Abstract
The article is about the future of NVH. First, article narrates the meaning of NVH and then tells about the future improvements in its technologies. It discusses the role of NVH in a vehicle that how much it is important and then further tells its advantages for making a vehicle smoother and quieter. This article also examines the conventional NVH practices and the future improvements. Then it ends with the example of Ford motor company. Then the article further reflects the achievements of TI Company. It also discusses in details about CAE and its role and then its future progress.
NVH situates for noise vibration and harness. It is the medium of searching the foundation of a noise, vibration or shake. Noise is generally taken as unwanted sound, vibration can be felt instead of hearing and harshness describes the relentlessness that is linked with unwanted sound. NVH can also be associated with sound quality analysis that absorbs sharpness, loudness and some other levels (S. Vidyasankar, 2005).
Sound and vibration have big impact on environment and all of us. They affect everything like the construction of our buildings, the safety of our vehicles etc. The cars go through some tests to determine that they can bear the mechanical shocks. So some safety equipments like airbags are good that use vibration transducers which can work as critical censors. These censors indicate danger and activate right action (S. Vidyasankar, 2005).
It is appreciating that everywhere whether it is a science community, any sector of industry or in our daily life; people take care of sound and vibration and manage their dangerous effects. Lawmakers, consumers, health and professional experts are very much keen about noise that is a handy contaminant. Contemporary studies give us a chance to understand it in well manner so the new technologies can be developed (S. Vidyasankar, 2005).
Now this has become a primary goal for any automotive industry to reduce NVH. Making of the quietest and smoothest cars has become competitive. Many strict laws are being introduced in automotive industry where especially noise norms are being set for automotive industry.
It is being observed that the demand for NVH test equipment is increasing and the market for this has good scope. NVH is considered to be an essential part of any product development that collects all the processes as validation, design, predictive analysis development. NVH test equipment has noise dosimeters, shakers and controllers, analyzers, sound level meters and microphones (S. Vidyasankar, 2005).
Due to new technologies that are emerging everyday, the PC based analyzers are being developed. Some multi channel NVH data acquisition systems, anechoic test cells, acoustic holography devices, laser vibrometers all are being developed.
Before discussing the future of NVH in details, the applications of NVH test equipment should be understood. Its applications are following (S. Vidyasankar, 2005):
- Testing of Sound Power
- Testing of Engine Noise Vibration
- Testing of Acoustic Performance
- Testing of Pass by Noise
- Testing of telephone
- Occupational Health and Safety
- Testing of Structural Vibration
- Environmental Noise Measurements
Now we talk about future techniques for high frequency NVH. It can be observed that automotive manufactures are facing too much market pressures for fulfilling consumer demands that need more advanced designed vehicles with high technologies like for making them ride comfort and quiet. A vehicle’s good characteristics help in making it more competitive product that is manly for luxury market. Some major improvements in vehicle sound and vibration have happened. Some other NVH reductions can only happen when there is an investigation related to design with extra reliability and exactness (Stan Posey et al).
Now it is assumed that NVH model parameters develop more than common modeling practice so that NVH modeling with higher frequencies can catch better audible range for additional NVH reduction. The common international practice for NVH analysis on BIW that is body-in-white has frequencies in between 250HZ and 300HZ. Now many automotive companies are thinking to increase this limit up to 600Hz in the coming few years. These estimations for higher frequency modeling have some concerns related to numerical accuracy and apt job turn around (Stan Posey et al).
History says that automotive industry has spent in vector systems to fulfill the demands of CAE applications to encourage the high-performing computing that is HPC. NVH needs high quality HPC resources as memory bandwidth, storage, CPU. It also requires I/O rates for TBs to perform a single NVH job.
Now the concern is how the automotive industry is going to fulfill the needs of the NVH modeling. Currently many automotive companies are shifting from vector to RISC that is being considered most cost effective. Actually this transfer happened in 1995. This shift now has produced new algorithms and methods that are currently executed in almost all automotive HPC applications excluding NVH (Stan Posey et al).
