Block Geometry Research Articles

Hot Spot Cause Analysis and Shaping Optimization Design of the Monoblock Divertor Target Plate in EAST

The monoblock divertor target plate (MDTP) is a mainstream divertor target plate. MDTP was installed in EAST and in WEST and will be used in ITER. Local high-temperature hot spots (HS) were observed on MDTP during a plasma experiment. HS will reduce the lifetime of MDTP. In this paper, the causes of HS on MDTP are determined through theoretical analysis and are verified by numerical simulations. The HS on MDTP seem to be caused by small high-density heat load areas on the toroidal and poloidal direction surfaces facing the incident direction of the plasma strike line (PSL) of the MDTP tungsten block. When toroidal HS and poloidal HS appear simultaneously, a super local high-temperature HS will be formed at the corner (facing the incident direction of PSL) of the MDTP tungsten block. The HS on MDTP can be eliminated by optimizing the geometry of the MDTP tungsten block, when the plasma configuration is determined. A method and the scope of application of the method, which can be used for tungsten block geometry optimization, are given in this paper. In order to facilitate the selection of a divertor configuration, the heat flux–carrying performance of the optimized MDTP was evaluated. In order to attain a maximum temperature within MDTP of less than 900 K, it was found that if the poloidal incidence angle between PSL and MDTP can be stably controlled as 5 deg (or 35 deg), MDTP can directly withstand PSL with a peak heat flux density of no more than 90 (or 40 ).

Seismic Overturning Fragility Analysis for Rigid Blocks Subjected to Floor Motions

This paper investigates the seismic rocking-overturning fragility of freestanding rigid blocks subjected to one-sine acceleration pulses from a probabilistic perspective. An equivalent single-degree-of-freedom (SDOF) model with a bespoke discrete damper is used to simulate the responses of four blocks with varying geometries under excitation with various characteristics. The simulation results are used to perform an overturning fragility analysis and evaluate the performance of various intensity measures (IMs). An IM strip, referred to as a hybrid strip, can be observed in the analysis, within which both safe rocking and overturning occur. For IM values outside of the hybrid strip, there exists a clear distinction between these two states. In this study, we introduce the hybrid ratio, a parameter that can estimate the size of the hybrid strip of different IMs. The hybrid ratio is defined as the combination of two ratios of hybrid strip width and the two IM strip widths corresponding to safe rocking and overturning, respectively. The effect of the different analysis strip widths is also examined in the overturning fragility analysis. The results suggest that the IM determined by excitation magnitude, frequency, and block geometry parameters demonstrates its superiority compared with some well-known IMs by having the smallest hybrid ratio and coefficient of variation, as well as good robustness of the overturning fragility curves against the change of the analysis strip width.

Therapeutic radiation beam output and energy variation across clinics, technologies, and time.

Over the past several decades, a medical physics service group covering 35 clinical sites has provided routine monthly output and energy quality assurance for over 75 linear accelerators. Based on the geographical spread of these clinics and the large number of physicists involved in data acquisition, a systematic calibration procedure was established to ensure uniformity. A consistent measurement geometry and data collection technique is used across all machines for every calendar month, using a standardized set of acrylic slabs. Charge readings in acrylic phantoms are linked to AAPM's TG-51 formalism via a parameter denoted kacrylic , used to convert raw charge readings to machine output values. Statistical analyses of energy ratios and kacrylic values are presented. Employing the kacrylic concept with a uniform measurement geometry of similar acrylic blocks was found to be a reproducible and simple way of referencing a calibration completed in water under reference conditions and comparing to other machines, with the ability to alert physicists of outliers.

An Intensity Measure for the Rocking Fragility Analysis of Rigid Blocks Subjected to Floor Motions

A novel intensity measure (IM), dimensionless floor displacement, is presented for evaluating the seismic fragility of freestanding rigid blocks subjected to one-sine acceleration pulses in this paper. The rocking responses of rigid blocks are simulated using an equivalent single-degree-of-freedom (SDOF) model with a bespoke discrete damper to account for energy dissipation. The performance of various IMs is compared using simulation results for four different block models under different excitation conditions. In comparison to some well-known IMs, the proposed IM, determined by excitation magnitude and frequency as well as block geometry parameters, displays a considerably stronger correlation with the peak rotation of the rocking block. The comparative results show that effective IMs should consider not only the excitation characteristics but also the block geometric parameters. Finally, the fragility curve generated by the proposed IM performs best by significantly reducing the dispersion.

