Showing 15 results for Pension System
Volume 10, Issue 4 (12-2010)
Abstract
Vehicles are subject to random road excitations due to road unevenness and variable velocity which causes ride discomfort and fatigue. Ride comfort could be improved by decreasing vehicle accelerations. In this paper, to evaluate the vehicle ride comfort, root mean square acceleration response (RMSAR) is calculated using power spectral density (PSD) of road excitations and these quantities are compared with the ISO2631 boundary values. Then by considering ISO2631, the vehicle’s RMSAR is minimized by optimal design of vehicle suspension viscous damping and stiffness parameters. To solve this nonlinear constrained optimization problem, we utilize genetic algorithms. Also, in the design process the physical restrictions are included. Obtained results demonstrate a considerable improvement of vehicle ride comfort and its dynamic response as a result of reduced accelerations. Comparing the obtained results with those obtained by method of nonlinear programming confirms the supremacy of genetic algorithms.
Volume 11, Issue 1 (6-2011)
Abstract
In this paper the idea of energy regeneration of active suspension system in hybrid electric vehicle is presented and its influence on the fuel consumption and emissions of vehicle is investigated through computer simulations. Active suspension systems employ active actuators to apply force and control the vibrations of vehicle body. The active actuators either insert energy to the system or extract the energy of vibrations when required. Using an energy regeneration system, the extracted energy of vibrations can be recovered and stored in the energy storage system. In hybrid electric vehicles, the active suspension supplies its required energy from the electric energy storage system of vehicle. In this work, a hybrid battery/supercapasitor energy storage system is employed to supply the required energy of active suspension and other electric components of vehicle. The simulation results show that with application of the energy regeneration system, the fuel consumption and exhaust emissions of vehicle is reduced.
Volume 13, Issue 12 (2-2014)
Abstract
During modal testing, the test structure is connected to its surroundings by a suspension system. Cable suspension system is one of the most common suspension systems which is used to simulate the free-free condition, due to its low stiffness. In this condition, the measured modal properties are assumed to be free-free dynamic properties of the test structure. But in situations in which the test structure is big and flexible, the stiffness of the suspension system is comparable with the stiffness of the test structure and cannot be neglected. In this paper, the suspension effects are eliminated from measured modal frequencies of a flexible structure which is suspended by a cable suspension system. The eigenvalue sensitivity analysis is done and then, the effective stiffness of the cable suspension system is derived. Based on the eigenvalue sensitivity and the effective stiffness of the suspension system, an iterative procedure is proposed to eliminate the suspension effects from measured modal frequencies of the test structure. The proposed iterative procedure is verified using a finite element model. Finally, the proposed iterative procedure is used to eliminate the suspension effects from measured modal frequencies of a real flexible structure.
Volume 15, Issue 11 (1-2016)
Abstract
In this paper, a novel test rig for a quarter car suspension system of Samand with McPherson mechanism is fabricated and its elasto-damping elements are dynamically identified. The inputs of test rig are road roughness and its acceleration and the outputs are sprung mass acceleration, un-sprung mass acceleration, suspension deflection, and tire deflection which are recorded by sensors. The test rig of suspension system includes McPherson mechanism with nonlinear spring and damper. This system is categorized as a multi-input-multi-output (MIMO) identified system. The nonlinear least squares iterative method, as a gray-box identification method, is used for finding the elasto-damping coefficients of tire and suspension elements. In this method, a nonlinear mathematical model is considered for the system and its parameters are calculated using the test rig data. The Levenberg–Marquardt algorithm (LMA) is used to solve the non-linear least squares problem. The outputs of the identified nonlinear model are compared with the measured experimental data. As a result, the test rig outputs are followed by the outputs of the identified model with acceptable errors. The compared results indicate a good performance of the proposed model to estimate the behavior of the nonlinear suspension elements.
Volume 16, Issue 2 (4-2016)
Abstract
In this paper, a new approach has been presented for dynamic control of active suspension vehicle system subject to the road disturbances. The active suspension system (ASS) which has been considered in this paper is operated by a hydraulic actuator. The input of this hydraulic actuator is a servo valve. In the other word, both mechanical equation of system (related to hydraulic actuator) and its electrical equation (related to servo valve) are considered. Therefore, the equations are complicated and only the input current of servo valve is accessible as the input control signal. The proposed approach is based on dynamic sliding mode control (DSMC).In DSMC chattering is removed due to the integrator which is placed before the input control signal of the plant. However, in DSMC the augmented system (the system plus the integrator) is one dimension bigger than the actual system and then, control of the plant is more complicated. But, its advantage is that the input control signal is obtained from a dynamic system or a low pass filter, while the robust performance (invariance property) of the system is reserved even in the presence of disturbance. Another advantage of proposed approach is that the desired output force of the hydraulic actuator is obtained by the controller.
