Influence Of Changes In Geometry Research Articles

Online adaptive radiotherapy: Assessment of planning technique and its impact on longitudinal plan quality robustness in pancreatic cancer

Background and PurposePlanning on a static dataset that reflects the simulation day anatomy is routine for SBRT. We hypothesize the quality of on-table adaptive plans is similar to the baseline plan when delivering stereotactic MR-guided adaptive radiotherapy (SMART) for pancreatic cancer (PCa). Materials and MethodsSixty-seven inoperable PCa patients were prescribed 50 Gy/5-fraction SMART. Baseline planning included: 3–5 mm gastrointestinal (GI) PRV, 50 Gy optimization target (PTVopt) based on GI PRV, conformality rings, and contracted GTV to guide the hotspot. For each adaptation, GI anatomy was re-contoured, followed by re-optimization. Plan quality was evaluated for target coverage (TC = PTVopt V100%/volume), PTV D90% and D80%, homogeneity index (HI = PTVopt D2%/D98%), prescription isodose/target volume (PITV), low-dose conformity (D2cm = maximum dose at 2 cm from PTVopt/Rx dose), and gradient index (R50%=50% Rx isodose volume/PTVopt volume).A novel global planning metric, termed the Pancreas Adaptive Radiotherapy Score (PARTS), was developed and implemented based on GI OAR sparing, PTV/GTV coverage, and conformality. Adaptive robustness (baseline to fraction 1) and stability (difference between two fractions with highest GI PRV variation) were quantified. ResultsOAR constraints were met on all baseline (n = 67) and adaptive (n = 318) plans. Coverage for baseline/adaptive plans was mean ± SD at 44.9 ± 5.8 Gy/44.3 ± 5.5 Gy (PTV D80%), 50.1 ± 4.2 Gy/49.1 ± 4.7 Gy (PTVopt D80%), and 80%±18%/74%±18% (TC), respectively. Mean homogeneity and conformality for baseline/adaptive plans were 0.87 ± 0.25/0.81 ± 0.30 (PITV), 3.81 ± 1.87/3.87 ± 2.0 (R50%), 1.53 ± 0.23/1.55 ± 0.23 (HI), and 58%±7%/59%±7% (D2cm), respectively. PARTS was found to be a sensitive metric due to its additive influence of geometry changes on PARTS’ sub-metrics. There were no statistical differences (p > 0.05) for stability, except for PARTS (p = 0.04, median difference −0.6%). Statistical differences for robustness when significant were small for most metrics (<2.0% median). Median adaptive re-optimizations were 2. ConclusionWe describe a 5-fraction ablative SMART planning approach for PCa that is robust and stable during on-table adaption, due to gradients controlled by a GI PRV technique and the use of rings. These findings are noteworthy given that daily interfraction anatomic GI OAR differences are routine, thus necessitating on-table adaptation. This work supports feasibility towards utilizing a patient-independent, template on-table adaptive approach.

Parametric geometry model design of a wingsuit

PurposeThis paper aims to introduce a process chain spanning from scanned data to computer-aided engineering and further required simulations up to the subsequent production. This approach has the potential to reduce production costs and accelerate the procedure.Design/methodology/approachA parametric computer-aided design (CAD) model of the flyer wearing a wingsuit is created enabling easy changes in its posture and the wingsuit geometry. The objective is to track the influence of geometry changes in a timely manner for following simulation scenarios.FindingsAt the final stage, the two-dimensional (2D) pattern cuts were derived from the developed three-dimensional (3D) wingsuit, and the results were compared with the conventional ones used in the first stages of the wingsuit development.Originality/valueProposing a virtual development process chain is challenging; apart from the fact that the CAD construction of a wingsuit flyer – in itself posing a complicated task – is required at a very early stage of the procedure.

Mathematical model of flat plate solar thermal collector and its validation

In order to predict solar thermal collector’s performance and optimization of control algorithms, proper mathematical models are necessary. Computer calculation technique provides tools for determination of modern materials impact on improvement of heat transfer inside the collector and minimization of heat loss. Such analysis is impossible by using standard technical datasheet provided by producer or by using empirical formulas. In the paper the authors present a mathematical model of a flat plate solar thermal collector based on the Hottel-Whiller-Bliss equation and criterial formula. The iterative algorithm solved steady state heat transfer equations for a glazed and an unglazed collector. The validation experiment was conducted under class AAA sun simulator for different inlet temperature and solar irradiation values. The unglazed PV/T and glazed solar thermal collectors were tested. For PV/T the relative difference, between measured and computed outlet temperatures, was below 5% and the highest value was reached for the lowest inlet temperature. The validation study showed that the experimental results reached good agreement with simulation predictions. Presented computation algorithm enables to predict influence of geometry changes on collector performance. The model could be used for optimization of the construction without using CFD methods, which need large computation resources.

