Want a literature review.This is a research project.Select a topic which is relevant to " Challenges electrical vehicles face compared to IC engines "
Select a topic for electrical vehicles and any subtopic as " batteries" or any other related to electrical vehicles.Should do a research related assignment. : LITERATURE REVIEW" , My previous assignment which was a small one is attached , and view the comments by the professor.
2 Wold solar challenge: Long distance driver fatigue in lightweight vehicles – Objective evaluation and monitoring of seat discomfort Executive Summary The purpose of this study is to investigate an objective measurement of seat discomfort for long distance drivers in lightweight vehicles, by comparing subjective rating with the correlation between full body vibration and pressure distribution on a seated body. Pressure distribution will be mapped out using tactile sensor system, which will allow the collection of data for the duration of testing. This will be evaluated against perceived discomfort, which will be acquired through scoring by test subjects, as well as the vibration transmitted onto the driver, recorded via an accelerometer. Literature has indicated that similar studies have been undertaken, but the vibrational aspect has been left out in many cases or when included other aspects have been investigated. This proposal includes the theoretical background and the experimental setup to be able to reach the sub aims and goals. These aims and goals include the evaluation on how pressure changes with excessive vibration present, determining a suitable a subjective scoring method, test procedure and possible discrepancies between the data sets. This has been amalgamated into a project plan where a tactical approach has been made to deliver the completed project within 14 weeks. The potential findings of this research will allow for impartial seat evaluation, which can be used to be able to find a seat with optimal comfort to weight ratio, or for the monitoring of seated behaviour. 1. Introduction The University of Technology Sydney is aiming to compete in the world solar challenge competition in 2019. The competition requires a vehicle running on solar energy as its only power source, requiring the vehicle to be extremely lightweight. This will cause excessive vibrations, which are transmitted straight onto the driver. High magnitudes of vibration have been seen to cause fatigue at a quick rate due to the mental and physical strain, interfering with the performance of the driver. Whilst lower magnitudes of vibration can be annoying but not as prominent, the exposure under a long period of time does eventually cause discomfort and physical fatigue (Mansfield 2012). The competition covers a drive of 300 kilometres, where a driver will be seated for hours under harsh conditions. To be able to find a seat to fit the application in the solar car there is a need to evaluate if and how discomfort of a driver is affected when exposed to vibration. The proposed project aims to investigate the subjective rating of discomfort and pressure distribution when high frequency vibration is present. The ideal goal is to find an objective method to evaluate seat discomfort, independent from driver perception, physical characteristics and behaviour. This way the method can be used to evaluate an optimal seat for the solar car, where weight of the seat is restricted. Coments: Was penalised - should be more concise.The outline should be inlcude in the Introduction. 3 Literature indicates that similar research has been undertaken previously, though the studies have not shown if the correlation of perceived discomfort and pressure changes when excessive vibration is present. A lightweight vehicle such as the solar car can be expected to be exposed to frequencies of about 10-20 Hz. These types of frequencies were not presented in any of the investigated research. The seat is also considered to be relatively rigid due to safety requirements of the competition combined with the weight constraint, meaning the transmissibility from the vehicle body onto the driver will be high. 2. Literature Review The sensation of maintaining a seated position for an extensive period of time, is often referred to as seat discomfort (Balasubramanian & Jagannath 2013). Seat discomfort will occur regardless to vibration being present or not, however earlier onset to discomfort has been found when vibration is introduced (Mansfield, 2012; Mansfield, Sammonds & Nguyen 2015). Although an early onset to discomfort with vibration present has been established, seat performance has been recommended to be evaluated after a period of at least 2 hours for accuracy (Sammonds, Fray & Mansfield 2017). This could be seen in a study by Mandsfield, Sammonds & Nguyen (2015) where the short-term seat comfort did not show a significant difference when evaluating seat foam composition, whilst the long-term comfort test was remarkably improved. Due to the non-linear behaviour of the human body and the seat when exposed to vibration it has been found challenging to evaluate the combined effect of the two (El Falou et al. 2003; Kim, Fard & Kato 2016). The seat effective amplitude transmissibility (SEAT) was found to be significantly greater than measured subjective discomfort for vibrations at low frequencies (Basri & Griffin 2014). This would suggest that there is a difference between perceived discomfort compared to objective calculations. However, the study only measured a single frequency axis and vibration in vehicles is correctly measured via the x-axis, y-axis, z-axis and the rotational