Papers by K.-u. Bletzinger
CRC Press eBooks, Jun 27, 2023
Coda wave interferometry is an ultrasound-based technology for structural health monitoring of co... more Coda wave interferometry is an ultrasound-based technology for structural health monitoring of concrete structures that is based on a correlation evaluation of two ultrasonic signals. To detect damage locations, sensitivities of the coda waves are used. These sensitivities are derived from wave propagation approximations that are computed with the finite element method applied on a diffusion problem. So far, the actual value of localized damage has little meaning in real experiments. This study compares results from strucutral analysis to the actual measurements. The analysis results should be used as the basis of a measurement classification that in the end should identify damage with a threshold. The comparison is performed at a real four-point bending test of a reinforced concrete specimen.
Computational Mechanics
The Material Point Method (MPM) is an established and powerful numerical method particularly usef... more The Material Point Method (MPM) is an established and powerful numerical method particularly useful for simulating large-scale, rapid soil deformations. Therefore, it is often used for the numerical investigation of mass movement hazards such as landslides, debris flows, or avalanches. It combines the benefits of both mesh-free and mesh-based continuum-based discretization techniques by discretizing the physical domain with Lagrangian moving particles carrying the history-dependent variables while the governing equations are solved at the Eulerian background grid, which brings many similarities with commonly used finite element methods. However, due to this hybrid nature, the material boundaries do not usually coincide with the nodes of the computational grid, which complicates the imposition of boundary conditions. Furthermore, the position of the boundary may change at each time step and, moreover, may be defined at arbitrary locations within the computational grid that do not nec...
XI Textile Composites and Inflatable Structures
Standardized wind loading is the prescribed way of design for structures. Constructions with doub... more Standardized wind loading is the prescribed way of design for structures. Constructions with doublecurved surfaces, typical in case of prestressed membrane roofs, are only minimally addressed by codes and standards. Our contribution set out to investigate the needs and possibilities for standardizing loads in case of representative scenarios by computational means. We are motivated by landmark constructions, such as the German Expo Pavilion in Montreal 1967 or the shading umbrellas on the Haram Plaza in Medina 2010. These and similar works are unique, requiring specific design aspects, and the lightness of their structure makes them especially vulnerable to wind loads. Some insights on the hyperbolic paraboloid shape have been included in the Italian guidelines [1] as a result of multiple studies and various scientific contributions, such as . Our aim is to cover more generic shapes, of sizes and configurations that often occur in more common use cases. Here we follow the suggested focus points outlined in the Round Robin 3 call by the Tensinet Group in 2015 [3] and . We present our investigation on five representative shapeshypar, tent, barrel, upward umbrella, inverted umbrellafor roof canopies, without enclosing walls, i.e. freestanding. The chosen configurations are those commonly met when using technical membranes in public spaces, such as schoolyards, fairs, transport hubs or even leisure venues. We comment on the adequacy of the current guidelines and outline our contributions in form of wind pressure maps to better aid design. We contribute to the existing knowledge base with high-resolution pressure maps, sensitivity of local loading patterns to changes in aspect ratio of the geometry (and corresponding curvature), also exploring the effect of grouped configurations. Recent advances in computational wind engineering support the accuracy and the efficiency of our study. The project makes use of high-performance computing on the SuperMUC-NG facilities by LRZ. This context allows us to investigate the structures at real-geometric scale and proper atmospheric boundary layer turbulence conditions. The scope is limited to studying rigid shapes, which is valid as long as the constructions are under high levels of prestress.
XI Textile Composites and Inflatable Structures
Sensitivity analysis can be used to investigate the effects of varied input variables (e.g., Youn... more Sensitivity analysis can be used to investigate the effects of varied input variables (e.g., Young's modulus) on the variation of output quantities (e.g., stress) of structural models. Hybrid lightweight structures consist of elastic elements like beams and tensile elements as membranes or cables. To aim of this contribution is the application of computational sensitivity analysis approaches as the adjoint method [1] on hybrid lightweight structures. In that regard we face two main challenges. First, the material and cross-sectional properties of the elastic elements influence the form-found shape. Hence, the impact of those variables during the form-finding process has to be considered in sensitivity analysis. Second, hybrid lightweight structures cannot be analyzed in a single stage analysis. Instead, a sequenced simulation process which typically consists of form-finding and subsequent structural analyses is required. For this reason, computation results need to be transferred from one analysis to another one [2] which must also be considered in sensitivity analysis. In our contribution, we discuss both challenges and show the required modifications to the sensitivity equations. Furthermore, we evaluate the additional computational effort and demonstrate the application on exemplary structures.
