Non-linear 2-DOF model and centre manifold theory to study limit cycle oscillations caused by drum-brake judder

This paper presents the research on the laws of systematic-parameter dependent variation in the vibration amplitude of drum-brake limit cycle oscillations (LCO). We established a two-degree non-linear dynamic model to describe the low-frequency vibration of the drum brake, applied the centre manifold theory to simplify the system, and obtained the LCO amplitude by calculating the normal form of the simplified system at the Hopf bifurcation point. It is indicated that when the friction coefficient is smaller than the friction coefficient at the bifurcation point, the amplitude decreases; whereas with a friction coefficient larger than the friction coefficient of bifurcation point, LCO occurs. The results suggest that it is applicable to suppress the LCO amplitude by changing systematic parameters, and thus improve the safety and ride comfort when applying brake. These findings can be applied to guiding the design of drum brakes.

Stabilization for nonlinear systems via a limited capacity communication channel with data packet dropout

This paper addresses the stabilization problem for a class of nonlinear systems. It is assumed that the controller can only receive the transmitted sequence of finite coded signals via a limited digital communication channel. Both state and output feedback coder-decoder-controller procedures are proposed. Stabilization conditions involving the size of coding alphabet, the sampling period, system state growth rate and data packet dropout rate are obtained. Finally, an example is given to illustrate the design procedures and effectiveness of the proposed results.

Randomized Constraint Limit Linear Programming in Risk Management

Traditional linear program (LP) models are deterministic. The way that constraint limit uncertainty is handled is to compute the range of feasibility. After the optimal solution is obtained, typically by the simplex method, one considers the effect of varying each constraint limit, one at a time. This yields the range of feasibility within which the solution remains feasible. This sensitivity analysis is useful for helping the analyst get a feel for the problem. However, it is unrealistic because some constraint limits can vary randomly. These are typically constraint limits based on expected inventory. Inventory may fall short if there are overdue deliveries, unplanned machine failure, spoilage, etc. A realistic LP is created for simultaneously randomizing the constraint limits from any probability distribution. The corresponding distribution of objective function values is created. This distribution is examined directly for central tendencies, spread, skewness and extreme values for the purpose of risk analysis. The spreadsheet design presented is ideal for teaching Monte Carlo simulation and risk analysis to graduate students in business analytics with no specialized programming language requirement.

Effect of New Suggested Ferroresonance Limiter on the Stability Domain of Chaotic Ferroresonance in the Power Transformer with Linear Core Model

This Paper studies the effect of new suggested ferroresonance limiter on controlling ferroresonance oscillations in the power transformer. It is expected that this limiter generally can control the ferroresonance. For studying these phenomena, at first ferroresonance is introduced and a general modeling approach is given. A simple case of ferroresonance in a three phase transformer is used to illustrate these phenomena. Then, effect of new suggested ferroresonance limiter on the onset of chaotic ferroresonance and control of these oscillations in a power transformer including linear core losses is studied. Simulation is done on a three phase power transformer while one of its phases is opened, and effect of varying input voltage on occurring ferroresonance overvoltage is studied. Results show that connecting the ferroresonance limiter to the transformer exhibits a great controlling effect on the ferroresonance overvoltage. Phase plane diagram, FFT analysis along with bifurcation diagrams are also presented. Significant effect on occurring chaotic ferroresonance, the range of parameter values that may lead to overvoltage and magnitude of ferroresonance overvoltage is obtained, showed and tabulated.

新型船舶轻量化整体隔音舱室的研究与设计

提出一种国内首创的船舶轻量化整体舱室装置设计方案,该方案深入应用于船舶舱室领域以及轮机机械领域。这一创新设计,旨在提升船舶舱室的舒适性和安全性,同时降低船舶的整体重量,提高燃油效率。该装置的独特之处在于,它可以通过限位卡合结构,对船舶舱室内的一些家用家具进行精确的限位固定。这种方式相比于传统的膨胀螺丝等固定方法,更具灵活性和便捷性。当需要拆卸家具时,限位卡合结构可以迅速解锁,实现快速拆卸。这一设计大大提高了船舶舱室的实用性和人性化程度。此外,该装置还在舱室的墙壁以及顶部采用了石膏板和隔音棉,取代了传统的泡沫板或水泥板。这种创新的设计,不仅能有效提升舱室的隔音效果,还能进一步减轻船舶重量,提高燃油效率。总体来说,这种新型的船舶轻量化整体舱室装置设计理念,将为船舶行业带来全新的变革。它不仅提升了船舶的性能,提高了船舶舱室的舒适度,也为船舶制造带来更高的效率和更低的成本,将对我国船体建造方式产生重要影响,并提供一种全新的思路。

