A comparison of deterministic,reliability-based and risk-based structural optimization under uncertainty

In this paper, the effects of uncertainty and expected costs of failure on optimum structural design are investigated, by comparing three distinct formulations of structural optimization problems. Deterministic Design Optimization (DDO) allows one the find the shape or configuration of a structure that is optimum in terms of mechanics, but the formulation grossly neglects parameter uncertainty and its effects on structural safety. Reliability-based Design Optimization (RBDO) has emerged as an alternative to properly model the safety-under-uncertainty part of the problem. With RBDO, one can ensure that a minimum (and measurable) level of safety is achieved by the optimum structure. However, results are dependent on the failure probabilities used as constraints in the analysis. Risk optimization (RO) increases the scope of the problem by addressing the compromising goals of economy and safety. This is accomplished by quantifying the monetary consequences of failure, as well as the costs associated with construction, operation and maintenance. RO yields the optimum topology and the optimum point of balance between economy and safety. Results are compared for some example problems. The broader RO solution is found first, and optimum results are used as constraints in DDO and RBDO. Results show that even when optimum safety coefficients are used as constraints in DDO, the formulation leads to configurations which respect these design constraints, reduce manufacturing costs but increase total expected costs (including expected costs of failure). When (optimum) system failure probability is used as a constraint in RBDO, this solution also reduces manufacturing costs but by increasing total expected costs. This happens when the costs associated with different failure modes are distinct. Hence, a general equivalence between the formulations cannot be established. Optimum structural design considering expected costs of failure cannot be controlled solely by safety factors nor by failure probability constraints, but will depend on actual structural configuration.     

In-depth analysis of accidental oil spills from tankers in the context of global spill trends from all sources

This study gives a global overview of accidental oil spills from all sources (> or =700t) for the period 1970-2004, followed by a detailed examination of trends in accidental tanker spills. The present analysis of the number and volume of tanker spills includes temporal and spatial spill trends, aspects of spill size distribution as well as trends of key factors (i.e., flag state, hull type, tanker age, accident cause and sensitivity of location). Results show that the total number and volume of tanker spills have significantly decreased since the 1970s, which is in contrast to increases in maritime transport of oil and to popular perceptions following recent catastrophic events. However, many spills still occur in ecologically sensitive locations because the major maritime transport routes often cross the boundaries of the Large Marine Ecosystems, but the substantially lower total spill volume is an important contribution to potentially reduce overall ecosystem impacts. In summary, the improvements achieved in the past decades have been the result of a set of initiatives and regulations implemented by governments, international organizations and the shipping industry.     

考虑多次余震的钢筋混凝土框架结构地震损伤分析

在时变条件下,考虑结构的累积损伤是风险决策的关键点,对结构性能评估及寿命估算有重要意义。但是,结构累积损伤的计算通常涉及复杂的数学运算。基于此,该文的主要目的是在地震高发区,提出一种简化的估算结构寿命分布的模型。该模型假设给定结构的累积损伤仅由设计基准期内可能发生的一系列地震作用产生,此方法的优点在于可以通过简单的数学运算实现结构寿命估算。对所提出的简化结构寿命模型进行实例应用,以验证该方法的可行性。

     

Risk assessment in maritime transportation

A review is presented of different approaches to quantify the risk in maritime transportation. The discussion of several accident statistics provides a global assessment of the risk levels and its differentiation in ship types and main types of ship losses. Early studies in the probability of ship loss by foundering and capsizing are reviewed. The approaches used to assess the risk of structural design are addressed. Finally a brief account is given of recent development of using formal safety assessments to support decision making on legislation applicable internationally to maritime transportation.     

