Non-uniform Mass Distribution Research Articles

A Comparative Study on Seismic Behaviour of Plan Irregular Buildings

Abstract: Asymmetrical plan irregularities occur when the horizontal layout of a building is non uniform or unsymmetrical in one or more axes. These irregularities may arise from variations in building shape, size, or configuration, leading to nonuniform distribution of mass, stiffness, or load paths throughout the structure. Considering equivalent static analysis (ESA) and response spectrum analysis (RSA) as per IS 1893-Part 1 (2016) considering seismic zones III, structure with square shaped plan performs better than the other shaped models (viz. T, L, H and Plus shapes) with least values of storey displacement and storey drift ratio, and also with higher value of storey stiffness. Thus, square plan shaped structure is seismically more resistant than T, L, H and Plus shaped structures.

The Study of the Balancing Process for Starting Rotors in Heavy-Duty Vehicles: An Industrial Application

In the heavy-duty vehicle industry, unbalance in the armature is one of the most common problems affecting starters’ performance and durability. This research presents a comprehensive study to improve the balancing process for starting rotors in heavy-duty vehicles. The complete manufacturing process of armatures was analyzed to understand the contribution of assembly processes to unbalancing. The analysis revealed that the primary factor leading to high unbalance in these parts is the misalignment of conductors within the armature winding. During assembly, these conductors experience axial movements, resulting in non-uniform mass distribution and causing unbalanced values ranging from 150 to 350 g·mm. These values surpass the permissible limit, making rectification during the balancing process at the end of the assembly impossible. Consequently, a novel alignment tool was designed to address this issue, significantly reducing the effect and achieving the maximum allowable unbalance of 100 g·mm. This allowed the balancing machine used in the process to correct the initial unbalance of the reinforcements in a single work cycle, improving operation efficiency by about 15%.

Designing a personalized thermo-mechanically optimized liner for transfemoral prosthetics

Elastomeric interphases (liners) protect the residual limb and distribute mass bearing to the prosthetic socket. However, discomfort due to excessive sweat and heat in the residual limb is the most relevant factor that negatively affects the quality of life in transfemoral prosthetics users. Additionally, a warm and humid environment and the non-uniform mass distribution can compromise blood flow in the residual limb; these factors favor the development of skin lesions, the dropout rate of prosthetic use, and subsequent amputations. Previous mathematical models that predict skin temperature distribution based on Pennes' model and explain the Fourier and non-Fourier thermic response are available. However, these models require knowledge of difficult parameters to obtain in conditions that lead to amputation. Therefore, the current study aims to propose an experimentally based method to design a personalized liner with areas of different diffusivity rates by using perforations according to thermal needs, preserving the mechanical properties of the liner. After thermal and mechanical characterization, we elaborated a personalized plane liner according to the thermal expression of the anterior thigh using infrared analysis. We tested the liner to probe its ability to dissipate heat.

Shape correction of deep-towed seismic arrays by using floaters and a cone-shaped drogue

Deep-towed multi-channel seismic arrays play vital role in marine geological exploration. However, these arrays often assume a "W" shape due to the weight of digital transmission units, adversely affecting hydrophone positioning and strata imaging. Floaters and a cone-shaped drogue are designed to correct the array shape, and numerical simulations are employed to validate the corrective effect in this paper. Additional drag forces induced by the floaters and drogue are identified using computational fluid dynamics, then they are integrated into the array model compiled to express the nonuniform mass distribution and concentrated loads based on absolute nodal coordinate formulation. Moreover, bending characteristics of arrays is fine-tuned through physical tests. Finally, simulation results indicate the floater has obvious effect than the drogue in the array shape correction, and the array shape becomes a simple convex curve with the presence of floaters and drogues under various towing conditions, facilitating hydrophone positioning. Furthermore, the array shape from the travel time positioning in sea trials also exhibit similar convex curves, and the signal-to-noise ratio of the seabed profile is much improved compare to previous one. This study also underscores the efficiency of numerical simulation in developing stabilization equipment for deep-towed multi-channel seismic arrays.

