Showing 16 results for Disturbance
Volume 3, Issue 1 (3-2015)
Abstract
Livestock grazing and rangelands fire are important ecological disturbances influencing the vegetation and soil properties in rangelands ecosystem. This study was conducted to determine the effects of different burned treatments and distances from the water sources on some soil and vegetation properties of rangelands ecosystem. The experiment was conducted in Lashgar Dar Rangelands. Vegetation samplings were done based on the randomized systematic method across transects. Fifty randomized quadrats were sampled at each transect. One hundred soil samples per each transect were systematically taken by auger along each transect. The ANOVA and Duncan tests were employed for statistical analyses. The results indicated that the highest and the lowest above-ground biomass production (630 and 117 kg ha-1), Shannon-Wiener diversity index (2.37 and 1.07), soil TOC (18.34 and 6.66 g kg-1), soil gravimetric water content (16.4 and 6 %) and soil porosity (69.43 and 57.74%) values were found in the unburned rangelands with 2000 m distance from the water source and the one year post burned rangelands with 10 m distance from the water source, respectively. Whereas, the maximum and the minimum values of soil bulk density and soil EC were seen in the one year post burn with 10 m distance from the water source and the unburned rangelands with 2000 m distance from the water source, respectively. There were no relations between the soil pH change trends and the different burned treatments or distances from the water source.
Volume 8, Issue 1 (3-2020)
Abstract
Aim: The present study aimed to 1) determine the extent
of arbuscular mycorrhizal fungi symbiosis with Amygdalus scopariain in Melah-Roteh region in Dareshahr City, western Iran, and 2) model the presence or absence of different arbuscular mycorrhizal fungi on Almonds (
A. scoparia) in relation to soil physicochemical properties.
Materials & Methods: In the study area (Melah-Roteh region in Zagros Woodlands), 57 soil samples were taken from the 0-30cm depth under
A. scoparia in the Dareshahr City forest west of Iran. Soil samples were processed in the laboratory to extract and identify spores and fungi, determine spore frequency, and to measure physicochemical soil properties.
Findings: The results of two-way indicator species analysis (TWINSPAN) classification showed that arbuscular mycorrhizal fungi symbiotic with
A. scoparia in the study could be classified into two groups. The evaluation of indicator species in each group using the importance value method and significance of indicator values based on Monte Carlo tests (p<0.01) showed that
Rhizophagus fasciculatus and
Funneliformis caledonium (Indicator value= 90 and 89, respectively) were prominent in the first group and
Funneliformis mosseae,
Claroideoglomus drummondii, and
Glomus gigantea (Indicator value= 95, 93, and 81, respectively) were representative of the second group.
Conclusion: The presence-absence, symbiosis rate and spore density of arbuscular mycorrhizal fungi species associated with Almonds changes with varying physicochemical soil properties that can be modeled using certain soil attributes.
Volume 10, Issue 2 (7-2010)
Abstract
Detection & Classification of power quality (PQ) disturbances are the most important problems in distribution systems. In this paper, a new approach for the detection and classification of single and combined PQ disturbances is proposed which utilizes fuzzy logic and particle swarm optimization (PSO) algorithms. In this approach, first suitable features of the waveform of PQ disturbances are extracted. Extraction of these specifications is done based on the Fourier and Wavelet transforms. Then, the proposed Fuzzy systems make decision about the type of each of the PQ disturbances by employing these specifications. The PSO algorithm is used for accurate determination of each parameter of the membership functions of the systems. To test the proposed approach, the waveform of PQ disturbances was assumed to be in a sampled form from single and combined categories. Impulse, interruption, swell, sag, notch, transient, harmonic, and flicker phenomena are considered as single disturbances for voltage signal. More over, harmonic with swell, swell with harmonic, swell with transient, harmonic with sag, sag with harmonic and sag with transient are considered as combined disturbances for the voltage signal. Simulation results denote capability of the proposed approach for identification of single and combined disturbances with about 99% accuracy.
Volume 11, Issue 3 (9-2023)
Abstract
Aims: In this study, the response of individual trees and the stand structure to windstorm damage were investigated in a mixed broad-leaf forest stands located in Darabkola Forest, Sari, northern Iran. A field survey was conducted over an area of 2612 ha of the given stands.
