Slip Force Research Articles

Dynamic characteristics of magnetorheological fluid squeeze flow considering wall slip and inertia

Magnetorheological fluid has been investigated intensively nowadays, and magnetorheological fluid shows large force capabilities in squeeze mode with wide application potential such as control valve, engine mounts, and impact dampers. In these applications, magnetorheological fluid is flowing in a dynamic environment due to the transient nature of inputs and system characteristics. Hence, this article undertakes a comprehensive study of magnetorheological fluid squeeze flow dynamics behaviors with wall slip, yield, and inertia. First, the dynamic model with the bi-viscous constitutive of magnetorheological fluid squeeze flow including wall slip and inertial force is presented. Then, the mathematical model is validated, matching magnetorheological fluid squeeze dynamic test results very well. Finally, the dynamics behavior and mechanism of magnetorheological fluid squeeze flow with inertia, yield, and wall slip are explored. Results show that (1) increasing yield stress and decreasing initial gap will increase the magnetorheological fluid vertical force greatly; (2) the wall slip affects the yield surface of magnetorheological fluids in the squeeze zone and affects the squeeze force; (3) the inertial force is increasing tremendously as the increased excitation frequency and yield stress and should be included with high-frequency excitation or yield stress.

Monotonic and Fatigue Performance of Double-skin Push-out and Tensile Segments of Divers Shear Connectors – Review

Double skin composite (DSC) construction or Steel/concrete/steel sandwich construction (SCSS) is an innovative and relatively new form of composite construction that can be used in submerged tube tunnels, bridges deck, nuclear structures, liquid and gas containment structures, offshore and onshore structures, military shelters, and shear walls in buildings. The system consists of a plain concrete core sandwiched between two steel plates interconnected together by various types of mechanical shear connectors. The DSC construction perceives advantages that the external steel plates act as both formwork and primary reinforcement, and also as impermeable, blast and impact resistant membranes. The major duty of the shear connectors is to withstand longitudinal shear force and beam/slab separation, while in the bi-steel type where shear connectors are friction welded at both their two ends to two parallel steel plates, the longitudinal and transverse shear force, as well as plate buckling are resisted. The present paper highlights the previous prime researches concerning the subjects of SCSS composite construction, specifically on the conducted tests (push-out tests, tensile, direct shear tests, and bending tests) in which the components of partial interaction (uplift and slip forces) are resisted by various types of shear connectors.

Evaluation of bond–slip behaviour of embedded rebars through control field equations

Anchorage of steel bars is critical in reinforced concrete design to ensure composite action between concrete and rebars. The force–slip relationship of rebars is another factor governing the failure mode and rotation of structural joints. These two aspects can be predicted by bond–slip models and depend on bond behaviour at the reinforcement–concrete interface. However, current bond–slip models show either low accuracy and limited applications due to simplified assumptions or complicated computation due to nested iteration loops. This paper proposes analytical models derived from control field equations, which are characterised by low computational cost, high accuracy and broad application. The control field equations describe force equilibrium of embedded rebars by second-order differential equations and give accurate predictions by incorporating the local bond stress–slip relationship. The proposed models are appropriate for adequate and inadequate embedment lengths of rebars and can describe the evolution of the bond–slip distribution along embedment length. Closed-form solutions can be obtained for perfect anchorage and obviate iterative nested computations. If closed-form solutions are unavailable, owing to free-end slip for short embedment length, a mathematical function in Matlab is used to solve non-linear control field equations and complicated nested iteration is avoided. Finally, the proposed models show good agreement with published experimental results.

Shape effects of wheel grousers on traction performance on sandy terrain

This paper presents the effects of different wheel grouser shapes on the traction performance of a grouser wheel traveling on sandy terrain. Grouser wheels are locomotion gears that allow small and lightweight exploration rovers to traverse on the loose sand on extraterrestrial surfaces. Although various grouser shapes have been analyzed by some research groups, a more synthetic and direct comparison of possible grousers is required for practical applications. In this study, we developed a single wheel testbed and experimentally investigated the effects of four grouser shapes (parallel, slanted, V-shaped, and offset V-shaped) on the traction performance of linear movement on flat sand. The wheel slip, sinkage, traction and side force acting on the wheel axle, the wheel driving torque, and the efficiency of each wheel were examined. Thereafter, the effects on the lateral slope traversability of a small and lightweight four-wheeled rover with different grouser shapes were also examined. The traversability experiment demonstrated the vehicle mobility performance in order to contribute to the design optimization of rover systems. These experimental results and their comparisons suggested that, of the shapes studies herein, the slanted shape was the optimal grouser design for use in wheeled rovers on lunar and planetary soil.