带分段限位刚度的双向限位单层隔振系统冲击动力学理论模型研究

[目的]针对在冲击激励作用下带限位器的隔振系统刚度呈非线性变化的问题,开展冲击动力学理论模型及其抗冲击性能研究。[方法]首先,利用分段线性等效思想,建立带分段线性刚度限位器的双向限位单层隔振系统冲击动力学理论模型;然后,利用解析法对理论模型进行解析求解,并与不同冲击工况下的有限元法冲击响应进行对比验证。[结果]在不同的冲击工况下,动力学理论模型的解析解与有限元数值解具有高度的一致性。[结论]通过对比分析,验证了带分段限位刚度的双向限位单层隔振系统冲击动力学理论模型及求解方法的准确性,可为带限位器隔振系统的工作原理与性能特点研究提供理论依据。

InGaN基蓝光激光器p型覆盖层和波导层优化

[目的]为了进一步提升蓝光激光器的性能,基于实验样品结构,研究了p型覆盖层和波导层对InGaN基边发射蓝光激光器性能的综合影响.[方法]将p型覆盖层优化为多层Al组分渐变的结构,以降低p型覆盖层与电子阻挡层的Al组分差值;优化波导层的In组分浓度,以提高波导层的光限制能力.利用PICS3D软件模拟计算其光输出功率、能带结构、光场分布、载流子电流密度分布等特性.[结果]随着p型覆盖层层数的增加,以及p型覆盖层与电子阻挡层之间Al组分差值的减小,光输出功率和斜率效率不断提高;随着上波导层In组分的增加,光输出功率提升明显.同时优化两者得到的最终优化结构,光输出功率可达到0.421 W,相较标准结构提升了65.75%.[结论]降低p型覆盖层与电子阻挡层之间的Al组分差值,可以有效降低两者之间的晶格失配和势垒差,进而提高有源区的空穴注入;增加p型覆盖层的层数可降低晶格失配,进而降低载流子的传输损耗.增加波导层的In组分浓度可以提高有效提高光限制因子,尤其是上波导的In组分增加对提高光限制因子非常明显.

有限转角力矩电机电磁转矩与霍尔感应磁场研究

永磁式齿槽式集中绕组形式有限转角力矩电机一般具有较小的气隙,进而可以增加电机的气隙磁密幅值,提高力矩输出能力。根据这一优势,通过理论设计和有限元仿真软件设计出一种符合基本性能要求的旋转式直驱阀有限转角力矩电机,并研究了充磁方向、斜槽对齿槽转矩和输出转矩的影响,从而达到抑制转矩波动、改善转矩波形的目的。根据线性霍尔具有体积小、反馈信号线性度好等优点,选用线性霍尔接收信号,并研究霍尔位置和偏心距对霍尔波形畸变率的影响。研究表明,对霍尔波形进行优化后成功将谐波畸变率从最初的4.9%降低到0.1%以下,这在工程研究领域具有重要参考意义。

Vortex-Induced Vibration of a Tension Leg Platform Tendon:Multi-Mode Limit Cycle Oscillations

This paper studies the application of mathematical models to analyze the vortex-induced vibrations of the tendons of a given TLP along the Indian coastline, by using an analytical approach, using MATLAB. The tendon is subjected to a steady current load, which causes vortex-shedding downstream, leading to cross-flow vibrations. The magnitude of the excitation(lift and drag coefficients) depends on the vortex-shedding frequency. The resulting vibration is studied for possible resonant behavior. The excitation force is quantified empirically, the added mass by potential flow hydrodynamics, and the vibration by normal mode summation method. Non-linear viscous damping of the water is considered. The non-linear oscillations are studied by the phase-plane method, investigating the limit-cycle oscillations. The stable/unstable regions of the dynamic behavior are demarcated. The modal contribution to the total deflection is studied to establish the possibility of resonance of one of the wet modes with the vortex-shedding frequency.

