A Comparative Study of Integrated Vehicle–Seat–Human Models for the Evaluation of Ride Comfort

In the literature the value of the driver’s head acceleration has been widely used as an objective function for the modification of the suspension and/or the seat characteristics in order to optimize the ride comfort of a vehicle. For these optimization procedures various lumped parameter Vehicle–Seat–Human models are proposed. In the present paper a Quarter Car model is integrated with three Seat–Human models with different levels of detail. The level of detail corresponds to the number of degrees of freedom used to describe the Seat–Human system. Firstly, the performance of the Quarter Car model, used as a basis, is analyzed in six excitations with different characteristics. Then, the performance of the three lumped parameter Vehicle–Seat–Human models are monitored in the same excitations. The results indicated that in the case of single disturbance excitations the Quarter Car model provided 50–75% higher values of acceleration compared with the eight degrees of freedom model. As far as the periodic excitation is concerned, the Vehicle–Seat–Human models provided values of acceleration up to eight times those of the Quarter Car model. On the other hand, in stochastic excitations the Vehicle–Seat–Human model with three degrees of freedom produced the closest results to the Quarter Car model followed by the eight degrees of freedom model. Finally, with respect to the computational efficiency it was found that an increase in the degrees of freedom of the Vehicle–Seat–Human model by one caused an increase in the CPU time from 2.1 to 2.6%, while increasing the number of the degrees of freedom by five increased the CPU time from 7.4 to 11.5% depending on the excitation

Efficient Mounting of a Tank for the Transport of Flammable Liquids on a Freight Vehicle

The design and construction of tanks used for the carriage of dangerous liquid materials fall within strict standards (i.e., EN13094:2015, R111). According to these standards, their supporting structures (Ss), used for the mounting of the tank on the freight vehicle, need to be able to sustain the developed stresses. Optimizing the number of supporting structures can lead to more efficient tank designs that allow the tank to transport more liquid material and need less time to be manufactured. In the present paper, the effect of the reduction of the number of supporting structures in (a) the structural integrity of the tank construction, (b) its dynamic behavior and (c) the load-sharing of the tank to the axles of the freight vehicle is investigated using the finite element (FE) method. As a case study a box-shaped tank mounted on a four-axle freight vehicle with a technical permissible maximum laden mass of 35 tn, five Ss are used. Four FE models with a decreasing number of Ss were built in ANSYS® 2020R1 CAE Software and their structural integrity was investigated. For each design, a feasible design was developed and evaluated in terms of structural integrity, dynamic behavior and axle load distribution. The results of the FE analysis were reviewed in terms of maximum equivalent Von Mises stress and stress developed on the welding areas. Additionally, the axle-load sharing was qualitatively assessed for all feasible designs. The main outcome of this work is that, overall, the use of two Ss leads to a more efficient design in terms of the manufacturing and the mounting of the tank construction on the vehicle and on a more efficient freight vehicle. More specifically, the reduction of the number of Ss from five to two lead to reduction of the tank tare weight by 9.6% with lower eigenfrequencies

Sensitivity Analysis of a Driver’s Lumped Parameter Model in the Evaluation of Ride Comfort

The ride comfort provided by a vehicle to the driver and the passengers is an important feature, directly correlated to the technical characteristics of the suspension system of the vehicle. In the literature, several lumped-parameter models simulating the vehicle and the driver are proposed for the computational evaluation of ride comfort. In order to quantify ride comfort, other than the values of acceleration, metrics such as seat effective amplitude transmissibility (SEAT) and seat-to-head transmissibility (STHT) are utilized. In this paper, a quarter car model is coupled with a six-degree-of-freedom lumped-parameter model, consisting of the driver’s seat and the driver. A sensitivity analysis is performed on the values of the lumped parameters of the seated human body with regard to ride comfort in order to evaluate the effect of their accuracy relative to the ride comfort evaluation. The results of the sensitivity analysis revealed that the values of the mass, the stiffness and the damping parameters of the seated human model influence the ride-comfort metrics to a different extent. Furthermore, it was depicted that ride-comfort metrics were affected in different manners depending on the characteristics of the excitation of the vehicle, yet less than 10% Finally, the importance of the consideration of single-disturbance excitations in such sensitivity studies emerged

