Scantling optimization based on convex linearizations and a dual approach—Part II

The development of the LBR-5 “Stiffened Panels Software” is included in the development of a new design methodology to ease and to improve preliminary studies of naval structures and floating hydraulic structures. It allows, as of the first draft, an optimization of the scantling of the structure's constituent elements. The ultimate target is to link standard design tools (steel structure CAD, hull form, hydrostatic curves, floating stability, weight estimation, etc.) with a rational optimization design module and a minimum construction cost (or minimum weight) objective function. It is developed to be a user-oriented tool. The optimization module is composed of three basic modules (OPTI, CONSTRAINT and COST) and a group of sub-modules (in external databases). Among these the user selects a set of relevant sub-modules (i.e. geometrical and structural constraints). Since the present optimization deals with least construction costs (as objective function), and uses an explicit objective function (not empirical), the user must specify labor costs (unitary material costs, welding, cutting, etc.). This paper is the second part of a series of two articles. The previous paper focused on the ‘Module-Oriented Optimization’ methodology and on the rational constraints (Rigo, Marine Structures 2001). This paper presents the optimization algorithm based on convex linearization and a dual approach (OPTI module). It also includes the optimization of a FSO unit as a detailed example.     

Towards a unified methodology for the simulation of rupture in collision and grounding of ships

The aim of the work is the definition of a procedure for the numerical simulation of the response of ship structures under accidental loading conditions, which suffer various different modes of failure, such as tension, bending, tearing and crushing and in particular to investigate the effect of material modeling, i.e. material curve and rupture criterion as well as mesh size and strain rate effect on the results. To this end, different material models and simulation techniques were used for the simulation of eighteen indentation tests conducted by different research groups. The simulations were performed using the explicit finite element code ABAQUS 6.10-2. The tests refer to the quasi-static and dynamic transverse and in-plane loading of various thin walled structures which represent parts of a ship structure. Three rupture criteria are incorporated into VUMAT subroutine, which interacts with the explicit finite element code and refers to an isotropic hardening material that follows the J₂ flow theory assuming plane stress conditions, in order to investigate the prediction and propagation of rupture. The focus is on investigating whether it is possible to define a unified methodology, which is appropriate for the simulation of all different tests. Consistency in the numerical results is observed with the use of an equivalent plastic strain criterion, in which formulation a cutoff value for triaxialities below −1/3 is included.     

轮对内侧距对机车车辆动力学性能影响的试验研究

在分析国内外轮对内侧距方面已有研究结果的基础上,在不改变车轮踏面形状、轨距和钢轨轨头形状的情况下,进行单纯改变车辆轮对内侧距的滚动台试验研究,分析等效锥度对轮轨接触几何关系的影响,得出以下结论。①在保持轮轨接触几何关系相同的情况下,增加轮对内侧距有利于改善轮轨关系和机车车辆动力学性能。②在车轮踏面形状、轨距、钢轨轨头形状等保持不变的情况下,单纯改变轮对内侧距,必然会导致轮轨接触关系的变化,从而影响机车车辆的动力学性能;对于我国目前采用的车轮踏面形状、轨距、钢轨轨头形状而言,轮对内侧距从1 353 mm变化到1 360 mm,将导致轮轨接触等效锥度的增加,从而降低车辆的运动稳定性临界速度。③轮对内侧距的选取与车轮踏面形状的选择密切相关,在改变轮对内侧距以后,必须根据轮轨接触几何关系的变化重新对其进行综合优化,确定合适的车轮轮缘踏面外形。     

基于等效渗透系数计算衬砌水压力方法研究

对于设置防水板和排导系统的复合式衬砌,由于防水板的隔水作用,围岩渗水主要通过防水板背后的盲管、反滤层及二次衬砌边墙底部排水孔排入隧道底部排水沟.这种地下水排导系统的设置,使得衬砌水压力的计算很难通过简化的解析方法求得.文章从工程实用化角度出发,提出了复合式衬砌等效渗透系数的概念和确定方法,其主要是通过引入虚拟的二次衬砌等效渗透系数“k1”,将设置防水板和排导系统的复合式衬砌的透水能力用等效渗透系数“k1”来表示.在复合式衬砌等效渗透系数的基础上,可以利用整体式衬砌结构的水压力计算方法估算衬砌水压力,等效渗透系数“k1”为复合式衬砌水压力的简化计算提供了有利条件.最后,通过算例验证了这种方法的合理性、有效性.     

自动变速箱换档品质分析模型

建立了自动变速箱换档过程分析的等效模型，所建立的等效模型能够较准确反映出换挡过程的动态特性，可用于换档品质控制的研究，应用所建立的等效模型，对换档过程进行了初步分析，得出了若干有用的结论。     

基于反馈线性化的汽车AMT离合器滑模控制

电控离合器系统中，因为外界环境相当复杂，控制系统存在多种非线性，使得数学模型中参数是摄动的并且同时受到干扰，给机械式自动变速系统（AMT）的控制带来困难，针对离合器液压扫行机构，建立系统非线性动力学模型，进一步应用基于微分几何的反馈线性化方法，将原非线性系统等价为完全可控型线性化模型，然后设计滑模控制器，实车实验结果表明，设计的非线性控制器跟踪精度高，鲁棒性好。     

Optimal controller design for a constrained polynomial vehicle system with an input-state linearized model

This paper presents a new controller design method based on a data-mining polynomial algorithm. We show application of a polynomial data-mining algorithm, where an input-state linearized polynomial vehicle model is developed for very low speed operation and, without introducing any processes with fudge factors, control inputs of a nonlinear system are obtained in the original coordinates. We verify the developed modeling method and controller design method through numerical experiments.     

预应力钢束与空间体单元求交算法研究

预应力钢束在体单元作用时常转化为等效荷载,这时首先需要求出预应力筋与空间四面体单元交点。针对这一问题,提出了常见的预应力圆弧筋和直线筋与四面体单元求交算法,并通过实例验证本算法的准确性,供科研人员与设计人员参考。     

GSM-R中高线性功率放大器的研究

分析非线性失真对于GSM-R的影响;阐述射频功率放大器中的非线性指标;对前馈射频功率放大器前馈系统进行软件仿真,实现了中心频率为932 MHz,带宽为4 MHz,输出功率为20 W的前馈功率放大器.为提高GSM-R中的射频功率放大器线性度提供T一种实用、有效的设计方法.     

水下超高速航行体非线性鲁棒控制器设计

水下航行体在高速运动时,其表面大部分被空泡包裹.航行体尾部与空泡壁的相互作用力的存在使航行体模型具有较强的非线性.文中将基于反馈线性化的非线性鲁棒控制策略应用于水下超高速航行体纵向运动控制.反馈线性化可以实现航行体动力学模型的非线性解耦,得到系统精确线性化模型.针对线性化模型设计系统鲁棒控制器,解决由于模型不准确、参数摄动等引起的鲁棒性问题,仿真结果表明,所设计的鲁棒控制器是有效的.