nvh analysis of car cabin compartment

ISSN: 2455-2631 © July 2018 IJSDR | Volume 3, Issue 7

IJSDR1807053 International Journal of Scientific Development and Research (IJSDR) www.ijsdr.org 317

NVH Analysis of Car Cabin Compartment

Sidramappagoud Patil1, G. U. Raju2, Chetanakumar Chavan3

Research Scholars1,3, Associate Professor2

School of Mechanical Engineering

KLE Technology University, Hubballi, Karnataka

Abstract: The lightening of the vehicles body structure aggravates the noise, vibration and harshness (NVH). Since the noise,

vibration and harshness performance affect the overall image of vehicles, therefore now these are considered as important

factors in the entire vehicle design process. Now days, the global approach of vehicle’s quality is important by its interior

noise as well as vibration characteristics. NVH is a process that desires the integration of customer device confidence with

the design and improvement process. The surface modelling is accomplished for the vehicle body in CATIA and meshed in

HYPERMESH tool. Then, modal analysis in a frequency range between 0-50 Hz is done by NASTRAN. By observing both

natural frequency and the mode shapes it is found that the Eigen frequency and the working frequency (50Hz) are not same,

so resonance is not occurring for this condition. In response analysis (steady state dynamic analysis), Sound pressure level

is within 60 dB in all four responses ID. Hence, NVH analysis for car cabin compartment is satisfactory.FEA model chosen

gives good results related to NVH analysis. Analysis results of deflection are compared with theoretical results, it is found

that percentage error are in permissible limits to validate the model. We are expressive into a time of maximum awareness

of environmental aspect as well as cars that reflect a genial life style and aesthetic.

Keywords: Car cabin compartment, HYPERMESH, NASTRAN, Modal analysis, Steady state dynamic analysis

________________________________________________________________________________________________________

1. INTRODUCTION

Now days, the global approach of vehicle’s quality is important by its interior noise as well as vibration characteristics. Present

day’s driver has come to forecast smooth and peaceful ride in entire operating condition. So the interest on NVH characteristics has

turned into popular. When vehicles noise as well as vibration eclipse the driver expectation, hence the vehicle’s market comedown.

NVH is a process that desires the integration of customer device confidence with the design and improvement process. Noise,

vibration and harshness are examined few of the huge challenges that automotive engineers look in industry and are one of the huge

customer warranty objection. Interior NVH approach with noise and vibration accomplished by the occupier of the cabin, while

exterior NVH is generally worried with the noise diffuse by the car. The modern design procedure is starting to study NVH problems

thought the entire design process. This includes integrating extensive design, simulation, evaluation and optimization methods

inside the design process to secure both noise and vibration satisfaction. The society for automotive engineers (SAE) is a series of

teaching courses attention on important areas inside the automobile that provides to the problems that consumer with their cars.

Noise is defined as an unpleasant sound generated by any vibrating body. The terms used to describe the noise are as below in NVH

applications. Road noise exists, while driving on a roughly paved roads or gravel. This type of noise is continuous and has a constant

character. If two sound sources of same pitch and slightly different frequency over laps each other, occurrence of beat noise will be

seen. Brake squeal occurs when friction is created between the brake components during braking. Droning is experienced while

driving in to a tunnel at high speed, or climbing to a high altitude caused due to the change in atmospheric pressure. The human

audible range of sound varies from 20 Hz to 20000 Hz. Shake occurs at the steering wheel, seat and annoying vibration at the floor.

Vibration that causes the steering wheel to oscillate and sometimes even the body of the vehicle vibrates laterally. Shudder transmits

through brake hydraulic lines to steering system, suspension system and brake pedal. Pedal pulsation generates during application

of brake. The noise, vibration and harshness (NVH) accomplishment influence the total picture of car. These are expressed as

valuable factors in whole car design process, commitment to develop the model for safety and comfort intention. Carry out Beat,

Brake squeal, Shimmy, Shudder analysis and reduce the vibration of car.

