Rigid Mass Research Articles

Therapeutic and diagnostic approach to craniofacial osteoma in a dog: a case report

Osteoma is a bone neoplasm that can affect dogs of any age, often underdiagnosed due to its low incidence and slow growth. The aim of this study was to discuss a case of craniofacial osteoma in a Shih-Tzu bitch, highlighting the importance of proper diagnosis and treatment of this condition. In this case, the patient presented with a rigid mass near the left eye, which was evaluated radiographically and diagnosed histopathologically after complete excision of the tumor. No signs of recurrence were observed during follow-up, demonstrating the effectiveness of the surgical treatment. The main findings of the case include an osteoproliferative reaction observed in the radiograph and well-differentiated fibrogranulomatous and osseous proliferation observed in the histopathology. The treatment consisted of complete surgical resection, and no postoperative complications were observed. The patient showed rapid recovery and absence of postoperative pain. It is concluded that osteoma is a benign neoplasm treatable with complete surgical resection, without the need for adjuvant chemotherapy. The study emphasizes the importance of considering osteoma as a differential diagnosis among bone neoplasms in dogs.

Envelope vector solitons in nonlinear flexible mechanical metamaterials

In this paper, we employ a combination of analytical and numerical techniques to investigate the dynamics of lattice envelope vector soliton solutions propagating within a one-dimensional chain of flexible mechanical metamaterial. To model the system, we formulate discrete equations that describe the longitudinal and rotational displacements of each individual rigid unit mass using a lump element approach. By applying the multiple-scales method in the context of a semi-discrete approximation, we derive an effective nonlinear Schrödinger equation that characterizes the evolution of rotational and slowly varying envelope waves from the aforementioned discrete motion equations. We thus show that this flexible mechanical metamaterial chain supports envelope vector solitons where the rotational component has the form of either a bright or a dark soliton. In addition, due to nonlinear coupling, the longitudinal displacement displays kink-like profiles thus forming the 2-components vector soliton. These findings, which include specific vector envelope solutions, enrich our knowledge on the nonlinear wave solutions supported by flexible mechanical metamaterials and open new possibilities for the control of nonlinear waves and vibrations.

Nonlinear Energy Harvesting From a Base Excited Size-Dependent Flexoelectric Nanostructure with Off-Center Rigid Tip Mass Subjected to Axial Pulsating Excitation

This study explores the incorporation of flexoelectricity and size-dependence effects in electricity harvesting from a novel nanostructure. This nanostructure, featuring a cylindrical-shaped rigid tip mass, is stimulated at the base with axial pulsating excitation. Designed with a nanobeam material, the energy harvester accounts for structural nonlinearity, flexoelectricity, and the presence of an off-center rigid mass, operating under multiple excitations. The eigenanalysis is employed to delve into the dynamic characteristics of the system, providing engineers with insights to identify safe operating regions and operational constraints. Additionally, perturbation techniques are utilized to estimate steady-state voltage and power characteristics, with a focus on maximizing voltage and power generation. The study underscores the impact of size dependence on nanoscale design, flexoelectricity, asymmetric tip mass, and various excitation parameters within a constrained operating range. Analysis reveals how saddle-node and pitchfork bifurcations can disrupt energy harvesting performance and suggests strategies for mitigating these issues by adjusting operational parameters. Moreover, the study emphasizes the significant role of the off-center rigid tip mass in energy estimation compared to conventional microstructure-based energy harvesters. Analytical findings are rigorously validated against numerical results under different resonant scenarios, showcasing the accuracy of the analytical approach in capturing nonlinear sources and optimizing energy harvesting from nanostructures.

