• Geomechanics and Engineering
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• 제30권6호
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• pp.539-549
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• 2022

Accidental anchor drop can cause disturbances to seabed materials and pose significant threats to the safety and serviceability of submarine structures such as pipelines. In this study, a series of anchor drop tests was carried out to investigate the penetration mechanism of a Hall anchor in sand and clay. A special anchor drop apparatus was designed to model the inflight drop of a Hall anchor. Results indicate that Coriolis acceleration was the primary cause of large horizontal offsets in sand, and earth gravity had negligible impact on the lateral movement of dropped anchors. The indued final horizontal offset was shown to increase with the elevated drop height of an anchor, and the existence of water can slow down the landing velocity of an anchor. It is also observed that water conditions had a significant effect on the influence zone caused by anchors. The vertical influence depth was over 5 m, and the influence radius was more than 3 m if the anchor had a drop height of 25 m in dry sand. In comparison, the vertical influence depth and radius reduced to less than 3 m and 2 m, respectively, when the anchor was released from 10 m height and fell into the seabed with a water depth of 15 m. It is also found that the dynamically penetrating anchors could significantly influence the earth pressure in clay. There is a non-linear increase in the measured penetration depth with kinematic energy, and the resulted maximum earth pressure increased dramatically with an increase in kinematic energy. Results from centrifuge model tests in this study provide useful insights into the penetration mechanism of a dropped anchor, which provides valuable data for design and planning of future submarine structures.

• Structural Engineering and Mechanics
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• 제86권1호
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• pp.119-137
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• 2023

The purpose of this research is to assess the performance of CBN and ceramic tools during the dry turning of gray cast iron EN GJL-350. During the turning operation, the variable machining parameters are cutting speed, feed rate, depth of cut and type of the cutting material. This contribution consists of two sections, the first one deals with the performance evaluation of four materials in terms of evolution of flank wear, surface roughness (2D and 3D) and cutting forces. The focus of the second section is on statistical analysis, followed by modeling and optimization. The experiments are conducted according to the Taguchi design L₃₂ and based on ANOVA approach to quantify the impact of input factors on the output parameters, namely, the surface roughness (Ra), the cutting force (Fz), the cutting power (Pc), specific cutting energy (Ecs). The RSM method was used to create prediction models of several technical factors (Ra, Fz, Pc, Ecs and MRR). Subsequently, the desirability function approach was used to achieve a multi-objective optimization that encompasses the output parameters simultaneously. The aim is to obtain optimal cutting regimes, following several cases of optimization often encountered in industry. The results found show that the CBN tool is the most efficient cutting material compared to the three ceramics. The optimal combination for the first case where the importance is the same for the different outputs is Vc=660 m/min, f=0.116 mm/rev, ap=0.232 mm and the material CBN. The optimization results have been verified by carrying out confirmation tests.

• Steel and Composite Structures
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• 제46권3호
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• pp.385-401
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• 2023

Steel is becoming increasingly popular due to its high strength, excellent ductility, great assembly performance, and recyclability. In reality, steel structures serving for a long time in atmospheric, industrial, and marine environments inevitably suffer from corrosion, which significantly decreases the durability and the service life with the exposure time. For the mechanical properties of corroded steel, experimental studies are mainly conducted. The existing numerical analyses only evaluate the mechanical properties based on corroded morphology at the isolated time-in-point, ignoring that this morphology varies continuously with corrosion time. To solve this problem, the relationships between pit depth expectation, standard deviation, and corrosion time are initially constructed based on a large amount of wet-dry cyclic accelerated test data. Successively, based on that, an in-situ pitting evolution method for evaluating the residual tensile strength of corroded steel is proposed. To verify the method, 20 repeated simulations of mass loss rates and mechanical properties are adopted against the test results. Then, numerical analyses are conducted on 135 models of corrosion pits with different aspect ratios and uneven corrosion degree on two corroded surfaces. Results show that the power function with exponents of 1.483 and 1.091 can well describe the increase in pit depth expectation and standard deviation with corrosion time, respectively. The effect of the commonly used pit aspect ratios of 0.10-0.25 on yield strength and ultimate strength is negligible. Besides, pit number ratio α equating to 0.6 is the critical value for the strength degradation. When α is less than 0.6, the pit number increases with α, accelerating the degradation of strength. Otherwise, the strength degradation is weakened. In addition, a power function model is adopted to characterize the degradation of yield strength and ultimate strength with corrosion time, which is revised by initial steel plate thickness.

