Viscous Hydraulic Shock Absorbers

The construction industry has seen a remarkable development in recent decades, making it possible to build infrastructure elements capable of withstanding considerable demands on traffic, wind or seismic actions. These achievements have been made due to the solutions used for isolation against dynamic actions that may require the structure at a given time. In order to ensure the protection of construction structures against seismic actions, many constructive solutions have been developed which can be mounted inside the resistance structure. These are mechanical systems used for isolation and seismic energy dissipation, which by operation are able to modify structural behaviour at earthquake. A hybrid seismic isolation model is described which is classified under the building base isolation systems category. This system consists of concave roller elements in combination with elastomeric shock absorbing elements. An experimental model has been developed and analysed, and the results are presented in terms of accelerations in time and frequency at the level of the structural elements at which the recordings are made during excitation simulating the action of a seismic event. The isolation system is used on the low model of a bridge or viaduct structure. Analyses are made for different models of insulation system layout at the isolated structure and distinct cases regarding the construction of the component parts regarding the rolling elements in contact with the concave surface. The results are presented for each structural element in part describing the registered values of acceleration due to the excitation on the supporting pier and the superstructure over the three main directions of movement according to the constructive type of the rolling elements that are included in the isolating system. Experimental analysis was performed on a small-scale system under laboratory conditions, based on a set of simplified assumptions. The advantage of this approach is supported by multiple possibilities of simulation of real dynamic loading situations, static and dynamic loading states, structural and functional schemes and functional configurations of the supporting and isolation systems against dynamic actions. Thus, the transfer of experimental results from reduced models to real systems through mathematical and computer models associated with them is ensured by appropriate transfer functions.

There are solutions in terms of seismic isolation and energy dissipation that are successfully applied all over the world to building structures but also to high-way and rail infrastructure elements represented by bridges and viaducts. These structures must remain functional even after they have been requested by a considerable magnitude earthquake. This is why research activities aiming the development and modernization of these mechanical systems, which play a decisive role in ensuring the optimal stability of these structures, are justified. Fluid dissipation systems were originally developed as passive protection systems but over time they have been constructively improved with intelligent control systems that have the potential to considerably increase the efficiency of these systems by making use direct control over the amount of energy which can be dissipated through these protection systems. Such a dissipative viscous fluid system is described in this paper as a more evolved constructive system than the passive principle model. Active control over the operation of this device is materialized by altering the working fluid flow rates through the constructional elements of the dissipation device assembly. This flow rate adjustment is made by means of a flow controller present within the control unit. The mathematical model characterizing the functioning of an active viscous fluid dissipation system is presented, as well as a numerical analysis describing the function of such a dissipative system depending on the additional mass of the isolated structure to which the protective device is attached. The numerical analysis is based on a set of specific values presented in the paper. These dissipation systems are primarily used in bridge or viaduct structures, being responsible for limiting the relative displacements between the structural elements where they are mounted. This method provides greater security through the rigid connection achieved between the structural frames acting as anchorages. Entry into action is made in the occurrence of a seismic event when the piston displacement is recorded and by changing the momentarily flow rate values of the circulating fluid the amount of energy dissipated is adjusted by means of the viscous fluid device. There are presented the advantages and disadvantages related to the use of such seismic energy dissipative systems attached to the construction structures.

In order to achieve an uncontrolled stop of the movement of working equipments driven by hydraulic cylinders, some procedures are used. They usually consist in stopping the piston consecutively to an impact between the piston and either: -Special stoppers, preventing piston to reach the bottom of the hydraulic cylinder, -The bottom of the cylinder, itself, on the head side. The inertia and rate of change of speed and momentum causes huge impact on the working equipment. That is why a more rational and economical solution would be to reduce the piston speed before any impact. For that reason, hydraulic cylinders have to slow down by decelerating before the piston reaches the bottom or the head of the cylinder.

seismic isolation system meant to protect architectural monuments structures subjected to a variety of seismic ground motions. This scientific paper presents a solution that is adequate for the seismic isolation of a small building or a man-made monument, having height and side of the base less than 10 meters. This paper concentrates on the analysis and experimental implementation of an adaptive isolation system for an architectural monument represented by the statue of Ovidius in Constanta (Romania). The solution proposed by the authors is one of a composed type. The isolation system consists of sliding isolation bearings in combination with a central fluid viscous damper device. In order to acquire a good seismic isolation and due to the symmetry in the vertical diametric plane, the chosen solution consists of four sliding bearings (friction pendulum type), located in the corners of the base support. Additionally, the monument is attached to the upper plate of the base support through a dissipative hydraulic element. This one has the role of insulating the monument against the normal movement of soil, mostly due to location of the monument in a public square, accessible to road traffic. The results of the research have revealed a favorable characteristic of this isolation system. The proposed system is therefore capable of simultaneously limiting the response of both sliding base isolation system and superstructure, for a large variety of seismic ground motions.

The paper defines the functional parameters of a recuperatory system based on a mechanical-inertial principle, system which accumulates the energy generated, but not consumed, at a given moment, transferring it back to the equipment in the increased energy use periods. Up to now technical solutions have been developed to cover the energy necessary for the equipments for at least 15-25% of the work cycle duration, but, considering that the theoretical coverage of those is relatively limited, the authors have researched in depth the specific relations which allow the dimensioning of recuperative systems based on inertial-mechanic accumulators, relations that apply in the hypothesis of neglecting the flow losses in the system. KEYWORDS Hydro inertial gyro accumulators, Recuperative systems, Functional parameters. NOMENCLATURE R m radius of the rotation disc, m   Kg mass of the rotation disc, J   2 Kgm mechanical moment of inertia, reported to the rotation axes max E J maximum energy accumulated as rotation kinetic energy, Vm  [-] volumetric efficiency of the hydraulic unit,  [rad/s] momentary angular speed of the gyro accumulator.