Laminated acoustic metamaterials for low-frequency broadband ultra-strong sound insulation

In this paper, a kind of laminated acoustic metamaterials (LAMS), which can realize the bandwidth widening and amplitude improvement through the parallel coupling of in-plane gradient parameters and the series laminated design in the thickness direction of the local resonance units, is proposed. The designed LAMS consists of two different layers of single-layer acoustic metamaterials (SLAMs) laminated in series in the thickness direction. During the design process of the two layers of SLAMs, non-uniform mass distribution and non-consistent frame coupling layouts are respectively introduced to broaden the sound insulation frequency band of the acoustic metamaterials. Through careful design, the two layers of SLAMs have distinct working frequency bands, effectively preventing the occurrence of sound insulation valleys with low amplitude. Based on numerical analysis of two layers of SLAMs, this study discusses the results of transmission loss (TL) and the working mechanism of interlayer superposition coupling sound insulation. The analysis of TL for LAMS reveals its capability to achieve ultra-strong sound insulation effects across a low-frequency broadband range. The accuracy of the numerical analysis in this study is verified through semi-analytical methods and small-scale impedance tube experiments. The LAMS proposed in this paper holds significant potential for wide-band noise reduction control in various high-noise mechanical equipment or workplaces.

An inelastic beam-like model for nonlinear dynamic analyses of multi-storey buildings

This paper presents an equivalent non-uniform inelastic beam-like model for the evaluation of the nonlinear behaviour of multi-storey buildings subjected to earthquake loadings. The proposed beam can be used to model buildings with non-uniform mass and stiffness distribution. The model is characterised by a number of degrees of freedom corresponding to the number of floors of the building and is conceived to predict its nonlinear dynamic response after a proper calibration based on the results of pushover analyses performed on a nonlinear FEM model. In spite of its simplicity, the proposed equivalent model provides, with a very low computational effort, an accurate representation of the nonlinear dynamic behaviour of the building comparable to that obtained through the more demanding nonlinear 3D FEM models. The effectiveness of the proposed simplified modelling approach is here validated by means of nonlinear dynamic analyses firstly performed on a benchmark known in the literature as SAC9 building, modelled as a plane steel frame structure and secondly on a three-dimensional reinforced concrete structure, designed according to old standard structural design rules. The very good agreement with the results obtained through accurate 3D FEM frame modelling, for different earthquake loadings, on the considered benchmarks provides a first validation of the proposed inelastic equivalent beam-like model and suggests its potential use for the seismic assessment of building structures. The low computational cost related to the beam-like model could be particularly advantageous for all the seismic vulnerability approaches requiring several nonlinear dynamic analyses, as those related to large scale applications, or those expressed in terms of probability of failure generally expressed in terms of fragility curves.

Settling and collision of spheroidal particles with an offset mass centre in a quiescent fluid

Gravitational sedimentation and the collision of particles play key roles in various natural and engineering processes. In practice, particles are often non-spherical in shape with non-uniform mass distribution. In this study we investigate how the mass eccentricity influences the settling and gravitational collision of non-spherical particles in a quiescent fluid. Firstly, we theoretically analyse the effect of mass centre offset on the settling motion of a single spheroid under the low-Reynolds-number assumption. We find that the competition of fluid-inertia torque and gravitational torque determines the terminal settling mode of the spheroid. As the mass centre offset increases from zero to a critical value, the orientation of a settling spheroid undergoes a transition from the broad-side-on to narrow-side-on alignment. With an intermediate mass centre offset, the settling spheroid prefers an oblique orientation with a horizontal drift. Secondly, we investigate the gravitational collision rate of settling spheroids. With the change of particle orientation, the collision kernel exhibits a non-monotonic variation with a maximum when particles settle with an intermediate oblique orientation. Therefore, adjusting the mass centre offset to alter particle orientation can indirectly affect the collision rate of settling spheroidal particles. In summary, our findings reveal the significance of the mass eccentricity on particle dynamics in fluid flows, and suggest a potential approach for manipulating the settling motion and collision rate of non-spherical particles by adjusting their mass centre position.

