• Journal of the Society of Naval Architects of Korea
• /
• v.52 no.5
• /
• pp.372-379
• /
• 2015

The blade root fillets which have strong influences on the performance of propellers in the both structural and hydrodynamic points of view, are mechanical parts for smooth connection surface with a blade and a hub. A few related researches (Sabol, 1983; Kennedy, 1997) have noted that 3T-T/3 double radius section design would be suitable for reducing Stress Concentration Factor(SCF) and increasing Cavitation Inception Speed(CIS). In this paper, it is confirmed that this compound cross-section design has come close to the optimum solution in the shape optimization standpoint so that it could protect the propeller blade under the frequent and various loading cases. On that basis, we suggest the definite and simple fillet design methodology that has the cross-section with nT-T/n compound radius and elliptic shape which could sustain the given derivatives information as well as the offsets at the boundary and all inner region of the fillet surface. In addition, the result of design is presented in form of IGES file format in order to connect with NC machine seamlessly.

• Interaction and multiscale mechanics
• /
• v.2 no.2
• /
• pp.177-187
• /
• 2009

Machine or structural members subjected to fatigue loading will have a crack initiated during early part of their life. Therefore analysis of members with cracks and other discontinuities is very important. Finite element method has enjoyed widespread use in engineering, but it is not convenient for crack problems as the region very close to crack tip is to be discretized with very fine mesh. However, as the body force method (BFM), requires only the boundary of the discontinuity (crack or hole) to be discretized it is easy versatile technique to analyze such problems. In the present work fundamental solution for concentrated load x + iy acting in the semi-infinite plate at an arbitrary point $z_0=x_0+iy_0$ is considered. These fundamental solutions are in complex form ${\phi}(z)$ and ${\psi}(z)$ (England 1971). These potentials are known as Melan potentials (Ramakrishna 1994). A crack in the semi-infinite plate as shown in Fig. 1 is considered. This crack is divided into number of divisions. By applying pair of body forces on a division, the resultant forces on the remaining 'N'divisions are to be found for which ${\phi}_1(z)$ and ${\psi}_1(z)$ are derived. Body force method is applied to calculate stress intensity factor for crack in semi-infinite plate. Also for the case of crack emanating from circular hole in semi-infinite plate radial stress, hoop stress and shear stress are calculated around the hole and crack. Convergent results are obtained by body force method. These results are compared with FEM results.

• Journal of Ocean Engineering and Technology
• /
• v.23 no.1
• /
• pp.74-80
• /
• 2009

In this study, the static and modal analyses to find the characteristic of eigenvalues for a towed cable were with a free boundary condition at the bottom end carried out with numerical study. The resulting numerical code with finite element method was used to study sample problems for a cable with towing speeds. After tracing the equilibrium state with a towing speed through the static analysis, modal analysis on the basis of static results was performed. The static top tension for a critical towing speed is nearly 50 percent of what it was for a free hanging pipe. From static analyses, it is found that towing speed has a noticeable effect on top tension of a towed pipe. At a high towing speed, differences between the first and second periods become larger. Compared to the fundamental period for a free hanging pipe, that for a towed pipe with a critical towing speed is approximately 1.4 times larger. This result is very important point in that the lock in condition and tension of the towed cable system with top excitation can be predicted. The corrected close form solution to solve natural periods for a towed cable was presented in this study. The code is validated by comparison of the results of theoretical and numerical studies. Two results were in very good agreement. This study can contribute to predicting the lock-in condition and tension for a towed cable or pipe with top excitation.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.11C
• /
• pp.901-906
• /
• 2010

Low density parity check (LDPC) code, first introduced by Gallager and re-discovered by MacKay et al, has attracted researcher's interest mainly due to their performance and low decoding complexity. It was remarkable that the performance is very close to Shannon capacity limit under the assumption of having long codeword length and iterative decoder. However, comparing to turbo codes widely used in the current mobile communication, the encoding complexity of LDPC codes has been regarded as the drawback. This paper proposes a solution for DVB-S2 LDPC encoder to reduce the encoder latency. We use the fast IRA encoder that use the transformation of the parity check matrix into block-wise form and the partial parallel process to reduce the number of system clocks for the IRA code encoding. We compare the proposed encoder with the current DVB-S2 encoder to show that the performance of proposal is better than that of the current DVB-S2 encoder.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.12 no.1
• /
• pp.755-767
• /
• 2020