Iterative learning based fault diagnosis for discrete linear uncertain systems

In order to detect and estimate faults in discrete lin-ear time-varying uncertain systems, the discrete iterative learning strategy is applied in fault diagnosis, and a novel fault detection and estimation algorithm is proposed. And the threshold limited technology is adopted in the proposed algorithm. Within the chosen optimal time region, residual signals are used in the proposed algorithm to correct the introduced virtual faults with iterative learning rules, making the virtual faults close to these occurred in practical systems. And the same method is repeated in the rest optimal time regions, thereby reaching the aim of fault diagnosis. The proposed algorithm not only completes fault detection and estimation for discrete linear time-varying uncertain systems, but also improves the reliability of fault detection and decreases the false alarm rate. The final simulation results verify the validity of the proposed algorithm.

LIMITING DIRECTION AND BAKER WANDERING DOMAIN OF ENTIRE SOLUTIONS OF DIFFERENTIAL EQUATIONS

In this paper, we mainly investigate entire solutions of complex differential equations with coefficients involving exponential functions, and obtain the dynamical properties of the solutions, their derivatives and primitives. With some conditions on coefficients, for the solutions, their derivatives and their primitives, we consider the common limiting directions of Julia set and the existence of Baker wandering domain.

LIMITING DIRECTIONS OF JULIA SETS OF ENTIRE SOLUTIONS TO COMPLEX DIFFERENTIAL EQUATIONS

In this paper,we mainly investigate the dynamical properties of entire solutions of complex differential equations.With some conditions on coefficients,we prove that the set of common limiting directions of Julia sets of solutions,their derivatives and their primitives must have a definite range of measure.

Limit equilibrium analysis for rock slope stability using basic Hoek–Brown strength criterion

Hoek–Brown(HB)strength criterion can reflect rock’s inherent failure nature,so it is more suitable for analyzing the stability of rock slopes.However,the traditional limit equilibrium methods are at present only suitable for analyzing the rock slope stability using the linear equivalent Mohr–Coulomb(EMC)strength parameters instead of the nonlinear HB strength criterion.Therefore,a new method derived to analyze directly the rock slope stability using the nonlinear HB strength criterion for arbitrary curve slip surface was described in the limit equilibrium framework.The current method was established based on certain assumptions concerning the stresses on the slip surface through amending the initial normal stressσ0 obtained without considering the effect of inter-slice forces,and it can satisfy all static equilibrium conditions of the sliding body,so the current method can obtain the reasonable and strict factor of safety(FOS)solutions.Compared with the results of other methods in some examples,the feasibility of the current method was verified.Meanwhile,the parametric analysis shows that the slope angleβhas an important influence on the difference of the results obtained using the nonlinear HB strength criterion and its linear EMC strength parameters.Forβ≤45°,both of the results are similar,showing the traditional limit equilibrium methods using the linear EMC strength parameters and the current method are all suitable to analyze rock slope stability,but forβ>60°,the differences of both the results are obvious,showing the actual slope stability state can not be reflected in the traditional limit equilibrium methods,and then the current method should be used.

6种商品化酶抑制-比色法农残速测试剂盒测定5种农药的比较研究

使用6种商品化酶抑制-比色法农残速测试剂盒在5个浓度水平下测定乐果等5种农药的抑制率,绘制抑制率对农药浓度的效应曲线图,用抑制率和农药浓度的对数进行线性拟合,求出决定系数、IC_(50)和IC_(10),根据IC_(10)以试剂盒对乐果等5种农药的敏感性进行比较研究。结果表明:6种试剂盒对乐果和甲基异柳磷均不敏感,对其他3种农药的敏感性也各不相同,就所测定的5种农药而言,试剂盒C较优。综合而言,为适应市场监管和试剂盒检测方便,建议生产商在生产试剂盒时,对所使用的酶和底物进行测定,必要时将几种不同来源、性质相近的酶按一定的比例进行混合,以使试剂盒敏感的农药更多,从而减少假阴性样品。

