Internal Friction Forces Research Articles

Study on the origin of 1/f noise in quartz resonators

Intrinsic frequency fluctuations with a power spectral density limit the short-term stability in quartz crystal ultra-stable oscillators. The physical origin of this noise remains not clearly explained. In this paper, a review of an experimental study on numerous ultra-stable quartz crystal resonators is presented. A comparison with past measurements is given. A theoretical approach, based on the fluctuation–dissipation theorem, is used in order to put numerical constraints on a model of noise caused by an internal (or structural) dissipation proportional to the amplitude and not to the speed, in the limit of low frequencies. The order of the magnitude of the noise is then discussed using a candidate physical process. Comparisons between theoretical and experimental results show that internal damping of thickness fluctuations by any internal friction force proportional to strain and independent of frequency may not be the dominant noise mechanism for the best SC-cut quartz resonators. Finally, we conclude on the work that could be done to solve the remaining open problems.

Evaluation of internal and external stresses on the SPT sampler

The N<sub>SPT</sub> index is usually used in empirical correlations to estimate parameters of the soil, carrying capacity, foundation settlement, etc. Because these correlations have no scientific basis, researchers have been developing rational methods of analysis, based on energy concepts. The amounts of energy involved in the SPT test are evaluated by the EFV method. With force and acceleration records, amounts of energy, equipment efficiency, experimental dynamic reaction force of the soil and stresses acting on the sampler were assessed. In this study, a sample extractor system was designed, which consists of a base, a hydraulic cylinder and a load cell. The objective of this equipment is to experimentally quantify the internal friction force, allowing the stresses acting on the sampler to be evaluated. Also, the Aoki's a parameter, which is the ratio of internal friction and external friction between the ground and the sampler, could be calculated.

リンク式流体慣性ダンパによる建物の制振に関する研究

Recently, Inertia Mass Dampers have been developed and realized. The damper can exert negative stiffness with neither energy supply from outside nor complicated electronic control devices. It is possible for the damper to exert inertia mass much greater than physical mass. In practical applications to controlling relatively large structures, great mass would be required inertia mass. But in the case of controlling small structures, smaller inertia force yielded by flowing fluid would be enough. In this paper, we propose a Linked Fluid Inertia Mass Damper (LFIMD) which is effective to reduce seismic response of low-rise structure. The damper is composed of two cylinders, two piston rods and two link tubes that connect two oil chambers of each cylinder. There is no orifice in the piston and the fluid runs in the tube at high velocity when piston rod moves back and forth. The ratio of two piston displacements can be adjusted based on the ratio of cross section area of two oil chambers linked with a tube. The damper works in three ways. They are viscous damping effect by flowing fluid, negative stiffness by inertia mass effect with moving fluid at high velocity in the tube and the displacement control by hydraulic link mechanism. The damper is quite effective in reducing acceleration response, because load-displacement relationship of the damper has negative stiffness by inertia force, decreasing the maximum shear force of a total structure. The LFIMD yields negative stiffness by means of simple passive mechanism. It can prevent damage concentration to a specific part of a multi-story building, as well as the torsional vibration of a building with stiffness or strength eccentricity. In the first part of the paper, we propose seismic response control method with LFIMD and show its dynamic mechanical properties by performance test on a LFIMD. Important findings are; there exists constant internal friction force between the cylinder and the piston, the damping force depends on the squared piston velocity, inertia force depends on frequency and linking force depends on the compression stiffness of the fluid and rigidity of the tube. It was confirmed that the test results conclude with simulated results fairly well. We perform seismic response analysis of a wooden house with LFIMDs. It is shown that LFIMD is capable of exerting seismic response control in multiple ways. In the case of no damper, the deformation and absorbed energy are concentrated to either of the story. On the other hand, in the case of using LFIMDs, it is possible to make structural deflection distribution uniform and to reduce the maximum deformation with link mechanism. Maximum acceleration is reduced due to negative stiffness by inertia force. Finally, we confirmed the use of LFIMD is quite effective in reducing seismic response of low to mid rise building structure.