• Geomechanics and Engineering
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• 제34권3호
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• pp.251-265
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• 2023

In urban construction projects, it is crucial to evaluate the impacts of excavation-induced ground movements in order to protect surrounding structures. These ground movements resulting in damages to the neighboring structures and facilities (i.e., parking basement) are of main concern for the geotechnical engineers. Even more, the danger exists if the nearby structure is an ancient or masonry brick building. The formations of cracks are indicators of structural damage caused by excavation-induced ground disturbances, which pose issues for excavation-related projects. Although the effects of deep excavations on existing brick masonry walls have been thoroughly researched, the impact of twin excavations on a brick masonry wall is rarely described in the literature. This work presents a 3D parametric analysis using an advanced hypoplastic model to investigate the responses of an existing isolated brick masonry wall to twin perpendicular excavations in dry sand. One after the other, twin perpendicular excavations are simulated. This article also looks at how varying sand relative densities (D_r = 30%, 50%, 70%, and 90%) affect the masonry wall. The cracks at the top of the wall were caused by the hogging deformation profile caused by the twin excavations. By raising the relative density from 30% to 90%, excavation-induced footing settlement is greatly minimized. The crack width at the top of the wall reduces as a result of the second excavation in very loose to loose sand (D_r = 30% and 50%). While the crack width on the top of the wall increases owing to the second excavation in medium to very dense sand (D_r = 70% and 90%).

• Geomechanics and Engineering
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• 제36권6호
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• pp.589-599
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• 2024

Dispersion occurs when clay soil disperses under specific conditions and is rapidly washed away. While there are numerous methods for rectifying it, they are neither cost nor time-effective. The current study used metakaolin and zeolite to improve heavily dispersive clay soil either separately or in combination at 0%, 2%, 4%, 6%, and 8% of the soil weight. After 7 days of curing, the samples were tested to determine the extent of change in the dispersion potential, as well as the improvement of the geotechnical properties of the soil. The results indicated that the addition of 2% zeolite with 6% to 8% metakaolin decreased the dispersion potential considerably. Double hydrometry test findings revealed that the dispersion potential decreased by almost 70% and entered the non-dispersive group; the crumb test also revealed this. Atterberg limits testing indicated a decrease in the plasticity index which reduced the flexibility of the samples. The greatest decrease in PI (67.5%) was achieved with the addition of 8% zeolite plus 8% metakaolin to the soil. The results of density tests revealed that a decrease in the optimal moisture content increased the maximum dry density of soil. This increase in density was a response to the high reactivity of metakaolin with calcium hydroxide and the formation of calcium hydroxide hydrate gel. This eventually caused an increase in the unconfined compressive strength, the greatest increase in strength of about 1.8-fold was observed with a combination of 2% zeolite and 6% metakaolin compared to the unmodified sample.