Material & Methods: A full inventory was performed for all trees with diameter at breast height≥ 10cm and all damaged (i.e., snapped, snags, branch loss, broken trunk or uprooted) trees were identified within the study area. Tree height was measured using Laser Distance Meter for trees more than 10 m high and a Clinometer for all trees <10m. The percentage of trees damaged was the dependent variable; but, independent variables included number, mean height (m), total basal area (m2) and volume trees (m3). Independent t-test was performed to compare the mean of trees based on diameter classes. Also, the affection of height on susceptibility to windstorm effects was tested by comparing mean trees height within each class.
Findings: The number of the damaged trees varied with species, ranging from 0.04 % (2 individuals) in Tilia begonifolia Stev to 53.7 % (2709 individuals) in Fagus orientalis L. Among the damaged trees 5054 recorded, 2231 (44.20 %) had been snapped and 787 (15.6 %) uprooted, and 2028 (40.20 %) were snags. Among the species, Fagus orientalis L. (47.7 %), Alnus subcordata C. A. Mey. (19.7 %) and Carpinus betulus L. (18.8 %) were most susceptible to uprooting, whereas Populus caspica Bornm, Quercus castaneifolia C. A. Mey. and Ulmus glabra Huds. were the least susceptible to uprooting. The species differed significantly in their susceptibility to snapping. Trees ≥60cm dbh were more likely to be snapped (78 %) or snags (69 %), whereas trees <60 cm dbh were more presumably to be uprooted (50 %). Also, about one third (33 %) of total trees larger than 60 cm (D.B.H) have showed distinct effects and individual trees >20 m were more commonly uprooted. The number of snapped trees, snags and uprooted trees had a sharp increase in trees taller than 20m.
Conclusion: Our finding showed that Oriental beech and Common hornbeam to be species that were most susceptible to both being snapped and snagged, whereas Caucasian alder had the most uprooting damage among the other species. Overall, features like species, D.B.H, height and height to diameter ratio (H/D.B.H), were intensively related with the type and severity of windstorm damage. The findings showed that windstorms cause substantial structural effects in mixed stands of beech and hornbeam.
Adel Rabie, Maryam Malekzadeh, Majid Abnili,
Volume 15, Issue 3 (5-2015)
Abstract
This paper talked about spacecraft formation flying control. Leader-flower structure is used in formation flying. A non-linear PID controller is designed based on predictive control. The formation relative equation is obtained from nonlinear Hill equation. First, the frequency control is achieved with the using of predictive control algorithm. In control frequency, disturbances have been replaced from disturbance observer. Equations are rewritten in the form of PID gains. Stability of the closed-loop system is proven by closed-loop error dynamics. Nonlinear PID controller performance in the pursuit of desired arrangement has been tested in simulations. Also effects of various factors on the quality of controller results are studied. It is shown that choosing predictive horizon time and disturbance observer gains have the most effect on system response. It is shown that if predictive time increase the settling time increase and the control effort decrease. if disturbance observer gain increase from a limit, it has no effect on settling time but control effort increase. As shown in simulation, the tracking response show the controller method ability. the simulation show the ability of this nonlinear control method in tracking.
Hemad Keshavarzpour, Seyyed Mohammad Hasheminejad,
Volume 15, Issue 4 (6-2015)
Abstract
Active structural acoustic radiation control of a piezolaminated arbitrary thick rectangular plate with a mixed-norm H_2/H_∞ robust controller is developed. The structure is made of a transversely isotropic host layer with a distributed piezoelectric sensor layer as well as a matched piezoelectric actuator layer, facing high frequency uncertainties and random external disturbances. The elasto-acoustic formulation, based on the exact linear 3D piezo-elasticity theory, is developed for problem of fully coupled structure and acoustic mediums. Identification of the fluid/structure interaction system with subspace algorithm is implemented on actuator/sensor data sets. A multi-objective controller with regional pole placement, formulated in LMI framework, is synthesized while unmodeled dynamics are treated as multiplicative uncertainties. Numerical simulations confirm effectiveness of the implemented multi-objective robust active control scheme for reduction of radiated acoustic power from a piezocomposite plate, without stimulating any instability. Also, better tracking performance and disturbance rejection of mixed-norm controller is observed in comparison to that of H_2 and H_∞ controllers. Finally, validity of the elasto-acoustic model is proved by results obtained from a finite element software, as well as with the data available in the literature.
