| 1. |
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- 2019
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Kumar, Arun, 1991, et al.
(författare)
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Analysis of Subjective Qualitative Judgement of Passenger Vehicle High Speed Drivability due to Aerodynamics
- 2019
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 12:14
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Tidskriftsartikel (refereegranskat)abstract
- The flow created by the shape of a vehicle and by environmental conditions, such as cross-winds, will influence the dynamics of a vehicle. The objective of this paper is to correlate the driver's subjective judgement of drivability with quantities which are measurable during a vehicle test. For this purpose, a sedan vehicle, fitted with different aerodynamic external devices that create disturbances in the flow field, were assessed on a test track. These configurations intend to result in substandard straight line drivability. The aerodynamic devices investigated are an inverted wing, an inverted wing with an asymmetric flat plate and an asymmetric air curtain attached under the bumper. The devices generate more lift and asymmetric forces resulting in increased vehicle sensitivity to external disturbances. Pairs of configurations with and without bumper side-kicks are also tested. The side-kicks create a defined flow separation which helps to stabilize the flow and increase drivability. Plots of mean and standard deviation and ride diagram of lateral acceleration, yaw velocity, steering angle and steering torque are used to understand vehicle behaviour for the different configurations. Ride diagrams are used to visualize vehicle excitations with transient events separated from the stationary signal. The range of the measured quantities for understanding the drivability is not predicted in advance and it turns out that the error margins of the measurements are smaller than the measurement uncertainty of the Inertia Measurement Unit. Although the outcome lacks the ability to objectively quantify subjective judgements, it provides a useful qualitative assessment of the problem as the trends agree well with the subjective judgement of the driver.
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| 3. |
- Kumar, Arun, 1991, et al.
(författare)
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Improved Predictive Model of Drivers’ Subjective Perception of Vehicle Reaction under Aerodynamic Excitations
- 2023
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Ingår i: International Journal of Automotive Technology. - 1976-3832 .- 1229-9138. ; 24:6, s. 1655-1664
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Tidskriftsartikel (refereegranskat)abstract
- In vehicle development, rating vehicle reactions to external disturbances such as aerodynamic excitations are important for improving safety and comfort of passengers. Vehicle motion reactions under such conditions are dependent on both disturbance and drivers’ steering actions. A predictive model has been developed to correctly anticipate the drivers’ ability to identify unexpected external disturbances for straight-line, high-speed driving in a driving simulator. The measured variables were band-pass filtered to desired frequency ranges. Excess yaw and roll velocities, defined as the difference between actual rotations and rotations predicted with a dynamic model from the cause of actual steering, were calculated. The standard deviations of the measured variables in a time window around disturbances were used in a regression model to predict the driver responses. Replacing actual rotations with excess rotations reduced the importance of steering input as a predictor by approximately 2/3, thus improving the accuracy of the predictive model. The model showed the change in driver sensitivity to rotations at different frequency intervals. It also showed that only driver input in around 1 ∼ 2 Hz reduces driver sensitivity and that drivers are not necessarily sensitive to high rotational accelerations, but rather to large differences between actual vehicle yaw and roll and expected vehicle yaw and roll responses from the steering input The result from this study were later compared to succeeding on-road tests which confirmed that the predictive model was improved with the use of excess motion variables.
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| 4. |
- Kumar, Arun, 1991, et al.
(författare)
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Prediction of Drivers’ Subjective Evaluation of Vehicle Reaction Under Aerodynamic Excitations
- 2024
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Ingår i: Human Factors. - : SAGE Publications. - 1547-8181 .- 0018-7208. ; 66:5, s. 1600-1615
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Tidskriftsartikel (refereegranskat)abstract
- Objective: The objectives are to determine which quantities are important to measure to determine how drivers perceive vehicle stability, and to develop a regression model to predict which induced external disturbances drivers are able to feel. Background: Driver experience of a vehicle’s dynamic performance is important to auto manufacturers. Test engineers and test drivers perform several on-road assessments to evaluate the vehicle’s dynamic performance before sign-off for production. The presence of external disturbances such as aerodynamic forces and moments play a significant role in the overall vehicle assessment. As a result, it is important to understand the relation between the subjective experience of the drivers and these external disturbances acting on the vehicle. Method: A sequence of external yaw and roll moment disturbances of varying amplitudes and frequencies is added to a straight-line high-speed stability simulation test in a driving simulator. The tests are performed with both common and professional test drivers, and their evaluations to these external disturbances are recorded. The sampled data from these tests are used to generate the needed regression model. Results: A model is derived for predicting which disturbances drivers can feel. It quantifies difference in sensitivity between driver types and between yaw and roll disturbances. Conclusion: The model shows a relationship between steering input and driver sensitivity to external disturbances in a straight-line drive. Drivers are more sensitive to yaw disturbance than roll disturbance and increased steering input lowers sensitivity. Application: Identify the threshold above which unexpected disturbances such as aerodynamic excitations can potentially create unstable vehicle behaviour.