Application of CFD Simulation in the Development of a New Generation Heating Oven

This paper deals with the application of Computational Fluid Dynamics simulation in the development of a new generation cooking appliance in Gorenje concern. As the oven is multifunctional, radiation, conduction, natural and forced convection mechanisms of heat transfer are used. The Discrete Ordinate (DO) model is used for radiation. The density of air is described by incompressible ideal gas equation in a natural convection model. The intention was to create the best possible baking conditions for different heating systems. Several discrete models were created. The influence of geometry change and boundary conditions variations to the velocity and temperature field distribution in the oven cavity was analyzed. The results of numerical simulations are validated with measurements taken from an oven prototype. The agreement was good. After successfully passing the standard tests, the oven came into serial production and was launched on the market.

Flow-Induced Sound of Wall-Mounted Cylinders with Different Geometries

The objective of this work was to investigate the influence of changes in geometry of a wall-mounted square cylinder in crossflow on the generated aerodynamic noise. The flowfield and acoustic field of several geometries are obtained and their interaction is analyzed. The results of the subset of geometries investigated indicate that the reduction in turbulent kinetic energy does not necessarily also lead to a reduction in radiated noise. Reducing the fluctuations of the stagnation point in front of the cylinder, maintaining a fixed separation line, and reducing the symmetry of the vortex street and its stability seem to be effective measures for reducing aerodynamic noise, among other known approaches.

Dynamic rigid-plastic deformation of arbitrarily shaped plates

A rigid, perfectly-plastic model of solids is applied to study the dynamic behavior of simply supported or clamped, arbitrarily shaped plates on visco-elastic foundation. The role of membrane forces and transverse shear forces in the yield condition and the influence of geometry changes are neglected. The plate is subjected to explosive loads uniformly distributed over the surface. Several mechanisms of dynamic deformation of the plate are considered. For each mechanism, equations of the dynamic behavior are obtained. Operating conditions of these mechanisms are analyzed. Analytical expressions for the limit and high loads and for the maximum final deflections are obtained. Detailed analyses are given for an astroid-shaped plate, for a plate with a contour consisting of two arcs and for a plate with an internal free hole or a rigid insert.

Modelling the characteristics of axial compressor of variable flow passage geometry, working in the gas turbine engine system

Modelling the characteristics of axial compressor of variable flow passage geometry, working in the gas turbine engine system This paper concerns application of mathematical modelling methods to analyzing gas-dynamic processes in marine gas turbines. Influence of geometry changes in axial compressor flow passage on kinematical air flow characteristics, are presented. The elaborated mathematical model will make it possible to realize - in the future - simulative investigations of gas-dynamic processes taking place in a compressor fitted with controllable guide vanes.

Whole heart modeling: from validation of animal experiments to the reconstruction of the human magnetocardiogram

Our interest in heart modeling is on one hand strongly motivated by the desire to compare cardiac simulation results with data obtained from magnetocardiogram (MCG) measurements of human beings and animals in various setups. On the other hand, we have started to integrate imaging data at various levels in our modeling approach. In the first part, we report in detail on simulations of anatomically realistic models for animal ventricles using the modified Beeler-Reuter ionic model and compare these with experimental data. Simulations of a rabbit heart were carried out and compared with experiments in Langendorff perfusion. The time evolution of the spatial profiles of the extracellular potential on the surface of the rabbit heart was correctly reproduced. The effects of ajmaline (Na-channel blockage) and palmitoleic acid (decrease of intracellular conductivity) were included subsequently in the model. In addition, pacing simulations of the ventricles have been performed using different frequencies. Occurrence of action potential duration alternans was found for frequencies greater than 230 bpm. Fibrillation occurred for frequencies greater than 260 bpm. Finally, the influence of geometry change during the human heart beat on MCG signals was investigated. We computed the MCG using the ten Tusscher ionic model for 2-dimensional cuts through the ventricles recorded by magnetic resonance imaging during systole resp. diastole and found a much shorter QRS for the diastolic geometry. Furthermore, the dynamic geometry of the heart was recorded and translated into a moving finite element mesh used in 3-dimensional simulations of the heart.

Influence of geometry change on creep failure life of 90° pressurised pipe bends with no initial ovality

The influence of the geometry change during creep on the failure life of 90° pipe bends, subjected to internal pressure, was investigated using finite element creep damage analyses. The bends were considered to be circular in shape with no initial ovality. The failure lives obtained using the material properties for a CrMoV pipe steel at 640 °C clearly show a significant life reduction when the geometry change is included. In the range of the pipe bend dimension ratios investigated, it was found that the failure lives could be reduced to between 65 and 78% of those obtained from constant geometry cases, indicating that the influence of geometry change may need to be appraised for detailed numerical analysis. The results were compared with those of the corresponding straight pipes and their relevance considered. It has been shown that under constant geometry conditions, the failure life for pipe bends is about 30% lower than that for the straight pipes.

