Simplified Vehicle Model Research Articles

Effects of seatback angle, seat rotation, and impact speed on injury risk of occupants in highly automated vehicles in frontal crashes

Objective The objective of this study is to examine the effects of seatback angle, seat rotation, and impact speed on occupant kinematics and injury risk in highly automated vehicles. Methods The study utilized the Global Human Body Models Consortium midsize male (M50-OS+B) simplified occupant model in a simplified vehicle model (SVM) to simulate frontal crashes. The M50-OS+B model was gravity-settled and belted into the driver and left rear passenger seat. To investigate the effects of seatback angle, seat rotation, and impact speed on occupant kinematics and injury risk in frontal crashes, a design of experiments (DOE) was conducted. The DOE incorporated four seatback angles (13°, 23°, 45°, and 57.5° about vertical), four seat rotation angles (0°, 25°, 45°, and 90°), three impact speeds (25, 35, and 45 kph), and four frontal crash type configurations. All four seatback angles were used with 0° seat rotation, whereas 13° seatback angle was used with the remaining seat rotation configurations because of cabin fit considerations. Injury risks were estimated for the head, neck, shoulder, thorax, pelvis, and lower extremities for both occupants for each simulation (n=588). Results Statistically significant differences between all the groups within each independent variable category were observed based on the analysis of variance. HIC-based head injury risk and chest injury risk decreased and femur force for the driver and tibia force for the passenger increased with an increase in seatback angles. The head injury risk increased with seat rotation. All the injury risks increased with an increase in impact speed. The driver airbag was able to safeguard the driver from head injuries for all seat rotations except at 90° of seat rotation. Conclusion This is the first vehicle modeling study that collectively looked at the effects of seatback angle, seat rotation, and impact speed along with the interaction of occupants on the risk of injury in frontal crashes. The rear passenger experienced higher seatbelt loads than the driver. More reclined seats decreased head and chest injury risk, but increased driver femur injury risk and rear passenger tibia injury risk. Results underscore the necessity for additional anti-submarining mechanisms and driver airbag designs adapted for the anticipated occupant positions.

Pediatric occupant-to-occupant interaction responses in side impact conditions using Q-dummy and child human body models

Objective Road safety of children has improved considerably over the past decade; however, there is still much scope to better protect these occupants. Ensuring adequate protection of children seated in the rear seats requires a greater understanding of how children are injured in side crashes. The purpose of this study was to enhance the knowledge of children’s potential injuries in side impact collisions by the investigation of two different child sizes seated in different positions in the rear seats. The injury metrics associated with the occupant-to-occupant or occupant-to-child restraint system interaction was also identified. Methods Finite Elements Method simulations were performed using a validated simplified vehicle model with fully deformable side components. Dynamic virtual tests according to the Euro NCAP Child Occupant Protection Protocol were performed considering three different scenarios in terms of occupants´ distribution in the rear seats. Simulations were conducted with dummy and human body models. The injury metrics associated with near-side and far-side positions and the occupant-to-occupant interaction were analyzed. Results The 10-year-old child seated in the far-side position presented higher injury values, especially in the head due to the contact with the adjacent child or child restraint occupying the near-side seating position. Similar responses were observed in human body and dummies models in terms of head and neck injury values. However, human body models showed an increase in the chest measurements. Conclusions This study highlighted that the potential injuries of a child seated on the rear seats in a side impact crash are likely to be increased by the presence of an adjacent seat occupant, especially when larger children were seated in the far-side seating location or a CRS was installed in the near-side seating position. Results offer insight into the occupant-to-occupant interaction and occupants’ size as relevant factors to improve children safety under side impact conditions.

