A Review of the Calculation Methods of Lifting Capacity in Wind Loads on Ocean Platforms

Wind load is a control load that affects the safety of structures in the design of ocean platforms. It has not only direct and powerful effects that may cause structure resonance but also has indirect effects causing waves or currents in the ocean. By analyzing the domestic and international norms, this study presents a review of calculation methods of wind load on ocean platforms, which belongs to large-scale non-entity structure used in the open sea while surrounding wind has no fixed direction. Current computations according to the norms are not accurate, which even not takes the force of the wind against the surface perpendicular to the structure into consideration. Additionally, this study also introduces and compares the lift model of platforms based on different theories, such as vortex-excitation and vibration, engineering structure dynamics, gas flow pressure theory, analyzing their applicability, advantages, and disadvantages. This paper analyzes the limitations and applicable conditions of the existing calculation method itself, such as the lift model is suitable for the existence of stable vortex wake;the calculation method of the structural dynamics of marine engineering must be combined with the wind tunnel test and consider the mistakes caused by the position relationship;the numerical simulation method is accurate but tedious. This study provides an insight into the calculation methods of lift in designing ocean platforms, including the finite element method for simulating fluid force and updating formulas in Chinese norms.

Analysis of Influencing Factors on Lift Coefficients of Autonomous Sailboat Double Sail Propulsion System Based on Vortex Panel Method

Sail is the core part of autonomous sailboat and wing sail is a new type of sail. Wing sail generates not only propulsion but also lateral force and heeling moment. The latter two will affect the navigation status and bring resistance. Double sail can effectively reduce the center of wind pressure and heeling moment. In order to study the effect of distance between two sails, airfoil and attack angle on the total lift coefficient of double sail propulsion system, pressure coefficient distribution and lift coefficient calculation model have been established based on vortex panel method. By using the basic finite solution, the fluid dynamic forces on the two-dimensional sails are computed.The results show that, the distance in the range of 0 to 1 time chord length, when using the same airfoil in the fore and aft sail, the total lift coefficient of the double sail increases with the increase of distance, finally reaches a stable value in the range of one to three times chord length. Lift coefficients of thicker airfoils are more sensitive to the change of distance. The thicker the airfoil, the longer distance is required of the total lift coefficient toward stable.When different airfoils are adopted in fore and aft sail, the total lift coefficient increases with the increase of the thickness of aft sail. The smaller the thickness difference is, the more sensitive to the distance change the lift coefficient is. The thinner the fore sail is, the lower the influence will be on the lift coefficient of aft sail.

A Lifting Line Theory for a Three-dimensional Hydrofoil

Prandtl’s lifting line theory was generalized to the lifting problem of a three-dimensional hydrofoil in the presence of a free surface. Similar to the classical lifting theory, the singularity distribution method was utilized to solve two-dimensional lifting problems for the hydrofoil beneath the free surface at the air-water interface, and a lifting line theory was developed to correct three-dimensional effects of the hydrofoil with a large aspect ratio. Differing from the classical lifting theory, the main focus was on finding the three-dimensional Green function of the free surface induced by the steady motion of a system of horseshoe vortices under the free surface. Finally, numerical examples were given to show the relationship between the lift coefficient and submergence Froude numbers for 2-D and 3-D hydrofoils. If the submergence Froude number is small free surface effect will be significant registered as the increase of lift coefficient. The validity of these approaches was examined in comparison with the results calculated by other methods.

Second-generation wavelet finite element based on the lifting scheme for GPR simulation