A fuzzy-logic-based approach to qualitative safety modelling for marine systems

Safety assessment based on conventional tools (e.g. probability risk assessment (PRA)) may not be well suited for dealing with systems having a high level of uncertainty, particularly in the feasibility and concept design stages of a maritime or offshore system. By contrast, a safety model using fuzzy logic approach employing fuzzy IF–THEN rules can model the qualitative aspects of human knowledge and reasoning processes without employing precise quantitative analyses. A fuzzy-logic-based approach may be more appropriately used to carry out risk analysis in the initial design stages. This provides a tool for working directly with the linguistic terms commonly used in carrying out safety assessment. This research focuses on the development and representation of linguistic variables to model risk levels subjectively. These variables are then quantified using fuzzy sets. In this paper, the development of a safety model using fuzzy logic approach for modelling various design variables for maritime and offshore safety based decision making in the concept design stage is presented. An example is used to illustrate the proposed approach.     

Cost-effectiveness criteria for marine oil spill preventive measures

Oil tanker accidents resulting in large quantities of oil spills and severe pollution have occurred in the past, leading to major public attention and an international focus on finding solutions for minimising the risks related to such events. This paper proposes a novel approach for evaluating measures for prevention and control of marine oil spills, based on considerations of oil spill risk and cost effectiveness. A cost model that incorporates all costs of a shipping accident has been established and oil tanker spill accidents have been further elaborated as a special case of such accidents. Utilising this model, novel implementation criteria, in terms of the Cost of Averting a Tonne of oil Spilt (CATS), for risk control options aiming at mitigating the environmental risk of accidental oil spills, are proposed. The paper presents a review of previous studies on the costs associated with oil spills from shipping, which is a function of many factors such as location of spill, spill amount, type of oil, etc. However, ships are designed for global trade, transporting different oil qualities. Therefore, globally applicable criteria must average over most of these factors, and the spill amount is the remaining factor that will be used to measure cost effectiveness against. A weighted, global average cleanup cost of USD 16,000/tonne of oil spilt has been calculated, considering the distribution of oil tanker traffic densities. Finally, the criteria are compared with some existing regulations for oil spill prevention, response and compensation (OPA 90).     

Drivers,barriers and social considerations for AI adoption in SCM

This study explored the challenges and recommendations for implementing Artificial Intelligence (AI) in SC Management (SCM). The experts identified several drivers for AI adoption in SCM, including increased efficiency, improved decision-making, and reduced costs. However, they highlighted several barriers to AI adoption, such as data quality and management issues, resistance to change, and lack of understanding and trust in AI. To overcome these barriers and ensure successful AI implementation, companies should involve all stakeholders, focus on data quality and management, and ensure the AI solution integrates with existing processes and workflows. In addition, companies should also avoid common mistakes when implementing AI, such as neglecting the importance of explainability and transparency in AI decision-making, underestimating the importance of involving all stakeholders, and rushing into large-scale implementation without conducting small-scale pilot projects. By following the recommendations and avoiding common mistakes, companies can harness the benefits of AI in SCM while minimizing risks and challenges.     

Incorporating end-user models and associated uncertainties to investigate multiple stakeholder preferences in system design

The essence of systems engineering lies in enabling rational decision-making that is consistent with the preferences of the system’s stakeholders. Modern approaches, such as value-driven design, attempt to convey the true preferences of the stakeholder using mathematical formulations like value models. A critical step to the formation of value models is the identification of the stakeholders. A primary stakeholder must be identified and then it must be determined how the other stakeholders’ preferences impact the preference of the primary, if they do at all. This paper looks at three stakeholders of an electric vehicle system, all of which could be considered the primary stakeholder dependent on the situation. Novel customer, commercial, and government-oriented value models are created. To understand the impact of customers on the primary stakeholder’s designs, an end-user value-based demand model is developed and a method for integrating end-user preferences into the manufacturer’s value model is demonstrated. Uncertainties associated with the end-users, including those associated with the economy, are quantified and incorporated into a value-based design framework through Monte Carlo simulations. Possible stakeholder risk attitudes are discussed and a rational decision-making strategy to maximize stakeholder’s system value under uncertainty is presented. The resulting designs and the influences of the multiple stakeholders are discussed, showing that the identification and incorporation of the important stakeholders are critical to the systems engineering process and value-based design in particular.     

