• Steel and Composite Structures
• /
• 제49권6호
• /
• pp.615-631
• /
• 2023

To investigate the seismic behavior of steel slag self-stressing concrete-filled circular steel tubular (SSSCFCST) columns, 14 specimens were designed, namely, 10 SSSCFCST columns and four ordinary steel slag (SS) concrete (SSC)-filled circular steel tubular (SSCFCST) columns. Comparative tests were conducted under low reversed cyclic loading considering various parameters, such as the axial compression ratio, diameter-thickness ratio, shear-span ratio, and expansion ratio of SSC. The failure process of the specimens was observed, and hysteretic and skeleton curves were obtained. Next, the influence of these parameters on the hysteretic behavior of the SSSCFCST columns was analyzed. The self stress of SS considerably increased the bearing capacity and ductility of the specimens. Results indicated that specimens with a shear-span ratio of 1.83 exhibited compression bending failure, whereas those with shear-span ratios of 0.91 or 1.37 exhibited drum-shaped cracking failure. However, shear-bond failure occurred in the nonloading direction. The stiffness of the falling section of the specimens decreased with increasing shear-span ratio. The hysteretic curves exhibited a weak pinch phenomenon, and their shapes evolved from a full shuttle shape to a bow shape during loading. The skeleton curves of the specimens were nearly complete, progressing through elastic, elastoplastic, and plastic stages. Based on the experimental study and considering the effects of the SSC expansion rate, shear-span ratio, diameter-thickness ratio, and axial compression ratio on the seismic behavior, a peak displacement coefficient of 0.91 was introduced through regression analysis. A simplified method for calculating load-displacement skeleton curves was proposed and loading and unloading rules for SSSCFCST columns were provided. The load-displacement restorative force model of the specimens was established. These findings can serve as a guide for further research and practical application of SSSCFCST columns.

• Elastomers and Composites
• /
• 제35권2호
• /
• pp.106-114
• /
• 2000

상온에서의 충격 흡수특성과 compression set 특성을 향상시키기 위하여 ethylene vinyl acetate copolymer (EVA)와 styrene vinyl isoprene styrene triblock copolymer (SVIS)를 블렌드하여 발포체를 제조하였다. 발포제 및 EVA/SVIS 블렌드비가 발포배율 및 기계적 물성에 미치는 영향을 조사하였다. SVIS 함량이 증가함에 따라 블렌드의 점도는 증가하였고 가교 속도는 감소하였으며, 발포배율은 감소하여 비중은 증가하였다. 발포제 함량 증가, 즉 발포배율 증가에 따른 반발탄성은 변화가 없는 반면에, SVIS 함량 증가에 따라 발포체의 상온에서의 tan ${\delta}$ 값은 증가하였으며 따라서 반발 탄성은 감소함을 알 수 있었다. EVA/SVIS 블렌드 발포체에서 SVIS 함량 증가에 따라 가교밀도와 비중이 증가하므로 compression set 값도 낮은 값을 나타내었다.

• 대한기계학회논문집B
• /
• 제21권9호
• /
• pp.1139-1148
• /
• 1997

Compression waves propagating in a high-speed railway tunnel develops large pressure fluctuations on the train body or tunnel structures. The pressure fluctuations would cause an ear discomfort for the passengers and increase the aerodynamic resistance of trains. As a fundamental research to resolve the pressure wave phenomenon in the tunnel, experiments were carried out by using a shock tube with an open end. A blockage to model trains inside the tunnel was installed on the lower wall of shock tube, thus forming a sudden cross-sectional area reduction. The compression waves were obtained by the fast opening gate valve instead of a conventional diaphragm of shock tube and measured by the flush mounted pressure transducers with a high sensitivity. The experimental results were compared with the previous theoretical analyses. The results show that the ratio of the reflected to the incident compression wave at the sudden cross-sectional area reduction increases but the ratio of the passing to the incident compression wave decreases, as the incident compression wave becomes stronger. This experimental results are in good agreements with the previous theoretical ones. The maximum pressure gradient of the compression wave abruptly increases but the width of the wave front does not vary, as it passes over the sudden cross-sectional area reduction.