Ground-penetrating radar(GPR)is a highly efficient,fast and non-destructive exploration method for shallow surfaces.High-precision numerical simulation method is employed to improve the interpretation precision of detection.Second-generation wavelet finite element is introduced into the forward modeling of the GPR.As the finite element basis function,the second-generation wavelet scaling function constructed by the scheme is characterized as having multiple scales and resolutions.The function can change the analytical scale arbitrarily according to actual needs.We can adopt a small analysis scale at a large gradient to improve the precision of analysis while adopting a large analytical scale at a small gradient to improve the efficiency of analysis.This approach is beneficial to capture the local mutation characteristics of the solution and improve the resolution without changing mesh subdivision to realize the efficient solution of the forward GPR problem.The algorithm is applied to the numerical simulation of line current radiation source and tunnel non-dense lining model with analytical solutions.Result show that the solution results of the secondgeneration wavelet finite element are in agreement with the analytical solutions and the conventional finite element solutions,thereby verifying the accuracy of the second-generation wavelet finite element algorithm.Furthermore,the second-generation wavelet finite element algorithm can change the analysis scale arbitrarily according to the actual problem without subdividing grids again.The adaptive algorithm is superior to traditional scheme in grid refinement and basis function order increase,which makes this algorithm suitable for solving complex GPR forward-modeling problems with large gradient and singularity.

Epistemic-Based Investigation of the Probability of Hazard Scenarios Using Bayesian Network for the Lifting Operation of Floating Objects

Owing to the increase in unprecedented accidents with new root causes in almost all operational areas, the importance of risk management has dramatically risen. Risk assessment, one of the most significant aspects of risk management, has a substantial impact on the system-safety level of organizations, industries, and operations. If the causes of all kinds of failure and the interactions between them are considered, effective risk assessment can be highly accurate. A combination of traditional risk assessment approaches and modern scientific probability methods can help in realizing better quantitative risk assessment methods. Most researchers face the problem of minimal field data with respect to the probability and frequency of each failure. Because of this limitation in the availability of epistemic knowledge, it is important to conduct epistemic estimations by applying the Bayesian theory for identifying plausible outcomes. In this paper, we propose an algorithm and demonstrate its application in a case study for a light-weight lifting operation in the Persian Gulf of Iran. First, we identify potential accident scenarios and present them in an event tree format. Next, excluding human error, we use the event tree to roughly estimate the prior probability of other hazard-promoting factors using a minimal amount of field data. We then use the Success Likelihood Index Method(SLIM) to calculate the probability of human error. On the basis of the proposed event tree, we use the Bayesian network of the provided scenarios to compensate for the lack of data. Finally, we determine the resulting probability of each event based on its evidence in the epistemic estimation format by building on two Bayesian network types: the probability of hazard promotion factors and the Bayesian theory. The study results indicate that despite the lack of available information on the operation of floating objects, a satisfactory result can be achieved using epistemic data.

AN ANALYSIS OF PROPELLER LIFTING－LINE THEORY BY MATCHED ASYMPTOTIC EXPANSIONS

Lifting-line model is developed for a propeller of large aspect ratio inblade-attached noninertial system. In the analysis of the method of matched asymptoticexpansions, a fictitious velocity potential is introduced. Control equation, boundarycondition and Bernoulli equation are derived in blade- attached system. The analysis ofthe matched asymptotic expansions shows that if the advance ratio of propeller is notvery small, lifting-line theory is still valid in blade-attached noninertial system for propeller.

KINETIC MODELLING AND PERFORMANCE ANALYSIS OF THE FOUR-POST-FRAME LIFTING MECHANICAL SYSTEM

The kinetic model of the four-post-frame lifting mechanical system was established. The stiffness and damping matrices of differential equations of motion were obtained by using Lagrange’s equations. And the dynamic characteristics of system were analyzed by modal analysis method. Based upon this, the modifications of structural parameters which can improve dynamic performance were discussed. The low-level high-speed palletizer MDJ1200L was taken as a real case in the paper.

Maneuver strategy of lifting reentry vehicle

An optimal maneuver strategy is proposed for lifting reentry vehicle to reach the maximum lateral range after reentering the atmosphere. Aiming at problems that too many co-state variables and difficulty in estimating the initial values of co-state variables,the equilibrium glide condition (EGC) is utilized to reduce the reentry motion equations and then the optimal maneuver strategy satisfied above performance index is derived. This maneuvering strategy is applied to the lifting reentry weapon platform CAV which was designed by America recently to realize both longitudinal and lateral trajectory design by controlling the attack angle and the bank angle respectively. The simulation result indicates that the maneuver strategy proposed enables CAV to reach favorable longitudinal range and lateral range.

