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This paper introduces a novel deep learning approach for generating fine resolution structures that preserve all the information from the topology optimization (TO). The proposed approach utilizes neural networks (NNs) that map the desired engineering properties to seed for determining optimized structure. The main novelty of this framework is the utilization of parameters such as density and nodal deflections to predict optimized topologies for a wide range of design space. In this research, a three-stage NN framework is employed, wherein the first stage is a feedforward deep neural network. The second stage uses a convolutional neural network (CNN), and the final stage is the post-processing of results obtained from CNN. The first stage maps input design variables vector to output density distribution image. The image output of the first stage and design variables vector inputted to the first network serve as inputs to the second stage, which outputs optimized structure. Finally, post-processing of this optimized structure is done to ensure volume fraction constraint and optimal solution. These structures can be tessellated per the nodal displacement of an FEA solved larger structure. Because of this framework, the proposed approach makes TO computations faster and captures essential physics while using NNs to determine the final structure. The application of the proposed model to three-dimensional problems is also demonstrated.

The vibrations of ultrathin silicon cantilever microbeams are studied using consistent couple-stress theory to investigate size-dependent effects. The corresponding Euler-Bernoulli beam the...

Stress waves scatter upon entering a new medium. This occurs due to the reflection and transmission of the waves, which depends on the impedance mismatch between the two materials and the angle of incidence. For a bi-layered structure with finite dimensions and constant impedance ratio, the scattering and intensity of the stress waves may be varied by changing the interface profile between the two layers. In this paper, a methodology is proposed for optimizing the interface profile between the layers of a finite bi-layered plate for the objective of planar stress wave attenuation. The bi-layered plates are subjected at one end to highly impulsive loadings with various durations, and the geometry of the internal interface is optimized for the purpose of minimizing the amplitude of the maximum reaction force at the opposite fixed end. The optimization methodology is based on a genetic algorithm, which is coupled with a finite element method for analyzing the wave propagation behavior of the plates. It is observed that the interface profile and the amount of stress wave attenuation depend on the duration of the applied impulsive loading, with higher amounts of attenuation obtained when the wavelength associated with the impulsive load is small compared to the dimensions of the bi-layered plates.

Dynamic Ratcheting (DR) is a phenomenon in which plastic deformation in a hysteretic damping system increases asymmetrically in successive cycles. In the present paper, DR in single degree-of-freedom (SDOF) systems under earthquake excitation is investigated based on strong motion data collected in California between 2002 and 2012. The characteristics of earthquakes in the time–frequency domain are studied on spectrograms; furthermore, linkages between the spectrogram, displacement time history, and the Fourier Transform are identified to locate intervals during which DR is expected to occur. It is observed that DR occurs for 10 out of 160 studied earthquakes according to the proposed DR investigation procedure. The likelihood of DR seems to mainly depend on local site conditions; however, the likelihood significantly increases as the magnitude of earthquakes increases.

In the bonding of dissimilar materials, there is usually a stress singularity at the edge surface whose effects cause failure at the surface, resulting in a premature failure of the joint. In this work, the corresponding generalized stress intensity factor (GSIF) for an aluminum–epoxy joint is studied to determine the angles for which the stress singularity at the edge disappears. Experimental results are gathered for three different edge angles: a “concave” angle of 37° and a butt joint with 90°, both associated with interface stress singularities, and a “convex” angle of 143° that from theory is singularity free. It is demonstrated that the joint strength can be greatly improved by avoiding stress singularities through the selection of the proper edge angle, still preserving the external surfaces of the cylindrical samples. Testing with a larger diameter rod joint for the convex angle geometry shows the same nominal fracture strength, indicating that the measured strength is a material property independent of size when the stress singularity is absent.

A computational framework is proposed as an automated design cycle for the optimal seismic design of steel frames with self-centering connections. This paper demonstrates the approach by co...

