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RISS 인기검색어
- 검색키워드
- 저자 : Ghader Rezazadeh (검색결과 4 건)
- 무료
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Application of Solar Chimney for Pest Control in Agricultural Crops
Mina Ghanbari,Ghader Rezazadeh 한국농업기계학회 2019 바이오시스템공학 Vol.44 No.4
Purpose Due to the importance of air ventilation of greenhouses or gardens in producing healthy agricultural crops, the aim of this research is presenting the application of solar chimney to help prevent pest distribution in agricultural products through ventilating the garden. Methods For this purpose, a ventilating chimney works with renewable solar energy is proposed. The circular solar collector placed surrounding the chimney absorbs solar radiations, which causes temperature increment of the air in passing through the collector. The produced natural driving force causes the air to flow into the chimney. Considering reasonable assumptions, the equations demonstrating the motion of the airflow are presented and therefore, the flow rate of air passing through the chimney is calculated. Results Results indicate that selecting a chimney with lofty altitude and a collector with a considerable value of collector radius to chimney radius ratio increases the airflow rate, which leads to a better performance of the chimney. For higher chimneys operating in lower values of solar radiation, a collector with a large radius should be selected. Results show that selecting a chimney with a diameter of 1 m will cause the decrement of airflow rate due to friction forces up to 13%. Conclusions It is concluded that a high chimney shows a better performance when it is utilized in gardens having low sea-level altitude.
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Nonlinear behavior of capacitive micro-beams based on strain gradient theory
Mohammad Fathalilou,Morteza Sadeghi,Ghader Rezazadeh 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.4
This paper studies the size dependent behavior of materials in MEMS structures. This behavior becomes noticeable for a structurewhen the characteristic size such as thickness or diameter is close to its internal length-scale parameter and is insignificant for the highratio of the characteristic size to the length-scale parameter, which is the case of the silicon base micro-beams. However, in some types ofmicro-beams like gold or nickel bases, the size dependent effect cannot be overlooked. In such cases, ignoring this behavior in modelingwill lead to incorrect results. Some previous researchers have applied classic beam theory on their models and imposed a considerablehypothetical value of residual stress to match their theoretical results with the experimental ones. The equilibrium positions or fixedpoints of the gold and nickel micro-beams are obtained and shown that for a given DC voltage, there is a considerable difference betweenthe obtained fixed points using classic beam theory, modified couple stress theory, and modified strain gradient theory. In addition, it isshown that the calculated static and dynamic pull-in voltages using higher order theories are much closer to the experimental results andare higher several times than those obtained by classic beam theory.
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Mechanical behavior of a cylindrical capacitive micro - switch compared to a straight beam type
Ashkan Attar,Mohammad Fathalilou,Ghader Rezazadeh 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.5
This paper introduces a novel cylindrical capacitive micro-switch which has different pull-in voltage, frequency response and contact area compared to the conventional straight beam switch. After presenting a mathematical model, governing equation of motion of the cylindrical switch has been solved by Galerkin-based reduced order models. The results have shown that the presented model has lower pull-in voltage than straight beam with the same dimensions. Also, the novel model exhibits considerable difference in frequency response in comparison with the other model. By applying the HERTZ relations for the contact area, a mathematical rough estimation for the contact area in switching state has done. The estimated results reveal that the contact area in cylindrical switch is about 56 % of the straight switch with the same dimensions.
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Stability analysis of a parametrically excited functionally graded piezoelectric, MEM system
Saber Azizi,Mohammad-Reza Ghazavi,Siamak Esmaeilzadeh Khadem,Jie Yang,Ghader Rezazadeh 한국물리학회 2012 Current Applied Physics Vol.12 No.2
In this paper the mechanical behavior of a parametrically actuated functionally graded piezoelectric (FGP) clampedeclamped micro-beam is investigated. The micro-beam is supposed to be a composite material with silicon and piezoelectric base. The mechanical properties of the structure, including elasticity modulus, density, and piezoelectricity coefficient are supposed to vary along the height of the micro-beam with an exponential functionality. It is supposed that the FGP clampedeclamped microbeam is actuated with a combination of direct and alternative electric potential difference. Application of DC and AC actuation voltage leads in a constant and a time-varying axial force. The governing differential equation of the motion is derived using Hamiltonian principle and discretized using expansion theorem with the corresponding shape functions of a clampedeclamped beam. The discretized system is governed by Mathieu equation which’s stability is investigated using Floquet theory for single degree of freedom systems and verified using multiple time scales of perturbation technique.
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