Non-Dimensional Values for Convergence of Lift Prediction Using Panel Method

This paper presents an implementation and posterior analysis of the convergence of the panel method. The implemented panel method is based on vortex lines and an unsteady wake on a flat plate as a wing. The main goal of the study was to discover parameters and their values range to obtain convergence of the solution. Results of lift convergence in function of control panel’s position, the effect of the size of the wake panels, the dimension of the wake, and the computation time are quantitatively described. The lift results are similar to the predictions by the lifting-line theory and the wake exhibited an expected shape, showing wingtip, and start vortices. Geometric parameters and non-dimensional values were developed to increase accuracy and stability of the method.

Truss-type maintenance devices and corresponding pipeline lifting control strategies

For new submarine pipeline maintenance lifting equipment,a specialized analysis model is constructed in this study.A pipeline can be divided into the lifted portion and the touch-down portion that lies on the seabed,and each of these portions can be analyzed separately by converting the continuity conditions at the touch-down points to boundary conditions.The typical two-point sequence secant iterative technique is used to obtain the unknown lifted length and determine pipeline lifting confgurations.The BVP4C module in MATLAB software is used to solve this multiple-point boundary value problem issued from frst-order diferential equations.Also,the triple-point lifting mode of truncated maintenance and the two-point lifting mode of online maintenance are discussed.When the lifted heights at truss positions are shown,the lifting deformation,lifting forces,bending moment distribution,and axial force distribution can be analyzed using a dedicated analysis program.Numerical results can then be used to design a lifting strategy to protect the pipeline.

Optimal trajectory and heat load analysis of different shape lifting reentry vehicles for medium range application

The objective of the paper is to compute the optimal burn-out conditions and control requirements that would result in maximum down-range/cross-range performance of a waverider type hypersonic boost-glide(HBG) vehicle within the medium and intermediate ranges,and compare its performance with the performances of wing-body and lifting-body vehicles vis-a-vis the g-load and the integrated heat load experienced by vehicles for the medium-sized launch vehicle under study.Trajectory optimization studies were carried out by considering the heat rate and dynamic pressure constraints.The trajectory optimization problem is modeled as a nonlinear,multiphase,constraint optimal control problem and is solved using a hp-adaptive pseudospectral method.Detail modeling aspects of mass,aerodynamics and aerothermodynamics for the launch and glide vehicles have been discussed.It was found that the optimal burn-out angles for waverider and wing-body configurations are approximately 5° and 14.8°,respectively,for maximum down-range performance under the constraint heat rate environment.The down-range and cross-range performance of HBG waverider configuration is nearly 1.3 and 2 times that of wing-body configuration respectively.The integrated heat load experienced by the HBG waverider was found to be approximately an order of magnitude higher than that of a lifting-body configuration and 5 times that of a wing-body configuration.The footprints and corresponding heat loads and control requirements for the three types of glide vehicles are discussed for the medium range launch vehicle under consideration.