Currently there is a need of vector class system for effective job turn around. The present NVH techniques don’t fulfill the requirements for conventional NVH modeling targets for the future with the coming vector systems. The vector architectures are going to be hit by these model constraints. The conventional NVH analysis method of modal frequency response that is MSC/NASTRAN SOL 103 and/or 111 is used by every automotive supplier (Stan Posey et al).
Currently an automotive body’s model sizes ranges from 1.5M DOF having 1250 modes which is supposed to be the most effective execution on a vector class of system. Now these sizes are increasing from 3M to 5M with more than 2500 modes. The following profile describes the behavior of some particular MSC/NASTRAN jobs that are related to NVH analysis (Stan Posey et al):
MSC/NASTRAN and NVH analysis:
Computer Tasks Memory Cycles CPU Cycles
Sparse Direct solver 7% 93%
Lanczos Solver 60% 40%
Iterative Solver 83% 17%
1/O Activity 100% 0%
The profile tells the importance of balanced system. As in compare to RISC systems, the vector architecture propose better rates of memory bandwidth, that is why they are the most preferential architecture for conventional NVH.
For the automotive industry, one well recognized style is the extensive broaden application of finite element analysis that is FEA. It is an application that needed vector HPC resources just four years ago for any practically sized model. Now-a -days it is executed on desktop computer systems (Stan Posey et al).
At present direct sparse solvers are reasonably executed in every commercial FEA package and their performance is ten times better than the previous profile solvers. Sparse solvers contribute in reducing storage requirements and conduct meaningful FEA modeling on desktop systems. This penetration in sparse solvers increased the growth of commercial FEA software that could be used as a significant instrument for mechanical designing for automotive industry.
Now the future demands the similar kind of penetration to accomplish the same design from the point of view of an automotive industry. The growth in high frequency model sizes presents great commercial benefits to automotive manufacturers. This penetration also demands improvement in the performance of Lanczos algorithm or a substitute of it. It also requires the same kind of performance improvement with same numerical accuracy.
All these kinds of prospects have been examined by MSC and SGI at the time the growth of the MSC/NASTRAN release, 70.7. It has been found that its performance is growing year by year. It also shows good parallel scaling for conventional NVH modeling. The following table highlights it (Stan Posey et al):
SOL 103 MPI Parallel for:
Processors Elapsed Seconds Parallel Speeds Up
1 61,595 1.0
2 36,734 1.7
4 24,501 2.5
8 19,474 3.2
16 14,660 4.2
Two prospective substitutes to Lanczos have been recognized for future modeling requirements. One is about transferring from modal direct frequency response and the other is about new algorithm called Automated Multi-level Substructuring. These both are based upon MSC/NASTRAN. This parallelization is executed for the independent frequency where each does the same type of work and provides high-quality balance. The next example shows the model xlifr that is a body of vehicle with536K DOF that has 96 frequency steps. In the second example the model has 525K DOF and 2714 modes to analyze 96 frequency steps. And the following example shows the results of same performance between SOL 111on a single processor Cray T90 and four processor SOL 108 that has better density than today. It is assumed that it can be more representative of future modeling performances (Stan Posey et al).
The results are very positive which are based on the performances with improved solution accuracy.
SOL 108 MPI Parallel for (Stan Posey et al):
Processors Elapsed Seconds Parallel Speed-Up
1 114.264 1.0
2 57,282 2.0
4 28,887 4.0
8 14,883 7.8
16 8,070 14.2
32 5,047 22.6
Comparison with Cray T90/SOL 111 (Stan Posey et al):
Processors Elapsed Seconds Parallel Speed- Up
1 120,720 1.0
2 61,680 2.0
4 32,160 3.8
8 17,387 6.9
Now it can be seen that the need of future modeling for trimmed body NVH is not realistic with the conventional performance. It also can be seen that a highly parallel direct frequency response method can be a better substitution with same numerical accuracy. Automotive industry can shift from vector to most cost effective RISC that is suggested by the direct frequency response method. It is also assumed that the cost- effective RISC will encourage the quick development of design optimization. It will also be easy to practice multi-discipline optimization. The NVH solution like direct frequency response is very important to those engineers who would be able to practice this model critically.
