• Journal of Electrical Engineering and Technology
• /
• v.4 no.3
• /
• pp.410-417
• /
• 2009

The objective of this paper is to study the discharge phenomenon for a point-plane air interval using an original fuzzy logic system. Firstly, a physical model based on streamer theory with consideration of the space charge fields due to electrons and positive ions is proposed. To test this model we have calculated the breakdown threshold voltage for a point-plane air interval. The same model is used to determine the discharge steps for different configurations as an inference data base. Secondly, using results obtained by the numerical simulation of the previous model, we have introduced the fuzzy logic technique to predict the breakdown threshold voltage of the same configurations used in the numerical model and make estimation on the insulating state of the air interval. From the comparison of obtained results, we can conclude that they are in accordance with the experimental ones obtained for breakdown discharges in different point-plane air gaps collected from the literature. The proposed study using fuzzy logic technique shows a good performance in the analysis of different discharge steps of the air interval.

• Journal of Welding and Joining
• /
• v.21 no.6
• /
• pp.71-76
• /
• 2003

For the purpose of clarifying the influence of welding residual stress to the fatigue crack propagations behaviour, an analytical investigation based on finite element method is performed to examine the opening behaviour of tip-closed crack in the compressive residual stress. A finite element model comprised of contact elements for the crack plane and plane stress elements for the base material is used to evaluate crack opening stress of the crack existing in the residual stress field. Also an analytical method based on the superposition principle to estimate the length of opened part of tip closed crack and the stress distribution adjacent to the crack during uploading is applied to the finite element model. The software for the analysis is ABAQUS, which is a general purpose finite element package. The results show that stresses distributed on the crack surfaces are reduced and approached to zero as the applied stresses are increased up to crack tip opening stress and no mechanical discontinuity is found at the boundary of contact elements and plane stress elements. It is verified that the opening behavior of the fatigue crack in the residual stress can be predicted by finite element method with the proposed analytical method.

• Journal of Welding and Joining
• /
• v.17 no.2
• /
• pp.66-75
• /
• 1999

Weld bead quality in tailored blank(TB) is critically affected by edge preparation of sheets. The edge quality of prepared sheets for TB can be classified into straightness and the cross section quality of sheared plane such as a ratio of shear face, shear plane angle, etc. In order to have a good edg quality for butt-welding sheets, precision shearing will be recommended. In this paper, the feasibility of a conventional mechanical shearing as the edge preparation for tailored blanks is studyied. It reveals that fine shearing may not be the unique solution as it is generally accepted. To obtain the good shearing condition with a conventional mechanical shearing, experiments were carried out using Tahuchi method. The major parameters affecting a sheared contour are the clearance between upper blade and lower blade, and shear angle. The optimal shearing condition yields a very good straightness along the entire length of the cut, which gives a butt joint gap less than 10% of the base material thickness. The good cross section of sheared plane is also achieved in the optimal shearing condition such as a ratio of the shear face above 65%, a cross section's shear plane angle above 85%, little burr, which is providing finally good weld beads.

• Geomechanics and Engineering
• /
• v.18 no.4
• /
• pp.391-406
• /
• 2019

The aim of this paper was to study the influence of the footing shape and the effect of the roughness of the foundation base on the bearing capacity of shallow foundations on rock masses. For this purpose the finite difference method was used to analyze the bearing capacity of various types and states of rock masses under the assumption of Hoek-Brown failure criterion, for both plane strain and axisymmetric model, and considering smooth and rough interface. The results were analyzed based on a sensitivity study of four varying parameters: foundation width, rock material constant (mo), uniaxial compressive strength and geological strength index. Knowing how each parameter influences the bearing capacity depending on the footing shape (circular vs strip footing) and the footing base interface roughness (smooth vs rough), two correlation factors were developed to estimate the percentage increase of the ultimate bearing capacity as a function of the footing shape and the roughness of the footing base interface.

• Proceedings of the KIEE Conference
• /
• 2000.11d
• /
• pp.650-652
• /
• 2000

Although Fuzzy Logic Controller(FLC) adopted three terms as input gives better performance. FLC is in general composed of two-term control because of the difficulty in the construction of fuzzy rule base. In this paper, a three-term FLC which is similar to PID control but acts as a nonlinear controller is proposed. To reduce the complexity of the rule base design and increase efficiency, a simplified fuzzy PID control is induced from a hybrid velocity/position type PID algorithm by sharing a common rule base for both fuzzy Pi and fuzzy PD parts. It is simple in structure, easy in implementation, and fast in calculation. The phase plane technique is applied to obtain the rule base for fuzzy two-term control and them. The resultant rule base is Macvicar-Whelan type. The frequency response information is used in tuning of membership functions. Also a tuning strategy for the scaling factors is Proposed based on the relationship between PID gain and them. Simulation results show better performance and the effectiveness of the proposed method.

• Journal of Industrial Technology
• /
• v.20 no.B
• /
• pp.155-162
• /
• 2000

Although Fuzzy Logic Controller(FLC) adopted three terms as input gives better performance, FLC is in general composed of two-term control because of the difficulty in the construction of fuzzy rule base. In this paper, a three-term FLC which is similar to PID control but acts as a nonlinear controller is proposed. To reduce the complexity of the rule base design and to increase efficiency. a simplified fuzzy PID control is induced from a hybrid velocity/position type PID algorithm by sharing a common rule base for both fuzzy PI and fuzzy PD parts. It is simple in structure, easy in implementation, and fast in calculation. The phase plane technique is applied to obtain the rule base for fuzzy two-term control and the resultant rule base is Macvicar-Whelan type. And the membership function is a Gaussian function. The frequency response information is used in tuning of the membership functions. Also a tuning strategy for the scaling factors is proposed based on the relationship between PID gain and the scaling factors. Simulation results show better performance and the effectiveness of the proposed method.

