In this paper the identification problem is considered for initial conditionsin a non-minimal state-space model that includes interpretable state variablesgenerated by non-stationary stochastic processes. In order to solve theidentification problem, structural restrictions are imposed on initial conditionsin a state-space model with redundant state variables. The correspondingrestricted maximum likelihood estimator of initial conditions is derived.The restricted estimator of initial conditions can be used in order tocompute uniquely identified realizations of interpretable latent variables. Theidentification problem is illustrated analytically using a simple structuraleconomic model.
Redundant constraints in MBS models severely deteriorate the computational performance and accuracy of any numerical MBS dynamics simulation method. Classically this problem has been addressed by means of numerical decompositions of the constraint Jacobian within numerical integration steps. Such decompositions are computationally expensive. In this paper an elimination method is discussed that only requires a single numerical decomposition within the model preprocessing step rather than during the time integration. It is based on the determination of motion spaces making use of Lie group concepts. The method is able to reduce the set of loop constraints for a large class of technical systems. In any case it always retains a sufficient number of constraints. It is derived for single kinematic loops.
Redundancy based methods are proactive scheduling methods for solving the Project
Scheduling Problem (PSP) with non-deterministic activities duration. The fundamental
strategy of these methods is to estimate the activities duration by adding extra time to the
original duration. The extra time allows to consider the risks that may affect the activities
durations and to reduce the number of adjustments to the baseline generated for the project.
In this article, four methods based on redundancies were proposed and compared from two
robustness indicators. These indicators were calculated after running a simulation process.
On the other hand, linear programming was applied as the solution technique to generate
the baselines of 480 projects analyzed. Finally, the results obtained allowed to identify the
most adequate method to solve the PSP with probabilistic activity duration and generate
robust baselines.
This article takes up the matter of contemporary threats to cities and urbanity, setting the problems cities face today against the background of the two categories of the resilient city and the city developing sustainably. The author describes and presents the evolution of the sustainable development concept as such, as well as the generational change in priorities that has taken place where the development of urbanised areas is concerned, given the way the concept has undergone a certain devaluation, in the light of its failure to achieve fulfi lment. The challenges cities face today require multi-faceted activity, in respect of increased inclusivity, robustness and resilience, and flexibility. This leaves today’s idea of the resilient city embracing old elements of the sustainable city, but also augmenting them in various ways.
The paper considers parametric optimization problems for the steel bar structures formulated as nonlinear programming ones with variable unknown cross-sectional sizes of the structural members, as well as initial prestressing forces introduced into the specified redundant members of the structure. The system of constraints covers load-bearing capacity constraints for all the design sections of the structural members subjected to all the design load combinations at ultimate limit state, as well as displacement constraints for the specified nodes of the bar system, subjected to all design load combinations at serviceability limit state. The method of the objective function gradient projection onto the active constraints surface with simultaneous correction of the constraints violations has been used to solve the parametric optimization problem. A numerical technique to determine the optimal number of the redundant members to introduce the initial prestressing forces has been offered for high-order statically indeterminate bar structures. It reduces the dimension for the design variable vector of unknown initial prestressing forces for considered optimization problems.
In order to investigate the progressive collapse performance of steel open-web sandwich plate structure, the sensitivity index and the importance coefficient of the bars are analyzed by the alternate path method. The condition that the model has perimeter supports with different parameters shows the result that: the redundancy index of structure increases at the structural edge, and the redundancy index will be reduced to changing degrees at the middle structure, when the stiffness of higher ribs increases. The redundancy index has little change, when the stiffness of lower ribs or shear keys increases. The sensitivity index of the shear keys dropped significantly, but the sensitivity index of the higher ribs and lower ribs increase, when the span to depth ratio increases. The sensitivity index of the higher ribs in L1 line increases significantly, when the span to depth ratio declines. So it is advisable to strengthen the higher ribs to avoid excessive sensitivity of ribs, when the span to depth ratio declines.
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