36 research outputs found

    Experimental investigation of ice loads on vertical and slope offshore structures

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    An experiment was carried out to study the ice loads of level ice and ridge on the vertical and slope structures. The prototype of the model is the lighthouse Nordströmsgrund, which is a vertical structure and locates in the north Baltic sea. Nevertheless, a conical part was added to the model to study the ice load on slope structures in addition to the study of the ice loads on vertical structures. Three ice sheets with ridges were targeted to design the ice condition around Nordströmsgrund, including the flexural strength, ice thickness, geometrical cross-sectional profile of ridge, etc. Every ice sheet had a constant thickness, ranging from 0.04m to 0.043m in model-scale, but its flexural strength could be changed by using tempering procedure. Eight tests were successfully conducted and the ice loads were measured and recorded with three components divided according to the Cartesian coordinate system. The effect of ice properties and degrees of consolidation were also observed and analyzed with the measured data. The history curve and its envelope were utilized to study the ice loads on structures. The ice loads were decomposed into rubble loads (loads induced by accumulated rubbles) and level ice/consolidated layer loads (loads induced by breaking the level ice/consolidated layer). The upper envelope was assumed to represent the total ice loads and the lower envelope was assumed to represent the rubble loads. Thus, the difference between the upper and lower envelopes could be considered the level ice/consolidated layer loads. Fast Fourier Transform was applied to study the energy distribution of ice loads. The splitting of level ice was observed in front of the ridge at three tests. The histogram and return period are employed to study the distribution of ice loads and affecting parameters. The most important discovery of this research was that the horizontal range of rubbles moved by the structure had stronger influence on the ice ridge loads than the depth of rubble accumulation in front of the structure. Actually, the ridge loads were proportional to the volume of rubble accumulation and the strength of freeze bond in the keel. The zigzag pattern in the curve of horizontal range reflected the process of breaking the keel. This resulted in that the accumulation volume increased with a zigzag pattern in the curve of volume against the structure’s penetration distance into the ridge

    A LID APPROACH FOR PREDICTING WAVE INDUCED MOTIONS OF TRIMARAN IN REGULAR WAVES

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    The wave induced motions of a trimaran sailing in regular head waves were predicted by using the three dimensional boundary integral method. Large wave elevation on the free surface in between the trimaran’s main-hull and the outriggers occurred at some specific frequencies in the numerical model. The large wave elevation also induced large heave and pitch motions of trimaran. However, the large wave elevation and corresponding large motions were not observed during towing tank tests. A lid approach was introduced in this paper by placing lid on the free surface in between hulls to suppress the unrealistically large wave elevation and to correctly predict the induced motions of trimaran. The feasibility and practicability of lid approach were validated against experimental results

    A comparison of zero-profile anchored spacer (ROI-C) and plate fixation in 2-level noncontiguous anterior cervical discectomy and fusion- a retrospective study

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    Abstract Background Anterior cervical discectomy and fusion (ACDF) is the classic surgical treatment for symptomatic cervical degenerative disc disease (CDDD). However, there is controversy over the best surgical management in patients with two noncontiguous symptomatic levels of CDDD. Methods From April 2011 to May 2014, 44 patients with two noncontiguous symptomatic levels of CDDD underwent skip-level ACDFs. In Group NoPlate, 23 cases underwent 2 noncontiguous levels of ACDF using zero-profile anchored spacer; and in Group Plate, 21 cases underwent 2 noncontiguous levels of ACDF using cages and plates. Operation-related paraeters for each group were recorded and compared. Japanese Orthopedic Association (JOA) scores and Neck Disability Index (NDI) scores at preoperation and postoperation were compared with at least a 2-year follow-up. Cervical lordosis was analyzed before surgery, 1 month after surgery, 3 months after surgery, and at final follow-up. Results Mean follow-up was 35.4 ± 6.5 (range 24–48) months. Significant improvement on the JOA, NDI scores and cervical lordosis was noted in each group (p  0.05). The operation time in Group NoPlate was significantly shorter than in Group Plate (p < 0.05), and the incidence of dysphagia and adjacent segment degeneration in Group NoPlate was significantly lower than in Group Plate (p < 0.05). Conclusions ROI-C and cages with plate fixation were both effective in two-level noncontiguous ACDF, and there were no significant difference in clinical outcomes, fusion rate, and cervical lordosis. However, ROI-C was associated with shorter operative time, lower incidence of dysphagia and adjacent segment degeneration

    Percutaneous kyphoplasty for the treatment of very severe osteoporotic vertebral compression fractures with spinal canal compromise

