Showing 6 results for Estimator
Volume 11, Issue 2 (9-2011)
Abstract
The error estimation should be a main tool in every adaptivity process. This is the reason for
the great importance of the estimation. It allows us to know the quality of the solution, and
hence, if it is acceptable or not. Moreover, it provides some information about the changes
that are necessary to be made in the mathematical model to reach, in an economic way, the
desired solution. In this paper, a new error estimator for solving the hyperbolic problems to be
used in conjunction with the Collocated Discreet Least Square Meshless (CDLS) method is
presented. The error estimator is shown to be naturally related to the least-squares method,
providing a suitable measure of the errors in the solution. The estimator is easily calculated by
the use of already existing matrices of the least-squares computation, hence, it is very cheap.
The proposed error estimator was implemented with CDLS method to solve three benchmark
examples from the literature and the effect of collocation points on them was investigated.
These examples are nonlinear burgers equation, dam break problem and the problem of
shoaling a wave on sloping shallow waters. The results showed that the error estimator works
very well in all numerical examples.
Reza Kazemi, Shahram Azadi, Naser Esmaeili, Seyed Hamed Tabatabaei Oreh,
Volume 15, Issue 2 (4-2015)
Abstract
In articulated vehicle, the importance of adjustment or confinement of the side slip angle has not yet been investigated. However, their proper dynamic behavior is of great significance. In this research, based on a planar model of articulated vehicle and adopting a proper method, the significance of this quantity is examined. In this article, after a review of the literature, the articulated vehicle model is clarified. The selected model is a validated model of articulated vehicle with 14 degrees of freedom that simulates the vehicle’s directional dynamics. In the analysis of the stability, phase plane method based on the nonlinear model of articulated vehicle with three degrees of freedom is used, which includes the major degrees of freedom in planar motion. In this section, the traction phase plane is drawn via two variables, the side slip angle and the rotational velocity of the articulated vehicle by terms of constant longitudinal velocity of the vehicle as the critical condition and then stable and unstable zones are separated. Fuzzy estimator systems have been based on the Takagi-Sugeno fuzzy model and offer a stable range for the articulated vehicle’s motion according to the results from the phase plane. Finally, the application of phase plane in studying the stability would be magnified by designing two control systems based on the stable range, in order to control the articulation angle and the side slip angle. Eventually, the results are analyzed, and the method is tested based on the vehicle’s full model.
Moharam Habibnejad Korayem, Saeed Rafee Nako, Naim Yousefi Lademakhi,
Volume 16, Issue 8 (10-2016)
Abstract
Full feedback data is mostly essential in control design. The measurement of the variation of flexible joint robot (FJR) actuators is not easy as the measurement of the changes of FJR links’ angles. The measurement of the states is also affected by noise, and the disturbance in the workspace of the robot is not ignorable. Hence a state observer or a nonlinear estimator is necessary to improve the performance of the dynamic system. The state-dependent Riccati equation (SDRE) is one of the most promising nonlinear optimal control methods for estimating variables of systems. Systematic procedure, simple structure, and incorporating wide range of systems (under observability condition) are some advantages of SDRE method. The majority of nonlinear techniques linearize the model, but the SDRE directly uses the nonlinear state space; it is one of the reasons for its precision and flexibility in design with respect to other methods. The goal of this work is to merge the SDRE controller and estimator simultaneously to reduce the state error of the system in presence of external disturbance and measurement noise. So, first, the controller and the observer formulation has been stated. Then, the procedure has been applied to design and to simulate a 3 DOF robot arm with flexible joints. Next, the process has been tested experimentally using Scout robot and the simulation results have been verified. Finally, the proposed method of this paper has been compared with the optimal sliding mode.
Mahmoud Mazare, Mostafa Taghizadeh,
Volume 16, Issue 10 (1-2017)
Abstract
In this paper, constraint equations are derived based on the kinematic model of the robot and Lagrange method is applied to derive the dynamic equations. In order to control the robot position on planned reference trajectories, in presence of uncertainties of the dynamic model, an adaptive robust controller with uncertainty estimator is designed which is robust against the uncertainties and induced noises. The proposed controller consists of an approximately known inverse dynamics model output as model-based part of the controller, an estimated uncertainty term to compensate for the un-modeled dynamics, external disturbances, and time-varying parameters, and also a decentralized PID controller as a feedback part to enhance closed-loop stability and account for the estimation error of uncertainties. Performance of the designed controller is simulated and evaluated in different conditions including the presence of noise and parameters variation. In this regard, a comparison has been made between the response of the proposed adaptive robust controller and response of a feedback linearization controller, indicating their capabilities in noise rejection and compensation of parameters variation. Also, the results show that the proposed sliding mode controller has a desirable performance in tracking the reference trajectories in presence of the model uncertainties and noises for this kind of parallel mechanism.
