VIBRATIONAL ANALYSIS OF A MULTIBODY VIRTUAL DUMMY FOR CAR AND MOTORCYCLE USERS Nicola Cofelice*, Roberto Zanni, Davide Locatelli, Alessandro Toso, David Moreno Giner, Jian Kang, Stijn Donders Agenda 1 Introduction 2 MBS model description 3 Results 4 Future activities 1
Virtual Dummy For Vibrational Evaluations AIM OF THE WORK 1. Development of 3D model of virtual human dummy to represent the biomechanical response due to whole body vibration. 2. Validation of a tool to automatically calculate the FRFs of a multibody system created by LMS Virtual.Lab Motion. Frequency domain - Hz Modal analysis Vertical transmissibility SIMULATION Time domain - s Estimation of Vertical transmissibility Agenda 1 Introduction 2 MBS model description 3 Results 4 Future activities 2
Dummy s Structure THE WHOLE BODY The body of the dummy is composed of 5 main sub-systems: 1 spine sub-system; 2 arms sub-systems; 2 legs sub-systems. VALENTINI, P.P Virtual dummy with spine model for automotive vibrational comfort analysis, Int. J. Vehicle Design, Vol. 51, Nos. 3/4, pp.261 277, (2009) Spine Sub-System SPINE STRUCTURE The complete sub-system is made of 33 bodies: Head; 24 vertebrae: from C1 to C7, cervical region; from T1 to T12, thorax region; from L1 to L5, lumbar region; 1 segment to model the sacrum; 7 visceral masses 3
Spine Joints CONNECTIONS BETWEEN VERTEBRAE Vertebrae are connected with revolute joint. CONNECTIONS OF VISCERAL MASS AND VERTEBRAE Visceral masses are connected between the correspondent vertebra with a bracket joint excluding translations into the sagittal plane. Spine Forces SPINE FORCES Vertebrae are connected with the RSDA in order to simulate a real behavior of the spine in the sagittal plane. Visceral masses are connected to the correspondent vertebra with a TSDA, with relative stiffness and damping coefficients. TSDA are also defined between each visceral mass. All elements have a linear behavior (valid for small displacement) Kitazaki, S. and Griffin, M.J. (1998) Resonance behavior of the seated human body a summary of experimental data, Journal of Biomechanics, Vol. 31, No. 2, 12 May 1997, pp.143 149. TSDA = translational spring damper element RSDA = rotational spring damper element 4
Arms and Legs ARMS STRUCTURE (LEFT AND RIGHT) The sub-system is composed of 3 bodies: upper arm, lower arm, hand. LEGS STRUCTURE (LEFT AND RIGHT) The sub-system is composed of 3 bodies: upper leg, lower leg, foot. JOINTS: spherical joints: shoulders, hips revolute joints: elbows, knees bracket joints: wrists, ankles FORCES: Bushing: shoulders, hips (damping negligible) RSDA: knees, elbows (damping negligible) bushing= six degree-of-freedom spring-damper element between two bodies RSDA = rotational spring damper element Parametric Model SIZE, MASS AND INERTIA The dummy is fully parametric and a script in VBA has been created for an easy control of the parameters. This type of structure has been developed for the size and mass parameters. For the parameterizations these correlations are used : Size Mass 5
Automotive Environment STANDARD POSITION The car model is composed by seat, steering wheel and foot rest. 150º Automotive Environment CONNECTIONS BETWEEN CAR AND DUMMY Connections dummy car: 2 TSDA between the ischial tuberosities and the seat; 2 TSDA between the thighs and the seat; 1 TSDA between the vertebra T6 and the seat; 2 TSDA between the feet and the foot rest; 2 TSDA between the hands and the steering wheel. Constant Values for stiffness and damping 6
Agenda 1 Introduction 2 MBS model description 3 Results 4 Future activities Frequency Domain Simulation Modal Analysis 1 - MBS model 2 Linearization Motion equations Solution of eigenvalues-eigenvectors problem Natural frequencies Modal frequency (Hz) Description 2.5 Bending mode of the spine 5.2 Principal Vertical seat-body mode 6.4 Horizontal seat-body mode 9.0 Visceral masses vertical mode 7
Frequency Domain Simulation - Modal Analysis 5.2 Hz Frequency Domain Simulation - Transmissibility Functions 1 - MBS model 2 - Linearization 3 - Transfer Function Input Seat Acceleration Output Pelvis/Head Acceleration x Ax Bu TF ( s) C ( si A) 1 B D y Cx Du 5- Results 5.2 Hz 4- FRF s jw 8
Frequency Domain Simulation - Transmissibility Functions Input Vertical Seat Acceleration Output Vertical Head Acceleration Increasing mass and height Slight Decrease Peak VT Value Decrease Peak Frequency Frequency Domain Simulation - Transmissibility Functions Input Vertical Seat Acceleration Output Vertical Pelvis Acceleration Increasing mass and height Increase Peak VT Value Decrease Peak Frequency 9
Time Domain Simulation - Transmissibility Functions 1 - Vibrational input Random seat Acceleration (time) 2 Time domain Simulation MBS model 4 - Estimate Vertical Transmissibility EVT in _ out ( f ) P in P in out in ( f ) ( f ) 3 Output Vertical Head Acceleration (time) Conclusions A dummy for vibrational analysis within automotive environment has been developed and validate against literature in frequency and time domain. The dummy is completely parametric and the influence of its size and its mass have been investigated The FRF script in VL Motion has been tested 10
Agenda 1 Introduction 2 MBS model description 3 Results 4 Future activities Motorcycle Environment The motorcycle model, is composed from 6 Bodies: - Front Wheel - Rear Wheel - Lower Fork - Upper Fork - Chassis - Swinging Arm and 4 forces elements: - Front suspension - Rear suspension - Contact front wheel-road - Contact rear wheel-road 11
Rider positions 3 POSITION of the rider are now implemented: Standard position High position Low position Open questions for the Motorcycle Environment - Model the connections motorcycle-dummy (hands, feet, seat) Possible solutions: 1) Perform some tests to evaluate the mechanical behavior of the seat 2) Using the bracket joints for the connections (not totally correct, but we overestimate the vibration absorbed). - Evaluation the Vertical Transmissibility (selection of acceleration component) In rider position the acceleration direction of the head is not vertical. - Perform comfort assessment (according to ISO 2631) 12
THANKS FOR YOUR ATTENTION! IS THERE ANY QUESTION? Nicola.cofelice@lmsintl.com 13