An analytical method for free vibrations of the fuel rod with non-uniform mass of small modular reactor

The intricate internal structure of fuel rods results in a non-uniform mass distribution, making it imperative to employ analytical methods for accurate assessment. The study utilizes Euler beam theory to derive the transverse vibration equation for beams with varying mass distribution. The approach involves transforming the non-uniform mass beam into a multi-segment beam with concentrated mass points. Modal function relationships between adjacent uniform segments are established based on continuous conditions at connection points. This transformation leads to the conversion of the variable coefficient differential equation into a nonlinear matrix equation. The Newton-Raphson method is then applied to calculate the characteristic equation and mode shapes, essential for determining natural frequencies. To validate precision, the results obtained are compared with those derived from the finite element method. Furthermore, the developed method is employed to assess the impact of gas plenum location and length on the natural frequency of fuel rods. The proposed methodology serves as a rapid design tool, particularly beneficial during the design phase of fuel rods with non-uniform mass distribution, aiding in configuring structural aspects effectively.

Investigation on performance of full-scale proton exchange membrane fuel cell: Porous foam flow field with integrated bipolar plate/gas diffusion layer

Aiming at the problems of inconsistent local distribution of reactant gas and easy blockage of water in the traditional “bipolar plate (BP) + gas diffusion layer (GDL)” structure flow field (FF). A new type of porous foam flow field (PFFF) with integrated BP/GDL (taking the pore of decahedral structure as matrix) is proposed. Firstly, three-dimensional (3D) proton exchange membrane fuel cell (PEMFC) saturation model is applied to analyze the influence of the availability of GDL components and different channel (CH) widths. GDL is essential for channel-rib (CR) FF because its elimination leads to the non-uniform mass distribution in fuel cell (FC). Secondly, by comparing CRFF and PFF with “BP + GDL” structure and PFFF with integrated BP/GDL, it is found that the limiting current density of PFF increases by 49.9 % compared with CRFF, and the mass transmission loss is reduced. Compared with PFF, the performance of PFFF is greatly enhanced, the pressure drop is moderate, and the amount of liquid water in CH is reduced by 39.1 %. Therefore, GDL component that eliminate PFF is extremely beneficial to improve FC efficiency and reduce stack volume. Finally, the output performance of FC under various porosities and pore number is explored.

Learning to Predict 3D Rotational Dynamics from Images of a Rigid Body with Unknown Mass Distribution

In many real-world settings, image observations of freely rotating 3D rigid bodies may be available when low-dimensional measurements are not. However, the high-dimensionality of image data precludes the use of classical estimation techniques to learn the dynamics. The usefulness of standard deep learning methods is also limited, because an image of a rigid body reveals nothing about the distribution of mass inside the body, which, together with initial angular velocity, is what determines how the body will rotate. We present a physics-based neural network model to estimate and predict 3D rotational dynamics from image sequences. We achieve this using a multi-stage prediction pipeline that maps individual images to a latent representation homeomorphic to SO(3), computes angular velocities from latent pairs, and predicts future latent states using the Hamiltonian equations of motion. We demonstrate the efficacy of our approach on new rotating rigid-body datasets of sequences of synthetic images of rotating objects, including cubes, prisms and satellites, with unknown uniform and non-uniform mass distributions. Our model outperforms competing baselines on our datasets, producing better qualitative predictions and reducing the error observed for the state-of-the-art Hamiltonian Generative Network by a factor of 2.

