Robust optimum design of tuned liquid column damper in seismic vibration control of structures under uncertain bounded system parameters

The optimum design of a tuned liquid column damper (TLCD) considering system parameter uncertainty is usually performed by minimising the performance measure obtained by the total probability theory without any consideration to the variation of its performance due to parameter uncertainty. However, such a design method does not necessarily correspond to an optimum design in terms of maximum response reduction as well as its minimum dispersion. Furthermore, such approach cannot be applied in many real situations when the required detailed information about the uncertain parameters is limited. The robust design optimisation (RDO) of a TLCD system to mitigate seismic vibration effect in which the bounds on the magnitude of the uncertain properties of the structural and ground motion model parameters are only required is attempted in this study. The RDO is formulated as a two-criterion optimisation problem where the weighted sum of the maximum root mean square displacement of the structure and its dispersion is minimised. The conventional interval analysis-based bounded optimum solution is also obtained to demonstrate the effectiveness of the proposed RDO approach. A numerical study elucidates the effect of parameter uncertainty on the RDO of TLCD parameters by comparing the RDO results with the bounded optimum results.     

Applied Energy

It is acknowledged that the conventional design methods can easily lead to oversized system or unsatisfactory performance for different design conditions. Most existing studies on design optimization of net zero energy building ( nZEB) are conducted based on deterministic data/information. However, the question is:How is the actual performance of a design nZEB in different years considering uncertainties? This study, therefore, proposed a robust design method for sizing renewable energy systems in nZEB concerning uncertainties in renewable resources and demand load. The proposed robust design method is applied to the planning of renewable energy system for the Hong Kong Zero Carbon Building. The annual performance of nZEB under the optimal design options are systematically investigated and compared using the proposed robust design method and the deterministic method. It is meaningful to obtain a fitting formula to identify the relationship between the probability of achieving annual zero energy balance and the design mismatch ratio. On the basis of Monte Carlo uncertainty propagation methods, the uncertainty of nZEB performance is quantified which provides flexibility for designers in selecting appropriate design options according to the required probability of achieving nZEB during the design stage.     

Robust optimal design of renewable energy system in nearly/net zero energy buildings under uncertainties

It is acknow ledged that the conventional design methods can easily lead to oversized system or unsatisfactory performance for different design conditions. M ost existing studies on design optimization of net zero energy building( nZ EB) are conducted based on deterministic data / information. How ever,the question is: How is the actual performance of a design nZ EB in different years considering uncertainties? This study,therefore,proposed a robust design method for sizing renew able energy systems in nZ EB concerning uncertainties in renew able resources and demand load. The proposed robust design method is applied tothe planning of renew able energy system for the Hong Kong Zero Carbon Building. The annual performance of nZ EB under the optimal design options are systematically investigated and compared using the proposed robust design method and the deterministic method. It is meaningful to obtain a fitting formula to identify the relationship betw een the probability of achieving annual zero energy balance and the design mismatch ratio. On the basis of M onte Carlo uncertainty propagation methods, the uncertainty of nZ EB performance is quantified w hich provides flexibility for designers in selecting appropriate design options according to the required probability of achieving nZ EB during the design stage.     

基于变形的土石坝地震易损性分析

地震易损性分析是地震风险分析的重要组成部分,可以预测结构在遭受不同等级地震荷载作用下发生各级破损的概率。土石坝在地震作用下易发生不同程度的破坏,对其进行易损性分析可以为土石坝地震风险分析及评价提供有效途径。考虑土石坝材料参数及地震动输入不确定性因素的影响,提出了基于变形的土石坝地震易损性分析方法。采用正交设计法选取材料参数样本组合,分别施加不同地震峰值加速度进行地震反应分析,基于坝顶相对沉陷破损评价指标,给出了大坝的易损性曲线。以云鹏心墙土石坝为例进行了地震易损性分析,得到大坝不同震损等级的风险概率,对土石坝地震风险评估和抗震设计优化、维修加固决策等具有重要意义和应用价值。     

Integrating robustness indicators into multi-objective optimization to find robust optimal low-energy building designs

Uncertainties can have a large influence on building performance and cause deviations between predicted performance and performance during operation. It is therefore important to quantify this influence and identify robust designs that have potential to deliver the desired performance under uncertainties. Generally, robust building designs are identified by assessing the performance of multiple design configurations under various uncertainties. When exploring a large design space, this approach becomes computationally expensive and infeasible in practice. Therefore, we propose a simulation framework based on multi-objective optimization and sampling strategies to find robust optimal designs at low computational costs. The genetic algorithm parameters of optimization are fine tuned to further enhance the computational efficiency. Furthermore, a modified fitness function is implemented to use minimax regret robustness method in the optimization loop. The implemented simulation framework can save up to 94–99% of computational time compared to full factorial approach, while identifying the same robust designs.     

