Related Geometrical Parameters Research Articles

Study on unsupported overhangs of AlSi10Mg parts processed by Direct Metal Laser Sintering (DMLS)

A well-known limitation of powder bed additive manufacturing techniques for metals is the requirement of support structures on down-facing surfaces. The aim of this research is addressed to the evaluation of geometrical parameters of self-supporting faces and estimation of the achievable tolerance of surfaces built without requiring a support structure. In order to accomplish the purpose of this study a Design of Experiment (DoE) approach is adopted to explore the significance of key parameters such as angle, curvature and slenderness of overhanging surfaces. Deviation between the actual and the nominal CAD geometries is computed, and results are processed following the tolerance unit method defined in international standards (IT grade). At the end of this study, the closest tolerance obtainable on self-supporting faces and related geometrical parameters are identified, limited to Direct Metal Laser Sintering (DMLS) of aluminium parts.

Heat transfer and pressure drop in rectangular channels with crossing fins (a Review)

Channels with crossing finning find wide use in the cooling paths of high-temperature gas turbine blade systems. At different times, different institutions carried out experimental investigations of heat transfer and pressure drop in channels with coplanar finning of opposite walls for obtaining semiempirical dependences of Nusselt criteria (dimensionless heat-transfer coefficients) and pressure drop coefficients on the operating Reynolds number and relative geometrical parameters (or their complexes). The shape of experimental channels, the conditions of experiments, and the used variables were selected so that they would be most suited for solving particular practical tasks. Therefore, the results obtained in processing the experimental data have large scatter and limited use. This article considers the results from experimental investigations of different authors. In comparing the results, additional calculations were carried out for bringing the mathematical correlations to the form of dependences from the same variables. Generalization of the results is carried out. In the final analysis, universal correlations are obtained for determining the pressure drop coefficients and Nusselt number values for the flow of working medium in channels with coplanar finning.

Generation and verification of three-dimensional network of fractured rock masses stochastic discontinuities based on digitalization

Accuracy of seepage simulation in rock masses is directly influenced by related geometrical parameters of DFN (discrete fracture network) models. In this paper a well-planned investigation of rock mass discontinuities was conducted on well-exposed outcrops in Beishan (Gansu province), one of the main candidate sites for the Chinese high-level radioactive waste repository using digital techniques, e.g. global positioning system, close range digital photogrammetry and geographical information system. This allows for very efficient collection of large volumes of data, over 10,000 discontinuities were obtained at the study site (Jijicao block), based on statistical parameters two homogeneities were identified, and the dominant sets were also delineated, which suggested that two sets exist in homogeneity I, while three sets in homogeneity II. In homogeneity I, The optimal fracture diameter probability distributions of both sets were lognormal. Three-dimensional stochastic DFN models were established for both homogeneities based on stochastic process as well as statistical parameters. The reliability of the model was validated by both graphical and numerical methods. Results showed that: digital techniques used in this study can overcome the problem of sample size and precision restriction posed by traditional methods, which leads to a more effective application of DFN model, and are thus suitable for tasks such as detailed mapping of rock masses in large area. It is believed that this verified DFN model is more appropriate for subsequent calculations of mechanical properties and seepage of fractured rock masses.

Failure evaluation of steam‐side oxide scales in superheater tubes during unsteady thermal processes: A probabilistic method

Issues resulting from failure of steam‐side oxide scales in boiler superheater or reheater tubes seriously influence the safety of coal‐fired power plants. In this work, an analysis model for the failure of steam‐side oxide scales during unsteady thermal processes is established. This model employs the advanced oxide scale failure diagram as the failure criterion, and also takes into account the influence of temperature on the coefficients of thermal expansion of both metal substrate and oxide scale. Since the stochastic nature of related geometrical, mechanical, and thermophysical parameters may hinder the usual deterministic investigation from obtaining a reliable evaluation, probabilistic failure evaluation which is not based on bivalent logic is thus performed. Focusing on the unsteady thermal processes induced by the variation of steam temperature, effects of oxide scale thickness as well as different steam temperature variation processes on the failure probability of steam‐side oxide scales are analyzed. It is found that the failure probability of thicker steam‐side oxide scales is higher, while through reasonably selecting steam temperature variation mode and appropriately lengthening variation duration, lower failure probability can be achieved. Feasible measures are presented with the aspiration to solve the steam‐side oxide scale failure issues.

Intuitive Class/Shape Function Parameterization for Airfoils

An airfoil parameterization method is proposed, which combines the flexibility and accuracy of Kulfan’s class/shape function transformation method and the intuitiveness of Sobieczky’s parameterization method for airfoil sections. The proposed intuitive class/shape function transformation method has been evaluated by comparing it with the class/shape function transformation and parameterization method for airfoil sections regarding their accuracy in inversely fitting a wide range of airfoils. The results show that the intuitive class/shape function transformation method is able to successfully transform the class/shape function transformation method into a fully intuitive parametric method (in which all of the design variables are aerodynamically related geometrical parameters) without loss of the accuracy and flexibility of the class/shape function transformation method for the airfoils tested.

