06.06.2011 Page 1 VECOM Suppliers Workshop: Vehicle Concept Modeling in the Automotive Sector. NVH CAE concept modeling and optimization at BMW. 06.06.2011 VLEVA, Brussels Page 2 NVH CAE concept modeling and optimization. Overview. - Introduction to the BMW Group and the structural dynamics and vibrations team. - Global static car body stiffness modeling and optimization with Beams and Shells concept models. - Full vehicle vibro-acoustic comfort modeling. - Structural intensity modeling. - Full vehicle vibration comfort simulation using multibody simulation models - Aero-acoustic modeling. 1
Page 3 NVH CAE concept modeling at BMW. Introduction to the BMW Group. BMW Group brands Minii BMW Rolls-Royce R BMW Motor-cycles Husqvarna Headquarters Munich Production & assembly FIZ R&D centre in Munich Page 4 Introduction to the team. Vehicle architecture and integration Acoustics and vibrations Structural dynamics and vibrations Targeting, analyzing and monitoring static and dynamic car body stiffness and vibration levels for optimal full vehicle NVH performance throughout the complete development phase. Early-phase FE car body concept modeling and optimization. Static car body testing, modal analysis and vibration comfort measurements of complete vehicles, car bodies and components. local and global car body static stiffness. natural frequencies and mode shapes. Local dynamic stiffness at car body connection points sensitivity analysis based on modal data. FE optimization of the car body structure. analysis of panel vibrations (ERP). 2
Page 5 Activities throughout the development phase. Project phase/tools: Concept phase Development phase Series production MB/FEM Simulation Prototypes and concept cars Hybrid modelling (Assembly and substructuring) Plant quality monitoring Testing (Modal analysis, holography, 4-poster...) Page 6 Beams and shells FE concept models original beam cross section equivalent standard cross section H B t 2 optimized equivalent cross section t 1 First functional assessments of car body concepts Goal of the optimisation is to reach a minimal car body weight... considering functional design targets for the complete car... by varying the constructed space... using the beam cross section dimensions height, width and plate thickness as design variables... while respecting design constraints e.g. package constraints 3
Page 7 In the past: Cross Section substituted with equivalent Beam Library property dim1 dim2 dim4 dim3 Desvars: dim1 dim4 State of the art: Exact geometrical description with Nastran PBxSECT w t(1) t(3) h t(2) Desvars: w, h, t(1) t(3) Page 8 Beams and shells FE concept models. Example with ABCS-modelling. original beam cross section geometry! 4
Page 9 Beams & shells FE concept model Optimization, Nastran sol200 (10 load cases, well over 1500 design variables) Nastran f06 results file Optimization history Optimization results crash statics dynamics freq. separation steering roll-over wheel Nastran.f06-file statics dynamics freq. sep. crash roll-over steering weight wheel statics dynamics freq. sep. crash roll-over steering weight wheel Page 10 Design model: creation of large number of desvars, geometrical responses and constraints with OptiCenter Application region Desvars for outer dimensions and wall thicknesses Geometrical responses and constraints 5
Page 11 Design model: Creation of functional responses, constraints and objective function with OptiCenter Responses and constraints for dynamic stiffnesses Responses and constraints for static stiffnesses Weighting factors Page 12 Post Processing: Visualization of optimization results Changes in construction space Changes in wall thickness 6
Page 13 Application case: BMW 3-Series with Al car body Material switch Steel Al Page 14 Application case: BMW 3-Series with Al car body Change in weight and functional performance after one-to-one material switch Masse [kg] Statik [%] Dynamik [Hz] 11,9 64,4 E90 Alu E90 Alu optimiert 235,1 7
Page 15 Application case: BMW 3-Series with Al car body Aluminum car body optimization Target: Equal global static and dynamic car body stiffness in comparisson with steel body. Design space: full car body beam structure (red) Geometric constraints: construction space max. +50% Page 16 Application case: BMW 3-Series with Al car body 8
Page 17 Application case: BMW 3-Series with Al car body Page 18 Application case: BMW 3-Series with Al car body Rocker panel Roof carier 9
Page 19 Application case: BMW 3-Series with Al car body Masse [kg] Statik [%] Dynamik [Hz] 7,2 1,2 11,9 64,4 E90 Alu E90 Alu optimiert 235,1 168,6 At the cost of construction space! in what areas is it usefull to introduce light weight materials? Page 20 Full vehicle vibro-acoustic comfort. Sound sources. Target of NVH engineering: optimal vibro-acoustic comfort for driver and passengers. Wind excitation Engine Exhaust Gearbox Drive shaft and differential Road excitation 10
