Research on the Dynamic Response of Submerged Floating Tunnels to Wave Currents and Traffic Load

Submerged floating tunnel(SFTs)are typically subjected to complex external environmental and internal loads such as wave currents and traffic load.In this study,this problem is investigated through a finite element method able to account for fluid-structure interaction.The obtained results show that increasing the number of vehicles per unit length enhances the transverse vibrational displacements of the SFT cross sections.Under ultimate traffic load condition,one-way and two-way syntropic distributions can promote the dynamic responses of SFTs whereas two-way reverse distributions have the opposite effect.

Dynamics and stabilization of peak current-mode controlled buck converter with constant current load

The discrete iterative map model of peak current-mode controlled buck converter with constant current load（CCL）,containing the output voltage feedback and ramp compensation, is established in this paper. Based on this model the complex dynamics of this converter is investigated by analyzing bifurcation diagrams and the Lyapunov exponent spectrum. The effects of ramp compensation and output voltage feedback on the stability of the converter are investigated. Experimental results verify the simulation and theoretical analysis. The stability boundary and chaos boundary are obtained under the theoretical conditions of period-doubling bifurcation and border collision. It is found that there are four operation regions in the peak current-mode controlled buck converter with CCL due to period-doubling bifurcation and border-collision bifurcation. Research results indicate that ramp compensation can extend the stable operation range and transfer the operating mode, and output voltage feedback can eventually eliminate the coexisting fast-slow scale instability.

Experimental study on bed-load sediment transport under irregular wave and current combined flow

Using an irregularly oscillating tray and flume, a series of experiments are completed to evaluate bed-load sediment transport rate under irregular wave -current coexistent field. Testing conditions include three interaction angles 0', 45', 90' and two kinds of median sizes (0.38 and 1.10 mm). The results of transport rate show that the net sediment transport rate can be expressed approximately as the function of the maximum bottom shear stress of waves, mean shear stress of current and the grain size.

A DISCUSSION ON CURRENTS AND SUSPENDED LOAD TRANSPORT IN SURF ZONE

In this paper, the distribution characteristics of the breaking wave current and suspended load transport in the surf zone are discussed in main. Based on the measured data of the waves, the form of breaking wave, the breaking wave current and the sediment concentration of suspended load in the offshore surf zone near Nouakchott, the Islamic Republic of Mauritania, the author has analized the law governing the distribution of longshore current and sediment concentration of suspended load by means of statistical method, and presented a calculation method for the longshore sediment transport in offshore surf zone.

Effects of drive current rise-time and initial load density distribution on Z-pinch characteristics

A two-dimensional, three-temperature radiation magneto-hydrodynamics model is applied to the investigation of evolutional trends in x-ray radiation power, energy, peak plasma temperature and density as functions of drive current rise-time and initial load density distribution by using the typical experimental parameters of tungsten wire-array Z- pinch on the Qiangguang-I generator. The numerical results show that as the drive current rise-time is shortened, x-ray radiation peak power, energy, peak plasma density and peak ion temperature increase approximately linearly, but among them the x-ray radiation peak power increases more quickly. As the initial plasma density distribution in the radial direction becomes gradually flattened, the peak radiation power and the peak ion-temperature almost exponentially increase, while the radiation energy and the peak plasma density change only a little. The main effect of shortening drive current rise-time is to enhance compression of plasma, and the effect of flattening initial load density distribution in the radial direction is to raise the plasma temperature. Both of the approaches elevate the x-ray peak radiation power

Analysis of load status and management strategies of main caregivers of patients with malignant tumors of digestive tract

Caregiver load refers to the subjective and objective negative impact of caregivers in the care of patients,and excessive load will have a serious impact on patients and caregivers themselves and can reduce their quality of life.For the main caregivers,it not only needs to care for the patients in life and daily life,but also needs to pay the cost of treatment for the patients,coupled with the need to carry out their own original work,life,etc.excessive life pressure,economic pressure,work pressure,emotional pressure,etc.lead to heavy load of the main caregivers,which can easily cause caregivers to have different degrees of psychological problems,which will cause serious adverse effects on the caregivers themselves and cancer patients,not conducive to the construction of a harmonious family and society.This article analyzes the current situation of primary caregiver burden in patients with gastrointestinal malignant tumors,analyzes its influencing factors,and specifies specific treatment strategies.It is hoped to provide scientific guidance for later related research and application.

