• 대한수학회보
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• 제44권2호
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• pp.215-223
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• 2007

We in this note introduce the concept of NCI rings which is a generalization of NI rings. We study the basic structure of NCI rings, concentrating rings of bounded index of nilpotency and von Neumann regular rings. We also construct suitable examples to the situations raised naturally in the process.

• 대한수학회보
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• 제55권2호
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• pp.675-677
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• 2018

• 대한수학회보
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• 제46권6호
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• pp.1091-1097
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• 2009

In this paper, we investigate the extensions of generalized stable rings. It is shown that a ring R is a generalized stable ring if and only if R has a complete orthogonal set {e$_1$, . . . , e$_n$} of idempotents such that e$_1$Re$_1$, . . . , e$_n$Re$_n$ are generalized stable rings. Also, we prove that a ring R is a generalized stable ring if and only if R[[X]] is a generalized stable ring if and only if T(R,M) is a generalized stable ring.

• 충청수학회지
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• 제32권4호
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• pp.401-408
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• 2019

A ring R is called right (resp., left) nilpotent-duo if N(R)a ⊆ aN(R) (resp., aN(R) ⊆ N(R)a) for every a ∈ R, where N(R) is the set of all nilpotents in R. In this article we provide other proofs of known results and other computations for known examples in relation with right nilpotent-duo property. Furthermore we show that the left nilpotent-duo property does not go up to a kind of matrix ring.

• International Journal of Fluid Machinery and Systems
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• 제8권1호
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• pp.46-54
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• 2015

Thrust-ring-pump is a kind of extreme-low specific speed centrifugal pump with special structure as numerous restrictions from thrust bearing and operation conditions of hydro-generator units. Because the oil circulatory and cooling system with thrust-ring-pump has a lot of advantages in maintenance and compactness in structure, it has widely been used in large and medium-sized hydro-generator units. Since the diameter and the speed of the thrust ring is limited by the generator set, the matching relationship between the flow passage inside the thrust ring (equivalent to impeller) and oil bath (equivalent to volute) has great influence on hydrodynamic performance of thrust-ring-pump. On another hand, the head and flow rate are varying with the operation conditions of hydro-generator units and the oil circulatory and cooling system. As so far, the empirical calculation method is employed during the actual engineering design, in order to guarantee the operating performance of the oil circulatory and cooling system with thrust-ring-pump at different conditions, a collaborative hydrodynamic design and optimization is purposed in this paper. Firstly, the head and flow rate at different conditions are decided by 1D flow numerical simulation of the oil circulatory and cooling system. Secondly, the flow passages of thrust-ring-pump are empirically designed under the restrictions of diameter and the speed of the thrust ring according to the head and flow rate from the simulation. Thirdly, the flow passage geometry matching optimization between thrust ring and oil bath is implemented by means of 3D flow simulation and performance prediction. Then, the pumps and the oil circulatory and cooling system are collaborative hydrodynamic optimized with predicted head-flow rate curve and the efficiency-flow rate curve of thrust-ring-pump. The presented methodology has been adopted by DFEM in design process of thrust-ring-pump and it shown can effectively improve the performance of whole system.

• KSTLE International Journal
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• 제2권2호
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• pp.127-132
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• 2001

The steady state performance of the counterrotating floating ring journal bearings is analyzed with isothermal finite bearing theory. The effect of counterrotating speed of the sleeve on the performance of the bearing is investigated. It is shown that counterrotating floating ring journal bearings can have considerable load capacity at the same counterrotating speeds, while conventional circular journal bearings with one fluid film cannot. Investigating the relationship between the frictional torques exerted on the ring due to the inner and outer films and the rotational speed of the ring, the stability of the equilibrium state is identified and the operating characteristics of the counterrotating floating ring journal bearing according to the method of acceleration or deceleration of the rotational speeds of the journal and sleeve are clarified. It is theoretically confirmed that floating ring journal bearings can be used in counterrotating journal-bearing system and become good substitutes for rolling bearings in counterrotating systems.

