Separate Substructures Research Articles

A novel optimization framework using frequency-based substructuring for estimation of linear bolted joint stiffness and damping

Estimating the stiffness and damping coming from a joint is a major challenge. This work proposes a novel framework to estimate the unknown parameters using frequency-based substructuring and a maximum a posteriori optimization approach. The idea is to minimize the discrepancy between the measured responses of an assembled system and the responses obtained by coupling the measured responses of the individual substructures with a joint model. The system’s dynamics are assumed to be linear. However, the FRFs of the coupled system (which drive the objective function) change nonlinearly with the linear joint parameters, making it a nonlinear optimization problem. Therefore, the joint parameters are estimated iteratively using the Gauss minimization method, a well-established linearization scheme. The framework is numerically validated on simple mdof systems, and the method’s effectiveness is tested by adding noise to the generated data. To demonstrate the framework’s applicability on real structures, joint stiffness and damping of a known benchmark structure are estimated based on real measurements. Two different underlying joint models are applied. The first assumes just flexibility at the connection. The second assumes the joint is a separate substructure. The algorithm can find realistic stiffness parameters and a range for the damping parameters providing a good compromise between the measurements in both cases.

Dosimetric Impact of Delineation and Motion Uncertainties on the Heart and Substructures in Lung Cancer Radiotherapy

AimsDelineation variations and organ motion produce difficult-to-quantify uncertainties in planned radiation doses to targets and organs at risk. Similar to manual contouring, most automatic segmentation tools generate single delineations per structure; however, this does not indicate the range of clinically acceptable delineations. This study develops a method to generate a range of automatic cardiac structure segmentations, incorporating motion and delineation uncertainty, and evaluates the dosimetric impact in lung cancer. Materials and methodsEighteen cardiac structures were delineated using a locally developed auto-segmentation tool. It was applied to lung cancer planning CTs for 27 curative (planned dose ≥50 Gy) cases, and delineation variations were estimated by using ten mapping-atlases to provide separate substructure segmentations. Motion-related cardiac segmentation variations were estimated by auto-contouring structures on ten respiratory phases for 9/27 cases that had 4D-planning CTs. Dose volume histograms (DVHs) incorporating these variations were generated for comparison. ResultsVariations in mean doses (Dmean), defined as the range in values across ten feasible auto-segmentations, were calculated for each cardiac substructure. Over the study cohort the median variations for delineation uncertainty and motion were 2.20–11.09 Gy and 0.72–4.06 Gy, respectively. As relative values, variations in Dmean were between 18.7%–65.3% and 7.8%–32.5% for delineation uncertainty and motion, respectively. Doses vary depending on the individual planned dose distribution, not simply on segmentation differences, with larger dose variations to cardiac structures lying within areas of steep dose gradient. ConclusionRadiotherapy dose uncertainties from delineation variations and respiratory-related heart motion were quantified using a cardiac substructure automatic segmentation tool. This predicts the ‘dose range’ where doses to structures are most likely to fall, rather than single DVH curves. This enables consideration of these uncertainties in cardiotoxicity research and for future plan optimisation. The tool was designed for cardiac structures, but similar methods are potentially applicable to other OARs.

Parameter Identification of Multispan Rigid Frames Using a Stiffness Separation Method.

Identifying the parameters of multispan rigid frames is challenging because of their complex structures and large computational workloads. This paper presents a stiffness separation method for the static response parameter identification of multispan rigid frames. The stiffness separation method segments the global stiffness matrix of the overall structure into the stiffness matrices of its substructures, which are to be computed, thereby reducing the computational workload and improving the efficiency of parameter identification. Loads can be applied individually to each separate substructure, thereby guaranteeing obvious local static responses. The veracity and efficacy of the proposed methodology are substantiated by applying it to three- and eight-span continuous rigid frame structures. The findings indicate that the proposed approach significantly enhances the efficiency of parameter identification for multispan rigid frames.

