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In this work, a novel distribution-based control strategy of semi-active vehicle suspensions is tested under different conditions. The novelty lies in the use of an appropriate threshold in the operational condition of the control algorithm, with which the operational conditions severity is quantified and the state of the damper is controlled according to the magnitude of the operational conditions and not their sign. The value of the threshold depends on the vibrations induced to the sprung mass by the road profile. In order to be evaluated, the operational conditions of the algorithm are fitted to a t-student distribution. The cumulative distribution function of this distribution is used in order to decrease the fraction of the sample operating with the damper’s stiff state. The strategy is applied to traditional SH control algorithms and is tested using a quarter car model excited by different road excitations. A sensitivity analysis for various threshold values is performed, investigating the impact of adopting the cumulative distribution functioned (CDF) controller to various performance metrics. The results illustrate an increase of up to 13% in the ride comfort of the passengers and increase of 6% in the road holding of the vehicle. Both are achieved by minimizing the switches of the damping ratio up to 80%.

One of the most important systems in ground vehicles is the suspension system, which is responsible for the ride comfort, the road holding and handling. A crucial part of a passenger car passive suspension system is the control arm or wishbone arm or A-arm. Its main function is to provide a link between the body of the vehicle and the wheels. In this paper, the studied control arm is a part of a MacPherson strut suspension and its dimensions correspond to a front right suspension of a SUV vehicle. Two geometrical models of the control arm were developed in Solidworks® CAD-CAE Software, one with the measured dimensions and one with the outline dimensions of the control arm. A finite element model of the first one was built, using typical loading conditions, in order to determine the deformation and the stress contours. Then a topology optimization analysis was carried out to the second one in order to obtain a new design for the control arm. The FE results of the existing control arm and the optimized one were compared in terms of weight and structural integrity in different loading conditions leading to conclusions regarding the optimization procedure.

A seat that provides good vibration isolation is of prime importance for passenger’s safety and health. The main conflict in seat suspensions implies that the increasing initial deformation of the system (increase in “static discomfort”) leads to better isolation of accelerations (increase in “dynamic comfort”). Many researchers have focused on overcoming or at least suppressing this conflict between load support capacity and vibration isolation by modeling new suspension systems, such as the so-called negative suspension systems. However, apart from the modeling of new suspension systems, optimization is an important part in designing a seat and finding the best compromise between these two objectives. Thus, in this work, four types of seat suspension systems with embedded negative stiffness elements are implemented and optimized in order to be benchmarked. Three of them have already been tested either in passenger or in an off-road vehicle seat. All the vibration isolators are optimized with genetic algorithms in respect to static and dynamic factors of ride comfort by applying constraints oriented to the objectives and the design of the structure. The optimization is implemented for two excitations, which correspond to a vehicle driving over road profiles of Classes A and B, and the common solutions are outlined.

Various vibration isolators using negative stiffness elements have been proposed in order to improve ride comfort of passengers in vehicles. In this paper, five different ones are compared. Four of...

In recent studies, the suspension parameters of a vehicle model are estimated using multi-objective optimization procedures with genetic algorithms in order to overcome the well known conflict of ride comfort and road holding. However, the researchers sometimes end up using more than one objective function representing the same requirement, growing the dimension of the optimization problem. Thus, the optimization procedure becomes very quickly ineffective and the merits of the GAs are put aside because of the increased computational time of the simulations. This work focuses on indicating that the inconsiderate selection of objective functions noticed in the literature, in order to obtain the optimum solution of a suspension design, doesn't lead to extra quality in the solution. In this direction, six objective functions widely used in the literature depicting the ride comfort and the road holding, were selected. In our experiments, various SOO approaches (Part A) and two MOO approaches (Part B and C) were selected, where Part B is proposing a novel way of handling the optimization objectives. All the MOO approaches presented combine GAs for obtaining the Pareto set and a sorting algorithm for pointing out their optimum solution among the Pareto alternatives. The optimum solutions of the two approaches are presented and compared in terms of convergence and computational time, concluding to the fact that the economy in the objective functions could provide not only a better solution but also could save significant computational time.