The automotive industry conducts the high level models today for audio response but new facility with high direct frequency response will surely encourage turbo machinery, aerospace, and other fields to judge the audible improvements to their designs. Some of the analyzers believe that this high cost effective NVH methodology that uses direct frequency response has the capability to transfer modeling practices for manufacturing on international basis (Stan Posey et al).
Ford Motor company’s researches show some improvements in its designs and engines’ sound quality. They have made remarkable improvements in their NVH in many of its 2002 engines that includes the 5.4 liter Triton V-8 and 3.0 liter Duratec V-6. The company is concentrating on some future vehicles like Lincoln Aviator with 4.6 liter V-8 engine.
According to John Koszewnik who is the chief engineer of V-Engine engineering over the past ten years, powertrain refinement has become the biggest area. Now the engines are much quieter than before.
It has been the goal for the engineering team to reduce NVH on the 5.4 liter Triton V-8. They have felt that customers demand the quieter and smoother engines. Ford has changed many of its models to get customer’s satisfaction. In its models like Ford Ranger, Ford Taurus, Ford Windstar and Ford F-Series Superduty, it has made changes between four to twelve percent.
According to Tolben G. Nielson, Business Manager Automotive the Pulse NVH vehicles are very important elements to help automotive customers.
A case study done at TI Automotive Global Test Group at Caro, Michigan says that this group applies two PULSE systems for noise and vibration testing. Almost twelve years back, the NVH laboratory at Caro was constructed. TI automotive that is fully dedicated to customer’s satisfaction has various international certifications for its quality system like ISO 9000, VDA 6.1, QS 9000, EAQF and the most recent TS 16949. Its Global Test Group is supposed to be the company’s top-notch systems with its laboratories all over the world. Its policy is to constantly increase and improve its test facilities. The laboratory’s hemi-anechoic room is so big that it can contain a full vehicle. It is not only the house for the products of Caro plant, but also it tests the products from all over the world. The demand of testing is growing as TI automotives’ customers need improved levels of test data. Specifications related to fuel delivery systems are continuously growing.
There are many sound and vibration expertise at Caro. According to Kirk Doane, the Test Engineer at Caro, all the products should meet with their high specifications before using for productions. He favored the purchase of PULSE. Brian Kukla, the Senior Technician in the NVH laboratory tries that they get reliable data to extend IT resources for NVH lab. For collecting data and using it anywhere comfortably PULSE has been proved very reliable as it is compressed and flexible. It is very easy to use. The TEDS (Transducer Electronic Data Sheet) lessens the time and risks of mistakes.
According to Brian systematic tests are made on everything from a single item to full vehicle.
The NVH laboratory includes the following test data:
- TI Automotive uses the test data in R and D applications for the development of new product
- Batch Testing is done to check the reliability of its existing products
- End-of Line production Testing
- Durability Testing for pressure, pulse, vibration
- Benchmark testing of Competitors products
Here NVH specifications are developed for fluid delivery systems. The measurement of pump noise is on the whole vehicle, which is kept in the hemi-anechoic room. For this two microphones are used: one is kept by the driver’s headrest and the other is near the passenger’s headrest at the back of the car. The tests are made with both the engines and the fuel pump that run with same speed.
Some other kind of tests like checking the natural resonance frequency of a fuel tank or the vibration of hotspot are made by the use of an accelerometer that is connected to PULSE. So basically here role of PULSE has been very significant that has made all the tests related to NVH more reliable, which are fully devoted to customers’ whole satisfaction. The NVH laboratory at Caro has very good future and it is expected that it will be certified to A2LA.
At present the growing demand of commercial pressures need more intellectual testing to build up and distribute reliable products. For which CAE procedures like multi body dynamics (MBD), fatigue life analysis (FLA) and finite element analysis (FEA) are combined with some other testing methods to receive clear engineering process (Robert J. Plaskitt and Christopher J.Musiol, 2002).
Fatigue Analysis: It includes three basic methodologies: the strain-life method; the stress life method and linear elastic fracture mechanics. The strain-life method includes elastic plastic methods. The stress-life method is related with catastrophic failure and Linear elastic fracture mechanics predicts the quickness of pre-existing cracks’ growth.
