1,721,289 research outputs found
Cold rolling mill process: a numerical procedure for industrial applications
No full textThis paper proposes a model which is useful for forecasting the
reduction of strip thickness in high-speed strip rolling
with an emulsion lubricant that is able to maintain hydrodynamic
lubrication.
The approach of the model is different when compared
to those of other authors who assume to know:
the original and the final thickness of the strip, the
length of the three zones, the film shape or the film
thickness at the edges, the pressure at the end of
the work zone or the pressure gradients equal to zero
in the work zone; and who in addition integrate the
outlet zone backwards from the exit.
However, in this work, even though the model is
analyzed as a combination between classical equations
of slab analysis and equations of lubrication the
pressure gradient null in the work zone is not considered
but the well-known bi-dimensional expression of
Reynolds, in its full equation, is applied.
In this way the shape of the lubricant film,
not known a priori, could be evaluated by using the
integration procedure with adequate boundary conditions
at the edges of the three zones.
Furthermore, the problem is formulated as a free boundary
one, and a numerical procedure, applied to an industrial plant, is presented
with some results. The model includes lubricant flow and lubricant viscosity depending on pressure
Reply to the letter to the editor 'European cancer mortality predictions for the year 2019 with focus on breast cancer, by Malvezzi M et al' by Marsden and Hamoda, on behalf of the British Menopause Society Medical Advisory Council
No full textDevelopment and implementation of a differential elastic wheel-railcontact model for multibody applications
No full textThe wheel-rail contact analysis plays a fundamental role in the multibody modelling of railway vehicles. A good contact model must provide an accurate description of the global and local contact phenomena (contact forces, position and shape of the contact patch, stresses and displacements) and a general handling of the multiple contact. The model has also to assure high numerical efficiency (in order to be implemented directly online within multibody models) and a good compatibility with commercial multibody software (Simpack Rail, Adams Rail). In this work, an elastic wheel-rail contact model that satisfies the previous specifics is presented. The model considers the wheel and the rail as elastic deformable bodies and requires the numerical solution of Navier's elasticity equation. The contact between wheel and rail has been described by means of suitable analytical contact conditions. Subsequently, the contact model has been inserted within the multibody model of a benchmark railway vehicle (the Manchester Wagon) in order to obtain a complete model of the wagon. The model has been implemented in the Matlab/Simulink environment. Finally, numerical simulations of the vehicle dynamics have been carried out on many different railway tracks with the aim of evaluating the performances of the model. The results obtained with the proposed method have been compared with those obtained by means of a standard commercial software. The main purpose is to achieve a better integration between the differential modelling and the multibody modelling. This kind of integration is almost absent in the literature (especially in the railway field) due to the computational cost and to the memory storage needs. However, it is very important because only the differential modelling allows an accurate analysis of the contact problem (in terms of contact forces, position and shape of the contact patch, stresses and displacements) while the multibody modelling is currently the standard in the study of the railway dynamics. © 2011 Taylor & Francis
Does Trauma Change the Way Individuals with Post-Traumatic Stress Disorder (PTSD) Deal with Positive Stimuli?
No full textIntroduction: Post-Traumatic Stress Disorder (PTSD) is a highly prevalent disorder and a highly debilitating condition. Although current theories focused on depressed mood and intrusion as critical dimensions, the mechanism through which depression increases the risk of PTSD remains unclear. Research usually concentrates on the hyperactive negative valence system (NVS) (e.g., increased fear and threat responses), but some evidence suggests a significant role for the hypoactive positive valence system (PVS) (e.g., less neural activation towards rewards). Method: The main aim of the present research was to investigate whether probable PTSD leads to a different evaluation of the implicit processing in a refugee's sample. Ratings of arousal, dominance, and valence from 60 International Affective Picture System (IAPS) pictures (positive, neutral, and negative) were collected from 42 individuals with probable PTSD, and a group of 26 trauma-exposed individuals (M-age = 28.49 years, SD = +/- 7.78). Results: ANOVA results revealed a main group effect (eta 2p = 0.379) on arousal, dominance, valence dimensions, and pictures' categories (eta 2p = 0.620), confirming evidence according to which PTSD origins a state of maladaptive hyperarousal and troubles the regulation of emotions, and not supporting the view that such difficulties arise only with negative stimuli. Participants with probable PTSD deemed negative stimuli as more threatening than they really are, reacting to unpleasant images with greater negative emotionality (i.e., enhanced arousal and lower valence ratings) compared with individuals without PTSD. Moreover, they rated positive stimuli as less pleasant. Furthermore, arousal ratings were negatively correlated with valence (r = -0.709, p < 0.01) indicating that pictures with high arousal (negative) were associated with lower valence. Discussion: Our findings supported evidence according to which PTSD caused a constant state of hyperarousal and difficulties in regulating emotions facing environmental stimuli. Positive stimuli are considered less pleasant, and this inhibits from completely benefiting from them. Conclusion: Our study provides evidence for a differential and potentially complementary involvement of NVS and PVS in PTSD development. Intervention for PTSD may, thus, target both negative and positive valence processing