Robust nonlinear decision mapping approach for online bus speed control under uncertainty

The degradation of bus system attractiveness is primarily caused by low-level service quality and reliability. As an essential technology for bus operation management, online bus speed control has proven to be a flexible and effective solution to mitigate bus bunching and enhance the service level of bus operation systems. In this study, we propose a robust nonlinear decision mapping (RNDM) approach that uses real-time key bus system states to control bus speeds and accounts for uncertainties associated with passenger demands at stations and traffic speeds of interstation links. We develop this approach through a design process that involves learning the input–output mapping relation of a nonlinear programming simulation-based optimization (NLPSO) method using regression tree with AdaBoost. Critical parameters of the fitted regression tree with AdaBoost are then optimized offline using a distributionally robust simulation-based optimization (DRSO) model that is solved by a simulation-based optimization (SO) algorithm. The resulting RNDM method effectively handles two types of uncertainties, expressed by two ambiguity sets of probability distributions, and ensures good bus operation performance even under worst-case uncertainty levels. Numerical experiments reveal that the RNDM, NLPSO, and integer programming SO (IPSO) methods successfully mitigate bus bunching and improve service efficiency and robustness, compared to the no-control scenario. Furthermore, the RNDM method outperforms NLPSO and IPSO in terms of comprehensive performance under uncertainties and demonstrates practical operability. In conclusion, this study presents an innovative general framework that uses a nonlinear decision mapping optimized offline by an SO approach to address online simulation-based optimal decision-making problems under uncertainties, which can be applied to solve similar problems.     

Estimating uncertainty in terrestrial critical loads and their exceedances at four sites in the UK

Critical loads are the basis for policies controlling emissions of acidic substances in Europe and elsewhere. They are assessed by several elaborate and ingenious models, each of which requires many parameters, and have to be applied on a spatially-distributed basis. Often the values of the input parameters are poorly known, calling into question the validity of the calculated critical loads. This paper attempts to quantify the uncertainty in the critical loads due to this "parameter uncertainty", using examples from the UK. Models used for calculating critical loads for deposition of acidity and nitrogen in forest and heathland ecosystems were tested at four contrasting sites. Uncertainty was assessed by Monte Carlo methods. Each input parameter or variable was assigned a value, range and distribution in an objective a fashion as possible. Each model was run 5000 times at each site using parameters sampled from these input distributions. Output distributions of various critical load parameters were calculated. The results were surprising. Confidence limits of the calculated critical loads were typically considerably narrower than those of most of the input parameters. This may be due to a "compensation of errors" mechanism. The range of possible critical load values at a given site is however rather wide, and the tails of the distributions are typically long. The deposition reductions required for a high level of confidence that the critical load is not exceeded are thus likely to be large. The implication for pollutant regulation is that requiring a high probability of non-exceedance is likely to carry high costs. The relative contribution of the input variables to critical load uncertainty varied from site to site: any input variable could be important, and thus it was not possible to identify variables as likely targets for research into narrowing uncertainties. Sites where a number of good measurements of input parameters were available had lower uncertainties, so use of in situ measurement could be a valuable way of reducing critical load uncertainty at particularly valuable or disputed sites. From a restricted number of samples, uncertainties in heathland critical loads appear comparable to those of coniferous forest, and nutrient nitrogen critical loads to those of acidity. It was important to include correlations between input variables in the Monte Carlo analysis, but choice of statistical distribution type was of lesser importance. Overall, the analysis provided objective support for the continued use of critical loads in policy development.     

垃圾填埋场重力式垃圾坝的工程设计

结合承德市垃圾填埋场工程,探讨了垃圾坝的结构设计原则、主要计算公式、设计参数以及设计计算中存在的常见问题,并对重力式垃圾坝的结构设计提出了优化措施.通过科学设计保证了砌石垃圾坝的新旧坝嵌套工程的安全性和可行性.     

预应力人字形斜支柱加固法的设计及应用

某水库老闸交通桥是连接水库大坝与前方基地的惟一交通要道 ,原框架构件载重按照汽 - 13设计 ,现要求将原框架构件按照汽 - 15进行加固改造设计。在不影响正常交通的条件下 ,工程运用系统优化原理 ,选择了预应力人字形斜支柱加固的方法 ,并进行了设计及计算     