An enhancement in thermal performance of partially ionized fluid due to hybrid nano-structures exposed to magnetic field

This article considers ethylene glycol as a partially ionized base fluid whose rheological characteristics can be exhibited by Carreau stress-strain relations. This dispersion of nanoparticles (MoS2) and hybrid nanoparticles (a combination of (MoS2 and SiO2) in ethylene-glycol is considered and thermal performance of MoS2-Carreau nanofluid and hybrid nanofluid (MoS2-SiO2-ethylene glycol) are investigated numerically using FEM. The results are validated. The present theoretical analysis has shown that thermal performance of working fluid can be enhanced by the use of hybrid nano fluid rather than nano fluid. Unfortunately, shear stress on elastic surface exerted by hybrid nanofluid is greater than the shear stress exerted by nanofluid. Although the thermal performance of hybrid nano fluid is greater than the thermal performance of nanofluid but one must be cautious about strength of surface as it can afford sufficient stress otherwise thermal system may experience failure. Failure analysis prediction while using hybrid nanonfluid must be in mind. As ethylene glycol is partially ionized and its interaction with applied magnetic field induces Hall and ion slip currents. Due to Hall and ion slip currents, ethylene glycol experiences Hall and ion slip forces which are opposite to the Lorentz force of applied magnetic field. This Lorentz force is reduced Hall and ion slip forces. Consequently, the flow of ethylene glycol is accelerated when Hall and ion slip parameters are increased.

Hysteresis analysis of pre-pressed spring self-centering energy dissipation braces using different models

The ability of an idealized piecewise-linear restoring force model and a nonlinear mechanical model to describe the hysteretic performances of the pre-pressed spring self-centering energy dissipation braces was evaluated based on experimental data. The hysteretic behaviors predicted by these two proposed models were compared with the experimental results of a typical prototype brace, and the results demonstrated that the two models can explain the brace force-time responses, and that the nonlinear mechanical model is more effective in describing the stiffness transition and energy dissipation of the brace. The two proposed models can be used for the design of the pre-pressed spring self-centering energy dissipation brace specimens, and the nonlinear mechanical model may be more useful for designing the structures with the pre-pressed spring self-centering energy dissipation braces. An orthogonal experiment was applied to analyze the influences of the key parameters on the performances of pre-pressed spring self-centering energy dissipation braces based on the nonlinear mechanical model. The results indicate that the friction slip force of energy dissipation mechanism, the pre-pressed force of self-centering mechanism, and the post-activation stiffness significantly affect the hysteretic performances and equivalent viscous damping ratios of the bracing system, while the changes in other parameters only produce slight effects. The determination of the pre-pressed force of the self-centering mechanism should be coordinated with the friction slip force of the energy dissipation mechanism to achieve a better hysteretic performance of the pre-pressed spring self-centering energy dissipation brace.

Understanding the Effects of a Discrete Element Soil Model's Parameters on Ground Vehicle Mobility

The Army's mission is to develop, integrate, and sustain the right technology solution for all manned and unmanned ground vehicles, and mobility is a key requirement for all ground vehicles. Mobility focuses on ground vehicles' capabilities that enable them to be deployable worldwide, operationally mobile in all environments, and protected from symmetrical and asymmetrical threats. In order for military ground vehicles to operate in any combat zone, mobility on off-road terrains should be extensively investigated. Mobility on off-road terrains is poorly understood because of the empirical and semi-empirical height-field based methods which are often used for predicting vehicle mobility, such as Bekker–Wong type models. Those methods do not capture the three-dimensional soil deformation/flow as well as the soil's nonlinear behavior. The discrete element method (DEM) in which soil is modeled using discrete particles was identified as a high-fidelity method that can capture the deformation of the soil and its nonlinear behavior. In this paper, a simulation study is undertaken to understand the influence of DEM soil model parameters on vehicle mobility. A typical wheeled vehicle model was built in ivress/dis software and simulated over different cohesive and noncohesive soils modeled using DEM, with a particular emphasis on weak soils (with both low friction angle and low cohesion). Some characteristics of these soils were varied, namely, the interparticle cohesion, the interparticle friction, the particle size, and the particle mass. The mobility measures, including vehicle speed, wheel sinkage, wheel slip, and tractive force were evaluated using the model and correlated to the DEM soil model parameters. This study shows that the vehicle speed increases with cohesion, friction, soil density, and particle size while wheel sinkage, wheel slip, and tractive force decrease with those parameters. The combined influence of those parameters is more complex. Extensive studies of those and other soil parameters need to be carried out in the future to understand their effect on vehicle mobility.