Dynamic characteristics of density-graded cellular materials for impact mitigation

Due to their exceptional impact resistance capabilities, density-graded cellular materials have immense potential in applications where crashworthiness requirements are of prime importance. Under impact loading, the deformation in these materials is characterized by compaction front propagation. Previous studies have utilized numerical techniques to solve the equations governing compaction shock propagation for cellular materials with density gradation. In this study, analytical solutions are formulated using compaction front position as the independent variable. The expressions for the velocity of the impinging rigid mass, energy absorption, incident stress, and transmitted stress are determined. The analytical solutions are shown to be in excellent agreement with the cell-based finite element solutions. The effect of density gradient on energy absorption and stresses is studied. The impact resistance factor is employed to assess different density-graded cellular materials for their effectiveness in impact mitigation. This study demonstrates that density-graded cellular materials can offer superior impact protection to objects at both the incident and transmitted ends. Lower density toward the incident end enhances impact resistance to objects located there, and likewise, lower density at the transmitted end offers more impact resistance to objects at that end.

Incomplete Caudal Duplication With Correction of Pygomelia in a Dog

Congenital malformations are structural defects that occur in all species during fetal development. Pygomelia is a type of polymelia in which the redundant legs are joined to the pelvis. This abnormality is observed in both human beings and animals. A mixed female (Shih Tzu) puppy with a rigid mass resembling two pelvic hindlimbs was referred to a pet clinic in Mashhad City, Iran. In radiographic assessments, two extra hindlimbs stemmed from malformed pelvic bones and were shorter than normal limbs. Both extra acetabula were detected on the hemipelvis, with two extra coxofemoral joints perpendicular to the regular hip joints in the caudal direction. Also, two vulvas and two anuses were seen, but only one vulva and anus were functional. The additional limbs were amputated by surgery. This case is the first report of a dog with incomplete caudal duplication and successful correction of pygomelia in Iran.

Structure design and kinematic performance of the deployable translational parallel tape-spring manipulator

AbstractA deployable manipulator has the characteristics of a small installation space and a large workspace, which has great application prospects in small unmanned platforms. Most existing deployable manipulators are designed based on rigid links, whose complexity and mass inevitably increase sharply with increasing numbers of rigid links and joints. Inspired by the remarkable properties of tape springs, this paper proposes novel deployable parallel tape-spring manipulators with low mass, simple mechanics, and a high deployed-to-folded ratio. First, a double C-shaped tape spring is presented to improve the stability of the structure. The combined fixed drive component (CFDC) and combined mobile drive component (CMDC) are designed. Then, novel 2-DOF and 3-DOF deployable translational parallel manipulators are proposed based on the CFDC and CMDC, and their degrees-of-freedom (DOFs), kinematics, and stability are analyzed. The coiled tape spring is regarded as an Archimedean spiral, which can significantly improve the accuracy of kinematic analysis. The correction coefficient of the Euler formula is obtained by comparison with simulation results and experimental results. Furthermore, the stability spaces of the 2-DOF and 3-DOF deployable parallel manipulators are given. Finally, a prototype is fabricated, and experiments are conducted to validate the proposed design and analysis.

Vibration isolation by relative resonance perceived in combination of rigid bodies and elastic beams

This paper develops a novel low-frequency vibration isolation device based on rigid body dynamics called a Rigid Elastic Vibration Isolator (REVI). The REVI model is realized by coupling four elastic beams with two rigid bodies monolithically made using 3D printing. The system operates based on the vibration of the intermediate rigid bodies, which leads to the anti-resonance phenomenon at low frequencies. The dynamic analysis of the proposed REVI system has been meticulously investigated through analytical methods and real-world experimentation. The analytical method uses the Spectral element method to obtain the dynamic response, which is also validated by the experimental findings. Furthermore, the REVI transmittance sensitivity analysis was conducted by adjusting the rigid mass and system load and exploring methods for generating wide low-frequency bandgaps. The inclination angle of the REVI system is also varied, revealing the bandgap characteristics regarding negative transmittance level. The parametric study varying the geometric properties of the REVI system enhances our understanding of the bandgap and attenuation characteristics within the attenuation band. The REVI mechanism is practical and easily implemented, allowing for accurate and repeatable modeling. Moreover, the analytical observations assist in refining the shape of the REVI mechanism to achieve the necessary bandgap for the desired transmittance.