This article presents the design of a test device for cryogenic testing of concrete samples. Cryogenic tests consisted of compression and expansion tests of liquid nitrogen on cylindrical concrete specimens and their scope was to determine the linear coefficient of thermal expansion of the concrete material at temperatures from zero to minus 160° C. This article presents a design. Τhe test chamber and the new strategies that were used; along with the corresponding challenges posed by the heating and measurement problems. Affected heat transfer transient and steady state problems, which were realized using digital analysis using commercial FEM software, are presented along with the measurement equipment and methods that were used to match the numerically calculated temperature profiles along with the measured ones. In addition, the sample temperature measurement topology that was chosen for the experiments is compared with conventional ones in their ability to provide information representing the temperature state of the sample. Finally, the raw data from three tests are analyzed and the results are presented in appropriate graphs, taking into account the systematic errors introduced by thermal compression of the metrological equipment used for measuring length. The results are consistent with those available in the concrete literature.

The role of the roll center on vehicle dynamics has been the subject of several works in the literature. However, the majority of them has been based on low-fidelity models and on roll center’s effect on the vehicle roll dynamics, because of the importance of predicting accurately the time of rollover. In this paper, we aim to conduct an sensitivity analysis of the impact of varying roll center height on vehicle’s performance, while varying also other K&C characteristics. More specifically, the roll centers are varied at the same time with the anti-roll bars. In this respect, we use a vehicle model of 14DOFs, which includes non-equal jacking forces and is validated with CarMaker Software. The vehicle model is excited at the same time with appropriate steer inputs and road profiles in order to focus on handling and ride comfort. The sensitivity analysis provides a fundamental understanding of the exchange between the K&C characteristics to vehicle performance metrics, which represent the transient and steady state handling and the passenger’s ride comfort. ...

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.

Various simulation models are used extensively for the design and the optimisation of vehicle suspension systems, as well as the application of various control algorithms in them. The selection of the most suitable model for these purposes is never explained and many times unnecessary complexity is added in them. In this respect, an assessment regarding the accuracy of the most common vehicle models is conducted. Thus, four vehicle models with various configurations are compared in terms of accuracy. More specifically, both passive and semi active suspensions are employed to the models, while the effect of adding anti-roll bars and tire dampers is also investigated. The transient behaviour of the suspension system and the overall vehicle performance are assessed in terms of ride comfort, vehicle handling and road holding using different road excitations. The results illustrate the ability of lower accuracy models to cope well and that they should be preferred most of the times. Also, anti-roll bars and tire dampers should be neglected when the ride comfort is investigated, whereas they have to be included when simulations regarding road holding are conducted.

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.

Rolling element bearings are critical parts of modern wind turbines as they carry the loads of the turning structure and the wind force. The stochastic nature of the wind loads makes it difficult to estimate the useful operational life of the bearings. Condition monitoring of these bearings in a real time environment could be very helpful in estimating their performance and in scheduling maintenance actions when a condition-based maintenance strategy is followed. This procedure can be successfully implemented by using vibration analysis in the time domain or in the frequency domain, giving useful results about the current condition of bearings and the location of potential faults. Permanently located transducers on proper positions on the bearings’ housings can be used in order to collect, process and evaluate real time measurements and provide information about the bearing’s performance. In this work, a test rig is utilized in order to evaluate the performance of rolling bearings. The results of the experimentation are satisfactory and the progress of fatigue failures can be predicted through vibration analysis techniques showing that implementation in real scale may be useful.

The study aims to present the objectives and the results of the project with title “Smart Recovery of materials and upgrade of organic compost and RDF in existing mechanical biological treatment plants by using NIR technology” which is funded by the Greek General Secretariat for Research and Technology. The main goals for the SmartWasteTech project are summarized to the smart recovery of the materials by using NIR technology in order to increase the quality of the produced compost and recovered materials (PET, PE/PP, LDPE film) and to optimize the process by using online monitoring software for the MBT plant operation. The paper presents the results of the recovery rate, the purity of the final products, the efficiency of the technology performance and the effective role of the NIR technology in existing MBT plants.

A simple, stiff, statically and dynamically stable linear oscillator incorporating a negative stiffness element is used as a template to provide a generic theoretical basis for a novel vibration damping and isolation concept. This oscillator is designed to present the same overall static stiffness, the same mass and to use the same damping element as a reference classical linear SDoF oscillator. Thus, no increase of the structure mass or the viscous damping is needed, as in the case of a traditional linear isolator, no decrease of the overall structure stiffness is required as in the case of ’zero-stiffness’ oscillators with embedded negative stiffness elements. The difference from these two templates consists entirely in the proper redistribution and reallocation of the stiffness and the damping elements of the system. Once such an oscillator is optimally designed, it is shown to exhibit an extraordinary apparent damping ratio, which is even several orders of magnitude higher than that of the original SDoF system, especially in cases where the original damping of the SDoF system is extremely low. This extraordinary damping behaviour is a result of the phase difference between the positive and the negative stiffness elastic forces, which is in turn a consequence of the proper redistribution of the stiffness and the damping elements. This fact ensures that an adequate level of elastic forces exists throughout the entire frequency range, able to counteract the inertial and the excitation forces. Consequently, a resonance phenomenon, which is inherent in the original linear SDoF system, cannot emerge in the proposed oscillator. The optimal parameter selection for the design of the negative stiffness oscillator is discussed. To further exhibit the advantages that such a design can generate, the suggested oscillator is implemented within a periodic acoustic metamaterial structure, inducing a radical increase in the damping of the propagating acoustic waves. The concept may find numerous technological applications, either as traditional vibration isolators, or within advanced composite materials and metamaterials.

