Mass Block Research Articles

Improving optimal chatter control of slender cutting tool through more accurate tuned mass damper modeling

The slender cutting tools are employed in many conditions like boring and milling processes, but those machining processes often accompany with chatter phenomenon which will aggravate the machining efficiency and surface quality. The use of tuned mass damper (TMD) to damp slender tools is considered as a practical and effective way for chatter suppression. Generally, the TMD is embedded inside the hollow cutting tool with two spring-damping elements supporting the mass block at both ends. For the convenience of optimization calculation, the damped tool is generally modeled as an oscillation system with two equivalent lumped mass. With this simplified model, the difference of vibration displacements between two spring-damping elements is ignored. This makes it very difficult to tune the TMD to the best according to the optimization result in practical application especially when both cutting tool and TMD have a slender characteristic. This paper improves the optimal chatter control through a more accurate modeling method which considers the cutting tool as a cantilever Euler–Bernoulli beam and the TMD as a two degrees of freedom system including translation vibration and rotation vibration of the mass block. Based on the proposed model, the influences of the position and length of TMD on the optimal design parameters of two spring-damping elements are analyzed through a series of optimization. The results show that there are great differences in the chatter control mechanism of two spring-damping elements and it is very important to choose respective appropriate stiffness and damping parameters for two spring-damping elements in the TMD damped slender cutting tools. Only in this way can the TMD be tuned in practice to the best performance for chatter control of slender cutting tools. Furthermore, based on the simulation results and comparisons with other conventional modeling methods, the difference and superiority of tuning optimization are discussed and the accuracy and practicability of the proposed modeling method are verified with a designed damped end mill cutter and some impact tests.

An investigation of a novel LuGre-based friction force model

The LuGre friction force models are amongst the most popular and powerful approaches to treat frictional contact in modeling, simulation and control of mechanical systems. However, these friction force models have some numerical difficulties related to physical inconstancies, when the systems under analysis include frictional contacts with significant variations in the normal loads. The LuGre friction force models can exhibit some problems resulting in the ratio between the friction and normal contact forces exceeding the friction coefficients. Another limitation deals with the drift problem which might occur during sticking periods. Thus, this work is aimed at presenting a new investigation based on the LuGre friction foundation capable of overcoming those limitations. In a simple manner, the new solution for the LuGre friction force model includes a stiffness coefficient to adjust and accommodate the variations of the normal contact forces in dynamical systems. In this study, two LuGre friction force models are revisited to facilitate the description of the proposed solution. Finally, several numerical application examples regarding a block of mass on a horizontal plane are presented to compare and examine the advantages and potentials of the original, amended and proposed models.

The numerical modeling of heterogeneities by the finite element method in 3D setting

The paper proposes a variant of the algorithm for 3D numerical simulation of the rock mass stress-strain state in the vicinity of structural heterogeneities by the finite element method. Modeling of the stress-strain state is used, among other things, when analyzing the fractures in the rock mass, which can occur as a breakage or a shear along the weakening planes. The rock massif has a block structure, where the boundaries of various-scale blocks are structural disturbances of different orders. The surface planes of structural heterogeneities usually have complex geometry and spatial orientation, so the most adequate results can be obtained by 3D modeling of the disturbed rock mass. Besides, it is important to take into account the type of the stress-strain state, which can be not only gravitational, but also gravitational-tectonic, including horizontal loading of the rock mass. Accounting these features allows obtaining the most adequate geomechanical model of the studied object. For this purpose, the authors have studied and analyzed the existing approaches to modeling heterogeneities in the rock mass, including using the Goodman contact element, and developed its 3D modification. A mining engineer needs to have a handy tool that allows creating and editing a geomechanical model, taking into account mining plans and related sections. The model navigation, edition of its individual blocks to specify geology and creation of local sub-models make it necessary to use structured meshes of finite elements. Modification of the model with the introduction of contact elements entails the creation of an unstructured mesh, which complicates further manipulations with it. To solve this problem, a special zero element was developed, which allows saving a structured mesh format when implementing a contact element. This zero element, like the contact element, has zero thickness, and its nodes have averaged strength characteristics of adjacent blocks of the undisturbed rock mass. The result of these studies is a tool that allows creating 3D models of the rock mass stress-strain state, taking into account its structural heterogeneities and preserving the regular structure of the finite element mesh.

