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11.
In this paper, the propulsion performance of a spanwise flexible oscillating wing, which is broadly similar to the undulation of a fin fluke, is investigat 相似文献
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The interest in shake tables stems from a need to simulate earthquake behavior in laboratory settings. However, the inherent properties and nonlinearities associated with electromechanical and servohydraulic shake tables, combined with issues of table-structure interaction, make accurate reproduction of earthquake acceleration time histories a challenging problem. The classical approach to control shake tables has been the Transfer Function Iteration (TFI) method. The tuning of the TFI controller is an offline iterative process, conducted using small amplitude ground motions. Effective compensation is not achievable for system nonlinearities that are not projected in the iterative tuning process. To address this problem, researchers have developed online compensation techniques, which can maintain tracking performance for the earthquake signals more effectively. Model-based controllers (MBC) are a class of online controllers which use an identified model of the shake table-structure for compensation. The MBC employs feedforward and feedback controllers to ensure that the shake table tracks a specified earthquake ground motion despite the presence of table and structural nonlinearities. However, the feedback controllers in MBC do not always maintain tracking accuracy and can result in loss of robustness when changes occur in the shake table and structure dynamics. This paper introduces a modified model-based controller (mMBC) for acceleration tracking as an improvement on the existing MBC architecture. A stability condition is introduced to assess the robustness of the new modified control architecture. Through numerical and experimental studies, the improved tracking robustness of the mMBC architecture is demonstrated. 相似文献
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GIS-based frequency ratio and index of entropy models for landslide susceptibility assessment in the Caspian forest,northern Iran 总被引：12，自引：1，他引：11
A. Jaafari A. Najafi H. R. Pourghasemi J. Rezaeian A. Sattarian 《International Journal of Environmental Science and Technology》2014,11(4):909-926
This study presents a landslide susceptibility assessment for the Caspian forest using frequency ratio and index of entropy models within geographical information system. First, the landslide locations were identified in the study area from interpretation of aerial photographs and multiple field surveys. 72 cases (70 %) out of 103 detected landslides were randomly selected for modeling, and the remaining 31 (30 %) cases were used for the model validation. The landslide-conditioning factors, including slope degree, slope aspect, altitude, lithology, rainfall, distance to faults, distance to streams, plan curvature, topographic wetness index, stream power index, sediment transport index, normalized difference vegetation index (NDVI), forest plant community, crown density, and timber volume, were extracted from the spatial database. Using these factors, landslide susceptibility and weights of each factor were analyzed by frequency ratio and index of entropy models. Results showed that the high and very high susceptibility classes cover nearly 50 % of the study area. For verification, the receiver operating characteristic (ROC) curves were drawn and the areas under the curve (AUC) calculated. The verification results revealed that the index of entropy model (AUC = 75.59 %) is slightly better in prediction than frequency ratio model (AUC = 72.68 %). The interpretation of the susceptibility map indicated that NDVI, altitude, and rainfall play major roles in landslide occurrence and distribution in the study area. The landslide susceptibility maps produced from this study could assist planners and engineers for reorganizing and planning of future road construction and timber harvesting operations. 相似文献
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Geochemistry and petrography of REE-bearing Fe-oxide assemblages in Choghart iron deposit,Yazd, Iran
Younes Shekarian Ardeshir Hezarkhani Nima Najafi Anaraki Arash Nikvar Hassani 《Arabian Journal of Geosciences》2017,10(12):273
The Choghart magnetite-apatite deposit situated in the Bafq district, Central Iran, has been scrutinized for rare earth elements (REEs) by precise geochemical investigation. The Central Iran is a susceptible area of rare earth elements. One of the Choghart’s prominent points is the existence of hydrothermal zones which made prediction of REEs occurrence within the deposit possible. Choghart is placed within felsic volcanic tuffs, rhyolitic rocks, and volcanic sedimentary sections belonging to the lower Cambrian. Abundance and distribution pattern of REEs in Choghart iron deposits reveal a part of deposit formation and its mineralogical modifications. Petrography and mineralogy of the ore body demonstrated two main types of alterations (sodic and calcic) associated with iron ore mineralization in Choghart deposit. The main ore includes a large quantity of massive magnetite in the lower part of Choghart deposit. The minor mineralization involves apatite, pyrite, alkaline amphibole, especially actinolite and tremolite, calcite, talc, quart, monazite, and bastnasite. Geochemical sampling from north–northeast (N-NE) side of the mine denotes the presence of these elements in hydrothermal zones. Statistical populations of the area were categorized by fractal geometry into four main differentiations: host rock type (albitofyre), iron, metasomatose, phosphate zones, and a subset of the phosphate zone which is named high iron high phosphate type. REEs like lanthanum, neodymium, yttrium, and niobium constitute the most quantity of Choghart. Deposit characteristics demonstrate its similarity to Kiruna type. The significant feature of iron oxide-apatite deposits of Kiruna ore type is the existence of monazite inclusions within apatite. These inclusions were also observed within apatite type I and II of Choghart mineralization. Moreover, REEs geochemistry in Choghart deposit was identified by investigation on geochemical data analyses. The analysis represents negative Eu anomaly and further enrichment of light REEs compared to the heavy ones. Chondrite normalized REEs patterns are defined by negative anomalies of Eu, which is the main characteristic of Kiruna ore type. The results showed that REEs concentration in phosphate zone, as a high absorption of REEs, is much higher than metsomatose, albitofyre, and iron zones. REEs distribution in N-NE side of the mine indicated that the contact of iron ore with tailings in N-NW side of the mine leads REEs to be enriched nearly 1% , as well as that of NE with high contents of REEs 1.5% ), which is very significant. 相似文献
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P. Vaníček W. Sun P. Ong Z. Martinec M. Najafi P. Vajda B. ter Horst 《Journal of Geodesy》1996,71(1):21-34
. The aim of this contribution is to show that mean Helmert's gravity anomalies obtained at the earth surface on a grid of
a `reasonable' step can be transferred to corresponding mean Helmert's anomalies on the geoid. To demonstrate this, we take
the by mean Helmert's anomalies from a very rugged region, the south-western corner of Canada which contains the two main chains
of the Canadian Rocky Mountains, and formulate the problem of downward continuation of Helmert's anomalies for this region.