Slipping hydrodynamics of Powell–Eyring fluid in a cylindrical microchannel under electrical double layer phenomenon

The electroosmotic flow of a Powell–Eyring fluid through a cylindrical microchannel activated by an electric field, taking the interfacial slip into account is presented. The study employs an analytical framework of homotopy perturbation method to obtain the underlying flow dynamics of Powell–Eyring fluid over interfacial scales. The rich physical interaction between the fluid rheology, interfacial slip and electrical forces uncovers alteration in the flow dynamics and shear stress profile for Powell–Eyring fluid. Different regimes of flow enhancement in the cylindrical microchannel, triggered by the combined effects of slipping dynamics and electrical double layer phenomena are established through the study. The present analytical framework is canonical with the numerical results for all the cases as considered in this study. The inferences obtained from the present analysis may improve the design of bio-MEMS and microfluidic devices applied for medical diagnostics and transportation of biofluids.

Damage-based optimal design of friction dampers in multistory chevron braced steel frames

In this paper, a probability-based design methodology of the friction dampers in multi-story steel frames is proposed. Both the slip force of the device and the stiffness ratio of the system are analyzed as two important parameters, which affect the behavior of the structures equipped with friction devices. The seismic fragility of friction damped braced frames is evaluated and used to identify the optimal ranges of the above-mentioned design parameters so as to minimize the overall damage probability of the structure under the action of strong ground motions. For this purpose, fragility functions of the structural models are derived using nonlinear incremental dynamic analyses. To demonstrate the efficiency of the proposed method, three structural models of steel moment resisting frames with friction damper systems (including chevron braces and damper devices) are considered for the purpose of the seismic performance analysis. The results of the analyses show that the largest damage probability in each structural model corresponds to the case with the higher slip force and the lower stiffness ratio, where the undesirable buckling failure will govern before full activation of friction damper. For the three considered building frames, the optimal range of slip force lies between 40% and 55% of the total weight of structures and the recommended value for stiffness ratio is 2.

Optimal Damper Slip Force for Vibration Control Structures Incorporating Friction Device with Sway‐Rocking Motion Obtained Using Shaking Table Tests

In this study, a series of shaking table tests were conducted using a specimen that consisted of a superstructure, incorporating a friction device and a sway‐rocking mechanism under the superstructure to determine the optimal damper slip force of a passive vibration control system considering the effects of sway‐rocking motion. The adopted simple friction device, composed of rubber bands and stainless steel plates, allowed the magnitude of the slip force to be easily set. The optimal slip force of the friction device, which minimizes the peak and root‐mean‐square response of the superstructure subjected to earthquakes, was determined from the shaking table tests. Based on the results, the optimal slip force of the friction device was found to vary according to the input level of the ground motions and the sway‐rocking conditions. The obtained results suggest that the effect of sway‐rocking motion should be considered in the design of passive control structures and the determination of their optimal damper slip force.

Development of new oil damper with spring for architectural vibration control and experimental research on structural characterization

This paper shows test and analyses results of a new oil damper, “The Oil Damper with Stiffness”. It was developed to solve some issues around seismic retrofit. There are difficulties in reinforcing buildings which were designed before 1981 in accordance with The Old Buildings Standards Act and many buildings have low stiffness. Therefore, it has become common to retrofit old buildings using braces and oil dampers, but this requires many areas to be reinforced. It causes some problems relating to construction period, cost, and convenience of access. This paper confirms that the test specimens have sufficient capabilities regarding stiffness, constant slip force, durability, etc. in test results and advantages of this damper in analyses using the factory model and the high-rise building model.

ULTIMATE SLIP BEHAVIOR OF PERFOBOND STRIP UNDER THE LATERAL CONFINEMENT PARALLEL TO THE PBL PLATES

Perfobond strip (called PBL, hereafter) proposed by Leonhardt in Germany is widely used as the validated shear connector in steel-concrete composite structures. Fujii et al. proposed a fracture mechanism of PBL as follows: Slip force (shear force) acting on a PBL causes the expanding force which splits the concrete around the PBL. If restraint force, which is caused by cover concrete, rebar etc., resisting the expanding force exist, the slip strength is enhanced. Consequently, the fracture of PBL will happen when the expanding force exceeds the restraint force. Also, based on the above concept, they have given the evaluation formula of PBL slip strength and verified it by comparing previous experimental results. However, bonding force and frictional force are not taken into account in the formula. Through the loading tests of the composite girder, we found that the bonding and the frictional force, which appear along the boundary surface between concrete deck and steel flange, work as resistance force to not only the slip strength but also the expanding force. In this paper, the effects of the bonding force and the frictional force on the ultimate slip behavior of PBL are investigated experimentally, and an evaluation formula of PBL slip strength is improved by taking their effects into account.

