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The force-displacement characteristic of a shock absorber [19] The cavitation phenomenon occurs, when oil does rupture under the influence of tensile stress, the rupture of the fluid manifests itself as a number of very small cavities in the oil [1]. The process of cavitation depends among other considerations, on the purity of the liquid and the rate at which the liquid is stressed. Cavitation is the formation of pockets of vapor in a liquid. When the local ambient pressure at a point in the liquid falls below the liquid's vapor pressure, the liquid undergoes a phase change to a gas, creating "bubbles," or, more accurately, cavities, in the liquid. Changing temperatures alter the vapor pressure of a liquid dramatically, making it easier or harder for the local ambient pressure to dip below the vapor pressure to cause cavitation. The violent collapse of cavitation or aeration bubbles results in the production of noise as well as the possibility of material damage to nearby solid surfaces [1].
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![Fig. 1. The force-displacement characteristic of a shock absorber [19]...](profile/Damian-Gasiorek/publication/257303896/figure/fig4/AS:668357233741828@1536360190318/The-force-displacement-characteristic-of-a-shock-absorber-19-The-cavitation-phenomenon_Q320.jpg)
The aim of this paper is to develop a method for optimizing the design of a disc spring valve system by reducing the aeration and cavitation effect which negatively influences the performance of a shock absorber. A fluid-structure interaction (FSI) model is used in order to modify the geometry of the valve interior and, in turn, to achieve better p...
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... of gas or vapor. The dissolved gas has a significant influence on the oil mixture and thus on the shock absorber's behavior. The presence of gas bubbles is the cause of the damping force loss in the shock absorber. It is an undesirable and negative effect visible as asymmetry of the force displacement charac- teristic and should be minimized. Fig. 1 shows the influence of aeration on the damper performance based on the force-displacement characteristic obtained for a sequence of 1500 cycles. The energy of hydraulic friction absorbed by a shock absorber caused an increase in its temperature. The damper was cycled with high velocity of 1.5 m/s, three sequences (the first, the ...
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... While the previous works are limited to a combination of separated hydraulic and structural behaviors, 2-way f luid-structure interaction is an advanced method to numerically evaluate an interactive hydro-mechanical behavior of a damper. The method was included in the published works from Czop, et al [8] and Buczkowski, et al [9]. Buczkowski's team showed the modeling techniques and the results to a comprehensive level in both structural and hydraulic sides. ...
div class="section abstract"> As the automotive industry undergoes significant changes in the dynamic behavior of vehicles and increasing demand for rapid product design, accurate prediction of product performance in the early stages has become more crucial than ever in the competitive environment. Shim-stack-type hydraulic dampers are widely used in automotive parts for both internal combustion engine (ICE) vehicles and electric vehicles (EV). EVs are even more sensitive to damper performance as ICE, which is a major NVH source has been removed. However, the industry still faces challenges in obtaining accurate models of dampers due to their highly nonlinear hydro-mechanical behavior. Bleed slits in a shim-stack-type hydraulic damper play a key role in determining the blow-off characteristics of dampers, and therefore, accurate prediction of the blow-off characteristics is crucial in evaluating the damping performance of a vehicle. Bleed flow analyses are conducted at two levels: component level and assembly system level. For the component level analysis, computational fluid dynamics (CFD) is utilized to analyze bleed flow characteristics corresponding to various bleed slits, which are validated by conducting experimental flow bench tests. For the assembly system level analysis, a dynamic 1-dimensional (1-D) system model is developed for a target passive hydraulic damper to evaluate the effect of bleed slits on the assembly level. The damper characteristic of the proposed method and a conventional method with a constant discharge coefficient are compared. An experimentally measured damper characteristic from a dynamo is used to validate the system model.
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... Such elements include, for example, shock absorbers. A large number of works related to the research of shock absorbers are devoted to the development of mathematical models (Domnyshev et al., 2019;Hou et al., 2011;Mollica and Youcef-Toumi, 1997;Ramos et al., 2005), parameter optimization and structural modernization (Ankitha and Rupa Sri, 2021;Czop et al., 2012;Duym, 2000;Więckowski et al., 2018;Wszołek, 2016), as well as research using CFD and FEM analysis (Chen et al., 2013;Duym, 2000;Herr et al., 1999;Lee, 1997;Shams et al., 2007). It should be noted that a significantly smaller number of works are devoted to the study of the operation of components and assemblies of cars (including shock absorbers) during operation in cold climates (Chernukhin, 2013;Chernukhin et al., 2020;Dolgushin et al., 2019), although this is an actual scientific direction for many regions of the world. ...
