Influence Of Oscillation Frequency Research Articles

Investigation of nonlinear squeeze-film damping involving rarefied gas effect in micro-electro-mechanical systems

In this paper, the nonlinear squeeze-film damping (SFD) involving rarefied gas effect in the micro-electro-mechanical systems (MEMS) is investigated. Considering the motion of structures (beam, cantilever, and membrane) in MEMS, the dynamic response of the structure is affected greatly by the SFD. In the traditional model, a viscous damping assumption that the damping force is linear with the moving velocity is used. As the nonlinear damping phenomenon is observed for a micro-structure oscillating at a high velocity, this assumption does not hold and will cause error results for predicting the response of the micro-structure. Meanwhile, due to the small size of the device and the low pressure of the encapsulation, the gas in MEMS is usually rarefied gas. Therefore, to correctly predict the damping force, the rarefied gas effect must be considered. To study the nonlinear SFD problem involving the rarefied gas effect, a kinetic method, i.e., discrete unified gas kinetic scheme (DUGKS), is introduced in this paper. Also, based on the DUGKS, two solving methods, i.e., a traditional decoupled method (Eulerian scheme) and a coupled framework (arbitrary Lagrangian-Eulerian scheme), are adopted. With these two methods, two basic motion forms, i.e., linear (perpendicular) and tilting motions of a rigid micro-beam, are studied under forced and free oscillations. For a forced oscillation, the nonlinear SFD phenomenon is investigated. For a free oscillation, in the resonance regime, some numerical results at different maximum oscillating velocities are presented and discussed. Besides, the influence of oscillation frequency on the damping force or torque is also studied, and the cause of the nonlinear damping phenomenon is investigated.

Influence of Oscillation Frequency and Nonlinear Structural Material of Airfoil in Wind Turbine System During Dynamic Stall

Influence of Oscillation Frequency and Nonlinear Structural Material of Airfoil in Wind Turbine System During Dynamic Stall

Effect of acoustic excitation on fiber-reinforced polypropylene and the influence on melt viscosity

The paper describes a novel technological approach to influencing the rheological properties of thermoplastic materials exposed to acoustic energy. The flow behavior of polypropylene with different mass percentages of glass fibers is investigated in a parallel plate rheometer under high-frequency longitudinal excitation. The influence of oscillation frequency on the melt viscosity is explained by means of shear thinning criteria. The dependence of the oscillation shape using sinusoidal excitation on shear thinning as a function of different fiber reinforcement percentages is also investigated. A phenomenological view describes the mutually influencing parameters with regard to different material compositions and different excitation frequencies over the time course of the rheometric measurement. Interacting relationships are analyzed and discussed and the potential of the actuator system to influence the plastic melt is worked out. Based on this, a technological approach follows which describes the transfer of an oscillating mold surface to plastics processing methods, which, especially in the case of energy-intensive injection molding technology, leads to the expectation of possible resource efficiency in energy and material.

Vibrodynamic mechanism control automation in soil compacting machine

Article investigates relevance of high-quality compaction of soil bases during construction of different buildings. Influence of oscillation frequency on to values of disturbing force, total applied load and vertical travel range of the drum is substantiated. Improvement in performance of vibratory roller compactors during operation is provided by resonating frequency, which is optimal during soil-vibratory drum system interaction. Article presents schematic diagram and description of the operation concept for automatic controller with microprocessor, which performs continuous analysis of the interaction between soil and drum, which allows to set optimal frequency of vibratory drum vibrations, to achieve required degree of soil compaction, compensating for disturbing force.

Molecular-dynamics investigation of the initial failure of the nanosized rod under uniaxial cyclic load

The paper studies the disturbance energy absorption and distribution according to the type of system internal energy under cyclic uniaxial tension of a nanosized rod. The external action is described as follows: VX = V0 ⋅ sin (ωt). For calculations the method of molecular dynamics was applied. The influence of oscillation frequency and amplitude on the external disturbance energy absorption by the system has been determined.

Propagation of Waves of Different Geometries in a Porous Medium Saturated with Two Immiscible Liquids

Propagation of waves of different geometries (plane, cylindrical and spherical) in a porous medium saturated with two immiscible liquids: a wetting (water) and a non-wetting (oil/gas) is considered. Unified dispersion relations for waves with different geometries are obtained. It is shown that the dependence of phase velocities on frequency is the same for plane, cylindrical and spherical waves (with axial symmetry) and independent of the geometry of the process. Using dispersion relations, the influence of oscillation frequency on the phase velocities of longitudinal and transverse waves at various viscosity ratios of the wetting and non-wetting phases and the capillary pressure difference in the phases is investigated.

