Aquifer-wide estimation of longitudinal dispersivity by the combination of empirical equations, inverse solution, and aquifer zoning methods

Longitudinal dispersivity is a key parameter for numerical simulation of groundwater quality and this parameter is highly variable in nature. The use of empirical equations and the inverse solution are two main methods of estimating longitudinal dispersivity. In this study, the estimation of values and aquifer-wide spatial distribution of longitudinal dispersivity parameter using a combined approach i.e. a combination of empirical equation method (Pickens and Grisak, Arya, Neuman, and Xu & Eckstein equations), the inverse solution method (using the MT3DMS model with non-automatic calibration) and the aquifer zoning technique is investigated. The combined approach applied to Bandar-e-Gaz aquifer in northern Iran, and Willmott’s index of agreement was used to assess the precision of simulation of total dissolved solids in this aquifer. The values of this criterion were 0.9985 to 0.9999 and 0.9756 to 0.9992 in calibration and validation periods that show the developed combined approach resulted in obtaining high precision for both calibration and validation periods and the simulation show remarkable consistency. Also, the one-way sensitivity analysis indicates that the longitudinal dispersivity is more sensitive than the effective porosity in this simulation. The investigation of the spatial distribution of the estimated longitudinal dispersivity by the combined approach indicates that the value of the parameter has a decreasing trend from the south to the north (50 to 8 m) in the aquifer environment which is consistent with the changes in the characteristics of porous media in this study area, and therefore it concludes that the combined approach provides a reliable and appropriate estimation of the spatial distribution of longitudinal dispersivity.

Modeling Method of Autonomous Robot Manipulator Based on D-H Algorithm

With the continuous development of science and technology, robotics is widely used in various fields. In recent years, more and more research studies have been done on the control of autonomous robotic manipulators. How to quickly, accurately, and smoothly grasp objects has always been a difficult point of research. As the robot’s executive mechanism, the robot arm plays an important role in whether the robot can complete a specific task. Therefore, the research on the robot arm is also the main topic in the development of robot technology. The control theory, kinematics, and human-computer interaction of robotic arms are the focus of the research in the field of robotic arms. Based on the above background, the research content of this paper is the research on the modeling method of autonomous robotic manipulator based on D-H algorithm. This paper uses D-H modeling method to model a four-degree-of-freedom robotic arm and gives the forward kinematics equation of the robotic arm. The inverse solution of the manipulator was given by the method and the geometric method, and the joint variable values were calculated. Finally, through experimental simulation, the experimental results show that the inverse solution of the end position of the machine by the geometric method is in the range of 2∼4 mm, and the inverse solution of the end position of the machine by the algebraic method is in the range of 6∼14 mm. It is more accurate to find the inverse solution of the geometrical method of the manipulator than the algebraic method.

Precise semi-analytical inverse kinematic solution for 7-DOF offset manipulator with arm angle optimization

Seven-degree-of-freedom redundant manipulators with link offset have many advantages, including obvious geometric significance and suitability for configuration control. Their configuration is similar to that of the experimental module manipulator (EMM) in the Chinese Space Station Remote Manipulator System. However, finding the analytical solution of an EMM on the basis of arm angle parameterization is difficult. This study proposes a high-precision, semi-analytical inverse method for EMMs. Firstly, the analytical inverse kinematic solution is established based on joint angle parameterization. Secondly, the analytical inverse kinematic solution for a non-offset spherical-roll-spherical (SRS) redundant manipulator is derived based on arm angle parameterization. The approximate solution of the EMM is calculated in accordance with the relationship between the joint angles of the EMM and the SRS manipulator. Thirdly, the error is corrected using a numerical method through the analytical inverse solution based on joint angle parameterization. After selecting the stride and termination condition, the precise inverse solution is computed for the EMM based on arm angle parameterization. Lastly, case solutions confirm that this method has high precision, and the arm angle parameterization method is superior to the joint angle parameterization method in terms of parameter selection.