Dynamic Response Analysis of Risers Subjected to Combined Wave and Current Loading

A dynamic response analysis in the frequency domain is presented for risers subjected to combined wave and current loading. Considering the effects of current, a modified wave spectrum is adopted to compute the linearized drag force. An additional drag force convolution term is added to the linearized drag force spectrum, therefore the error is reduced which arises from the truncation of higher order terms in the drag force auto-correlation function. An expression of linearized drag force spectrum is given taking the relative velocity into account. It is found that the additional term is a fold convolution integral. In this paper dynamic responses of risers are investigated, while the influence of floater motion on risers is considered. The results demonstrate that the accuracy of the present method reaches the degree required in time domain analysis.

双路电源的主动均流电路系统研究

广泛使用的低成本电源管理芯片或直流电源模块通常并未集成输出均流控制功能,因此不能直接并联输出使用。而使用特殊的电源管理芯片或是额外的均流控制电路会提高电源电路的复杂程度,造成电路成本的提高。针对此应用场景,提出了一种具有主动均流功能的双路电源开关,作为负载开关或电源多路复用器应用于电路之中,利用开关电流的方法均分输出电流,在几乎不增加电路成本的同时对两路电源进行均流。阐述了所提双路电源开关的工作原理与参数设计方法,并通过仿真与实验证明了所提方法的正确性与可行性。

地铁车站弱电设备间设备发热量确定方法

介绍了一种地铁车站弱电设备间设备发热量确定新方法,该方法利用弱电设备发热量实测数据与模型预测数据相互验证,可以有效提高弱电设备发热量确定结果的准确性。研究了室内气温、地铁是否运营、设备额定功率和车站类型等因素对设备发热量的影响。研究结果表明:基于间接测量和预测模型的地铁车站弱电设备间设备发热量确定方法可以提高和保障设备发热量计算结果的准确性;室内气温会显著影响设备外表面和围护结构内表面温度及围护结构内表面热流密度,但对设备外表面热流密度的影响较小;地铁是否运营对弱电设备间设备发热量有较大影响,地铁运营期间设备发热量大于非运营期间;设备额定功率对弱电设备间设备发热量峰值有较大影响,车站类型和建筑面积对设备发热量峰值的影响很小。

基于负荷电流的综合管廊电缆发热量计算

综合管廊属于密闭型地下构筑物,廊内敷设的电缆是主要的发热源。准确估计入廊电缆的发热量有助于通风设备的合理选择和工艺的科学设计,避免造成资源和成本的浪费。本文提出了基于负荷电流的电缆发热量计算方法,通过对出变电站母线段电缆进行分析,得到了更为精确的电缆负荷电流。通过计算可知,使用负荷电流进行电缆发热量计算得到的结果比使用载流量进行电缆发热量计算的结果更为准确,且明显减小,可以实现在满足规范要求和功能需要的前提下降低能耗、节约成本。

