Search results for "Friction."
showing 10 items of 350 documents
Bubbles and Crowding-in of Capital via a Savings Glut
2017
This paper uncovers a mechanism by which bubbles crowd in capital investment. If capital formation is initially depressed by a binding credit constraint, a bubble triggers a savings glut. Higher returns in a new bubbly equilibrium attract additional savings, which are channeled to expand investment at the extensive margin, leading to permanently higher capital, output, and wages. We demonstrate that crowding-in through this channel is a robust phenomenon that occurs along the entire time path.
Frictional and Non-Frictional Unemployment in a Labor Market with Matching Frictions
2016
Using the Mortensen and Pissarides model of a labor market with frictions, this paper proposes a new method, simpler than the one presented in Michaillat (2012), for decomposing unemployment into frictional and non-frictional (rationing) unemployment for a derived rigid wage-setting rule. We use it to compute the frictional and non frictional unemployment rate for two economies characterized by different labor market institutions, namely the US and the Spanish economy. For the entire period under study, the US frictional unemployment rate is around 36 per cent of total unemployment, whereas for Spain, approximately 20 per cent of all unemployment is due to frictions. This outcome may be exp…
Application of 5E model for learning Mechanics through inquiry in secondary education
2018
En este trabajo se examina el proceso de resolución de una actividad de indagación sobre las leyes de Newton que consiste en diseñar un montaje con el cuál averiguar qué superficie es la más adecuada para arrastrar cajas de ropa en un almacén. Los participantes son 23 estudiantes de 4º de ESO. Para la toma de datos se recogen sus respuestas escritas relativas al diseño del dispositivo, a la toma de datos, interpretación de resultados y establecimiento de conclusiones. Para el análisis se examinan utilizando como herramienta el modelo de instrucción 5E. Los resultados principales apuntan a ciertas dificultades en los desempeños del alumnado relativos a la elaboración del montaje y a la expli…
Joining by plastic deformation
2013
Abstract As the scale and complexity of products such as aircraft and cars increase, demand for new functional processes to join mechanical parts grows. The use of plastic deformation for joining parts potentially offers improved accuracy, reliability and environmental safety as well as creating opportunities to design new products through joining dissimilar materials. This paper aims to provide an overview of the state of the art in such joining processes, including cold welding, friction stir welding, self-pierce riveting, mechanical clinching and joining by forming. The paper includes description of the mechanism of joint formation, and analysis of joint performance and applicability.
Globally convergent adaptive and robust control of robotic manipulators for trajectory tracking
2004
This paper deals with a globally convergent adaptive and robust control of robotic manipulators for trajectory tracking in the presence of friction modelled as static nonlinearities. Two control loops are designed according to the cascade control scheme: (a) an inner adaptive control loop, which includes computed torque and PD control actions and friction compensation and (b) an outer robust control loop for unmodelled dynamics compensation. With reference to item (a), two friction compensation schemes are presented; one of them uses both the reference and the actual velocities, whereas the other employs only the actual velocity. Experimental tests carried out on a two-link SCARA manipulato…
An Analytical Tire Model with Flexible Carcass for Combined Slips
2014
Published version of an article in the journal: Mathematical Problems in Engineering. Also available from the publisher at: http://dx.doi.org/10.1155/2014/397538 The tire mechanical characteristics under combined cornering and braking/driving situations have significant effects on vehicle directional controls. The objective of this paper is to present an analytical tire model with flexible carcass for combined slip situations, which can describe tire behavior well and can also be used for studying vehicle dynamics. The tire forces and moments come mainly from the shear stress and sliding friction at the tread-road interface. In order to describe complicated tire characteristics and tire-roa…
Angle Displacement Robust Controller for the Port Plate of the Hydraulic Transformer
2013
The hydraulic transformer is used in the hydraulic system to enhance the efficiency. However, how to control the angle displacement of the port plate is becoming a critical issue because of the new structure of the hydraulic transformer. This paper presents a new method for the angle displacement control system. Firstly, the basic principle of the system is presented. Then, the disturbance which is mainly the friction torque between the port plate and the cylinder block is calculated to estimate the range. Furthermore, the guaranteed cost control (GCC) is analyzed and combined with the disturbance and the characteristics of parameter uncertainties. Finally, the proposed control method is co…
A Neural Network Based Approach for the Design of FSW Processes
2009
Friction Stir Welding (FSW) is an energy efficient and environmentally "friendly" welding process. The parts are welded together in a solid-state joining process at a temperature below the melting point of the workpiece material under a combination of extruding and forging. This technology has been successfully used to join materials that are difficult-to-weld or ‘unweldable’ by fusion welding methods. In the paper a neural network was set up and trained in order to predict the final grain size in the transverse section of a FSW butt joint of aluminum alloys. What is more, due to the relationship between the extension of the “material zones” and the joint resistance, the AI tool was able to…
Seismic response of braced frames with and without friction dampers
1995
Abstract The dynamic response of friction damped bracing systems and ordinary cross-bracing systems inserted into surrounding frames without lateral stiffness is analysed in order to compare the typical behaviour of the two different bracing systems. The cyclic force-displacement relationship in the two cases is accurately modelled on the basis of experimental and related numerical models which are available in the literature, and the structural dimensionless parameters defining the shapes of the cycles are stressed. Systems having the same average period of vibration in the elastic phase of the response are assumed to be comparable with one another, which leads to a relationship linking th…
A Critical Analysis on the Friction Modeling in Orthogonal Cutting of Steel
2007
Numerical simulation of cutting process is today moving towards two different directions. The former concerns the development of high performance codes able to approach the 3D phenomena, the latter is already focused on the study of some fundamental aspects whose full understanding may be strategic for the knowledge enhancing in this very complex field. In the paper this second way was pursued and a wide analysis on the numerical robustness of the 2D orthogonal cutting process is presented. In particular, the role played by the friction modeling is discussed taking into account a wide integrated numerical and experimental campaign.