Analytical and Numerical Solution for Interaction between Batter Pile Group

Mahmoud Ghazavi,Pedram Ravanshenas,Arash Alimardani Lavasan 대한토목학회 2014 KSCE JOURNAL OF CIVIL ENGINEERING Vol.18 No.7

Vertical and inclined piles in a group may be used where large lateral loads are present. The effects of the presence of the receiver pile and batter angle on pile-soil-pile interaction has not yet been fully recognized. In the present study, a two pile group is considered to determine such interaction. For this purpose, a simple method in closed form solution is used to characterize the inclined and vertical isolated prismatic piles. The behavior of the soil and the pile are assumed to be elastic. The free field movement of the ground in the vicinity of the loaded pile (source pile) is determined and used to find its influence on the other pile located closely (receiver pile). Numerical analyses were also performed using FLAC 3D to verify the data obtained from the developed analytical solution. The results gained from the developed analytical solution indicate that the presence of the neighboring pile is important, resulting in a lesser ground movement at the source pile head. Parametric studies have been carried out to determine the influence of contributing parameters such as pile-pile distance, group geometry, length of piles, and inclined angles.

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.

Measured and Predicted Durability and Mechanical Properties of Frozen-Thawed Fine Soils

Mohammad Vahdani,Mahmoud Ghazavi,Mahya Roustaei 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.3

An efficient experiment has been aimed in engineering fields for many years, which is provided through minimum number of tests and maximum amount of applicable results. Frozen soil is conceived to be an attractive subject for optimization processes. To reach an optimized design of experiment, a statistical method known as response surface method was used to largely reduce the number of tests and formulate a reasonable model for predicting the triaxial compressive strength and electrical resistivity. Considering the potential benefits of response surface method, a variety of effective factors including minimum freezing temperature during a cycle, number of freeze and thaw cycles and duration of freezing and/or thawing were investigated in order to have an overall outlook on the behavior of sandy lean clay subjected to different thermal regimes resembling natural conditions. In this study, triaxial compressive tests under confining pressures of 30 kPa and 90 kPa together with electrical resistivity tests were performed. In total, 38 treatments were performed under closed system to develop and verify models depending on mentioned factors, by which the mechanical behavior and durability of frozen soil could be reasonably estimated. The repeatability and relative errors of the derived models were also evaluated. It was shown that the derived statistical models were able to quantify the level of significance of each single input factor and their interactions with modeled properties, which can simplify the test protocol required to find the most destructive parameter and thermal regime. Minimum temperature and number of cycles were found to have the most significant effects on mechanical properties and durability, respectively.

Non-linear vibration and stability analysis of an axially moving rotor in sub-critical transporting speed range

Ghayesh, Mergen H.,Ghazavi, Mohammad R.,Khadem, Siamak E. Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.34 No.4

Parametric and forced non-linear vibrations of an axially moving rotor both in non-resonance and near-resonance cases have been investigated analytically in this paper. The axial speed is assumed to involve a mean value along with small harmonic fluctuations. Hamilton's principle is employed for this gyroscopic system to derive three coupled non-linear equations of motion. Longitudinal inertia is neglected under the quasi-static stretch assumption and two integro-partial-differential equations are obtained. With introducing a complex variable, the equations of motion is presented in the form of a single, complex equation. The method of multiple scales is applied directly to the resulting equation and the approximate closed-form solution is obtained. Stability boundaries for the steady-state response are formulated and the frequency-response curves are drawn. A number of case studies are considered and the numerical simulations are presented to highlight the effects of system parameters on the linear and nonlinear natural frequencies, mode shapes, limit cycles and the frequency-response curves of the system.

Normalization and Valuation of Research Evaluation Indicators in Different Scientific Fields

Chakoli, Abdolreza Noroozi,Ghazavi, Roghayeh Korea Institute of Science and Technology Informat 2016 Journal of Information Science Theory and Practice Vol.4 No.1

Given the difference in research performance in various scientific fields, this study aims to weight and valuate current indicators used for evaluation of scientific productions (publications), in order to adjust these indicators in comparison to each other and make possible a more precise evaluation of scientific productions. This is a scientometrics study using documentary, evaluative, and survey techniques. The statistical population consisted of 106 top Iranian researchers, scientists, and scientific and research managers. Then their research résumé information was gathered and analyzed based on research questions. In order to compare values, the data gathered from research production performance of the population was weighted using Shannon entropy method. Also, the weights of each scientific production importance according to expert opinions (extracted from other works) was analyzed and after adjustment the final weight of each scientific production was determined. A pairwise matrix was used in order to determine the ratios. According to the results, in the area of engineering sciences, patents (0.142) in the area of science, international articles (0.074) in the area of humanities and social sciences, books (0.174), and in the area of medical sciences, international articles (0.111) had the highest weight compared to other information formats. By dividing the weights for each type of publication, the value of each scientific production compared to other scientific productions in the same field and productions of other fields was calculated. Validation of the results in the studied population resulted in very high credibility for all investigated indicators in all four fields. By using these values and normalized ratios of publication indicators it is possible to achieve precise and adjusted results, making it possible to feasibly use these results in realistic policy making.

Non-linear vibration and stability analysis of an axially moving rotor in sub-critical transporting speed range

Mergen H. Ghayesh,Mohammad R. Ghazavi,Siamak E. Khadem 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.34 No.4

Parametric and forced non-linear vibrations of an axially moving rotor both in non-resonance and near-resonance cases have been investigated analytically in this paper. The axial speed is assumed to involve a mean value along with small harmonic fluctuations. Hamilton’s principle is employed for this gyroscopic system to derive three coupled non-linear equations of motion. Longitudinal inertia is neglected under the quasi-static stretch assumption and two integro-partial-differential equations are obtained. With introducing a complex variable, the equations of motion is presented in the form of a single, complex equation. The method of multiple scales is applied directly to the resulting equation and the approximate closed-form solution is obtained. Stability boundaries for the steady-state response are formulated and the frequency-response curves are drawn. A number of case studies are considered and the numerical simulations are presented to highlight the effects of system parameters on the linear and nonlinear natural frequencies, mode shapes, limit cycles and the frequency-response curves of the system.