Cycle‐by‐Cycle Adaptive Force Compensation for the Soft‐Landing Control of an Electro‐Mechanical Engine Valve Actuator

AbstractElectro‐mechanical valve actuators (EMVA) are a solution for implementing variable valve actuation in internal combustion engines. Their use can increase engine power, reduce fuel consumption and pollutant emissions, while significantly improving engine efficiency. The control of this actuator is a complex task since non‐smooth nonlinearities, parameter variations and external forces strongly affect plant dynamics. In addition, the impact of the valve at its end‐strokes translates into mechanical wear and unacceptable noise, and in the worst case the electromagnet may also fail to catch the valve, causing system failure. The design of effective control strategies to ensure valve capture with low impact velocities is therefore essential for the correct functioning of such a mechatronic device. In this paper, the control problem of reducing the impact velocity at “landing” known in the literature as soft landing control, is tackled via novel cycle‐by‐cycle adaptive force compensation control algorithms. Two schemes are presented: a discrete adaptive proportional integral controller to regulate landing velocity to a preassigned set‐point, and a gradient descent method based controller to automatically achieve the minimum admissible impact velocity. The effectiveness of both methods in limiting landing velocities is shown numerically using a high predictive simulator of the EMVA system, when considering unknown varying environmental conditions, such as internal friction and external gas pressure forces.

Shear zone liquefaction in mass transport deposit emplacement: A multi-scale integration of seismic reflection and outcrop data

Abstract We present the integrated outcrop-geophysical study of two mass transport complexes, the exhumed Specchio unit in the Northern Apennines of Italy and the Holocene Poverty unit in the Hikurangi margin of New Zealand. The combination of micro- to meso-scale structural, stratigraphic and sedimentologic analyses carried on continuous three-dimensional outcrops, with large-scale structural and morphologic data deriving from seismic/acoustic imaging of the present-day continental margins, allow important considerations on submarine landslide processes and mechanisms through the broader (up-scaled and down-scaled) understanding of the mass transport-related structural associations. We compare the discontinuous high-amplitude, reverse-polarity reflectors observed within the Poverty with the syn-sedimentary, ductile shear zones found within the Specchio mass transport complex. The seismic signature of such structures suggests localized fluid overpressure along detachment/thrust zones due to shearing and loading of undrained, water-saturated, fine-grained material, developed along with the slide mass movement. The outcrop expression of these structures is tentatively attributed to m- to tens of m-thick shear zones comprising large amounts of sedimentary matrix which separate and accommodate the differential movements of the internal slide components (e.g. slide blocks, olistoliths). The sedimentary matrix is an unsorted, lithologically mixed medium characterized by a scale-invariant “block-in-matrix” fabric (i.e. brecciated, mud-supported), that injects, sustain and surrounds discrete slide elements (from particles to blocks) and interpreted as a hyper-concentrated (liquefied/fluidized) suspension of water and scattered sediments developed in fluid overpressure conditions. We highlight the fundamental role of shearing-related liquefaction as one of the main factors controlling slide mobility through the “lubrication” of the internal and basal friction forces. The analysis of such features can therefore provide important information for the characterization of mass transport deposits developed from potentially catastrophic, long run-out mass transport events, and consequently, to better understand their possible socio-economic impact in terms of tsunamigenic potential.

Transduction channels' gating can control friction on vibrating hair-cell bundles in the ear.

Hearing starts when sound-evoked mechanical vibrations of the hair-cell bundle activate mechanosensitive ion channels, giving birth to an electrical signal. As for any mechanical system, friction impedes movements of the hair bundle and thus constrains the sensitivity and frequency selectivity of auditory transduction. Friction is generally thought to result mainly from viscous drag by the surrounding fluid. We demonstrate here that the opening and closing of the transduction channels produce internal frictional forces that can dominate viscous drag on the micrometer-sized hair bundle. We characterized friction by analyzing hysteresis in the force-displacement relation of single hair-cell bundles in response to periodic triangular stimuli. For bundle velocities high enough to outrun adaptation, we found that frictional forces were maximal within the narrow region of deflections that elicited significant channel gating, plummeted upon application of a channel blocker, and displayed a sublinear growth for increasing bundle velocity. At low velocity, the slope of the relation between the frictional force and velocity was nearly fivefold larger than the hydrodynamic friction coefficient that was measured when the transduction machinery was decoupled from bundle motion by severing tip links. A theoretical analysis reveals that channel friction arises from coupling the dynamics of the conformational change associated with channel gating to tip-link tension. Varying channel properties affects friction, with faster channels producing smaller friction. We propose that this intrinsic source of friction may contribute to the process that sets the hair cell's characteristic frequency of responsiveness.