• 동력기계공학회지
• /
• 제19권6호
• /
• pp.82-88
• /
• 2015

In this paper, cycle performance analysis of two-stage compression and one-stage expansion refrigeration system applied various refrigerants is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include degree of superheating and subcooling, compressor efficiency, evaporation temperature, condensing temperature, mass flow rate ration into inter-cooler, effectiveness of internal heat exchanger. The main results were summarized as follows : The COP of two-stage compression and 1-stage expansion refrigeration system increases with the increasing subcooling, mass flow rate ration of inter-cooler, evaporation temperature, but decreases with the increasing condensing temperature and superheating degree. Therefore, subcooling degree, mass flow rate ratio of inter-cooler of two-stage compression and 1-stage expansion using substitute refrigerant have an effect on COP of this system. The COP of alternative refrigerants was higher than the COP of R22 in this study, although the COP of some mixed refrigerants were lower than COP of R22.

• 한국자동차공학회논문집
• /
• 제5권2호
• /
• pp.50-59
• /
• 1997

When a front head of train enters a tunnel at a high speed, compression wave is generated at tunnel entrance due to the confinement effect and propagated along the tunnel with sound of speed. The propagated compression wave is reflected at tunnel exit due to abrupt pressure change at passage. The reflected wave is expansion pressure wave. And when the rear head of train goes through the tunnel entrance, another expansion pressure wave is generated and propagated along the tunnel. The pressure drop occurs seriously around train when the two expansion pressure waves come cross on train in the tunnel. In order to reduce the pressure drop, the compression wave front must be controlled because the intensity and magnitude of pressure drop is nearly proportional to that of compression wave at tunnel entrance. This study relates to reduction of the pressure wave gradient with respect to tunnel entrance shape change with various kind of angle and rounding. The results show characteristics of wave propagation in tunnel, usefulness of characteristic curve to estimate proper time domain size in numerical study and measuring time in actual experiment. Also rounding is contributed to improve pressure wave front even if its radius is very small at tunnel entrance. In order to improve of pressure wave front at tunnel entrance, proper angle is prefered to rounding with big radius and an angle of around 14$^{\circ}$ is recommended according to this simulations, And it is expected to reduce additional pressure drop in tunnel when the location and the size of the internal space for attendant equipment are considered in advance.

• 한국분무공학회지
• /
• 제26권2호
• /
• pp.81-87
• /
• 2021

This study was performed to calculate the swirl ratio of a diesel engine intake port by a 1D computer simulation under actual engine operating conditions. The swirl ratio of the intake port was simulated according to the change of the engine speed during the operation of the motoring without fuel injection. The swirl ratio of the intake port was simulated according to changes in the crank angle during the four-cycle operation of intake, compression, expansion and exhaust. The swirl ratio represented by the three regions of the piston, center and squish was simulated. Among the three regions, the piston-region swirl ratio is important for effective air-fuel mixing in the engine cylinder. In particular, it was confirmed during the simulation that the piston swirl ratio before and after the compression top dead center (TDC) point when fuel is injected in the DI diesel engine can have a significant effect on the mixing of air and fuel. It was desirable to set the average piston swirl ratio over a crank angle section before and after compression TDC as the representative swirl ratio of the cylinder head intake port according to the change of the engine speed.

• 한국안전학회지
• /
• 제13권4호
• /
• pp.142-154
• /
• 1998

A stirling engine is a mechanism used to convert heat to power and operates on a closed regenerative thermodynamic cycle with compression and expansion of the working fluid at different temperature. The performance of a stilting cycle machine is a function of six independent parameters, namely; (1) speed N(r.p.m), (2) pressure of the working fluid p(Pa), (3) ratio of the temperature in the compression and expansion space ${\tau}(=T_C/T_E)$ , (4) ratio of the swept volumes in these two spaces K, (5) phase angle $\alpha$ and (6) dead volume ratio X. This paper describes the procedure and presents the results of computations carried out to establish the optimum combinations of these six parameters for maximum engine output for the machine acting as a prime mover, over a combined temperature range from $300^{\circ}K$ to $1000^{\circ}K$ and dead volume ratio X ranging from 0.1 to 2.0. The output of a stilting cycle machine can be expressed in terms of nondimensional power in several different ways. Four methods were studied in detail, the parameters optimized and design charts and engine power charts prepared. The results of this paper may be useful as a guide to the likely effects on the performance of some of the important design parameters and regenerator design.