Achievable dynamic responses of general undamped mass-chain systems

The attention of this work is focused on the achievable dynamic responses, i.e., the sets of all possible frequency responses of system transfer functions with all possible proper rational stabilizing controllers, of general undamped mass-chain systems. The Youla parametrization is adopted to obtain all possible proper rational stabilizing controllers and all possible frequency spectrums of a transfer function of the general undamped mass-chain system according to different system measurements. Some conclusions are presented to show the relation of the achievable responses of a transfer function using different system measurements. The achievable dynamic responses of the transfer function from the vibration source to the top mass block using some two-feedback-signal measurements and the full-signal measurement are first obtained, from which the achievable dynamic disturbance responses of other transfer functions are then deduced. The conclusions, which are obtained in this work, explain some classical results of 2-degree-of-freedom undamped vibration systems, and generalizes these results into arbitrary n-degree-of-freedom undamped systems.

Power Density Improvement of Piezoelectric Energy Harvesters via a Novel Hybridization Scheme with Electromagnetic Transduction.

A novel hybridization scheme is proposed with electromagnetic transduction to improve the power density of piezoelectric energy harvester (PEH) in this paper. Based on the basic cantilever piezoelectric energy harvester (BC-PEH) composed of a mass block, a piezoelectric patch, and a cantilever beam, we replaced the mass block by a magnet array and added a coil array to form the hybrid energy harvester. To enhance the output power of the electromagnetic energy harvester (EMEH), we utilized an alternating magnet array. Then, to compare the power density of the hybrid harvester and BC-PEH, the experiments of output power were conducted. According to the experimental results, the power densities of the hybrid harvester and BC-PEH are, respectively, 3.53 mW/cm3 and 5.14 μW/cm3 under the conditions of 18.6 Hz and 0.3 g. Therefore, the power density of the hybrid harvester is 686 times as high as that of the BC-PEH, which verified the power density improvement of PEH via a hybridization scheme with EMEH. Additionally, the hybrid harvester exhibits better performance for charging capacitors, such as charging a 2.2 mF capacitor to 8 V within 17 s. It is of great significance to further develop self-powered devices.

Severe Snoring in a Young Healthy Female: A Diagnostic Surprise.

Laryngeal Inflammatory myofibroblastic tumors or plasma cell granulomas are unusual benign lesions. Subglottic laryngeal lesions of various benign and malignant types usually present with acute or chronic stridor and respiratory obstruction features. We describe the first case in the literature where severe snoring was the presenting complaint in a patient of subglottic mass lesion with comfortable breathing during wake hour. A 28years old female presented with loud snoring and apneic episodes during sleep for three years which showed severe Obstructive Sleep Apnoea (OSA) (AHI, Apnoea- Hypoapnoea Index: 46.5) in polysomnography (PSG) and surprisingly smooth mucosa covered subglottic mass blocking 75% of airway lumen in the laryngoscopic examination. The patient underwent tracheostomy and coblation assisted endoscopic excision, and subsequent histopathology revealed an inflammatory myofibroblastic tumour. She was later decannulated and with no features of sleep apnea post decannulation. Subglottic mass can rarely present with severe snoring and requires solid clinical suspicion for early diagnosis. Hence, subglottic lesion should be one of the differentials for atypical presentations of severe OSA.

Mesoscale structure of the atmospheric boundary layer and its impact on regional air pollution: A case study