Coupling of Component Models with Mismatching Interfaces for an Efficient NVH Vehicle Design

<div class="section abstract"><div class="htmlview paragraph">The NVH optimization of new vehicle models can in principle only be carried out in a relatively late stage of the development process, when the geometrical data (CAD) are available and can be used to generate detailed Finite Element (FE) models of the car body. Unfortunately, in this stage of the development process most of the geometrical data are already fixed and countermeasures are limited and expensive. In order to be able to evaluate design concepts in an earlier conceptual stage of the development process existing models of similar predecessor vehicles must be used leading to techniques such as “mesh-morphing” or “concept modelling” (see for instance [<span class="xref">1</span>, <span class="xref">2</span>]). Here, a different approach is investigated based on a substructuring technique. In principle the coupling of the component-structures coming from different models would require post-processing in order to obtain compatible interface degrees-of-freedom (DOFs), an operation which in most cases must be carried out manually and is very time consuming. This paper presents a novel substructuring approach that tackles a continuous interface by only considering a small set of coupling DoFs. This approach employs the discretisation of interfaces between structural parts or structural-acoustic domains in terms of pivotal points and patches. In this manner, the requirement of spatial continuity between the models of the separate substructures is no longer needed and subsystems with incompatible interfaces can be coupled. Thus, an efficient vibro-acoustic design optimisation procedure for components shared by different vehicle models, such as the car floor, is enabled. It will be shown that a single car floor model can be successfully coupled with different upper-body structures, even when they have a different location of coupling DoFs.</div></div>

A Structural Configuration with Separate Substructures towards Reducing the Seismic Damage of Spatial Structures with Rectangular Plan

Seismic damage of spatial structures of rectangular plan with RC substructures was observed in several earthquakes, especially in the RC substructures. In order to reduce the seismic damage potential, a new structural configuration of spatial structure of rectangular plan is proposed, the substructures of which are composed of the steel substructure and the RC substructure. The latter only bears the vertical load of roof by the arrangement of horizontal sliding bearings between the roof and the RC substructure. The pushover analyses are performed on a steel braced frame and an RC frame with similar lateral stiffness, and the results show that the lateral capacity of the steel structure is much larger than those of the RC structures. A spatial structure of rectangular plan with two different substructures is designed according to Chinese structural designing codes. Seismic time history analyses are carried out for the spatial structure under five ground motions. The results show that the damage mainly concentrates on the substructures, and the seismic performance of the structure with steel and RC substructures is much better than that of the structure with RC substructures.

Limits of applicability of the standard method for estimating the torsional rigidity of spatial frames of buggy vehicle

The article provides an assessment of the limits of applicability of the standard methodology for estimating the torsional rigidity of spatial rod-bearing systems of automobiles. Torsional stiffness, as shown by numerous studies and practices, is one of the most important indicators of the carrying capacity of vehicle bodies (frames) of all types of vehicles - including such highly specialized ones as buggy. The authors show on the example of the bearing structure of an off-road vehicle of the “buggy” class that the general application approach to the assessment of the torsional rigidity of the bearing systems using torsion deflection stumbles upon limitations when it comes to spatial frames of complex construction. These restrictions are dictated by the difference in stiffness between design zones (zones should be understood as the floor area, the waist area and the roof area), which is reflected in the significantly different distribution of displacements in them. As a result, it becomes impossible to unequivocally give an opinion on the torsional rigidity of the frame using torsion deflection, since it is impossible to select a reference point in any of the zones (or the entire zone) to adequately describe the torsional rigidity of the whole structure (or a separate substructure). In this regard, the authors proposed the limits of applicability of the traditional method for estimating the torsional stiffness of a spatial core structure, and also proposed a method for overcoming these difficulties encountered when trying to assess the torsional stiffness of the supporting structure. The object of the research is a typical spatial frame of an all-terrain automobile of the D2 class buggy.

Peculiarities of the coherence time of a spectral supercontinuum generated in microstructured fibers with two zeros in the group-velocity dispersion

We used a numerical simulation to calculate the coherence time of the spectral supercontinuum generated in a microstructured fiber in which the group velocity dispersion as a function of wavelength and pump pulse width has two zeros. We determined the contribution to the total coherence time from each of the separate substructures in the resulting spectral supercontinuum for various models of the initial pulse parameters. We show that, near the zeros in the group-velocity dispersion, the spectral supercontinuum coherence time is observed to be a rapidly increasing function of the central wavelength of the initial pulse. This is because the primary contribution to the coherence time near the zeros in the group-velocity dispersion in such cases comes from regular structures formed during generation of the supercontinuum. At intermediate wavelengths between the zeros in the group dispersion, the contribution to the interference signal from the regular structures shifts from one substructure to another and depends on the central wavelength of the emission.