Validation of a generic finite element vehicle buck model for near-side crashes

Objective Finite element (FE) reconstructions of motor vehicle crashes using human body models are effective tools for developing a better understanding of occupant kinematics and injuries in real-world lateral crash conditions, but current near-side reconstruction methods are limited by the paucity of full-scale FE vehicle models. The objective of this study was to validate a generic vehicle model equipped with left-side airbags and intrusion capability by simulating a series of near-side crash tests for a range of vehicles and assessing model accuracy using objective evaluation methods. Methods Moving deformable barrier crash tests were reconstructed for five common vehicle classifications (compact passenger, mid-size passenger, sport utility vehicle, pickup truck, and van) using an updated version of a previously developed simplified vehicle model. Unknown vehicle and intrusion properties (pretensioner force, seatback airbag pressure, curtain airbag pressure, door panel stiffness, ratio of dynamic-to-static intrusion, intrusion velocity, and intrusion scaling factor) were estimated by parameterizing them across 224 simulations per crash test using a Latin hypercube design of experiments. Model accuracy was assessed for 13 anthropomorphic test device signals using the Correlation and Analysis (CORA) objective rating method and injury metric comparisons. Results Maximum ratings of 0.69, 0.67, 0.52, 0.52, and 0.62 were achieved for the compact passenger, midsize passenger, sport utility vehicle, pickup truck, and van classifications, respectively. On average, the abdomen displayed the most accurate behavior (0.51 ± 0.12), followed by the thorax (0.50 ± 0.10) and head (0.50 ± 0.07). The pelvis displayed the least accurate behavior (0.46 ± 0.18) of any region. Reconstructions overpraedicted injury metrics in all cases. Conclusions All vehicles achieved “fair” biofidelity ratings and the compact passenger and midsize passenger vehicles achieved “good” biofidelity ratings, validating them for kinematic evaluations with vehicle-to-vehicle nearside crash reconstructions. Regression models were developed for injuries and CORA ratings and can be used to optimize vehicle parameters in future studies.

Feasibility region analysis of active systems: investigating the lateral performance envelope of sports cars

Active systems are gaining significant importance because of their ability of enhancing handling performance, stability, and driver engagement, especially in sports cars. The upfront study of the achievable handling characteristics with a specific actuator set is crucial, given the involved development costs and time. In this context, although several recent studies have compared the cornering response associated with different chassis actuations, none of them has analysed in detail the resulting performance envelope, i.e. the feasibility region, based on the operating limit of the available hardware. This study targets the identified gap and presents a methodology for obtaining the feasibility region of chassis actuation systems, defined as the locus of the achievable understeer characteristics. The analysis considers front and rear active camber (FAC and RAC), rear-wheel-steering (RWS) and variable roll moment distribution (RMD). Simplified vehicle models with reduced number of degrees of freedom (DoFs) and other features to accurately obtain the feasibility region and the relevant dynamic response indicators in the early design stages of the vehicle are compared with a high-fidelity model based on VI-CarRealTime. The results highlight the favourable trade-off between complexity and accuracy of a 3-DoF nonlinear model accounting for suspension kinematics and compliances.

Particulate dispersion in turbulent wake of Ahmed body and experimental investigation of impact of rear slant angle

This study investigates the particle dispersion characteristics in the turbulent wake of a simplified vehicle model (Ahmed body) for two values of the rear slant angle ϕ (25° and 40°) to study the effect of flow separation. In the experiments (Reynolds number Rel=1.90 ×105), smoke particles were released from a source and visualized with a laser sheet. Concentration fields were analyzed to calculate the vertical (Sy) and lateral (Sz) smoke spread. The findings indicate that the flow topology and concentration fields in the wake are highly dependent on ϕ. In the ϕ=40° case, separation on the rear slant disrupts the trailing vortices originating on the rear slant edges and significantly alters the wake topology. The growth of vertical smoke spread saturates after the recirculation region. The uniform mixing and absence of trailing vortices concentrate the smoke particles in the model midplane. In the ϕ=25° case, the signatures of trailing vortices were observed in the concentration fields behind the model. The vertical smoke spread is less, and the lateral smoke spread is more compared to the ϕ=40° case. The growth of the smoke spread (Sy, Sz) driven by the trailing vortices persists for a long distance, even after the recirculation region. The disruption of trailing vortices brought about by the flow separation appears to be an important effect driving the vertical smoke spread in the wake. The connection between the turbulent velocity structures and concentration structures will need to be explored with combined velocity and concentration measurements in the wake.