The atmospheric boundary layer (ABL) is known for its vertical structure in affecting air pollution due to the dilution and ventilation capacity. But how this effect playing over horizontal scales is not well investigated. This study reveals the ABL structure over a sub-synoptic scale or mesoscale related to regional PM2.5 (particulate matter with an aerodynamic diameter less than 2.5 μm) pollution in the North China Plain (NCP). A typical PM2.5 pollution episode from December 1–4, 2017, is chosen for analysis, which is characterized by the rapid development of a vast polluted air mass along the mountainous side of the NCP extended hundreds of kilometers. In association with this episode, a shallow trough and a warm tongue at 850 hPa, with warm air advection in the upper layer and an orographic trough at the surface, provide favorable conditions for low-level warm front formation in the NCP. Surface meteorological data from 116 observatories and pollution-monitoring data recorded at 40 stations on the NCP are used to diagnose the hourly evolution of the meteorological and PM2.5 concentration fields, based on the California Meteorological (CALMET) model and a simple interpolation scheme. In addition to the surface wind, the equivalent potential temperature (EPT) is used to analyze air-mass boundaries or fronts at the surface. The results show that a block of colder air mass is gradually confined by warmer air, driven both from the southeast by a warm front and from the northwest by the thermal effect of the mountains. Consequently, a polluted air mass develops, with sharp boundaries indicated by both the discontinuity of wind fields and a strong gradient in the EPT. Numerical simulation using the Weather Research and Forecast model reproduces the meteorological evolution at the surface, revealing a three-dimensional ABL structure during this episode. With a dome-like warm cap covering the colder polluted air mass, an abrupt drop of ABL height occurs at the cross section from outside into this zone. Strong stratification suppresses the daytime ABL height to as low as 300 m over this zone. Thus, the cold air mass is confined not only laterally but also vertically. This ABL structure persisted throughout the daytime and night, in addition to weak winds in the nearly isolated air mass, which constitutes adverse dispersion conditions. This may help to explain the simultaneous increase in PM2.5 concentrations over a vast area of the NCP.

Anthropometric Profile of FIVB Volleyball Girls' U18 World Championship Volleyball Players According to the Playing Position- World Championship 2017

Identifying the anthropometric characters of adolescent elite players may be useful in developing the recognition of volleyball talents and key physical abilities needed to perform at a high level. The purpose of this study was to describe anthropometric characteristics, including height, weight, body mass index (BMI), spike height, and block height in elite volleyball youth players participating in the 2017 FIVB Volleyball Girls' U18 World Championship. Also, comparisons of these parameters were evaluated based on individual game position (libero, setter, middle blocker, outside hitter, opposite), team continent, and team rank. The variables studied in this study were extracted from the list of players registered on the website of the International Volleyball Federation (FIVB) and included 240 players of 20 teams. The results of one-way ANOVA showed that players in the G1 group (rank 1 to 4) had higher height, weight, spike height, and block height than other groups (rank 5 to 20). Also, the middle blockers had the tallest height (185.9 cm), weight (71.4 kg), spike height (294.5 cm) and block height (282.7 cm). This study presents anthropometric data that show different levels of success for elite girls' volleyball players in the 2017 championship. This information should serve as a reference for average body height, weight, BMI, spike height, and block height for identifying athletic talents for various positions in volleyball.

A new approach to improve the assessment of rock mass discontinuity spacing using image analysis technique

The mean discontinuity spacing can significantly varies with varying the scanline direction. To clarify the assessment of mean discontinuity spacing using measurement and relevant conventional equations, several artificial cubic models having three different discontinuity sets with various spacings and orientations were made by foam. The grand mean measured discontinuity spacing (XGMM) of various scanline directions on different profile planes had a linear correlation with the block size (XBS) of the typical artificial models (XGMM = 0.725XBS). Then, a new method using image analysis of in-situ rock mass was applied to assess mean rock mass block size as an alternative solution to represent the mean discontinuity spacing. The scaled images were prepared from ninety-four cases of twenty zones of in-situ rock masses in several mines, and the discontinuity spacing was also measured in six scanline directions for each case, as measurement was carried out in 564 scanlines. The images of in-situ rock masses were analyzed by Split-Desktop software and rock block size distribution, X20, X50 (mean size) and X80 were determined. The rock block size obtained by the images analysis (X50-image analysis) had a good linear correlation with the grand mean measured discontinuity spacing of six scanline directions of each case (XGM-measured) for various rock mass conditions (XGM-measured = 0.70X50-image analysis). The obtained relation can be a reliable solution to specify the mean value of discontinuity spacing using image analysis of rock mass.