Towards a Novel, Implantable Limb Lengthening Device1

Several surgical techniques and devices have been developed to help patients born with limb deformities, limb length inequalities, and extreme short stature. People with such ailments often experience pain, dysfunction, and joint degeneration. The primary method of treating such deformities is an osteotomy followed by callus distraction [1]. Commonplace lengthening devices are external fixators and intramedullary devices, but each has its drawbacks. Traditional external fixators, such as the Ilizarov device and Taylor spatial frame, are cumbersome, painful, and produce large residual scars [2]. Due to pin tract infection rates of 10–20%, lengthening with these methods requires careful surveillance [3]. Intramedullary lengthening devices can cause severe complications such as intramedullary infection [4]. Surgeons have recently experienced success with a motorized, intramedullary nail (Fitbone), but pediatric use of this device can be limited due to interference with open growth plates [5]. The investigators have designed an extramedullary device that retains the attractive qualities of an intramedullary nail, without the risk of deep infection or damage to growth plates. Additionally, the device can be equipped with a six-axis force-torque sensor capable of measuring forces and moments in real time.

Transduction Channels' Gating Controls Friction on Vibrating Hair-Cell Bundles in the Ear

Hearing starts when sound-evoked mechanical vibrations of the hair-cell bundle activate mechanosensitive ion channels, giving birth to an electrical signal. As for any mechanical system, friction impedes movements of the hair bundle and thus constrains the sensitivity and frequency selectivity of auditory transduction. Friction is generally thought to result mainly from viscous drag by the surrounding fluid. We demonstrate here that the opening and closing of the transduction channels produce internal frictional forces that can dominate viscous drag on the micrometer-sized hair bundle. We characterized friction by analyzing hysteresis in the force–displacement relation of single hair-cell bundles in response to periodic triangular stimuli. For bundle velocities high enough to outrun adaptation, we found that frictional forces were maximal within the narrow region of deflections that elicited significant channel gating, plummeted upon application of a channel blocker, and displayed a sublinear growth for increasing bundle velocity. At low velocity, the slope of the relation between the frictional force and velocity was nearly fivefold larger than the hydrodynamic friction coefficient that was measured when the transduction machinery was decoupled from bundle motion by severing tip links. A theoretical analysis reveals that channel friction arises from coupling the dynamics of the conformational change associated with channel gating to tip-link tension. Varying channel properties affects friction, with faster channels producing smaller friction. We propose that this intrinsic source of friction may contribute to the process that sets the hair cell’s characteristic frequency of responsiveness.

Model updating of rotors supported on journal bearings

Heavy power-plant rotors are generally supported on journal bearings. However, hydrodynamic actions in journal bearings generate spin speed-dependent stiffness and damping forces, which induce instability beyond a spin speed limit called the stability limit speed. The presence of other rotating forces such as due to internal friction may further decrease the stability limit speed. Therefore, identification of journal bearing parameters and other rotating damping forces is important. This work extends Inverse eigen-sensitivity method to update a finite element model of a rotor-shaft system to identify journal bearing parameters and internal friction. Eccentricity ratio and coefficient of shaft material damping are updated in this process to identify bearing model and internal friction force at any speed. Updating of eccentricity ratio to identify journal bearing coefficients as proposed in this work is a novel approach that eliminates the need to update eight bearing coefficients per bearing and hence helps in effective parameterization in the model updating process.

Comparative study on debris flow initiation in limestone and sandstone spoil

Large spoil tips from reconstruction works as a result of the Wenchuan Earthquake in China are new debris flow hazards to the human society. However, there is a lack of detailed comparative study on debris flow initiation in different spoil materials. This paper describes a series of tests and analyses on debris flow characteristics (initiation, scale and mechanism) at six sites with limestone and sandstone materials near the Dujiangyan area. Research shows the limestone spoil contains debris flow prone clay content with high concentration of montmorillonite (highly expandable). In addition, limestone spoil is of such a low permeability that water mainly concentrates in the upper surface layer. Those factors make it easy for the increase of pore water pressure, decline of internal friction and conhesion force, leading to the occurence of large debris flows. In contrast, the sandstone spoil is less problematic and causes no major debris flow threats. Based on our research on the mechanism, the"stereometric drainage"method is sucessfully applied to control limestone spoil debris flows.