• 자원리싸이클링
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• 제15권3호
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• pp.38-45
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• 2006

슬러지 층에 열을 가함으로서 내부증발압, 여액 점도 저하에 따른 유동성 증대 그리고 기공형성 용이성을 통하여 슬러지의 탈수율을 향상시킬 수 있는 열 필터프레스 탈수 기술을 개발하였다. 크기 $470{\times}470mm$인 PP재질의 맨브레인 플레이트 사이에 열수가열판을 장착하여 온도 $95^{\circ}C$, 압력 $1.2kg_f/cm^2$의 열 수를 공급한다. 그리고 슬러지는 최초 슬러지의 $5kg_f/cm^2$의 공급압력에 의해 1 차 탈수가 이루어지며, 맨브레인의 압착력 $15kg_f/cm^2$에 의해 2차적 탈수 공정으로 이루어진다. 갈수기와 우수기때의 슬러지의 초기 함수율 및 유기물 함량을 고려하여 열 탈수 특성을 평가한 결과 우수기의 슬러지는 케이크의 함수율이 약 35 wt%이며, 탈수 속도는 $4DSkg/m^2{\cdot}hr$로 매우 탈수성 우수하였으며, 갈수기 때의 슬러지 또한 함수율이 50 wt%, 탈수속도가 $1.5kg/m^2{\cdot}hr$이상으로 기계식 탈수의 탈수율(함수율 70 wt%, 탈수속도 $0.9kg/m^2{\cdot}hr$)에 비하여 우수하였다. 이를 바탕으로 열 필터프레스 탈수장치의 추가 소요 에너지를 평가한 결과 고형물(DS) 1 kg처리하는데 소요되는 에너지는 약 300kJ로 평가되었다. 이는 탈수케이크를 재차 건조하는 시스템과 의 에너지 투입비를 분석해 본 결과 열 탈수장치의 에너지 소요량은 약 1/3정도로 감소된 것으로 분석되었다. 본 기술은 기존의 필터프레스에 비하여 탈수 속도가 빠르고 저 함수율 탈수 케이크 생산이 용이할 뿐만 아니라 건조장치에 비하여 에너지 소모량이 적어 경제성이 우수한 시스템으로 파악되었다.

• Steel and Composite Structures
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• 제34권5호
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• pp.681-698
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• 2020

The paper addresses contribution to the modeling and optimization of major machinability parameters (cutting force, surface roughness, and tool wear) in finish dry hard turning (FDHT) for machinability evaluation of hardened AISI grade die steel D₃ with PVD-TiN coated (Al₂O₃-TiCN) mixed ceramic tool insert. The turning trials are performed based on Taguchi's L₁₈ orthogonal array design of experiments for the development of regression model as well as adequate model prediction by considering tool approach angle, nose radius, cutting speed, feed rate, and depth of cut as major machining parameters. The models or correlations are developed by employing multiple regression analysis (MRA). In addition, statistical technique (response surface methodology) followed by computational approaches (genetic algorithm and particle swarm optimization) have been employed for multiple response optimization. Thereafter, the effectiveness of proposed three (RSM, GA, PSO) optimization techniques are evaluated by confirmation test and subsequently the best optimization results have been used for estimation of energy consumption which includes savings of carbon footprint towards green machining and for tool life estimation followed by cost analysis to justify the economic feasibility of PVD-TiN coated Al₂O₃+TiCN mixed ceramic tool in FDHT operation. Finally, estimation of energy savings, economic analysis, and sustainability assessment are performed by employing carbon footprint analysis, Gilbert approach, and Pugh matrix, respectively. Novelty aspects, the present work: (i) contributes to practical industrial application of finish hard turning for the shaft and die makers to select the optimum cutting conditions in a range of hardness of 45-60 HRC, (ii) demonstrates the replacement of expensive, time-consuming conventional cylindrical grinding process and proposes the alternative of costlier CBN tool by utilizing ceramic tool in hard turning processes considering technological, economical and ecological aspects, which are helpful and efficient from industrial point of view, (iii) provides environment friendliness, cleaner production for machining of hardened steels, (iv) helps to improve the desirable machinability characteristics, and (v) serves as a knowledge for the development of a common language for sustainable manufacturing in both research field and industrial practice.

