液压支架油缸内壁缺陷修复机械臂的运动学分析与仿真

针对矿用液压支架油缸内壁局部缺陷修复,设计一种能深入液压支架油缸筒内进行内壁修复的焊接机械臂。基于改进D-H参数建模方法,对设计的内表面修复焊接机械臂进行运动学建模,并求解了内表面修复焊接机械臂的正、逆运动学。借助MATLAB软件,采用蒙特卡洛法,对该焊接机械臂的有效工作空间进行了仿真分析,利用Robotics Toolbox工具箱对油缸内壁缺陷修复机械臂进行关节轨迹规划,通过仿真得到各关节的角位移、角速度、角加速度曲线。仿真结果表明：该机械臂运行平稳,轨迹连续,满足运动学要求。     

基于涂层厚度模型的机器人喷涂轨迹规划研究

为了实现大型复杂曲面的喷涂轨迹规划,提出一种基于涂层厚度模型的高铁白车身机器人喷涂轨迹规划方法。基于静态涂层厚度的椭圆双β分布模型,分析喷涂的累计涂层厚度分布规律,提出一种用于评估相对不均匀性的指标RU,并基于RU指标,通过轨迹重叠的方式保证了涂层厚度的一致性。通过曲曲面的分割与合并,实现了喷涂区域的划分,同时基于包围盒法确定了机器人喷涂路径点空间坐标信息。实验结果表明：基于涂层厚度模型的轨迹规划方法能够有效保证喷涂效果的均匀性,并成功应用于高铁白车身的机器人喷涂加工,显著提升了喷涂质量与效率。     

基于改进粒子群算法的线缆路径规划方法研究

针对复杂机电产品布线路径规划过程中存在的效率较低、可应用性差等问题,提出一种改进粒子群算法,使用栅格法对布线空间进行划分,对障碍物建模并进行方向包围盒处理。为了避免算法在迭代过程中陷入局部最优,引入非线性逐渐递减的惯性权重与异步变化的学习因子,并且将贴壁约束加入到路径规划的过程中,保证线缆在敷设时路径的合理性。最后在仿真试验中,与标准粒子群算法进行对比,验证了改进后算法的合理性与可行性。     

基于Hermite插值的管片拼装机轨迹规划

盾构施工中,管片拼装机需要先完成一环的拼装,才能往前进行推进。目前管片拼装机工作效率较低,直接影响着掘进速度。为了提高管片拼装机的拼装效率,结合Hermite插值算法提出一种新的拼装轨迹规划方法,通过各动作始末两点进行Hermite插值,构造出五次多项式,通过加速度、功率等约束解出各具体解。选取用时最长的作为时间基准,重新构造其余五次多项式。在降低启动冲击的同时,将管片拼装机的拼装效率提升了近一倍。     

Untangling decision tree and real options analyses: a public infrastructure case study dealing with political decisions,structural integrity and price uncertainty

Managerial flexibility in infrastructure investment and replacement decisions adds value. Real options analysis (ROA) captures this value under uncertain market prices. The concept of ROA is that future unfavourable payoffs can be deferred as soon as more information about market prices becomes available. The popularity of ROA is seen in a growing number of case studies on real assets. Despite its increasing popularity, ROA has not gained a foothold in public infrastructure decision making. One of the difficulties in the application of ROA is the required estimation of market variables. To avoid this, a simplified but not correct version of ROA is easily applied, referred to as a Decision Tree Approach (DTA) to ROA. Another difficulty is that infrastructure assets are subject to other types of uncertainties, defined here as asset uncertainties. This study investigates the value of managerial flexibility in a public infrastructure replacement decision. The uncertainty drivers are the strength of a bridge, political decisions regarding traffic flow and the price development of construction costs. Three valuation approaches are compared: DTA, ROA and the DT approach to ROA. Although it is complex, ROA certainly adds value in public infrastructure decision making when market price uncertainty is prevalent. However, in the absence of reasonable estimates of market variables, the DT approach to ROA is the best alternative. In the absence of market price uncertainties, ROA should be avoided DTA is to be preferred.     

David Godschalk

David R. Godschalk, professor emeritus in the Department of City and Regional Planning at the University of North Carolina, Chapel Hill, passed away in early 2018. In this essay we reflect on Dave’s planning scholarship and practice. We discuss his main contributions in 4 prominent areas. First is the importance of public participation and collaboration for the planning and governance of communities. He argued for democratizing and recasting public participation, with planners working alongside community members coproducing plans and incorporating uncertainty, new information, and different viewpoints. Second is Dave’s focus on the tenets of the comprehensive plan and its core element, the land use plan. In the plan, central principles of livable urban forms and model planning processes can be integrated and translated to practice. With academic collaborators and practitioners he pioneered theoretical and empirical research on what constitutes a high-quality plan, a fundamental question at the heart of planning. Third is his research demonstrating how spatial planning can be used for hazard mitigation and urban resilience. This work forged a new generation of planning academics and practitioners who focused on hazard plans for predisaster mitigation and postdisaster recovery at multiple governmental levels. Finally, fourth is his personal involvement in planning-related institutions that he helped create, lead, or steer. In his various roles as scholar, teacher, mentor, collaborator, supervisor, planning director, and elected official, Dave touched the lives of many who now build on his contributions in creating better communities.     

