• Steel and Composite Structures
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• 제44권2호
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• pp.199-210
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• 2022

This study build finite element analysis (FEA) models describing the bending events of coiled tubing (CT) at the wellhead and trips into the hole, accurately provide the state of stress and strain while the CT is in service. The bending moment and axial force history curves are used as loads and boundary conditions in the diametrical growth models to ensure consistency with the actual working conditions in field operations. The simulation diametrical growth results in this study are more accurate and reasonable. Analysis the factors influencing fatigue and diametrical growth shows that the internal pressure has a first-order influence on fatigue, followed by the radius of the guide arch, reel and the CT diameter. As the number of trip cycles increase, fatigue damage, residual stress and strain cumulatively increase, until CT failure occurs. Significant residual stresses remain in the CT cross-section, and the CT exhibits a residual curvature, the initial residual bending configuration of CT under wellbore constraints, after running into the hole, is sinusoidal. The residual stresses and residual bending configuration significantly decrease the buckling load, making the buckling and buckling release of CT in the downhole an elastic-plastic process, exacerbating the helical lockup. The conclusions drawn in this study will improve CT models and contribute to the operational and economic success of CT services.

• Earthquakes and Structures
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• 제22권5호
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• pp.461-473
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• 2022

Energy-saving block and invisible multiribbed frame composite wall (EBIMFCW) is an important shear wall, which is composed of energy-saving blocks, steel bars and concrete. This paper conducted seismic performance tests on six 1/2-scale EBIMFCW specimens, analyzed their failure process under horizontal reciprocating load, and studied the effect of axial compression ratio on the wall's hysteresis curve and skeleton curve, ductility, energy dissipation capacity, stiffness degradation, bearing capacity degradation. A formula for calculating the peak bearing capacity of such walls was proposed. Results showed that the EBIMFCW had experienced a long time deformation from cracking to failure and exhibited signs of failure. The three seismic fortification lines of the energy-saving block, internal multiribbed frame, and outer multiribbed frame sequentially played important roles. With the increase in axial compression ratio, the peak bearing capacity and ductility of the wall increased, whereas the initial stiffness decreased. The change in axial compression ratio had a small effect on the energy dissipation capacity of the wall. In the early stage of loading, the influence of axial compression ratio on wall stiffness and strength degradation was unremarkable. In the later stage of loading, the stiffness and strength degradation of walls with high axial compression ratio were low. The displacement ductility coefficients of the wall under vertical pressure were more than 3.0 indicating that this wall type has good deformation ability. The limit values of elastic displacement angle under weak earthquake and elastic-plastic displacement angle under strong earthquake of the EBIMFCW were1/800 and 1/80, respectively.

• Geomechanics and Engineering
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• 제37권3호
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• pp.293-306
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• 2024

Influenced by the alternating effects of dynamic and static pressure during the mining process of close range coal seams, the surrounding rock support of cross mining roadway is difficult and the deformation mechanism is complex, which has become an important problem affecting the safe and efficient production of coal mines. The paper takes the inclined longwall mining of the 10304 working face of Zhongheng coal mine as the engineering background, analyzes the key strata fracture mechanism of the large inclined right-angle trapezoidal mining field, explores the stress distribution characteristics and transmission law of the surrounding rock of the roadway affected by the mining of the inclined coal seam, and proposes a segmented and hierarchical support method for the cross mining roadway affected by the mining of the close range coal seam group. The research results indicate that based on the derived expressions for shear and tensile fracture of key strata, the ultimate pushing distance and ultimate suspended area of a right angle trapezoidal mining area can be calculated and obtained. Within the cross mining section, along the horizontal direction of the coal wall of the working face, the peak shear stress is located near the middle of the boundary. The cracks on the floor of the cross mining roadway gradually develop in an elliptical funnel shape from the shallow to the deep. The dual coupling support system composed of active anchor rod support and passive U-shaped steel shed support proposed in this article achieves effective control of the stability of cross mining roadways, which achieves effective control of floor by coupling active support and preventive passive support to improve the strength of the surrounding rock itself. The research results are of great significance for guiding the layout, support control, and safe mining of cross mining roadways, and to some extent, can further enrich and improve the relevant theories of roof movement and control.