• 대한수학회보
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• 제50권5호
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• pp.1711-1723
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• 2013

P. V$\acute{a}$mos called a ring R 2-good if every element is the sum of two units. The ring of all $n{\times}n$ matrices over an elementary divisor ring is 2-good. A (right) self-injective von Neumann regular ring is 2-good provided it has no 2-torsion. Some of the earlier results known to us about 2-good rings (although nobody so called at those times) were due to Ehrlich, Henriksen, Fisher, Snider, Rapharl and Badawi. We continue in this paper the study of 2-good rings by several authors. We give some examples of 2-good rings and their related properties. In particular, it is shown that if R is an exchange ring with Artinian primitive factors and 2 is a unit in R, then R is 2-good. We also investigate various kinds of extensions of 2-good rings, including the polynomial extension, Nagata extension and Dorroh extension.

• 한국해양공학회지
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• 제18권6호
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• pp.70-78
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• 2004

In order to increase the load carrying capacity of tubular structures, the joints of tubular members are usually reinforced with various reinforcement system. A stiffening method with internal ring stiffeners is effectively used for the steel tubular joint with a large diameter. In this study, the behavior of internally ring-stiffened tubular T-joints subjected to axial loading is assessed. For the parametric study, nonlinear finite element analyses are used to compute the static strength on non-stiffened and ring-stiffened T-joints. Based on the numerical results, an internal ring stiffener is found to be efficient in improving the static strength. The influence of geometric parameters has been determined, and the reinforcement effect are evaluated. Based on the FE results, regression analises are performed considering the practical size of ring stiffener. Finally strength estimation formulas for ring-stiffened tubular T-joints are proposed.

• 한국자동차공학회논문집
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• 제15권2호
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• pp.143-150
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• 2007

Ring and cylinder bore wear may not be a problem in most current automotive engines. However, a small change in ring face and cylinder bore diameter can significantly affect the lubrication characteristics and ring axial motion. This in turn can cause to change inter-ring pressure, blow-by and oil consumption in an engine. Therefore, by predicting the wear of piston ring face and cylinder bore altogether, the changed ring end gap and the changed volume of gas reservoir can be calculated. Then the excessive oil consumption can be predicted. Here, the oil amount through top ring gap into combustion chamber is estimated as engine oil consumption. Furthermore, the wear theories of ring and cylinder bore are included. The changed oil consumption caused by the new end gap and the new volume of oil reservoir around second land, can be calculated at some engine running interval. Meanwhile, the wear amount and oil consumption occurred during engine durability cycle are compared with the calculated values. The wear data of rings and cylinder bore are obtained from three engines after engine durability test. The calculated wear data of each part are turn out to be around the band of averaged test values or a little below. It is shown that the important factor regarding oil consumption increasement is the wear of ring face.

• 대한수학회지
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• 제47권5호
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• pp.879-897
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• 2010

Y. Hirano introduced the concept of a quasi-Armendariz ring which extends both Armendariz rings and semiprime rings. A ring R is called quasi-Armendariz if $a_iRb_j$ = 0 for each i, j whenever polynomials $f(x)\;=\;\sum_{i=0}^ma_ix^i$, $g(x)\;=\;\sum_{j=0}^mb_jx^j\;{\in}\;R[x]$ satisfy f(x)R[x]g(x) = 0. In this paper, we first extend the quasi-Armendariz property of semiprime rings to the skew polynomial rings, that is, we show that if R is a semiprime ring with an epimorphism $\sigma$, then f(x)R[x; $\sigma$]g(x) = 0 implies $a_iR{\sigma}^{i+k}(b_j)=0$ for any integer k $\geq$ 0 and i, j, where $f(x)\;=\;\sum_{i=0}^ma_ix^i$, $g(x)\;=\;\sum_{j=0}^mb_jx^j\;{\in}\;R[x,\;{\sigma}]$. Moreover, we extend this property to the skew monoid rings, the Ore extensions of several types, and skew power series ring, etc. Next we define $\sigma$-skew quasi-Armendariz rings for an endomorphism $\sigma$ of a ring R. Then we study several extensions of $\sigma$-skew quasi-Armendariz rings which extend known results for quasi-Armendariz rings and $\sigma$-skew Armendariz rings.