Ulrich Montag

New natural draft cooling tower of 200 m of height

In the years 1999 to 2001 a new natural draft cooling tower has been built at the RWE power station at Niederaussem, with 200 m elevation the highest cooling tower world-wide. For many reasons, such structures can not be designed merely as enlargement of smaller ones, on the contrary, it is full of innovative new design elements. The present paper starts with an overview over the tower and a description of its geometry, followed by an elucidation of the conceptual shape optimization. The structural consequences of the flue gas inlets through the shell at a height of 49 m are explained as well as the needs for an advanced high performance concrete for the wall and the fill construction. Further, the design and structural analysis of the tower is described with respect to the German codified safety concept for these structures. Finally, the necessity of extended durability of this tower is commented, the durability design concept is explained in detail and illustrated by virtue of a series of figures.

An efficient formulation of integration algorithms for elastoplastic shell analysis based on layered finite element approach

For geometrically and physically nonlinear analyses of shell structures a computational model employing a Reissner-Mindlin type kinematic assumption, a layered finite element approach and a closest-point projection return mapping algorithm, completely formulated in tensor notation is presented. As a result of a consistent linearization, a tangent modulus is derived, expressed also in tensor components. The applied constitutive model includes a von Mises yield criterion and linear isotropic as well as kinematic hardening. All stress deviator components are employed in the formulation. The material model is implemented into a four-noded isoparametric assumed strain finite element, which permits the simulation of geometric nonlinear responses considering finite rotations. The proposed numerical concept is unconditionally stable and allows large time steps, as the numerical examples illustrate. Further, the numerical simulations demonstrate the expected quadratic convergence in a global iterative technique.

Increasing solution stability for finite-element modeling of elasto-plastic shell response

Abstract The present article introduces a highly efficient numerical simulation strategy for the analysis of elasto-plastic shell structures. An isoparametric Finite Element, based on a Finite Rotation Reissner–Mindlin shell theory in isoparametric formulation, is enhanced by a Layered Approach for a realistic simulation of nonlinear material behaviour. A general material model including isotropic hardening effects is embedded into each material point. A new, highly accurate integration scheme is combined with consistently linearized constitutive relations in order to achieve quadratic rate of convergence. A global Riks–Wempner–Wessels iteration scheme enhanced by a linear Line-Search procedure was used to trace arbitrary deformation paths. Numerical examples show the efficiency of the present concept.

On the increase of computational algorithm efficiency for elasto‐plastic shell analysis

Presents a robust and unconditionally stable return‐mapping algorithm based on the discrete counterpart of the principle of maximum plastic dissipation. Develops the explicit expression for the consistent elasto‐plastic tangent modulus. All expressions are derived via tensor formulation showing the advantage over the classical matrix notation. The integration algorithm is implemented in the formulation of the four‐node isoparametric assumed‐strain finite‐rotation shell element employing the Mindlin‐Reissner‐type shell model. By applying the layered model, plastic zones can be displayed through the shell thickness. Material non‐linearity described by the von Mises yield criterion and isotropic hardening is combined with a geometrically non‐linear response assuming finite rotations. Numerical examples illustrate the efficiency of the present formulation in conjunction with the standard Newton iteration approach, in which no line search procedures are required. Demonstrates the excellent performance of the a...

World’s Tallest Natural Draft Cooling Tower, near Cologne, Germany

RWE Energie AG, the second largest German electricity producer, operates since 1961 a lignite power plant at the small village of Niederaussem, 20 km west of Cologne. Construction began on a new Niederaussem power station in 1998 with an intended electricity capacity of 965 MW, which, after completion in 2002, will become the largest lignite power block in the world. The cooling component of this new electricity station is a natural draft cooling tower 200 m high, the tallest cooling tower and the largest shell structure in the world. The reason for increasing height and cooling capacity to such an extent is merely the desire to enhance the total net efficiency of the electricity generating process at this plant, as one of several innovative steps.

Computer Simulation of Nonisothermal Elastoplastic Shell Responses

Shell structures are extremly efficient, thin walled load-carrying components, in the elastic as well as in the inelastic regime. Realistic and efficient computational strategies lately are in rapid development. Such computational strategy for modelling of nonisothermal, highly nonlinear hardening responses in elastoplastic shell analysis has been proposed in this article. Therein, the closest point projection algorithm employing the Reissner-Mindlin type kinematic model, completely formulated in tensor notation, is applied. A consistent elastoplastic tangent modulus ensures high convergence rates in the global iteration approach. The integration algorithm has been implemented into a layered assumed strain isoparametric finite shell element, which is capable of geometrical nonlinearities including finite rotations. Under the assumption of an adiabatic process, the increase of the temperature is analysed during elastoplastic deformation. Finally, numerical examples illustrate robustness and efficiency of the proposed algorithms.