Fatigue results say the terms of the numbers of cycles. The sensitivity is serious because of the relationship between load and life. The following figure illustrates the exploitation of some processes by some industries depending on their needs (Robert J. Plaskitt and Christopher J.Musiol, 2002):
Multi Body Dynamics (Robert J. Plaskitt and Christopher J.Musiol, 2002):
:
This model can be used to replicate vehicle behavior. These kinds of models are very commonly used in a development program to deliver some important features of the vehicle vibrant behavior. In an automotive industry these models are often used to handle uniqueness.
Recently it is used in combination with FEA as part of CEA durability process for semi and fully analytical modeling with FEA results by being the part of fatigue analysis. Semi-analytical methods have physical measurement to support loads. Fully analytically loads need full vehicle models that should have a digital representation of the surface profile. This method is mainly used for relative durability calculations to choose designs and to examine module change effect. Most are the companies thinking to apply this method in place of semi-analytical method so they can get rid of any physical data. The physical measurement requires ‘time histories’. They are the input to CAE durability. During whole durability process ‘time histories’ are considered in many different ways. Before using time histories as inputs to a multi body dynamic model, they require variation. They need polarity (Robert J. Plaskitt and Christopher J.Musiol, 2002).
Finite Element Analysis:
FEA is a deep-rooted CAE analysis tool. It is extensively used in all engineering industries. It is used to calculate the stress distribution for the whole component. It is a perfect predecessor to fatigue analysis. The life at each element can be calculated by joining the linear elastic finite (Robert J. Plaskitt and Christopher J.Musiol, 2002).
Transient time step FEA calculation is needed when the structure shows a non-linear stress. Loading histories are calculated clearly in each time step. This methodology takes too much time when it handles nonlinearities because it needs a complete finite element analysis. A large number of FE models are required by the increasing number of model variants. So it is required to reduce the number of developed models. For example to analyze car bodies, it is not uncommon to develop many models of the car body to fulfill the contradictory analysis requirements for NVH and durability. The great need of NVH consists of exact prediction of global stiffness while the durability requires exact stress in critical areas.
CAE durability means multiple fatigue life analysis for elements within a finite element model. There are three CAE durability methodologies: i) linear static superposition of elastic finite element stress; ii) model superposition combining multi body dynamic stress; iii) the transient time step analysis.
The fatigue analysis methodologies are the same as available to CAE durability and the test engineers. The sole difference is that the first practices loads from the stress that comes by means of finite element analysis and the other from the measured strain histories (Robert J. Plaskitt and Christopher J.Musiol, 2002).
There is a challenge for CAE durability that how to speed up the analysis process. The period that is acceptable for the analysis is about twelve hours that is similar to running the analysis whole night.
To beat these computational challenges, distributed computing with similar processing is required as fatigue life calculation is equivalent to each element. To select these elements intelligently and reduction of time history can help to beat these challenges. Suitable fatigue methods will be introduced to the fatigue life analysis by taking practiced knowledge and executing it within the software. The software will select the most suitable fatigue method for each location and it will also note the choices (Robert J. Plaskitt and Christopher J.Musiol, 2002).
References:
Case Study, IT Group automotive System, http://www.bksv.com/pdf/ba0527.pdf
Plaskitt, Robert J. and Musiol, Christopher J., 2002, Developing a Durable Product, Pp 1-24, ASAE D # 26, Distinguished Lecture, Agriculture Equipment Technology Conference, Kansas City, Missouri
Posey, Stan, Future Techniques for High Frequency NVH, http://www.mscsoftware.com/support/library/conf/auto99/p00799.pdf
Vidyasankar, S., 2005, what is NVH, http://www.frost.com/prod/servlet/market-insight-top.pag?docid=35405241
Ford puts Emphasis on NVH, Refinement and Sound Quality, http://media.ford.com/newsroom/release_display.cfm?release=12090
Evaluate the Sound before you build the Vehicle, http://www.bksv.com/3895.asp