Volume 16, Issue 9 (11-2016)
Abstract
Recently, H-Infinity adaptive fuzzy controller (HAFC) and its potential application in improving vehicle stability has some attention. This paper studied this application by developing a nonlinear model for the vehicle suspension mounting point displacement (SMD) and the variable geometry suspension system (VGS). The VGS model was developed by deriving the kinematic equations from the vehicle double wishbone suspension system for the vehicle handling model with eight degrees of freedom (8DOF). The limited area of the SMD necessitates the use of a proper controller, so this paper investigated the suitability of a proportional-integral-derivative controller (PID), an adaptive fuzzy controller (AFC), and HAFC for this purpose. The stability status and adaptation laws were assessed by Lyapunov synthesis and the result showed that integral of square error (ISE) achievable by HAFC for two standard maneuvers is lower than PID and AFC. The result also showed that SMD of HAFC is lower than AFC and extremely PID. The use of HAFC also resulted in the best vehicle stability, soft response and robustness.
Volume 17, Issue 4 (6-2017)
Abstract
Design of fault detection and diagnosis systems (FDDS), although extending the control strategies, they are challenged by controller interferences in fault diagnosis. In this study, in order to improve performance and accuracy of FDDS in the fault detection process, considering influential parameters and the level of corresponding interferences is investigated. To achieve this enterprise, a powerful method in fault pattern recognition of industrial plants based on dynamic behavior and dynamic model by using soft computing is designed and tested on simulated suspension system of a vehicle. The suspension system is one the parts, most affecting reliability and safety of the vehicle. For investigating the level of interference caused by the control unite, the simulations of both passive and active (equipped with hydraulic actuator) suspension systems are utilized in association with the control unite. The results of tests under variable circumstances (using random values) demonstrate that the presence of control unite, strict the FDDS process and reduces the robustness of the system against disturbances and noise. Considering the way in which the control unite affects the process, application of suggested solutions in this research, have a considerable impact on amendment of the adverse effects.
Fault detection program which is provided by Matlab software benefits special possibilities to investigate and define the effect of controlling unite and can be considered as a useful device to facilitate and precipitate conduction of tests in different stages of the research.
Volume 17, Issue 12 (2-2018)
Abstract
In this article, a robust model predictive control (RMPC) using linear matrix inequalities (LMIs) is proposed for vehicle suspension design with parameter uncertainties. Since, in vehicle suspension design, it is desired to improve ride comfort and road holding while satisfying suspension constraints such as suspension deflection and maximum of control input, model predictive control is proposed which is among the most common approaches in constrained optimization problems. On the other hand, to handle suspension constraints, linear matrix inequalities are utilized here. Stability of the designed suspension system is proved, if the proposed linear matrix inequalities are feasible. In addition, uncertain parameters in suspension system are inevitable. In this paper, model predictive control is extended to care for parameter uncertainties by proposing new LMIs. To evaluate the effectiveness of the proposed approach, the proposed control method is applied to quarter car suspension model with parameter uncertainty. Simulation results endorse that the designed controller shows a competitive robust performance while satisfying suspension constraints existing parameter uncertainties. Moreover, simulations with different road profiles, show that the proposed controller is independent from various road excitations.
Volume 18, Issue 3 (5-2018)
Abstract
The Moving Least Square (MLS) interpolation method is proposed for approximation of adaptive fuzzy controller parameters for two degrees of freedom suspension system and each one has two inputs, one output with twenty-five linguistic fuzzy IF-THEN rules. Fuzzy systems are designed by using five Gaussian membership functions for each input, product inference engine, singleton fuzzifier and center average defuzzifier. The constructed fuzzy systems is composed with adaptation rules. For this purpose, Lyapunove approach is implemented for stability of the adaptation rules. The Gravity Search Algorithm (GSA) is implemented for achieve the optimum controller parameters. The relative displacement between sprung mass and tire and the body acceleration are two objective functions used in the optimization algorithm. Since, choose the suitable controller coefficients are important and when the parameter of the system change, Optimum coefficients of the controller will also change. In order to solve this obstacle, the MLS predictive model is purposed that is interpolation method based on a radius of the neighborhood, a basis function and a weight function for points of interest. Finally online model is implemented on the two degrees of freedom suspension system and results compared with the offline optimal systems.
