Structural and thermal performances of topological optimized masonry blocks

Structural topology optimization is the most fundamental form of structural optimization and receives an increasing attention from engineers and structural designers. The method enables the exploration of the general topology and shape of structural elements at an early stage of the design process and gives rise to inspiring and innovative improvements. In this paper, topology optimization as a principle is used to design new types of insulating masonry blocks. Two main objectives are addressed: maximizing the structural stiffness and minimizing the thermal transmittance. The first part of this paper uses these objectives to create new block topologies. A general problem is formulated and the influences of boundary conditions, external loading, and filter value on the resulting geometry are discussed. In general, maximizing the stiffness is in strong contrast to minimizing the thermal transmittance. This causes problems not encountered in conventional topology optimization. Nevertheless, by adjusting the interpolation schemes and adding multiple load groups, convergent solutions are found. An isotropic material model with an enforced solid-or-empty distribution is considered as the primary method. The optimized block topologies are then thoroughly analyzed to review their structural and thermal performance using the commercial finite element software Abaqus. The direct compressive strength of the block is a measure of the structural performance and the equivalent thermal conductivity gives an indication of the thermal performance. The second part then gives some thoughts on three-dimensional optimization and the incorporation of mesostructures in the design

FEM modelling techniques for simulation of 3D concrete printing

Three-dimensional concrete printing (3DCP) has gained a lot of popularity in recent years. According to many, 3DCP is set to revolutionize the construction industry: yielding unparalleled aesthetics, better quality control, lower cost, and a reduction of the construction time. In this paper, two finite element method (FEM) strategies are presented for simulating such 3D concrete printing processes. The aim of these models is to predict the structural behaviour during printing, while the concrete is still fresh, and estimate the optimal print speed and maximum overhang angle to avoid print failures. Both FE analyses involve solving multiple static implicit steps where sets of finite elements are added stepwise until failure. The main difference between the two methods is in the discretization of the 3D model. The first method uses voxelization to approximate the 3D shape, while the second approach starts from defining the toolpath and constructs finite elements by sweeping them along the path. A case study is presented to evaluate the effectiveness of both strategies. Both models are in good agreement with each other, and a comparable structural response is obtained. The model's limitations and future challenges are also discussed. Ultimately, the paper demonstrates how FEM-based models can effectively simulate complex prints and could give recommendations with regards to a better print strategy. These suggestions can be related to the maximum printing speed and overhang angle, but also the optimal layer height and thickness, the specific choice of the infill pattern, or by extension the mixture design. When print failures can be avoided, this methodology could save time, resources and overall cost. Future work will focus on the validation of these numerical models and comparing them to experimental data.Comment: fib Symposium 2020 ONLINE (22nd to 24th November 2020

FEM modelling techniques for simulation of 3D concrete printing

Three-dimensional concrete printing (3DCP) has gained a lot of popularity in recent years. According to many, 3DCP is set to revolutionize the construction industry: yielding unparalleled aesthetics, better quality control, lower cost, and a reduction of the construction time. In this paper, two finite element method (FEM) strategies are presented for simulating such 3D concrete printing processes. The aim of these models is to predict the structural behaviour during printing, while the concrete is still fresh, and estimate the optimal print speed and maximum overhang angle to avoid print failures. Both FE analyses involve solving multiple static implicit steps where sets of finite elements are added stepwise until failure. The main difference between the two methods is in the discretization of the 3D model. The first method uses voxelization to approximate the 3D shape, while the second approach starts from defining the toolpath and constructs finite elements by sweeping them along the path. A case study is presented to evaluate the effectiveness of both strategies. Both models are in good agreement with each other, and a comparable structural response is obtained. The model's limitations and future challenges are also discussed. Ultimately, the paper demonstrates how FEM-based models can effectively simulate complex prints and could give recommendations with regards to a better print strategy. These suggestions can be related to the maximum printing speed and overhang angle, but also the optimal layer height and thickness, the specific choice of the infill pattern, or by extension the mixture design. When print failures can be avoided, this methodology could save time, resources and overall cost. Future work will focus on the validation of these numerical models and comparing them to experimental data

Powerful Shocks and Cavities in the Hot Atmosphere of the MS 0735 Galaxy Cluster

Cool core clusters host bright centres that radiate away their energy in less than 10^9 yr. If uncompensated by heating, the hot atmosphere will cool and form stars at rates of hundreds to thousands of solar masses per year. However, high resolution spectroscopy from the Chandra and XMM-Newton X-ray Observatories have failed to find evidence of gas cooling to low temperatures at the expected rates. Instead, feedback from active galactic nuclei (AGN) is heating the intracluster medium and suppressing cooling flows. X-ray observations have revealed large cavities, weak shocks, and sound waves in the intracluster medium that are produced by the relativistic jets launched by the central AGN. In this thesis I present a deep Chandra X-ray analysis of MS 0735.6+7421 (MS0735), the cool core galaxy cluster with the most energetic AGN outburst known. I use this deep observation to study the energetics of the powerful AGN outburst, as well as analyze additional effects that the outburst has on the intracluster medium. Two large cavities, with diameters of 200-240 kpc, are embedded in the hot atmosphere of MS0735. A power output of over 10^46 erg/s is required to inflate the bubbles, exceeding the X-ray luminosity by over a factor of 60 and easily offsetting radiative losses. A continuous, weak shock front of Mach number 1.26 encompasses the cavities, injecting energy at a rate comparable to the cavities. This shock causes a temperature jump that varies azimuthally, and is highest where the shock front is strongest. Cool gas from the centre of the cluster is entrained in the radio jet and is being dragged toward high altitudes. Two more cavities are observed near the cluster centre, indicating that the AGN is rejuvenating on a timescale shorter than the central cooling time. These cavities, while small compared to the older outburst, still contain ample energy to offset radiative losses. With the addition of MS0735, I prepare a sample of 10 clusters and groups with multiple generations of cavities. Three systems with detected sound waves are also included, two of which overlap with the cavity sample. In these systems I compare the mean time interval between AGN outbursts to the central cooling time and cavity heating time. On average the AGN rejuvenate on a timescale that is approximately 1/3 of their mean central cooling time, indicating that jet heating is outpacing cooling in these systems. Finally, I present a preliminary analysis of integral field spectroscopy of MS0735's brightest cluster galaxy. A velocity gradient extends across the cluster nucleus and is inconsistent with being a rotating disk. Instead, it is more likely that the atomic gas has been entrained in the jets and is being dragged away from the nucleus. The ionized gas mass exceeds estimates based on the upper limits of molecular gas, indicating either that the atomic gas is not condensing into molecular gas or that a source of heat is reionizing the H-alpha nebula