Effects of scaling and geometry on the performance of piezoelectric microphones

Recent advances in microfabrication and nanofabrication techniques have allowed for the construction of ever-smaller sensors for the measurement of acoustic signals. The physics of sensor transduction and acoustics however place fundamental constraints on performance and limit the benefits of continual reductions in size. Key operating parameters such as sensitivity, minimum detectable signal (MDS) and resonant frequency are directly affected by device scale. Besides overall scale, relative sensor geometry (e.g. thickness ratio) can drastically alter performance. Through finite element and lumped element modeling, we study the effects of sensor geometry and scale on the sensitivity and noise performance of a piezoelectric microphone. The results indicate optimal relative geometric parameters for maximum performance and demonstrate the strong dependence on device geometry.

Stiffness Modeling and Analysis of Passive Four-Bar Parallelogram in Fully Compliant Parallel Positioning Stage

In order to investigate the influence of the stiffness of the compliant prismatic pair, a planar four-bar parallelogram, in a fully compliant parallel mechanism, the stiffness model of the passive compliant prismatic pair in a compliant parallel positioning stage is established using the compliant matrix method and matrix transformation. The influences of the constraints and the compliance of the connecting rods on the flexibility characteristics of the prismatic pair are studied based on the developed model. The relative geometric parameters are changed to show the rules of the stiffness variation and to obtain the demands for simplification in the stiffness modeling of the prismatic pair. Furthermore, the finite element analysis has been conducted to validate the analytical model.

Bandstop filter for photonic integrated circuits using photonic crystal with circular ring resonator

A two-dimensional (2-D) photonic crystal ring resonator-based bandstop filter is conceived, its stopband efficiency is investigated using the 2-D finite difference time domain method, and its band diagram is calculated by plane wave expansion method. The stop-band efficiency of the filter, ∼98%, is observed over the wavelength range 1562-1573 nm. Furthermore, the effects of the relative permittivity and geometrical parameters are considered for determining stop-band efficiency and stop-band width. The overall dimension of the device is 11.4 × 11.4 μm, which is highly suitable for photonic integrated circuits.

Homogenization of problems of elasticity theory on composite structures with thin armoring

The paper considers the problems of elasticity theory on a flat slab armored by a periodic thin mesh or in a three-dimensional body armored by a periodic thin box structure. The composite medium depends on two small mutually related geometric parameters; one of them controls the periodicity cell and the other controls the thickness of the armoring structure.

Interlaboratory experiments on the characterization of the acoustical and related nonacoustical properties of porous media

A series of reproducibility experiments on the characterization of acoustical parameters of selected samples of porous media is carried out on a range of porous samples in several independent laboratories in Europe and North America. The data on the characteristic acoustic impedance and complex propagation constant are presented in this work. In addition, the assessment of the related geometrical parameters required for modeling the acoustic performance of porous media, namely the steady-state flow resistivity, porosity, tortuosity, viscous and thermal characteristic lengths, and thermal permeability, is carried out. Detailed procedures related to sample preparation, and installation are discussed together with data on the material property variation observed between individual material samples and laboratories.

Divalent propargylenic C 2H 2M group 14 elements:Structures and singlet–triplet energy splittings (M=C, Si, Ge, Sn and Pb)

Relative stabilities and singlet (s)–triplet (t) energy splittings (Δ E s–t) of divalent propargylenic H–C C–M–H group 14 elements are investigated at B3LYP/6-311++G** and MP2/6-311++G** levels of theory (M=C, Si, Ge, Sn and Pb). Plotting B3LYP calculated relative energies of each H–C C–M–H as a function of the divalent bond angle ∠HMC, gives cross points between the singlet and triplet states of divalent C, Si, Ge, Sn and Pb. A linear correlation is found between the LUMO–HOMO energy gaps of the singlet species, and their corresponding Δ E s–t. No significant group 14 element d orbital valence participation is found for any of the scrutinized structures. Comparisons between relative stabilities and geometrical parameters for structures with different divalent atoms and multiplicities are discussed.