Partial factors for imposed loads in areas for storage and industrial use

The procedures for reliability verification of new or existing buildings are calibrated to account for uncertainties and variability of resistance and load parameters. However, present standards often provide a single approach to specification of design values of all imposed loads on buildings without particular distinction between loads associated with considerable uncertainties and well-defined loads. While the former are represented by common loads in office and residential buildings, the latter, including loads due to storage of materials, material handling equipment, machinery or tanks, require different approaches for estimating design values. This contribution identifies the characteristics of well-defined imposed loads and proposes a methodology for calibrating partial factors. Key steps of the methodology consist of assessing static load effect, dynamic amplification if relevant, model uncertainty, sensitivity factors and target reliability. Careful consideration of these influences then yields partial factors that reflect reduced uncertainties in estimating the effects of well-defined imposed loads. It appears that the commonly accepted partial factor of 1.5 in Eurocodes may be reduced. When multiple crossings are considered, the partial factor can be taken independent of the number of crossings while the characteristic value is adjusted. Further studies should be particularly focused on advanced probabilistic modelling of dynamic amplification and of model uncertainties.     

高心墙堆石坝坝基廊道受力特性研究

在中国水资源最为丰富的西部地区,河床覆盖层厚达数十米甚至百米,一大批土石坝正在和将在这些大江大河上建设。坝体心墙与坝基防渗墙多采用廊道这种结构型式进行连接,廊道受力条件复杂,是工程成败的关键,但是有些已建工程却出现了廊道漏水的现象,廊道开裂和结构缝破坏成为亟待解决的问题。为了对廊道受力情况和开裂规律有一个清楚的认识,分析总结了几个工程廊道的监测资料,同时基于混凝土非线性本构理论,建立有限元模型对廊道进行了数值模拟。对监测结果和数值计算结果进行对比分析之后,探讨了廊道中的结构缝问题和廊道整体的受力规律,指明了廊道中需要重点关注的易开裂部位,为廊道合理配筋提供了指导,同时为类似工程的决策提供参考。     

小型水坝的地震安全(英文)

大多数用于灌溉和供水的坝为高度小于 15 m 的土坝,并称之为乡村坝。国际大坝委员会所辖大坝的坝高都在15 m 以上,这些小型水坝并不在委员会管辖范围之内。通常,乡村坝由地方社区或水坝工程建设经验不足的组织资助修建起来的,印度尤其如此。例如 1 月 26 日发生在印度古茶拉底省的 Bhuj 地震,波及到 240 座水坝。显然这些坝的质量远比不上水电站大坝的质量,然而小型水坝的事故将会影响到整个大坝行业的前景,所以这些乡村水坝也应该满足基本的设计与安全准则,以免对整个大坝行业造成负面影响。     

Optimization of structures under stochastic loads

The objective of this study is to develop a method for design under multiple stochastic loads based on optimization. The objective function, such as cost, is minimized under the constraint that the probabilities of various limit states being reached are within allowable limits. The loads are treated as random processes and their combined effects evaluated by the load coincidence method. The limit states considered are either yielding or first plastic hinge at the member level or plastic collapse at the system level. A penalty function approach and a Sequential Unconstrained Minimization method are used. Sensitivity studies with respect to the load parameters are carried out. The dependence of the resultant optimal design on the constraints used, e.g. at the member or system level, is investigated. The proposed approach to the problem is shown to be a viable method and the design using bi-level (member and system) reliability constraints is shown to yield more risk-consistent results.     

钢管混凝土截面形状的比选研究

不同截面形状的钢管混凝土在不同的压弯条件下所表现出来的承载力性质是不同的,当给定压弯设计荷载后不同截面形状的钢管混凝土具有不同的经济性。通过计算和分析不同形状钢管混凝土的承载能力,找出了一种实用的优选截面形状的方法,使构件在满足承载力要求的前提下经济性最佳,对钢管混凝土截面选型具有参考价值。     

Proposed robust tuned mass damper for response mitigation in buildings exposed to multidirectional wind

The most common device for control of tall buildings under wind loads is the tuned mass damper (TMD). However, during their lifetimes, high‐rise and slender buildings may experience natural frequency changes under wind speed, ambient temperatures and relative humidity variations, among other factors, which make the TMD design challenging. In this paper, a proposed approach for the design of robust TMDs is presented and investigated. The approach accounts for structural uncertainties, optimization objectives and input excitation (wind or earthquake). For the use of TMDs in buildings, practical design parameters can be different from the optimum ones. Nevertheless, predetermined optimal parameters for a primary structure with uncertainties are useful to attain design robustness. To illustrate the applicability of the proposed approach, an example of a very slender building with uncertain natural frequencies is presented. The building represents a case study of an engineered design that is instructive. Basically, due to its geometry, the building behaves differently in one lateral direction (cantilever building) than the other (shear building). The proposed approach shows its robustness and effectiveness in reducing the response of tall buildings under multidirectional wind loads. In addition, linear‐quadratic Gaussian and fuzzy logic controllers enhanced the performance of the TMD. Copyright © 2012 John Wiley & Sons, Ltd.     