• Steel and Composite Structures
• /
• 제38권2호
• /
• pp.151-164
• /
• 2021

During the pipe forming process, a steel plate undergoes inelastic behavior multiple times under a load condition repeating tension and compression in the circumferential direction. It derives local reduction or increase of yield strength within the thickness of steel pipes by the plastic hardening and Bauschinger effect. In this study, a combined hardening model is proposed to effectively predict variations of yield strength in the circumferential direction of API-X65 and X70 steel pipes with relatively low t/D ratio during the forming process, which is expected to experience accumulated plastic strain of 2~3%, the typical Lüder band range in a low-carbon steel. Cyclic tensile tests of API-X65 and X70 steels were performed, and the parameters of the proposed model for the steels were calibrated using the test results. Bending-flattening tests to simulate repeated tension and compression during pipe forming were followed for API-X65 and X70 steels, and the results were compared with those by the proposed model and Zou et al. (2016), in order to verify the process of material model calibration based on tension-compression cyclic test, and the accuracy of the proposed model. Finally, parametric analysis for the yield strength of the steel plate in the circumferential direction of UOE pipe was conducted to investigate the effects of t/D and expansion ratios after O-forming on the yield strength. The results confirmed that the model by Zou et al. (2016) underestimated the yield strength of steel pipe with relatively low t/D ratio, and the parametric analysis showed that the t/D and expansion ratio have a significant impact on the strength of steel pipe.

• 한국통신학회논문지
• /
• 제27권6A호
• /
• pp.618-627
• /
• 2002

2차원 이산 웨이블릿 변환(2D-DWT)을 이용한 영상처리에서 영상의 경계부분 화소들을 처리하는 방법은 영상의 화질과 구현비용에 영향을 미친다. 본 논문에서는 하드웨어 및 소프트웨어 구현에 적합하고 화질의 손실이 거의 없는 효과적인 경계화소 처리방법을 제안하였다. 이 방법은 2차원 영상을 1차원 배열로 처리하는 방법으로, DWT 진행방향에 따라 영상을 직렬의 연속적인 데이터구조로 간주하고 DWT를 수행(Serial-Sequential Processing)한다. 제안한 방법의 성능 및 구현의 용이성을 보이기 위하여 영상을 압축하고 복원하는 영상압축 코덱을 구현하여 실험하였다. 여기에는 로그-스케일의 고정 양자화기를 사용하였으며, 엔트로피 코더는 구현하지 않았다. 실험결과 압축률 2:1 이상의 경우(엔트로피 코딩을 제외한 압축율) 주기적 확장(Periodic Expansion, PE)방법과는 거의 동일한 SNR(Signal to Noise Ration)을 보였으며, 대칭적 확장(Symmetric Expansion, SE)방법에 비해서는 15.3%, 0-화소 삽입(Zero-Padding Expansion, ZPE)방법에 비해서는 9.6% 높은 SNR을 보였다. 또한 주기적 확장방법은 본 논문의 방법에 비해 12.99%의 메모리가 더 필요하였으며, 영상의 압축동작만을 고려할 때 제안한 방법에 비해 SE 방법과

• 대한기계학회논문집B
• /
• 제21권1호
• /
• pp.89-98
• /
• 1997

Compression waves propagating in a high speed railway tunnel impose large pressure fluctuations on the train body or tunnel structures. The pressure fluctuations can cause ear discomfort for the passengers and increase the aerodynamic resistance of trains. As a fundamental research to resolve the pressure wave phenomenon in the tunnel, a steady theory of Chester-Chisnell- Whitham was applied to a simple shock tube with a sudden cross-sectional area reduction to model trains inside the tunnel. The results of the present theoretical analysis were compared with the experiments of the shock tube. The results show that the reflected compression wave from the model becomes stronger as the strength of incident compression wave and the blockage ratio increase. However, the compression wave passing through the model is not strongly dependent on the blockage ratio. The theoretical results are in good agreement with the experiments.