Transport vibration analysis of mobile liquid Pb-Bi micro-reactors with non-uniform mass distribution

The mobile micro-reactors, as advanced nuclear systems, had the capability to provide energy to remote areas and islands. However, the non-uniform mass distribution characteristic of Liquid Lead-Bismuth Eutectic (LBE), which possessed a high density, substantial mass, and compact volume, mobile micro-reactors required special attention during transportation when mounted on trucks and passing through rough roads. This paper aimed to investigate the vibration responses of the mobile micro-reactor with non-uniform mass distribution during transportation. To achieve this, a separated model was developed using the Lagrange multi-body dynamic equations, the recorded responses data were evaluated using MATLAB, a numerical simulation software. Furthermore, a parametric study was conducted to examine the influence of the mass of LBE mass and the positions of the micro-reactor on the vibration responses during transportation. The results indicated that the mass of the micro-reactorwas directlyproportionaltothe vibration responses, and the responses could be different with the moveable situation of the reactor. This study demonstrated that the separated model could evaluate the transportation vibration responses of both the mobile micro-reactors and the truck more accurately, thereby facilitating the safe transportation of mobile micro-reactors with non-uniform mass distribution.

Dynamics of size-dependent multilayered shear deformable microbeams with axially functionally graded core and non-uniform mass supported by an intermediate elastic support

The current study investigates the coupled dynamics of a size-dependent third-order shear deformable multilayered microbeam with an axially functionally graded core, a non-uniform mass distribution (mass imperfection) and an intermediate elastic support. A power-law function is used to model the material properties in the longitudinal direction of the core. The equations of motion are obtained by formulating the energies of the system while employing the modified couple stress theory to include miniature size effects within the multilayered microbeam structure. Hamilton's principle and the modal decomposition method are utilised to derive and solve the coupled motion equations. The equations of motion are first verified against a former work on a simplified microbeam system, while the numerical results are validated by comparison to those of a simplified functionally graded in axial direction obtained by finite element macrobeam simulation. It was concluded that increasing either the power term constant of the material grading or the value of the localized mass imperfection (when xm*=0.3) causes the first and second transverse and axial natural frequencies of the three-layered microbeam to decrease, whereas increasing the length-scale parameter causes the natural frequencies of transverse modes to increase, demonstrating the size-dependent effects of the three-layered microbeam.

Comparative Study on Seismic Analysis of RC Structure with and Without Floating Column Including Lateral Load Resisting Systems

: Soft storey, vertical or plan irregularity, floating column, and high loads are all common features of modern multi-story structures. In metropolitan India, these kinds of buildings are becoming increasingly popular. According to the findings of previous earthquake research, most RC buildings with such flaws are extremely undesirable in seismically active locations. These effects occurred as a result of a variety of factors, including nonuniform mass distribution, stiffness, and strength. This study uses the software STAAD PRO V8i to discuss the seismic analysis of a multi-storey G+7 building with floating column built in seismically active area, observing its responses to external lateral force generated on the building in seismic zone 5,including different lateral load resisting systems. The structure is represented in ten different model cases. Model 2 contains a floating column structure, Model 3includes increased column size on the ground floor. Models 4, 5, 6 and 10 contain different types of bracing (type 1, type 2, type 3 and type 4) which are installed one after another from the ground floor to the top floor and modelled separately. Shear core/shear tube is introduced in model 7 and 9 with thickness 0.2m running from ground to top. Shearwalls of 4 typesareintroducedinmodel8withthicknessofwallas0.3mrunning from ground floor to top. Thus, alternative measures involving improving non uniform distribution in irregular buildings, such as multi storey buildings with floating columns, were highlighted, and the safer design of such buildings in seismically active areas was recommended, taking into account the results observed from base shear, storey drifts, storey displacements, bending moment using Equivalent static method. As a consequence of the results, we determined that the introduction of a single bracing/strut contributes to the maximum reduction in shear force and bending moment compared to all model cases, Shear core structure withstands the highest seismic load of any model, When the columns are completely removed to create a floating column design, the % increase in maximum drift is 67.65%, indicating the minimum lateral resistance compared to all model cases.

Structural challenges for seismic stability of buildings in hilly areas.