2. MATERIAL PROPERTIES

2.1 Properties of steel

The important element of choosing material especially for frame is broad collection of characteristics like as chemical, thermal and

mechanical resistance, comfort of production and lifespan. We need to select a material along these Features; Steel is the best

valuable choice. There is more improvements in irons and steels from proceed set of decades that fashioned the steel more light-

weight, powerful, stiffer also developing other performance features. Decline in a frame structure that has better strength and

structural fulfillment. Equivalent mass decrement also other advantage managed for doors, hoods, and the hatchbacks. The prime

explanation behind utilizing steel in the body structure is its characteristic capacity to retain affect vitality in a crash circumstance.

2.2 Properties of structural steel

Structural steel is Greater flexibility and Adaptability of body work to development of use, Booming useful life of vehicle. Structural

steel has High stiffness, toughness, and ductile properties.

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2.3 Properties of glass

The significance attributes of glass are straight forwardness, warm opposition and synthetic obstruction and breaking opposition.

Contrary to strong collections of crystalline structure, glass has no characterized liquefying point. It ceaselessly changes from the

strong state to the plastic state.

Table 1: Material properties of model

Material Young’s Modulus

GPA

Poisson’s Ratio

Density

Kg/m3

Steel 210 0.280 7800

Structural steel 210 0.280 7800

Glass 80 0.250 2800

Fig 1: Material view of model

3. MESH QUALITY

The grid of a finite element system represents a geometric object as a set of finite elements. In computational arrangements of

fractional differential conditions, fitting is a discrete portrayal of the geometry that is associated with the issue. Basically, it segments

space into components (or cells or zones) over which the conditions can be approximated. Zone limits can be allowed to make

computationally best molded zones, or they can be settled to speak to interior or outside limits inside a model. Cross section quality

can be definitively dictated by in view of the rate of joining, arrangement precision and CPU time required.FE demonstrating is

done in HYPERMESH V12 programming since it is devoted programming for finish pre-preparing action, for example, coinciding

(Discretization) of complex geometry, material properties appointing, sectional properties doling out and applying limit conditions

and so on can finished no sweat.

Fig 2: Mesh quality of model

Table 2: Mesh quality of model

Element Type War

page

Jacobian Aspect

Ratio

Skew Min

length

Max

length

Min

angle

Max

angle

CQUAD 05 0.7 5 60 7.5 20 45 135

CTRIA NA NA 5 60 7.5 20 20 120

The FE model quality has great influence on the results and computational efficiency of FE analysis.

Grid density and Boundary layer mesh.

Adjacent cell length/volume proportions.

Skewness.




4. DIFFERENT VIEWS OF CAR CABIN COMPARTMENT

Fig 3: Property view of model Fig 4: Isometric views of vehicle trim body

Fig 5: Trim connection overview of model Fig 6: Sealing of model

Sealing or weather strip purpose RBE3 and RBE2 celas are used

Stiffness of spring selected as 10 N/mm based on data hand book

Contact method used for sealing using connection using RBE2

RBE2 – uniformly to dependent nodes

RBE3 – load distribution depend on distance

5. ANALYSIS OF CAR CABIN COMPARTMENT

5.1. Analysis performing on car cabin compartment

In the car cabin structure we are interested to know about the behaviour of the NVH. So we have performed the following analysis

on NVH of car cabin compartment.

1. Modal analysis

2. Response analysis(Steady state dynamic analysis)

5.2. Modal analysis of Car cabin compartment

Modular examination is the dynamic investigation, completed to discover the dynamic conduct of the structure. The objective of

modular examination in basic mechanics is to decide the common mode shapes and frequencies of structure amid free vibration.

Usually to utilize the limited component strategy (FEM) to play out this examination since, as different estimations utilizing the

FEM, the protest being broke down can have self-assertive shape and the aftereffects of the counts are adequate. The kinds of

conditions which emerge from modular investigation are those found in Eigen frame works. The physical elucidation of the Eigen

esteems and eigenvectors which originate from tackling the framework are that they speak to the frequencies and comparing mode

shapes. Here and there, the main wanted modes are the least frequencies since they can be the most conspicuous modes at which

the protest will vibrate, ruling all the higher repeated modes.