An ALMA View of Molecular Gas in Brightest Cluster Galaxies

In this thesis I use ALMA observations to map the distribution and kinematics of molecular gas in the brightest cluster galaxies of three galaxy clusters: 2A0335+096, RXJ0821+0752, and RXCJ1504-0248. The goal is to understand how the coldest gas in clusters is formed, identify any long-lived structures that could fuel sustained black hole accretion, and explore star formation in cluster environments. I use the J=1-0 and J=3-2 rotational transitions of carbon monoxide (CO) as tracers of the total molecular gas distribution. The two transitions provide different resolutions and fields of view. The molecular gas in all three central galaxies are complex and disturbed. None show evidence for rotationally-supported nuclear structures, such as a disk or ring, that would be expected from either a merger origin or long-lived cooling flow. Instead, the molecular gas is either clumpy with no clear velocity structure or extends away from the galactic center in filaments that are several kiloparsecs long. The molecular filaments are coincident with nebular and bright X-ray emission, suggesting that they have condensed out of the hot intracluster medium. They are also generally associated with cavities in the X-ray emission inflated by the active galactic nucleus (AGN), suggesting that AGN feedback has stimulated the formation of molecular gas. The narrow velocity gradients along the filaments are only consistent with freefall if the filament is situated close to the plane of the sky. This is a common feature in brightest cluster galaxies. Since ram pressure is ineffective at slowing dense molecular clouds, the filaments must either be pinned to the hot atmosphere by magnetic fields or have condensed in-situ relatively recently. In RXCJ1504-0248 I combine the ALMA analysis with spatially-resolved ultraviolet emission tracing young stars. The central gas falls on the Kennicutt-Schmidt relation, while the filament has elevated star formation surface densities. The ongoing consumption of a finite fuel supply by star formation, or spatial variations in the CO-to-H2 conversion factor, may be diminishing the molecular gas surface density to produce this effect. Despite their drastic differences in morphology and environment, the molecular gas in clusters is still converted into stars following the same relation as in spirals and starbursts. I have also detected the J=3-2 transition from 13CO, an optically thin isotopologue of 12CO, in RXJ0821.0+0752. This enables a measurement of the conversion between CO intensity and molecular column density for the first time in a galaxy cluster. The CO-to-H2 conversion factor in RXJ0821+0752 is half of the Galactic value. If this value applies to other clusters, then it would alleviate the high coupling efficiencies required for molecular filaments to be uplifted by X-ray cavities. This analysis also provides reassurance that the molecular gas masses measured in BCGs are unlikely to be overwhelmingly biased by adopting the Galactic conversion factor

Density-based topology optimization for 3D-printable building structures

This paper presents the study of a new penalty method for density-based topology optimization. The focus is on 3D-printable building structures with optimized stiffness and thermal insulation properties. The first part of the paper investigates the homogenized properties of 3D-printed infill patterns and in the second part a new penalty method is proposed and demonstrated. The method presents an alternative way to implement multi-material topology optimization without increasing computational cost. A single interpolation function is created, based on the homogenized properties of a triangular infill pattern. The design variables are linked to the different possible infill densities of the pattern. A high density represents a solid structure with high stiffness, but weak thermal properties, while an intermediate density provides the structure with good insulation qualities. On the other hand, when the air cavities become too large (i.e., low infill densities), the heat flow by convection and radiation again decreases the thermal performances of the material. The optimization study is performed using the GCMMA algorithm combined with a weighted-sum dual objective. One part of the equation aims to maximize stiffness, while the other attempts to minimize the thermal transmittance. Different case studies are presented to demonstrate the effectiveness of this multi-physics optimization strategy. Results show a series of optimized topologies with a perfect trade-off between structural and thermal efficienc

Multi-physics topology optimization for 3D-printed structures

General topology optimization optimizes material layout within a given design space based on structural aspects. In this paper, structural topology optimization is extended to enable optimization of thermal performances. A novel multi-physics interpolation scheme is proposed and its link with 3D-printed structures is explained. Each design variable now has three optimal states: one state represents the surrounding air, having weak structural and thermal material characteristics; another state represents the solid structure with good structural, but less efficient thermal properties; a third state symbolizes a weight-efficient mesh-structure, improving the structure's thermal conductivity while retaining some structural integrity. The optimization study is performed using the GCMMA algorithm with a weighted-sum mono objective. One part of the equation aims to maximize stiffness, while the other attempts to minimize the thermal transmittance. The design domain of choice is a 2-dimensional roof component that is simply supported at the edges. Results show that using this multi-physics optimization strategy can be very useful to find the optimal trade-off between structural integrity and thermal efficiency. The maximum deflection and U-value of the optimized components are also compared to more traditional design approaches. The topologically-optimized solutions clearly outperform the others