Inertial stratification of a dispersing multicomponent gas cloud

The possibility of the spatial stratification of the components of an expanding gas ball at the inertial stage of dispersion is considered. Based on numerical investigations into the dispersion of a gas cloud consisting of hydrogen and aluminum, it is shown that, starting from certain dispersion radii, the force of collisional interaction is incapable of providing identical velocities of the components and their radial stratification occurs. The time behavior of the forces of internal pressure and friction is analyzed, and it is demonstrated that the light-component front is far ahead of the heavy-component front as time elapses. This effect is confirmed by experimental data of explosion experiments carried out in the upper layers of the ionosphere.

Modelling the Influence of Composite Stiffness on Energy Dissipation in Reinforced Composite Concrete Floors / Modelowanie Wpływu Sztywnosci Zespolenia Na Rozpraszanie Energii W Warstwie Kontaktowej Zelbetowych Stropów Zespolonych

Abstract A continuous contact layer exists between the top and bottom layer of concrete composite reinforced floors. The contact layer is characterised by linear elasticity and frictional properties. In this paper a model of single degree of freedom of composite floor is determined. The model assumes that the restoring forces and the non-conservative internal friction forces dissipating energy are produced within the contact layer. A hysteresis loop is created in the process of static loading and unloading of the model, with the energy absorption coefficient being defined on this basis. The value of the coefficient is rising along with the growing stiffness of the composite.A critical damping ratio is a parameter describing free decaying vibration caused by non-conservative internal friction forces in the contact layer and in the bottom and top layer. The value of the ratio in the defined model is rising along with the lowering stiffness of the element representing contact layer.The findings resulting from the theoretical analyses carried out, including the experimental tests, are the basis for the established methods of determining the concrete layer state for reinforced concrete floors. The method is based on energy dissipation in the contact layer.

Development of an Apparatus to Investigate Friction Characteristics of Constant-Velocity Joints

Constant-velocity (CV) joints have become standard design and an integral part of modern vehicles, primarily due to their superiority in terms of CV torque transfer. Despite widespread usage of constant velocity joints there are certain aspects of their friction, wear, and contact characteristics that are not well understood. In this article, the need to directly measure CV joint internal contact and friction forces is addressed by designing and constructing an instrumented advanced CV joint friction apparatus using actual tripod-type joint assemblies. The apparatus is capable of measuring key performance parameters such as friction and wear under different realistic operating conditions of oscillatory speeds and CV joint articulation angles. The apparatus incorporates a custom-installed triaxial force sensor inside of the CV joint to measure in situ internal CV joint forces (including friction). The CV joint apparatus is under full computer control and is communicating with all measurement components via a master Labview control program. Experiments under different articulation angles and lubrication conditions were performed and the measurements were correlated with published data. Presented at the STLE Annual Meeting in Las Vegas, Nevada May 15-19, 2005 Review led by Bill Marscher

Diffusional limits to the speed of protein folding: fact or friction?

Proteins fold by diffusional motion, driven by molecular collisions but limited byfrictional drag. We then expect that the timescale of simple diffusional motionsof the polypeptide chain defines the minimum time, or the maximum rate, forfolding phenomena in general. However, such ‘speed limits’ are very rapid. Theyfar exceed the rate of folding that is observed in even the fastest-folding smallproteins. Why do proteins fold much more slowly than the diffusional limits predict?We present experimental evidence that, in addition to solvent friction, internaldissipative forces within a protein can slow the dynamics. These internal frictionforces may ultimately set a much more restrictive limit on the speed of folding.

Intraoperative measurement of distraction for ligament tensioning in total ankle arthroplasty.

Intraoperative measurement of distraction for ligament tensioning in total ankle arthroplasty.