The use of modern materials and technical fluids allows you to operate cars at negative temperatures, but in some regions of the world (for example, in Siberia), the ambient air temperature can fall below 243 K for several weeks or even months. The operation of trucks at such a temperature refers to extreme conditions that force the special preparation of equipment. This preparation consists not only of special maintenance, but also of carrying out some activities that are carried out immediately before starting the engine and driving. The essence of these measures is, among other things, the thermal preparation of the components and assemblies of the vehicle before departure.This work is devoted to the thermal preparation of truck shock absorbers. It is revealed that the use of oils, the kinematic viscosity of which significantly depends on the ambient temperature, is a limiting factor in the winter operation of shock absorbers. The simulation of the operation of electric flexible heaters for shock absorbers in the SolidWorks Flow Simulation environment was carried out and the preheating efficiency was evaluated. It is established that the temperature distribution of the shock absorber fluid during heating of two-pipe shock absorbers occurs unevenly, but despite this, preheating significantly improves the characteristics of shock absorbers and contributes to the safe and long-lasting operation of trucks.
... Yang (2001) carried out multiparameter coupling simulation and experimental research on the mechanical characteristics of the impact, obtained the shock absorber flowfield characteristics and tested the controllable design ability of the shock absorber. Czop et al. (2012) carried out numerical calculations and analysis on fluid-solid coupling of hydraulic shock absorbers, obtained the flowfield characteristics in the damping valve of a hydraulic shock absorber, proposed a method to optimize the internal structure of the damping valve and carried out experimental verification. ...
To design a high-quality vehicle shock absorber, the internal structure of the piston assembly of a shock absorber is analyzed in this study. Using the fluid–solid coupling method, a high-precision flow grid model and a solid finite element model of the stacked valve are built and analyzed. A bidirectional fluid–solid coupling method is proposed, which can be adopted to simulate and analyze the dynamic nonlinear response characteristics for a stacked valve slice of a vehicle shock absorber in Workbench software. The results indicate that the superposition valve slice maximum occurs at the inner radius, but the area of maximum deformation is near the piston hole and the maximum deformation is about 0.0636 mm. When the stack valve plate just opens the valve, the displacement and speed of the stack valve plate will simultaneously produce a jump change. The results of the calculation analysis are broadly in line with the test results, which indicates that the bidirectional fluid–solid coupling method is accurate and dependable, and can be used to study the dynamic characteristics of vehicle shock absorbers. This has important reference value for the optimization design of the internal valve system of vehicle shock absorbers.
... It consists of a FEM mechanical (stress/strain) model and a flow model. In this topic Czop et al. (2012) proposed an advanced FSI model to understand and optimize performance of a valve system assembled in a piston-rod of a double-tube shock absorber regarding aeration/cavitation phenomena. This is a modification of the two-way FSI method: firstly, the deformations of a stack of discs, caused by a pressure load, are transferred to the CFD-model; then the CFD-model is re-evaluated in the deformed configuration. ...
The paper investigates cavitation effect which negatively influences the performance of a monotube shock absorber of road vehicle (passenger car). For better understanding of this phenomena, three physical models of shim stack valves are analyzed. Validation results allowed selecting the most appropriate valve model in presence of cavitation processes. A mathematical model of monotube damper with consideration of fluid compressibility and cavitation phenomena is developed. Simulation results are validated by experimental data obtained on hydraulic test rig. Based on the selected approach, a simplified method suitable for assessment of cavitation processes in automotive monotube shock absorbers is proposed. After investigation it is found that damping force when cavitation occurs mainly depends on the initial pressure and absorber inner diameter.
... Shock absorber or damper is a power dissipating device, no matter if an existing, dry friction one or a recently created Magnetorheological damper which utilizes Magnetically Responsive fluid, all transforms the kinetic energy of actions into thermal energy [1]. Damping powers might be exceptionally difficult. ...