利用导重法进行结构轻量化设计

结构轻量化设计的目的是以最少的设计资源设计出性能合格的产品结构,以降低产品生产成本,提高产品性价比和市场竞争力。结构轻量化的实质是材料重量在结构几何空间内及构件间的合理分配。导重法是可用于产品结构轻量化的结构优化有效方法,它可适用于包括各类单元的各种产品结构构件尺寸优化与结构几何形状优化以及结构拓扑优化;其目标与约束可以涉及各种结构静动力性态。首先给出结构优化导重法用于结构轻量化设计的具有广泛一般性的数学模型及其求解方法。接着给出一种新的包络函数-方根包络函数,使数目庞大的应力与位移约束凝聚为单值强度约束与单值精度约束;还给出适用于多数产品结构轻量化设计的单性态约束优化实用模型与解法;最后给出两个产品结构轻量化的应用实例,验证了导重法用于轻量化设计的有效性与广泛适用性。     

多级递阶工程结构系统抗地震设计的全局优化

多级递阶工程结构系统是复杂工程项目的主要工程结构依照功能逻辑关系所构成的多层次分支结构系列,表征了常见建设项目的一般性分布。以结构设防烈度为决策变量、地震灾害的多级设防为工程背景,建立了该系统全局优化的数学模型;考虑到系统的结构特点和目标函数的离散性,提出二个层次的优化计算方法,其中递级凝聚法用于大系统建模分析,改进的离散型共轭梯度法和改进的离散型 Lagrange 直接法分别执行具体的最优或次优化计算;算例讨论了复杂项目在抗震设防标准、工程造价和总投资分配方面的优化决策。上述概念、原则与方法为复杂工程的系统化设计、土木工程问题的科学决策提供了理论分析的基础。     

Hexagonal Voronoi pattern detected in the microstructural design of the echinoid skeleton

Repeated polygonal patterns are pervasive in natural forms and structures. These patterns provide inherent structural stability while optimizing strength-per-weight and minimizing construction costs. In echinoids (sea urchins), a visible regularity can be found in the endoskeleton, consisting of a lightweight and resistant micro-trabecular meshwork (stereom). This foam-like structure follows an intrinsic geometrical pattern that has never been investigated. This study aims to analyse and describe it by focusing on the boss of tubercles—spine attachment sites subject to strong mechanical stresses—in the common sea urchin Paracentrotus lividus. The boss microstructure was identified as a Voronoi construction characterized by 82% concordance to the computed Voronoi models, a prevalence of hexagonal polygons, and a regularly organized seed distribution. This pattern is interpreted as an evolutionary solution for the construction of the echinoid skeleton using a lightweight microstructural design that optimizes the trabecular arrangement, maximizes the structural strength and minimizes the metabolic costs of secreting calcitic stereom. Hence, this identification is particularly valuable to improve the understanding of the mechanical function of the stereom as well as to effectively model and reconstruct similar structures in view of future applications in biomimetic technologies and designs.     

不确定视角下产品结构性能优化设计综述与展望

目的 复杂产品在工程装备、航空航天等我国优先发展的战略领域中扮演着不可替代的重要角色,在其结构设计过程中普遍存在着各种不确定性,导致产品结构性能很难实现最优,甚至出现重大故障。方法 针对复杂产品设计过程中的多粒度模糊不确定、随机不确定、不完备区间不确定和高维混合不确定等特点,将不确定性理论与产品结构设计过程相结合,系统地构建了不确定视角下产品结构性能优化设计理论体系,提出了多粒度模糊不确定下产品质量特性精准提取、随机不确定下产品功能结构模块化求解、不完备区间不确定下产品结构方案多属性决策、高维混合不确定下产品关键结构可靠性优化等关键技术,并指出了产品结构性能优化设计的未来发展方向。结论 此设计理论能够充分适应和利用产品设计过程的多种不确定信息,为在结构设计环节切实提升产品性能提供了有力参考。     