The objective of this study is to apply a constitutive damage model for cyclic response of E-shaped dampers as well as metal and metallic plate dampers in order to be used in more broad areas such as material and component levels. The seismic isolation system used as sliding bearings and metallic dampers undergoes almost elastoplastic behavior due to seismic excitation. Accordingly, a two surface damage model is applied to understand inelastic behavior and to evaluate the potential damaged state of E-shaped dampers in the seismic isolation system. This damage model is originally formulated through a thermodynamic approach based on the entropy production equation. The cyclic damage model proposed in this study can be implemented into a user subroutine in the finite element (FE) software ABAQUS. Finally, the numerical results for E-shaped energy dissipation devices in the seismic isolation system are compared with the experimental test results so as to check the validity of the proposed model.

The objective of this study is to develop a new constitutive model for cyclic response of metals with much broader applicability. Accordingly, a two-surface damage thermoplasticity model is proposed to understand inelastic behavior and to evaluate a potential damaged state of the metals. This model, which derived from small strain theory, is formulated through a thermodynamic approach to damage mechanics based on entropy production. A simple shear problem was utilized to examine several effects of this model, such as fatigue by cyclic loading and temperature, and to allow for the thermal effects on metals. Following this, the proposed cyclic damage model is implemented as a user subroutine in the finite element software ABAQUS. Finally, numerical results of energy dissipation devices are compared with experimental data for validity of this model.

The effectiveness of a non-homogeneous soil profile for horizontal ground source heat pumps (GSHPs), defined as natural backfill with an intermediate layer of material having different thermal characteristics, is investigated. Steps toward development of a comprehensive model to consider the effects of the non-homogeneous layer are described. The developed model is utilized successfully in conjunction with a genetic algorithm (GA) search method to obtain the optimized operational parameters for a GSHP in three different climate conditions. A properly sized and engineered non-homogeneous soil profile demonstrated the potential to increase the energy extraction/dissipation rates from/to the ground to a significant level. The potential benefit of a recycled product, Tire Derived Aggregate (TDA), as an insulating non-homogeneous layer is assessed. TDA is demonstrated to be more effective in the cold climate (Buffalo) by increasing the energy extraction rates from the ground approximately 15% annually. TDA's effectiveness is less pronounced in a relatively moderate climate (Dallas) by increasing the energy extraction rates from the ground about 4% annually. For the cooling only scenario (Miami), a high conductive intermediate layer of saturated sand exhibited greater potential to increase the energy dissipation to the ground.

In real world applications, the response of structures may be dependent on the rate of loading and thus can be affected by transient loading, especially when the rate of loading is significant. In such situations, the rate of loading may become a major issue to understand structures during earthquake excitation or under blast or high velocity impact. In some cases, the rate effect on structures under strong earthquake excitation cannot be ignored when attempting to understand inelastic behavior of structures. Many researchers developed the constitutive theories in cyclic plasticity and viscoplasticity. In this study, numerical simulation by cyclic visocoplasticity models is introduced and analyzed. Finally, the analytical results are compared with experimental results as a means to evaluate and verify the model.

In this paper, aconceptual evolutionary framework for aseismic decision support for hospitalsthat attempts to integrate a range of engineering and sociotechnical models is presented. Genetic algorithms are applied to find the optimal decision sets. A case study is completed to demonstrate how the frameworkmay applytoa specific hospital.The simulations show that the proposed evolutionary decision support framework is able to discover robust policy sets in either uncertain or fixed environments. The framework also qualitatively identifies some of the characteristicbehavior of the critical care organization. Thus, by utilizing the proposedframework, the decision makers are able to make more informed decisions, especially toenhance the seismic safety of the hospitals.

Flow diverter (FD) is an emerging neurovascular device based on self-expandable braided stent for treating intracranial aneurysms. Variability in FD outcome has underscored a need for investigating the hemodynamic effect of fully deployed FD in patient-specific aneurysms. Image-based computational fluid dynamics, which can provide important hemodynamic insight, requires accurate representation of FD in deployed states. We developed a finite element analysis (FEA) based workflow for simulating mechanical deployment of FD in patient-specific aneurysms. We constructed FD models of interlaced wires emulating the Pipeline Embolization Device, using 3D finite beam elements to account for interactions between stent strands, and between the stent and other components. The FEA analysis encompasses all steps that affect the final deployed configuration including stent crimping, delivery and expansion. Besides the stent, modeling also includes key components of the FD delivery system such as microcatheter, pusher, and distal coil. Coordinated maneuver of these components allowed the workflow to mimic clinical operation of FD deployment and to explore clinical strategies. The workflow was applied to two patient-specific aneurysms. Parametric study indicated consistency of the deployment result against different friction conditions, but excessive intra-stent friction should be avoided. This study demonstrates for the first time mechanical modeling of braided FD stent deployment in cerebral vasculature to produce realistic deployed configuration, thus paving the way for accurate CFD analysis of flow diverters for reliable prediction and optimization of treatment outcome.