• Journal of the Korean Wood Science and Technology
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• 제37권4호
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• pp.388-396
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• 2009

본 연구에서는 두부비지 가수분해물과 페놀수지로 조제된 마루판 화장용 접착제의 접착성능을 확인하기 위하여 수행하였다. 먼저 두부비지를 황산과 수산화나트륨으로 화학적으로 개량한 후 가교제로 phenol formaldehyde (PF) prepolymer와 혼합하여 접착제를 조제하였는데, 이 접착제는 고형분 함량을 기준으로 35%의 황산 가수분해물(AC), 35%의 수산화나트륨 가수분해물(AK) 그리고 30%의 PF로 조제하였다. 이렇게 조제된 접착제를 고밀도섬유판에 $300g/m^2$의 비율로 도포한 후 참나무 무늬목을 접착시켜 $7kg/m^2$의 압력으로 $120^{\circ}C$에서 열압하여 마루판을 제조하였다. 제조된 마루판에 대하여 formaldehyde/phenol 몰비(1.8, 2.1, 2.4), 퇴적시간(0분, 10분, 20분), 열압시간(90초, 120초)이 평면인장강도, 준내수 박리율, 포름알데히드 방산량에 미치는 영향에 대해 조사하였다. 두부비지 접착제를 이용하여 제조된 목질마루판의 평면인장강도는 KS 규격의 최소값을 상회하였으며, 대부분의 포름알데히드 방산량 값은 KS 규격의 E0 기준에 근접하는 것으로 나타났다. 따라서 두부비지 접착제가 마루판 화장용 접착제로 사용될 수 있다는 가능성을 보여 주었으나, 상용화를 위하여 내수성의 향상과 포름알데히드 방산량의 저감을 위한 연구가 필요할 것으로 생각한다.

• Journal of the Korean Wood Science and Technology
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• 제10권3호
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• pp.118-131
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• 1982

1. 이 연구(硏究)는 Yale대학교(大學校) 임과대학목재이학교실(林料大學木材利學敎室)에서 최근(最近) 새로히 쓰기 시작(始作)한 phenolic resin의 일종(一種)과 soy-bean glue 1auxein 10-B에 대(對)하여 assembly time의 변동(變動)이 제작(製作)된 합판(合板) shear strength에 어떠한 영향을 주는가를 알고 또한 그의 비교적(比較的) 적당(適當)한 실질적(實質的)인 assembly time의 범위를 결정(決定)하기 위하여 실시(實施)된 것이다. 2. 이 연구(硏究)에서 쓴 단판은 동실험실(同實驗室)에 실험용재료(實驗用材料)로 비치(備置)된 1/22in. 너도 밤나무(beech) 단판을 사용(使用)하였으며 수지는 phenolic resin U.S.P. low temperature liguid resorcinol type 와 Lauxein No. 10-B cold press water - resistant soygule 등으로 실험용(實驗用) sample을 구입(購入)하여 사용(使用)하였다. 3. 실험용(實驗用) ply-wood는 삼합식(三合式)으로 실험(實驗)을 하게 된 assembly time의 variation은 일분(一分)에서 시작(始作)하여 5, 10. 15, 25, 35, 50, 70분(分)등으로 8개(個)의 variation이 있게 하고 assembly 법(法)으로는 open assembly와 closed assembly의 2법(法)으로 하였으며 제작(製作)된 ply-wood의 성질비교(性質比較)는 dry test와 wet test의 shear strength test를 통(通)하여 나타나는 shear strength와 목파율을 가지고 하였다. 4. assembly time의 variation에 따른 합판의 shear strength와 목파율은 Table 1. 2. 3. 4에 표시(表示)된 바와 같은 결과(結果)를 보였으며 phenolic resin을 갖이고 closed assembly 법(法)으로 제작(製作)된 합판의 wet test를 제외하고는 모두 assembly time이 증가(增加)됨에 따라 shear strength와 목파율은 감소(減少)되여 가는 경향(傾向)을 보이고 있다. 그리고 실질적(實質的)으로 유효(有效)한 assembly time의 범위는 다음 표(表)(8)과 같다. 5. 이 실험(實驗)을 하는 동안 친절(親切)한 충고(忠告)와 지도편달(指導鞭達)를 애끼지 않고 도와주신 Yale 대학교(大學校) 목재이용학교수(木材利用學敎授) Dr. F.F.Wangaard씨(氏)와 Prof. Hess a. 그리고 실험실(實驗室) 담임자(擔任者)인 Mr. Clanch씨(氏)에게 충심(衷心)으로 사의(謝意)를 표시(表示)한다.