Underreporting of maritime accidents to vessel accident databases

Underreporting of maritime accidents is a problem not only for authorities trying to improve maritime safety through legislation, but also to risk management companies and other entities using maritime casualty statistics in risk and accident analysis.This study collected and compared casualty data from 01.01.2005 to 31.12.2009, from IHS Fairplay and the maritime authorities from a set of nations. The data was compared to find common records, and estimation of the true number of occurred accidents was performed using conditional probability given positive dependency between data sources, several variations of the capture–recapture method, calculation of best case scenario assuming perfect reporting, and scaling up a subset of casualty information from a marine insurance statistics database.The estimated upper limit reporting performance for the selected flag states ranged from 14% to 74%, while the corresponding estimated coverage of IHS Fairplay ranges from 4% to 62%. On average the study results document that the number of unreported accidents makes up roughly 50% of all occurred accidents. Even in a best case scenario, only a few flag states come close to perfect reporting (94%).The considerable scope of underreporting uncovered in the study, indicates that users of statistical vessel accident data should assume a certain degree of underreporting, and adjust their analyses accordingly. Whether to use correction factors, a safety margin, or rely on expert judgment, should be decided on a case by case basis.     

Multi-criteria risk analysis to improve safety in manufacturing systems

The drive to lower operating costs and improve manufacturing efficiency has led many manufacturing companies to implement different methodologies in order to identify a suitable risk assessment model. So, the concern for safety in industrial activities, both inside the establishments and in their surroundings, has a crucial role. As a result, many laws, regulations and risk analysis techniques are well adapted to industry needs since they were developed for its purpose. However increasing safety is often difficult, especially when you have already obtained good results, so the aim of our paper is the proposal of a new methodological approach called the safety improve risk assessment (SIRA) by integrating the conventional aspects of the popular failure mode, effects, and criticality analysis (FMECA) procedure with economic considerations in order to take into account the risk and to minimise the total safety costs by defining a specific index called total risk priority number (TRPN) index. The index proposed is based on the improved risk priority number (IRPN) and the analytic network process (ANP), a multi-criteria decision-making technique.     

Multi-item distribution network design problems under volume discount on transportation cost

This study considers the distribution network design problems of multi-echelon, multi-item supply chains under volume (weight) discounts on transportation costs. Minimising the total network cost requires determining the following: (1) the service area of distribution centres (DCs); (2) the assignment of retail stores to DCs; and (3) the inventory volume at DCs. This study compares various replenishment policies and discusses the effects of such policies on distribution network design. In general, the results show that single-cluster replenishment is superior to joint cluster replenishment. However, joint cluster replenishment may be superior to single-cluster replenishment under volume (weight) discounts on transportation costs. The results additionally show that single-item replenishment is inferior to multi-item replenishment under volume (weight) discounts on transportation costs. All the problems are formulated as piecewise non-linear programming models with multiple variables. Algorithms are proposed for solving these piecewise non-linear programming problems. Several numerical studies demonstrate the solution procedures and the effects of changing parameters on decision-making.     

Underreporting of maritime accidents to vessel accident databases

Underreporting of maritime accidents is a problem not only for authorities trying to improve maritime safety through legislation, but also to risk management companies and other entities using maritime casualty statistics in risk and accident analysis.This study collected and compared casualty data from 01.01.2005 to 31.12.2009, from IHS Fairplay and the maritime authorities from a set of nations. The data was compared to find common records, and estimation of the true number of occurred accidents was performed using conditional probability given positive dependency between data sources, several variations of the capture–recapture method, calculation of best case scenario assuming perfect reporting, and scaling up a subset of casualty information from a marine insurance statistics database.The estimated upper limit reporting performance for the selected flag states ranged from 14% to 74%, while the corresponding estimated coverage of IHS Fairplay ranges from 4% to 62%. On average the study results document that the number of unreported accidents makes up roughly 50% of all occurred accidents. Even in a best case scenario, only a few flag states come close to perfect reporting (94%).The considerable scope of underreporting uncovered in the study, indicates that users of statistical vessel accident data should assume a certain degree of underreporting, and adjust their analyses accordingly. Whether to use correction factors, a safety margin, or rely on expert judgment, should be decided on a case by case basis.     