This paper describes the development of new material architectures for mitigating the effects of impulsive loadings using layered structures. The underlying concept explored in this research relies on stress wave attenuation associated with geometric dispersion phenom- ena in layered structures. When an incident stress pulse passes through a layered structure, a reduced stress amplitude and elongated pulse duration can be obtained with proper selection of layer materials and dimensions. Consequently, an optimal design procedure is proposed to obtain effective material architectures. The optimization involves tuning material properties and adjusting the length of each layer, along with the total length of a multilayer structure. Attenuation of elastic stress waves propagating through the proposed simple and bundled one-dimensional elastic media are investigated by considering various layered structures situated between free and fixed surfaces. DOI: 10.1061/(ASCE)CP.1943-5487.0000143. © 2012 American Society of Civil Engineers. CE Database subject headings: Layered systems; Stress; Wave propagation; Algorithms; Optimization; Elasticity. Author keywords: Layered structure; Wave propagation; Genetic algorithm; Optimization.

In this study, a two surface plasticity model was developed and used to simulate the uniaxial ratchetting response of CS 1026 steel. Most cyclic plasticity models used in ratchetting simulations are Chaboche-type nonlinear kinematic hardening models, which deal with dynamic recovery terms considering the back stress tensor. This paper describes the ratchetting simulation of steel by the two surface model based on yield theory following both isotropic and kinematic hardening rules in order to obtain enhanced ratchetting response. The parameters used in the simulation were obtained from a parametric study and were determined from the initial range and stabilized range of CS 1026 steel. In addition, the two surface model was validated by comparing the results of a ratchetting simulation with experimentally determined maximum axial strain per cycle. The ratchetting responses obtained from the two surface model are an improved simulation results compared with results from bilinear and kinematic hardening models.

The dynamic analysis of progressive collapse faces a great number of obstacles that often lead to the collapse of the analysis prior to the actual analysis of collapse. Hence, the Mixed Lagrangian Formulation that has been shown to be very robust was adopted as a framework to accommodate such analysis. By modifying the loading function and the numerical scheme, the capabilities of this framework were extended to account for strength degradation and fracture, while some insight to its behavior is introduced as well. The examples presented show a very robust and stable behavior of the numerical scheme in terms of the time step size required, even in cases where a sudden fracture takes place.

The problem of multi-objective seismic design optimization is examined within the context of passive energy dissipation systems. In particular, a genetic algorithm approach is developed to enable the evaluation of the Pareto front, where maximum inter-story drifts and maximum total accelerations, both important measures for damage, serve as objectives. Here the cost of the passive system is considered as a constraint, although it could be included instead as a third objective. Hysteretic, viscoelastic and viscous dampers are all considered as possible design strategies, as well as the weakening plus damping concept. Since different types of passive systems are included, diversity of the Pareto front becomes a key issue, which is addressed successfully through an innovative definition of fitness. The multi-objective framework enables the evaluation of trade-offs between the two objectives and, consequently, provides vital information for the decision maker. Furthermore, the results presented offer valuable...

Dynamic ratchetting is a phenomenon in which plastic deformation increases in successive cycles. In the present paper, first, various characteristics of dynamic ratchetting are demonstrated based on numerical simulation. Second, iterated maps are developed as a tool for the investigation of dynamic ratchetting in a single degree of freedom (sdof) system. When an elasto-perfectly-plastic model is employed to represent hysteretic damping, a piecewise linear solution can be obtained and used to develop iterated maps. A stability investigation in the iterated maps shows that dynamic ratchetting is developed under a stable cycling. In this stable cycling, dynamic ratchetting occurs when an excitation function loses antiperiodicity (shift symmetry).