The modelling and analysis of splices used in synthetic ropes

The analysis of eye splices used in synthetic rope is considered by categorizing splice geometries and then developing the modelling for each type. The three splices considered are those originally used in wire ropes and now applied to six–round–one aramid ropes; the splices are the long––or transmission––splice, the Admiralty splice and the Liverpool splice. The geometry of each type is analysed and then applied, to determine the load capacity for each type. The internal friction and contact forces are also discussed.

Bifurcation of a shaft with hysteretic-type internal friction force of material

The bifurcation of a shaft with hysteretic internal friction of material was analysed. Firstly, the differential motion equation in complex form was deduced using Hamilton principle. Then averaged equations in primary resonances were obtained using the averaging method. The stability of steady-state responses was also determined. Lastly, the bifurcations of both normal motion (synchronous whirl) and self-excited motion (nonsynchronous whirl) were investigated using the method of singularity. The study shows that by a rather large disturbance, the stability of the shaft can be lost through Hopf bifurcation in case the stability condition is not satisfied. The averaged self-excited response appears as a type of unsymmetrical bifurcation with high orders of co-dimension. The second Hopf bifurcation, which corresponds to double amplitude-modulated response, can occur as the speed of the shaft increases. Balancing the shaft carefully to decrease its unbalance level and increasing the external damping are two effective methods to avoid the appearance of the self-sustained whirl induced by the hysteretic internal friction of material.

The influence of particle size on the flow of fluidised powders

Fluidised particles can form thin coherent flows that move swiftly over horizontal surfaces. When the particles are cohesionless, Eames and Gilbertson [J. Fluid Mech. 424 (2000) 169] demonstrated that the flow may be understood through vertically integrated momentum and mass balances, and good agreement was found between the model predictions and experimental observations. The behaviour of gas fluidised fine particles (diameter of the order of tens of micrometres) differs significantly from that of larger particles. This is true with respect to their flow which takes place through a series of episodic avalanches and waves rather than as a continuous flow. This behaviour can be explained in terms of a mild cohesive force between the particles. When cohesion is included in the vertically averaged momentum equation, the dynamics of fine particle flows can be reasonably predicted for low and high gas flow rates, when the cohesive forces are respectively weaker than internal frictional forces or drag forces generated by the gas flow. A quasi-static analysis of the combined effect of gas flow and cohesion shows that where cohesive sediments are thin they are not necessarily mobilised, even when fluidised, and this is supported by new experimental observations. A flow of cohesive particles thus has two distinct regions: a thin nose region where the material is not mobilised and a pile of mobile particles behind it. At intermediate gas flow rates comparable to the point of minimum fluidisation, the internal structure of the particle flow dominates how the pile flows along a horizontal surface, and continuum models fail to predict the pile dynamics.

Application of vibrational densimeter to systems with internal friction

The period and phase of the input and output signals from a commercial vibrational densimeter were analyzed using an equation of motion including terms of internal friction and external force. The apparatus constants were obtained from measurements for air, water and organic solvents. The expansion coefficient of the stainless-steel tubing cell calculated from the apparatus constants was consistent with a reference value. The reduced internal frictional coefficient was determined as a function of temperature for aqueous solutions of gelatin and ethylene glycol mono-isobutyl ether. Sharp peaks were observed near the gel to sol transition temperature and the cloud point temperature, respectively. This methodology is applicable to measure densities of viscous samples and to detect a slight inhomogeneity in the systems near the phase transition points.

Analysis of elastic behaviour of steel shell subjected to silo loads

The paper presents theoretical and numerical studies of the behaviour of steel shells subjected simultaneously to internal pressures and frictional forces (distributed forces tangential to the shell surface). The type of combined loading used for this analysis (horizontal pressure and wall frictional pressure which occur in the silos) is given in Eurocode 1 Part 4 [Eurocode 3, Design of steel shells, CEN/TC250/SC3. Draft prENV, 1993.] and in the French draftcode P22-630 [Norme Francaise P22-630 edition AFNOR, 1992]. The cylindrical shell is symmetrically loaded (symmetrical filling and discharge). For this problem a new analytical method is developed to determine the stress distribution in the steel silo by resolving the equilibrium equations of the cylindrical shell subjected to loads due to particulate materials (wheat for example). The finite element method analysis of the shell using the Abaqus program enables a comparison with our analytical approach. The stress distribution predicted by Abaqus agreed well with our analytical results.