Buildings on hills behave dynamically, very different from buildings on flatlands. Due to irregularity in horizontal and vertical planes, they inhibit non-uniform mass and stiffness distribution and are subjected to torsional forces. Studies in various Indian cities in hilly terrains have highlighted serious concerns about existing construction practices. Lack of adequate planning and design has resulted in haphazard development in hilly regions. This state-of-the-art review investigates the factors that influence the structural performance of buildings on slopes while explaining reasons that have caused enormous damages and even collapse of hill buildings in the recent earthquake events. The work discusses building configurations, comparison of various vital building regulations, the major problems encountered in building stocks and associated structural deficiencies on hill slopes. The significance of intensification of earthquake-related losses due to soil amplification has been well documented in the past. Insights from experimental and numerical studies focusing on impacts of topographical and geological factors on damage amplification of hillside buildings are fetched, the results of which are in good corroboration with the findings of post-earthquake surveys and reviews. This study establishes that a higher slope gradient necessitates more slope cutting than a lower slope gradient to get the same building footprint, and many times, this value exceeds the permissible height of slope cutting given in existing building byelaws. Such excessive slope cutting makes the slope weak and unstable. Recommendations and solutions to help enhance structural resilience, reduce disproportionate damages and mitigate failure of hill buildings have been delineated.

A simplified beam model for the numerical analysis of masonry arch bridges –A case study of the Veresk railway bridge

This paper presents the development of a simplified analytical model, able to substitute high fidelity-three-dimensional (3D) finite element (FE) models, for the analysis of complex mechanical and civil structures such as masonry arch bridges. The non-uniform mass and stiffness distribution along the length of masonry arch bridges presents significant challenges when used for the development of beam models. Such models can be coupled with structural health monitoring schemes for the development of quick online decision-making tools and the optimal structure operation and management. As a case study, the behavior of the Veresk railway masonry arch bridge located in north Iran was investigated. Initially, the dynamic behavior of the bridge has been structurally assessed using a complex 3D FE model under operational load conditions. The 3D FE model was calibrated against field data from sensors placed in the bridge. Later, a simplified model using the dynamic parameters equivalent to the bridge has been developed and subjected to operational moving loads, masses and oscillators. The results of maximum displacement spectra were derived under the passage of different in mass and speed trains using an undamped/damped beam model. The analytical results of the beam model present good accuracy when compared with those from the three-dimensional finite element model.

A novel constrained optimal tuning method with application to helicopter rotor track and balance

Low-frequency vibration and blade track spread caused by non-uniform mass and aerodynamic distributions in the main rotor system may affect pilot’s health and shorten the life span of helicopter components. To eliminate these hazards, the manual passive maintenance procedure on the ground is adopted, but it is typically complex, time-consuming, and expensive; and the other existing active control algorithms do not simultaneously minimize the once-per-revolution (1/rev) vibration and blade track spread with complicated parameter tuning. In this work, a constrained optimal tuning (COT) method, is proposed to suppress both rotor 1/rev vibration and blade track spread utilizing pitch rod lengths as the control inputs. The COT method defines a constrained vibration control formulation, and it takes the track and the stroke range of pitch rods as a control constraint to ensure that the track spread is within specification and that the control inputs have no effect on the rotor’s performance. Moreover, the optimality and stability of the COT are mathematically proven. The numerical simulations about non-uniform rotor were performed successfully utilizing the established main rotor dynamic model. The results show that the 1/rev vibration in the X, Y, and Z directions can all be decreased by more than 90 %, and the track spread can be reduced by more than 80 %. The introduction of input constraints maintains the control safety while also easing the burden of parameter tuning. Meanwhile, the 2/rev components of the lateral forces are similarly reduced. Furthermore, the control algorithm is modeled in software and built into real-time code to verify its effectiveness through the wind tunnel experiments. The experimental results reveal that 1/rev vibration is effectively reduced in three directions. The proposed controller also improves the aerodynamic environment of the blades, reducing almost all strange harmonic components (n-0.5)/rev (n = 1 to 10) to near zero.

Computational Study of the Thermal Rectification Properties of a Graphene-Based Nanostructure.