The attenuation of elastic stress waves propagating through layered structures situated between free and fixed surfaces is investigated. A stress transfer function, which relates the stress response at the fixed support to the applied stress pulse, is derived for several specific layered structures. An analysis of these responses indicate that when an incident stress pulse passes through a layered structure, a reduced stress amplitude and elongated pulse duration could be obtained with proper selection of materials and layer dimensions. Consequently, a design procedure is proposed to obtain the optimal layered structure, and several specific cases of layered structures are investigated.

This work investigates applications and limitations of iterative modulus variation procedures combined with linear elastic analysis to calculate lower bounds of collapse loads. These modulus variation procedures are currently used to account for inelastic behavior in pressure vessel and piping system design. Here, applications to framed structures are studied. Three different modulus variation procedures are implemented within a conventional linear elastic finite element code and compared. The procedure that reduces only elastic moduli at high stressed elements of a structural model is found to be the most convenient strategy to estimate collapse conditions. This procedure is then applied to two- and three-dimensional frames, with homogeneous and non-homogeneous cross-sections, and assuming both constant and proportional loading. Using this procedure, it is possible to predict satisfactory approximations of collapse loads and failure mechanisms. In earthquake engineering practice if the earthquake motions are simulated as equivalent static proportional loads, this simplified procedure may be a useful and economical tool in the implementation of performance based design procedures in preliminary engineering, in verification processes, in structural optimization, and when facing complex geometric configurations. This procedure can be used to estimate approximations of both load redistribution in collapse conditions and failure modes when assuming different lateral load patterns along with gravity loads. It can be useful to determine optimum failure modes in new structures or weak links in existing structures. The method requires only minimal conceptual bases for application and moderate computational effort.

This paper describes the wave-propagation behavior of multilayered structures and proposes an optimization procedure for designing layered stress wave attenuators. Two types of stress wave attenuators were investigated, straight and nonstraight configurations, and their wave behaviors were analyzed using the concept of longitudinal waves in rods and flexural waves in Timoshenko beam formulations. The underlying concept in this research relies on the reflection and transmission of waves at different types of discontinuities, such as boundaries, impedance mismatches, and angled joints. Therefore, the effects of these discontinuities were explored thoroughly, and their attenuation capacity was investigated using explicit formulas. These concepts then were used to develop a heuristic optimization procedure to obtain efficient layered stress wave attenuators by properly tuning the length and material of each layer. It was assumed that the stress wave attenuators were subjected to impulsive transient lo...

This paper presents an analytical study to determine the effects of bearing stress distributions on concrete bearing strength and bearing plate flexural demand, for concrete blocks loaded concentrically through nonanchored flexible steel plates. Finite-element (FE) analyses of concrete specimens tested in previous investigations are employed to determine the bearing strength of the concrete when loaded through flexible plates. An FE parametric study is performed to derive formulas for the calculation of the concrete bearing stress distribution for flexible circular steel bearing plates. The results of this parametric study are used to develop a procedure for the design of concentrically loaded circular steel bearing plates on plain (unreinforced) concrete. The proposed procedure is compared with a standard design procedure.

In dynamic analysis, hysteretic damping often provides a reasonable model of the inelastic behavior of a structure. Nonlinearity presented by hysteretic damping, however, introduces the possibility of developing complicated motions not expected in linear dynamics. In this study, motions of a single-degree-of-freedom system with hysteretic damping under dual-frequency sinusoidal excitations are investigated through numerical simulation. Hysteretic damping behavior is represented by three different plasticity models: the elasto-perfectly-plastic model; the linear kinematic hardening model; and the two-surface model. Under certain conditions, the resultant motions from the elasto-perfectly-plastic model and the two-surface model exhibit a continual increment of plastic deformation in successive cycles. Parametric study shows that this dynamic ratcheting develops when applied frequencies are commensurable (i.e., related to each other with integer ratio), and the product of terms comprising the ratio is an eve...

Most control techniques in the structural engineering literature are aimed at improving performance of the primary structural system, but may have limited or even adverse effect on nonstructural components during strong seismic events. In this paper, we emphasize nonstructural performance using an active controller with a cubic nonlinearity. The controller is optimized based on the frequency response functions of a SDOF nonlinear oscillator. An eight-storey base-isolated benchmark building recently proposed by the ASCE structural control committee is studied as a demonstration by considering both structural and nonstructural performance indices. We compare the performance of the proposed cubic controller with that of a LQG-based semiactive control system and a passive energy dissipation system. It is shown from the simulation results that in most benchmark test cases, the cubic control system produces better nonstructural performance while maintaining good response characteristics of the primary structural system. Further research directions for this cubic control system are also pointed out. Copyright © 2005 John Wiley & Sons, Ltd.