Numerical investigations of a membrane morphing wind turbine blade under gust conditions
Journal of Wind Engineering and Industrial Aerodynamics, 2022
Advances in Aerodynamics, 2019
A three-dimensional-membrane-type wing is investigated applying fluid-structure-interaction compu... more A three-dimensional-membrane-type wing is investigated applying fluid-structure-interaction computations and complementary experiments. An analysis for three Reynolds numbers is conducted at various angles of attack. The computations are performed by means of the TAU-Code and the FEM Carat++ solver. Wind-tunnel tests are carried out for performance analysis and to estimate the accuracy of the computations. In the results, the advantages of an elasto-flexible-lifting-surface concept are highlighted by comparing the formvariable surface to its rigid counterpart. The flexibility of the material and its adaptivity to the freestream allow the membrane to adjust its shape to the pressure distribution. For positive angles of attack, the airfoil’s camber increases resulting in an increase in the wing lifting capacity. Furthermore, the stall onset is postponed to higher angles of attack and the abrupt decrease in the lift is replaced by a gradual loss of it.
Computer Methods in Applied Mechanics and Engineering, 2017
Embedded structural entities in NURBS-based isogeometric analysis, Comput. Methods Appl.
Shape optimisation in the design of thin-walled shells as components of aerospace structures
The Aeronautical Journal, 2012
One of the most resent efforts in aircraft design is the replacement of aluminium structures by c... more One of the most resent efforts in aircraft design is the replacement of aluminium structures by carbon fibre reinforced polymer composites. Due to lower material and manufacturing costs, doubly curved shapes covering big areas are preferred over simpler surfaces which integrate stiffening profiles. In this context, CAD parameterisation of surfaces allows design solutions by means of classical shape optimisation. Related geometrical parameters are manipulated towards optimal design, generating innovative geometries and detailing.The presented structure is optimised by reducing the overall weight. The final optimum is guided using stability and strength restrictions in order to assure the safety of the component. Geometrical considerations are also included due to operational reasons. A hierarchical design procedure is developed which results in a work flow from preliminary ‘parameter-free’ form finding motivated by solving the minimal surface problem. The geometrical model for optimi...
The coupling of enclosed fluid with inflatable membranes
International Journal of Mechanical Sciences, 2014
The classical problem of the circular inflated membrane fixed at its rim and expanded under gas p... more The classical problem of the circular inflated membrane fixed at its rim and expanded under gas pressure is studied in this paper. Numerical and analytical solutions considering pressure-volume coupling are investigated. It should be pointed out that the application of the analytical solutions described in this section to closed chambers considering pressure volume coupling requires the adoption of recursive solutions scheme. The deformed configuration and volume are updated followed by the pressure update through the ideal gas law. The analytical solutions presented in the literature for this problem consider only the presence of small strains. In the present study the solutions given by Hencky, Fichter and Campbell are studied. A novel finite strain solution is derived, as an extension of Fichter's solution. The numerical solution is based on the finite element method and also considers finite strain kinematics. The results of numerical and analytical models for an enclosed circular membrane are compared, where the effects of small and finite strains with or without the consideration of the pressure-volume coupling are highlighted.
Computer Methods in Applied Mechanics and Engineering, 2011
This paper presents a novel approach for isogeometric analysis of thin shells using polynomial sp... more This paper presents a novel approach for isogeometric analysis of thin shells using polynomial splines over hierarchical T-meshes (PHT-splines). The method exploits the flexibility of T-meshes for local refinement. The main advantage of the PHT-splines in the context of thin shell theory is that it achieves C 1 continuity, so the Kirchhoff-Love theory can be used in pristine form. No rotational degrees of freedom are needed. Numerical results show the excellent performance of the present method.