Damped Normal Compliance (DNC) and the restitution coefficient

This work introduces and studies a novel normal compliance contact condition with damping, the Damped Normal Compliance (DNC), which is more realistic than the usual normal compliance condition that is often used in modeling contact between solids. The condition is applied in a model for the contact of a rigid mass with a reactive obstacle and allows for energy dissipation during contact. We analyze the model and show that the condition is of mathematical, as well as applied, interest. Then, we establish its relationship with the so-called “coefficient of restitution,” e , and show that the concept is not well defined, since e depends on the system parameters, applied force, and initial data. The various theoretical results are depicted using computer simulations.

On the validity of periodic boundary conditions for modelling finite plate-type acoustic metamaterials.

Plate-type acoustic metamaterials (PAMs) are thin structures that exhibit antiresonances with high sound transmission loss (STL) values, making PAMs a promising new technology for controlling tonal noise in the challenging low-frequency regime. A PAM consists of rigid masses periodically attached to a thin baseplate. The periodicity of PAM can be exploited in simulations, allowing to model only a single unit cell using periodic boundary conditions. This approach essentially represents the PAM as an infinite structure, but real PAM implementations will always be finite and influenced by boundary conditions. In this paper, extensive numerical simulations of different PAM configurations have been performed to study the performance of finite PAM compared to infinite PAM. The results indicate that as the number of unit cells in a finite PAM increase, the STL converges toward that of an infinite PAM. The impact of the finite PAM edge boundary conditions becomes negligible at some point. Based on the numerical results, a simple criterion is proposed to determine a priori how many unit cells are required in a finite PAM design to consider it quasi-infinite. This criterion aids in justifying unit cell models with periodic boundary conditions for efficient design optimizations in practical PAM applications.

Negative stiffness and inerter-based dampers: Novel seismic response control approach for base isolated liquid storage tanks

Liquid storage tanks (LSTs) have become indispensable to civil engineering infrastructure. LSTs are used not only for storing harmless fluids but also explosive, toxic, and hazardous substances. Thus, the ability of LSTs to withstand significant seismic activity without damage is a major worry. Strong pulse-type characteristics in near fault (NF) type of ground motions have shown significant base and sloshing displacements for a commonly adopted structural control measure: base isolation (BI). The current study introduces negative stiffness and inerter dampers (NSIDs) as supplemental response control measures to LSTs with BI (BILSTs). Conventional supplemental damping applications in the isolation system are helpful in displacement reduction at the isolator level, but the upper structure response gets severely affected. This study presents NSIDs, characterised by the damping magnification effect, as supplemental dampers to BILSTs. The continuous liquid mass within the tank is represented by discrete lumped masses referred to as sloshing, impulsive, and rigid mass. The stiffness constants of these lumped masses are derived by considering the tank wall and stored liquid physical parameters. The optimal supplemental damping parameters are deduced by developing contour plots describing the sloshing and base displacement response reduction (mitigation) ratios. Through analytical studies conducted using real earthquake records, it has been demonstrated that appropriately designed Negative Stiffness and Inerter Devices (NSIDs) yield enhanced performance for Base Isolated Liquid Storage Tanks (BILSTs). These optimised combinations of NSIDs effectively mitigate isolator displacement, base shear, lumped sloshing mass displacement, and sloshing mass height in response to both near-field (NF) and far-field (FF) base excitations.