A Receptance Coupling Approach to Optimally Tune and Place Absorbers on Boring Bars for Chatter Suppression

A receptance coupling based method to optimally tune and place a tuned mass damper (TMD) on slender boring bars is presented. The boring bar and the TMD are treated as separate substructures. Substructural receptances are synthesized while optimizing TMD parameters as well as its location on the bar to target an increase in dynamic stiffness of the boring bar to improve chatter-free cutting conditions. Simulation based results with the proposed approach agree with classical analytical models reported in the literature. Methods presented are generalizable and can be extended to other slender cantilevered tools to increase their resistance against chatter vibrations.

Finite element modeling and pyroshock response analysis of separation nuts

Separation nuts are widely used as release devices to fasten and separate substructures of launching systems in aerospace applications. High shock transient response is generated during the separation of release devices, which tends to cause damage to the nearby micro mechanism and hardware. The purpose of this article is to predict the shock response of separation nut and find out the sensitive parameters for shock response. In this article, the explicit dynamics method hydrocodes is adopted to model the separation nuts, upon which the pyroshock response is investigated. Firstly, the separation mechanism of the nuts is introduced. Then, a FE model for the separation nuts is developed using hydrocodes software ANSYS/Autodyn, which is validated by comparing the simulation results with the pyroshock test data in shock response spectrum (SRS). Finally, the effects of the preload level and the amount of explosive on the pyroshock response are discussed. The simulation results demonstrate that decreasing the preload level is a more efficient way to reduce the pyroshock received by the spacecraft.

Major substructure in the M31 Outer Halo: the East Cloud

We present the first detailed analysis of the East Cloud, a highly disrupted diffuse stellar substructure in the outer halo of M31. The core of the substructure lies at a projected distance of $\sim100$ kpc from the centre of M31 in the outer halo, with possible extensions reaching right into the inner halo. Using Pan-Andromeda Archaeological Survey photometry of red giant branch stars, we measure the distance, metallicity and brightness of the cloud. Using Hubble Space Telescope data, we independently measure the distance and metallicity to the two globular clusters coincident with the East Cloud core, PA-57 and PA-58, and find their distances to be consistent with the cloud. Four further globular clusters coincident with the substructure extensions are identified as potentially associated. Combining the analyses, we determine a distance to the cloud of $814^{+20}_{-9}$ kpc, a metallicity of $[Fe/H] = -1.2\pm0.1$, and a brightness of $M_V = -10.7\pm0.4$ mag. Even allowing for the inclusion of the potential extensions, this accounts for less than $20$ per cent of the progenitor luminosity implied by the luminosity-metallicity relation. Using the updated techniques developed for this analysis, we also refine our estimates of the distance and brightness of the South-West Cloud, a separate substructure analyzed in the previous work in this series.

Purification, characterization and crystallization of the F-ATPase from Paracoccus denitrificans.

The structures of F-ATPases have been determined predominantly with mitochondrial enzymes, but hitherto no F-ATPase has been crystallized intact. A high-resolution model of the bovine enzyme built up from separate sub-structures determined by X-ray crystallography contains about 85% of the entire complex, but it lacks a crucial region that provides a transmembrane proton pathway involved in the generation of the rotary mechanism that drives the synthesis of ATP. Here the isolation, characterization and crystallization of an integral F-ATPase complex from the α-proteobacterium Paracoccus denitrificans are described. Unlike many eubacterial F-ATPases, which can both synthesize and hydrolyse ATP, the P. denitrificans enzyme can only carry out the synthetic reaction. The mechanism of inhibition of its ATP hydrolytic activity involves a ζ inhibitor protein, which binds to the catalytic F1-domain of the enzyme. The complex that has been crystallized, and the crystals themselves, contain the nine core proteins of the complete F-ATPase complex plus the ζ inhibitor protein. The formation of crystals depends upon the presence of bound bacterial cardiolipin and phospholipid molecules; when they were removed, the complex failed to crystallize. The experiments open the way to an atomic structure of an F-ATPase complex.