A method of reducing the radial load of the shaft of a vertical axis wind turbine based on movable mass blocks

Fatigue failure caused by unsteady loads on the shaft is an important limiting factor in the development of large VAWT. This study proposes an active control method that relies on movable mass blocks to reduce the unsteady loads. Then on the basis of the aerodynamic load of the VAWT simulated by computational fluid dynamics, the motion laws of the mass blocks with different masses are investigated. When the mass of mass block is 0.075 kg, the radial load of the shaft can be reduced by 97.1% and the shaft deformation can be eliminated by 99% without affecting the power output of wind turbine. However, further research on the start-up performance of the VAWT indicates that the active control method also prolongs the start-up time. Thus a method of adjusting the moment of inertia of wind turbine with a rotation speed of 15.6 m/s is proposed to save 40.6% of the start-up time with respect to the method used for direct start-up with large moment of inertia of 0.036 kg m2. After the start-up, a transition displacement curve is plotted to aid in the switching design of the operation mode of mass blocks between the start-up phase and the normal operation phase.

EFFECTS OF CLIMATE ON THE ARCHITECTURAL AND URBAN DESIGN OF TRIPOLI

Tripoli is a city of a Mediterranean Sea climate; this has contributed with some social and religious factors to affect the architectural and urban design, which all originally has come from the Islamic content. This study argues the climatic features of Tripoli in order to show the ways followed by the Libyan Muslim architect. In other words, these ways were used to adapt with the climate and create the demanding architectural treatments, which have served the building units. This is considered as a study case that can discuss the possibility of the climatic reflection on the walls. That is to say, the walls’ thickness, the type of the used substance in building, the substance’s properties, the type of roof used in covering the building units and the architectural design of the building as treatments achieved professionally by the architect in decreasing the heat in summer and increasing the heat in winter through the mass block. Additionally, the researchers have stated that Tripoli’s building design respected the privacy of the inhabitants and their isolation from the world outside their buildings. That is because they wanted to have their own cold spaces inside which were rich of light, air and shadow. As a result of the aforementioned considerations, the architectural buildings contained the uncovered space and the broken entrance to keep the privacy from the passengers and to protect the inhabitants from wind and sand. These were regarded as final solutions for the architectural and climatic problem. Further, this study illustrates the active role of using the planning including the architectural formations and the treatments of motion path. That is according to their width, their length, their form, their guidance and their direction change in order to make shadow and isolate the front of buildings. This also contributed to give the streets the northern wind which in turn helped to keep the air moving as long as possible to tone down the climatic influences. Moreover, the planning aimed to show its turn through analytical, architectural and documentary survey for realistic examples in the archeological registrar of the potential city treatments. These architectural elements were important in making the sustainable architecture in respect to the environment and human relaxation requirements. Finally, the researchers measured the following factors temperatures, wind, rain, and ratio humidity for variety of spaces in the city. That was followed by qualitative and quantitative statistical analysis supported by graphs

Experiment Investigation of Bistable Vibration Energy Harvesting with Random Wave Environment

The energy harvested from the renewable energy has been attracting a great potential as a source of electricity for many years; however, several challenges still exist limiting output performance, such as the package and low frequency of the wave. Here, this paper proposed a bistable vibration system for harvesting low-frequency renewable energy, the bistable vibration model consisting of an inverted cantilever beam with a mass block at the tip in a random wave environment and also develop a vibration energy harvesting system with a piezoelectric element attached to the surface of a cantilever beam. The experiment was carried out by simulating the random wave environment using the experimental equipment. The experiment result showed a mass block’s response vibration was indeed changed from a single stable vibration to a bistable oscillation when a random wave signal and a periodic signal were co-excited. It was shown that stochastic resonance phenomena can be activated reliably using the proposed bistable motion system, and, correspondingly, large-scale bistable responses can be generated to realize effective amplitude enlargement after input signals are received. Furthermore, as an important design factor, the influence of periodic excitation signals on the large-scale bistable motion activity was carefully discussed, and a solid foundation was laid for further practical energy harvesting applications.

Micro-opto-electro-mechanical gyroscope based on the Talbot effect of a single-layer near-field diffraction grating.