Numerical study of unsteady hydromagnetic radiating fluid flow past a slippery stretching sheet embedded in a porous medium

This article reports an unsteady two-dimensional Magneto-hydrodynamic (MHD) boundary layer flow of an incompressible electrically conducting fluid over a slippery stretching sheet surrounded in a porous medium. The Roseland boundary layer approximation with the radiative heat flux is employed within the current analysis. The influence of the velocity slip, thermal radiation, heat source, and buoyancy force is also considered within the current analysis, which makes significant effects on the flow field passages. The unsteady system of non-dimensional partial differential equations (PDEs) with corresponding boundary conditions are solved by implementing the explicit finite difference scheme. In the presence of pertinent parameters such as viscous dissipation, heat source or sink, Prandtl number, Grashof number, thermal radiation, magnetic field, and Darcy number, the accurate movement of the electrically conducting fluid over a slippery sheet is shown graphically in the form of velocity, temperature, skin friction coefficient, and Nusselt number. Unlike the other studies, wherein the system of PDEs is commonly transformed into a system of ordinary differential equations via the similarity transformations, the current study provides an efficient numerical procedure to solve a given system of PDEs without using the similarity transformations which exemplify the precise movement of an electrically conducting fluid over a slippery surface. It has been anticipated that the current boundary layer analysis would provide a platform for solving the system of the nonlinear PDEs of the other unsolved boundary layer models that are associated with the two-dimensional unsteady MHD flow over a slippery stretching surface embedded in a porous medium.

Steering dynamic performance analysis of the tracked mobile robot

In order to obtain the relationship and the change regulation of dynamic parameters of the tracked mobile robot in the steering process, the dynamic models under the influence of slip and centrifugal force are established respectively. At the same time, the mathematical expressions of the deflection of the steering center and the pressure on the track are obtained. The relationship of parameters is analyzed by Simulink simulation software and the error of the slip model, the centrifugal force model and the ideal model and is compared.

Experimental and numerical performance of shear connections in CLT–concrete composite floor

The hybrid cross-laminated timber (CLT) and concrete system has drawn attention as an attractive application for residential and commercial buildings. However, it is crucial to fully understand the mechanical characteristics of the CLT–concrete composite connections before such a hybrid structure becomes widely applicable. This paper assesses the structural performance (force–slip response, slip modulus, and failure mode) of a CLT–concrete composite by conducting fifteen pushout test specimens, which were designed by using the γ-method (Eurocode 5). In these composite specimens, the CLT floor panels were connected to concrete slabs using common mechanical connectors, and the effect of different connection types, connection angles, the penetration depth of the connector, and concrete topping thickness were investigated. The results show that all of the specimens had good trend in the failure mechanisms with a little crush occurred in the CLT and concrete. The finding revealed that the inclination connectors were appeared as an attractive connector layout for CLT–concrete composite components. Non-linear 3D finite element analysis was also developed to simulate the load-slip behavior of the CLT-concrete specimens under shear load. In general, a reliable non-linear finite element model using ANSYS is a great tool for capturing shear capacity and the overall behavior of the hybrid push-out specimens.

Investigation on Friction Features of Dissipative Lap Shear Connections by Means of Experimental and Numerical Tests

Background:Beam-to-column joints equipped with friction dampers are a viable solution to improve the dissipative capacity of moment Resisting Frames without any damage after severe seismic events. Recently, novel systems have been developed within the RFCS FREEDAM research project.Objective:The objective of the work is to provide a rational selection based on engineering judgment, of possible materials to be used in friction dampers.Methods:Both experimental analysis and Finite Element (FE) simulations have been carried out to assess the friction coefficients of several interfaces evaluating also their ability to withstand cyclic loading histories.Results:The experimental campaign showed that both hard and soft metals can be used in combination with stainless steel obtaining satisfactory performance under cyclic loads. In addition, at high slip velocities, large temperatures are developed within the specimen. Modelling this effect is crucial as it causes a reduction in the slip force capacity. This is due to the transverse dilatation that initially increases the pressure, while bolt tightening reduces due to elongation of the shank.Conclusion:The experimental results, together with other similar data selected from technical literature, have been employed to validate FE models able to simulate the behaviour of lap shear friction connections, showing the influence of different modelling approaches over the simulated data. Subsequently, the validated model has been used to perform a set of simulations devoted to highlight the key parameters affecting the response of the lap shears and the possible strategies to improve the performance of the friction dampers.

