Based on the resistance characteristics, a model of theoretical  digging force was proposed in this paper, taking the tangential force, the normal force, and the bending moment into account simultaneously. Utilizing the relation among the normal resistance, the resistance moment, and the tangential resistance in practical digging process, three independent unknown quantities are transformed into only one variable. Afterwards, according to different digging patterns and complete machine limiting conditions, this research derived the constraint inequalities of the limiting digging force (LDF) and established the calculation models for LDF. Then, based on the value distribution laws of the digging resistance coefficient and the resistance moment coefficient, the calculation process and corresponding method of LDF under a given digging posture were obtained. Taking the digging resistance obtained by testing for 35 t hydraulic excavator with backhoe attachment as the reference, this paper compared the calculation results of the theoretical digging force for complete machine with those of the LDF model proposed in this research. The comparative results indicate that the LDF is consistent with the fact that the theoretical digging force is larger than or at least equal to the actual digging resistance. So, the LDF can exactly show the real limiting digging ability of the excavator more accurately. In this way, it can provide basis for mechanism optimization, structural strength design, trajectory planning, and control automation of the excavator.

No abstract

The digging resistance in a normal state is the key to excavator design and automated excavation. It is difficult to accurately predict, simulate, or directly measure the digging resistance in a normal state due to uncertainties in the soil properties and excavation parameters. In this paper, a research idea is proposed that uses the working device as the entry point to indirectly calculate the digging resistance in a normal state by measuring the motion parameters and the cylinder pressure intensity. Based on the rule of combination for spatial force systems, a method for combining and projecting the system of the digging resistance is proposed in which the system is projected as six parts, and the tangential force, normal force, and bending moment in the plane of symmetry of the working device are the objects of the solution to avoid redundant equations. Based on kinematics and dynamics models of the excavator and the force and moment equilibrium conditions of the working device, equations for the active-side calculation of the incomplete digging resistance are derived. Based on these equations, the motion parameters of the working device and data on the cylinder pressure intensity obtained by measurement are used to calculate the incomplete digging resistance. The validation scheme and process proposed use the incomplete digging resistance as the external load to obtain the simulated stress of the working device through transient analysis. The simulated stress and the measured stress corresponding to the position of the measurement point are extracted and compared. The results show that there is a difference in the size of the numerical value between the simulated and measured stress, but the variation law is highly consistent, which validates the calculation method. In this paper, an active-side calculation method is provided for the incomplete digging resistance in a normal state without considering the soil-tool interaction relationships, which lays a theoretical foundation for the study of the digging resistance characteristics in a normal state, as well as excavator design and automated excavation.

In order to reduce the weight and improve aerodynamic characteristics, the new aircraft generally adopts lightweight composite materials and high-aspect-ratio layout. Such the structural layout aircraft will produce large nonlinear aeroelastic deformation under the action of aerodynamic loads. Due to the anisotropy of the composite, the composite ply angle of wing skin has a great influence on the elastic deformation of the high-aspect-ratio wing. In order to study the influence of the ply angle on the nonlinear static aeroelastic wing deformation, based on CFD/CSD unidirectional fluid-solid coupling, the structural deformation and stress of high-aspect-ratio composite wing were numerically solved. The wing deformation along the lift direction was taken as the optimization target. The structure strength was taken as the constraint. The ply angle for the composite skin of the high-aspect-ratio composite wing was optimized by the Screening method. The optimization results show the nonlinear static aeroelastic deformation of the wing in the lift direction is reduced by 39.1 %. The maximum stress of the wing beam and rib is reduced by 39.0 %. The maximum Tsai-Wu failure factor of the wing skin is reduced by 47.1 %.

In this paper, in order to understand the influence of the unbalanced coefficient of composite laminates on the static aeroelasticity of high aspect wings, a series of numerical simulation calculations were carried out, and this work wants to provide some reference for the structural design of aircraft. Considering the influence of geometric nonlinearity, the unidirectional fluid-solid coupling calculation method based on loose coupling is used to control the change of unbalanced coefficient of laminates on the basis of layering angle, layering thickness, and layering region, so as to observe the changes caused to the wings. The relationship between the unbalanced coefficient and the constant thickness layup and the variable thickness layup with 0° and ±45° layup angles was studied, respectively. Then, the layup angle of 90° was added to study the influence of the unbalanced coefficient on the static aeroelasticity of the wing structure with the change of the layup angle and the different choice of layup region. The results show that the deformation is the smallest when the unbalanced coefficient is 0.5, and the deformation trend is evenly distributed along both sides when the unbalanced coefficient is 0.5. When the unbalanced coefficient is changed, adding the 90° layup angle can significantly reduce the overall deformation of the wing and show different sensitivity characteristics to different layup areas. The increase of the unbalanced coefficient makes the chordal displacement gradually change from linear distribution to nonlinear distribution along the spread direction, and the displacement will gradually decrease.