• The Journal of the Acoustical Society of Korea
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• v.38 no.2
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• pp.184-192
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• 2019

Compared to 31-mode rings, 33-mode rings are highly utilized as wide bandwidth underwater acoustic transducers because the electro-mechanical coupling and piezoelectric constant d are high. On the other hand, the 31-mode ring is an axial symmetry structure, so it is possible to model it as a simple two-dimensional asymmetrical model for numerical analysis, but the 33-mode ring requires a three-dimensional numerical analysis. That is, a lot of computing resources and computation time are required. In this study, the effective material properties of an equivalent 31-mode ring were derived to simulate the electro-mechano-acoustical responses of the 33-mode ring transducer. Using the effective material properties derived from this study, a numerical analysis of rings in vacuum, air backed rings in water, and FFR (Free Flooded Ring) transducers were performed to compare the responses of 33-mode rings.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.68 no.2
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• pp.262-268
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• 2019

Previous dynamic models of hysteresis motor use an extended induction machine equivalent circuit or somewhat different equivalent circuit with conventional one, which makes unsatisfiable results. In this paper, the hysteresis dynamic characteristics of the motor rotor are analyzed using the inverse Preisach model and the hysteresis motor equivalent circuit considering eddy current effect. The hysteresis loop for the rotor ring is analyzed under full-load voltage source static state. The calculated hysteresis loop is then approximated to an ellipse for simplicity of dynamic computation. The permeability and delay angle of the elliptic loop apply to the dynamic analysis model. As a result, it is possible to dynamically analyze the hysteresis motor according to the applied voltage and the rotor material. With this method, the motor speed, generated torque, load angle, rotor current as well as synchronous entry time, hunting effect can be calculated.

• 전기의세계
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• v.19 no.2
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• pp.6-11
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• 1970

For the variable speed in automatic control, this paper describes, at first, performance equations of an induction motor which has the free rotating stator. This motor with rotating stator has a speed control factor itself by equivalent variable frequency in stator side. Secondly, an additional invertor source on the rotor slip ring serves the purpose of improving the speed control factor. The advantages decribed above permit to control the speed continuosly from zero to maximum allowable speed with low energy of thyristor a feed-back device may be used for speed stabilization under variable load.

• Korean Journal of Mathematics
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• v.5 no.2
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• pp.107-112
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• 1997

For a ring R with 1, the higher K-theory of Quillen is defined by the higher homotopy groups of the plus construction of the general linear group of R. On the other hand, the Volodin K-theory is defined by the higher homotopy groups of the Volodin space. In this paper we show that these two K-theories are equivalent. We show that the Volodin space is a homotopy fiber of the acyclic map from BGL(R) to its plus construction.

• Journal of the Korean Mathematical Society
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• v.47 no.1
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• pp.101-112
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• 2010

In [3] we showed that a polynomial over a Noetherian ring is divisible by some other polynomial by looking at the matrix formed by the coefficients of the polynomials which we called the resultant matrix. In this paper, we consider the polynomials with coefficients in a field and divisibility of a polynomial by a polynomial with a certain degree is equivalent to the existence of common solution to a system of Diophantine equations. As an application we construct a family of irreducible quartics over $\mathbb{Q}$ which are not of Eisenstein type.

• East Asian mathematical journal
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• v.31 no.3
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• pp.357-362
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• 2015

For a ring R of imaginary quadratic integers, using a concept of a unitary number system in place of the Motzkin's universal side divisor, we show that the following statements are equivalent: (1) R is Euclidean. (2) R has a unitary number system. (3) R is norm-Euclidean. Through an application of the above theorem we see that R admits binary or ternary number systems if and only if R is Euclidean.