Study of flow in a planar asymmetric diffuser using large-eddy simulation

Large-eddy simulation (LES) has been used to study the flow in a planar asymmetric diffuser. The wide range of spatial and temporal scales, the presence of an adverse pressure gradient, and the formation of an unsteady separation bubble in the rear part of the diffuser make this flow a challenging test case for assessing the predictive capability of LES. Simulation results for mean flow, pressure recovery and skin friction are in excellent agreement with data from two recent experiments. The inflow consists of a fully developed turbulent channel flow at a Reynolds number based on shear velocity, Reτ=500. It is found that accurate representation of the in flow velocity field is critical for accurate prediction of the flow in the diffuser. Although the simulation in the diffuser is well resolved, the subgrid-scale model plays a significant role for both mean momentum and turbulent kinetic energy balances. Subgrid-scale stresses contribute a maximum of 8% to the local value of the total shear stress with the maximum values found in the inlet duct and along the flat wall where the flow remains attached. The subgrid-scale model adapts to the enhanced turbulence levels in the rear part of the diffuser by providing more than 80% of the dissipation rate for turbulent kinetic energy. The unsteady separation excites large scales of motion which extend over the major part of the duct cross-section and penetrate deeply into the core of the flow. Instantaneous flow reversal is observed along both walls immediately behind the diffuser throat which is far upstream of the location of main separation. While the mean flow profile changes gradually as the flow enters the expansion, turbulent stresses undergo rapid changes over a short streamwise distance along the deflected wall. An explanation is offered which considers the strain field as well as the influence of geometry changes. The effect of grid resolution and spanwise domain size on the flow field prediction has been documented and this allows an assessment of the computational requirements for carrying out such simulations.

Analysis of Chemical Phenomena by Solving the Constrained Hartree–Fock Equation. III. Influence of Geometry Change on the Energy of π Electrons in Conjugated Hydrocarbons

Abstract The total energy of a conjugated unsaturated hydrocarbon can formally be partitioned into the energy of π electrons and the frame energy. This type of partitioning has been used to study the role of π electrons; to know the relationship between the π-electronic structure and its energy, the molecular geometry has been varied. This paper examines the influences of such geometry change on the energy of π electrons from a basic point of view. It was found that there are four types of geometrical influences which disguise the relationship between the π-electronic structure and its energy. Contrary to this, the constrained Hartree–Fock method was shown to disclose the relationship between π-electronic structure and its energy clearly. Application of the constrained Hartree–Fock method to D6h and D3h benzenes showed that in a D6h benzene π electrons favor the symmetrically uniform distribution independently of the bond length and the partitioning method, while in a D3h benzene the uniform distribution of π electrons is destroyed. Analysis of gradients of partitioned energies with respect to the bond order at a D3h-distorted benzene indicated that π electrons favor a more uniform delocalization, but this is opposed by one- and two-electron potentials.

Visualisation of flow conditions inside a shoreline wave power-station

The particle flow inside an oscillating water column type wave power-station varies with time and changes direction. In order to establish flow patterns and energy dissipating mechanisms, and to assess the influence of geometry changes on the hydraulic performance, flow visualisation experiments were conducted on a 1/36 two-dimensional model of the Islay prototype wave power-station. It was found that large vortices develop around the comparatively thin front wall for in- and outflow and that internal sloshing occurs during the inflow period. From the observations it could be deduced that the front lip curvature and thickness have to be increased. Previous suggestions to structure the front wall surface in order to reduce wave loads had to be revised as these obstacles would interfere with the inflow. An internal breaker was observed, indicating that the loads on the back wall might be considerably higher than assumed.

Geometric effects on shakedown and ratchetting of axisymmetric cylindrical shells subjected to variable thermal loading

This paper presents results obtained from numerical simulations of the responses of an elastic-plastic thin cylindrical shell to fluctuating axisymmetric temperature in the presence of uniform axial stresses. The engineering situation considered has practical importance in nuclear reactors and has been the subject of a number of earlier studies. The main purpose is to assess quantitatively the influence of geometry changes, primarily due to plastic yielding, on shakedown and ratchetting (incremental collapse) phenomena. In particular, these phenomena are investigated with respect to both the stabilizing effects of tensile primary stresses on them, and their strong interference with elastoplastic buckling. The systematic evolutive analyses presented herein are also intended to critically assess the validity of earlier results (mainly condensed in the so-called Brussels diagrams) which have been established by simplified methods of shakedown based on the small deformation (no geometric effects) hypothesis.