The paper defines the functional parameters of the most commonly used accumulators, the hydro-pneumatic type, which apply force to a liquid by using a compressed gas that acts as the spring, system which is therefore able to accumulate the energy generated, but not consumed, at a given moment and transferring it back to the equipment in the increased energy use periods. Up to now technical solutions have been developed to cover the energy necessary for the equipments for at least 15-25% of the work cycle duration, but, considering that the theoretical coverage of those is relatively limited, the authors have researched in depth the specific relations which allow the dimensioning of recuperative systems which use, relations that apply in the hypothesis of neglecting the flow losses in the system.

This paper analyses the theoretical and experimental characteristics of the hydraulic energy dissipaters used as dissipative joints for the mechanical structures subject to earthquakes, and vibrations. The paper allows the understanding of the dynamic behaviour of the dissipative joints which represent particular cases for the rheonomic and nonholonomic constraints.

The research presented in this scientific paper investigates an adaptive seismic isolation system meant to protect building structures subjected to a variety of seismic ground motions. This scientific paper presents a solution that is adequate for the seismic isolation of small buildings, bridges or viaducts, having main dimension less than 10 meters. The solution proposed by the authors is one of a composed type. The isolation system consists of sliding isolation bearings in combination with fluid viscous damper devices. The results of the research have revealed a favorable characteristic of this isolation system. The proposed system is therefore capable of simultaneously limiting the response of both sliding base isolation system and superstructure, for a large variety of seismic ground motions.

This study presents an innovative solution of a hydraulic damping system that can perform a certain level of seismic energy dissipation, adequate for man-made structures. The system is represented by an adaptive isolation system, expected to improve the behavior of certain structures during seismic actions. The proposed system consists of a hydraulic damper, where the viscous damping device is represented by a cylinder with piston and piston rod, filled with a viscous fluid, fluid which can be mineral oil or silicone oil. The seismic driven translational motion of the piston rod together with the piston is forcing the viscous fluid to circulate inside the cylinder through a certain number of orifices bored in the piston. A CFD analysis was performed using a simplified model of hydraulic dissipation device, with the purpose to highlight the fluid particles motion inside the device when connected to the mobile part of the structure driven by seismic movements. The proposed system is therefore capable of simultaneously limiting the response of both base isolation system and superstructure, for a large variety of seismic ground motions.

Seismic actions are of great interest because - especially in very dense populated areas - an earthquake can have strong effects on building structures. When estimating these effects on building structures one may find that the main characteristic of these actions is that they present significant inertial forces. That’s why, when discussing about large structures with large openings, such as bridges, it is advisable that the superstructure should be disconnected from the groundwork. Therefore, in order to protect bridges from earthquake damages, seismic isolation technology has to be applied. One frequently used method is to use friction bearing systems. A newer variant is that which uses, for some friction systems, hydraulic fluid damper system devices, in conjunction with the friction bearings system, in order to provide supplementary energy dissipation. These hydraulic fluid damper systems act as a special safety devices acting mainly at the end of the stroke and play the role of anchoring points for the structure.

When driving mechanisms where it takes considerable forces, then hydraulic cylinders are used, especially since they develop large forces in relatively low volumes. Increasing speeds has led to an increase in the intensity of the impact between piston and cylinder body at the end of the race. Hence aroused a need for reducing mobile assembly speed before the impact starts. This paper tries to explain why only the cylinder equipped with hydraulic cushioning system at the end of the race it is not satisfactory for carrying out cushioning. In fact, cushioning is based on the reduction of flow with replenished active room of the hydraulic cylinder. The main factors on which depends the cushioning process are: hydraulic power system, kinematics of the actuated mechanism and the geometry of the cushioning system placed inside the hydraulic cylinder. To develop a cushioning system without taking into account all these factors it is not therefore possible.

The specific innovative device presented in this paperwork is a hydraulic system operating with viscous fluid that provides damping for shocks and vibrations. A basic viscous fluid device is constructed on the principle of linear hydraulic motor (cylinder with a plunger), but the device presented here has a certain number of orifices made inside the piston head. This allows the fluid circulation during the forced displacement of the piston within the cylinder body, without the need of any external hydraulic connection. Therefore it may be considered to be a passive system that will run without any other attached devices, on a passive principle. Typically, this particular device is used for bridges or viaducts endowment, as connection point between structural elements (base pier and path-way) ensuring in this way a safe anchoring and displacements limitation for the superstructure, especially when unexpected dynamic actions occur. The viscous fluid device operation achieves an energy dissipation role, because it opposes to the relative motion between structural frames, where it was positioned. Due to the viscosity properties of the working fluid, the piston movement is strongly attenuated and the energy received from the environment is partially consumed by the internal viscous friction, then it is transmitted back to the external environment, as heat energy. The value of the diameter of crossing orifices made in the piston head is important for an adequate operation of the viscous fluid device. Therefore, in this paperwork are presented the CFD analysis results obtained for a virtual model of a hydraulic device, when the orifices diameter is changed.