motion yaw, pitch and roll (Mansfield 2012). In a study looking at pressure distribution for discomfort and postural changes, it was suggested that there is a correlation between subjective discomfort and pressure distribution. This was observed by comparing subjective ratings of discomfort did pressure change, which was increased over time (Na, Lim, Choi & Chung 2005). However, the study did not expose subjects to vibration and the pressure changes only accounted for pressure variation rather than pressure mean and peak values. The pressure variations were concluded to be due to postural changes (Na, Lim, Choi & Chung 2005). Similar findings were made by Kyung & Nussbaum (2008) where different pressure variables where investigated and compared to subjective ratings. The testing period was only 20 minutes and there was no vibration exerted on the test subjects. Le et al. (2014) also tried to quantify objective data using pressure distribution and perceived discomfort. It was found that shorter and taller test subjects reported the discomfort differently. This was concluded to be because of the ways they are seated differently to be able to fit. This could correspondingly be seen on the pressure mapping as they distributed the pressure differently (Le et al. 2014). The study allowed for a testing time of 2 hours but 4 did not expose the subjects to vibrations. Due to unclear presentation of data, there was no evident correlation between the pressure distribution and perceived discomfort for the individuals. When vibration was introduced during a research using pressure mapping, it was found that the overall pressure increased. The pressure peaks could be located where vibration caused resonance in the seat. The subjects exposed to vibration on a ridged seat experienced higher pressure than when on a cushioned seat (Wu, Rakheja and Boileau, 1999). The research did not mention exposure duration, or how the pressure changed over time, nor how discomfort was perceived by subjects. 3. Research Objective The objective of this study is to investigate an impartial measurement of seat discomfort for long distance drivers in lightweight vehicles, by comparing subjective rating with the pressure distribution on a seated body when excessive vibration is present. The study aims to evaluate how and at what rate the pressure distribution changes when vibration is present. The ideal goal is to find an objective method to evaluate seat discomfort, independent from driver perception, physical characteristics and behaviour. An example of an application the method could be used for is to find optimal comfort for a seat with restricted properties such as weight limitations. To complete this research the project has been divided into sub aims as following: Determine suitable subjective scoring in consideration to the pressure mapping. Determine suitable test procedure, including: test time, how and how often subjective scoring will be recorded and if the experimental setup is applicable for the data acquisition. Evaluate possible discrepancies between data, postural, external factors, human errors. The proposed project intends to answer the following research questions: 1. Does the pressure distribution areas correspond with the areas of perceived discomfort when vibration is present? 2. Does the vibration affect the pressure distribution? 4. Theoretical Content Full Body Vibration Per the standard ISO 2631-1:1997 “Mechanical vibration and shock- Evaluation of human exposure to whole-body vibration”, the vibration coordinate system is defined as 6DOF system for vehicles. The horizontal and vertical motions referred to via the x-axis, y-axis, z- axis and the rotational motion yaw, pitch and roll (Mansfield 2012). Since seats often are slightly inclined and the coordinate system needs to be shifted correspondingly. 5 The vibration magnitude can be calculated from the acceleration at the point an accelerometer is placed. The signal can digitally be processed to model the response to different frequencies. Mathematically the vibration, measured in acceleration root-mean- square (m/s2 r.m.s.), can be expressed from the frequency-weighted acceleration ? ?, measurement duration (T) and the frequency-weighted acceleration at time t ( ? ?(?)). ? ? = √ 1 ? ∫ ?? 2 (?)?? ? 0 Equation 1. Frequency-weighted m/s2 r.m.s. (Mansfield 2012) To measure the vibration exerted on the driver by the seat, the seat transmissibility needs to be obtained by comparing the vehicle vibration and the vibration of the seat surface. The dynamic response of transmissibility (?(?)) can be expressed via the ratio between the seat and vehicle at any frequency. ?(?) = ?????(?) ???ℎ????(?) Equation 2. Transmissibility (Mansfield 2012) Since the transmissibility is a function of frequency, performance of a seat is not constant as road conditions vary. An alternative method to evaluate the performance is by using the seat effective amplitude transmissibility (SEAT), which is expressed by: ????% = ????????? ?? ???? ????????? ?? ????? ∗ 100 Equation 3. Seat Effective Amplitude Transmissibility (Mansfield 2012) For the vibrations at the different points the frequency-weighted acceleration can be used or the vibration dose value (VDV). The VDV takes varying vibration conditions into consideration by combining the exposures into a single dose value. VDV can be calculated from the testing duration (T) and the frequency-weighted acceleration at time t ( ? ?(?)): ??? = √∫ ?? 4 (?)?? ? 0 4 Equation 4. Vibration Dose Value (Mansfield 2012) SEAT values under 100% indicate that the seat is reducing the vibration, whilst