P-85 Inflammatory myofibroblastic tumor: An extremely rare tumor of the thyroid gland poses challenges in diagnosis and management

Abstract Introduction Inflammatory myofibroblastic tumor (IMT) is an exceedingly rare mesenchymal tumor characterized by myofibroblastic spindle cells and an inflammatory cell infiltrate. The clinical presentation of IMT in the thyroid gland varies widely, ranging from an asymptomatic thyroid nodule to a diffuse, rigid, fixed, and painful mass. While IMT of the thyroid gland is generally considered a benign borderline tumor with very low metastatic potential, its diagnosis and management can be intricate. Surgery remains the preferred treatment, with recurrence being rare following successful removal. Nonetheless, the optimal management of residual tumors is contentious and may involve a second surgery or the use of immunosuppressants and chemotherapeutic agents. Clinical Case A 47-year-old female patient presented with painless discomfort and stiffness around the thyroid gland. A neck ultrasound revealed a hypoechoic nodule measuring 21×12 mm on the left lobe and a hypoisoechoic heterogeneous nodule 35×28 mm in size on the right lobe of the thyroid gland. These nodules displayed low vascularity, and no pathologic lymph nodes were detected. Fine needle aspiration biopsies (FNABs) were performed on the nodules in both lobes at different times, indicating thyroiditis in the right lobe and spindle-shaped cells with atypia of uncertain significance in the left lobe. Subsequent evaluation of FNAB materials at a referral center suggested a high suspicion of lymphoid malignancy. The patient underwent thyroidectomy; however, the surgeon chose to preserve the left thyroid lobe due to its extreme fibrotic and stone-like consistency, thereby preserving recurrent laryngeal nerve function. Histological analysis confirmed the presence of an inflammatory myofibroblastic tumor characterized by spindle cells accompanied by abundant histocytes, plasma cells, and lymphocytes. The tumor cells exhibited positivity for SMA. Postoperative ultrasound revealed a residual tumor approximately 2 cm in size located in the left isthmus and adjacent left lobe, which remained stable over a 6-month follow-up period. Conclusion Our case highlights the potential for misdiagnosing IMT of the thyroid gland as malignant thyroid tumors. Furthermore, the management of a residual tumor presents a complex clinical challenge. The surgical team is reluctant to pursue a second surgery due to potential risks to recurrent laryngeal nerve function. In this session, we aim to solicit expert opinions and engage in interactive discussions regarding the management of the residual tumor in this specific case.

Frequency response of a mass grounded by linear and nonlinear springs in series: An exact analysis

An exact analytical solution for the frequency response of a system consisting of a mass grounded by linear and nonlinear springs in series was derived. The system is applicable in the study of beams carrying intermediate rigid mass. The exact solution was derived by naturally transforming the integral of the governing nonlinear ODE into a form that can be expressed in terms of elliptic integrals. Hence, the exact frequency–amplitude solution was derived in terms of the complete elliptic integral of the first and third kinds. Periodic solutions were found to exist for all real values of [Formula: see text] and for [Formula: see text]. On the other hand, linear or weakly nonlinear frequency–amplitude responses were found to occur during small-amplitude vibrations ([Formula: see text]), very large-amplitude vibrations with strong hardening nonlinearity ([Formula: see text] and [Formula: see text]), and for all amplitudes when [Formula: see text]. Simulations showed that the system’s periodic response is significantly influenced by the nonlinearity parameter ([Formula: see text]), linearity parameter ([Formula: see text]), and amplitude of vibration ([Formula: see text]). Besides, the existence of bifurcation points at [Formula: see text] and different values of [Formula: see text] was confirmed. Lastly, an approximate frequency solution obtained using the He’s frequency–amplitude formulation was found to produce errors less than 1.0% for a wide range of input parameters. In conclusion, the present study provides a benchmark solution for verification of other approximate solutions, and the He’s frequency–amplitude formulation can be used to obtain fast and accurate solutions for complex nonlinear systems.