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    Abstract Background Very severe osteoporotic vertebral compression fractures (vsOVCFs) are osteoporotic vertebral compression fractures with vertebral body collapse to less than one third of their original height. Few data are available about the use of percutaneous kyphoplasty (PKP) in treating vsOVCFs with spinal canal compromise. The aim of this study was to evaluate the safety and efficacy of percutaneous kyphoplasty (PKP) for the treatment of vsOVCFs with spinal canal compromise. Methods Thirty-five patients who suffered vsOVCFs with spinal canal compromise but without neurological deficits were treated by PKP between January 2009 and October 2014. The vertebral height, local kyphotic angle (LKA), visual analogue scale (VAS) and Oswestry Disability Index (ODI) values were assessed before the operation, 1 day after the operation and at the final follow-up. Results Significant improvements on the VAS and ODI were noted 1 day post-operatively (p < 0.01), and these results were preserved at the final follow-up. The vertebral height was restored and the LKA was improved after surgery (p < 0.01). No neurological deterioration was found. Five of 35 vertebrae (14.3%) of cement leakages were all asymptomatic. Four new OVCFs in three patients were identified. Conclusion PKP is a safe and effective procedure for the treatment of vsOVCFs with spinal canal compromise, achieving significant vertebral height restoration and kyphotic angle reduction and leading to a significant pain relief and improvement in function

    A CFD investigation of the effects of passing ship on a small size ice floe

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    A RANS (Reynolds Averaged Navier-Stokes) CFD STAR-CCM+ model is used to investigate the hydrodynamic interactions between a ship and a circular ice floe. The overset mesh technique is employed to simulate the advancing movement of the passing ship. The ship has a hull of similar configuration to the KCS MOERI container ship. The ice floe has a diameter of 30% of the ship's length and a thickness of 3 m. The paper primarily focuses on the motions of the ice floe and the hydrodynamic forces induced by the ship progressing in different speeds and calm water conditions. A parametric study on the influence of the ice floe surge and sway motions and associated hydrodynamic loads is presented. It is concluded that ship-generated waves can significantly affect the motions of the ice floe and the influence on sway is greater than that on surge. The ship speed is also found to have a distinct impact on ice floe motions.Peer reviewe

    Reinforcement learning-based fixed-time trajectory tracking control for uncertain robotic manipulators with input saturation

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    A fixed-time trajectory tracking control method for uncertain robotic manipulators with input saturation based on reinforcement learning (RL) is studied. The designed reinforcement learning control algorithm is implemented by radial basis function (RBF) neural network, in which the actor neural network is used to generate the control strategy and the critic neural network is used to evaluate the execution cost. A new non-singular fast terminal sliding mode technique is used to ensure the convergence of tracking error in fixed time, and the upper bound of convergence time is estimated. To solve the saturation problem of an actuator, a nonlinear anti-windup compensator is designed to compensate for the saturation effect of the joint torque actuator in real time. Finally, the stability of the closed-loop system based on Lyapunov candidate is analyzed, and the timing convergence of the closed-loop system is proved. Simulation and experimental results show the effectiveness and superiority of the proposed control law.</div

    Biphasic positive airway pressure spontaneous breathing attenuates lung injury in an animal model of severe acute respiratory distress syndrome

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    Abstract Objective To compare the effects of unassisted spontaneous breathing (SB) and complete muscle paralysis (PC) on early severe acute respiratory distress syndrome (ARDS) in an animal model, and to explore the possibility of biphasic positive airway pressure (BIPAP) as lung protective ventilation support for patients in the early stage of severe ARDS. Methods Twelve healthy beagle dogs between the ages of 10 and 15 months were randomly divided into two groups: the SB group (BIPAPSB) and the PC group (BIPAPPC). Arterial blood samples were drawn before modelling. Arterial blood gas analysis and mechanical tests were conducted. The animal model of severe ARDS was established using a deep intravenous injection of oleic acid, and BIPAP ventilation was performed for 8 hours. Lung tissue and blood were taken to detect lung function, inflammatory reactions and degree of pathological damage. Results At the beginning of the experiment, there was no significant difference in the arterial blood gas analysis between the two groups (p > 0.05). After successful modelling, the oxygenation index and the end-expiratory lung volume in the SB group were significantly higher than those in the PC group 8 hours after MV. Pathologically, the wet-dry ratio and pathological score of the PC group were higher than those of the SB group; the lung injury in the gravity-dependent area in the SB group was less than that in the PC group (p< 0.05). Conclusions In the early stage of severe ARDS induced by oleic acid, compared with PC, retention of the BIPAP mode of SB can reduce the risk of lung injury and improve respiratory function