A new computational framework is developed for the design and retrofit of building structures by considering aseismic design as a complex adaptive process. For the initial phase of the development within this framework, genetic algorithms are employed for the discrete optimization of passively damped structural systems. The passive elements may include metallic plate dampers, viscous fluid dampers and viscoelastic solid dampers. The primary objective is to determine robust designs, including both the non-linearity of the structural system and the uncertainty of the seismic environment. Within the present paper, this computational design approach is applied to a series of model problems, involving sizing and placement of passive dampers for energy dissipation. In order to facilitate our investigations and provide a baseline for further study, we introduce several simplifications for these initial examples. In particular, we employ deterministic lumped parameter structural models, memoryless fitness function definitions and hypothetical seismic environments. Despite these restrictions, some interesting results are obtained from the simulations and we are able to gain an understanding of the potential for the proposed evolutionary aseismic design methodology. Copyright © 2005 John Wiley & Sons, Ltd.

A boundary element method is developed for the determination of generalized stress intensity factors associated with bi-material interfaces. The new formulation, which is based on the theory of boundary eigensolutions, employs displacements and weighted tractions as primary variables. As a result, the solution is obtained exclusively in terms of bounded quantities enabling the attainment of mesh-independent results while requiring only surface discretization. Several numerical examples are considered to assess the performance of the method, including a detailed strength analysis of epoxy-steel cylindrical butt joints.

Within the framework of linear two-dimensional elastodynamics, stress wave intensity attenuators are studied under material and boundary condition discontinuities collectively. The influence of various parameters on the efficiency of stress wave attenuators is investigated thoroughly and a comprehensive understanding of the response is developed under dynamic loadings for a wide range of frequencies. In particular, the effect of in-plane and out-of-plane dimensions, incident wave frequencies (wavelength), rigidity of the host structure, and impedance mismatch between different layers have been examined. The dependence of stress wave attenuator efficiency and robustness are found to be a complex function of all relevant parameters, and performance is observed to vary significantly for various combinations. To illustrate the significance of combined effects of various parameters on the potential efficiency of the stress wave intensity attenuators, an optimization problem is solved. An optimal material set-up of a 12-layered structure, subjected to transient loadings with varying durations and wide range of frequency contents, is presented. A coupled genetic algorithm-finite element methodology is developed specifically for the optimal design of layered structures. This methodology is highly suitable for investigating the solution space that is too large to be explored by an exhaustive parametric study. The results of the optimal designs evidently show that the efficiency of the stress wave attenuators depends significantly on the duration of transient loading, and high efficiency can be attained for short durations.

An application of the new active aerodynamic control device proposed in the companion paper is presented in this paper. The equations for closed-loop dynamics of tall buildings under the influence of AFS are derived based on the theory presented in the companion paper. The approximate formulae based on the dynamic models are also derived to develop a design methodology for AFS application to tall buildings. An example is presented to illustrate some important issues related to design. Influence of various parameters is evaluated numerically and several practical aspects related to the installation of AFS on tall buildings are investigated.

A new aerodynamic method for controlling bidirectional wind-induced motion of bluff bodies is proposed. A generic bluff body model is suggested to develop a mathematical description of the control system dynamics. The motion in the along-wind direction is assumed to be generated by incident turbulence, while vortex-induced resonant vibrations are assumed for the across-wind direction. The control system equations are derived and the closed-loop algorithms are presented. Experiments conducted to verify the basic assumptions and to study the basic fluid dynamical features of the new device are also reported.

