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Constraint decision-making systems in engineering
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BOOK
On the Sensitivity of Equilibria to the Method of Realization of Unilateral Constraints with Piecewise Smooth Boundaries
Two ways of implementing unilateral holonomic constraints with piecewise smooth boundaries are considered. Examples are given that testify both in favor of the proposed methods and against them. The sensitivity of the equilibria of a system subjected to holonomic constraints with piecewise smooth boundaries to the way these constraints are implemented is also discussed using examples. Two problems from the mechanics of systems constrained by a pair of inextensible weightless tethers are considered. In one of these problems, which is most likely academic in nature, equilibria are found and small oscillations near these equilibria are studied. Another problem relates to tethered systems deployed near a uniformly rotating celestial body. For it, the relative equilibria of a load suspended on a pair of tethers are found, and sufficient conditions for the stability of these relative equilibria are studied.
Journal Article
The impact of public procurement on financial barriers to general and green innovation
This study investigates whether public procurement mitigates or exacerbates innovative enterprises’ financial constraints. We distinguish between general and environmentally beneficial innovative enterprises. Theory suggests that the treatment effects of public procurement, particularly when mediated by the demand-pull effect, may lower a company’s funding constraints for innovation. We test this theory with extended probit models allowing for endogenous treatment and selection. The findings reveal a significantly positive treatment effect of public procurement on the probability of facing financial constraints in both areas: general and environmentally beneficial innovative activities. Thus, the principal implications of this study are (1) that being an innovating SME exacerbates financial constraints and (2) that strengthening SMEs’ participation in European public tenders would not contribute to lowering SMEs’ financial constraints. On the contrary, complementary grants or other financial incentives might be necessary to substantially increase the SMEs’ bidding rates in public tenders.Plain English SummaryPublic procurement incre ases the chance of innovative firms, in particular SMEs, to face financial constraints. This study investigates whether public procurement mitigates or exacerbates financial constraints of enterprises with general or environmentally beneficial innovative activities. The principal implication is that owning a public procurement contract is no instrument to lower innovative firms’, in particular SMEs’, financial constraints. On the contrary, complementary grants or other financial incentives might be necessary to substantially increase the SMEs’ bidding rates in a public tender.
Journal Article
An adaptive NHC-assisted GNSS/INS integrated positioning method
Accurate positioning is essential for train operational efficiency and automation. Although GNSS/INS/Non-Holonomic Constraints (NHC) integration provides continuous navigation, enforcing NHC during train side-slip, vibration, or track irregularities introduces significant positioning errors. To resolve this, we propose an adaptive NHC-assisted GNSS/INS integrated positioning method. First, an EKF tightly couples GNSS and INS measurements. Crucially, we design an NHC validity detector that constructs a test statistic from NHC observation residuals. This statistic is continuously compared against a detection threshold: NHC constraints are selectively activated only when residuals indicate validity; otherwise, they are automatically disabled to prevent error contamination. Field tests on railway lines demonstrate that the adaptive strategy: reduces lateral positioning RMS error by 11.4% compared to forced-NHC approaches.
Journal Article
An integrated scheduling genetic algorithm based on process constraint matrix and family definition coding
To address the complex product-integrated scheduling problem, an improved genetic algorithm based on process constraint matrix and family definition is proposed. The algorithm features a coding method that accurately represents the processing sequence constraints in the product process tree and introduces a simplified method for defining families and sub-processes. On this basis, a hierarchical relationship matrix is derived from the constraint matrix. To resolve the issue of infeasible solutions arising from crossover and mutation operations, a family-based single-parent genetic improvement algorithm is designed. Experimental results validate the effectiveness of the proposed algorithm.
Journal Article
Learning to select SAT encodings for pseudo-Boolean and linear integer constraints
Many constraint satisfaction and optimisation problems can be solved effectively by encoding them as instances of the Boolean Satisfiability problem (SAT). However, even the simplest types of constraints have many encodings in the literature with widely varying performance, and the problem of selecting suitable encodings for a given problem instance is not trivial. We explore the problem of selecting encodings for pseudo-Boolean and linear constraints using a supervised machine learning approach. We show that it is possible to select encodings effectively using a standard set of features for constraint problems; however we obtain better performance with a new set of features specifically designed for the pseudo-Boolean and linear constraints. In fact, we achieve good results when selecting encodings for unseen problem classes. Our results compare favourably to AutoFolio when using the same feature set. We discuss the relative importance of instance features to the task of selecting the best encodings, and compare several variations of the machine learning method.