Toppling susceptibility of a single rock block resting on a regularly rough base

Toppling of individual rock blocks resting on an inclined surface has often been observed in nature. This instability mechanism has typically been analysed for simple block geometries, considering the contact between the block and the base where it lies is a planar surface. In this study, the authors analyse the case where this contact is a regularly rough surface. To do that, the authors resort to analytical limit equilibrium formulations, laboratory physical models and discrete element methods. All these approaches show a consistent trend of behaviour, where roughness does affect the toppling response. Regularly rough surfaces are studied in detail and a general analytical formulation able to show the potential influence of roughness on the block toppling response is derived. Additionally, some considerations are provided regarding the combined effects of rough bases and rounded corners on toppling stability. The authors show how under particular circumstances, roughness can control the potential failure mechanism of a block to produce toppling instead of sliding, and they eventually discuss the impact of rough bases on the toppling response of natural rock blocks.

Effect mechanism of block convexity on the shear behaviors of soil-rock mixtures by the developed 3D spherical harmonics-based modeling approach

The effect of block convexity on the shear behaviors of soil-rock mixtures (S-RMs) can be investigated using accurate 3D models constructed with the discrete element method (DEM). Based on the improved spherical harmonics series, a new block geometry modeling approach was proposed for generating 3D blocks with different convexities but the same form and angularity. By introducing tracer particles, a DEM modeling approach was also proposed for generating S-RM models with the same block distribution characteristics and possible block breakage. Numerical direct shear tests were performed on the generated stiff and soft S-RM models with different block convexities. The meso- and the macro-shear behaviors of the S-RMs were analyzed in detail to reveal the effect mechanism of block convexity. The results showed that the breakage degree of soft blocks increased linearly with the block convexity degree. The interlocking degrees of blocks with higher convexities are higher, leading to higher contributions of the blocks to the shear strength and greater block rotation. As the effect of block breakage is more significant, soft blocks with higher convexity degrees contribute smaller to the shear resistance. For S-RMs with higher block convexity degrees, the shear strength of stiff S-RMs is higher owing to their higher block interlocking degrees, while the shear strength of soft S-RMs under high normal stress is smaller due to their higher block breakage degrees. The dilation magnitude is greater for stiff S-RMs while lower for soft S-RMs with higher convexity degrees, owing to the greater effect of block breakage than the rotation behavior. The friction angles of stiff S-RMs with higher block convexity degrees are larger due to their higher block interlocking degrees, while the friction angles of soft S-RMs with lower block convexity degrees are smaller under high normal stress due to their higher block breakage degrees.

The performance of vertically perforated clay block masonry in fire tests predicted by a finite-element model including an energy-based criterion to identify spalling

Fire tests on masonry are one of the most expensive experiments in developing new vertically perforated clay block geometries. Numerical simulations might be a reasonable substitute for such experiments, leading to a significant cost reduction in the development phase. However, the prediction of such tests with numerical modeling concepts is challenging due to large temperature and stress gradients, highly non-linear material effects, and the complex geometry of the blocks. Herein, we present a finite-element-based concept, including thermal and mechanical simulations, a unit-cell approach, a smeared damage model, and a novel energy-based spalling criterion to describe the structural and material behavior of a masonry wall in a fire experiment. We could predict the obtained spalling times of longitudinal webs and the total endurance of a masonry wall without any empirical fitting parameters in good agreement with experimental data. These results show that we can use our modeling approach for simulating such fire tests, enabling a much cheaper and more efficient development of block geometries.