Page 21 Full vehicle vibro-acoustic comfort. Vibro-acoustic car body transmission paths. Important aspects: SPL at driver s ear local dynamic stiffness at excitation points. p panel radiation acoustic field vibro-acoustic coupling Panel radiation Car body excitation Page 22 Full vehicle vibro-acoustic comfort. Local dynamic stiffness FE modeling. Local vibration due to harmonic load at engine mounts (225 Hz) 11
Page 23 Full vehicle vibro-acoustic comfort. Local dynamic stiffness FE modeling. Local resonance problem Point mobility engine mount x-direction: Red z-direction: Blue Target: Black Page 24 Full vehicle vibro-acoustic comfort. Local dynamic stiffness FE modeling. x-richtung y-richtung z-richtung 50 100 100 200 200 400 50 100 100 200 200 400 50 100 100 200 200 400 Frontal Strut Tower +12-2 0 +9 +18 +4 +7 +7 Front Axle Mount, Front Screw -1 0 0 +12 +12 +12 +15 +5-4 Front Axle Mount, Middle Screw -4-6 -6 +2 +2 Target violation in db Front Axle Mount, Rear Screw Engine Mounts -2-3 -2-3 -4-4 +10 +4-1 +3-5 +6 +6 +2 +11 +2 +12 Strong targetviolation Target violation, check significance Gear-box Bridge Drve Shaft Mount Rear Axle Mount, Front Screw Rear Axle Mount, Rear Screw Rear Shock Absorber 0 +2 +9-2 -4-3 +6-2 -10-8 +7 +1-7 +5 +10 +4 +7 +12 +11 +7 +4 +12 +12 +3 +17 +11 +22 +7 +10 +6 +12 +17 +6 +7 +2 +12 +3 +10 0 OK. Rear Strut Tower Tunnel bridge screw +7-22 +4-4 0-9 0 +2 +2 +1 +1 +4 +9 +10 +5 +6 0 +6 12
Page 25 Full vehicle vibro-acoustic comfort. Panel vibration FE modeling Radiated power. Example of Panel Vibration at 60 Hz Page 26 Full vehicle vibro-acoustic comfort. Panel vibration FE modeling Radiated power. Example for weak point in floor panel (excitation at gear-box bridge) Sum Floor Panel Magnitude Frequency 13
Page 27 Full vehicle vibro-acoustic comfort. Vibrational energy flow through the car body. How does the energy flow through the car body from excitation point towards the radiating panels? SPL at driver s ear Panel radiation? Page 28 Car body excitation Structural intensity analysis. Time Domain Measurements. High Resolution Measurement: Example: Tube Frame Excitation 1 2 3 4 14
Page 29 Structural Intensity Calculation. Time Domain Calculation. Simulation Vibration Energy Flow. Page 30 Structural Intensity Calculation. Example Frequency Domain: Vehicle Underbody. Initial configuration, real STI, detailed view. 15
Page 31 Full vehicle vibration comfort simulation. Multi body simulation toolbox. car body (rigid) car body (flexible) engine / gearbox drive train exhaust system (flexible) Hinterachse Vorderachse Tires Page 32 Full vehicle vibration comfort simulation. 4-poster test simulation. Torsion load case rigid body flexible body Displacement (mm) Vibration response at customer relevant car body positions Frequency (Hz) Bending load case rigid body flexible body Acceleration (m/s 2 ) Frequency (Hz) 16
Page 33 Full vehicle vibration comfort simulation. Engine idle comfort simulation. [Hz] 16 14 13-15 15 Hz Engine roll 12 10 8 6 4 2 0 9-11 Hz 5-7 Hz 1,5. MO 1. MO 0,5. MO engine idle rpm 550 700 0 200 400 600 800 [1/min] Vehicle lateral Engine lateral / roll Vehicle roll on tire springs Page 34 Aero-acoustic modelling. Isosurface of constant velocity (BMW 3series). 17
Page 35 Aero-acoustic modelling. Streamlines of the airflow around the car body. Page 36 Aero-acoustic modelling. Streamlines of the airflow around the car body. 18
Page 37 Aero-acoustic modelling. Sound pressure level on the car body surface. Page 38 Aero-acoustic modelling. Sound pressure level on the car body surface. 19
Page 39 Thank you for your attention. Page 40 Optimization result Global static and dynamic stiffness Targets for statics not specified Modell A Delta Target M Modell B Delta Target Dl Delta A-B Tunnel Rocker panel Tail center Tail longitudinal carrier Wheel house torsion Engine mount torsion Front vehicle cross bending 1. bending 1. torsion front vehicle torsion 20
Page 41 Optimization history Global dynamic stiffness target frequency target frequency and feasibility region indicator final frequency and mode number initial frequency frequency history weighting factor Page 42 Optimization history Global static stiffness target stiffness final stiffness and FE node number target stiffness and feasibility region indicator initial stiffness stiffness history 21
Page 43 Optimization history Weight weight history reference weight Page 44 Optimization history Pseudo-Crash stress level reached in maximum loaded element and element number max. allowable stress level (steel: 400 N/mm²) and feasibility region indicator 22
Page 45 Optimization history Mode separation final frequency separation in Hz with mode-numbers of modes involved minimal frequency separation in Hz between two selected modes and feasibility region indicator Page 46 Optimization history Steering wheel impedance maximum normalized amplitude of steering wheel FRF normalized steering wheel FRF amplitude by excitation between 10 and 40 Hz 23