1,720,983 research outputs found
Setup of a 1D Model for Simulating Dynamic Behaviour of Motorcycle Forks
No full textShock absorbers and damper systems are important parts of automobiles and motorcycles because they have effects on safety, ride comfort, and handling. In particular, for vehicle safety, shock absorber system plays a fundamental role in maintaining the contact between tire and road. Generally, to assure the best trade-off between safety and ride comfort, a fine experimental tuning on all shock absorber components is necessary. Inside a common damper system the presence of several conjugated actions made by springs, oil and pressurized air requires a significant experimental support and a great number of prototypes and test. Aimed to reduce the design and tuning phases of a damper system, it is necessary to join these phases together with a numerical modelling phase.
The aim of this paper is to present the development of a mono-dimensional (1D) model for simulating dynamic behaviour of damper system. In particular, a conventional telescopic fork produced by PAIOLI MECCANICA has been considered as testing bench. It is important to underline that the same approach could be used to simulate the dynamic behaviour of an automobile shock absorber system. Fork numerical modelling has to assure a faster design process and a performance optimisation, reducing at the same time, the design time between the product idea and its final assembly. PAIOLI MECCANICA had the necessity of modelling its forks in order to quickly test different solutions and to improve actual fork performances. The present research concerns only fore-carriage forks for road applications, i.e. forks used in motorcycle not dedicated to races.
The fork model is developed in AMESim code using both hydraulic and pneumatic libraries. A sinusoidal displacement is directly impressed to the fork rod at different axial velocities (from 100 to 2000 mm/s) for simulating the axial excitation imposed to an actual fork by the road discontinuities. Numerical results are compared with experimental data recorded by PAIOLI MECCANICA. In particular, the fork numerical model demonstrates of being capable to reproduce the testing fields typically used as experimental test bench for motorcycle forks
Coupling Between 1D-3D Simulation Results to Predict Cavitation in Motorcycle Forks
No full textFork system is a primary component for motorcycles because it assures the contact between tires and road, therefore the safety and the driving feeling. Usually fork optimization and tuning are experimentally made involving the generation of a high large number of prototypes and an expensive experimental campaign. To reduce the design and the tuning phases of a generic damper system, the numerical simulation should be considered.
In this paper, a one-dimensional (1D) model of fore-carriage forks for road applications is presented. The model was built-up in AMESim code. In particular, the authors’ attention was focused on the detection and analysis of cavitation phenomenon inside the fork. As well known, the cavitation is a complex three-dimensional (3D) phenomenon that implies the phase transition. Cavitation development and prediction are beyond 1D model capabilities, therefore the 1D fork model was improved by 3D Computational Fluid Dynamic (CFD) multiphase simulations performed by using Fluent v12 (beta version). 3D numerical results were integrated into the 1D model to define a new numerical test methodology able to reproduce the overall fork behaviour.
All 1D numerical results were compared to experimental damping force traces obtained for different fork rod axial velocities
Evidence that the β-acid fraction of hops reduces central GABAergic neurotransmission
No full textHumulus lupulus (hops) is traditionally used as a tranquilizing herbal remedy. Here, we investigated the in vivo and in vitro effect of hop β-acids on central nervous system function. Oral administration of β-acids (5–10 mg/kg) in rats produced an increased exploratory activity in the open field, a reduction in the pentobarbital hypnotic activity and a worsening of picrotoxin-induced seizures. When dosed at 10 mg/kg, β-acids increased, in the elevated plus maze, open arm entries reducing in parallel those in closed arms. In the forced swimming test, we observed a reduction in the immobility time that could suggest an antidepressant-like activity. Electrophysiological studies performed on cerebellar granule cells in culture showed that the β-acids fraction decreased GABA-evoked current in a dose-dependent way. The effect was not inhibited by the benzodiazepine antagonist Ro 15-1788. Benzodiazepine receptors involvement was also excluded by [3H]-Ro 15-1788 binding assay. In conclusion, the behavioral effects of β-acids fraction could be explained by a reduction in the GABAergic activity although we cannot rule out the involvement of other neurotransmitter system
Activity of single components of Ferula hermonis on male rat sexual behavior
No full textThe influence of the single components of Ferula hermonis extract on sexual behavior was studied in male rats. Sexually potent and sluggish/impotent animals were orally treated acutely (2.5 mg/kg) and subchronically (0.25 mg/kg/day for 10 days) with ferutinin, teferdin and teferin. Ferutinin alone acutely administered in potent rats was able to reduce mount and intromission latencies, while in sluggish/impotent animals, it induced the same effects and additionally shortened the ejaculation latency, as teferdin did. Both substances increased testosterone levels in rats. Unlike teferdin, ferutinin subchronically administered in potent rats negatively affected appetitive and consummatory sexual behavior, reducing also testosterone serum levels. In conclusion, if repetitively administered, ferutinin was able to stimulate sexual behavior after acute ingestion, but exerted a negative influence on the sexual capacity of potent male rats, whereas teferdin only improved copulatory performance of sluggish/impotent animals
Analysis of Air/Cavitation Interaction Inside a Rotary Vane Pump for Application on Heavy Duty Engine
No full textThis paper deals with a CFD three-dimensional multiphase simulation of rotary vane pump.