A significant development has been made on a new fatigue damage model applicable to Gaussian wide band stress response spectra using numerical approximation methods such as data processing, time simulation, and regression analysis. So far, most of the alternative approximate models provide slightly underestimated or overestimated damage results compared with the rain-flow counting distribution. A more reliable approximate model that can minimize the damage differences between exact and approximate solutions is required for the practical design of ships and offshore structures. The present paper provides a detailed description of the development process of a new fatigue damage model. Based on the principle of the Gaussian wide band model, this study aims to develop the best approximate fatigue damage model. To obtain highly accurate damage distributions, this study deals with some prominent research findings, i.e., the moment of rain-flow range distribution MRR(n), the special bandwidth parameter μk, the empirical closed form model consisting of four probability density functions, and the correction factor QC. Sequential prerequisite data processes, such as creation of various stress spectra, extraction of stress time history, and the rain-flow counting stress process, are conducted so that these research findings provide much better results. Through comparison studies, the proposed model shows more reliable and accurate damage distributions, very close to those of the rain-flow counting solution. Several significant achievements and findings obtained from this study are suggested. Further work is needed to apply the new developed model to crack growth prediction under a random stress process in view of the engineering critical assessment of offshore structures. The present developed formulation and procedure also need to be extended to non-Gaussian wide band processes.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.36 no.6
• /
• pp.603-608
• /
• 2023

Carbon black with high purity and excellent conductivity is used as a conductive filler in the semiconductive compound for EHV (Extra High Voltage) power cables of 345 kV or higher. When carbon black and CNT (carbon nanotube) are applied together as a conductive filler of a semiconductive compound, stable electrical properties of the semiconductive compound can be maintained even though the amount of conductive filler is significantly reduced. In EHV power cables, since the semi-conductive layer is close to the conductor, stable electrical characteristics are required even under high-temperature conditions caused by heat generated from the conductor. In this study, the theoretical principle that a semiconductive compound applied with carbon black and CNT can maintain excellent electrical properties even under high-temperature conditions was studied. Basically, the conductive fillers dispersed in the matrix form an electrical network. The base polymer and the matrix of the composite, expands by heat under high temperature conditions. Because of this, the electrical network connected by the conductive fillers is weakened. In particular, since the conductive filler has high thermal conductivity, the semiconductive compound causes more thermal expansion. Therefore, the effect of CNT as a conductive filler on the thermal conductivity, thermal expansion coefficient, and volume resistivity of the semiconductive compound was studied. From this result, thermal expansion and composition of the electrical network under high temperature conditions are explained.

• Journal of the Korean institute of surface engineering
• /
• v.47 no.1
• /
• pp.39-47
• /
• 2014

The peculiar feature of cathodic protection in seawater has the capability to form mineral calcareous deposits such as magnesium and calcium on metal surfaces. It is assumed that $OH^-$ ions are generated close to the metal surface as a result of cathodic protection and generated $OH^-$ ions increases the pH of the metal/seawater interface outlined as the following formulae. (1) $O_2+2H_2O+4e{\rightarrow}4OH^-$, or (2) $2H_2O+2e{\rightarrow}H_2+2OH^-$. And high pH causes precipitation of $Mg(OH)_2$ and $CaCO_3$ in accordance with the following formulae. (1) $Mg^{2+}+2OH^-{\rightarrow}Mg(OH)_2$, (2) $Ca^{2+}+CO{_3}^{2-}{\rightarrow}CaCO_3$. The focus of this study was to increase the amount of $CO{_3}^{2-}$ with the injection of $CO_2$ gas to the solution for accelerating process of the following formulae. (1) $H_2O+CO_2{\rightarrow}H_2CO_3$, (2) $HCO^{3-}{\rightarrow}{H^+}+CO{_3}^{2-}$. Electrodeposit films were formed by an electro-deposition technique on steel substrates in solutions of both natural seawater and natural seawater dissolved $CO_2$ gas with different current densities, over different time periods. The contents of films were investigated by scanning electron microscopy(SEM) and X-ray diffraction(XRD). The adhesion and corrosion resistance of the coating films were evaluated by anodic polarization. From an experimental result, only $CaCO_3$ were found in solution where injected $CO_2$ gas regardless of current density. In case of injecting the $CO_2$ gas, weight gain of electrodeposits films hugely increased and it had appropriate physical properties.