Volume 19, Issue 7 (7-2019)
Abstract
In this paper, the effect of different sensors on the observer performance of vehicle suspension system is investigated. For this purpose, the concept of observable degree analysis is used to quantitatively measure the observability for different sensor choices. A new method, for determining the observable degree of linear time invariant (LTI) systems has been developed on the basis of distance of system from set of similar unobservable systems. A long distance is equivalent to a strong observability and a short distance is equivalent to a weak observability. The zero distance means that the system is unobservable. Since the distance to different unobservable modes can be determined separately, a comprehensive investigation of system observability and the effect of different sensor choices on the observer performance can be provided. In the following, the observable analysis of the suspension system was performed based on the proposed method and the effect of different outputs on the observer performance has been investigated. The results show that when the observable degree is increased for a specific sensor, the observer gain is decreased and consequently the sensitivity of observer relative to the noise and measurement errors is decreased. The increased accuracy of observer demonstrates a good conformity between observable degree analysis and observer performance. Also, a comparative study showed that, contrary to previous criteria that only considered a certain aspect of observability, the proposed method is more comprehensive and realistic, and the results obtained from the previous criteria can easily be achieved through the proposed method.
Volume 22, Issue 1 (12-2021)
Abstract
The aim of this research is to develop a semi-active secondary suspension system equipped with magnetorheological dampers to reduce the amplitude of vibrations and shocks to sensitive payloads in the cargo section of road truck. First, a double-ended magnetorheological damper was modeled, designed and built for use in a secondary suspension system of light trucks. Next, a pallet with a secondary suspension system consisting of four magnetoreheological dampers was constructed to be installed on the load side of the light truck. Then, the behavior of the system was examined by testing it by passing the vehicle on the speed-bump profile. By performing dynamic tests with harmonic excitation on the damper, the results showed that the maximum damping force with the electric current of 2 Amp is increased 11.6 times compared to 0 Amp. Furthermore by using the forces obtained from the Spencer model in predicting the dynamic behavior of the damper with an average relative error of %1.49 compared to the force obtained from the experimental test and implementing the two-dimensional model of the half-truck, the performance of the system in passing the speed-bump profile was investigated.The results of simulations and experimental tests showed that with increasing electric current intensity from 0 to 2 Amp, the maximum amplitudes of the sensitive payload decreased in passing the speed-bump %43.6 and %32.4 in simulations and experimental tests comparing to the situation without the secondary suspension system respectively.
Dr Naeim Shokri, Dr Abbas Assari Arani, Dr Ali Asgary, Dr Amirhosein Mozayani, Dr Nematollah Akbari,
Volume 22, Issue 3 (9-2022)
Abstract
Today, the share of government aid from the public expenditures to support military and civil servants' pension funds has increased from about 11% in 2013 to 19% in 2021 and this trend has been increasing in recent years. This study aims to use DSGE models to simulate and apply corrective measures to enhance the financial misalignment of Iran's pension system. For this purpose, the model has been calibrated once for the PAYG-DB system that is currently used in Iran and then for the system based on financial provision based on the amount of partial savings to compare their welfare and distributional effects. The simulation results show that people reduce their savings by switching to a partial savings system, which increases consumption in all generations and capital accumulation in the whole society. In the second part of the article, impulse response functions were used to investigate the effects of emerging diseases and population aging variables on the financial misalignment of pension funds. The results show that the financial misalignment of pension funds increases following the positive shock in the above variables. Based on the results, parametric reforms such as a mechanism linking the retirement age to life expectancy and transition to a partial savings system can reduce financial misalignment and increase financial sustainability in Iran's pension system.
Dr. Naeim Shokri, Dr. Abbas Assari Arani, Dr Ali Asgary, Dr Amirhosein Mozayani, Dr Nematollah Akbari,
Volume 22, Issue 4 (12-2022)
Abstract
Aim and Introduction
The pension system is of special place in the employment regulations of the private and public sectors of all countries of the world. In addition, pension funds are known as one of the most sensitive and complex financial institutions in today's world, whose main goal is to preserve the livelihood and dignity of people in old age. Pension funds have been created to provide social rights for citizens, and a long-term horizon is one of the main features of such funds. By receiving insurance premiums from the insured and investing the resources gathered in the early years and the so-called youth period of the fund, pension funds provide pensions for retirees during their maturity. The process of maturity of pension funds occurs naturally and if it is accompanied by the aging of the country's population, it will intensify. According to the International Monetary Fund, pension expenditures in the Social Security Organization and the civil serpents' Pension Fund will increase from 5.3% in 2015 to 11% in 2040 and 19.6% of GDP in 2080 and in the future, a large part of the country's budget should be spent on paying pensions.