The 3D Printing Potential for Heat Flow Optimization: Influence of Block Geometries on Heat Transfer Processes

The building envelope is a crucial element in the regulation of thermal energy in the indoor environment, from which comfortable living inevitably depends. Designing a low-dispersion envelope represents a fundamental strategy to minimize the energy demand and HVAC systems’ consumption. To this end, the need to select suitable insulation has become increasingly important, and the search for new solutions is constantly evolving. This justifies the great interest in the study of energy-efficient and sustainable insulation materials that are able to provide the low thermal transmittance values of multilayer components. To date, 3D printing has experienced a growing popularity for the research of alternative building materials (e.g., concrete). Conversely, it still appears to be very uncommon for the research of purely energy-efficient solutions. The aim of this work is to compare the thermal performance of three 3D-printed PLA (polylactic acid) blocks, characterized by different internal geometries and air cavities: (i) a multi-row structure; (ii) a square structure; (iii) a honeycomb structure. The study was conducted theoretically, with two-dimensional heat transfer modeling, and experimentally, by means of a heat flow meter and infrared thermography. The results showed that the configurations of the 3D-printed blocks reduced the flow of heat exchange. In addition, as the complexity of the blocks’ internal structure increased, a heat flow reduction could be observed. In particular, the honeycomb structure showed a better behavior than the other two blocks did, with an experimental transmittance value that was equal to 1.22 ± 0.04 W/m2K. This behavior, which was mainly due to an attenuation of convective and radiative internal heat exchanges, suggests that the 3D printing has great potential in this field.

Geometrical investigation of cooling channels with two alternated isothermal blocks under forced convective turbulent flow

The present work performs a numerical analysis of the geometrical investigation of a two-dimensional channel with two alternated isothermal rectangular blocks subjected to turbulent forced convective flows. Constructal Design associated with Exhaustive Search is used to investigate the influence of the geometry of the isothermal blocks over the performance of the cooling convective flows in a multi-objective viewpoint, i.e., considering the pressure drop and heat transfer rate. The time-averaged equations of continuity, momentum, and energy conservation are solved with the finite volume method. The k–omega shear stress transport model is used for the closure of turbulence. The effect of the two proposed degrees of freedom, the height/length ratio of the two blocks (H_{1}/L_{1} and H_{2}/L_{2}), is analyzed in relation to the proposed objectives. Regarding the thermal purpose, the geometry with the highest insertion into the channel led to the best performance, while the opposite configuration led to the best fluid dynamic performance. This behavior was similar to that previously found in the literature for forced convective laminar flows. For a multi-objective perspective, the use of technique for order preference by similarity to ideal solution indicated that asymmetric blocks led to the best multi-objective performance when both performance indicators had the same weight.

Intensity measures, fragility analysis and dimensionality reduction of rocking under far‐field ground motions

AbstractProblems for which it is impossible to make a precise causal prediction are commonly tackled with statistical analysis. Although fairly simple, the problem of a rocking block on a rigid base subjected to seismic excitation exhibits a fascinating, complex response, making it extremely difficult to validate numerical models against experimental results, thus calling for a statistical approach. In this context, this paper statistically studies the rocking behaviour of rigid blocks, excited by synthetic far‐field ground motions. A total of 50 million analyses are performed, considering rocking blocks of height ranging from 1 to 20 m and slenderness angle ranging from 0.1 to 0.35 rad. The results are used to explore the performance of different ground motion intensity measures (IMs), in terms of their ability to predict the maximum rocking rotation. By comparing the efficiency, sufficiency and proficiency of the IMs, it is found that the peak ground velocity (PGV) performs optimally. Then, fragility curves are constructed using different IMs, concluding again that the PGV is the most efficient IM. Impressively, the fragility curves for different block sizes collapse to a single curve, if a non‐dimensional IM that involves PGV and the block geometry is used. Finally, the results produced on the basis of far‐field synthetic motions are compared to results based on recorded ground motions.