Dynamic analysis and design of novel distributed lump-parameters mounting system for marine power devices

Marine power devices (MPD) are one of the dominant vibration and noise sources on board marine vessel. Its vibration can be attenuated effectively through floating raft mounting system. But this becomes unsuitable to implement due to a more stringent light-weighting request. In this paper, a novel distributed lump-parameters mounting system (NDLMS) for MPD is proposed consisting of two-stage mounting subsystem, attitude monitoring and controlling subsystem, and emergency protection subsystem. A theoretical model under multiple excitations is presented to estimate the vibration isolation effectiveness (VIE) using equivalent mobility matrix methods. To improve the VIE of NDLMS, distributed dynamic vibration absorbers (DDVA) are introduced. Compared with the equally weighted rigid mass blocks, DDVA has a qualitative improvement in the attenuation ability of the characteristic spectrum. Replacing part of the mass of mounting system with finely tuned DDVA can greatly reduce the vibration transmitted from vibratory MPD to the foundation. DDVA are validated to compensate for the vibration transmission loss by light-weighting. A scaled and a practical NDLMS prototypes are manufactured and tested. Experimental results validate the effectiveness of theoretical models and show that the performance of NDLMS satisfies the operation requirements of MPD.

Research on the application of laser camera to support LVDT in geotechnical laboratory work

Laboratory tests are essential for analyzing the behavior of geotechnical materials and models. Two of the most common methods for measuring displacement in laboratory tests are Dial indicator and Linear variable differential transformer (LVDT). However, using these equipments has some limitations, such as measuring only discrete points, and Dial indicators require surfaces to be measured must have a certain hardness. This feature is a significant limitation because geomaterials are not usually rigid masses. To overcome these limitations, the authors studied using laser cameras to support the LVDTs and the Dial indicators. Laser cameras offer high sampling rates, but their accuracy needs to be carefully investigated as they are mainly used to measure large distances. In this paper, we show how to investigate the accuracy of laser cameras with reliable, intuitive observations, reviewing recent studies on using laser cameras in laboratory tests. Experiments, including their advantages, limitations and potential applications: The potential application of laser cameras to measure distances can be evaluated instead of LVDT. We also discuss the challenges and future directions of using laser cameras in laboratory testing. The results showed that laser cameras could improve the accuracy and efficiency of laboratory tests and may become a preferred method for displacement measurement in the future.

Investigation on active vibration isolation with multi-axis control: Analysis and experiment

Vibration isolators are usually used to attenuate the transmission of vibration of power machinery to the flexible foundation. Since vibration energy is transferred nearly through all the degrees of freedom of an isolator, it is difficult to guarantee sufficient vibration attenuation by the single-axis control at each active isolator. In order to enhance attenuation at each vibration isolator, a novel configuration of active vibration isolation is proposed. Each active isolator is composed of two rubber isolators and one intermediate rigid mass in which eight electromagnetic actuators and six error accelerometers are attached. Six control forces are applied on the intermediate mass to suppress its multi-axis vibration. Moreover, the weakened interaction between isolators allows independent local control at each isolator. A numerical model is established to verify the proposed active vibration isolation and the results show that the transmission of vibration from the source to the flexible hull structure can be nearly cut off when the error vibrations of each intermediate mass are attenuated completely. The effectiveness is also proved by an experimental active vibration isolation system and the proposed isolation configuration with multi-axis control can achieve more significant attenuation of vibration of the hull structure than the commonly used active vibration isolation with only single-axis control.

A SDoF Response Model for Elastic–Plastic Beams under Impact at Any Point on the Span

This study aims to investigate the elastic–plastic response of a clamped-clamped beam struck by a rigid heavy mass with a low velocity at any point on the span. The impact system is simplified as a single-degree-of-freedom (SDoF) mass-spring model to formulate the beam’s equations of motion during loading and unloading. With the consideration of material elasticity and large deflection, elastic–plastic analytical solutions are derived to predict the global deformation behavior of the beam. Validation and comparison are conducted against numerical simulations performed using ABAQUS, and satisfactory agreement is achieved for the predictions of the structural dynamic behavior. Meanwhile, a parametric study is presented to assess the influence of the impact location on the characteristic response parameters, which suggests that the structural stiffness increases as the impact location approaches the beam’s support. The findings drawn from analytical and numerical studies can be useful in the anti-impact design of engineering structures.