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| 5. |
- Kumar, Arun, 1991, et al.
(författare)
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Predictive Model of Driver's Perception of Vehicle Stability under Aerodynamic Excitation
- 2023
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Ingår i: SAE Technical Papers. - 0148-7191 .- 2688-3627.
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Konferensbidrag (refereegranskat)abstract
- In vehicle development, a subjective evaluation of the vehicle's behavior at high speeds is usually conducted by experienced drivers with the objective of assessing driving stability. To avoid late design changes, it is desirable to predict and resolve perceived instabilities early in the development phase. In this study, a mathematical model is developed from measurements during on-road tests to predict the driver's ability to identify vehicle instabilities under excitations such as aerodynamic excitations. A vehicle is fitted with add-ons to create aerodynamic excitations and is driven by multiple drivers on a high-speed track. Drivers' evaluation, responses, cabin motion, and crosswind conditions are recorded. The influence of yaw and roll rates, lateral acceleration, and steering angle at various frequency ranges when predicting the drivers' evaluation of induced excitation is demonstrated. The drivers' evaluation of vehicle behavior is influenced by driver-vehicle interactions. Excess rotational rates, defined as the part of rotational rates that are not the result of steering action, reduce the importance of steering as a predictor and improve the accuracy of the predictive model. The present model is compared with an earlier developed model derived from data from a driving simulator under preconditioned aerodynamic excitations.
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| 6. |
- Kumar, Arun, 1991
(författare)
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Predictive model of perceived driving stability at high speeds under aerodynamic excitations
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The automotive industry is continuously advancing towards more energy-efficient vehicle designs. Streamlined vehicles have low aerodynamic drag but have the potential to be unstable when exposed to external excitations such as unsteady aerodynamic forces created by the flow of air around them. Before signing off a new vehicle for production, several on-road test scenarios are conducted by professional drivers to evaluate the performance. Finding vehicle instabilities and proposing solutions to problems during late phases of development is challenging and costly. The objective of this thesis is to correlate and predict the driver's subjective evaluation of high speed straight-line driving stability with measurable quantities in early design phases. In this work, substandard straight-line drivability was investigated on-road using different aerodynamic devices for generating high rear lift and asymmetric aerodynamic forces. These aerodynamic devices were then paired with stabilizers, called side-kicks, which helped to define the flow separation and improved the drivability of the tested vehicle. Vector plots of the mean and standard deviation of lateral acceleration, yaw velocity, steering angle, and steering torque were used to understand vehicle behavior for the paired configurations and relate to the difference of subjective evaluation of drivability within each pair. The ride diagram was used to separate the presence of transient behavior and study its impact on subjective evaluation. The qualitative assessment of the resulting trends agrees well with the subjective evaluation of the driver. Following this, experimental trials were conducted in driving simulators and on-road, in order to have an in-depth understanding of drivers' subjective evaluation and responses to external excitations. Both common and professional test drivers were involved in the study. The results provided insight into the excitation frequencies and amplitudes of interest. From the test data, mathematical models were generated that can predict the drivers' subjective evaluation after experiencing induced external excitations. The outcome showed the impact of drivers' steering on their subjective evaluations towards these excitations. The on-road study revealed that higher roll and longitudinal noises reduce the drivers' sensitivity to external excitations. Headwind magnitude and lateral motion in a certain frequency range experienced by the human upper body contribute to drivers' identification of excitations. The resulting predictive model can be used to pinpoint the time of occurrence of observable aerodynamic excitations and provides their characteristics in early development phases. Since the models represent measurements from the cabin, they should be valid for different vehicles.