Comparison of full-scale rockfall tests with 3D complex-shaped discrete element simulations

Trajectory analysis is often needed to handle rockfall hazards. It is crucial to understand and to refine ground and rock interactions during a rockfall, which can be related to the elements involved. They include the topology, ground and rock nature, but also the volume and shape of the falling blocks. This work focuses on replicating field observations using a 3D discrete elements model (DEM) in order to further analyze the possible rockfall deposition areas, which may not be accessible due to the limited number of experimental data available. The numerical model implements blocks of more realistic shapes that were reconstructed from in situ blocks obtained by photogrammetry. The dissipation of kinetic energy at the collision point is suitably managed. In the experimental campaign, dozens of boulders (rock block) releases were conducted on two slope profiles of a quarry located in Authume (France). Block passing heights, velocities and runout distances were assessed at specific ground points. We analyzed lateral spreads, propagation distances, and energy balances computed for 3 different block geometries. These numerical results were confronted with experimental observations. Although time-consuming compared to lumped mass and rigid body dynamics models where the impact duration is zero, the DEM used in this work is versatile thanks to an explicit consideration of geometrical effects throughout the life of multiple contacts. It allows to simulate quite accurately a multitude of configurations. Among the properties of the terrain and the blocks, geometric features are shown to be crucial. For the sake of efficiency, a simplified shape coefficient based on block’s elongation is proposed.

Counter-current imbibition and non-linear diffusion in fractured porous media: Analysis of early- and late-time regimes and application to inter-porosity flux

The displacement of non-aqueous phase liquid (NAPL) in permeable porous rock by water saturating the surrounding fractures is studied. In many situations of practical interest, capillarity is the dominant driving force. Using the global pressure concept, it is shown that the water saturation is driven by a generic non-linear diffusion equation governing the matrix block counter-current spontaneous imbibition. In addition, in most cases, the saturation-dependent diffusion coefficient vanishes at the saturation end points, that renders the driving equation highly singular.In this paper, two exact asymptotic solutions valid for short and long times are presented, under the assumption that the conductivity vanishes as a power-law of both phase saturations at the extreme values of the fluid saturation.Focusing on the late-time domain, the asymptotic solution is derived using an Ansatz that is written under the form of a power-law time decay of the NAPL saturation. In the spatial domain, this solution is an eigenvector of the non-linear diffusion operator driving the saturation, for a problem with Dirichlet boundary conditions. If the diffusion coefficient varies as a power law of the NAPL saturation, the spatial variations of the solution are given analytically for a one-dimensional porous medium corresponding to parallel fracture planes. The analytical solution is in very good agreement with results of numerical simulations involving various realistic sets of input transport parameters.Generalization to the case of two- or three-dimensional matrix blocks of arbitrary shape is proposed using a similar Ansatz, solution of a non-linear eigenvalue problem. A fast converging algorithm based on a fixed-point sequence starting from a suitable first guess was developed. Comparisons with full-time simulations for several typical block geometries show an excellent agreement.These results permit to set-up an analytical formulation generalizing linear single-phase representation of matrix-to-fracture exchange term. It accounts for the non-linearity of the local flow equations using the power-law dependence of the conductivity for low NAPL saturation. The corresponding exponent can be predicted from the input conductivity parameters. Similar findings are also presented and validated numerically for two- or three-dimensional matrix blocks. That original approach paves the way to research leading to a more faithful description of matrix-to-fracture exchanges when considering a realistic fractured medium composed of a population of matrix blocks of various size and shapes.

Local hotspot thermal management improved by ionic wind generator coupled with porous materials

Ionic wind is induced by corona discharge caused by extremely inhomogeneous electric field between two electrodes. Due to its compact size, energy saving, flexible design, and easy integration, ionic wind technique exhibits great potential to improve hotspot cooling, especially for compact electronic devices. However, the heat removal capability towards high power density is relatively low due to the limited heat transfer area and low air thermal conductivity. The principle and designs are still lacking for local hotspot cooling. Here, an ionic wind generator with a novel architecture coupled with porous medium is conceived to enhance cooling performance. It is demonstrated that when a porous medium block is coupled, heat transfer can be significantly boosted due to the modified heat and mass transfer in the porous block. It is also found that electrode configuration significantly influences the device performance. There is a trade-off between heat transfer area and airflow impediment in the device. The geometry and property parameters of the porous block are critical for the cooling performance, which is attributed to the modified flow field by changing porous structure. Based on this principle, another ionic wind generator improved by a coupled heat sink with porous fins is proposed, whose performance can be further enhanced by optimizing its design parameters. The optimized heat sink structure can maintain the max temperature of the cooling surface below 83.2 °C at a heat flux of 90 kW/m2. This study provides a promising way for air-side thermal management of hotspot. The findings are helpful for understanding EHD-induced airflow heat transfer in porous medium and shed new light on designing ionic wind generators with better performance.