• Journal of Dental Anesthesia and Pain Medicine
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• 제24권1호
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• pp.19-35
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• 2024

Background: This study investigated a safe and effective bolus dose and lockout time for patient-controlled sedation (PCS) with dexmedetomidine for dental treatments. The depth of sedation, vital signs, and patient satisfaction were investigated to demonstrate safety. Methods: Thirty patients requiring dental scaling were enrolled and randomly divided into three groups based on bolus doses and lockout times: group 1 (low dose group, bolus dose 0.05 ㎍/kg, 1-minute lockout time), group 2 (middle dose group, 0.1 ㎍/kg, 1-minute), and group 3 (high dose group, 0.2 ㎍/kg, 3-minute) (n = 10 each). ECG, pulse, oxygen saturation, blood pressure, end-tidal CO₂, respiratory rate, and bispectral index scores (BIS) were measured and recorded. The study was conducted in two stages: the first involved sedation without dental treatment and the second included sedation with dental scaling. Patients were instructed to press the drug demand button every 10 s, and the process of falling asleep and waking up was repeated 1-5 times. In the second stage, during dental scaling, patients were instructed to press the drug demand button. Loss of responsiveness (LOR) was defined as failure to respond to auditory stimuli six times, determining sleep onset. Patient and dentist satisfaction were assessed before and after experimentation. Results: Thirty patients (22 males) participated in the study. Scaling was performed in 29 patients after excluding one who experienced dizziness during the first stage. The average number of drug administrations until first LOR was significantly lower in group 3 (2.8 times) than groups 1 and 2 (8.0 and 6.5 times, respectively). The time taken to reach the LOR showed no difference between groups. During the second stage, the average time required to reach the LOR during scaling was 583.4 seconds. The effect site concentrations (Ce) was significantly lower in group 1 than groups 2 and 3. In the participant survey on PCS, 8/10 in group 3 reported partial memory loss, whereas 17/20 in groups 1 and 2 recalled the procedure fully or partially. Conclusion: PCS with dexmedetomidine can provide a rapid onset of sedation, safe vital sign management, and minimal side effects, thus facilitating smooth dental sedation.

• Geomechanics and Engineering
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• 제23권2호
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• pp.151-163
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• 2020

Grouting method is an effective way of reinforcing cracked rock masses and plugging water gushing. Current grouting diffusion models are generally developed for horizontal cracks, which is contradictory to the fact that the crack generally occurs in rock masses with irregular spatial distribution characteristics in real underground environments. To solve this problem, this study selected a cement-sodium silicate slurry (C-S slurry) generally used in engineering as a fast-curing grouting material and regarded the C-S slurry as a Bingham fluid with time-varying viscosity for analysis. Based on the theory of fluid mechanics, and by simultaneously considering the deadweight of slurry and characteristics of non-uniform spatial distribution of viscosity of fast-curing grouts, a theoretical model of slurry diffusion in an oblique crack in rock masses at constant grouting rate was established. Moreover, the viscosity and pressure distribution equations in the slurry diffusion zone were deduced, thus quantifying the relationship between grouting pressure, grouting time, and slurry diffusion distance. On this basis, by using a 3-d finite element program in multi-field coupled software Comsol, the numerical simulation results were compared with theoretical calculation values, further verifying the effectiveness of the theoretical model. In addition, through the analysis of two engineering case studies, the theoretical calculations and measured slurry diffusion radius were compared, to evaluate the application effects of the model in engineering practice. Finally, by using the established theoretical model, the influence of cracking in rock masses on the diffusion characteristics of slurry was analysed. The results demonstrate that the inclination angle of the crack in rock masses and azimuth angle of slurry diffusion affect slurry diffusion characteristics. More attention should be paid to the actual grouting process. The results can provide references for determining grouting parameters of fast-curing grouts in engineering practice.