钻井法凿井气-液-固耦合排渣流场及刀盘吸渣口优化

针对西部地区侏罗系地层煤矿立井钻井法施工中出现的气举反循环洗井排渣与钻进效率低下问题,以陕西可可盖煤矿中央回风立井ϕ4.2 m超前钻井为工程背景,基于CFD-DEM(计算流体力学和离散单元法耦合)研究方法,建立了气-液-固多相耦合排渣数值模型,揭示了排渣管内、井底流场的速度及压力分布规律,并基于自研的气举反循环排渣试验装置,采用PIV(粒子图像测速法)测试技术对流场分布的正确性进行验证;提出了优化刀盘吸渣口评判指标和方法,对吸渣口的数量、长径比、面积比、总面积占比进行优化,得到了超前钻头刀盘吸渣口布置的最佳方式和相关参数;讨论了钻头转速、注气量、风管没入比和泥浆黏度等主要因素对排渣流场的影响。研究结果表明:(1)排渣管内流体的运移以轴向流动为主,且途经注气端时,流速发生跳跃式剧增;井底流体的运移主要以水平流动为主,流体的垂直上返仅存在于吸渣口附近;井底流体的水平流动以切向流动为主,径向流动仅在吸渣口两侧较为明显,且远离吸渣口处,径流速度较小易产生岩屑沉积;(2)当刀盘吸渣口数量为2,长径比为0.4,面积比为1,总面积占比为1.94%时,吸渣口的布置方式最佳,且清渣率较现行吸渣口布置方式提高66%;(3)增大钻头转速可显著增强吸渣口的吸附作用,注气量、风管没入比与井底和排渣管内流体的轴向速度均呈正相关关系,低黏、低密度的泥浆易获取高流速,但携岩能力较差。研究结果可为破解侏罗系地层深大立井钻井法洗井排渣与钻进效率低下技术难题,提供有益的理论参考。

改进贝叶斯网络模型在起重作业人机交互差错风险分析中的应用

为量化分析起重作业人机交互差错风险,根据安全工效学原理及安全技术规范将起重作业人、机、环相关影响因素作为根节点,按照事故致因层次关联关系确定子节点,构建起重作业人机交互差错的3层级贝叶斯网络模型(Bayesian Network, BN);基于模糊集理论,采用认知可靠性与失误分析方法(Cognitive Reliability and Error Analysis Method, CREAM),厘定贝叶斯网络父节点失效概率以及中间节点条件概率;利用逆向推理仿真技术分析起重作业人机交互差错发生的因果链,探究起重伤害事故发生的人机交互差错风险。结果表明:起重作业人机交互差错最可能致因链为起重设备安全检查不到位→管理人员失误→人员操作失误→起重伤害事故发生;单因素失效条件下,起重作业人机交互差错风险概率呈线性增长趋势;在多因素失效条件下,一级节点因素失效概率愈大则人机交互差错效应愈显著,且呈现非线性增长态势。

模拟手抬烧伤患者的悬吊架和起升方法的研究与设计

在烧伤患者治疗过程中,徒手过床搬运不仅会增加患者疼痛和出现皮肤损伤的风险,还会给医护人员带来较大负担。为改善这种情况,本研究设计了一种模拟手抬烧伤患者的悬吊架,其包括烧伤患者的悬吊装置、模拟手抬烧伤病人的悬吊架,其起升方法是模拟人手伸入患者的背部将患者抱起的过程,操作方便,可以避免烧伤患者在搬运过程中出现二次损伤,提高过床安全性及优质护理服务质量,减少过床的人力资源,极大地降低护理人员的劳动强度,为烧伤患者的治疗和康复提供了便利。

深海钻探泥浆举升系统双泵协同机制研究

深海钻探泥浆举升系统在无隔水管泥浆循环钻井(RMR)工艺中具有关键作用。为了提升举升系统的安全余量和适应性,本文对多泵串并联机制进行了深入研究,详细描述了泥浆举升泵的串并联结构设计和工作原理,探讨了串联和并联运行时流量与扬程的关系以及泵组串并联工况点的数解法和图解法步骤。进一步地,利用模型泵实测特性曲线,使用图解法获取了双泵串并联工况下的Q-H特性曲线和工况点,并提出了双泵协同控制的建议。

基于未确知测度方法的装配式建筑吊装风险研究

为实现对装配式建筑吊装风险的科学评价,基于AHP-熵组合赋权的未确知测度方法提出装配式建筑吊装风险量化评价方法。首先,遵循“4M1E”原则对风险因素进行梳理,从“人、物、技、环、管”5个方面对装配式建筑吊装风险因素进行识别,建立风险量化评价指标体系;然后,运用AHP计算评价指标主观权重,熵权法计算评价指标客观权重,结合最小熵原理计算组合权重,基于该权重与未确知测度方法提出装配式建筑吊装风险量化评价方法;最后,对湖南地区某装配式住宅项目进行实例研究。研究表明:该项目吊装总体风险判定为c4级(风险较小)。AHP-熵组合赋权未确知测度方法的可操作性较强,可用于装配式建筑吊装风险的量化评价。