Bi-material interfaces are prevalent in a broad range of natural and man-made components and systems. Failures often occur on the interface at a free edge, especially when the corresponding linear elastic solution exhibits a singularity in stress, which depends upon the material properties and the included angles of the two material bodies. In this paper, we combine finite element analysis and a compact self-organizing cellular automata-based genetic algorithm for topology optimization of the bi-material system. The objective is to eliminate stress singularities and furthermore to reduce peak interface stresses. The developed algorithm is applied to a simple bi-material plate in an attempt to maximize strength through geometric design.Copyright © 2013 by ASME

Objective The aim of this study is to explain the influence of peripheral interface stress singularities on the testing of tensile bond strength. The relationships between these theoretically predicted singularities and the effect of specimen size on the measured bond strength are evaluated. Methods Finite element method (FEM) and boundary element method (BEM) analyses of microtensile bond strength test specimens were performed and the presence of localized high stress concentrations and singularities was analyzed. The specimen size effect predicted by the models was compared to previously published experimental data. Results FEM analysis of single-material trimmed hour-glass versus cast cylindrical specimens showed different theoretical stress distributions, with the dumbbell or cylindrical specimens showing a more homogeneous distribution of the stress on the critical symmetry plane. For multi-material specimens, mathematical singularities at the free edge of the bonded interface posed a computational challenge that resulted in mesh-dependence in the standard FEM analysis. A specialized weighted-traction BEM analysis, designed to eliminate mesh-dependence by capturing the effect of the singularity, predicted a specimen size effect that corresponds to that published previously in the literature. Significance The results presented here further support the attention to specimen dimensions that has already broadened the empirical use of the microtensile test methods. FEM and BEM analyses that identify stress concentrations and especially marginal stress singularities must be accounted for in reliable bonding strength assessments. Size-dependent strength variations generally attributed to the effects of flaw distributions throughout the interfacial region are not as relevant as the presence of singularities at bonded joint boundaries – as revealed by both FEM and BEM analyses, when interpreted from a generalized fracture mechanics perspective. Furthermore, this size-dependence must be considered when evaluating or designing dental adhesive systems.

Metallic plate dampers, when incorporated into a structure, provide one of the most effective energy dissipation mechanisms available during an earthquake. Increasingly, they are applied in the seismic retrofit of structures which are found to be deficient. The design of these devices, however, has been largely based upon experiments and macroscopic modeling. In order to gain more insight into the response behavior of metallic plate dampers, a microscopic mechanistic approach is followed in this paper. Included is the development of an inelastic constitutive model for the damper material. Numerical results obtained for a class of metallic plate dampers are presented and comparisons are made with experimental data for validation of the mathematical model. It is also shown that this approach sheds light on several aspects of the damper response which heretofore have not been addressed adequately.

Thermal expansion of the part can be a significant source of dimensional and form errors in precision machining operations. This paper describes a method for calculating the thermal expansion of an axisymmetric workpiece. The analysis is based on a commercially available boundary element code modified to properly represent concentrated moving heat sources such as those produced in machining. The inputs required are the amount of heat entering the part from the cutting zone and the thermal properties of the workpiece material. Calculations are compared with direct measurements of expansion from tests on large diameter 2024 aluminum sleeves. The agreement between calculated and measured values is generally reasonable, although calculated expansions are consistently smaller than measured expansions. This error is probably due to errors in estimating the heat input to the part, and particularly the neglect of flank friction in heat input calculations. Sample calculations for hard turning of a wheel spindle show that expansions can approach tolerances on critical surfaces. Based on sample calculations, thermal expansion is likely to be significant when hard turning parts with tolerances on the order of 0.01 mm. For these applications, critical surfaces should be machined first, before cuts on other sections heat the part, and gaging should be carried out only after the part has cooled.

Despite numerous efforts to impose control measures on the heat pump side of Ground Source Heat Pump (GSHP) systems, there has been little thought into the potential of control on the ground characteristics. This is perhaps because of a predisposition to believe that ground related works usually are associated with extra capital investment that makes any modification less favorable than making changes to the heat pump unit. An effective control strategy with a non-homogeneous soil profile for the ground side of horizontal GSHPs was investigated in this research. The model incorporates the effects of a variety of surface energy fluxes to provide an accurate estimate of the ground thermal regime. The developed model was utilized successfully in conjunction with the MATLAB Genetic Algorithm (GA) toolbox to obtain the optimized operational parameters for a GSHP in a cold climate condition (Buffalo, NY). A properly sized and engineered non-homogeneous soil profile demonstrated the potential to boost the capacity of GSHP systems to a significant level. The potential benefits of a recycled product of tire industry, Tire Derived Aggregate (TDA), as an insulation blanket was assessed via the optimization algorithm. TDA was demonstrated to be effective in heating mode in a cold climate environment by increasing the energy extraction rates from the ground by about 15% annual. The annual percentage increase in energy dissipation rate to the ground, in cooling season, with TDA blanket was 7.6%. The results are suggestive of the beneficial application of a layered system to increase the performance of GSHPs. A shift in design perspective toward consideration of more control strategies for the ground pipe side of GSHPs is suggested based on the model results.Copyright © 2012 by ASME