A technique of computer-aided synthesizing a finite element model of wing center section and outer wing torsion box joint for a transport aircraft

A technique of synthesizing the finite element model of the flange joint of the outer wing torsion box with the wing center section for a transport aircraft is presented. The technique is based on the functional decomposition principle, in which the general model of wing torsion box is synthesized from the separate substructure models including the flange joint. It has been shown that the manual input is significantly reduced, when the computer-aided synthesis is applied. This made it possible to cut time of synthesis and decrease the probability of error occurrence.

Pseudo-Dynamic Analysis and Construction Methods of Substructure for Division Plate of New Tank

Combined with practical experience a kind of new horizontal storage tank with separate plate was put forward. In view of the lack of experience in the design of the new tank and limitations of carrying out shaking table test for full scale horizontal storage tank, the pseudo-dynamic analysis of separate plate substructure with 5m diameter is done by using ANSYS finite element software combined with the actual engineering. The fluid loads action and mechanical model were simplified, and elastic-plastic mechanical properties of separate plate substructure under the cyclic loading actions were investigated, then deformation and stress distribution of separate plate were obtained. The design thickness for separate plate which in the horizontal storage tank is verified by finite element analysis and the horizontal tank construction methods is given. These can provide technical support to improve the practical design of large horizontal storage tank.

A normal modes technique to reduce the order of poroelastic models: application to 2D and coupled 3D models

SUMMARY A reduced-order model for structures involving poroelastic materials is proposed in this paper. The approach is based on a separation of the solid and fluid phases of the porous material into separate substructures. For each individual substructure, a decoupled normal mode basis is considered, from which a set of vectors for the decomposition is selected. The preserved modes are completed by an additional family to correct for the influence of the static response of the non-preserved. It is shown that the only neglected phenomenons in the model are the inertia of the non-preserved modes and part of their intercoupling. The following three features render the proposed scheme computationally attractive: (i) real valued matrices are involved in the transformations; (ii) the assembly of complex, frequency dependent matrices is only performed at the stage of solving for a particular frequency; and (iii) the number of normal modes required are selected using a novel method. The computational efficacy is demonstrated, on a simple but realistic 3D case, through numerical results obtained using a reduced number of DOFs, showing a significant reduction of computational cost compared with traditional methods. Copyright © 2013 John Wiley & Sons, Ltd.

Structural acoustic optimization of ribbed panels excited by complex forcing functions

Structural acoustic optimization is performed on a ribbed panel exited by diffuse acoustic field and turbulent boundary layer (TBL) flow. In order to vary the rib location during the optimization, component mode synthesis (CMS) was used with the rib and plate treated as separate substructures. The CMS approach couples the individual modes of the rib and plate using impedances at the connection points thus only requiring full eigenanalysis and radiation resistance calculations once and allowing for more rapid function evaluation during the optimization. The optimization was then performed using an evolutionary strategy with covariance matrix adaption. The rib location and properties were varied by the optimizer to find the best low-noise panel. An exhaustive search was performed to verify the optimum solution and compare results for several objective functions. Alternative design variables and constraints will also be discussed.

Searching for phenotypic causal networks involving complex traits: an application to European quail

BackgroundStructural equation models (SEM) are used to model multiple traits and the casual links among them. The number of different causal structures that can be used to fit a SEM is typically very large, even when only a few traits are studied. In recent applications of SEM in quantitative genetics mixed model settings, causal structures were pre-selected based on prior beliefs alone. Alternatively, there are algorithms that search for structures that are compatible with the joint distribution of the data. However, such a search cannot be performed directly on the joint distribution of the phenotypes since causal relationships are possibly masked by genetic covariances. In this context, the application of the Inductive Causation (IC) algorithm to the joint distribution of phenotypes conditional to unobservable genetic effects has been proposed.MethodsHere, we applied this approach to five traits in European quail: birth weight (BW), weight at 35 days of age (W35), age at first egg (AFE), average egg weight from 77 to 110 days of age (AEW), and number of eggs laid in the same period (NE). We have focused the discussion on the challenges and difficulties resulting from applying this method to field data. Statistical decisions regarding partial correlations were based on different Highest Posterior Density (HPD) interval contents and models based on the selected causal structures were compared using the Deviance Information Criterion (DIC). In addition, we used temporal information to perform additional edge orienting, overriding the algorithm output when necessary.ResultsAs a result, the final causal structure consisted of two separated substructures: BW→AEW and W35→AFE→NE, where an arrow represents a direct effect. Comparison between a SEM with the selected structure and a Multiple Trait Animal Model using DIC indicated that the SEM is more plausible.ConclusionsCoupling prior knowledge with the output provided by the IC algorithm allowed further learning regarding phenotypic causal structures when compared to standard mixed effects SEM applications.