In this paper, we propose an Evolutionary Algorithm (EA) with a deterministic mutation operator which is a combination of EA with the Broyden, Fletcher, Goldfarb and Shanno (BFGS) method. The advantages of both optimization algorithms are retained and interconnected. The proposed algorithm shows faster convergence as well as increased reliability in the search for the global optimum. Results referring to the Fletcher and Powel test function in comparison with EA (Evolution Strategies, Evolutionary Programming, and Genetic Algorithms), provide sufficient indication for the performance of the new method. Finally, the proposed method is successfully implemented for the trajectory optimization of a four-bar mechanism.

The aim of this work is to present a comparison of the main semi active suspension systems used in a passenger car, after having optimized the suspension systems of the vehicle model in respect with ride comfort and road holding. Thus, a half car model, equipped with controllable dampers, along with a seat and a driver was implemented. Semi-active suspensions have received a lot of attention since they seem to provide the best compromise between cost (energy consumption, actuators/sensors hardware) and performance in comparison with active and passive suspensions. In this work, the semi active suspension systems studied are comfort oriented and consist of (a) the two version of Skyhook control (two states skyhook and skyhook linear approximation damper), (b) the acceleration driven damper (ADD), (c) the power driven damper (PDD), (d) the combination of Skyhook and ADD (Mixed Skyhook-ADD) and (e) the combination of the two with the use of a sensor. The half car model equipped with the above suspension systems was excited by a road bump, and was optimized using genetic algorithms (GA) in respect with ride comfort and road holding. This study aims to highlight how the optimization of the vehicle model could lead to the best compromise between ride comfort and road holding, overcoming their well-known trade-off. The optimum results were compared with important performance metrics regarding the vehicle's dynamic behaviour in general.

In this paper, a half car model of with nonlinear suspension systems is selected in order to study the vertical vibrations and optimize its suspension system with respect to ride comfort and road holding. A road bump was used as road profile. At first, the optimization problem is solved with the use of Genetic Algorithms with respect to 6 optimization targets. Then the k – e optimization method was implemented to locate one optimum solution. Furthermore, an alternative approach is presented in this work: the previous optimization targets are separated in main and supplementary ones, depending on their importance in the analysis. The supplementary targets are not crucial to the optimization but they could enhance the main objectives. Thus, the problem was solved again using Genetic Algorithms with respect to the 3 main targets of the optimization. Having obtained the Pareto set of solutions, the k – e optimality method was implemented for the 3 main targets and the supplementary ones, evaluated by the simulation of the vehicle model. The results of both cases are presented and discussed in terms of convergence of the optimization and computational time. The optimum solutions acquired from both cases are compared based on performance metrics as well.

t According to bibliography many researchers have contributed in the area of optimization of the suspension characteristics used in ground vehicles. In a number of papers different versions of Evolution Strategies are implemented for achieving this goal. A disadvantage of such methods is the large number of iterations for the convergence of the algorithm. We propose the acceleration of evolution strategy with means of deterministic algorithms, such as the steepest descent method, and we prove that such combinatlon yields significantly faster and more reliable cbnvergen~. The method combines the advantages of two categories of ""ptimization algorithms, deterministic and sto.chastic. ,1e half-car model of suspension systems, described with non-linear differential equations and subject to various road profiles, constitutes a suitable basis for the implementation of numerical optimization algorithms. The common objective of the presented optimization procedures is the improvement of the passengers' ride comfort, leading to minimization of the maximum acceleration of the sprung mass, with respect to the geometrical constraintsof the suspension as well as the necessary traction of the vehicle. The comparison between the performances of the implemented methOdologies states clearly the advantages of the proposed algorithm when the problem is of higher complexity, meaningthat the number of design variables is increased and also many several local minima of the objective function are introduced. In addition, plans and topics for further research are reported.