Methodology
This study seeks to simulate and apply corrective policies to improve the financial misalignment in the Iranian pension system using dynamic stochastic general equilibrium (DSGE) model based on the overlapping generations (OLG) model. In this regard, impulse response functions were used to examine the effects of the proposed parametric corrections. The DSGE models are stochastic, microeconomic-founded, provide the possibility of dynamic evaluation of parametric changes as well as random changes of exogenous variables of the system, and give inter-temporal optimization of the behavior of economic agents. In addition, the mechanism of intergenerational transfer in the pension funds, can be well evaluated and studied by these models, so it seems to be a suitable tool for studying the effects of demographic parametric changes on the financial balance of pension funds.
Findings
The results show that positive shocks to the variables of years of service, birth rate, and average years of insurance, the financial misalignment of pension funds decreases. According to the results, linking the retirement age with life expectancy and increasing the years of premium payment can reduce financial misalignment and increase financial stability in the Iranian pension system.
Discussion and Conclusion
The government's decision to implement reforms in Iran's pension system is essential, taking into account social considerations and the step-by-step nature of these reforms. However, according to our findings, the following policies should be presented to improve the financial imbalance of Iran's pension system:
1. The results of the positive shock analysis to the years of service variable showed that the later retirement of people reduces economic dissatisfaction, and considering the past and projected increase in life expectancy in Iran, increasing the retirement age is justified and logical. According to global experience, the average retirement age should be increased from 60 to 63 years for men and from 55 to 58 years for women (one year for every two years). Also, in the future, it is suggested that the average retirement age be linked to the growth of life expectancy.
2. The analysis results of the positive shock to the birth rate variable showed that the young population reduces the financial imbalance. Therefore, it is necessary to implement policies to encourage birth in the coming years, because the population aging phenomenon will have destructive effects on the stability of the pension system.
3. A positive shock to the average variable of years of insurance has positive effects on reducing the financial imbalance of pension funds. In this regard, it is suggested to change the calculation of pensions in all pension funds, including state, military, and social security organizations, based on the average salary of the last three to five years of employment, which it is currently based on the average of the previous two years.
Volume 23, Issue 10 (10-2023)
Abstract
In this research, an effort has been made to examine and evaluate the impactful forces on a simple and cost-effective rail system, which has been modified by the addition of a suspension system. The studied rails are part of a specialized machine designed for producing lightweight wooden components with a similar pattern. This mechanism comprises two shafts and four linear bearings, ensuring smooth and error-free sliding along the shafts. All loads and forces related to other perpendicular axes are concentrated on this rail system. Consequently, through the design and incorporation of a suspension system into this setup, the adverse effects of forces on the rails have been ameliorated and significantly reduced compared to the previous state. The influence of the suspension system on the axis has been assessed using MSC ADAMS software, with results demonstrating a substantial reduction in the range of oscillatory forces originating from machining operations on the shaft.
Volume 30, Issue 2 (1-2023)
Abstract
Financial imbalances and disparity between resources and expenditures in Iranian pension funds have made the need for reforms inevitable. Today, the share of government aid from public expenditures to two Civil and Military pension funds has increased from about 11 percent in 2013 to about 19 percent in 2021, and this trend has been increasing in recent years. However, despite the perception of the crisis in the pension system of various actors, these reforms have not been implemented. In this regard, the present study seeks pathology and finds a solution to solve the crisis of the Iranian pension system during 2013-2021. Due to the existence of different actors and stakeholders, one of the non-quantitative methods of game theory models, called the graph model, was used to resolve the conflicts. This model is an important tool for modeling and analyzing complex problems, expresses the most likely consequences of various problems in the world, and finally provide guidelines for its improvement. The modeling results of the retirement crisis show that the fourth mode of the model, i.e. the state of reform, is more likely to occur. Therefore, the current situation is not a stable one for all players, and they are motivated to leave. According to the results, limiting government support, changing the pension system, and carrying out structural and parametric reforms will improve the current situation.