We demonstrate a novel, to the best of our knowledge, micro-opto-electro-mechanical system (MOEMS) gyroscope based on the Talbot effect of a single-layer near-field diffraction grating. The Talbot effect of an optical grating is studied both theoretically and experimentally. A structure of grating-mirror combination, fabricated by the micro-nano processing method, is used for out-of-plane structure detection. The detection of a weak Coriolis force is realized by using the highly sensitive displacement characteristic of Talbot imaging of near-field diffraction with a mirror mass block and single-layer grating. The experimental results show that, the micro-displacement detection sensitivity can reach up to 0.09%/nm, and the MOEMS gyroscope can be moved in the driven direction, with a resonant frequency of 7048 Hz and a quality factor of 700, which indicates great potential of the Talbot effect in developing novel high-performance micro-gyroscopes.

The October 13, 2020, deadly rapid landslide triggered by heavy rainfall in Phong Dien, Thua Thien Hue, Vietnam

At about 12:00 a.m., on October 13, 2020, a rapid rotational landslide induced by rainfall swept over Ranger Station-7 in Phong Xuan commune, Phong Dien district, Thua Thien Hue province, Vietnam, claiming the lives of 13 rescue team members. This paper presents an overview of the fatal landslide at Ranger Station-7. The analysis indicates that the entire landslide had a volume of approximately 81,550 m3. The observed topographical features indicate that the landslide mass consists of lower and upper blocks. The lower block of the landslide mass started sliding first; the movement was then followed by the slide of the upper block.

Towards a model for structured mass movements: the OpenLISEM hazard model 2.0a

Abstract. Mass movements such as debris flows and landslides differ in behaviour due to their material properties and internal forces. Models employ generalized multi-phase flow equations to adaptively describe these complex flow types. Such models commonly assume unstructured and fragmented flow, where internal cohesive strength is insignificant. In this work, existing work on two-phase mass movement equations are extended to include a full stress–strain relationship that allows for runout of (semi-)structured fluid–solid masses. The work provides both the three-dimensional equations and depth-averaged simplifications. The equations are implemented in a hybrid material point method (MPM), which allows for efficient simulation of stress–strain relationships on discrete smooth particles. Using this framework, the developed model is compared to several flume experiments of clay blocks impacting fixed obstacles. Here, both final deposit patterns and fractures compare well to simulations. Additionally, numerical tests are performed to showcase the range of dynamical behaviour produced by the model. Important processes such as fracturing, fragmentation and fluid release are captured by the model. While this provides an important step towards complete mass movement models, several new opportunities arise, such as application to fragmenting mass movements and block slides.

Sensitivity analysis of control parameters errors and current parameters to motion accuracy of underwater glider using Sobol’ method

Control parameters errors and current can weaken the motion accuracy of underwater gliders, which will obstruct the achievement of high accuracy exploration missions. To improve the glider motion accuracy more pertinently, it is necessary to identify the key factors that affect the glider motion accuracy. To resolve the above problem, we employ Sobol’ method to analyze the sensitivity of control parameters errors and current parameters to the glider motion accuracy. The control parameters errors include the net buoyancy adjustment amount error, the movable mass block translation amount error and the movable mass block rotation amount error. The current parameters include the current intensity, action depth and direction. First, the dynamic model of an underwater glider is established, and this model considers the effects of hull deformation, water density variation and current simultaneously. Then the dynamic model is validated by experimental data. After the evaluation parameter of motion accuracy is given, the glide motion accuracy is preliminarily analyzed, and then the sensitivity analysis is carried out. In this paper, we calculate the sensitivity coefficients by Monte Carlo method. To reconcile calculation efficiency with calculation accuracy, a convergence rule is proposed to reduce the number of sample points that are used for calculating sensitivity coefficients as much as possible. Besides, based on simulation results of dynamic model, the surrogate models are established to participate in the calculation of sensitivity coefficients, which can improve analysis efficiency further. For two typical motion modes, analysis results identify the key factors affecting the glider motion accuracy and illustrate the form of their effect on the glider motion accuracy. This research may be valuable for the achievement of the glider precision operation.