• 한국산림과학회지
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• 제36권1호
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• pp.26-32
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• 1977

저질재(低質材) 건조(乾燥)의 한 방안(方案)으로 상수리나무 판재(板材)를 열판건조(熱板乾燥)하였다. 열판건조조건(熱板乾燥條件)을 변재(邊材)와 심재(心材)의 두께 1.5cm판재(板材)를 열판온도(熱板溫度) $175^{\circ}C$, 압력(壓力) 35psi로 건조(乾燥)항, 건조시(乾燥時) 내부온도(內部溫度), 건조중(乾燥中) 함수율(含水率) 및 건조속도(乾燥速度)의 변화(變化), 건조시간(乾燥時間)과 말기함수율(末期含水率), 건조재(乾燥材)의 치수변화(變化), 건조손상(乾燥損傷) 등(等)을 조사(調査)한 결과(結果)를 요약(要約)하면 다음과 같다. 1. 판재(板材)의 내부온도(內部溫度)는 건조초기(乾燥初期)에 급격히 상승(上昇)하여 얼마동안 일정(一定)하게 유지된 다음 서서히 상승(上昇)하였다. plateau temperature는 심재(心材)가 변재(邊材)보다 높고 유지기간도 길었다. 2. 건조시간(乾燥時間)에 따라 건조속도(乾燥速度)는 감소(減少)하였고 변재(邊材)의 건조속도(乾燥速度)는 logy=-2.7925-0.0811x, (r=-0.976), 심재(心材)의 건조속도(乾燥速度)는 logy=-3.3382-0.0468x (r=-0.976)의 곡선(曲線)을 나타났다. 3. 소요(所要)되는 건조시간(乾燥時間)은 심재(心材)가 변재(邊材)보다 길었고, 변재(邊材)는 초기함수율(初期含水率) 59%에서 말기함수율(末期含水率) 2.5%까지 건조(乾燥)하였는데 45분(分), 심재(心材)는 초기함수율(初期含水率) 64%에서 말기함수율(末期含水率) 3.3%까지 55분(分)이 각각(各各) 소요(所要)되었다. 4. 건조재(乾燥材)의 평균(平均) 두께수축율(收縮率)은 20.4%, 평균(平均) 폭수축율(幅收縮率)은 2.5%이고, 평균(平均) 두께복원율(復元率)은 11.4% 평균(平均) 폭복원율(幅復元率)은 49.4%로서 두께는 폭(幅)보다 수축율(收縮率)은 컸으나 복원율(復元率)은 적었다. 5. 변재(邊材)는 내부할열(內部割裂) 등(等)의 건조손상(乾燥損傷)이 거의 없었으나 심재(心材)는 내부할대(內部割袋)이 심하게 나타났다.

• 한국재료학회지
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• 제4권1호
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• pp.37-43
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• 1994

Y-BA-Cu-O계 고온초전도체의 미세조직을 가공과 열처리로써 제어하여 조직의 배향화와 치밀화를 기하여 높은 임계전류밀도($J_c$)를 갖는 초전도체의 개발을 목적으로sinter forging법으로 Y-BA-Cu-O/Ag 고온초전도복합체를 제조하였다. sinter forging을 통하여 고온 초전도체의 미세조직의 texture화를 가져왔으며, 이 경우 (123)결정립의 C축 방위가 단일축의 압축방향으로 배향화 되었다. 한편, texture의 orientation facter는 고온일수록, 압력이 클수록 크고, 조직의 배향화도 뚜렷하였으며 그에 따라 $J_c$역시 증가하였다. 이러한 결과로 미루어 결정의 배향도는 $J_c$를 좌우하는 중요한 변수라고 사려되었다. 또한 sinter forging 시킨Y-MA-Cu-O/Ag 복합체의 on set온도는 sinter forging온도에 크게 의존치 않았으나, 고온일수록 off set 온도($T_c\;^{zero}$)가 다소 떨어졌다. 한편, 첨가된 Ag는 주고(123)결정입계에 존재하였으며, 이들이 (123)결정립간의 결합을 촉진시켜 임계전류밀도를 크게 향상시켰으며, Y-BA-Cu-O/Ag 복합체의 $J_c$는 2,000 A/$\textrm{cm}^2$ 이상이었다.