• Korean Chemical Engineering Research
• /
• v.47 no.6
• /
• pp.740-746
• /
• 2009

In the present study, the drowning-out crystallization of L(+)-calcium lactate was investigated in order to develop the crystallization separation process. The crystallization of the calcium lactate was induced by injecting the alcoholic anti-solvent into the aqueous solution of calcium lactate and the control of the calcium lactate crystal size during the crystallization was primarily investigated under the consideration of the anti-solvent species, anti-solvent composition and agitation speed as the key operating factors. Alcohols of methanol, ethanol, n-propanol and i-propanol were used as the anti-solvent for the drowning-out crystallization. Prior to the crystallization experiment, the solubility of calcium lactate in the water-alcohol mixture was measured along with the variation of the alcohol species and composition, which was necessary to estimate the supersaturation level of the crystallization. By the drowning-out crystallization, the calcium lactate crystals of the fabric shape were obtained. Using the ethanol as the antisolvent, the fabric crystals close to the needle shape were produced. However, the hairy crystals were obtained by using the propanol as the anti-solvent. Due to such morphological features, the crystals was highly apt to form the aggregates. The aggregation of the crystals was intensified as increasing the alcohol fraction in the water-alcohol mixture. Meanwhile, the agitation caused the breakage of crystals, resulting in the decrease of the crystal size. Therefore, the crystal size in the crystallization was predominantly determined by the competition between the crystal aggregation and breakage.

• Archives of design research
• /
• v.17 no.4
• /
• pp.169-176
• /
• 2004

It is incontestable that the essence of the current fever of well-being is pseudo-ideology, which is the commercialized well-being. Nevertheless, the potential value as the cultural contests of Korean Design, reaching the philosophy of well-being, must not be overlooked. Being more than its dictionary meaning of 'happiness' and 'welfare', well-being aims peace of mind and richness in mentality, thus supports the life style of 'Body-Mind Monism'. As a trend that has taken a ride on the consumerism, it is inevitable to excavate the benign cultural value that an ordinary sign of well-being lacks in order to create a peculiar model of Korea's design contents by sublimating the commodity aesthetic of well-being into an alternative argument possessing the cultural identity of Korea. Well-being, not much different form an attitude of following the 'ways of nature', is a typical model of non-dualistic thinking of East Asia. By tracing back to the indication of well-being that already existed in the non-dualistic thought and design of East Asia, the genealogy connecting the current phenomena of well-being to the Body-Mind Monism can be found in the cultural traditions of as close as Korea and as far as East Asia. In the case of adopting the monistic way of East Asian thinking that sees body and mind as one not two as the theoretical background of well-being imported fro the West, it is expected to provide a solution for the design discourse of Korea to be out of colonialism. Well-being contributes to the monistic awareness in the period of self-reflected modernization, which needs to search new values based on the reconsideration of dualistic paradigm centered on the Western culture, thus it is worth putting anticipation on the potential significance well-being would have in the field of national as well as international design world.

• Journal of the Mineralogical Society of Korea
• /
• v.23 no.1
• /
• pp.73-84
• /
• 2010

We studied the geological occurrence, associated minerals, mineralogical properties and formation process of tremolites from two abandoned asbestos mines, Jungang (Sinsuk) and Daebosuksan, located in Boryoung area, Chungnam. Morphologically different tremolites such as long fibrous, needle-like, bladed and prismatic forms coexisted. Fibrous tremolite, known for its high toxieity to human health, was systematically analyzed by polarized light microscopy and scanning electron microscopy. The average length of tremolite fibers was 31.2 ${\mu}m$ although the maximum length of some asbestos was 210.0 ${\mu}m$. The average width and aspect ratio were 1.6 ${\mu}m$ and 19.9, respectively. Tremolite showed inclined extinction in the range of 6.1~20.2$^{\cric}$. X-ray diffraction patterns were slightly different between fibrous (asbestiform) and prismatic (non-asbestiform) tremolites. EPMA analysis of tremolites in the study area indicated extremely high Mg content with very low Fe content, close to the composition of tremolite in end-member in the tremolite-actinolite solid solution series. The formational conditions of asbestiform and non-asbestiform tremolite appear to be different. Asbestiform tremolite was estimated to have been formed in later stage.