A discontinuous model simulation for train start-up dynamics

ABSTRACTStart-up dynamics plays an essential role in ensuring the comfort and running safety and structural integrity of trains. Based on the discontinuous dynamics framework, in the present work, an efficient innovative model is proposed. The model is derived from previous train braking studies and in order to highlight the possibility of a non-smooth approach to train start longitudinal dynamics. Set-valued friction of Coulomb’s law type is accounted for and motion equations are formulated as a differential inclusion. Static friction forces which arise in buffers are computed in a very intuitive and efficient manner, using involving generalised inverses of matrices. The corresponding algorithm is described. Numerical integration is done by an event-driven algorithm. Indeterminate system configurations can be appropriately handled. The number of train vehicles may be easily adjusted, and any wagon connection model can be embedded. Specific phenomena like stick–slip or persistent longitudinal forces can be evidenced. Any feature or situation regarding train collisions may be modelled. A demonstrative application is presented.

Performance-based optimisation of RC frames with friction wall dampers using a low-cost optimisation method

Friction-based dampers can be considered as one of the suitable passive control systems for seismic strengthening and rehabilitation of existing substandard structures due to their high adjustability and good energy dissipation capability. One of the main issues in the design of these systems is to obtain the magnitude of the maximum slip force and the distribution of slip forces along the height of the building. In this study, a practical performance-based optimisation methodology is developed for seismic design of RC frame buildings with friction energy dissipation devices, which allows for an accurate solution at low computational cost. The proposed method aims at distributing the slip loads of the friction dampers to achieve a uniform distribution of damage along the height of the building. The efficiency of the method is evaluated through the optimum design of five different low to high-rise RC frames equipped with friction wall dampers under six natural and six synthetic spectrum-compatible earthquakes. Sensitivity analyses are performed to assess the reliability of the method using different initial height-wise slip load distributions, convergence parameters and earthquake records. The results indicate that optimum frames exhibit less maximum inter-storey drift (up to 43%) and global damage index (up to 75%), compared to uniform slip load distribution. The method is then developed to obtain the optimum design solution for a set of earthquakes representing a design spectrum. It is shown that the proposed method can provide an efficient tool for optimum seismic design of RC structures with friction energy dissipation devices for practical purposes.

Four-wheel independent brake control to limit tire slip under unknown road conditions

This paper presents a four-wheel independent brake control method for vehicle stability under various road conditions without any tire–road friction information. For safety reasons, it is important to guarantee vehicle stability under unknown road conditions. The proposed algorithm is based on analysis of vehicle dynamic behavior on a tire slip force plane, and consists of three parts, Lateral stability decision, Desired motion governor, and Brake allocation. Lateral stability decision identifies whether vehicle is stable or unstable based on ‘Peak slip line’. The desired motion governor determines both target yaw moment and deceleration to stabilize the vehicle. The brake allocation decides brake inputs of four wheels to achieve desired motions. The proposed algorithm has been evaluated via both computer simulations and vehicle tests. The performance evaluation has been conducted on dry asphalt and wet pebble road using E-segment car. It has been shown via both computer simulations and vehicle tests that the proposed algorithm can successfully maintain the vehicle stability under various road conditions. The performance of the proposed algorithm has been compared to previously developed reference yaw rate and side slip angle tracking algorithm at simulation level and built-in Electronic Stability Control(ESC) logic in the vehicle tests. It has been also shown that the proposed control law provides improved performance compared to others.

Analysis of Layered Composite Beam with Imperfect Shear Connection by Means of Energy Method

This paper formulates the principle of minimum of potential energy and principle of minimum of complementary energy for two-layer composite beams with deformable shear connection. The variational priciples formulated will be applied to determine the deflection, slip and internal forces in layered composite beams with non-perfect shear connection. The paper presents a derivation of the Rayleigh-Betti reciprocity relation for Euler-Bernoulli two-layer composite beams with interlayer slip. Applications of the derived reciprocity relation is illustrated by several examples. By the use of Ritz method for the cases of the presented two variational principles some examples are solved and numerical results obtained are compared.