The 1975 Ride Quality Symposium

A compilation is presented of papers reported at the 1975 Ride Quality Symposium held in Williamsburg, Virginia, August 11-12, 1975. The symposium, jointly sponsored by NASA and the United States Department of Transportation, was held to provide a forum for determining the current state of the art relative to the technology base of ride quality information applicable to current and proposed transportation systems. Emphasis focused on passenger reactions to ride environment and on implications of these reactions to the design and operation of air, land, and water transportation systems acceptable to the traveling public. Papers are grouped in the following five categories: needs and uses for ride quality technology, vehicle environments and dynamics, investigative approaches and testing procedures, experimental ride quality studies, and ride quality modeling and criteria

Front seat passengers’ experience of ride comfort and NVH in modern cars

Due to the refinements in combustion-engine and electric cars, ride comfort has become a prominent attribute when it comes to developing cars in the future. A variety of factors, such as seat, seatbelt, sound and vibration, have been shown to influence perceived overall ride comfort in passenger cars. Numerous studies have investigated human responses to sound and vibration. However, few studies have investigated passengers’ experiences of sound and vibration in real passenger cars, in different real-world driving scenarios. The purpose of this licentiate thesis is to identify human experiences of sound and vibration in modern passenger cars. An approach has been developed to investigate how sound and vibration influence overall perceived ride comfort in combustion-engine cars (CVs) and electric cars (EVs). The first research question relates to the definition of ride comfort, from the passenger’s perspective, and the methodology used to specify the factors that influence overall ride comfort. The second research question deals with specifying how ride comfort is influenced by sound and vibration.The research includes literature reviews of human responses to sound and vibration and a user study using a mixed-method research approach that focused on subjective judgements and objective measurements of overall ride comfort. The literature reviews found that several laboratory studies have covered the level and frequency ranges of interest for vibration and sound found in passenger cars. Other studies have employed realistic ride postures with populations of various ages, gender and anthropometric measures to investigate the influence of vibration on ride comfort. Studies of sound in passenger car have explored approaches to identify sound sources, assess sound quality and design product sound. The overall conclusion from the literature reviews was that there is a lack of studies that consider all the different parameters influencing the overall ride comfort experience of automotive vehicle passengers. Also, further studies are specifically needed to investigate the influence of sound and vibration on passengers’ experience of overall ride comfort. The user study comprised eight typical driving scenarios (initial comfort, start/stop, acceleration and deceleration, constant speed, speed bumps, long bumps and cornering, bridge joints and rough roads) with ten participants in a CV and an EV. The overall results indicated that the two cars were similar in terms of the prominent effects of ingress, room for the body, seat adjustment and seat support on initial comfort, but varied in terms of dynamic discomfort. Induced body movements dominated dynamic discomfort in the CV, while annoying sound dominated in the EV. Sound annoyance in the CV was primarily triggered by tyre noise at lower speeds and wind noise at higher speeds. In the EV it was the high-frequency tonal sound from electrical components that produced the most annoyance. In both cars, vibration discomfort was linked most strongly to induced body movement. Sound annoyance was judged lower when passengers perceived pronounced induced body movement or when participants experienced vibrations coherent to the sound. Nevertheless, the overall influence of sound accumulated over time, making it difficult for passengers to relax. In contrast, the instantaneous judgement of vibration discomfort was not affected noticeably by the simultaneous sound.The main conclusion of this licentiate thesis is that from the passenger’s perspective, ride comfort encompasses static comfort and dynamic discomfort. Static comfort is associated with ingress, room for the body, seat support and seat adjustment. While dynamic discomfort is attributed to the annoying sound, induced body movement, as well as discordance between sound and vibration. The influence of sound and vibration on perceived ride comfort varies depending on the type of driving scenario (e.g., road profile and speed) and on the type of cars (e.g., CV or EV). Moreover, dynamic discomfort could be controlled by controlling sound and vibration