• Communications of the Korean Mathematical Society
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• v.25 no.3
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• pp.343-347
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• 2010

In this paper we study the connection between 2-primal rings, (S,1)-rings and related conditions. And we investigate some condition which is the special case of pseudo symmetric. We also study the condition (KJ) which is given by J. Y. Kim and H. L. Jin. We introduce some condition and we prove that our condition is equivalent to the condition (KJ) when it is an (S,1)-ring.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.38 no.12
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• pp.49-57
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• 2001

In this paper, equivalent circuit model and novel model parameter extraction method of a silicon(Si) substrate are presented. Substrate coupling through Si-substrate is quantitatively investigated by analyzing equivalent circuit with operating frequency and characteristic frequencies (i.e., pole and zero frequency) of a system. For the experimental verification of the equivalent circuit and parameter extraction method, test patterns are designed and fabricated in standard CMOS technology with various isolation distances, substrate resistivity, and guard-ring structures. Then, these are measured in l00MHz-20GHz frequency range by using vector network analyzer. It is shown that the equivalent-circuit-based HSPICE simulation results using extracted parameters have excellent agreement with the experimental results. Thus, the proposed equivalent circuit and parameter extraction methodology can be usefully employed in mixed-signal circuit design and verification of a circuit performance.

• Korean Journal of Materials Research
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• v.24 no.2
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• pp.87-92
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• 2014

The Notched Ring Test(NRT) has proven to be very useful in determining the slow crack growth behavior of polyethylene pressure pipes. In particular, the test is simple and an order of magnitude shorter in experimental times as compared to the currently used Notched Pipe Test(NPT), which makes this method attractive for use as the accelerated slow crack growth test. In addition, since the NRT specimen is taken directly from the pipe, having maintained the cross-section, processing induced artifacts that would affect the slow crack growth behavior are not altered. This makes the direct comparison to the slow crack growth specimen in pipe from more meaningful. In this study, for comparison with other available slow crack growth methods, including the NPT, the stress intensity factor equation for NRT specimen was developed and demonstrated of its accuracy within 3% of that obtained from the finite element analysis. The equation was derived using a flexure formula of curved beam bending along with numerically determined geometric factors. The accuracy of the equation was successfully tested on 63, 110, 140, 160, 250, and 400 mm nominal pipe diameters, with crack depth ranging from 15 % to 45 % of the pipe wall thickness, and for standard dimensional ratio(SDR) of 9, 11, and 13.6. Using this equation the slow crack results from 110SDR11 NRT specimen were compared to that from the NPT specimen, which demonstrated that the NRT specimen was equivalent to the NPT specimen in creating the slow crack, however in much shorter experimental times.

• Structural Monitoring and Maintenance
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• v.8 no.4
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• pp.345-360
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• 2021

This paper presents an analytical approach to calculate the buckling load of the cylindrical ring structures subjected to both hydrostatic and hydrodynamic pressures. Based on the conservative law of energy and Timoshenko beam theory, a theoretical formula, which can be used to evaluate the critical pressure of buckling, is first derived for the simplified cylindrical ring structures. It is assumed that the hydrodynamic pressure can be treated as an equivalent hydrostatic pressure as a cosine function along the perimeter while the thickness ratio is limited to 0.2. Note that this paper limits the deformed shape of the cylindrical ring structures to an elliptical shape. The proposed analytical solutions are then compared with the numerical simulations. The critical pressure is evaluated in this study considering two possible failure modes: ultimate failure and buckling failure. The results show that the proposed analytical solutions can correctly predict the critical pressure for both failure modes. However, it is not recommended to be used when the hydrostatic pressure is low or medium (less than 80% of the critical pressure) as the analytical solutions underestimate the critical pressure especially when the ultimate failure mode occurs. This implies that the proposed solutions can still be used properly when the subsea vehicles are located in the deep parts of the ocean where the hydrostatic pressure is high. The finding will further help improve the geometric design of subsea vehicles against both hydrostatic and hydrodynamic pressures to enhance its strength and stability when it moves underwater. It will also help to control the speed of the subsea vehicles especially they move close to the sea bottom to prevent a catastrophic failure.