The paper presents a suitable methodology for the investigation of the cavitation effects and/or incondensable gases. All the 3D simulations were performed by using Fluent v12 (Beta version). A moving mesh methodology was defined to reproduce the change-in-time shape of the internal pump volumes. In particular, the pump analysis was focused on the generation, and evolution of the cavitation phenomena inside the machine to identify the locations where these phenomena could occur. Moreover, the influence of incondensable gas dissolved inside the operator fluid on both pump performance and cavitation evolution was evaluated. Significant results were obtained about the analysis of incondensable gas influence on the cavitation evolution showing that, today, CFD analysis can provide detailed information on such harmful phenomena which cannot be achieved by experiments.
The approach adopted is generic in nature, and the obtained results can be easily used to optimize other pump designs
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Implementation of a Finite-Element Based Mesh Motion Technique in an Open Source CFD Code
No full textNowadays, Computational Fluid Dynamic (CFD) codes are widely used in different industrial fields. Although hardware and numerical model improvements, the mesh generation remains one of the key points for a successful CFD simulation. Mesh quality is influenced by the adopted mesh generator tool and, after all, by the designer's experience and it becomes very important when moving meshes are required. In fact, mesh skewness, aspect ratio, and non-orthogonality have to be controlled during the deforming process since their wrong evolution could produce an unphysical behavior of the computed flow field. Mesh motion could be performed by different strategies: dynamic smoothing operation and dynamic re-meshing operation, are, today, two of the mainly used approaches. All of them can be combined to guarantee the correct reproduction of motion profile and a good mesh quality level. In this context, the authors have implemented a moving mesh methodology in the Open Source CFD code OpenFOAM®. A multiple number of meshes is used to cover the whole simulation period, and the grid point motion is accommodated by an automatic mesh motion techinque with polyhedral cell support. The Laplace equation is chosen to govern mesh motion. This guarantees that an initial valid mesh remains valid for arbitrary boundary motion. Mesh to mesh interpolation is performed by using a cell based, distance weighted interpolation technique. The proposed approach was tested on a real IC-engine geometry. In particular, the mesh quality evolution during motion, the numerical results and the computational costs were evaluated
Multi-dimensional modeling of the air/fuel mixture formation process in a PFI engine for motorcycle applications
No full textThe preparation of the air-fuel mixture represents one of the most critical tasks in the definition of a clean and efficient SI engine. Therefore it becomes necessary to consolidate the numerical methods which are able to describe such a complex physical process.
Within this context, the authors developed a CFD methodology into an open-source code to investigate the air-fuel mixture formation process in PFI engines. Attention is focused on moving mesh algorithms, Lagrangian spray modeling and spray-wall interaction modeling.
Since moving grids are involved and the mesh quality during motion strongly influences the computed in-cylinder flow-field, a FEM-based automatic mesh motion solver combined with topological changes was adopted to preserve the grid quality in presence of high boundary deformations like the interaction between the piston bowl and the valves during the valve-overlap period.
The fuel spray was modeled by using the Lagrangian approach, and the spray sub-models (atomization and breakup) were tuned according to experimental validations carried out in previous works. Specific submodels were implemented to describe the impingement of fuel spray with the engine walls. The evolution of the resulting liquid film was also taken into account by solving the mass and momentum equations with the Finite-Area discretization method.
The proposed methodology was applied to simulate a single-cylinder SI engine for motor-scooter applications at a low load operating condition. This operating point was chosen since these engines often run very close to idle conditions when they are used in the urban areas
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