Research on precise and standardized numerical simulation strategy for vehicle aerodynamics

PurposeThe purpose of this study is to propose a precise and standardized strategy for numerically simulating vehicle aerodynamics.Design/methodology/approachError sources in computational fluid dynamics were analyzed. Additionally, controllable experiential and discretization errors, which significantly influence the calculated results, are expounded upon. Considering the airflow mechanism around a vehicle, the computational efficiency and accuracy of each solution strategy were compared and analyzed through numerous computational cases. Finally, the most suitable numerical strategy, including the turbulence model, simplified vehicle model, calculation domain, boundary conditions, grids and discretization scheme, was identified. Two simplified vehicle models were introduced, and relevant wind tunnel tests were performed to validate the selected strategy.FindingsErrors in vehicle computational aerodynamics mainly stem from the unreasonable simplification of the vehicle model, calculation domain, definite solution conditions, grid strategy and discretization schemes. Using the proposed standardized numerical strategy, the simulated steady and transient aerodynamic characteristics agreed well with the experimental results.Originality/valueBuilding upon the modified Low-Reynolds Number k-e model and Scale Adaptive Simulation model, to the best of the authors’ knowledge, a precise and standardized numerical simulation strategy for vehicle aerodynamics is proposed for the first time, which can be integrated into vehicle research and design.

Input force contribution separation method for utilizing blocked force and operational TPA

In recent years, various transfer path analysis (TPA) methods have been proposed to separate contribution from multiple input points to the response point. In general, TPA methods require transfer function from input to the response points by hammering tests. However, obtaining accurate contribution becomes difficult in case the transfer function varies according to the operating condition or the complexity of the transfer path. In this study, we then considered input force contribution separation method for the difficult condition by combining operational TPA and blocked force used in component TPA. In the method, blocked force in the operational condition is obtained by component TPA at first, and operational TPA is applied between the obtained blocked force and the response point acceleration signals to obtain the transfer function without hammering tests. The contribution is calculated by multiplying the blocked force and the transfer function at the condition. As the verification, the proposed method was applied to a simple vehicle model equipped with a motor. And the response point vibration could be decreased well by measuring the high contributing part according to the contribution separation result. Through the verification test, the effectiveness of the proposed procedure was confirmed.

Simplified numerical model for the collapse analysis of RC frame under oblique impact

The objective of this study is to develop a simplified numerical model that can be used to accurately and quickly conduct collapse analysis of a reinforced concrete (RC) frame impacted by a vehicle obliquely at 45°. The simplified numerical model included introduces a simplified RC frame and a simplified vehicle. For the simplified RC frame, a mixed modelling technique was used, in which structural components that experienced serious damage were simulated using detailed elements, while the retained structural components were simulated by larger elements. A constraint algorithm of nodal rigid body in LS-DYNA was adopted to guarantee the displacement compatibility of two kinds of element. For the simplified vehicle model, the spring–mass system was improved on the basis of the energy conservation principle to represent the vehicle in a 45° impact. Combining the simplified RC frame model and vehicle model, the impact response of an RC frame subjected to vehicle impact was studied and compared with the results of a detailed RC frame model impacted by a detailed vehicle. The validation confirmed that these introduced simplifications could significantly improve the computational efficiency and ensure the computational accuracy for the collapse analysis of an RC frame subjected to vehicle impact.

Stochastic optimal control for autonomous driving applications via polynomial chaos expansions

AbstractModel‐based methods in autonomous driving and advanced driving assistance gain importance in research and development due to their potential to contribute to higher road safety. Parameters of vehicle models, however, are hard to identify precisely or they can change quickly depending on the driving conditions. In this paper, we address the problem of safe trajectory planning under parametric model uncertainties motivated by automotive applications. We use the generalized polynomial chaos expansions for efficient nonlinear uncertainty propagation and distributionally robust inequalities for chance constraints approximation. Inspired by the tube‐based model predictive control, an ancillary feedback controller is used to control the deviations of stochastic modes from the nominal solution, and therefore, decrease the variance. Our approach allows reducing conservatism related to nonlinear uncertainty propagation while guaranteeing constraints satisfaction with a high probability. The performance is demonstrated on the example of a trajectory optimization problem for a simplified vehicle model with uncertain parameters.