Changing Residential Land Use Regulations to Address High Housing Prices

Problem, research strategy, and findings: In the past 3 decades, a series of presidential administrations—and the APA—have recommended that cities update their zoning codes to enable more affordable and market-rate housing development. I identify 5 main categories of policy recommendations they have suggested and then assess Los Angeles’s (CA) zoning changes in these categories between 2000 and 2016. I answer 2 questions: First, what zoning changes did Los Angeles adopt to address housing affordability? Second, how were these changes initiated, and what were their scope and geographic extent? I find that Los Angeles made modest progress in the 5 policy categories. The city left its large-lot, single-family zoning mostly untouched, but it rezoned roughly 1,200 acres citywide to allow at least 50 housing units per acre, reduced parking requirements in some areas, made it easier to build accessory dwelling units, and adopted new incentives for affordable housing. Several policy changes resulted from new state laws, and Los Angeles voters approved new incentives for affordable housing near transit. Homeowner influence likely prevented the municipality from engaging in larger zoning reforms. I do not study the effects of Los Angeles’s regulatory changes on housing production and prices, but such research is an important next step. I also do not assess new regulations that counteracted the impact of the 5 categories of policy recommendations.

Takeaway for practice: This research suggests 2 lessons: 1) Planners should encourage state governments to preempt local zoning when it reduces affordable housing options and there is limited local political will for change, and 2) planners should identify feasible and effective zoning changes that would increase affordable housing given local considerations.     

Conceptualizing the pedestrian mall in post-war North America and understanding its transatlantic transfer through the work and influence of Victor Gruen

Pedestrianization was an established concept among modernist architects and planners long before the first post-war pedestrian malls were built in North American downtowns. Post-war pedestrian-oriented suburban shopping malls, such as Northland near Detroit, MI and Northgate in Seattle, WA, linked retail success to the pedestrian shopping experience. This propelled the existing but then-untested assumption that planning downtowns to mimic suburban shopping centres by pedestrianizing main streets would revitalize downtown retail districts. Despite the modern origins of the pedestrianization concept, the rhetorical cues of post-war architects and planners in North America mask its modern roots and employ nostalgic imagery of pre-industrial European urbanism, implying European origin of the concept. Although imagery of European charm became a means of packaging modernist ideas of pedestrianization, the design proposals rarely referenced or replicated actual European precedents. Furthermore, while much research implies a linear transfer of pedestrianization ideas from Europe to North America, professionals in Europe also looked to North American shopping malls and pedestrian streets for guidance in addressing their own challenges with accommodating automobiles in downtowns.     

Building urban resilience with nature-based solutions: How can urban planning contribute?

Cities face increasing environmental, social and economic challenges that together threaten the resilience of urban areas and the residents who live and work there. These challenges include chronic stresses and acute shocks, amplified by climate change impacts. Nature-based solutions have emerged as a concept for integrating ecosystem-based approaches to address a range of societal challenges. Nature-based solutions directly address and contribute to increased urban resilience. However, implementing nature-based solutions is inherently complex, given the range of ecosystem services, their multi-functionality and the trade-offs between functions, and across temporal and spatial scales. Urban planning can play a substantial role to support the implementation of nature-based solutions and to manage trade-offs and conflicts, as well as how social equity dimensions are considered. This paper presents a framework that guides the application of urban planning to nature-based solutions’ implementation, by addressing key trade-offs across temporal, spatial, functional and social equity aspects. The framework highlights the key questions, and the supporting information required to address these questions, to underpin the inclusion of nature-based solutions for urban resilience. We find that while urban planning can contribute substantially, there are continuing gaps in how the inherently anthropocentric urban planning processes can give voice to non-human nature.     

From mise en valeur to cooperation – Ponts-et-Chaussées engineers overseas and the rise of planning expertise in the twentieth century

By shedding light on the overseas branch of the Corps des Ponts-et-Chaussées (CPC), this article analyses the scientific and technical contribution of this sub-group of engineers in the post-Second World War era. After introducing the historical background of the early involvement of the CPC in the French colonies, this paper concentrates on the late colonial period. Details of the strong interconnectedness of metropolitan and overseas technical expertise are provided. It is shown that civil engineering practised overseas not only enhanced many technical fields within the traditional preserve of the Corps but also facilitated the rapid expansion of the Corps out of this very preserve. Engineers were prompt in including urban expertise and town planning, rural hydraulic and hydrogeology within their current field of activities. Consequences were highly significant not only for overseas urban and rural milieu, but also for metropolitan territories undergoing post-war redevelopment. The last section of this article shows how the techno-scientific practice acquired overseas was instrumental in the post-colonial years to foster the redeployment of the CPC as a whole in the different fields of civil engineering on an international scale.