A novel geometric parameter to evaluate the effects of block form on solar radiation towards sustainable urban design

The utilization of solar energy plays an important role in coping with global climate change and low-carbon development. Solar radiation in the urban environment is affected by urban block geometry. The relationship between solar radiation and urban block geometry in Nanjing, which has a temperate climate, was studied in this paper. Two hundred generic models in eight typologies that represent a diverse range of urban block density and forms were examined. Seven geometric parameters and three periods of solar radiation on urban blocks, including a year, one typical week in summer, and one typical week in winter, were calculated. Four aspects of solar radiation were investigated at the block scale: (1) the relationship between urban density and solar radiation, (2) the solar radiation on different layout types of urban blocks, (3) the seasonal effect of solar radiation on buildings and open spaces, and (4) the potential of solar photovoltaic technology utilization in block surface. In addition to the obvious negative effect of density, this study indicated that the solar radiation on buildings and surrounding open spaces was significantly influenced by block form. Block surface ratios are the most influential geometric parameters for the solar radiation on buildings, while open spaces are more affected by sky view factor. The seasonal effect on solar radiation presents a much greater impact on open spaces than on buildings. This study highlights the important role that urban geometry plays in the on-site solar energy harvesting.

Multi-Dimensional Regression Models for Predicting the Wall Thickness Distribution of Corrugated Pipes.

Corrugated pipes offer both higher stiffness and higher flexibility while simultaneously requiring less material than rigid pipes. Production rates of corrugated pipes have therefore increased significantly in recent years. Due to rising commodity prices, pipe manufacturers have been driven to produce corrugated pipes of high quality with reduced material input. To the best of our knowledge, corrugated pipe geometry and wall thickness distribution significantly influence pipe properties. Essential factors in optimizing wall thickness distribution include adaptation of the mold block geometry and structure optimization. To achieve these goals, a conventional approach would typically require numerous iterations over various pipe geometries, several mold block geometries, and then fabrication of pipes to be tested experimentally—an approach which is very time-consuming and costly. To address this issue, we developed multi-dimensional mathematical models that predict the wall thickness distribution in corrugated pipes as functions of the mold geometry by using symbolic regression based on genetic programming (GP). First, the blow molding problem was transformed into a dimensionless representation. Then, a screening study was performed to identify the most significant influencing parameters, which were subsequently varied within wide ranges as a basis for a comprehensive, numerically driven parametric design study. The data set obtained was used as input for data-driven modeling to derive novel regression models for predicting wall thickness distribution. Finally, model accuracy was confirmed by means of an error analysis that evaluated various statistical metrics. With our models, wall thickness distribution can now be predicted and subsequently used for structural analysis, thus enabling digital mold block design and optimizing the wall thickness distribution.

Comparative analysis of the optimum cluster number determination algorithms in clustering GPS velocities

SUMMARY The Global Positioning System (GPS), although it has existed for only 30 years, is an important source for active tectonics, resulting in estimates of plate motions very close to geologic estimates over millions of years. GPS is also used for elastic block models to calculate slip rates for a better understanding of Earth’s active crustal deformation. GPS-derived velocity fields may be used as the basis for clustering analysis to create a preliminary definition of block geometry. In this study, we used published horizontal velocity fields to evaluate the effects of data dependences on determining the optimum number of clusters with algorithms. For this purpose, we used different variations of velocity fields in Turkey and tested four different algorithms that are Davies–Bouldin index, the elbow method, GAP statistics algorithm and the silhouette method. We also clustered velocity components with the k-means technique and compared the results with previous studies.