Assessment of finite element human body and ATD models in estimating injury risk in far-side impacts using field-based injury risk

The objective of this study was to assess the ability of finite element human body models (FEHBMs) and Anthropometric Test Device (ATD) models to estimate occupant injury risk by comparing it with field-based injury risk in far-side impacts. The study used the Global Human Body Models Consortium midsize male (M50-OS+B) and small female (F05-OS+B) simplified occupant models with a modular detailed brain, and the ES-2Re and SID-IIs ATD models in the simulated far-side crashes. A design of experiments (DOE) with a total of 252 simulations was conducted by varying lateral ΔV (10-50kph; 5kph increments), the principal direction of force (PDOF 50°, 60°, 65°, 70°, 75°, 80°, 90°), and occupant models. Models were gravity-settled and belted into a simplified vehicle model (SVM) modified for far-side impact simulations. Acceleration pulses and vehicle intrusion profiles used for the DOE were generated by impacting a 2012 Camry vehicle model with a mobile deformable barrier model across the 7 PDOFs and 9 lateral ΔV’s in the DOE for a total of 63 additional simulations. Injury risks were estimated for the head, chest, lower extremity, pelvis (AIS 2+; AIS 3+), and abdomen (AIS 3+) using logistic regression models. Combined AIS 3+ injury risk for each occupant was calculated using AIS 3+ injury risk estimations for the head, chest, abdomen, and lower extremities. The injury risk calculated using computational models was compared with field-based injury risk derived from NASS-CDS by calculating their correlation coefficient. The field-based injury risk was calculated using risk curves that were created based on real-world crash data in a previous study (Hostetler et al., 2020). Occupant age (40 years), seatbelt use (belted occupant), collision deformation classification, lateral ΔV, and PDOF of the crash event were used in these curves to estimate field injury risk. Large differences in the kinematics were observed between HBM and ATD models. ATD models tended to overestimate risk in almost every case whereas HBMs yielded better risk estimates overall. Chest and lower extremity risks were the least correlated with field injury risk estimates. The overall risk of AIS 3+ injury risk was the strongest comparison to the field data-based risk curves. The HBMs were still not able to capture all the variance but future studies can be carried out that are focused on investigating their shortfalls and improving them to estimate injury risk closer to field injury risk in far-side crashes.

Hybrid Guidance Algorithm With Heat-Flux Constraint for Launch Vehicles

A hybrid guidance algorithm is developed to meet the heat flux constraint in the exo-atmospheric phase of launch vehicles. The minimum allowable altitude for a particular vehicle velocity is decided by the heat flux constraint. If the optimal trajectory of the vehicle is close to the allowable minimum altitude, then the heat flux constraint is violated. The hybrid algorithm combines the features of a predictor-corrector and a uniform gravity (flat earth) based optimal algorithm. The predictor use a simplified vehicle model with closed loop steering to predict the minimum clearance from the heat flux boundary. The corrector determines a factor for boosting the effective gravity computed by algorithm on-board thus ensuring safe margin from the heat flux boundary. The uniform gravity based analytical algorithm uses this factor, to compute the steering commands. The hybrid guidance algorithm is implemented in the final phase of a three stage launch vehicle. Validation studies carried out using deterministic cases as well as Monte Carlo propulsion and initial conditions dispersions.

Coordinated control of longitudinal and lateral movements considering dynamics for distributed drive electric vehicle platoon on curved roads

The control goal of the vehicle platoon is to maintain the same speed and desired distance. Most current studies are based on simplified vehicle models, and the leader’s state is also rarely considered. However, under complex working conditions, such as low adhesion or curves, the lateral stability of the platoon will be difficult to guarantee, and tracking errors of desired speed and spacing may further increase. To solve the above problems, a new hierarchical coordinated control strategy is proposed. Taking distributed drive electric vehicles (DDEVs) as research objects, the upper control level establishes a stability situation assessment model according to the vehicle’s dynamic characteristics. At the medium control level, variable weight model predictive control (MPC) coordinates conflicts between longitudinal tracking and lateral stability. A correction term is also introduced to revise the prediction model. At the same time, the weight of different control objectives of the leader and following vehicle was adjusted, respectively. Torque distribution is carried out at the lower level controller. Finally, the control strategy is tested on a hardware-in-the-loop (HIL) platform. The results show that the proposed control strategy can ensure lateral stability while improving the tracking performance of the vehicle platoon.