Ab initio study of singlet–triplet energy separations in C 2HXSi silylenes (X=H, F, Cl and Br)

Singlet–triplet energy separations in silylenes: C 2HSiX (where X=H, F, Cl and Br), are compared and contrasted, at six levels of theory: HF/6-31G*, HF/6-311++G**, B3LYP/6-311++G**, MP2/6-311++G**, MP4 (SDTQ)/6-311++G** and QCISD (T)/6-311++G**. Four possible structures are considered for each singlet ( s) and triplet ( t) states of C 2HSiX species: silacyclopropenylidene, 1; vinylidenesilylene, 2; propargylsilylene, 3; and ethynylsilylene, 4. The order of singlet–triplet energy separations for cyclic species, 1 t-X – 1 s-X (Δ E s–t, X ), as a function of X is: H>Br>F>Cl. In contrast, the order of singlet–triplet energy gaps, Δ E s–t, X , for their acyclic analogues ( 2 t-X – 2 s-X , 3 t-X – 3 s-X and 4 t-X – 4 s-X ), as a function of X, follows electro-negativity: F>Cl>Br>H. The order of stability for six isomers of C 2H 2Si is: 1 s-H > 2 s-H > 3 s-H > 2 t-H > 3 t-H > 1 t-H ; with the singlet cyclic 1 s-H appearing as the global minimum. These are compared to 24 divalent species of C 2HSiX, with the stability order of: 3 s-X > 1 s-X > 2 s-X > 3 t-X > 4 s-X > 2 t-X > 4 t-X > 1 t-X ; which have the singlet acyclic 3 s-X as their global minima. This demonstrates stabilization through resonance and/or induction, by electronegative α-halogens, being more pronounced for singlet silylenes than their reported singlet carbene analogues. Comparisons between relative stabilities, multiplicities, geometrical parameters and harmonic vibrational frequencies of 1– 4 are discussed.

1,3-Dipolar cycloaddition of azomethine ylide with ethene and 2-butene: a computational study

B3LYP/6-311 + G(d,p) has been used to calculate the relative energies and geometrical parameters of the respective reactants, transition states, and cycloadducts from the cycloadditions of azomethine ylide and ethene, ( Z)-2-butene, and ( E)-2-butene. The half-chair (envelope) transition state structures are consistent with a synchronous concerted cycloaddition mechanism.

Geometric Models to Calculate Intersection Sight Distance for Unprotected Left-Turn Traffic

At signalized intersections with opposing left-turn lanes, inadequate sight distance of left-turn drivers caused by obstructions from opposing left-turn vehicles can not only contribute to a serious safety problem due to drivers misjudging the gaps in the opposing through traffic but also cause increased intersection delay. This delay is created because drivers need more time to make sure that the opposing through lanes are clear. The 2001 AASHTO manual pointed out that the typical poor visibility of opposing through traffic usually occurs at signal intersections with medians wider than 18 ft and recommended two improvement methods: creating parallel offset left-turn lanes and tapered offset left-turn lanes. However, AASHTO did not provide the specific design guideline, nor did it present the related geometric design model. Sight-distance geometric models for unprotected left-turning vehicles from the major road onto the minor road at signalized intersections and vision improvement effects of the two offset methods were developed, and the relationship between available sight distance and related intersection geometric parameters was analyzed.

A density functional theory study of dinitrogen bonding in ruthenium complexes

Dinitrogen ruthenium complexes were theoretically studied by means of DFT technique. Several isomers of RuH 2(N 2)(PH 3) 2, RuH 2(N 2) 2(PH 3) 2 and RuH 2(H 2)(N 2)(PH 3) 2 were studied. Calculations of relative energies, geometrical parameters, vibrational frequencies and natural orbital bond analysis were performed. It is shown that the most stable isomer for each series is characterized by a trans position of the phosphines with the dinitrogen ligand trans to one hydride. As usually observed, the dinitrogen moiety adopts an end-on bonding mode and is weakly elongated from free N 2 (generally not >1%). As shown by NBO analysis, such a bonding mode involves σ-donation of about 0.2 electron from the lone pair orbital of the ruthenium-bound nitrogen toward ruthenium and back-donation of roughly 0.2 electron from the 4d occupied orbital of ruthenium to the two π g* dinitrogen orbitals.

Experimental evaluation of initial tooth displacement, center of resistance, and center of rotation under the influence of an orthodontic force.

The purpose of this study was to determine the location of the center of resistance and the center of rotation of the maxillary central incisors under the influence of a single simple force and to investigate related geometric parameters of the teeth and the surrounding periodontal tissues. By measuring the initial displacement of the central incisors with a magnetic sensing system, the location of the center of resistance and the centers of rotation associated with various forces were determined in 3 human subjects. The results show that the location of the center of resistance of the maxillary central incisor depends on the palatal bone level and is at approximately two-thirds of the palatal alveolar bone height, measured from the root apex. A greater moment-to-force ratio is needed for any controlled movement of the maxillary incisors during retraction in patients with reduced palatal alveolar bone height. This study suggests a method for estimating the location of the center of resistance of a tooth.

