A real-time multibody model of an off-road vehicle can be used to analyze the dynamics of tasks, such as loading and/or transferring material from deformable ground. This analysis requires an accurate description of the mechanics, hydraulic actuators, and the terrain. The objective of this paper is to introduce a novel, real-time capable, deformable terrain/soil model that can interact with the mechanics of a multibody system model and the dynamics of a hydraulics model. To this end, a tractor is modeled by using a semi-recursive multibody formulation based on velocity transformation. The hydraulic actuation of the tractor's front-loader is modeled by using the lumped fluid theory. The tractor loads and transfers sand material from a deformable sand field (the ground), which is modeled by combining mesh-based and particle-based soil representation approaches for the real-time simulation of soil deformation. The work cycle of the tractor model follows a 3D maneuver that is used to load and transfer sand material. During the digging and dumping operations, the static sand field is converted into sand particles and vice versa respectively. For the presented work cycle, the real-time capability of the system is analyzed and determined. Furthermore, the dynamic actuator forces in the hydraulic cylinders are compared with the static actuator forces. The introduced real-time capable tractor simulation model can be utilized in product development and other product processes. INDEX TERMSDeformable soil/terrain model, hydraulic actuators, multibody system dynamics, real-time simulation, semi-recursive formulation, vehicle dynamics.

The simulation of mechanical systems often requires modeling of systems of other physical nature, such as hydraulics. In such systems, the numerical stiffness introduced by the hydraulics can become a significant aspect to consider in the modeling, as it can negatively effect to the computational efficiency. The hydraulic system can be described by using the lumped fluid theory. In this approach, a pressure can be integrated from a differential equation in which effective bulk modulus is divided by a volume size. This representation can lead to numerical stiffness as a consequence of which time integration of a hydraulically driven system becomes cumbersome. In this regard, the used multibody formulation plays an important role, as there are many different procedures for the constraint enforcement and different sets of coordinates to choose from. This paper introduces the double-step semirecursive approach and compares it with a penalty-based semirecursive approach in case of coupled multibody and hydraulic dynamics within the monolithic framework. To this end, hydraulically actuated four-bar and quick-return mechanisms are analyzed as case studies. The two approaches are compared in terms of the work cycle, energy balance, constraint violation, and numerical efficiency of the mechanisms. It is concluded that the penalty-based semirecursive approach has a number of advantages compared with the double-step semirecursive approach, which is in accordance with the literature.

The estimation of the parameters of a simulation model such that the model’s behaviour matches closely with reality can be a cumbersome task. This is due to the fact that a number of model parameters cannot be directly measured, and such parameters might change during the course of operation in a real system. Friction between different machine components is one example of these parameters. This can be due to a number of reasons, such as wear. Nevertheless, if one is able to accurately define all necessary parameters, essential information about the performance of the system machinery can be acquired. This information can be, in turn, utilised for product-specific tuning or predictive maintenance. To estimate parameters, the augmented discrete extended Kalman filter with a curve fitting method can be used, as demonstrated in this paper. In this study, the proposed estimation algorithm is applied to estimate the characteristic curves of a directional control valve in a four-bar mechanism actuated by a fluid power system. The mechanism is modelled by using the double-step semi-recursive multibody formulation, whereas the fluid power system under study is modelled by employing the lumped fluid theory. In practise, the characteristic curves of a directional control valve is described by three to six data control points of a third-order B-spline curve in the augmented discrete extended Kalman filter. The results demonstrate that the highly non-linear unknown characteristic curves can be estimated by using the proposed parameter estimation algorithm. It is also demonstrated that the root mean square error associated with the estimation of the characteristic curve is 0.08% with respect to the real model. In addition, all the errors in the estimated states and parameters of the system are within the 95% confidence interval. The estimation of the characteristic curve in a hydraulic valve can provide essential information for performance monitoring and maintenance applications.

Gamification aims to redirect the motivating power of game mechanics towards a non-entertainment field to encourage user engagement. In the field of mechanical engineering, the gamification concept can be combined with real-time multibody simulation. The objective of this paper is to demonstrate how gamification can be used to analyze user experiences of a mobile machine. As a case study, an excavator is modeled using a semi-recursive multibody formulation. The excavator model is customizable and offers different sizes for a bucket and dipper arm's hydraulic cylinder. In the excavator model, gamification introduces game elements: goals such as filling the industrial hopper, obstacles such as utility poles, challenges such as fuel gauge, time constraint such as a timer, and fantasy element such as visualization graphics. The effect of different product features, such as the hydraulic system parameters, on the users' performance are analyzed. A product development team can utilize this information to improve the product design.

Dynamic simulation of mechanical systems can be performed using a multibody system dynamics approach. The approach allows to account systems of other physical nature, such as hydraulic actuators. In such systems, the nonlinearity and numerical stiffness introduced by the friction model of the hydraulic cylinders can be an important aspect to consider in the modeling because it can lead to poor computational efficiency. This paper couples various friction models of a hydraulic cylinder with the equations of motion of a hydraulically actuated multibody system in a monolithic framework. To this end, two static friction models, the Bengisu–Akay model and Brown–McPhee model, and two dynamic friction models, the LuGre model and modified LuGre model, are considered in this work. A hydraulically actuated four-bar mechanism is exemplified as a case study. The four modeling approaches are compared based on the work cycle, friction force, energy balance, and numerical efficiency. It is concluded that the Brown–McPhee approach is numerically the most efficient approach and it is well able to describe usual friction characteristics in dynamic simulation of hydraulically actuated multibody systems.