A Double-Layer Model Predictive Control Approach for Collision-Free Lane Tracking of On-Road Autonomous Vehicles

This paper proposes a double-layer model predictive control (MPC) algorithm for the integrated path planning and trajectory tracking of autonomous vehicles on roads. The upper module is responsible for generating collision-free lane trajectories, while the lower module is responsible for tracking this trajectory. A simplified vehicle model based on the friction cone is proposed to reduce the computation time for trajectory planning in the upper layer module. To achieve dynamic and accurate collision avoidance, a polygonal distance-based dynamic obstacle avoidance method is proposed. A vertical load calculation method for the tires is introduced to design the anti-rollover constraint in the lower layer module. Numerical simulations, with static and dynamic obstacle scenarios, are conducted on the MATLAB platform and compared with two state-of-the-art MPC algorithms. The results demonstrate that the proposed algorithm outperforms the other two algorithms regarding computation time and collision avoidance efficiency.

Design and Performance Research of a Wearable Airbag for the Human Body

In this paper, an integrated wearable airbag is proposed to protect the vulnerable pedestrian during a vehicle–pedestrian collision accident. To evaluate the protection performance of this newly proposed integrated wearable airbag, the airbag inflator finite element model is first verified via an inflator tank test, and the simulated results agree very well with the test. Next, the finite element model of the vehicle–pedestrian model is established, including a simplified vehicle model and a biomechanical HBM with the integrated wearable airbag. The numerical results show the newly proposed wearable airbag can effectively protect the pedestrian by significantly reducing injuries to the head and chest. Since head injury is the most important injury type, a complete set of injury indexes is adopted to evaluate severity of head injury, including HIC15, 3 ms resultant acceleration, and intracranial pressure. To further improve the protection performance of the airbag on the HBM’s head, a parametric study is conducted towards two design parameters of the wearable airbag: inflator gas mass and pulling strap length. The parametric investigation shows 26 g gas and a 20 mm pulling strap can provide the best protection for the HBM’s head.

Adoption of the Synchronous Reluctance Motor in Electric Vehicles: A Focus on the Flux Weakening Capability

This article presents the definition of the performance that the electric motor should have in order to satisfy the requirements of the electric vehicle in terms of acceleration time and maximum speed, starting from a simplified vehicle model, considering the motor torque minimization and the input power minimization. In order to verify the effectiveness of the synchronous reluctance motor in traction applications, it has been evaluated in two case studies: a high-performance vehicle and a city car, where different flux weakening capabilities from the motor in function of the minimization strategies can be pursued to satisfy the requirements. If the car requires high performance in terms of acceleration time and maximum speed, the poor flux weakening capabilities of the synchronous reluctance motor induces a machine oversizing in terms of peak power; by assuming this, it is, however, possible to satisfy the requirements considering the maximum available encumbrance due to an advanced and innovative optimized design procedure. The motor of the city car is obtained only by modifying the stack length and the windings (scaled version), and on this last solution, a prototype has been realized and fully tested; the experimental tests confirm the results of the simulations.

アイドリング振動とエンジンシェイクを考慮した簡易モデルを用いたエネルギー伝達特性による分析

In automotive development, it is important to balance various phenomena with a simplified vehicle body model in the initial design phase. Additionally, idling vibration, engine shake, and road noise are phenomena that affect vehicle ride comfort. Since they have different exciting components and target frequencies, each simplified vehicle model examined in the past report is different. Therefore, it is necessary to represent of each phenomenon in a single vehicle model. Therefore, in recent years, much research has been done in initial design techniques called Model Based Development (MBD) and 1D CAE. We have studied using the Statistical Energy Analysis (SEA) for the initial design. Especially an energy transmissibility parameter of SEA which is called by coupling loss factor (CLF) is focused on describing the phenomenon for various kinds of vibration and noise problem. In this paper, a fundamental study is conducted to examine the balance of multiple phenomena in the initial design phase by the energy transmissibility. At first, a simplified vehicle model that represents each phenomenon is constructed. Next, the energy transmissibility is used to represent each phenomenon, and vibration reduction guidelines are obtained and verified through balance design. The obtained guidelines are then applied numerically to the actual vehicle to confirm vibration reduction.