适配变压器全档位切换暂态分析的有载分接开关电路模型构建

有载分接开关(on-loadtap-changer,OLTC)是换流变压器的核心组件,其可靠切换过程关乎换流变的安全。然而目前国内在运特高压换流变用OLTC完全依赖进口,仿真获取OLTC不同运行状态的暂态特性数据是支撑OLTC关键电气参数设计与国产化制造的基础。经典的OLTC模型仅改变变压器变比或仅模拟单级档位切换过程,难以满足全档位电压调整与各级档位暂态特性数据同步获取的需求,导致OLTC设计优化、参数选型及故障分析缺乏足够的仿真数据支持。该文首先以真空OLTC为研究对象建立切换开关和极性开关等效电路模型,根据OLTC复杂的调压功能建立分层控制系统。其次,在PSCAD中搭建交流仿真系统,获取有载调压过程的暂态特性数据波形,与解析计算得到的电压和电流相比误差小于0.2%,证明该模型满足OLTC电磁暂态仿真研究的精度要求。最后,开展循环调压仿真,获得负载电压数据与波形。结果表明:该文提出的OLTC模型能够接收外部控制信号,进行全档位调压与极性转换仿真分析,能够为OLTC的调压研究、故障溯源分析和过渡电阻设计选型等提供基础模型。

基于在线特征库的非侵入式负荷特征提取方法

负荷特征是指负荷设备运行过程中具备某种统计规律的特殊标识,而包含负荷特征的数据库则是实现非侵入式负荷监测与分解的基本依据。对于纯阻性负荷设备,研究人员利用其运行状态切换过程中功率产生跃变的特点,可以准确提取相应状态下的负荷特征。然而,对非纯阻性设备,其负荷特征提取存在以下2个问题。问题1)运行状态切换过程中功率变化不显著,无法精准定位状态投切时刻点;问题2)负荷设备存在功率缓变化的运行状态,导致对应状态下的负荷特征不唯一,无法手动提取。为了解决非纯阻性设备负荷特征提取中存在的上述问题,提出一种基于在线特征库的非侵入式负荷特征提取方法,该方法分为2个阶段。第一阶段:基于负荷设备运行过程中的稳态周期电流数组建立在线特征库,通过改进Pearson相似系数构建滑窗函数,得到负荷设备运行时的周期电流数组与在线特征库的相似性,并同步判断在线特征库冗余性,实现负荷设备状态数据分割;第二阶段:计算在线特征库的特征矩阵,对特征矩阵进行K-means聚类分析,融合相似在线特征库,形成负荷设备的状态特征库,从而实现负荷设备特征电流数组的提取。在私人数据集和PLAID数据集上的测试结果证明,所提负荷特征提取方法在不同的用电场景下均有较好的鲁棒性。所提方法可大幅减少负荷特征提取阶段的人工参与,有利于缓解因负荷设备种类过多导致的负荷特征提取烦琐的问题,为后续建立负荷特征数据库提供了便利。

基于响应曲面中心组合设计的介质阻挡负载特征参数分析与优化

为了充分发挥介质阻挡放电(DBD)负载的性能,以高频脉冲激励作为介质阻挡负载的激励波形,以第一次放电时的负载电流幅值作为优化目标。基于响应曲面法中心组合设计建立数学模型,分析介质阻挡层厚度、脉冲电压幅值、脉冲升降沿时间和相对介电常数4个因素对高频脉冲激励下DBD负载第一次放电时负载电流幅值的影响,优化介质阻挡负载特征参数。结果表明,对DBD负载电流的影响强度从大到小依次为介质阻挡层厚度、脉冲电压幅值、脉冲升降沿时间、相对介电常数。在本文设定条件下,负载电流幅值的最大值8.692A在脉冲升降沿时间为200ns、脉冲电压幅值为4kV、介质阻挡层厚度为1mm、相对介电常数为8时获得。

深海采矿立管在波流载荷下的弯矩响应分析

采矿立管是深海采矿系统的重要组成部分,立管的弯矩分析是确保立管正常使用的重要指标。立管所处海洋环境复杂,且立管底部的自由边界条件使得立管弯矩特性难以分析。本文基于波浪理论,使用Abaqus有限元软件建立海洋采矿立管的模型,运用Abaqus中的AQUA海洋工程模块,考虑立管在轴向力、自重、浮力、波浪载荷、海流载荷及模拟海上平台水平和升沉运动共同作用下,对采矿立管进行弯矩分析,计算了提升泵不同安装位置、不同中继仓重量变化对弯矩的影响,结果表明:提升泵会增大安装位置的弯矩幅度,且安装在不同位置对立管弯矩会产生叠加影响;中继仓重量的增加提高了立管整体稳定性,但会使提升泵处弯矩波动产生向中部延伸的不利影响。