Simple Mathematical Models for the Dynamics Of Spacecraft With Deployed Solar Panels

Most present day spacecrafts have large interconnected deployed solar panels having very low natural frequencies. The control torque applied to maneuver the spacecraft sets up transient oscillations in the spacecraft. The present work studies the nature of these interactions. The spacecraft in orbit can be modeled as a free rigid mass with flexible elements attached to it. It is shown that the oscillations of the spacecraft body are characterized by the dynamic characteristics of the flexible panel even if the mass and mass moment of inertia of the body is signifcantly higher than that of the flexible panels. A simple model consisting of an Euler-Bernoulli beam attached to a mass can represents such a system. The infuence of various parameters of the Euler-Bernoulli beam and the rigid element on the disturbances caused in the rigid element are investigated. The characteristics are determined for a step and also for a torque input. The responses are obtained in terms of nondimensionalised quantities. It is demonstrated that using the simple model developed the responses of spacecraft body can be easily obtained.

Modulation instability in nonlinear flexible mechanical metamaterials.

In this paper, we study modulation instabilities (MI) in a one-dimensional chain configuration of a flexible mechanical metamaterial (flexMM). Using the lumped element approach, flexMMs can be modeled by a coupled system of discrete equationsfor the longitudinal displacements and rotations of the rigid mass units. In the long wavelength regime, and applying the multiple-scales method we derive an effective nonlinear Schrödinger equationfor slowly varying envelope rotational waves. We are then able to establish a map of the occurrence of MI to the parameters of the metamaterials and the wave numbers. We also highlight the key role of the rotation-displacement coupling between the two degrees of freedom in the manifestation of MI. All analytical findings are confirmed by numerical simulations of the full discrete and nonlinear lump problem. These results provide interesting design guidelines for nonlinear metamaterials offering either stability to high amplitude waves, or conversely being good candidates to observe instabilities.

How mass public transportation influences the retention intentions of Australian regional and remote university students

ABSTRACT Getting to and from campus matters, especially for students who have relocated from regional and remote (RR) areas who must wrangle, often for the first time, rigid mass public transportation (MPT). Little is known about MPTs’ influence on RR students’ retention intentions or how MPT interacts with other known geographic proximity barriers. Interviews with ten equity practitioners from three Australian universities revealed four interconnected themes. First, MPT access and accessibility can limit university participation. Second, MPT provides a time benefit, enabling study while commuting. Third, relocation anxieties interact with MPT as accommodation further from campus requires greater MPT usage. Fourth, parents are concerned about MPT access and accessibility which adds to other “mixed messages” that they give their children, affecting participation. Efforts that address MPT access and accessibility may improve RR higher education retention and educational outcomes.

Fault Characteristics Analysis of High-Speed Train Transmission Systems

The high-speed train speed has a higher requirement for stability and operating safety with its operating speed increasing. The main focus of this paper is on the fault characteristics analysis of a high-speed train transmission system. The governing equation and boundary conditions of the transmission system are derived using the finite element method, in which a Timoshenko beam element is introduced to represent the wheelset shaft, and a rigid mass element is utilized to represent the gears, bearings, and wheels. To investigate the vibration response mechanism of a high-speed train transmission system, the critical speed of the system and its modal response are given. According to the types of high-speed train component fault features, the local fault features of gear, bearing, and wheelset are given. Healthy and faulty systems with localized faults in gear, bearing, and wheelset are studied. The characteristics of amplitude and frequency are verified numerically and the transmission characteristics of signal and relation are explained when there is local fault defect in the system. The results show that under different fault types, the time domain response of the system has obvious periodic impulse response faults, and the fault frequency band characteristic distribution is different in the frequency domain response. The simulation results are consistent with the experimental results.