A. Gholami, M. Majidi, S. Raeisdana, V. Tavoosi,
Volume 20, Issue 2 (1-2020)
Abstract
The torque feedback of the vehicle's steering wheel or driver perception of the steering wheel is one of the aspects of steering quality that has been investigated extensively in recent decades. In this paper, the driver model for sensing torque feedback or haptic interaction between the vehicle equipped with a steer-by-wire system (SWB) and the driver has been designed. The driver model consists of a preview model and a neuromuscular model. The preview driver model calculates the desired angle of the steering wheel to follow the path, and the neuromuscular driver model that can perceive real-time torque feedback determines the real angle of the steering wheel according to muscular system transfer functions to follow its desired angle. Calculating of torques on the steering wheel requires estimation of the tire-road forces. Whereas directly calculating the tire-road forces is too difficult, particularly in the lateral vehicle dynamics, suitable estimator to estimate these forces designed. The simulation results using the Carsim and Simulink software indicate that the driver model performance improved 63 % when torque feedback is enabled. So the designed driver model with torque feedback has an important role in controlling and vehicle steering in conducting double lane-change maneuvers.
Volume 24, Issue 3 (9-2024)
Abstract
Introduction
Financial development is one of the effective factors on economic growth in different countries. The relationship between financial development and economic growth is influenced by various parameters and the economic structure of countries. One of the factors that can affect this relationship is the natural resource abundance and the degree of dependence on them. According to economic literature, natural resource abundance can impact financial efficiency, capital accumulation, and the optimal allocation and effectiveness of financial resources, thereby influencing the relationship between financial development and economic growth in resource-rich countries. This study aims to explore the impact of natural resource abundance on the relationship between economic growth and financial development through productivity in Iran.
Methodology
In order to investigate and empirically analyze the long-term and short-term dynamic relationship between variables, this research employs the Autoregressive Distributed Lag (ARDL) bounding test approach. The ARDL Bounding test method was developed by Pesaran and Shin (1999) and Pesaran et al. (2001). This method offers advantages over other conventional and previous cointegration methods, such as Johansen and Toda-Yamamoto approaches. Some advantages include applicability regardless of considering the order of cointegration between variables, its ability to handle cases where variables are I(0) or I(1), suitability for limited sample sizes, obtaining efficient estimates without risk of over-specification in long-run model relationships, and presenting a reduced form single-equation form rather than a systemic one for the long-run relationship.
Results and Discussion
Based on the results obtained from the research, financial development has not shown a significant impact on economic growth in Iran during the study period. This suggests that institutions and financial entities, particularly the banking system, have not effectively channeled financial resources towards productive investments and market stimulation. However, the abundance index of natural resources has demonstrated a positive and significant influence on economic growth.
Considering the substantial portion of Iran's GDP that is attributed to oil revenues, such a finding is not unexpected. The per capita capital impact on economic growth is also positive and statistically significant. Among the effective factors on economic growth in this study, this variable has exerted the most considerable impact, indicating that capital plays a crucial role in boosting economic growth in Iran. Estimating the factors affecting total factor productivity (which is calculated using the Solow method) also indicates that financial development has had a positive impact on total factor productivity during the study period. However, the ultimate impact of financial development on productivity is influenced by oil revenues, as per the estimated model. The negative and significant coefficient of the interaction variable between financial development and natural resource abundance suggests a negative effect of oil revenues on the relationship between financial development and productivity in Iran. This result could imply an indirect impact of resource abundance on the financial development-economic growth relationship through the productivity channel during the study period in Iran.
Furthermore, it signifies that the heavy dependence on oil, one of the most vital avenues for economic growth, has eroded the relationship with financial development. Hence, the research hypothesis, suggesting that the abundance of natural resources (oil dependence) weakens the relationship between financial development and economic growth in Iran due to its negative impact on productivity, is validated, and the "resource curse" hypothesis is confirmed for the study period in Iran.
Conclusion
The results of this study indicate that financial development had a positive and significant impact on total factor productivity in Iran. However, ultimately, it did not have a significant impact on economic growth. This is due to the abundance of natural resources (oil revenues) leading to a reduction in the positive influence of financial development on total factor productivity. As a consequence, it weakens the relationship between financial development and economic growth during the examined period in Iran. Based on these findings, it is plausible to confirm the hypothesis of the "resource curse" during the examined period in Iran.
The findings can encompass a set of policy recommendations for the Iranian economy. Firstly, the government should be aware of the indirect negative impact of oil dependence on the financial system and, consequently, on investment activities. It is logical for the government to maintain the degree of oil dependence at the lowest possible level, enhance economic diversification, and increase the contribution of other sectors to GDP growth. Additionally, the financial system should engage more in productive investment activities to strengthen its role in improving economic growth. In this regard, policymakers should pursue measures that facilitate improvement of banking intermediation efficiency.
Furthermore, one of the most significant mechanisms of the resource curse in oil-dependent economies is the mismanagement of these resources and neglect of human development. Easy access to oil revenues might exempt the government from investing in human capital development, which could potentially have a negative impact on the performance of the financial sector and other sectors of the economy. Therefore, it is recommended that policymakers prioritize the necessary prerequisites for enhancing human development, which plays a crucial role in enhancing productivity and investment efficiency.