基于栅极限流的SiC MOSFET栅电荷测试方案

SiC MOSFET是一种高性能的电力电子器件,其开通/关断过程中积累/释放的栅电荷Q_(g)对MOSFET的开关速度、功率损耗等参数有重要影响。通常采用在栅极设置恒流源驱动,对时间进行积分的方法来测量Q_(g)。为了降低驱动复杂度,提高测试结果精度和可视性,基于双脉冲测试平台的感性负载回路,改用耗尽型MOSFET限制栅极电流实现恒流充电,对SiC MOSFET进行测试。同时利用反馈电阻将较小的栅极电流信号转换为较大的电压信号。实验结果表明:在误差允许范围(±5%)内该测试方案能较为准确地测得SiC MOSFET的Q_(g),测试结果符合器件规格书曲线。

图腾柱功率因数校正器的二自由度控制分析

TPFC一般采用一自由度输出电压控制,在负载变化时输出电压动态特性较差,且启动过程存在明显超调。本文在推导TPFC双闭环控制结构基础上,引用了负载电流前馈控制和输出电压反馈补偿控制,构成两种二自由度(2DOF)控制结构。仿真分析表明,负载电流前馈型2DOF控制可以有效抑制负载变化引起的输出电压波动,但启动过程超调明显;输出电压反馈补偿型2DOF控制可以实现输出电压无超调启动,但是抑制负载变化的能力较差;综合负载电流前馈型和输出电压反馈补偿型的2DOF控制获得满意的输出电压控制效果,表现为启动过程无超调和变载过程无波动。

水轮机调节系统与轴系耦合模型对系统参数的敏感性分析

抽水蓄能电站频繁地暂态过程对轴系振动有重要影响,建立一个能够反映水电机组暂态响应的调节系统与轴系的耦合模型对于研究抽水蓄能电站的安全运行至关重要。以拉日朗日公式推导的扭矩方程为纽带,构建了水轮发电机组调节系统与考虑多振动诱发因素的轴系系统的瞬态耦合模型。计算了甩不同负荷下轴系的动态响应过程,分析了发电机偏心质量以及发电机励磁电流对轴系暂态过程的影响。研究发现,甩去的负荷越多,轴系在动态响应的过程中振动越剧烈,甩30%负荷,甩60%负荷,以及甩100%负荷后,发电机转子在x方向上的振幅较甩负荷前分别增加了68.7%,109.3%,以及126.3%。发电机的偏心质量越大,水轮发电机组轴系在动态响应过程中的幅值越高,系统越不稳定,而励磁电流越大,轴系在响应过程中的幅值越小,越有利于系统稳定运行。本文的目的是为水轮发电机组调速系统-轴系系统瞬态耦合模型的建立提供一种方法,探讨和评价甩负荷下瞬态耦合模型的参数敏感性,保障机组暂态下的安全稳定运行。

永磁无刷轮毂电机轮对系统同步工况下的协调控制策略

针对双轮毂电机在负载不平衡工况下转速同步精度不够及同步响应速度不快的问题,该文提出速度环补偿PID交叉耦合同步控制和电流环补偿PID交叉耦合同步控制策略。首先,建立双轮毂电机的数学模型,采用双闭环六步方波控制。基于该模型,采用速度环补偿PID交叉耦合同步控制代替单增益交叉耦合控制器,使转速同步调节精度提升。在两侧电机负载不平衡工况下,用电流环补偿PID交叉耦合控制方法进一步提升转速同步精度,同时加快同步响应速度,并兼顾了转矩精度。仿真和实验验证了所提控制策略的正确性和有效性。