Generalized analysis of coupled lines in multilayer microwave MCM-D technology-application: integrated coplanar Lange couplers

In this paper, the design and realization of coplanar Lange couplers integrated in a multilayer thin-film multichip module deposition (MCM-D) technology is discussed. The MCM-D technology has been well established for the interconnection of high-speed digital circuits, and is now being recognized to be very useful for the integration and interconnection of microwave components. In this way, passive structures, such as spiral inductors, filters, and couplers, may be realized efficiently and more cost effective in MCM-D compared to monolithic microwave integrated circuits. The presented coplanar Lange couplers have been designed using an equivalent coupled-line model. A general and computationally efficient method for the determination of the required modal characteristic impedances and the related geometrical parameters in a microwave multilayer coupled-line topology is presented. Also, a way to calculate the optimum coupled line length is given. Using the described method, coplanar Lange couplers have been realized and then measured. Comparison between the measurement results and HP Momentum simulations show good agreement and indicate the feasibility of designing and integrating such components in MCM-D.

The 1,3,5,7-Tetraazadecalins: Structure, Conformation, and Stereoelectronics. Theory vs Experiment1

cis- and trans-1,3,5,7-tetraazadecalin (TAD) (2 and 4) and several N-Me (7−9) and N-acyl (10−12) substituted derivatives in the cis and trans series were prepared and characterized. The X-ray structures of 4 and 12 were analyzed and the conformational equilibria of 2 and 11 were evaluated by VT-NMR. A QM (ab initio) and MM computational study was carried out, to provide relative stabilities and geometrical parameters, which were compared with experiment. The MM2-AE (modified for the anomeric effect in N−C−N containing molecules) and MM3 force fields are useful tools for these systems. The results were interpreted in the light of stereoelectronic effects in such fused 1,3-diazane systems.

Uniform Criteria for Level-of-Service Analysis of Freeways

For level-of-service analysis, the 1994 Highway Capacity Manual divides freeways into basic sections, ramps and ramp junctions, and weaving areas. Different criteria are applied to these components to define levels of service. This use of nonuniform criteria makes it difficult to assess operating consistency in terms of the spatial change of traffic operations throughout a freeway system. This problem can be alleviated by using vehicle speed to establish a set of uniform criteria for the systemwide evaluation of freeway design and operation. Toward this end, the relationships between speed and other related geometric design and traffic parameters should be established. The spatial variations of flow characteristics on freeways, and the need to account for such variations in capacity and level-of-service analysis, are discussed first by analyzing observed speed-flow relationships. This is followed by a discussion on the selection and application of uniform criteria for planning and design.

The existence of second, third and fourth row anomeric interactions. An ab initio study of the torsional behaviour in HSCH 2SH, HSeCH 2SeH, HSCH 2SeH, HTeCH 2TeH, HSCH 2TeH and HSeCH 2TeH

The torsional behaviour in the title compounds has been probed by ab initio calculations of the gauche, gauche (g,g), gauche.anti (g,a), anti.gauche (a,g) and anti,anti (a,a) conformations at the MINI-1 ∗, 3-21G( ∗) and 3-21G ∗ levels. In the case of HSCH 2SH, results at the 6-31G ∗ level have also been obtained. Although the trends in relative energies and geometrical changes computed with the 3-21G ∗ and MINI-1 ∗ basis sets are similar for the different conformations, the C-X and C-Y bond lengths are overestimated in the latter case. For the conformations of HSCH 2SH, good correspondence is obtained for the relative energies and geometrical parameters with the 3-21G ∗ and 6-31G ∗ basis sets. The existence of putative anomeric interactions in the HXCH 2YH molecules has been evaluated by examination of the relative energies and geometrical variations of the different conformers and also by the group separation energies obtained from the isodesmic reaction HXCH 2YH + CH 4 → CH 3XH + CH 3YH. In general, the a,a conformers either relax without barrier to another conformer or are not true minima. The stabilization of the g,g relative to the a,g conformation (the anomeric effect) decreases for the heavier chalcogens and the trend even reverses for HTeCH 2YH (Y = Te, S, Se). The group separation energies (3-21 G( ∗)) including zero-point energy corrections indicate anomeric stabilizations of about 1 kcal mol −1 for the most stable conformers (g,g) of XCH 2YH (X, Y = S, Se). The g,g and a,g forms are stabilized to the same extent in HSeCH 2SeH vis-a-vis the isodesmic reaction. For HTeCH 2TeH, a stabilization energy of only 0.17 kcal mol −1 is observed for the most stable conformer (a,g). We conclude that at the 3.21G ∗ level of computation even anomeric interactions with tellurium are small but nonetheless present. We propose also that with the heavier chalcogens the energy difference between the a,g and a,a conformations may provide a better measure of anomeric stabilization in diheterosubstituted methanes.