Effectiveness of maritime safety control in different navigation zones using a spatial sequential DEA model: Yangtze River case

This paper aims to analyze the effectiveness of maritime safety control from the perspective of safety level along the Yangtze River with special considerations for navigational environments. The influencing variables of maritime safety are reviewed, including ship condition, maritime regulatory system, human reliability and navigational environment. Because the former three variables are generally assumed to be of the same level of safety, this paper focuses on studying the impact of navigational environments on the level of safety in different waterways. An improved data envelopment analysis (DEA) model is proposed by treating the navigational environment factors as inputs and ship accident data as outputs. Moreover, because the traditional DEA model cannot provide an overall ranking of different decision making units (DMUs), the spatial sequential frontiers and grey relational analysis are incorporated into the DEA model to facilitate a refined assessment. Based on the empirical study results, the proposed model is able to solve the problem of information missing in the prior models and evaluate the level of safety with a better accuracy. The results of the proposed DEA model are further compared with an evidential reasoning (ER) method, which has been widely used for level of safety evaluations. A sensitivity analysis is also conducted to better understand the relationship between the variation of navigational environments and level of safety. The sensitivity analysis shows that the level of safety varies in terms of traffic flow. It indicates that appropriate traffic control measures should be adopted for different waterways to improve their safety. This paper presents a practical method of conducting maritime level of safety assessments under dynamic navigational environment.     

Optimal design base shear forces for reinforced concrete buildings considering seismic reliability and life-cycle costs

The objective of this study is to propose a novel estimation procedure for optimal design base shear forces for reinforced concrete (RC) buildings while considering the seismic reliability and life-cycle costs (LCCs) incurred by life-cycle earthquake events. By simulating life-cycle earthquake events within a specified period and using nonlinear dynamic analysis, including earthquake occurrences and their peak ground accelerations (PGAs), this study also derives the damage states of an RC building considering the effect of the cumulative damage. Additionally, besides life-cycle earthquake events, a simplified model is developed to modify the structural properties of a structure without seismic repair after earthquakes. Given the uncertainty of the occurrence time and PGAs of earthquake events, the seismic reliability, and expected current values of LCCs are calculated using Monte Carlo simulation. Although the case study addresses only an RC building with five stories in Taipei, optimal design base shear forces for low-rise RC buildings calculated via the same procedure can be derived and utilized when making decisions on the seismic level of a building based on safety and economic considerations. Therefore, the proposed method can help both owners and investors to identify LCCs of RC buildings due to seismic structural damage within a specified service life.     

不同抗震区结构承载力裕度的概率结构分析与比较

按现行规范设计的不同抗震区的结构安全性能和水平是否存在显著差异?为澄清这一问题,该文构造了一个能合理反映结构整体安全性能的承载力裕度参数,并通过承载力裕度概率密度函数的比较间接研究不同抗震区结构安全性能的差异.基于上述思路,在概率密度演化理论的框架下,由可靠度问题的不同求解方式出发,导出了承载力裕度的密度变换解及其δ序...     

A single-product network design model with lead time and safety stock considerations

Most existing network design and facility location models have focused on the trade-off between the fixed costs of locating facilities and variable transportation costs between facilities and customers. However, operational performance measures such as service levels and lead times are what motivates customers to bring business to a company and should be considered in the design of a distribution network. While some previous work has considered lead times and safety stocks separately, they are closely related in practice, since safety stocks are often set relative to the distribution of demand over the lead time. In this paper we consider a two-stage supply chain with a production facility that replenishes a single product at retailers. The objective is to locate Distribution Centers (DCs) in the network such that the sum of the location and inventory (pipeline and safety stock) costs is minimized. The replenishment lead time at the DCs depends on the volume of flow through the DC. We require the DCs to carry enough safety stock to maintain the prescribed service levels at the retailers they serve. The explicit modeling of the relationship between the flows in the network, lead times and safety stocks allows us to capture the trade-off between them. We develop a Lagrangian heuristic to obtain near-optimal solutions with reasonable computational requirements for large problem instances.