• The korean journal of orthodontics
• /
• v.18 no.1 s.25
• /
• pp.141-154
• /
• 1988

This study was designed to investigate the difference between craniofacial characteristics of the normal occlusion and those of Class II Div. 1 malocclusion. The sample was divided into 2 groups, the 50 subjects of Normal occlusion, the 50 subjects of Class II Div. 1 malocclusion in both sexes. Both groups aged from 11 to 14 years. The results of this study were as follows; 1. No significant difference was observed in cranial base shape between both groups, but anterior cranial base size of Class II Div. 1 malocclusion group was larger than that of normal group. 2. No significant difference in antero-posterior position of Maxilla to cranial base was founded between both groups. 3. No difference in Mandibular shapes and Mandibular plane angles to the cranial base was observed between Class II Div. 1 malocclusion and normal occlusion, but Mandibular position in Class II Div. 1 malocclusion was posterior to that of normal group. 4. Antero-posterior relationship of Maxilla and Mandible was significant difference between both groups, but vertical relationship of those was no difference. 5. Maxillary incisor position to cranial base of Class II Div. 1 malocclusion was anteior to normal occlusion, and Maxillary posterior teeth was posterior. Mandibular incisor and mandibular posterior teeth position was no difference. 6. Upper and lower lip position to esthetic line of Class II Div. 1 malocclusion was anterior to normal occlusion.

• Structural Engineering and Mechanics
• /
• v.23 no.5
• /
• pp.505-523
• /
• 2006

An unrestrained plane rigid body resting on a horizontal surface which shakes horizontally and vertically may assume one of the five modes of response: rest, slide, slide-rock, rock, and free flight. The first four are nontrivial modes of motion. It is important to study which one of these responses is started from rest as in most studies it is often assumed that the initial mode is the particular mode of response. Criteria governing the initiation of modes are first briefly discussed. It is shown that the commencement of response modes depends on the aspect ratio of the body, coefficients of static and kinetic friction at the body-base interface, and the magnitude of maximum base accelerations. Considering the last two factors as random variables, the initiation of response modes is next studied from a probabilistic point of view. Type 1 extreme value and lognormal distributions are employed for maximum base excitations and coefficient of friction respectively. Analytical expressions for computing the probability values of each mode of response are derived. The effects of slenderness ratio, vertical acceleration, and statistical distributions of maximum acceleration and coefficient of friction are shown through numerical results and plots.

• Journal of the Korean Geotechnical Society
• /
• v.34 no.10
• /
• pp.17-28
• /
• 2018

Important parameters for the stability checks of cantilever wall are the active earth pressure and the weight of soil above the heel of the base slab. If the heel length is so long enough that the shear zone bounded by the failure plane is not obstructed by the stem of the wall, the Rankine active condition is assumed to exist along the vertical plane which is located at the edge of the heel of the base slab. Then the Rankine active earth pressure equations may be theoretically used to calculate the lateral pressure on the vertical plane. However, in case of the cantilever wall with a short heel, the application of Rankine theory is not only theoretically incorrect but also makes the lateral earth pressure larger than the actual pressure and results in uneconomical design. In this study, for the cantilever wall with a short heel the limit analysis method is used to investigate the mechanism of development of the active earth pressure and then the magnitude and location of the resultants of the pressure and the weight of the soil above the heel are determined. The calculated results are compared with the existing methods for the stability check. In case of the cantilever wall with a short heel, the results by the Mohr circle method and Teng's method show max. 3.7% and 32% larger than those of the limit analysis method respectively.

• Imaging Science in Dentistry
• /
• v.49 no.2
• /
• pp.159-169
• /
• 2019

Purpose: Cone-beam computed tomography (CBCT) is widely used for 3-dimensional assessments of cranio-maxillo-facial relationships, especially in patients undergoing orthognathic surgery. We have introduced, for reference in CBCT cephalometry, an anatomical mid-sagittal plane (MSP) identified by the nasion, the midpoint between the posterior clinoid processes of the sella turcica, and the basion. The MSP is an updated version of the median plane previously used at our institution for 2D posterior-anterior cephalometry. This study was conducted to test the accuracy of the CBCT measures compared to those obtained using standard posterior-anterior cephalometry. Materials and Methods: Two operators measured the inter-zygomatic distance on 15 CBCT scans using the MSP as a reference plane, and the CBCT measurements were compared with measurements made on patients' posterior-anterior cephalograms. The statistical analysis evaluated the absolute and percentage differences between the 3D and 2D measurements. Results: As demonstrated by the absolute mean difference (roughly 1 mm) and the percentage difference (less than 3%), the MSP showed good accuracy on CBCT compared to the 2D plane, especially for measurements of the left side. However, the CBCT measurements showed a high standard deviation, indicating major variability and low precision. Conclusion: The anatomical MSP can be used as a reliable reference plane for transverse measurements in 3D cephalometry in cases of symmetrical or asymmetrical malocclusion. In patients who suffer from distortions of the skull base, the identification of landmarks might be difficult and the MSP could be unreliable. Becoming familiar with the relevant software could reduce errors and improve reliability.