电动缸举升伺服机构动力学建模与参数辨识

针对电动缸举升伺服机构动力学参数辨识困难的问题,本文提出了一种限定记忆区间的循环最小二乘辨识法,用于机构全行程内非线性模型、扰动参数的辨识拟合.首先,分析了机构完整模型的非线性参数成因,并提出了相应的简化模型;然后,分析了最小二乘法在平均位姿下的参数近似辨识特性,并提出了限定记忆区间的循环最小二乘法;最后,通过构造输入输出信号和选择辨识伺服环路,使得辨识过程不会超过机构的行程范围.实验结果表明:所提辨识法使得正弦速度和位移响应均方根误差相比最小二乘法分别下降了59.3%和84.2%.所提辨识法可给电动缸举升伺服机构的高精度动力学建模,控制器结合观测器的复合控制策略的实现提供参考.

非对称三塔连体超高层结构连廊施工方案研究

连体超高层结构属于大型复杂结构,时变特性显著。连廊作为连接各塔楼的纽带,其施工过程对整体结构安全性的影响较大,需要对其施工方案进行研究。以某非对称三塔连体超高层结构为研究对象,建立了该结构的数值模型。采用整体提升法和悬臂拼接法作为连廊的施工方案,分别进行了有限元计算,研究了不同施工方案下塔楼的竖向变形、连廊处各塔楼间的变形差、塔楼与连廊连接处单元的内力。结果表明:2种施工方案均不影响连体结构整体施工阶段的竖向变形规律。相较于整体提升法,悬臂拼接法将导致在连廊施工期间及竣工时刻塔楼结构产生更大的竖向变形、连廊处标高差及连廊连接处单元内力。整体提升法更适合本文研究对象的连廊施工。

Z形折叠翼厚度对其气动特性影响分析

Z形折叠翼飞行器可在飞行过程中改变机翼面积,改善气动特性,执行多种任务.然而机翼折叠过程中有效气动面积、重心、气动焦点等参数的变化,会对飞行器气动特性产生较大影响.此外,机翼表面相互靠近,由机翼厚度引发的气动干扰也会导致升力、折叠铰链力矩等气动力发生变化.为此,首先利用薄翼理论和升力面法推导理想气体来流条件下折叠翼的定常气动力表达式.然后,采用CFD法分析折叠过程中折叠角、攻角和机翼厚度对飞行器升力、折叠铰链力矩等气动特性的影响,并将分析结果与升力面法结果对比.结果表明机翼折叠过程中,有效气动面积减小,升力、阻力系数总体呈下降趋势;随着折叠角增大,机翼表面相互靠近产生的低压区强度增加,机翼厚度对折叠翼气动特性影响显著增强.另外相比于CFD法,忽略机翼厚度项的升力面法对于折叠翼的气动力计算会产生较大误差.

重载和客货共线铁路弹性支承块式无砟轨道快速换块关键技术

为选取合适的弹性支承块式无砟轨道抬轨换块施工参数,建立有限元模型,研究了抬轨点间距、扣件松开长度、抬轨量以及施工轨温与锁定轨温的温差对轨道结构变形和受力的影响,明确各参数最佳取值,提出存在空吊、离缝、套靴积水等病害的弹性支承块式无砟轨道快速换块施工方法,并在现场进行应用。结果表明:抬轨点间距宜取1.2~3.6 m,此时钢轨弯折变形较小,且钢轨拉力和扣件上拔力较小;抬升点间距每增加1.0 m,温差限值增加1℃。抬轨量16 cm,抬轨点间距1.2 m时,扣件松动长度宜大于31.8 m;温差每升高1℃,扣件松开长度应减少2.4 m。钢轨最大拉应力和扣件最大上拔力随抬轨量增加而增大,抬轨量每增加1 cm,钢轨最大拉应力增大0.66 kN,扣件最大上拔力增大0.075 MPa。