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.
Sadra Borji Monfared, Asghar Ebrahimi, Ashkan Parsa,
Volume 17, Issue 3 (5-2017)
Abstract
Airship is kind of aerial vehicles that has been a significant development of scientific research in recent years. Furthermore, stratospheric airship is in group of lighter-than-air aerial vehicles. This device is designed in order to the ability of unmanned autonomous operation with remote control at a height of 22 kilometers from Earth. With the development of control systems, there are still major challenges in this area. In this paper, in order to stabilizing and trajectory tracking of stratospheric airship, nonlinear H_∞ method has been developed. At first, the dynamic model of an airship is introduced and descriptive equations are presented in an appropriate state-space in order to design a controller based on nonlinear H_∞ method. Then the nonlinear H_∞ controller is designed. In the controller the integral of the position error is considered, allowing the achievement of a null steady-state error when sustained disturbances are acting on the system. The external disturbances are considered as aerodynamic forces and torque. This strategy is designed robustness, against of external disturbance. The results are shown that decrease in steady error and stabilizing system against external disturbance and uncertainties. Also for robustifying of designed control, comparison is done with adaptive control. Simulation results in the presence of aerodynamic disturbances, parametric and structural uncertainties are presented to corroborate the effectiveness and the robustness of the proposed strategy.
Meisam Kabiri, Mohammad Bagher Menhaj, Hajar Atrainfar,
Volume 17, Issue 8 (10-2017)
Abstract
This paper addresses the trajectory tracking of a Vertical Take-Off and Landing (VTOL) aircraft. Our objective is to design a controller for a VTOL aircraft in such a way that the aircraft tracks a predefined 3d spatial path in the presence of constant disturbances and uncertainty in the inertial matrix. Taking advantage of the extraction algorithm, we separate the design for the translational and rotational dynamics. First a virtual controller is designed for the translational dynamics from which the ideal thrust direction is extracted. To deal with the under-actuation of the translational dynamics, we have exploited an auxiliary system while an estimator is also involved in the design of the virtual controller to compensate for the effect of the translational disturbance. In order to keep our estimation bounded, we utilize the projection operator which is also smooth enough. An adaptive sliding mode control is used for rotational dynamics control such that the ideal thrust is accomplished. Since the inertial matrix and the bound on rotational disturbance is unknown, an adaptive structure is used to estimate the unknown bounds. The stability of the control framework is established through Lyapunov analysis. Finally simulation results are given to test the validity of the proposed control scheme.
Hadi Delavari, Atefeh Azizkhani, Pooya Shiuooei,
Volume 17, Issue 10 (1-2018)
Abstract
Energy saving, low robot mass to carried mass ratio, more ability to work in various environments, easier delivery of parts and lower production costs in flexible robots make these robots more attractive than rigid robots to many researchers and industries. But due to nonlinearities in flexible robot system and high vibration in operation points and also more sensitivity against external disturbances, control of these robots is more difficult and complex. In this paper a controller for a flexible link manipulator based on fractional calculus is practically implemented. At first the dynamic model of a single flexible-link robot is introduced. Then various controllers such as fuzzy control, PID control, and fractional order PID torque control are practically implemented on a single flexible-link robot made in laboratory, and then the performance of each controllers in decreasing of arm vibration in final desired point and tracking error reduction are investigated. Further, to compare the robustness of the designed controllers, a same constant disturbance is applied to all controllers and their performance are compared. Finally, the simulation results and experimental results show that the fractional order PID torque controller has the best results among the implemented controllers.
