Effective reduction of stiffness at peak frequency in hydraulic engine mounts by using magneto-rheological fluids

Hydraulic engine mounts are generally used in aerospace and automotive applications for the purpose of cabin noise and vibration reduction. By careful selection of hydraulic mount design parameters, at a certain frequency, namely the notch frequency, the dynamic stiffness will be smaller than the static stiffness and cabin vibration and noise reduction is provided at that frequency. Literature review indicates that in all previous designs of hydraulic engine mounts the dynamic stiffness increases after the notch frequency. This phenomenon undesirable because of the increase in the force transmitted to the cabin. This paper proposes a new hydraulic engine mount that uses two working fluids. The new design has two notch frequencies and two peak frequencies. In this study, effective reduction of the peak frequencies has been demonstrated by using a controllable fluid as one of the working fluids and a non-controllable fluid as the second working fluid. As a result, one can obtain a hydraulic engine mount design with only one notch frequency but having no peak frequency. The new hydraulic engine mount design and its mathematical model are presented in detail and some discussions on the simulation results are provided

Nonlinear vibration analysis of axially moving strings in thermal environment

In this study, nonlinear vibration of axially moving strings in thermal environment is investigated. The vibration haracteristics of the system such as natural frequencies, time domain response and stability states are studied at different temperatures. The velocity of the axial movement is assumed to be constant with minor harmonic variations. It is presumed that the system and the environment are in thermal equilibrium. Using Hamilton’s principle, the system equation of motion, and t[1]he boundary conditions are derived and then solved by applying Multiple Time Scales (MTS) method. The effect of temperature on the vibration characteristics of the system such as linear and nonlinear natural frequencies, stability, and critical speeds is investigated. Considering ideal and non-ideal boundary conditions for the supports, nonlinear vibration of the system is discussed for three different excitation frequencies. The bifurcation diagrams for ideal and non-ideal boundary conditions are presented under the influence of temperature at various speeds

A finite element model for extension and shear modes of piezo-laminated beams based on von Karman's nonlinear displacement-strain relation

Piezoelectric actuators and sensors have been broadly used for design of smart structures over the last two decades. Different theoretical assumptions have been considered in order to model these structures by the researchers. In this paper, an enhanced piezolaminated sandwich beam finite element model is presented. The facing layers follow the Euler-Bernoulli assumption while the core layers are modeled with the third-order shear deformation theory (TSDT). To refine the model, the displacement-strain relationships are developed by using von Karman's nonlinear displacement-strain relation. It will be shown that this assumption generates some additional terms on the electric fields and also introduces some electromechanical potential and non-conservative work terms for the extension piezoelectric sub-layers. A variational formulation of the problem is presented. In order to develop an electromechanically coupled finite element model of the extension/shear piezolaminated beam, the electric DoFs as well as the mechanical DoFs are considered. For computing the natural frequencies, the governing equation is linearized around a static equilibrium position. Comparing natural frequencies, the effect of nonlinear terms is studied for some example

Two-Mode Operation Engine Mount Design for Automotive Applications

Hydraulic engine mounts are applied to the automotive applications to isolate the chassis from the high frequency noise and vibration generated by the engine as well as to limit the engine shake motions resulting at low frequencies. In this paper, a new hydraulic engine mount with a controllable inertia track profile is proposed and its dynamic behavior is investigated. The profile of the inertia track is varied by applying a controlled force to a cylindrical rubber disk, placed in the inertia track. This design provides a hydraulic engine mount design with an adjustable notch frequency location and also damping characteristics in shake motions. By using a simple control strategy, the efficiency of the proposed hydraulic engine mount in two-mode operation meaning isolating mode in the highway driving condition and damping mode in the shock motions, is investigated

Hybrid evolutionary algorithms and Lagrangian relaxation for multi-period star hub median problem considering financial and service quality issues

Hub facilities are centralized locations that consolidate and distribute the commodities in transportation networks. In many real world applications, transport service providers may prefer to lease hub facilities for a time horizon rather than being owned or constructed. In this paper, a modeling framework is proposed for the multi-period hub location problem that arises in the design of the star–star network with two types of hubs and links. It includes a designated static central hub, some movable hub facilities and a set of nodes with pairwise demands. A periodic growth in the amount of budget is considered at each period to expand the transportation network and an interest rate is also applied to the unused budget available during each period. Since the overall quality of services in the hub and spoke systems rely on the length of the paths, upper bound constraints are considered for the paths between nodes. Numerical experiments are carried out to show the applicability of the proposed model. Due to the computational complexity of the model, an improved genetic algorithm (GA) and a hybrid particle swarm optimization (HPSO) are utilized to find near optimal solutions. Both algorithms employ caching strategy to improve the computation times. Moreover, the HPSO benefits from genetic operators and local search methods to update the particles. In order to assess the effectiveness of the proposed methods, the results are compared with a pure GA and a proper lower bound achieved by a Lagrangian relaxation method