Journal Article
On the Relatedness and Nestedness of Constraints
The purpose of this opinion paper is providing a platform for explaining and discussing the relatedness and nestedness of constraints on the basis of four claims: (a) task constraints are distributed between the person and the environment and hence are relational variables, (b) being relational, task constraints are also emergent properties of the organism/environment system, (c) constraints are nested in timescales, and (d) a vast set of constraints are correlated through circular causality. Theoretical implications for improving the understanding of the constraints-led approach and practical applications for enhancing the manipulation of constraints in learning and training settings are proposed.
Journal Article
Mining Time-constrained Sequential Patterns with Constraint Programming
Constraint Programming (CP) has proven to be an effective platform for constraint based sequence mining. Previous work has focused on standard frequent sequence mining, as well as frequent sequence mining with a maximum ’gap’ between two matching events in a sequence. The main challenge in the latter is that this constraint can not be imposed independently of the omnipresent frequency constraint. Indeed, the gap constraint changes whether a subsequence is included in a sequence, and hence its frequency. In this work, we go beyond that and investigate the integration of timed events and constraining the minimum/maximum gap as well as minimum/maximum span. The latter constrains the allowed time between the first and last matching event of a pattern. We show how the three are interrelated, and what the required changes to the frequency constraint are. Key in our approach is the concept of an extension window defined by gap/span and we develop techniques to avoid scanning the sequences needlessly, as well as using a backtracking-aware data structure. Experiments demonstrate that the proposed approach outperforms both specialized and CP-based approaches in almost all cases and that the advantage increases as the minimum frequency threshold decreases. This paper is an extension of the original manuscript presented at CPAIOR’17 [5].
Journal Article
Assessing Hierarchical Leisure Constraints Theory after Two Decades
This article assesses the status of hierarchical leisure constraints theory (Crawford & Godbey, 1987; Crawford, Jackson, & Godbey, 1991) regarding many issues. Such issues include clarification and elaboration of some aspects of the original model, a review of studies which have used or examined the model and the extent to which they are confirmatory, critiques of the original model by various authors, and avenues for further research. Conclusions drawn include that the model is cross culturally relevant, that the model may examine forms of behavior other than leisure, and that, while research to date has been largely confirmatory, there is a high potential for the theory to be expanded in order to advance leisure constraints research to the next level.
Journal Article
An identification method for enclosed voids restriction in manufacturability design for additive manufacturing structures
Additive manufacturing (AM) technologies, such as selective laser sintering (SLS) and fused deposition modeling (FDM), have become the powerful tools for direct manufacturing of complex parts. This breakthrough in manufacturing technology makes the fabrication of new geometrical features and multiple materials possible. Past researches on designs and design methods often focused on how to obtain desired functional performance of the structures or parts, specific manufacturing capabilities as well as manufacturing constraints of AM were neglected. However, the inherent constraints in AM processes should be taken into account in design process. In this paper, the enclosed voids, one type of manufacturing constraints of AM, are investigated. In mathematics, enclosed voids restriction expressed as the solid structure is simplyconnected. We propose an equivalent description of simply-connected constraint for avoiding enclosed voids in structures, named as virtual temperature method (VTM). In this method, suppose that the voids in structure are filled with a virtual heating material with high heat conductivity and solid areas are filled with another virtual material with low heat conductivity. Once the enclosed voids exist in structure, the maximum temperature value of structure will be very high. Based upon this method, the simplyconnected constraint is equivalent to maximum temperature constraint. And this method can be easily used to formulate the simply-connected constraint in topology optimization. The effectiveness of this description method is illustrated by several examples. Based upon topology optimization, an example of 3D cantilever beam is used to illustrate the trade-off between manufacturability and functionality. Moreover, the three optimized structures are fabricated by FDM technology to indicate further the necessity of considering the simply-connected constraint in design phase for AM.
Journal Article