Improving a resource­saving surfacing technology using two ribbon electrodes with a controlled transfer of electrode's metal

This paper reports results of research into a resource-saving technology of surfacing with two ribbon electrodes with a controlled transfer of the electrode's metal from the end sides of ribbon electrodes and with an adjustable ratio between the ribbon electrodes' feed speed. To implement the proposed technology of surfacing, we designed a device that makes it possible to change the ratio between feed speeds of the first and second electrodes in a wide range. That provides for a controlled heat-mass transfer to the welding bath. As well as, accordingly, a controlled fusion of ribbon electrodes and the distribution of thermal energy throughout a welding bath. This makes it possible to improve quality of the surfaced products using a simple and reliable resource-saving device. A given design makes it possible to optimize parameters for a pulsed mechanical transfer and prevent the deformation of ribbon electrodes, to ensure an alternating reciprocation motion of the ribbon electrodes' end sides at optimal frequency and amplitude. That provides for the optimal size of the surfaced bead while making it possible to reduce the consumption of an electrode's metal for loss and overheating, and, accordingly, the consumption of energy for melting, as well as ensure a resource saving technology of surfacing. The process of surfacing with two electrodes, even when using fluxes recommended for arc welding, occurs partially similar to the electroslag process, because a certain percentage of current is shunted by the molten slag. This helps reduce the depth of welding and lowers the share of the base metal in the surfaced metal. The main advantage of surfacing with two ribbon electrodes is obtaining the surfaced metal with the required chemical composition as early as in the first or second layer, in contrast to the single-electrode surfacing where it is necessary to apply from 3 to 5 layers. Results of research into the influence of oscillation frequency of ribbon electrodes have revealed that the maximum increase in a melting coefficient occurs at oscillation frequency in the range of 45‒55 Hz regardless of other mode parameters

Numerical and experimental research of flow control on an NACA 0012 airfoil by local vibration

A flow control technique by local vibration is proposed to improve the aerodynamic performance of a typical airfoil NACA 0012. Both wind-tunnel experiments and a large eddy simulation (LES) are carried out to study the effects of local vibration on drag reduction over a wide range of angles of attack. The application parameters of local vibration on the upper surface of the airfoil are first evaluated by numerical simulations. The mounted position is chosen at 0.065–0.09 of chord length from the leading edge. The influence of oscillation frequency is investigated both by numerical simulations and experiments. The optimal frequencies are near the dominant frequencies of shear layer vortices and wake vortices. The patterns of shear vortices caused by local vibration are also studied to determine the drag reduction mechanism of this flow control method. The results indicate that local vibration can improve the aerodynamic performance of the airfoil. In particular, it can reduce the drag by changing the vortex generation patterns.

Influence of oscillation frequency and focal diameter on weld pool geometry and temperature field in laser beam welding of high strength steels

As weld pool geometry and thermomechanical strains are known to affect formation of solidification cracks, the influence of a superimposed beam oscillation on these characteristics is investigated for this paper. In this context the effects of the oscillation frequency and focal diameter on the weld pool and temperature field are determined by means of infrared thermography. As a result an increase of the weld pool size for larger focal diameters and a more even shape of the seam edges for higher frequencies can be identified.

Filter cake compaction by oscillatory shear

ABSTRACTIn cake filtration, low values of residual moisture are desirable. This can be achieved by filter cake compaction. The present work proposes a new method for filter cake compaction by applying oscillatory shear superimposed with normal pressure. An experimental setup for the application of oscillatory shear is presented and the influence of oscillation frequency and displacement as well as the number of cycles and the magnitude of superimposed normal pressure on the compaction behavior is investigated. It was found that the reduction of residual moisture with number of cycles follows an exponential decay law. The variation of displacement implies that displacement and oscillation frequency are not independent parameters, but the resulting mean shear rate determines the degree of compaction that can be reached. The compaction behavior with frequency or shear rate, respectively, was strongly influenced by the superimposed normal pressure. The effect of oscillatory shear on the compaction of the filter cake was compared to the compaction obtained by applying solely mechanical pressure. By applying oscillatory shear, a significant reduction of compaction pressure needed to obtain a certain value of residual moisture could be obtained.

Study of Martensitic Transformation in Tini Intermetallic by the Methods of Low Frequency Internal Friction

The present article is dedicated to the study of thermoelastic martensitic transformation in the TiNi equiatomic composition by low-frequency internal friction. Considered the influence of oscillation frequency, strain amplitude and heating rate on the internal friction peak of the martensitic nature.

Numerical simulation of reciprocating turbulent flow in a plane channel

Computational results were obtained for oscillatory flow with zero time mean (reciprocating flow) in a plane channel using a finite-volume method. A forcing term that varied cosinusoidally in time was imposed, and its frequency and amplitude were made to vary so as to span a range of regimes from purely laminar to fully turbulent. The results were validated against analytical solutions and literature data. In turbulent flow, although the computational grid did not fully resolve all the turbulence scales, the results were judged to be sufficiently accurate to capture all the essential features of the problem. The present computational results confirmed the existence of four main flow regimes (laminar, disturbed laminar, intermittently turbulent, and fully turbulent), already identified in the previous literature. One of the most interesting results was that the relation between the amplitudes of the forcing term and of the flow rate was found to be approximately linear both in the laminar and in the turbulent regimes; the reasons for this peculiar behavior were investigated and discussed. The influence of oscillation frequency and forcing term amplitude on transition to turbulence was also studied; results were compared with transition criteria proposed in literature, and a flow regime chart was proposed. Finally, the effect of unsteadiness on heat transfer was investigated by imposing different temperatures at the opposite walls of the channel and computing mean and fluctuating temperature distributions and heat transfer rates. The Nusselt number was found to increase significantly even in the disturbed laminar regime and to vary as Re0.8 (as in steady turbulent flow) in the turbulent regime.