The large energy demand from the HVAC industry for residential buildings, along with the ever growing need for the utilization of renewable sources of energy, has brought considerable attention to the area of induced ventilation. Windcatchers are green architectural structures historically used for the passive ventilation of the indoor spaces with the minimal non-renewable energy consumption. In this paper, a computational fluid dynamics (CFD) model is used to assess a windcatcher’s performance with different characteristics of the windcatcher design. For a single room with heat emitting objects, the effects of the windcatcher louver design and height were thoroughly evaluated in conjunction with a variety of dominant wind velocity and incident angles. A comparison was drawn between the ventilation efficiency for the cases of circular and rectangular windcatcher designs. Thermal discomfort (PD) values due to draft were calculated for different temperature and wind velocities. The developed model was employed to obtain the optimized configuration for the windcatcher-room system. The effect of ambient weather conditions on the results was investigated by performing the simulations for a range of air temperature and velocities. Results obtained in this paper provide windcatcher designers with valuable insights on the important design parameters such as windcatcher height, louver design and impact of ambient conditions.Copyright © 2012 by ASME

An analytical approximate constitutive relation is derived for a form of fluid damper, which exhibits viscoelastic behavior. The damper is used for vibration isolation of piping systems and industrial equipment, as well as for vibration and seismic isolation of building structures. The damper consists of an open pot, filled with highly viscous fluid, and a piston that moves within the fluid. The analytical solution relates the damping constant of the unit at vanishingly small frequencies with the material constants of the fluid used in the damper and the geometric characteristics of the damper. With the determination of the damping constant, a macroscopic model may be constructed that describes the damper behavior over a large frequency range. The other parameters of the macroscopic model are identical to those in the corresponding constitutive relation of the damper fluid. The results of the analytical solution are in very good agreement with experimental data and with numerical solutions based on boundary-element analysis.

The stress intensity factors for cracks in three-dimensional, thermally stressed structures are computed by using the boundary element method. While many boundary and volume-integral-based formulations are available for the treatment of thermoelastic problems in solids, the present analysis is based on a recently developed boundary-only formulation. The accuracy of the solutions in the present work is improved by using special elements at the crack front that accurately model the variation of displacement, temperature fields and singularity of traction, flux fields.

We present some local wear calculations that compare the Standard pressure-based local wear model with a newer one (DSS) that includes von Mises stresses. The DSS model predicts the conforming wear tracks that one often finds at real contacts but cannot be predicted by the Standard approach. However, we find that the newer method, while giving conforming wear track shapes, can predict different amounts of global wear when identical materials in conformal contact are slid against one another. This is not found in experimental studies of a nominally similar system. We conclude that no universally local wear modeling approach exists and the present time.Copyright © 2010 by ASME

The effectiveness of hysteretic passive devices to protect and mitigate the response of a structure under seismic loading is well established by both analytical and experimental research. Nevertheless, a systematic and well-established methodology for the topological distribution and size of these devices in order to achieve a desired structural response performance does not exist. In this paper, a computational framework is proposed for the optimal distribution and design of yielding metallic buckling restrained braces (BRB) and/or friction dampers within steel moment-resisting frames (MRF) for a given seismic environment. A Genetic Algorithm (GA) is used to solve the resulting discrete optimization problem. Specific examples involving two three-story, four-bay steel MRFs and a six-story, three-bay steel MRF retrofitted with yielding and/or friction braces are considered. The seismic environment consists of four synthetic ground motions representative of the west coast of the United States with 5% probability of exceedance in 50 years. Non-linear time-history analyses are employed to evaluate the potential designs. As a result of the evolutionary process, the optimal placement, strength and size of the dampers are obtained throughout the height of the steel MRF. Furthermore, the developed computational approach for seismic design based upon GAs provides an attractive procedure for design of MRFs with hysteretic passive dampers.