    HLA-E–restricted regulatory CD8+ T cells are involved in development and control of human autoimmune type 1 diabetes

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    A key feature of the immune system is its ability to discriminate self from nonself. Breakdown in any of the mechanisms that maintain unresponsiveness to self (a state known as self-tolerance) contributes to the development of autoimmune conditions. Recent studies in mice show that CD8+ T cells specific for the unconventional MHC class I molecule Qa-1 bound to peptides derived from the signal sequence of Hsp60 (Hsp60sp) contribute to self/nonself discrimination. However, it is unclear whether they exist in humans and play a role in human autoimmune diseases. Here we have shown that CD8+ T cells specific for Hsp60sp bound to HLA-E (the human homolog of Qa-1) exist and play an important role in maintaining peripheral self-tolerance by discriminating self from nonself in humans. Furthermore, in the majority of type 1 diabetes (T1D) patients tested, there was a specific defect in CD8+ T cell recognition of HLA-E/Hsp60sp, which was associated with failure of self/nonself discrimination. However, the defect in the CD8+ T cells from most of the T1D patients tested could be corrected in vitro by exposure to autologous immature DCs loaded with the Hsp60sp peptide. These data suggest that HLA-E–restricted CD8+ T cells may play an important role in keeping self-reactive T cells in check. Thus, correction of this defect could be a potentially effective and safe approach in the therapy of T1D

    Characteristics of energy fields and the hydrocarbon migration-accumulation in deep strata of Tahe Oilfield, Tarim Basin, NW China

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    Deep energy fields in the Tahe Oilfield are studied and the relationship between energy fields and hydrocarbon migration and accumulation is discussed through the comprehensive analyses of energy field characteristics. Multi-phase tectonic stresses are the main controlling factor of the developmental morphologies of the present fractures. The characteristics of the present regional tectonic stress indicate that the Tahe Oilfield is a favorable area for hydrocarbon collection. The present pressure field of the Ordovician is a slightly low abnormal pressure system. The fluid potential characteristics show that there are two hydrocarbon migration trends: one is from east to west in part of the eastern area, and the other is from south to north in the whole southern area. The present formation water is of typical CaCl2 type. According to the formation water geochemistry, the Tahe Oilfield has a good seal capability, favorable for hydrocarbon accumulation and preservation. Aqueous inclusions indicate that homogenization temperatures are mainly 80–100°C, 120–130°C, and 150–170°C, therein, 80–100°C and 120–130°C represent two large scale hydrocarbon accumulation phases, Early Hercynian and Himalayan, and 150–170°C is controlled by tectonic event and Permian magmatic activities, representing a partial hydrocarbon accumulation event. 摘 要: 以塔河油田深层能量场为研究对象,通过系统分析能量场特征来探讨其与油气运聚的关系。研究认为,多期构造应力作用是塔河油田现今断裂发育形态的主控因素,现今区域应力场特征表明塔河油田是油气运移的有利指向区;奥陶系现今压力场整体上属于略偏低异常的压力系统,流体势特征显示油气运移存在东部自东向西局部性运移趋势以及南部由南向北区域性运移趋势;奥陶系现今地层水离子构成符合典型的CaCl2型水特征,地层水地化指标显示塔河主油区具有良好的封闭性,是油气聚集保存的有利区;盐水包裹体均一温度测试结果主要集中在80~100 ℃、120~130 ℃和150~170 ℃等3个温度段,前两个温度段分别对应于塔河油田2次大规模的油气成藏期:海西早期和喜马拉雅期,而最后一个温度段主要受控于构造变动和二叠系岩浆活动,代表了一期局部油气成藏事件。图7参22 Key words: Tahe Oilfield, deep carbonates, energy field, hydrocarbon migration, hydrocarbon accumulatio

    The Research on Characteristic Parameters and Resistance Chart of Operation and Maintenance Trimaran in the Sea

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    The paper determined the volume ratio of the main hull and side hull and their position characteristic parameter of operation and maintenance trimaran. Numerical simulation technology was used to do the analysis and calculation of trimarans which have different volume ratio of the main and side hull, and on this basis, the paper tried different positions of main and side hull, finally got the trimaran with optimum resistance performance and the chart of trimaran resistance estimation, so as to provide a new way in the selection of feature parameter of offshore wind farm maintenance trimaran and its resistance estimation
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