Parametric Study of Impulse Semi-active Mass Damper with Developing Directional Active Joint

High-rise buildings can easily suffer structural damage from dynamic excitation, which can be reduced with a tuned mass damper (TMD). However, TMDs can experience detuning or large displacement of the mass block. To prevent detuning, a newly developed directional active joint (DAJ) installed for automatic decoupling between the control mass block and the structure is proposed. The switching timing of several weight ratios for this DAJ and the response weighted control law were investigated with the vector form instinct finite element method and the fourth-order Runge–Kutta method. A ten-story building under excitation of near fault and far-field seismic records as the original structure and under TMD and semi-active mass damper (SAMD) (VwnA1) control was investigated to compare the displacement reaction of the top floor, efficiency of shock absorption and change in the shock absorption effect when the basic vibration frequency of the structure was misestimated. With the SAMD, the structure’s maximum displacement reaction was reduced by 37–42%. Regardless of the structural frequency misestimation ratio, the maximum displacement and average root mean square absorption rate at the top floor was only 4%, and the detuning phenomenon had little effect on it. With the TMD, a higher or lower misestimation ratio of the structure frequency caused a worse shock absorption effect. The SAMD is less sensitive to the basic vibration frequency of the structure and can indeed prevent the detuning effect of the TMD.

Diversity and Regularity of Periodic Impact Motions of a Mechanical Vibration System with Multiple Rigid Stops

The mechanical model of a two-degree-of-freedom vibration system with multiple rigid stops was established, and the effects of the multiple rigid stops to dynamic characteristics of two mass blocks of the system were studied. The judgment conditions and differential equations of motion of the system masses impacting rigid stops were analyzed. Based on the multiparameter and multiobjective collaborative simulation analysis, the correlation between the dynamic characteristics of the vibration system and the model parameters is studied. The basic periodic and subharmonic impact motions are analyzed with emphasis on the influences of dynamical parameters on the mode diversity and the distribution characteristics, and the law of emergence and competition of various periodic impact motions on the parametric plane is revealed. The singular points, the hysteresis transition domains, and the accompanying codimension-two bifurcations, caused by the irreversibility of the transition between adjacent basic periodic impact motions in the low-frequency domain, are analyzed. The reasonable parameter matching range, associated with dynamic characteristic optimization of the system, is determined.

Dynamic analysis of multi point winding hoisting system under non synchronous movements of wire ropes in deep well

Taking the multi point winding hoisting system with depth of 1000 m, drum radius of 0.4 m, drum radius difference of 0.1 mm as the research background, a model of multi point winding hoisting system under non synchronous movement of wire ropes is established, and the mathematical model is deduced by Lagrange equation. Then the dynamic characteristic of super deep multi point winding hoisting system under non synchronous movements of wire ropes is analyzed. The results show that: the rotational displacement of mass block is 5°, the rotational velocity is 0.07 °/s in the stage of constant speed. The rope length difference reaches 0.07 m, the tension of each wire rope changes 333 N, accounted for about 7 % of the average tension. And with the length difference increasing 35 mm, the force differences increasing 320 N, which indicates that the length difference has great impact on the tension difference of wire ropes. Finally, the mathematical model is verified through experiment.

Stability Analysis and Reliability Evaluation in Cataclastic Loose Rock Mass Blocks

Cataclastic rock masses with multiple failure modes and mechanisms are critical geological problems in the construction of rock slopes. Cataclastic rock masses are widely distributed in slopes of a hydropower project located on Lancang River, which is located in Tibet, China. In this study, the potentially unstable block of the slope is divided into key block and secondary key block based on the key block theory, and the system reliability evaluation theory is introduced. The method for quantitatively analyzing the rock mass stability of cataclastic slopes with sliding failure is established. Then, the spatial distribution of cataclastic rock masses and discontinuities in several rock slopes of a hydropower project are determined using traditional geological surveying and 3D laser scanning. At last, combining the BATE 2.0 software and the stereographic projection of the vector, the proposed method is applied to the study area. The results show that the main failure mode of the studied slope is wedge failure, and the system reliability is 1.69. With the increase in the instability probability of the key block, the increase in the instability probability of the system block is obvious, which reflects the controlling effect of the key block on the stability of the system block. The calculated system instability probability is slightly larger than the key block instability probability.