线性递推关系数列极限的求法

首先,探讨Fibonacci数列通项比的极限,并推广到一般线性递推关系通项比的极限,然后,根据条件p+q=1及通项比极限,求得具有一般线性递推关系式数列极限公式,可以直接用此极限公式解决一些极限问题,最后,探讨分式线性关系数列极限的求解,发现也可以推导出其求极限的公式。在探讨各类线性递推关系数列极限的求解方法时,给出了具体求极限的案例进行分析,为极限的学习和教学提供参考。

基于BP人工神经网络的有机化合物爆炸下限预测

运用定量结构-性质关系对458种有机化合物的爆炸下限展开预测研究。首先运用Dragon 2.1软件计算并预筛出708种分子描述符,随后采用遗传算法确定了5个特征分子描述符作为模型的输入变量,最后运用SPSS和MATLAB分别构建了多元线性回归线性模型、支持向量机与人工神经网络两种非线性模型。研究结果为:MLR模型的训练集和测试集的复相关系数R2分别为0.8387和0.8588;SVM模型的R^(2)分别为0.8569和0.8779;ANN模型的R2分别为0.9284和0.9328。由此表明,无论是训练集还是测试集,SVM模型的预测效果均优于MLR模型,ANN模型的预测效果均优于SVM模型,有机化合物的爆炸下限与其分子结构之间存在着较强的非线性关系。此外,本研究采用内外验证方法及与其他研究的比较对模型性能进行了验证,证实了ANN模型对爆炸下限具有较好的预测能力。通过绘制Wiliams图分析了模型的应用域,验证了所建模型均具有良好的泛化能力和鲁棒性。通过QSPR方法预测有机化合物的爆炸下限,能为危险化学品的风险管控及安全工艺的研究提供有力的理论和技术支持。

基于GaN二极管耦合检波的大功率高线性限幅器研究

现阶段接收链路的动态功率范围越来越大,对接收机限幅器的线性度带来挑战。要求限幅器在满足高功率的前提下,开启电平尽量高。GaN肖特基二极管具有较低的开启电压和较高的击穿电压,特别适用于高频大功率整流电路。为了满足限幅器高线性和高功率的需求,文章介绍了一种基于横向结构GaN肖特基二极管耦合整流的高线性限幅器。测试结果表明,在0.03~1 GHz频带内,小信号插入损耗小于1 dB,输入输出驻波比小于1.6;开启电平大于17 dBm,可承受连续波100 W的功率,泄露功率小于23 dBm。该限幅器体积小、耐功率高,可广泛应用于大动态接收机中,保证高线性的前提下提升其可靠性。

碳基柔性电阻式应变传感器的研究进展

碳基柔性电阻式应变传感器凭借其结构简单、设计灵活、潜在可量产化和综合传感性能优异等特点,在可穿戴柔性电子领域获得了广泛应用。根据不同碳基柔性电阻式应变传感器的应用现状,介绍了炭黑基、碳纳米管基和石墨烯基三种柔性电阻式应变传感器的制备、性能及应用研究。针对碳纳米管基和石墨烯基柔性电阻式应变传感器,按照碳纳米材料宏观结构的组装形式进行了分类(一维纤维或纱线、二维薄膜或织物和三维块体)综述。

半悬臂式燃料元件在间隙限制约束下非线性振动的等效方法研究

半悬臂式燃料元件为上端固定、下端间隙限制的结构形式,该结构可节省使用和安装空间,具有在小型反应堆应用的潜力。相较于传统的两端固定结构,半悬臂式燃料元件下端呈现弱约束特性,在振动工况下存在碰撞接触非线性行为。针对间隙引起的非线性问题,采用弹支梁等效方法,将底端间隙配合等效为弹簧结构。本文将半悬臂式燃料元件的非线性振动过程通过单摆—悬臂梁模型进行等效,推导出半悬臂式燃料元件振动周期公式,结合弹支梁振动方程,可快速准确得到等效弹簧刚度,从而建立半悬臂式燃料元件在间隙限制约束下非线性振动的等效方法。通过半悬臂式燃料元件抗震分析,对本文方法与传统有限元方法进行对比,结果显示:该案例计算时间大幅度减少,本文计算方法所用时间仅为传统有限元方法的1/74;两种方法的结果表明:在关键部位的振动响应基本一致,初步验证了本方法可快速有效求解具有间隙约束的半悬臂式燃料元件振动问题,为小型反应堆提供了快速设计工具。