单层网壳结构弹塑性稳定性和优化设计研究

以民航博物馆不规则连续单层网壳结构为例,对单层网壳考虑弹塑性稳定性和优化设计进行探讨。比较了各荷载工况作用下的几何非线性极限承载力、弹塑性非线性极限承载力与荷载标准值之比和线弹性外力势能的分布规律,初步探讨了在诸多荷载组合工况中选择单层网壳结构弹塑性稳定极限承载力控制工况的方法。探讨单层网壳考虑弹塑性稳定优化设计的实用简化方法,提出了杆件截面优化的应力比缩减分层法,使复杂的优化设计问题简单化。     

Challenges of high dam construction to computational mechanics

The current situations and growing prospects of China’s hydro-power development and high dam construction are reviewed, giving emphasis to key issues for safety evaluation of large dams and hydro-power plants, especially those associated with application of state-of-the-art computational mechanics. These include but are not limited to: stress and stability analysis of dam foundations under external loads; earthquake behavior of dam-foundation-reservoir systems, mechanical properties of mass concrete for dams, high velocity flow and energy dissipation for high dams, scientific and technical problems of hydro-power plants and underground structures, and newly developed types of dam-Roll Compacted Concrete (RCC) dams and Concrete Face Rock-fill (CFR) dams. Some examples demonstrating successful utilizations of computational mechanics in high dam engineering are given, including seismic nonlinear analysis for arch dam foundations, nonlinear fracture analysis of arch dams under reservoir loads, and failure analysis of arch dam-foundations. To make more use of the computational mechanics in high dam engineering, it is pointed out that much research including different computational methods, numerical models and solution schemes, and verifications through experimental tests and filed measurements is necessary in the future. Selected from Computational Mechanics, Proceedings of the Sixth World Congress on Computational Mechanics in Conjunction with the Second Asian-Pacific Congress on Computational Mechanics, Tsinghua University Press & Springer, 2004, 154–166     

Uncertainties in critical loads and target loads of sulphur and nitrogen for European forests: Analysis and quantification

An analysis of the uncertainties in critical loads and target loads of sulphur (S) and nitrogen (N) for 182 European forest soils was carried out using the Very Simple Dynamic (VSD) model. The VSD model was calibrated with a Bayesian approach using prior probability functions for model parameters based on literature data, data from 200 Dutch forest sites and from simulated denitrification rates from a detailed ecosystem model. The calibration strongly improved the fit of the model to observed soil and soil solution concentrations, especially for pH and base saturation. Calibration also narrowed down the ranges in input parameters. The uncertainty analysis showed which parameters contribute most to the uncertainty in the critical loads and target loads. Base cation weathering and deposition and the parameters describing the H-Al equilibrium in the soil solution determine the uncertainty in the maximum critical loads for S, CL_max(S), when based on the aluminium to base cation (Al/Bc) criterion. Uncertainty in CL_max(S) based on an acid neutralizing capacity (ANC) criterion is completely determined by base cation inputs alone. The denitrification fraction is the most important source of uncertainty for the maximum critical loads of N, CL_max(N). N uptake and N immobilisation determine the uncertainties in the critical load for N as a nutrient, CL_nut(N). Calibration of VSD reduced the uncertainty: the coefficient of variation (CV) was reduced for all critical loads and criteria. After calibration, the CV for CL_max(S) was below 0.4 for almost all plots; however for CL_max(N) high values occurred for plots with high denitrification rates. Model calibration also improved the robustness of target load estimates: after calibration, no target loads were needed in any of the simulations for 40% of the plots, with the uncalibrated model there was a positive probability for the need of a target load for almost all plots.     

Optimum design of laminated composite plates to maximize buckling load using MFD method

This paper presents optimal design of simply supported laminated composite plates subject to given in-plane static loads for which the critical failure mode is buckling. The objective function is to maximize the buckling load capacity of laminated plates and the fiber orientation is considered as design variable. The first-order shear deformation theory is used for the finite element analysis. In this paper, the effects of bending–twisting coupling are also included for the buckling optimization. The modified feasible direction method is used as an optimization method. Also, computer programs are coded in MATLAB and Golden Section method is adapted in this program for the optimal design of laminated plates for maximum buckling load. The effect of width-to-thickness ratio, aspect ratio, number of layers, material anisotropy, load ratios (N_y/N_x), uncertainties in material properties and functionally graded materials on the results is investigated and compared.     

拱坝体形优化的有限元分析研究

选择对数螺旋拱圈,以拱梁分载法为基础,采用有限元方法进行拱坝应力分析和体形优化,提出拱坝体形优化方案,对提高拱坝的安全度和降低造价、提高拱坝设计水平具有重要意义。