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| 7. |
- Kumar, Arun, 1991
(författare)
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Subjective perception and prediction model of vehicle stability under aerodynamic excitations
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The current automotive era is moving towards electrified vehicle propulsion. As a result, an energy efficient vehicle design becomes one of the top priorities. From an aerodynamics point of view, the vehicle should be more streamlined for minimal aerodynamic drag. Such designs have the potential to enhance vehicle sensitivity when exposed to external disturbances such as unsteady aerodynamic forces and moments created by the flow of air around the vehicle. Before signing off for production, several on-road test scenarios are conducted by professional drivers to evaluate the new vehicle’s performance. Finding vehicle instabilities and proposing solutions to problem’s during such late phases of development is challenging in many aspects. The objective of this paper is to correlate and predict the driver’s subjective perception on high-speed straight-line driving stability with measurable quantities in the early phase of development. In this work, different aerodynamic devices were used for generating higher lift and asymmetric aerodynamic forces resulting in substandard straight-line drivability on-road. An inverted wing, an inverted wing with an asymmetric flat plate, and an asymmetric air curtain attached under the bumper were the selected aerodynamic devices paired with and without bumper side-kicks. The side-kicks help define the flow separation, thus improving the drivability of the tested vehicle. Plots of mean and standard deviation and ride diagrams of lateral acceleration, yaw velocity, steering angle, and steering torque are used to understand vehicle behaviour for the paired configurations and relate to the difference of subjective judgment of drivability within each pair. The ride diagram was used to separate the presence of transient behaviour and study its impact on subjective judgement. The qualitative assessment of the resulting trends agrees well with the subjective judgement of the driver. Clinical tests were conducted using driving simulators, in order to have an in-depth understanding of the subjective perception and responses of drivers towards external disturbances. Both common and experienced test drivers were involved in this test. The results provided an insight towards the disturbance frequencies and amplitudes of interest. From the test data, a model is generated that can predict the drivers’ subjective perception after experiencing induced external disturbances. The outcome also shows the impact of drivers’ steering action on their subjective perceptions towards these disturbances.
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| 8. |
- Manni, Giovanni Li, et al.
(författare)
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The OpenMolcas Web : A Community-Driven Approach to Advancing Computational Chemistry
- 2023
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 19:20, s. 6933-6991
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Tidskriftsartikel (refereegranskat)abstract
- The developments of the open-source OpenMolcas chemistry software environment since spring 2020 are described, with a focus on novel functionalities accessible in the stable branch of the package or via interfaces with other packages. These developments span a wide range of topics in computational chemistry and are presented in thematic sections: electronic structure theory, electronic spectroscopy simulations, analytic gradients and molecular structure optimizations, ab initio molecular dynamics, and other new features. This report offers an overview of the chemical phenomena and processes OpenMolcas can address, while showing that OpenMolcas is an attractive platform for state-of-the-art atomistic computer simulations.
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| 9. |
- Padamsee, Mahajabeen, et al.
(författare)
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The genome of the xerotolerant mold Wallemia sebi reveals adaptations to osmotic stress and suggests cryptic sexual reproduction
- 2012
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Ingår i: Fungal Genetics and Biology. - : Elsevier BV. - 1087-1845 .- 1096-0937. ; 49:3, s. 217-226
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Tidskriftsartikel (refereegranskat)abstract
- Wallemia (Wallemiales, Wallemiomycetes) is a genus of xerophilic Fungi of uncertain phylogenetic position within Basidiomycota. Most commonly found as food contaminants, species of Wallemia have also been isolated from hypersaline environments. The ability to tolerate environments with reduced water activity is rare in Basidiomycota. We sequenced the genome of W. sebi in order to understand its adaptations for surviving in osmotically challenging environments, and we performed phylogenomic and ultrastructural analyses to address its systematic placement and reproductive biology. W. sebi has a compact genome (9.8Mb), with few repeats and the largest fraction of genes with functional domains compared with other Basidiomycota. We applied several approaches to searching for osmotic stress-related proteins. In silico analyses identified 93 putative osmotic stress proteins; homology searches showed the HOG (High Osmolarity Glycerol) pathway to be mostly conserved. Despite the seemingly reduced genome, several gene family expansions and a high number of transporters (549) were found that also provide clues to the ability of W. sebi to colonize harsh environments. Phylogenetic analyses of a 71-protein dataset support the position of Wallemia as the earliest diverging lineage of Agaricomycotina, which is confirmed by septal pore ultrastructure that shows the septal pore apparatus as a variant of the Tremella-type. Mating type gene homologs were identified although we found no evidence of meiosis during conidiogenesis, suggesting there may be aspects of the life cycle of W. sebi that remain cryptic.
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| 10. |
- Subbanna, Arun Kumar, et al.
(författare)
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Velocity Planning for a Racing Driver Model
- 2012
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Ingår i: Proceedings of the 11th International Symposium on Advanced Vehicle Control (AVEC ’12).
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Konferensbidrag (refereegranskat)abstract
- There is limited information found in literature concerning simulation of limit handling capability of a vehicle model using a driver model. Determining the limit handling capabilities can be a valuable tool for development and analysis of vehicle designs and using a driver model is a convenient way of achieving this . This work presents two different strategies to a driver models that uses the lane for lateral position and limited a priori information about the track in the form of pre-view about curvature ahead of the car. These driver models results in longitudinal velocity planners that uses one single and one multi preview of the reference path. Both strategies have been implemented in the Vehicle Dynamics Library from Modelon using the Modellica language and simulated to illustrate their performance.
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