Computers & Structures, 2001
Geometric constraints for node-based shape optimization of car body parts
Simulating coupled-field problems belongs to one of the most interesting and demanding topics in ... more Simulating coupled-field problems belongs to one of the most interesting and demanding topics in engineering. Taking coupled behavior into account is necessary within a broad range of applications, e.g. aeroelasticity, biomechanics, automotive or civil engineering. The emphasis of this work is in the context of civil engineering, in which wind-induced dynamic behavior of light-weight structures is of great interest. Therefore, this contribution belongs to the specific field of fluid-structure interaction (FSI), capturing flow-induced effects onto very thin shell and membrane structures. Having the intention of simulating real-world problems leads to very high requirements onto the used methods: Complex models have to be solved in an efficient and robust way, based on appropriate phys-ical models leading to reliable results. The development of an efficient parallel toolkit for the simulation of FSI problems is the aim of this work. A partitioned, surface-coupled approach is chosen, u...
Efficient computation of nonlinear isogeometric elements using the adjoint method and algorithmic differentiation
Computer Methods in Applied Mechanics and Engineering
Abstract We present a consistent and efficient approach to the formulation of geometric nonlinear... more Abstract We present a consistent and efficient approach to the formulation of geometric nonlinear finite elements for isogeometric analysis (IGA) and isogeometric B-Rep analysis (IBRA) based on the adjoint method. IGA elements are computationally expensive, especially for high polynomial degrees. Using the method presented here enables us to reduce this disadvantage and develop a methodical framework for the efficient implementation of IGA elements. The elements are consistently derived from energy functionals. The load vector and stiffness matrix are obtained from the first and second order derivatives of the energy. Starting from the functional, we apply the concept of algorithmic or automatic differentiation to compute the precise derivatives. Here, we compare the direct (forward) and adjoint (reversed) methods. Analysis of the computational graph allows us to optimize the computation and identify recurring modules. It turns out that using the adjoint method leads to a core-congruential formulation, which enables a clean separation between the mechanical behavior and the geometric description. This is particularly useful in CAD-integrated analysis, where mechanical properties are applied to different geometry types. The adjoint method produces the same results but requires significantly fewer operations and fewer intermediate results. Moreover, the number of intermediate results is no longer dependent on the polynomial degree of the NURBS. This is important for implementation efficiency and computation speed. The procedure can be applied to arbitrary element formulations and coupling conditions based on energy functionals. For demonstration purposes, we present the proposed approach specifically for use with geometrically nonlinear trusses, beams, membranes, shells, and coupling conditions based on the penalty method.
In this contribution we propose a generalized framework for multidisciplinary sensitivity analysi... more In this contribution we propose a generalized framework for multidisciplinary sensitivity analysis in civil engineering. We present a collaborative simulation environment for the optimization of human comfort in combination with static and geometric properties of a building section. The product model is based on the Industry Foundation Classes (IFC) and extended for the needs of the simulation environment. Flow, temperature and humidity fields required for human comfort prediction are computed by a CFD kernel based on the Lattice Boltzmann method whereas the structure problem is solved by a high order finite element method. Multidisciplinary sensitivity analysis is applied to several examples and shows the potential impact of our approach.
Explicit ApproximationOf Equality Constraints
Combination of optical measurement technique and virtual process optimisation in sheet metal forming
Due to their special load carrying behavior, membrane structures are using the material most ecie... more Due to their special load carrying behavior, membrane structures are using the material most eciently. As a consequence, the realized structures are extremely light but susceptible to ow-induc ed ee cts. The missing bending stiness results in a complex cou- pling of stress state and membrane shape. This necessitates special form nding techniques to determine the mechanically dene d shapes of equilibrium as prerequisite of the analysis of prestressed lightweight structures. Due to the almost negligible mass of the structure, the surface-coupled, partitioned uid-structur e-interaction computations with an explicit coupling scheme fail. To achieve numerically stable results, an implicit coupling strategy using intereld iterations with under relaxation is applied and for the sake of eciency, the Aitken's acceleration technique is used. A software environment with integrated form nding capabilities is proposed focusing on aspects related to the coupling strategies. Two examples of me...
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Papers by K.-u. Bletzinger