An ad hoc decision support method over additive vs. conventional manufacturing

The mechanical design process considers numerous factors. Requirements related to performance and quality, limitations by legislation, standards, methods utilized or technological boundaries, urgency, cost, data preparation and preservation, design flexibility and organizational aspects. Successful design consists of proper decisions on form, geometry, materials, manufacturing methods, quality, reliability and more. Nowadays, a critical decision during design and realization of technological objects is whether they should be made conventionally or with Additive Manufacturing (AM)/3D Printing methods. Such a decision occurs under time-pressure or via a broader strategy for technological switch, is complex, multi-parametric and bears uncertainty and risk. A simple, effective and substantiated method to assist decisions for switching from conventional to AM could prove very useful. This paper refers to recent trends and activity in international AM-related standards, then presents and discusses preliminary work of the authors for an ad hoc decision method to be used upon specific “go/ no-go” decisions for AM. The method is largely based on the Pareto principle, to limit critical design factors contributing to this decision. All steps of the method towards a final decision are described. The method is demonstrated with a hypothetical, yet realistic example of a short run coolant vessel manufacture

An ad hoc decision support method over additive vs. conventional manufacturing

The mechanical design process considers numerous factors. Requirements related to performance and quality, limitations by legislation, standards, methods utilized or technological boundaries, urgency, cost, data preparation and preservation, design flexibility and organizational aspects. Successful design consists of proper decisions on form, geometry, materials, manufacturing methods, quality, reliability and more. Nowadays, a critical decision during design and realization of technological objects is whether they should be made conventionally or with Additive Manufacturing (AM)/3D Printing methods. Such a decision occurs under time-pressure or via a broader strategy for technological switch, is complex, multi-parametric and bears uncertainty and risk. A simple, effective and substantiated method to assist decisions for switching from conventional to AM could prove very useful. This paper refers to recent trends and activity in international AM-related standards, then presents and discusses preliminary work of the authors for an ad hoc decision method to be used upon specific “go/ no-go” decisions for AM. The method is largely based on the Pareto principle, to limit critical design factors contributing to this decision. All steps of the method towards a final decision are described. The method is demonstrated with a hypothetical, yet realistic example of a short run coolant vessel manufacture

An AM-oriented vehicle chassis’ A-Pillar Design Approach

Design and production of highly demanding structural systems, such as the chassis, still rely on conventional forming and welding approaches, both because of their proven performance and the economies of scale achieved. Nevertheless, manufacturing of several chassis’ segments is also expected to soon gradually switch towards AM, for increased design freedom and optimized performance. This paper proposes an alternative design approach for the A-pillar, a typical passenger car chassis segment; a design suitable in form for AM and equally capable in terms of its dynamic behavior, without undermining the chassis’ safety. Prior A-pillar designs along with already published innovative AM-suited design approaches are reviewed. Moreover, these serve as a starting point for an inverse design towards the intended new AM-suited A-pillar alternative. Emphasis is given in the dynamic characteristics of the new structure, through proper modal analysis performed. Finally, the presented research concludes with a scaled-down assessment and verification prototype of the new design, planned to be built via FDM 3D Printing. The prototype is expected to demonstrate primary, as well as secondary/latent benefits from the use of AM in A-pillars, such as the increased diagonal visibility for drivers and passengers, arising from the redesigned, mesh-like form of the segment

An AM-oriented vehicle chassis’ A-Pillar Design Approach

Design and production of highly demanding structural systems, such as the chassis, still rely on conventional forming and welding approaches, both because of their proven performance and the economies of scale achieved. Nevertheless, manufacturing of several chassis’ segments is also expected to soon gradually switch towards AM, for increased design freedom and optimized performance. This paper proposes an alternative design approach for the A-pillar, a typical passenger car chassis segment; a design suitable in form for AM and equally capable in terms of its dynamic behavior, without undermining the chassis’ safety. Prior A-pillar designs along with already published innovative AM-suited design approaches are reviewed. Moreover, these serve as a starting point for an inverse design towards the intended new AM-suited A-pillar alternative. Emphasis is given in the dynamic characteristics of the new structure, through proper modal analysis performed. Finally, the presented research concludes with a scaled-down assessment and verification prototype of the new design, planned to be built via FDM 3D Printing. The prototype is expected to demonstrate primary, as well as secondary/latent benefits from the use of AM in A-pillars, such as the increased diagonal visibility for drivers and passengers, arising from the redesigned, mesh-like form of the segment