Influence of Block Geometry Configuration on Multi-Image Dense Matching

Digital photogrammetry is a widespread surveying technique in different fields of application due to its flexibility, versatility and cost-effectiveness. Despite its increasing automation and simplicity, a proper image block design is crucial to ensure high standards of performance and accuracy. Studies on camera network design have been largely dealt with in the scientific literature with reference to image orientation process, while they are still poor on dense matching. This paper investigates the influence of different block geometry configurations on multi-image dense matching. Starting from the same orientation solution, dense matching was performed considering different combinations of number of images and base length distance between the first and the last image within a strip. The raster Digital Elevation Models (DEM) resulting from each sequence of images were compared with a reference DEM to assess accuracy and completeness. The tests were conducted using different cameras and at various test sites to assess different survey conditions and generalize the findings. The presented results provide some operational guidance on block geometry optimization to maximize the accuracy and completeness.

SPATIAL SENSE ABILITY INSTRUMENT FOR PRIMARY SCHOOL STUDENTS

This research is motivated by the importance of spatial sense skills possessed by elementary school students. The research aims to develop an instrument of spatial sense ability suitable for elementary school students. The indicators developed in the preparation of questions include: 1) classifying real objects into 3D form (building space); 2) investigating, exploring, and describing geometry in nature and the real world; 3) exploring the directional relationship of objects in space; 4) analyzing the nature of 3D shapes and interpreting 3D shapes into 2D forms. Research and Development was chosen as the method of this research. A total of 33 grade VI students of SDN 1 Nagri Kidul, Purwakarta Regency, West Java Province, were the samples in this study. The sample was selected by purposive sampling. The instrument used is an essay test consisting of seven questions regarding the geometry of cubes and blocks. The expert (Professor in the field of mathematics education) validated the seven questions that had been prepared. Expert considerations are used as the basis for the improvement of the compiled questions. Then the questions that have been corrected are tested on the research sample. The results of the trial were calculated for validity, reliability, difficulty index, and discriminatory power. Of the seven questions compiled, six were declared valid, reliable, and had high discriminatory power, and the level of difficulty of the questions consisted of medium and difficult. Thus, 6 of the seven items developed can be used by teachers or researchers as an instrument to measure the spatial sense abilities of elementary school students, primarily fifth-grade students.

Vibration-induced assembly of topologically interlocked materials

Dense architectured, granular, and other material systems based on the assembly of discrete building blocks provide mechanical responses not ordinarily achieved in monolithic materials. The performances of these material systems can be tuned and expanded by simply changing the building block geometry, their packing arrangement, and/or their jamming states. Applications for these material systems have however remained limited, in part because of fabrication challenges and scalability. We explored the vibration-driven assembly method to form periodic arrangements of convex polyhedral building blocks into large-piece free-standing topologically interlocked panels. We used a combination of experiments and discrete elements modeling (DEM) to explore how vibration can be manipulated to steer polyhedral building blocks into one of three possible states: static, assembly, and fluttering and study the governing physics and mechanics underlying these states. The results specified the role of the normalized relative acceleration of mechanical agitation, bouncing, and rotation mechanisms on both phase transitions and crystallization and/or interlocking. The geometry-dependency, re-fragmentation, re-crystallization, and re-configurability of athermal out-of-equilibrium material systems can be understood and optimized based on our findings and provided guidelines in this study.

Seismic response distribution expressions for rocking building contents under ordinary ground motions

Analytical expressions are proposed for predicting the rocking response of rigid free-standing building contents subjected to seismic-induced floor excitations. The study considers a wide range of rigid block geometries and seismic floor acceleration histories that were recorded during actual earthquakes in instrumented Californian buildings, so as to cover, in a fully probabilistic manner, the entire spectrum of potential pure rocking responses, i.e. from the initiation of rocking up to the block overturning. Contrary to past observations on anchored building contents (prior to any failure in their anchorage system that could alter their response and mode of failure), it is shown that the response of free-standing blocks is not influenced by the predominant period of the supporting structure. The proposed set of equations can be utilised for estimating the response statistics and consequently for undertaking an analytical seismic fragility assessment on rocking building contents.