Modelling and validation of off-road vehicle ride dynamics

Increasing concerns on human driver comfort/health and emerging demands on suspension systems for off-road vehicles call for an effective and efficient off-road vehicle ride dynamics model. This study devotes both analytical and experimental efforts in developing a comprehensive off-road vehicle ride dynamics model. A three-dimensional tire model is formulated to characterize tire–terrain interactions along all the three translational axes. The random roughness properties of the two parallel tracks of terrain profiles are further synthesized considering equivalent undeformable terrain and a coherence function between the two tracks. The terrain roughness model, derived from the field-measured responses of a conventional forestry skidder, was considered for the synthesis. The simulation results of the suspended and unsuspended vehicle models are derived in terms of acceleration PSD, and weighted and unweighted rms acceleration along the different axes at the driver seat location. Comparisons of the model responses with the measured data revealed that the proposed model can yield reasonably good predictions of the ride responses along the translational as well as rotational axes for both the conventional and suspended vehicles. The developed off-road vehicle ride dynamics model could serve as an effective and efficient tool for predicting vehicle ride vibrations, to seek designs of primary and secondary suspensions, and to evaluate the roles of various operating conditions

Ride and directional dynamic analysis of articulated frame steer vehicles

ABSTRACT Pazooki Alireza, Ph.D. Concordia University, 2012 Articulated frame steer vehicles (ASVs), widely employed in different off-road sectors, are generally unsuspended vehicles. Owning to their complex operating environment, high mass center, relatively soft and large diameter tires, wide load variations and load distribution, and kineto-dynamics of the frame steering mechanism, these vehicles transmit higher magnitudes of low frequency whole-body vibration (WBV) to the operators and also exhibit lower roll and directional stability limits. While the superior performance potentials of axle suspension in limiting the WBV exposure have been clearly demonstrated, the implementations in ASVs have been limited due to the complex design challenges associated with conflicting requirements posed by the ride and roll/directional stability requirements. Growing concerns on human driver comfort and safety, and increasing demands for higher speed ASVs such as articulated dump trucks, however, call for alternate suspension designs for realizing an improved compromise between the ride and stability performance. This dissertation research is aimed at analysis of a torsio-elastic axle suspension concept for achieving improve ride, while preserving the directional stability limits of the ASV. For this purpose a comprehensive three-dimensional model of the articulated frame steer vehicles is developed for design and analysis of the proposed axle suspension concept. The model is formulated considering a three-dimensional tire model, tire lag, coherent right- and left-terrain track roughness, and kinematics and dynamics of the steering struts. Field measurements were performed to characterize the ride properties of a conventional forestry skidder and that of a skidder retrofitted with the rear-axle torsio-elastic suspension under different load conditions. The measured data were analyzed to assess the ride performance potential of the suspension and to examine validity of the simulation model. Both the field measured and simulation results revealed that the proposed suspension could yield significant reductions in the magnitudes of vibration transmitted to the operator location, irrespective of the load and speed conditions. A simple yaw-plane model of the vehicle is also formulated to study the role of steering system design including the steering valve flows, kineto-dynamics of the steering struts and leakage flows on the snaking stability limits of the ASV. The results showed that the critical speeds are strongly dependent upon the kineto-dynamics of the articulated steering system. The comprehensive three-dimensional model subsequently used for analysis of integrated ride and roll/directional stability limits of the vehicle and the axle suspension designs. The stability performance measures are defined to assess the vehicle stability limits under steady as well as transient directional maneuvers. The results show that the proposed rear-axle suspension deteriorates the stability performance only slightly, irrespective of the load condition. It is concluded that the proposed suspension concept could yield a very good compromise in ride and stability performance. The proposed model could serve as an effective and efficient tool for integrated ride and handling analysis and to seek primary suspension designs for an improved compromise between the ride and stability performance of ASVs

Collection, identification of Iranian fish parasites for “Iranian parasitology Museum”

Abstract: Identification and classification of aquatic parasites are more important by the day. Aquaculture development are faced with parasites previously "not pathogenic in normal conditions, but under certain conditions bacame diseases and have caused heavy losses to the aquaculture farms. The results of these studies recognize the importance of parasites in fish production has clear economic value. Before any action for economic aquatic breeding the parasites that can infect the fish have been identified and methods of control will be drawn. The current project is a part (the fishes) of the project Parasitology Museum in the Faculty of Veterinary medicine of Tehran University. In the first phase of the project, it was planned the fish parasites from different regions of the country were collected and the Iranian Fish Parasites Data Base has also set up. Required experts and various specialties were organized for implementation an recognation of the collected parasitese. The province executive and coordination necessary and the methods of sampling were discussed after a day of training workshop was held at the Faculty of Veterinary medicine of Tehran University. Due to the lack of funds needed to coordinate the implementation, it was conducted that the parasite specimens collected from other projects. In the first phase of projects 261 parasites various have been sent. Collected samples received a temporary code and announced. In the laboratory the specimens categoried and the shape designed and finally the consultants send the final identification of the parasites. Posted parasites according to the latest international standards are maintained. Each parasite has a unique code that represents the name of the sender, verification of the final consultant, host and fishing region. Simultaneously, reported fish parasites from 1327 AD (1949 AD) were collected to create a database, they classified to be placed on the site inPersian and English. Fish parasites that have been reported are available in four types: final report of the research projects conducted at research centers and universities, student theses, abstracts published in scientific conferences and finally "published in national and international research journals. “Iranian fish parasitesd database” included: Founders and Pioneers Monument, Iranian fish parasite fauna, History, Search, Resources, Executive Committee, links, News. Researchers can search through the five “key words”: the name of the parasite, the parasite class branch, region or provincial fishing, infected of host organ. After achieving the desired list of parasites, descriptions, and specifications can be observe. The resource section lists some of the articles published and will be visible as a “pdf”