The influence of geometry on the acoustic characteristics of duct bends for higher order modes

A two-dimensional finite element technique, corroborated with experimental results, was used to explore the acoustic characteristics of 90° bends when cross modes propagate. The influence of changes in geometry on these characteristics was established over a range of inner and outer radii and the effects of including a turning vane were examined. The energy reflected was related where possible to the aerodynamic characteristics.

The effects of flow and geometry on the acoustic characteristics of bends

A two‐dimensional finite element technique was used to investigate the acoustic characteristics of 90° bends for plane wave and for cross‐mode propagation. An experimental procedure was also developed which permitted measurement of these characteristics in terms of rigid walled duct modes when several higher order modes were admitted simultaneously. Numerical and experimental results displayed excellent agreement over a range of frequencies extending to the cut‐on value of the third cross mode. Characteristics were studied in terms of modal amplitudes of the reflected and transmitted waves and in terms of the corresponding energy coefficients. The energy transfer was also examined for the case when an evanescent mode was incident on a mitred bend. The influence of changes in geometry was established over a range of inner and outer radii and the effects of locating a turning vane in the bend were also examined. The energy reflected was related, where possible, to published aerodynamic characteristics. The effects of a mean compressible flow on the acoustic characteristics was examined for one geometry.

A study of the higher modal dynamic plastic response of beams

A theoretical and experimental investigation into the higher modal dynamic plastic response of fully clamped beams is reported herein. It is shown that the influence of geometry changes or finite-deflections is important which agrees with previous studies on the dynamic plastic behavior of uniformly loaded beams. It appears that the higher modal response of beams is a more efficient means of absorbing a given magnitude of kinetic energy than a single modal response.

Dynamic Analysis of Impact Attenuation Systems Utilizing Plastic Deformations : Case in Which Influence of Geometry Change After Initial Yield Is Considered

A structure whose load-displacement curve due to geometry change after initial yield is expressed approximately by a cubic nonlinear curve is represented by a dynamically equivalent system consisting of a nonlinear spring and a slider, and its dynamic response to the impact of a moving mass is analyzed by means of successive approximation. This analysis is carried out with a structure made of a rigid-perfectly-plastic material, but the results are applicable to the case of an elastic-perfectly-plastic material. Numerical examples are given for a U type beam subjected to an impulsive loading at the tip.

Dynamic Analysis of Impact Attenuation Systems Utilizing Plastic Deformations : Case in which Influence of Geometry Change after Initial Yield is Considered

Dynamic Analysis of Impact Attenuation Systems Utilizing Plastic Deformations : Case in which Influence of Geometry Change after Initial Yield is Considered

The Effect of Geometry Changes on the Load Carrying Capacity of Beams Under Transverse Load

This paper concerns the influence of geometry changes on the post-yield behavior of beams and other engineering structures. First, the extant literature on the subject is reviewed. Next, as a specific illustration, the particular problem of a simply supported axially restrained uniform beam, rectangular in cross section and made of rigid perfectly-plastic material, and subjected to vertical load uniformly distributed with respect to length measured along the current centerline of the beam is studied in detail. The beam’s response, following the initial yield associated with the formation of a central yield hinge, is in two consecutive phases. In the primary phase, plastic deformation is associated solely with the outwards movement of two boundaries such that the material behavior at beam cross sections stays rigid except precisely at these boundaries ; the phase terminates when each has moved out to a cross section originally at a distance of one-third of the semispan from the center. The secondary phase now begins with each of the two existing boundaries being joined by a new boundary that separates to travel inwards, and now plastic deformation completely extends over the two outer regions between the boundaries; the phase terminates when these boundaries reach the ends and the center of the beam, and then the beam’s response is simply that of a pure membrane, although this state is only asymptotically achieved. The analysis presented leads, for example, to a complete determination of the load deformation relationship, and the important influence of geometry changes on the response of the beam is thereby made clear. In particular, in practical circumstances of slender beams, it is found that even at central transverse deflections of the order of the beam thickness, the load carrying capacity is considerably enhanced and also the asymptotic membrane state is effectively realized. The results of the present exact analysis of the problem, which is based on the rate equations of equilibrium, extend those obtained earlier in approximate analyses given by other workers. Finally, mention is made of related beam problems, for which a similar analysis is possible and for which similar results obtain, and also of plate problems.

The influence of finite-deformations upon the creep behavior of circular plates

An experimental and approximate theoretical investigation has been conducted into the creep behavior of initially flat circular plates with particular emphasis on the influence of geometry changes induced during deformation. An energy technique which uses a simplified constitutive relation is described and solutions are obtained for the cases of clamped and simply supported circular plates under a uniform, time-independent, lateral load. This approximate method retains the effects of both bending moments and membrane forces. A series of experiments on circular lead plates is described and compared with the corresponding theoretical predictions. Both the theoretical and experimental results show that the effect of finite-deformations is important.