• Geomechanics and Engineering
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• 제28권3호
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• pp.299-311
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• 2022

Water-resisting key stratum (WKS) between coal seams is an important barrier that prevents water inrush from goaf in roof under multi-seam mining. The occurrence of water inrush can be evaluated effectively by analyzing the fracture of WKS in multi-seam mining. A "long beam" water inrush mechanical model was established using the multi-seam mining of No. 2+3 and No. 8 coal seams in Xiqu Mine as the research basis. The model comprehensively considers the pressure from goaf, the gravity of overburden rock, the gravity of accumulated water, and the constraint conditions. The stress distribution expression of the WKS was obtained under different mining distances in No. 8 coal seam. The criterion of breakage at any point of the WKS was obtained by introducing linear Mohr strength theory. By using the mechanical model, the fracture of the WKS in Xiqu Mine was examined and its breaking position was calculated. And the risk of water inrush was also evaluated. Moreover, breaking process of the WKS was reproduced with Flac3D numerical software, and was analyzed with on-site microseismic monitoring data. The results showed that when the coal face of No. 8 coal seam in Xiqu Mine advances to about 80 m ~ 100 m, the WKS is stretched and broken at the position of 60 m ~ 70 m away from the open-off cut, increasing the risk of water inrush from goaf in roof. This finding matched the result of microseismic analysis, confirming the reliability of the water inrush mechanical model. This study therefore provides a theoretical basis for the prevention of water inrush from goaf in roof in Xiqu Mine. It also provides a method for evaluating and monitoring water inrush from goaf in roof.

• Geomechanics and Engineering
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• 제37권6호
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• pp.599-614
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• 2024

To evaluate the safety status of deteriorated segments in a submarine shield tunnel during its service life, a seepage model was established based on a cross-sea shield tunnel project. This model was used to study the migration patterns of erosive ions within the shield segments. Based on these laws, the degree of deterioration of the segments was determined. Using the derived analytical solution, the internal forces within the segments were calculated. Lastly, by applying the formula for calculating safety factors, the variation trends in the safety factors of segments with different degrees of deterioration were obtained. The findings demonstrate that corrosive seawater presents the evolution characteristics of continuous seepage from the outside to the inside of the tunnel. The nearby seepage field shows locally concentrated characteristics when there is leakage at the joint, which causes the seepage field's depth and scope to significantly increase. The chlorine ion content decreases gradually with the increase of the distance from the outer surface of the tunnel. The penetration of erosion ions in the segment is facilitated by the presence of water pressure. The ion content of the entire ring segment lining structure is related in the following order: vault < haunch < springing. The difference in the segment's rate of increase in chlorine ion content decreases as service time increases. Based on the analytical solution calculation, the segment's safety factor drops more when the joint leaks than when its intact, and the change rate between the two states exhibits a general downward trend. The safety factor shows a similar change rule at different water depths and continuously decreases at the same segment position as the water depth increases. The three phases of "sudden drop-rise-stability" are represented by a "spoon-shaped" change rule on the safety factor's change curve. The issue of the poor applicability of indicators in earlier studies is resolved by the analytical solution, which only requires determining the loss degree of the segment lining's effective bearing thickness to calculate the safety factor of any cross-section of the shield tunnel. The analytical solution's computation results, however, have some safety margins and are cautious. The process of establishing the evaluation model indicates that the secondary lining made of molded concrete can also have its safety status assessed using the analytical solution. It is very important for the safe operation of the tunnel and the safety of people's property and has a wide range of applications.