A model for reactive porous transport during re-wetting of hardened concrete

A mathematical model is developed that captures the transport of liquid water in hardened concrete, as well as the chemical reactions that occur between the imbibed water and the residual calcium-silicate compounds residing in the porous concrete matrix. The main hypothesis in this model is that the reaction product—calcium-silicate hydrate gel—clogs the pores within the concrete, thereby hindering water transport. Numerical simulations are employed to determine the sensitivity of the model solution to changes in various physical parameters, and compare to experimental results available in the literature.     

Portfolio management in the binomial model: conditions for outperforming benchmarks

The performance of a portfolio manager is in practice usually measured by the result of his trading strategy compared to a benchmark. Therefore the information whether there exists a strategy that allows to outperform the benchmark is of high value for an active investor. The article shows how this information can be generated in the binomial model. In this context the connection between trading strategies and the investor's expectations concerning future asset prices is analyzed. Based on these findings several conditions are derived that allow the portfolio manager to judge whether the benchmark can be outperformed by an active trading strategy. RID="*" ID="*" Thomas Balzer now works in the Risk Measurement & Management Department of Credit Suisse First Boston in London. The views expressed in this article are those of the author, and do not necessarily represent those of Credit Suisse Group or Credit Suisse First Boston. The author thanks Dr. Michael Olbrich for careful reading and several useful comments.     

Selection of porous materials in marine system design: The case of heat exchanger aboard ships

Porous materials are processed in various areas of material science and manufacturing. Furthermore, the varieties of porous materials ensure great advantages to designers. This paper proposes a decision aid mechanism based on fuzzy axiomatic design (FAD) to select adequate form of porous materials in marine systems design. It enables elimination and choice of suitable material alternatives in respect to two sets of attributes: generic material selection attributes (GMSA) and specific material selection attributes (SMSA). Furthermore, the paper specifically addressed use of porous materials in plate type heat exchanger design to demonstrate the proposed model. It is expected that the paper ensures a novel procedure for marine engineers and naval architectures in conceptual design process of marine systems.     

Numerical investigation of crack growth in concrete subjected to compression by the generalized beam lattice model

The beam lattice-type models, such as the Euler–Bernoulli (or Timoshenko) beam lattice and the generalized beam (GB) lattice, have been proved very effective in simulating failure processes in concrete and rock due to its simplicity and easy implementation. However, these existing lattice models only take into account tensile failures, so it may be not applicable to simulation of failure behaviors under compressive states. The main aim in this paper is to incorporate Mohr–Coulomb failure criterion, which is widely used in many kinds of materials, into the GB lattice procedure. The improved GB lattice procedure has the capability of modeling both element failures and contact/separation of cracked elements. The numerical examples show its effectiveness in simulating compressive failures. Furthermore, the influences of lateral confinement, friction angle, stiffness of loading platen, inclusion of aggregates on failure processes are respectively analyzed in detail.     

An implicit finite element algorithm for the simulation of diffusion with phase changes in solids

A fixed grid technique is proposed for the numerical simulation of the phenomena of diffusion with phase changes in solids. This technique is based on the finite element method in space coupled with the implicit (backward) Euler algorithm in time. The examples given include the Stefan problem, heat transfer with non‐instantaneous metallurgical transformations in steels, and the simultaneous and coupled diffusion and precipitation of chemical elements during internal oxidation of steels. These examples clearly evidence the efficiency and robustness of the method developed. Copyright © 2009 John Wiley & Sons, Ltd.     

Time–stress correspondence in viscoelastic materials: an equation for the stress and temperature shift factor

Stress–time correspondence principle discovered experimentally by O’Shaughnessy already in 1948 [1] is considered. Using the Doolittle formula for the viscosity as a function of free volume [2], an equation for the generalized temperature–stress shift factor a_T,σ is obtained. An equation for the stress-dependent shift factor a_σ follows as a special case. The equation for the temperature shift factor a_T already derived in 1985 [3] and successfully used since also follows from the a_T,σ formula. Received: 26 April 2000 / Reviewed and accepted: 17 May 2000     

An integrated decision support system for strategic supply chain optimisation in process industries: the case of a zinc company

We introduce a menu-driven user-friendly decision support system (DSS) for supply chain planning based on optimisation. The DSS is based on a multi-source (supplier), multi-destination (warehouse) network having multiple manufacturing facilities, with multiple materials and multiple storage areas. This integrated supply chain model performs multiple period planning. The use of this DSS requires little knowledge of management sciences tools. We discuss the need for an integrated approach towards supply chain modelling for the process industry. We present the integrated model in the form of a database structure. We validate the model with the real data of a zinc company and demonstrate the impact of optimisation in terms of percentage improvement. The result shows that it is possible to improve unit contribution to profit from 1.89 to 4.66%.