,000

iii) Parts:- Start from 1,000

For the renumbering go to Model and Part > Renumber. After that change the value individually by toggling on and the checkbox for the entities, then click on Set and Renumber.

9) Control cards -

i) Termination:-

For that go to Model and Part > Keyword manager > All > Control > Termination. Provide the End time is 4.5ms.

10) Binary_D3plot and ASCII option -

i) BinaryD3plot:-

Here provide dT value is 0.1ms.

ii) Extent binary:-

This keyword is useful for strain tensor data. (STRFLG=1)

iii) ASCII option:-

Here we use only GLSTAT and MATSUM.

10) Model check -

After assigning all the keyword check the model using the model checker and check if it shows any warning or not. If it shows any type of error then remove it. After that save the file as a".k" format. Run the file in the LS-RUN solver and if it ends as a normal termination then model is correct.

5. Mass Scaling:

1) Without Mass-Scaling:

The estimated time required to complete the simulation was shown as 1 hrs 33 mins but actually, it took only 40 mins to complete the task. A mass scaling approach can be adopted to reduce the runtime.

2) With Mass-Scaling:

a. In 1st trial, we did this by keeping DT2MS = -6.0E-05 and TSSFAC=0.9 the runtime estimated is 1 hrs 27 min but actually it took 6 min 50 sec

with 0% mass addition.

Fig: Estimated data before the simulation run

Fig: Final data after the simulation run

b. In the 2nd trial, we did this by keeping DT2MS = -6.0E-04 and TSSFAC=0.9 the runtime estimated is 13 min but actually it took 1

min 24 sec with 2.42% mass addition.

Fig: Estimated data before the simulation run

Fig: Final data after the simulation run

c. In the 3rd trial, we did this by keeping DT2MS = -4.0E-04 and TSSFAC=0.9 the runtime estimated is 20 min but actually it took 1 min 55 sec

with 6.6% mass addition. (Acceptable).

Fig: Estimated data before the simulation run

Fig: Final data after the simulation run

d) For, DT2MS = -2.50E-4, the estimated clock time to complete the simulation for TSSFAC= 0.9 is 27 mins. The percentage increase in mass is 8.3602%.

Fig: Final data after the simulation run

As per industry standards, for a dynamic simulation, 10 % is the limit set for mass scaling. After simulating the current case I didn't see any significant changes between the one with mass scaling and the one without mass scaling. I also understand that we are doing mass scaling to only decrease the simulation time for the current model.

6. Debugging:

1. Include files are not included properly while running the simulation error showing no elements and nodes are present in the input files. To correct the issue again the files are included properly and the file is checked for duplicate nodes and elements and the simulation ran correctly.

2. While renumbering the nodes and other keywords files should be saved properly if the files are not saved properly it will create an error while running the simulation.

RESULTS AND DISCUSSION-

Von-mises stress plot-

This stress plot is taken on one of the elements of the blade where the impact takes with the bird at every time, but the stress peaks and reaches a

value of 0.04821 Gpa at the (time of 2.2 ms )moment of impact and drop to a value of 0.01 Gpa at the end of the simulation.

EFFECTIVE STRESS PLOT-

An element 508679 of the blade at the impact zone is taken to plot the graph of v-m stress. From the graph, it is observed that the v-m stress induced in the element is maximum and reaches a value of 0.06 GPa at around 0.5 ms which is more than the yield stress value of 0.013362 GPa of the blade material. Hence, the blade is damaged.

STRAIN-

EFFECTIVE PLASTIC STRAIN PLOT-

From the graph, it is observed that the Effective plastic strain induced in the element 508679 is maximum and reaches a value of 0.056 at time 0.6 ms during the impact and remains the same till the end of the simulation. Hence, the blade is deformed.

ENERGY PLOTS-

From the energy plot graph, it is observed that the kinetic energy is reduced during the time of the bird striking the blade of Aero Engine. The internal energy is increased due to the decrease in kinetic energy. The hourglass energy remains 0 during the entire time of the simulation since we are using the ELFORM 16 (Fully Integrated Element Formulation) for the blade and bird also we are using the *Control_Hourglass to reduce the hourglass effect. The total energy remains constant throughout the simulation.

Matsum energy data plot for the blades From the energy plot graph, it is observed that the kinetic energy is reduced during the time of the bird striking the blade of Aero Engine. The internal energy is increased due to the decrease in kinetic energy. The hourglass energy remains 0 during the entire time of the simulation since we are using the ELFORM 16 (Fully Integrated Element Formulation) for the blade and bird also we are using the *Control_Hourglass to reduce the hourglass effect. The total energy remains constant throughout the simulation.

CONCLUSION-

1) The keyword file to simulate a bird strike on an Aero Engine is created by following the necessary conditions and requirements.

2) In the simulation, the blades at the impact zone are damaged and deformed.

3) Mass scaling approach can be adopted to reduce the runtime with the optimum value of DT2MS.

4) Learned to create and organize as well as debug the input keyword files similar to a professional setting when dealing with large models and multiple people working with the same model simultaneously.

LEARNING OUTCOME-

1. LEARNED HOW TO DO A EXPLICIT ANALYSIS FOR A AERO ENGINE WHEN A BIRD STRIKES IT.

2. LEARNED ABOUT MASS SCALING AND HOW WE CAN REDUCE SIMULATION TIME.

3. THIS PROJECT THOUGHT ME HOW WE CAN INCLUDE DIFFERENT FILES TO RUN A SIMULATION.

4. LEARNED THE THEORY BEHIND DOING A EXPLICIT ANALYSIS AND ABOUT THE BIRD IMPACT TEST ON THE AERO ENGINEB BLADES.

FILES LINK-

https://drive.google.com/drive/folders/11AnpbAsM867Xsw3DQk6D760mVP4sGxsy?usp=sharing