Feasibility of Degraded Adhesion Tests in a Locomotive Roller Rig
No full textIn railway applications, the testing of on-board components is necessary to optimize the efficiency of the systems and to allow high safety levels. In order to reduce the time and the cost of the testing phase, the use of dedicated test rigs is being increased. The current paper summarizes some studies for the realization of a full-scale locomotive roller rig. The main mechanical and control problems that arise in the design of this type of test rig have been highlighted, and in particular, the feasibility of tests with degraded adhesion conditions between the wheel and the rail is simulated
Multibody modeling of railway vehicles: Innovative algorithms forthe detection of wheel-rail contact points
No full textThe multibody simulation of railway dynamics needs a reliable and efficient method to properly describe the contact between wheel and rail. In this work innovative methods to evaluate the position of contact points are presented. The aim is to develop a method which can be implemented on-line, assuring a calculation time consistent with real-time calculations of multibody dynamics. At the same time it has to be very accurate, to properly predict the local forces at contact in order to describe even the wear of contact surfaces. In this work the authors present two different approaches to find stationary points during a multibody simulation. In the former the conditions to define a local minima are wrote in an analytical way. This makes possible to combine the conditions in order to reduce the analytic problem's dimension and then to solve numerically the problem with a low computational burden. The latter approach calculates the location of local minima using a method based on neural networks. The paper will cover the details of the proposed methods and the performances, in terms of computation time and accuracy, will be compared with those of the conventional algorithms used by commercial softwares, showing their reliability and low computational burden. Moreover, an implementation of the proposed models in a multibody simulator will be presented, in order to show their suitability for this application. © 2010 Elsevier B.V
On Grasp Quality Measures: Grasp Robustness and Contact Force Distribution in Underactuated and Compliant Robotic Hands
Full text linkThe availability of grasp quality measures is fundamental for grasp planning and control, and also to drive designers in the definition and optimization of robotic hands. This work investigates on grasp robustness and quality indexes that can be applied to power grasps with underactuated and compliant hands. When dealing with such types of hands, there is the need of an evaluation method that takes into account the forces that can be actually controlled by the hand, depending on its actuation system. In this paper, we study the potential contact robustness and the potential grasp robustness (PCR, PGR) indexes. They both consider main grasp properties: contact points, friction coefficient, etc., but also hand degrees of freedom and consequently, the directions of controllable contact forces. The PCR comes directly from the classical grasp theory and can be easily evaluated, but often leads to too conservative solutions, particularly when the grasp has many contacts. The PGR is more complex and computationally heavier, but gives a more realistic, even if still conservative, estimation of the overall grasp robustness, also in power grasps. We evaluated the indexes for various simulated grasps, performed with underactuated and compliant hands, and we analyzed their variations with respect to the main grasp parameters
A numerical procedure based on orowan's theory for predicting the behavior of the cold rolling mill process in full film lubrication
No full textIn this paper, a numerical model for predicting the working parameters of the cold rolling
mill process in full film lubrication is presented. The model is useful from an industrial point
of view, because it can forecast the thickness reduction of the metal sheet and the pressure trend,
so that the rolling mill process parameters can be regulated to obtain a specific output thickness.
Experimental tests were performed, and results are compared to the theoretical ones resulting from
the model. The novelty of the proposed model is that it combines Orowan’s theory for the plastic
deformation analysis with the Reynolds equation in full film lubrication and the continuity conditions.
The lubricant flow and viscosity are studied, taking in account their dependence on pressure and
temperature. The proposed model describing the full film regime is also compared to another one,
previously proposed by the authors, based on the well-known slab analysis and sharing with it the
representation of the lubrication regime, the mathematical procedure, and the boundary conditions.
The results show that the proposed model provides a better prediction of the working parameters
with respect to the model based on the slab analysi
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