The liquid flow through orifices produces larger damping, whereas the cushioning effect comes from the fluid’s compressibility. The hydraulic damper design is subjected to constant high pressure necessary to achieve the required forces, which drastically increases during the dynamic operation. Damper has different orifices or piston valves that lead to different flow losses. The main objective behind this work is to investigate the effect of number of orifices on the damping force at different velocities for rear side two-wheeler automobile mono tube damper. Three different orifice opening cases are considered for simulations and experiments such as two-orifice opening, six-orifice opening and ten-orifice opening.
div class="section abstract"> A damper is one of the most important elements in a vehicle suspension system. The damper valves are a fully coupled hydraulic system where the suspension fluid flow interacts with the elastic response of the valve structure. The base valve in the hydraulic damper plays a significant role in compression damping force characteristics of a damper, and therefore designing of the base valve is critical for damping force tuning. In this paper, the impact of the base valve design complexity reduction is quantitatively analyzed. The Current base valve design is restrictive which prevents achieving the required compression damping force ranges without a substantial base valve body parts library. A new base valve assembly is suggested with one more degree of freedom via a restrictor plate. Introducing this new element allows reducing the number of base valve designs for damping performance tuning. The design of the new base valve is engineered from existing designs with the aid of computer aided simulation for improving the tuning range of the damper with reduced number of valve body parts. Finite Element (FE) methods are utilized to evaluate the new base valve structural strength and validated by conducting experimental structural hub crush strength test. For the hydraulic performance of the new base valve design, Computational Fluid Dynamics (CFD) simulations were carried out for meeting damping force requirement. A test flow bench was built to validate the computational models. The new base valve is also a cost-effective solution to meet compression damping force tuning range and resolution.
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Основою сучасної методології дослідження рейкових транспортних засобів є математичне моделювання. Математична модель повинна враховувати такі властивості як просторовий характер руху окремих рухомих частин досліджуваного об’єкту, нелінійні характеристики пружно-дисипативних елементів системи, випадковий характер збурень, які передаються на гідравлічний апарат, властивості рідини, як робочого тіла. Гідравлічний гаситель коливань являє собою гідравлічний циліндр з штоком та системою калібрувальних отворів і клапанів, які спрацьовують в залежності від режиму роботи. Для опису характеристики роботи гідравлічного амортизатора, як правило, використовується класичний закон течії рідини через дросельний отвір, заснований на законах Бернуллі і рівнянні витрати рідини [1]. Використання такої закономірності для сучасних конструкцій пристроїв гасіння коливань вагонів не відповідає опису дійних процесів, які відбуваються за типовими умовами експлуатації. До особливостей робочих процесів пасивних гасителів коливань слід віднести взаємодію робочої рідини з рухомими деталями та її течію по каналах і через калібровані отвори з місцевим штучним опором. Окрім того, внаслідок постійних перепадів тиску через зміну напрямків руху рідини виникають пульсації, які слід враховувати при проектуванні конструкції для більш ефективної роботи пристрою. У статті представлена розроблена узагальнена математична модель гідравлічного гасителя коливань пасажирського вагона типу НЦ-1100, яка враховує нестаціонарні гідромеханічні процеси, що дозволяє
провести дослідження впливу робочих параметрів на характеристики роботи апарату.
In this study, the development and validation of a simplified nonlinear dynamic model of a passive twin-tube hydraulic shock absorber is presented. First, the experimental dynamic response is characterized. Then, the numerical model is presented where flow, pressure, displacement, and velocity are considered. Finally, the numerical–experimental correlation is performed on force-movement dynamic behavior to prove the accuracy of the proposed model. The final goal of the model is to be integrated in a real-time driving simulator for ride comfort studies.
The objective of this paper is to investigate the operation of a mono-tube damper through the application of Computational Fluid Dynamics analysis to the piston and flows through a series of flexible shims which cover exits of the piston orifices. The shims and orifices combine to form a system of variable area flow paths of the damper in parallel with the permanent bleed orifices. Shim stack stiffness characteristics were obtained using experimental and Finite Element techniques. The deflection characteristics were non-linear and were highly dependent upon small gaps present between shims and the restraining bodies. With the nature of the shim deflection being highly complex the computational fluid dynamics models investigated the shim deflection using a global uniform displacement method and also a more representative displacement based upon the finite element shim modelling. It was observed that the global displacement models allowed radially inward flow to establish and also overpredicted pressure drops. Finite element analysis of the shims allowed accurate representation of flow paths to be simulated which closely matched experimental and mathematical predictions. The computational fluid dynamics analyses showed that the discharge velocity for the global shim offset is greater than that from a variable shim deflection calculation. The damper pressure drop is highly dependent upon the shape of the flow path formed by the shim deflection. The presence of sharp direction changes through the piston and valve assembly leads to increased damping rates and piston pressure drops.