Hossein Shahi, Aghil Yousefi Koma, Majid Mohammadi Moghadam,
Volume 17, Issue 11 (1-2018)
Abstract
In this paper, a new design approach for an admittance control method is presented to deal with the environmental disturbances for user-in-charge exoskeletons. Since the challenge of maintaining the stability of the robot and the human is met by the user, environmental disturbances as a set of external forces should be considered. However, the proposed control methods have already ignored the issue and focused on presenting a desired dynamic relation between the interaction forces and the robot motion. This paper aims to find a control solution to maintain the desired behavior of the classical controllers in response to the interaction forces as well as to deal with disturbances properly. For this purpose, a control structure is developed by substituting an impedance control method for the low-level layer of an admittance controller. A simulation on an exoskeleton leg is conducted to evaluate the performance of the proposed controller in comparison with the classical control methods for user-in-charge exoskeletons. In contrast to conventional control methods, the results shows that the proposed controller can deal with both the interaction forces and the disturbances properly as the consequence of establishing different dynamic mappings for each of them.
Javad Safehian, Ali Akbar Akbari, Sayyed Kamal Hosseini Sani,
Volume 17, Issue 12 (2-2018)
Abstract
A new method was provided to control linear time-varying systems in which the reference signal is a harmonic function with variable amplitude, mean or frequency, such as block loading. The results of practical tests on the voice coil actuator fatigue test machine indicate that this method is robust to noise and disturbance. Also proposed control method compensates unknown time-varying time-delay which leads to bandwidth increase in harmonic loading. On the other hand in this paper the central pattern generator (CPG) was used to design the trajectory of input signal to the main plant. Because of soft applying of changes by CPG, it prevents excitation of high frequency dynamics. To implement the proposed method main plant, which can be estimated with a fourth-order single-input single-output (SISO) model was considered as a two-input two-output (TITO) decoupled system that each relevant input-output is first-order. The level of control loop pairs to each other is investigated by calculation of dynamic relative gain array (DRGA) matrix. The test results also show that loading control was properly carried out in the presence of various uncertainties such as nonlinearities, unmodeled dynamics and time-varying parameters.
Naser Esmaili, , Hamed Hamed Tabatabaei Oreh,
Volume 18, Issue 4 (8-2018)
Abstract
Today, the use of articulated long vehicles is surging. The main reasons for tendency of utilizing these vehicles is use of less tractor unit fitted to carry two or more trailers. In other words, in order to carry the same amount of goods, instead of using some tractor semi-trailers, we can make use of fewer articulated long vehicles. Reduction of fuel consumption, a significant decrease in the production of greenhouse gasses as well as using less manpower to direct the vehicle to carry the same load which is related to typical articulated vehicle is of other advantages of long articulated vehicles. The major problems of these vehicles are poor maneuverability at low speed and inappropriate lateral performance at high speed, which would lead to crashes and financial damages. Hence, a control system is required for enhancing the safety of these vehicles, improving the performance of long vehicles and preventing from being unstable. In this study, after mining and verifying the dynamic model, a new control method based on a combination of active disturbance rejection control and backstepping sliding mode control for adjusting lateral dynamic of articulated long vehicles has been utilized. The results portray the superiority of this new method than LQR and sliding mode controllers.
M. Khamar, M. Edrisi,
Volume 18, Issue 9 (12-2018)
Abstract
Recently, a vast variety of wearable robots with various applications, including rehabilitation, have been produced, but a very challenging part of exoskeleton designing which is its motion control system still requires further investigation to be completed. Due to the nonlinearity in the dynamics of human-exoskeleton, uncertainty in parameters, unmodeled or simplified structures, and external disturbances (such as interaction of exerted human forces and movements), the use of robust control strategies is inevitable. Thus, in this research, a nonlinear disturbance rejection observer was used to estimate all of those as total disturbances. Then, a fractional order backstepping sliding mode (FOBSC) was utilized for enhanced tracking plus a Linear Quadratic Regulator (LQR) method to optimize the convergence to the equilibrium points. The advantage of using LQR is the optimum selection of the control input, and the FOBSC guarantees the robustness of the controller against uncertainties and disturbances. The combination of fractional order theory and control methods causes less chattering in the human-exoskeleton interactions. Moreover, particle swarm algorithm was used in order to select the coefficients of the cost function of LQR. In order to calculate the effect of the exoskeleton on human muscles and bones, the human parameters and knee motions, OpenSim was used. Matlab was used to implement the control strategy through OpenSim. The proposed method was then compared with the normal backstepping, fractional order system and LQR methods. The results show the superiority of this method compared to the classical methods.