Estimation method for vehicle interior noise and vibration contribution estimation by Operational and Component TPA - Basic consideration employing simple vehicle model -

Estimation method for vehicle interior noise and vibration contribution estimation by Operational and Component TPA - Basic consideration employing simple vehicle model -

A Novel Simplified FE Rail Vehicle Model in Longitudinal and Lateral Collisions

It is a challenge to efficiently and accurately predict train dynamic responses during complex collisions. In this paper, a novel numerical simplification method for high-speed rail vehicles during complex impact configurations is proposed. The central section of high-speed rail vehicles is a sandwich corrugated hollow double-shell structure. Starting with a baseline detailed finite element (FE) model of a high-speed train, the central section was first simplified as a solid single-shell structure. A parametric study with various simplification thickness ratios of the simplified FE rail vehicle model in different longitudinal rigid-wall collisions and lateral rigid-cylinder impacts was then performed using LS-DYNA. Furthermore, a correlation and analysis (CORA) objective rating method was used to evaluate the related responses between the simplified and detailed baseline FE rail vehicle models. The results demonstrate that the simplified FE model could effectively predict the rail vehicle impact responses. The displacement and impact force time histories of the simplified vehicle model with a thickness ratio of 0.38 matched closely with the results of the baseline detailed FE model under both longitudinal and lateral impacts (total combined CORA rating score: 93%). The rail vehicle impact deformations of the simplified vehicle model were similar to those of the baseline detailed model. The application of the simplified vehicle FE model substantially reduced the computational time (approximately 55% reduction). This work provides a solid basis for efficiently exploring train impact responses in complex collisions, and will be especially useful for train occupant injury assessment.

Sitting posture influence in autonomous vehicles for the evaluation of occupant safety in side impact

IntroductionAutonomous vehicles will give vehicle drivers greater freedom to engage in other activities while the vehicle is in operation that will lead to changes in the seating configurations as well as driver posture. Although it is expected that these vehicles will prevent crashes, collisions will still happen. Ensuring the adequate protection of occupants in these new unconventional positions is the main challenge. The objective of this study was to evaluate and analyse occupant responses in non-standard seating positions that may be expected to occur in automated vehicles occupants under side impact conditions. MethodsFinite Elements Method simulations were performed using the WorldSID 50th male dummy positioned in the driver position. A validated simplified vehicle model with fully deformable driver-side components was used. To explore the sensitivity to side impact across various occupant activities, five scenarios were defined: normal driving (S0), fall-back ready (S1), work (S2), leisure (S3) and relax/sleep (S4). All scenarios were subjected to the Euro NCAP Side Tests Protocols (deformable barrier and oblique pole impact). ResultsAs the distance from the pole impact point to the B-pillar decreased, the structure deformation increased due to the B-Pillar deformation. In cases S2 and S3 predicted thorax injury values were the highest, whereas scenarios S3 and S4 were the worst situation in deformable barrier impact test. Good pelvis protection was provided in all pole impact scenarios, but pelvis injury values were the highest in all scenarios in deformable barrier impact test. ConclusionsAttending to the new scenarios due to the new available driver activities, current safety standards are not enough to guarantee the highest level of protection. Reclined seating scenarios required a wide range of impact positions to be covered since injury responses were influenced by the initial impact alignment of the dummy relative to the vehicle and the pole. Large rotations of the seatback lead to high chest compressions.

Optimal Selection of Suspension and Tires for Vehicles’ Cornering Performance

It is difficult to accurately simulate the cornering performance of a vehicle using a simplified vehicle model; therefore, a proper evaluation process should be conducted from an experimental perspective. In addition, there are several possible combinations of subparts in suspension modules, such as springs, dampers, stabilizers, or other parts, and the characteristic identification of each part may require significant costs and time. In this study, the cornering performance of a vehicle system was experimentally evaluated using several combinations of subparts in the suspension module as well as candidate tire cases. All characteristic parameters used in the two indices were previously identified as separate steps, and vehicle tests were performed according to all the required test scenarios for cornering performance. The evaluation of the cornering performance of a vehicle was proposed using the suspension characteristic cornering performance (SCCP) index and suspension and tire characteristic cornering performance based-on-tests (STCT) index, respectively, using measured data from a vehicle test. The STCT index is revised from the SCCP index by considering the tires’ effects, and the optimal selection of the suspension and tires can be obtained from the proposed indices. The feasibility of the proposed STCT index was verified by evaluating the cornering performance from all the prepared test results.