Development of a Multi-Body Nonlinear Model for a Seat-Occupant System

A car seat is an important component of today\u27s cars, which directly affects ride comfort experienced by occupants. Currently, the process of ride comfort evaluation is subjective. Alternatively, the ride comfort can be evaluated by a series of objective metrics in the dynamic response of the occupant. From previous studies it is well known that the dynamic behavior of a seat-occupant system is greatly affected by soft nonlinear viscoelastic materials used in the seat cushion. Therefore, in this research, especial attention was given to efficiently modeling the behavior of seat cushion. In the first part of this research, a phenomenological nonlinear viscoelastic foam model was proposed and its ability to capture uniaxial behavior of foam was investigated. The model is based on the assumption that the total stress can be decomposed into the sum of a nonlinear elastic component, modeled by a higher order polynomial of strain, and a nonlinear hereditary type viscoelastic component. System identification procedures were developed to estimate the model parameters using uniaxial cyclic compression data from experiments conducted at different rates on two types of low density polyurethane foams and three types of high density CONFOR foams. The performance of the proposed model was compared to that of other traditional continuum models. For each foam type, it was observed that lower order models are sufficient to describe the uniaxial behavior of the foam compressed at different rates. Although, the estimated model parameters were functions of the input strain rate. Alternatively, higher order comprehensive models, with strain independent parameters, were estimated as well. The estimated comprehensive model predicts foam responses under different compression rates. Also, a methodology was proposed to predict the stress-response of a layered foam system using the estimated models of each foam in the layers. Next, the estimated foam model was incorporated into a single-degree of freedom foam-mass model which is also the simplest model of seat-occupant systems. The steady-state response of the system when it is subjected to harmonic base excitation was studied using the incremental harmonic balance method. The incremental harmonic balance method was used to reduce the time required to generate the steady-state response of the system. The incrementa

Assessing the risk of vibration exposure during wheelchair propulsion

Although the exposure to whole-body vibrations (WBV) has been shown to be detrimental to seated humans, the vibration levels to which wheelchair (WC) users are exposed to in their communities have not been thoroughly examined. Furthermore, some evidence suggests that the cushions used in WCs, the first line of protection, may amplify WBV, although conclusive evidence has not been presented in the literature. The purpose of this work was twofold. First, to evaluate and compare the transmissibility of commercially WC cushions with two laboratory test methods: (1) direct measurement of transmissibility while human subjects propelled a WC over a road course with different cushions and (2) characterization of cushions with a material testing system (MTS) combined with mathematical models of the apparent mass of the human body. Second, to evaluate WBV exposure to WC users in their communities using ISO 2631-1 methods, and determine whether exposure levels are correlated with WC type and/or back pain, which is a physiological symptom of WBV exposures. Results showed that although dynamic characterization of WC cushions is possible with an MTS, the results did not correlate well with the transmissibility obtained in the WC road course. Significant differences were found for transmissibility among the cushions tested, with the air-based cushions having lower transmissibility than the foam- or gel-based cushions. All WC users who participated in this community-based trial were continuously exposed to WBV levels that were within and above the health caution zone specified by ISO 2631-1 during their day-to-day activities. Our evidence suggested that WCs with suspension did not significantly impact the WBV transmitted to WC users. Finally, we found that WC users are exposed to other risk factors to LBP such as prolonged sitting and transfers. WBV exposure to WC users may be an important contributor to LBP as it has been shown to exceed international standards. Suspension systems need to be improved to reduce vibrations transmitted to the users. More research is needed to understand the interplay between posture, WC configuration, and WBV

An experimental investigation of the vibrational comfort of child safety seats.