• Applied Biological Chemistry
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• 제22권3호
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• pp.160-165
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• 1979

본(本) 실험(實驗)은 장류제조(醬類製造) 과정중(過程中)의 철분(鐵分)의 혼입경로(混入經路) 함량변화(含量變化) 및 제품(製品)의 질(質)에 미치는 영향(影響)을 규명(糾明)할 목적(目的)으로 시도(試圖)되었으며 그 일단계로서 간장 양조(釀造) 과정중(過程中)의 철분함량(鐵分含量)과 시판(市販) 간장중(中)의 철분함량등(鐵分含量等)에 대(對)하며 실험(實驗)한 결과(結果)는 아래와 같다. 1. 간장 양조원료중(釀造原料中)의 철분함량(鐵分含量)은 대두(大豆)에는 108 ppm, 탈지대두(脫脂大豆)에서 133ppm, 소맥에서 79ppm, 식염(食鹽)에서 5ppm, 종국(種麴)에서 58ppm, 황국균(黃麴菌) 포자(胞子)에서 $300{\sim}2000ppm$, gluten에서 240ppm, $Na_2CO_3$에서 20ppm(이상(以上) 건물당(乾物當))이며 HCl에서 6ppm, Caramel에서 18ppm, 양조용수(讓造用水)에서 0.3ppm으로 각각(各各) 나타났다. 2. 제국과정중(製麴過程中)의 철분합량(鐵分合量)은 $200{\sim}240ppm$(건물당(乾物當))으로 제국기간(製麴期間)의 경과(經過)에 따라 다소(多少) 증가(增加)하는 경향(傾向)을 보였다. 3. 간장 발효과정중(醱酵過程中)의 철분함량(鐵分含量)은 담금후 1개월(個月) 경과후(經過後)에 40ppm, 3개월(個月) 경과후(經過後)에 $43{\sim}47ppm$, 6개월(個月) 경과후(經過後)에 $49{\sim}62ppm$으로 각각(各各) 나타났다. 4. 양조(讓造)간장의 압착과정(壓搾過程)에서 즙액중(中)의 철분(鐵分)은 감소(減少)하나 살균과정(殺菌過程)에서는 별다른 변화(變化)가 없었다. 5. 화학(化學)간강 제조과정중(製造過程中)의 철분함량(鐵分含量)은 소맥 gluten의 염산(鹽酸) 분해액중(分解液中)에 159ppm, 중화액중(中和液中)에 184ppm으로 중화(中和)에 의(依)하여 다소(多少) 증가(增加)하였다. 6. 제품(製品) 양조(釀造)간장과 화학(化學)간장의 총질소농도(總窒素濃度)를 달리하여 철분함량(鐵分含量)을 측정(測定)한 결과(結果) 총질소(總窒素) 농도(濃度)가 증가(增加)함에 따라 철분함량(鐵分含量)은 증가(增加)하였으며 동일(同一)한 총질소농도(總窒素濃度)에 있어서 화학(化學)간장은 양조(釀造)간장은 비(比)해 철분함량(鐵分含量)이 높았다. 7. 시판(市販)간장중(中)의 철분함량(鐵分含量)은 제조원(製造元)에 따라 다양하나 총질소(總窒素) 1.0으로 환산(換算)하여 평균(平均) 62.7ppm이었으며 재래식(在來式) 간장의 철분함량(鐵分含量)은 평균(平均) 37.68ppm이었다.