Kineto-dynamic directional response analysis of an articulated frame steer vehicle

Owing to their high mass centre, relatively soft tyres, extreme variations in the load and load distributions during work cycles and greater flexibility of the steering system, the articulated steer vehicles (ASV) exhibit lower directional stability limits compared to vehicles with conventional steering. In this study, a kineto-dynamic model of the frame steering mechanism is formulated in conjunction with a nonlinear yaw-plane model of an articulated dump-truck. The validity of the model is demonstrated based on the available measured data. The proposed model is initially analysed to derive response characteristics of the steering system in terms of articulation angle, valve opening, strut orientations and deflections, fluid pressures and resultant strut forces and torque. The influences of variations in selected operating and design parameters on the steering system responses are investigated under a steady-turning and pulse steering inputs. The results provide important design guidelines with regard to kinematic and dynamic parameters of the steering mechanism and show that the lateral stability of the ASV is strongly influenced by the effective damping of the steering mechanism which is determined by kineto-dynamic characteristics of the articulated steering system including leakage flows across the struts piston, valve flow characteristics and struts orientations

Effect of terrain roughness on the roll and yaw directional stability of an articulated frame steer vehicle

Compared to the vehicles with conventional steering, the articulated frame steer vehicles (ASV) are known to exhibit lower directional and roll stability limits. Furthermore, the tire interactions with relatively rough terrains could adversely affect the directional and roll stability limits of an ASV due to terrain-induced variations in the vertical and lateral tire forces. It may thus be desirable to assess the dynamic safety of ASVs in terms of their directional control and stability limits while operating on different terrains. The effects of terrain roughness on the directional stability limits of an ASV are investigated through simulations of a comprehensive three-dimensional model of the vehicle with and without a rear axle suspension. The model incorporates a torsio-elastic rear axle suspension, a kineto-dynamic model of the frame steering struts and equivalent random profiles of different undeformable terrains together with coherence between the two tracks profiles. The simulations are performed to determine the stability limits of the ASV models while operating on different terrains, namely: a perfectly smooth surface, plowed field, pasture, gravel road, and the MVEE random course. The directional stability limits are defined in terms of the static and dynamic rollover thresholds, rearward amplification ratio, and critical speed corresponding to snaking instability under steady and transient steering inputs. The results suggest that the tire interactions with the rough terrains affect the stability limits of both the unsuspended and suspended vehicles in a highly adverse manner. The suspended vehicle responses, however, show less sensitivity to variations in the road roughness profile

Experimental and analytical evaluations of a torsio-elastic suspension for off-road vehicles

The ride performance potentials of a prototype torsio-elastic axle suspension for an off-road vehicle were investigated analytically and experimentally. A forestry vehicle was fitted with the prototype suspension at its rear axle to assess its ride performance benefits. Field measurements of ride vibration along the vertical, lateral, fore-aft, roll and pitch axes were performed for the suspended and an unsuspended vehicle, while traversing a forestry terrain. The measured vibration responses of both vehicles were evaluated in terms of unweighted and frequency-weighted rms accelerations and the acceleration spectra, and compared to assess the potential performance benefits of the proposed suspension. The results revealed that the proposed suspension could yield significant reductions in the vibration magnitudes transmitted to the operator's station. The field evaluations revealed that suspended vehicle could yield 35%, 43% and 57% lower frequency-weighted rms accelerations in the x -, y - and z -axis, respectively, compared to the unsuspended vehicle, when loaded. A 13-degrees-of-freedom model of the suspended vehicle was subsequently developed and validated using the measured data, which could serve as a design tool for deriving optimal suspension designs for a wide range of vehicles. The model results revealed reasonably good agreements with the measured vibration spectra. From the simulation results, it was further concluded that a reduction in the vertical stiffness of the torsio-elastic member would yield beneficial effects on the overall weighted vertical and pitch rms acceleration magnitudes

Ride dynamic evaluations and design optimisation of a torsio-elastic off-road vehicle suspension

The ride dynamic characteristics of a novel torsio-elastic suspension for off-road vehicle applications are investigated through field measurements and simulations. A prototype suspension was realised and integrated within the rear axle of a forestry skidder for field evaluations. Field measurements were performed on forestry terrains at a constant forward speed of 5 km/h under the loaded and unloaded conditions, and the ride responses were acquired in terms of accelerations along the vertical, lateral, roll, longitudinal and pitch axes. The measurements were also performed on a conventional skidder to investigate the relative ride performance potentials of the proposed suspension. The results revealed that the proposed suspension could yield significant reductions in magnitudes of transmitted vibration to the operator seat. Compared with the unsuspended vehicle, the prototype suspended vehicle resulted in nearly 35%, 43% and 57% reductions in the frequency-weighted rms accelerations along the x-, y- and z-axis, respectively. A 13-degree-of-freedom ride dynamic model of the vehicle with rear-axle torsio-elastic suspension was subsequently derived and validated in order to study the sensitivity of the ride responses to suspension parameters. Optimal suspension parameters were identified using the Pareto technique based on the genetic algorithm to obtain minimal un-weighted and frequency-weighted rms acceleration responses. The optimal solutions resulted in further reduction in the pitch acceleration in the order of 20%, while the reductions in roll and vertical accelerations ranged from 3.5 to 6%