A new boundary element formulation is developed to determine the complex stress intensity factors associated with cracks on the interface between dissimilar materials. This represents an extension of the methodology developed previously by the authors for determination of free-edge generalized stress intensity factors on bimaterial interfaces, which employs displacements and weighted tractions as primary variables. However, in the present work, the characteristic oscillating stress singularity is addressed through the introduction of modified weighting functions and corresponding numerical quadrature formulas. As a result, this boundary-only approach provides extremely accurate mesh-independent solutions for a range of interface crack problems. A number of computational examples are considered to assess the performance of the method in comparison with analytical solutions and previous work on the subject.Copyright © 2005 by ASME

In order to better understand the performance of clutches, brakes and seals, there is a need to study the multiscale thermomechanical interactions that occur across rough interfacial sliding contacts. While the full three-dimensional problem is at present somewhat beyond reach from a computational standpoint, we can gain some insight into the problem by examining the more idealized axisymmetric case. Here we develop a transient coupled thermomechanical boundary element method to investigate the behaviour of sliding rings with axisymmetric roughness. By incorporating our recently developed fast convolution algorithm, we are able to consider the spatially and temporally localized response at asperity-level contacts, along with the evolution toward a global component-level steady state. In particular, we investigate behaviour for the sliding ring problem by considering surface profiles that incorporate axisymmetric roughness over several orders-of-magnitude. One of the most interesting findings that emerge from these simulations is the development of roughness-dependent steady-state shapes. Details of the short-time transient interactions are found to significantly affect the long-term component level response. This suggests that one may be able to control overall component deformations through the careful specification of surface profiles.

In order to determine whether changes in glazing would affect the outcome of window accidents. over 8000 accidents reported in the Consumer Product Safety Commission's data bases were analyzed to find the patterns of human behaviour leading to glass breakage. Each pattern formed the basis for a simple biomechanical model to estimate the masses and velocities of human impacts with the glass. Two physical models of the effect of an impact on window glass were used to predict the probability of glass breakage in each pattern. Window parameters of glass size and thickness were varied to estimate the potential for protection by window design. It was concluded that in only two of the patterns (HIT and PUSH) was it possible to choose glass parameters which assured a high degree of protection for the victim. For whole body impacts (WALK and TRIP) extreme thicknesses of tempered glass would be needed to prevent breakage.

This paper presents the extension of a flexibility-based large increment method (LIM) for the case of cyclic loading. In the last few years, LIM has been successfully tested for solving a range of non-linear structural problems involving elastoplastic material models under monotonic loading. In these analyses, the force-based LIM algorithm provided robust solutions and significant computational savings compared to the displacement-based finite element approach by using fewer elements and integration points. Although in cyclic analysis a step-by-step solution procedure has to be adopted to account for the plastic history, LIM will still have many advantages over the traditional finite element method. Before going into the basic idea of this extension, a brief discussion regarding LIM governing equations is presented followed by the proposed solution procedure. Next, the formulation is specified for the treatment of the elastic perfectly plastic beam element. The local stage for the beam behavior is discussed in detail and the required improvement for the LIM methodology is described. Illustrative truss and beam examples are presented for different non-linear material models. The results are compared with those obtained from a standard displacement method and again highlight the potential benefits of the proposed flexibility-based approach.

A boundary element approach is developed for problems of hot fluid-structure interaction. The structure is idealized as a thermoelastic solid, and a time-domain, boundary-only integral formulation is described. Meanwhile, several approaches are discussed for the hot fluid. Integral equations are developed for both compressible and incompressible thermoviscous flow. Due to the presence of nonlinear convective terms in the governing differential equations, domain discretization is generally required. However, with the introduction of reference velocities, volume modeling often can be confined to regions near obstacles and walls. All formulations are implemented for two-dimensional problems in GP-BEST, a general purpose boundary element computer program. An overview of this numerical implementation is provided, along with several illustrative examples. The present fluid formulations are appropriate in the low to medium Reynolds number ranges, however, some enhancements required for higher speed simulations are noted.