The research of this thesis was performed to understand the vibrational dynamics of stage 0&1 child safety seats and of the children who occupy them. Since no previous vibration data for small children or child seats was found, the investigation took the form of experiments designed to shed light on the behaviour of the system consisting of child, child seat, vehicle safety belt and vehicle seat. To provide a background for interpreting the results a literature review was performed of child seat characteristics, of human whole-body response and of primate whole-body response. An industrial test procedure for measuring the vibration isolation properties of vehicular seats is also presented as an illustration of the concepts involved. A whole-body vibration bench for testing children in the vertical direction was built and apparent mass and absorbed power functions were measured for 8 children of age less than 24 months and mass less than 13 kg. An algorithm was developed for identifying the parameter values of a single degree of freedom mass-spring-damper model of the seated body using Differential Evolution optimisation. The parameter values were determined for each child and compared to those of adults and primates. This thesis also presents the results of modal testing of 2 child seat units and of operational deflection shape testing of 1 unit in an automobile under 3 loading conditions (empty, sandbag or child). In-vehicle transmissibility measurements were also performed in the vertical direction for 10 children and child seats using 9 automobiles. The floor-to-human transmissibilities were determined for each child and driver when passing over a reference road surface at both 20 and 40 km/h. Except for the damping ratio, all child mechanical response parameters were found to differ with respect to those of adults or primates, with the differences being greater with respect to adults. The first resonance frequency of children was found to be located at 8.5 Hz as opposed to 4.0 Hz for adults, raising questions regarding the applicability of standards such as ISO 2631 towards the evaluation of child vibrational comfort. The child seats were found to have higher transmissibilities on average than the vehicular seats occupied by adults. A characteristic low frequency rigid body rocking motion was noted at 1.8 Hz as were multiple flexible body resonances starting from frequencies as low as 15 Hz. Areas of possible improvement and topics for further research have been identified

The transmission of vibration by the human body with special reference to the problems of measurement and analysis

Modern forms of transportation can impose high levels of vibration upon their occupants. If one is concerned with the welfare and comfort of the passengers, or the ability of the pilots or drivers to perform their respective tasks in such an environment, then clearly one needs to be able to define the vibration levels experienced by such people. This definition must not only quantify the input levels but also include the levels measured at that part of the human body which will be most affected by the vibration. This thesis therefore covers work aimed at determining the frequency response of the human body under vibration conditions and presents amplitude ratio and phase angle plots of head, and shoulder, accelerations/seat acceleration against frequency for various postures and limb positions. [Continues.

LHD vibrations analysis and numerical modeling during operations

Load-haul-dump vehicles (LHDs) are extensively used as primary loaders in mining operations. LHDs have proven to be vigorous, extremely productive and reliable in mining applications. They have a wide range of tramming capacities that have enabled them to become an essential component in the hard rock mining industry. Increased mining economic challenges and global competition means the mining industry has to maximize productivity by cutting down operating and capital costs. Also, improvements in safety standards have led to the demand for safer and efficient machines. LHD operators are at a high risk of whole-body vibrations (WBVs) exposure leading to musculoskeletal disorders (MSDs) over long exposure periods, and elevated lower back and neck injuries. Thus, there is a health and safety concern among LHD operators. Despite manufacturer’s emphasis on ergonomics, there is lack of adequate fundamental vibration models of large mining equipment accessible to the public. This research focused on developing valid analytical and numerical models for determining the vibration propagation in LHDs. Also, this research pioneered the development and analysis of comprehensive dynamic virtual models of LHDs with detailed vibration analysis of the operator-seat interface. The introduced LHD virtual prototype has a total of 24-DOF and captures the complex vibration mechanics of the LHD, with emphasis on vibrations reaching the operator seat-interface in the three dimensions (3D), x, y and z-directions. The RMS accelerations recorded at the operator-seat interface are 0.62 m/s² in the x-direction, 0.51 m/s² in the y-direction, and 1.01 m/s² in the z-direction which exceed the ISO-2631 comfort level --Abstract, page iii

A descriptive model for determining optimal human performance in systems. Volume 3 - An approach for determining the optimal role of man and allocation of functions in an aerospace system

Optimal role of man in space, allocation of men and machines in aerospace systems, and descriptive model for determining optimal human performanc