Thermally rectifying materials would have important implications for thermal management, thermal circuits, and the field of phononics in general. Graphene-based nanostructures have very high intrinsic thermal conductance, but they normally display no thermal rectification effects. The present study relates to a thermally rectifying material and, more particularly, to a graphene-based nanomaterial for controlling heat flux and the associated method determining the rectification coefficient. Thermal rectifiers using a graphene-based nanostructure as thermal conductors were designed. Vacancy defects were introduced into one end of the nanostructure to produce an axially non-uniform mass distribution. Modified Monte Carlo methods were used to investigate the effects of defect size and shape, vacancy concentration, and ribbon length on the thermal rectification properties. Anharmonic lattice dynamics calculations were carried out to obtain the frequency-dependent phonon properties. The results indicated that the nanoscale system conducts heat asymmetrically, with a maximum available rectification coefficient of about 70%. Thermal rectification has been achieved, and the difference in temperature dependence of thermal conductivity is responsible for the phenomenon. Defects can be tailored to modulate the temperature dependence of thermal conductivity. The power-law exponent can be negative or positive, depending upon the ribbon length and vacancy concentration. A computational method has been developed, whereby the numerous variables used to determine the rectification coefficient can be summarized by two parameters: the power-law exponent and the thermal resistance ratio. Accordingly, the rectification coefficient can be obtained by solving a simple algebraic expression. There are several structure factors that cause noticeable effects on the thermal rectification properties. Defect size, vacancy concentration, and ribbon length can affect the thermal conductance of the nanostructure symmetrically and significantly. Graphene-based nanostructure thermal rectifiers can be arranged in an array so as to provide thermal rectification on a macroscopic scale.

Intrinsic equilibrium of stably autorotating samaras.

During descent, a single-winged maple seed (samara) can naturally reach a delicate equilibrium state, stable autorotation, before landing. This article reveals the intrinsic equilibrium of a particular type of samaras in terms of measurable aerodynamic and geometric parameters. To this end, we conducted a series of in situ measurements for the rate of vertical descent (exclusive of crosswind) of an autorotating samara in a natural range of samara sizes and masses. We then extended the range of size and mass by introducing artificial samaras, with discrete mass elements purposely designed to approximate the asymmetrical and nonuniform distribution of mass found with natural samaras. Based on the widened range, a fundamental nondimensional correlation of dynamic pressure and disc loading was generalized, where all stable autorotation descent profiles collapse to a single descent characteristic curve, irrespective of the size and mass of the natural and artificial samara's specimens. Results reveal that for stably autorotating (both natural and artificial) samaras, their terminal descent velocity (expressed as dynamic pressure) and disc loading attained equilibrium at a value that is inversely proportional to the coefficient of lift.

Finite-time composite control for gimbal system in SGCMG under high-frequency disturbance

This paper investigates the velocity-tracking problem of the gimbal system in a single gimbal control moment gyro (SGCMG) suffering from high-frequency disturbance. In order to accurately and quickly reject the high-frequency disturbance resulted from nonuniform mass distribution and manufacturing imperfection, a finite-time harmonic disturbance observer (FTHDO) is constructed according to the available information about the high-frequency disturbance. Then, a composite controller is developed to achieve simultaneous disturbance rejection and attenuation. The nominal control performance can be recovered under the high-frequency disturbance. It has been demonstrated that the velocity-tracking error can be stabilized by the proposed composite controller within finite time. Finally, numerical simulation results are presented to verify the superiority of the proposed method.

Free Vibration Analysis of Composite Grid Stiffened Cylindrical Shells Using A Generalized Higher Order Theory

The present study analyzes the free vibration of multi-layered composite cylindrical shells and perforated composite cylindrical shells via a modified version of Reddy’s third-order shear deformation theory (TSDT) under simple support conditions. An advantage of the proposed theory over other high-order theories is the inclusion of the shell section trapezoidal form coefficient term in the displacement field and strain equations to improve the accuracy of results. The non-uniform stiffness and mass distributions across reinforcement ribs and the empty or filled bays between the ribs in perforated shells were addressed via a proper distribution function. For integrated perforated cylindrical shells, the results were validated by comparison to other studies and the numerical results obtained via ABAQUS. The proposed theory was in good consistency with numerical results and the results of previous studies. It should be noted that the proposed theory was more accurate than TSDT.