Applied Mechanics and Materials Vol. 807

Abstract: Load carrying mechanical structures like trusses face uncertainty in loading along with uncertainty in their strength due to uncertainty in the development, production and usage. The uncertainty in production of function integrated rods is investigated, which allows monitoring of load and condition variations that are present in the product in every phase of its lifetime. Due to fluctuations of the semi-finished parts, uncertainty in governing geometrical, mechanical and electrical properties such as Young's moduli, lengths and piezoelectric charge constants has to be evaluated. The authors compare the different direct methodical approaches Monte-Carlo simulation, fuzzy and interval arithmetic to describe and to evaluate this uncertainty in the development phase of a simplified, linear mathematical model of a sensory rod in a consistent way. The criterion to compare the methodical approaches for uncertainty analysis is the uncertain mechanical-electrical transmission behavior of the sensory rod, which defines the sensitivity of the sensory compound.

Abstract: Models are often used to make predictions far from the region where they were trained and validated. In this paper attempts are made to analyse the credibility that can be placed in such predictions. The proposed approach involves treating a model’s parameters as time-variant (even if it is believed that this is not the case), before utilising Bayesian tracking techniques to realise parameter estimates. An example is used to demonstrate that, relative to a Bayesian approach where the parameters are assumed to be time-invariant, treating the parameters as time-variant can reveal important flaws in the model and raise questions about its ability to make credible predictions.

Abstract: In this article, we propose a nonlinear semidefinite program (SDP) for the robust trusstopology design (TTD) problem with beam elements. Starting from the semidefinite formulation ofthe robust TTD problem we derive a stiffness matrix that can model rigid connections between beams.Since the stiffness matrix depends nonlinearly on the cross-sectional areas of the beams, this leads toa nonlinear SDP. We present numerical results using a sequential SDP approach and compare them toresults obtained via a general method for robust PDE-constrained optimization applied to the equationsof linear elasticity. Furthermore, we present two mixed integer semidefinite programs (MISDP), onefor the optimal choice of connecting elements, which is nonlinear, and one for the correspondingproblem with discrete cross-sectional areas.

Abstract: Booster stations can fulfill a varying pressure demand with high energy-efficiency, because individual pumps can be deactivated at smaller loads. Although this is a seemingly simple approach, it is not easy to decide precisely when to activate or deactivate pumps. Contemporary activation controls derive the switching points from the current volume flow through the system. However, it is not measured directly for various reasons. Instead, the controller estimates the flow based on other system properties. This causes further uncertainty for the switching decision. In this paper, we present a method to find a robust, yet energy-efficient activation strategy.

Abstract: Cheap does not imply cost-effective -- this is rule number one of zeitgeisty system design. The initial investment accounts only for a small portion of the lifecycle costs of a technical system. In fluid systems, about ninety percent of the total costs are caused by other factors like power consumption and maintenance. With modern optimization methods, it is already possible to plan an optimal technical system considering multiple objectives. In this paper, we focus on an often neglected contribution to the lifecycle costs: downtime costs due to spontaneous failures. Consequently, availability becomes an issue.