5.2.1. Output Extracted From The Modal Analysis

Mode shape

Natural frequency and

Assembly integrity

5.2.2. The car working frequency

The engine runs at 3000 rpm

Frequency =3000

60 = 50 Hz

So to carry out modal analysis we need to concentrate about working frequency. Natural frequency or Eigen frequency should not

fall with working frequency.

5.2.3. Boundary condition

The modular examination is completed in free- free condition so the car cabin compartment is able to move in all direction i.e. all

the 6 degrees of freedoms are not constrained.




5.2.4. Mode shapes and Frequency of modal analysis

Fig 7: Mode 1 Fig 8: Mode 2








5.2.5. Natural frequency of modal analysis

Table 2: Natural frequencies of modal analysis

Mode No Working Frequency

(Hz)

Natural frequency

(Hz)

1 50 0.000115

2 50 0.000072

3 50 0.000053

4 50 0.000025

5 50 0.000056

6 50 0.000064

7 50 12.0

8 50 15.7

9 50 16.3

By observing both natural frequency and the mode shapes it is concluded that the Eigen frequency and the working frequency

(50Hz) are not same, so resonance is not occurring for this condition.

5.3. Steady state dynamic analysis of Car cabin compartment

In steady state dynamic analysis we are concentrating sound pressure level with respect to unit excitation of four responses Id.

5.3.1. Boundary condition

In this analysis, both the front as well as rear shock mountings are constrained in all the direction i.e. all six degree of freedoms is

fixed. Load was applied at the position of the driver (Response ID 2000001) locating in the car cabin compartment. In this analysis

unit (1N) force is applied at the response ID 2000001, response ID2000002, response ID 2000003, response ID 2000004 and we

have to reduce the sound pressure level below 60 dB with respect to working frequency 50 Hz with respect to all response ID.

Fig 14: Boundary condition for model

Table 3: Sound pressure levels for Response ID

Response ID Speed (RPM) Frequency (Hz) Sound pressure level

(dB)

2000001 3000 50 56

2000002 3000 50 56

2000003 3000 50 58

2000004 3000 50 58

From the above it is observed that sound pressure level is within 60 dB in all four responses ID. Hence, NVH analysis for car cabin

compartment is satisfactory. FEA model chosen gives good results related to NVH analysis.




6. RESULTS AND DISCUSSION

6.1. Modal analysis of car cabin compartment

i. Results

1 2 3 4 5 6 7 8 9 10 11 12

0

5

10

15

20

25N

atur

al fr

eque

ncy,

Hz

Modes Fig 15: Modes v/s Natural frequency

ii. Conclusion:

By observing the graph, it is found that first six modes are having approximately zero frequency because analysis is

executed for free- free condition i.e. the car cabin compartment is able to move in all six directions. Also, from the analyses

it is found that Natural frequency and working frequency are not matching with each other. Therefore resonance is not

occurring and the car cabin compartment is safe.

6.2. Steady state dynamic analysis of car cabin compartment

i. Results

Fig 16. Sound pressure level for Response ID 2000001







From the above it is observed that sound pressure level is within 60 dB in all four responses ID. Hence, NVH analysis for car

cabin compartment is satisfactory.FEA model chosen gives good results related to NVH analysis.




7. Conclusion

The present study is related to analysis and improvement of a car cabin compartment structure based on NVH behaviour. The

surface modelling is accomplished for the vehicle body in CATIA and meshed in HYPERMESH tool. The quality of mesh is good

enough for analysis of model. Then, modal analysis in a frequency range between 0-50 Hz is done by NASTRAN. By observing

both natural frequency and the mode shapes it is found that the Natural frequency and the working frequency (50Hz) are not same,

so resonance is not occurring for this condition. In response analysis (steady state dynamic analysis), both the front as well as rear

shock mountings are constrained in all the direction i.e. all six degree of freedom is fixed. Sound pressure level is within 60 dB in

all four responses ID. Analysis results of deflection are compared with theoretical results, it is found that percentage error are in

permissible limits to validate the model. Hence, NVH analysis for car cabin compartment is satisfactory.FEA model chosen gives

good results related to NVH analysis.

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nvh analysis of car cabin compartment

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