Rheological Behavior of Some Cationic Polyelectrolytes

The rheological behavior of some cationic polyelectrolytes in aqueous solution is presented. The polyelectrolytes under study consist of polycations that have positive charges (N,N-dimethyl-2-hydroxypropylenammonium chloride) located along the main chain with or without nonpolar side chains (PCA5D1 and PCA5, respectively). This investigation mainly considers the influence of oscillation frequency and temperature on their rheological behavior in salt-free aqueous solution at three polymer concentrations (cp = 2%, 4%, and 6%) as well as in the presence of low molar mass salt (NaCl). The results indicate the main effect of these parameters was to modify the hydrophobic interactions between the side nonpolar groups of the modified polyelectrolyte. The comparison between the complex viscosity values, at the same polymer concentration, cp = 4%, for PCA5D1 and PCA5 shows higher values in the whole interval of temperatures under study and a pseudoplastic behavior at temperatures greater than 50°C for the former system.

Cyclic upper body perturbations caused by a flexible pole: Influence of oscillation frequency and direction on trunk muscle co-ordination

Objective: The effect of a newly developed training device on trunk muscle co-ordination patterns was investigated. Design: A cross sectional survey of 30 healthy volunteers was executed. The task was to maintain position and motion of a flexible pole that was set into oscillation. Oscillations were applied at three frequencies (3, 3.5, 4.5 Hz), in horizontal and vertical directions. SEMG signals of five trunk muscles were measured. Co-ordination was assessed by calculating mean relative amplitudes and mean, as well as, grand averaged muscle ratios during oscillation cycle for front over back (F/B), internal over external oblique (OI/OE), and multifidus over erector spinae (MF/ES) muscles. Results: Vertical oscillation evoked increased mean MF relative amplitudes and mean F/B and MF/ES muscle ratios in comparison with horizontal oscillation. Grand averaged F/B ratio was phase shifted about 180 ◦ of relative cycle between both oscillation directions. With increasing oscillation frequency mean F/B ratio increased, but OI/OE ratio decreased. Amplitude range of grand averaged muscle ratios during oscillation cycle was augmented with increasing frequency. Conclusions: The gathered normative data can serve as an initial data basis for further investigations on low back pain patients. Relative to oscillation direction and frequency, demands on trunk muscles vary from primarily stabilizing towards mobilizing activities.

Influence of imposed oscillatory frequency on mass transfer enhancement of grooved channels for pulsatile flow

The present experimental study describes mass transfer enhancement in grooved channels with different cavity lengths for pulsatile flow. Overall and local mass transfer rates were measured by the electrochemical method with a high Schmidt number and also the vortical motion within the groove was visualized by the electrolytic precipitation method. We especially focused on the influence of oscillation frequency on mass transport enhancement. Transport enhancement by means of fluid oscillation is found to be higher in laminar flow than in turbulent flow. There is a noticeable enhancement at intermediate Strouhal numbers, depending on the cavity length and the net flow Reynolds number. It is revealed that the mechanism for a peak transport enhancement factor against Strouhal number is not explained by the hydrodynamic resonance proposed by Patera and Mikic, under a certain condition.

Mould heat transfer and continuously cast billet quality with mould flux lubrication Part 1 Mould heat transfer

With the drive to cast higher quality, many minimills are adopting mould powder as a lubricant for the continous casting of steel billets. Over the past three decades considerable experience has been accumulated on the relationship between mould behaviour and billet quality for oil lubrication, but comparatively few studies have been conducted for mould powder lubrication. This study, conducted at a Canadian minimill, involved instrumenting four faces of a copper mould with thermocouples and monitoring mould temperatures during casting of 208 × 208 mm billets with mould flux lubrication. Billet samples were also taken to coincide with periods of measurements. Mould temperatures were monitored for two different mould powder compositions, for different mould oscillation frequencies, two mould cooling water velocities, and a range of steel compositions. An inverse heat conduction model was developed to calculate mould heat transfer from the measured temperatures. In this paper, which is the first part of a two part series, details of the inverse heat conduction model and mould heat transfer data are presented. The results obtained for mould flux lubrication have been compared with those for mould heat transfer for oil lubrication. For peritectic steels, with carbon content in the range 0·12–0·14%, it was found that lubricant type has little influence on the measured mould heat flux distribution at the centreline of a face. The peak mould heat flux was found to be approximately 2500 kW m-2 . In contrast, for medium carbon steels, mould heat transfer with mould powder was significantly lower than when oil was employed as a lubricant. For instance, at the meniscus, the peak heat flux with mould powder was approximately 2500 kW m-2 , which was half that recorded with oil as a lubricant. The influence of oscillation frequency, mould cooling water velocity, and mould powder type on mould heat flux has also been presented.