This can be done exactly because Helmert's disturbing potential is harmonic everywhere outside the geoid, therefore even within
the topography. Then we solve the problem numerically by transforming the Poisson integral to a system of 53,856 linear algebraic
equations. Since the matrix of this system is well conditioned, there is no theoretical obstacle to the solution. The correctness
of the solution is then checked by back substitution and by evaluating the contribution of the downward continuation term
to Helmert's co-geoid. This contribution comes out positive for all the points. We thus claim that the determination of the
downward continuation of mean Helmert's gravity anomalies on a grid of a `reasonable' step is a well posed problem with a
unique solution and can be done routinely to any accuracy desired in the geoid computaion.
Received 27 October 1995; Accepted 9 July 1996 相似文献
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Golian Mohsen Katibeh Homayoon Najafi Zeinab Saadat Habib Saffarzadeh Ali Ahmadi Aboozar Khazaei Mahdi Sametzadeh Ershad 《Hydrogeology Journal》2021,29(6):2171-2186
The Dena rainstorm in Iran in March and April 2019 caused about US$ 8.3?×?109 damage in the country; however, it resulted in the replenishment of half of the dam reservoirs and 35% of ponds and lakes. Also, it increased the volume of groundwater stored in aquifers by 3.6?×?109 m3. In arid and semiarid regions such as most parts of Iran, which usually face water scarcity, getting water from rainstorms is essential for replenishing water resources. This research aims to quantify the direct and indirect effects of the Dena rainstorm on the replenishment of Iran’s groundwater storage using the groundwater balance method and water-table fluctuation method. Studies showed that the main mechanisms for replenishment of groundwater storage due to the rainstorm included increases in precipitation recharge, surface runoff recharge, and artificial recharge, and reductions in irrigation withdrawal and evapotranspiration, while the contribution of each factor is estimated to be about 23, 28, 2, 15, and 32%, respectively.
相似文献19.
Amirali Mostafavi Moghadam Abbas Ghalandarzadeh Majid Moradi Ikuo Towhata Pouria Hajialikhani 《Bulletin of Earthquake Engineering》2011,9(4):1259-1288
This research is to study the efficiency of displacement reducer fuses, installed behind the caisson quay walls for controlling
the dynamic backfill thrust and minimizing the displacement, settlement and tilting of the walls. For this purpose, two types
of fuses, Displacement Reducer Panels (DRP) and Displacement Reducer Elements (DRE), were constructed and installed behind
the wall. The DRPs were constructed by hollow Polypropylene sheets to reproduce elastoplastic and plastic mechanical behaviors.
The DREs were cylindrical stainless-steel dampers, working upon friction mechanism that can reproduce perfect plastic behavior.
Here, two series of shaking table 1-g tests were performed with DRP and DRE applications. In this regard, different mechanical
behaviors and capacities were considered for fuses against demand thrusts of backfill in order to compare the mitigation tests
with no-mitigation cases. Harmonic base motions with constant amplitude and constant frequency were used in the model test.
The foundation soil and the backfill soil were constructed with the relative densities of 85 and 25%, respectively, to reproduce
non-liquefiable base layer and loose backfill situations in the model, respectively. The results showed remarkable reduction
in kinetic energy, dynamic backfill thrust and consequently seaward movement, settlement and inclination of the caisson quay
wall in case of using fuses with plastic behaviors behind the wall. 相似文献
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H. Najafi Alamdarlo 《International Journal of Environmental Science and Technology》2016,13(8):2079-2090
Agriculture and natural resources have a mutual relationship with each other. The purpose of this study was to evaluate forward and backward relationship between natural resources and agricultural development. The relationship between the consumption of water and agricultural value added per capita income has been studied in order to obtain the forward relationship, and the relationship between carbon dioxide emissions and per capita income of the Iran’s agricultural sector has been assessed in order to obtain backward relationship. To test these relationships, the Kuznets theory is used. Therefore, Iran’s provinces information from 2001 to 2013 was used and models were estimated by using the panel data and spatial econometric. Results showed that there was an inverted U relationship between per capita income and water consumption and carbon dioxide emissions. Also, spatial estimation showed that both water consumption and carbon dioxide (CO2) emissions in agricultural sector had a direct relationship with the value of these two variables in the neighboring areas. 相似文献