Volume 23, Issue 1 (3-2023)
Abstract
Natural soils pose an inter particle bonds that makes their compression and failure behavior different than the compression and failure behavior of remolded soils. Different reasons have been suggested for the creatin of inter particle bonds, including natural cementation, carbonating agents, and aging. These classes of soils are called structured soil. Structured soils could also be produced from artificial cementation by cement, lime, and other chemical agents. Overconsolidated generally show different compression behavior in overconsolidated state and normally consolidated state and their compression index in both states are different. Structured materials show a highly nonlinear compression behavior after initial yielding in the normally consolidated state. Their compression index has a large value at the beginning of the virgin yielding and decreases as the structure of the soil crashes. This highly nonlinear behavior prevents from adapting the conventional linear compression models in both semilogarithmic or fully logarithmic scale in e-log(p) or ln(1+e)-ln(p) spaces. On the other hand, sampling disturbs the soil samples and destructs the soil structure. Although there are several new sampling methods and apparatuses to reduce the disturbance of the samples, however the disturbance could not be completely removed from sampling procedure. Disturbance of the samples makes the determination of the precompression pressure of the soil samples where the compression regime of the soil changes, very complicated. There are several methods for determination of the precompression pressure of disturbed samples that most of them are based on graphical procedures. This paper presents a contentious compression model for volumetric compression and yielding of structured soils considering the effect of the sample disturbance on the determination of the precompression pressure. The compression behavior of the structured soil in low stress levels where the structure of the soil is relatively intact (RI) is known and can be measured in the laboratory. Also, the compression behavior of a structured soil at very high stress level where in fully adjusted (FA) state is similar to the compression behavior of the same soil in remolded state. The compression behavior of the structured soil with some degree of the disturbance must lays between these two reference states. Based on the Disturbed State Concept (DSC) the behavior of any complex phenomenon between two reference states of RI and FA could be completely described using a coupling mechanism called the state function. In this paper, the compression curve of the soil in low stress levels at overconsolidated state was considered as RI state and the compression curve of the same soil in the remolded state was considered as FA state. A continuous sigmoid form state function was proposed for description of the continuous change of the e-log(p) curve of the soil from overconsolidated state to normally consolidated states. The effect of the sample disturbance was introduced in the state function by an intactness parameter. High values of the intactness parameter produce distinctive changes from overconsolidated regime to normally consolidated regime that is the main character of intact samples. Based on the proposed model the precompression pressure could be determined minimizing the deviations of the predicted results from observed results in compression test. The proposed model was verified by data reported in the literature and also laboratory tests conducted by the authors. The verification of the model showed the ability of the model in determination of the precompression pressure of artificially overconsolidated samples with known precompression pressures more precise than the other methods.
Volume 23, Issue 5 (4-2021)
Abstract
Background & Aim: Fluid-electrolyte balance is a dynamic process that is necessary for the continuation of life and homeostasis. Disorders in the bodychr('39')s electrolyte balance and renal dysfunction are related factors in aggravation of symptoms, mortality and length of hospital stay and treatment costs, so we decided To conduct a study by examining the status of electrolyte disorders and its related factors in patients admitted to Shohada Ghaen Educational and Medical Center.
Methods: The present study is a descriptive-analytical study that was performed by census method on all patients admitted to Shohada Ghaen Hospital in 2017. The tools used in this research included a researcher-made checklist that had 11 items that were completed by the researcher. For data analysis, descriptive statistics such as mean, standard deviation and frequency tables and chi-square test and Kruskal-Wallis. Significance level was set at (P <0.05).
Results: 873 patients with a mean age of 22.92 ± 58.42 were studied. The results showed that there was a significant relationship between electrolyte disorders and the level of education, type of disease and disease ward (P <0.05).
Conclusion: Increasing knowledge and awareness has a great effect on the prevention of electrolyte disorders. Also, due to the relationship between electrolyte disorders and the type of disease, special attention should be paid to this issue.