INVESTIGATION OF DYNAMIC RESPONSE CHARACTERISTICS OF GRAVITY DAMS BY SUB-STRUCTURE APPROACH

ABSTRACT In the sub-structure approach for dynamic response analysis of gravity dams the dam-foundation rock and the dam-reservoir water interaction forces are first estimated by solving the wave equation for the foundation-rock and the reservoir domains with suitable boundary conditions, and the response of the dam by treating it as a separate sub-structure with the earthquake and the interaction forces applied externally. Using this approach, the effect of various controlling parameters on the dynamic response of the tallest monolith of Koyna dam has been investigated with the accelerogram of the M6.5 earthquake of 10 December 1967 as input excitation. Nine different combinations of the Young's modulus of foundation rock, water level in the reservoir, thickness of the sedimentary deposits in the reservoir, and the Young's modulus of the rock underlying the sedimentary layer have been considered to investigate the significance of each of these parameters on the dam response. It has been established that the sub-structure approach is able to predict the response of gravity dams by accounting for the effect of various interaction forces in a quite realistic way, provided the foundation can be approximated to be a half-space.

Real-time substructuring technique for the shaking table test of upper substructures

In this study, a real-time substructuring technique for the shaking table test is proposed. The proposed technique adopts the upper part of the object structure as the experimental substructure and the lower part as the numerical substructure. The force exerted on the interface of the two separated substructures is calculated on-line using the feed-back from an absolute floor acceleration measurement. The acceleration at the interface of the two substructures is calculated through an on-line time history analysis of the numerical substructure and is used as a reference signal in the shaking table controller. The inverse transfer function of the shaking table is employed to minimize the errors between the reference signal and generated ground motion for the experimental substructure. Through a shaking table test, the validity and accuracy of the proposed technique is demonstrated, and a good agreement between experimental and numerical results is obtained.

Structural Organization of the Pedunculopontine Nucleus of the Tegmentum of the Dog Midbrain

The aim of the present work was to perform cytoarchitectonic studies of the pedunculopontine nucleus (PPN) of the tegmentum of the midbrain in dogs to define the margins of this structure and to describe its separate substructures. The Nissl and Kluver-Barrera methods and histochemical detection of NADPH-diaphorase, this being a selective marker for cholinergic neurons in the tegmentum, were used to analyze the fiber organization, the morphological types of neurons, and the neuron density in the PPN of the tegmentum. This yielded a map of this nucleus in the dog with descriptions of the margins of its component zones: the compact and the diffuse. The mesencephalic extrapyramidal part could not be discriminated from the general composition of the PPN of the tegmentum.

Damage detection of base‐isolated buildings using multi‐input multi‐output subspace identification

AbstractA damage detection algorithm of structural health monitoring systems for base‐isolated buildings is proposed. The algorithm consists of the multiple‐input multiple‐output subspace identification method and the complex modal analysis. The algorithm is applicable to linear and non‐linear systems. The story stiffness and damping as damage indices of a shear structure are identified by the algorithm. The algorithm is further tuned for base‐isolated buildings considering their unique dynamic characteristics by simplifying the systems to single‐degree‐of‐freedom systems. The isolation layer and the superstructure of a base‐isolated building are treated as separate substructures as they are distinctly different in their dynamic properties. The effectiveness of the algorithm is evaluated through the numerical analysis and experiment. Finally, the algorithm is applied to the existing 7‐story base‐isolated building that is equipped with an Internet‐based monitoring system. Copyright © 2004 John Wiley & Sons, Ltd.