Proposed Stability Model Research Articles

Stability analysis of the pile-prestressed anchor composite structure based on failure mode

Pile-prestressed anchor composite structure is widely used in retain engineering, whose stability analysis is mainly based on the slip line passing through the bottom of pile. However, the existing stability analysis is unable to comprehensively consider the actual slip line passing through pile body, pile bottom and the soil under pile. Based on multiple failure modes, a stability analysis model of composite structure considering both the effects of prestress and pile body is established, and the dynamic search algorithm for the model is proposed. We compare the proposed model with the software of LIZHENG deep foundation pit and the existing calculation model and find the effectiveness of our model. It is found that the safety coefficient of the composite structure is directly proportional to the prestress, pile length and pile diameter, but inversely proportional to the pile spacing. Meanwhile, the safety coefficient increases firstly and then decreases with the increase of slip line depth. Increasing the prestress of anchor in the middle and lower part of the slope has a more obvious effect on improving the safety coefficient. The proposed stability model and search algorithm can consider multiple failure modes and obtain the safety coefficient. In addition, it can comprehensively evaluate the stability of the pile-prestressed anchor composite structure retaining slope, which has superior application value.

Buckling analysis of planar linear uniform deployable structures consisting of scissor-like element in space under compression

This paper comprehensively investigates the buckling load and the stability of a planar linear array deployable structure composed of scissor-like element (SLE) under compression. At present, the researches on deployable structure are mainly focused on configuration design and dynamics characteristics of the mechanisms, but less research on structural instability. In fact, when the external load exceeds the structural critical load value, the deployable structure will be permanently deformed or even collapse directly and no longer have any bearing capacity. To address this issue, a new stability model is derived using linear elastic analysis method and substructure method to evaluate the buckling characteristics of the deployable structure with n SLEs when it is carried out in space, which can accurately obtain the structural instability load and can be used quantitatively to optimize the structure for making it have the most stable configuration. In addition, the effects of the number of elements, the length, material properties and flexibility of the bar, and the deployment degree on the buckling of the scissor deployable structure are investigated, and the results of the theoretical analysis are compared with simulation and analytical results, respectively, confirming that the proposed stability model not only is able to effectively predict the structural instability load but also determine which part of the deployable structure is unstable. It can be concluded that the stability of the deployable structure gradually decreases with the increase of the number of elements or the bar flexibility. In the calculation process, the critical load of each sub-element should be considered, and the minimum value of the critical loads of all subunits can be regarded as the instability load of the whole structure.

The effects of blast damage zone thickness on rock slope stability

The selection of the blast damage zone thickness T for the Hoek-Brown (HB) criterion is significant in open pit slope design and stability analysis. Traditional slope stability analysis adopts a single value of blast damage factor D for the entire rock mass, leading to the underestimation of slope stability. In this research, the parallel layer model (PLM), in which the rock mass is divided into a number of layers parallel to the slope face with a decreasing value of D applied to each layer, is used with the limit equilibrium method to investigate the effects of T on the stability of rock slopes. Based on extensive parametric studies, a blast damage zone thickness weighting factor fT is proposed to quantify the influence of T on the evaluation of the factor of safety (FOS) of given slopes. Results show that the selection of T in the slope model plays an important role in the calculation of FOS, especially, when the ratio of T to slope height H is <1.0. Based on fT and existing stability charts, a stability model is proposed for the estimation of the FOS of slopes with different slope geometries and rock mass properties. The reliability of the proposed stability model is tested against numerical solutions. The results show that FOS estimated from the proposed stability model exhibits only 5.6% average relative discrepancy compared with numerical solutions based on 1254 sets of data. The proposed stability model is simple and effective, and can be used for the preliminary assessment of rock slope stability, considering the effects of different degree of blast damages

Seismic performance analysis of BRBs and gussets in a full‐scale 2‐story BRB‐RCF specimen

SummaryThe implementation of buckling‐restrained braces (BRBs) for new reinforced concrete frame (RCF) constructions is limited. This study investigates the seismic forces and stability in the BRBs and gussets of a 2‐story full‐scale RCF specimen by using Abaqus models and a newly proposed stability evaluation method. The hybrid and cyclic loading test results are accurately predicted by the Abaqus analyses. Existing methods for computing the gusset interface forces for steel buildings from both the brace and the frame actions are compared with the Abaqus results. The applicability of these methods for the BRB‐RCF design is critically evaluated. It is confirmed that the Parallel‐2 method is suitable for estimating the BRB force demand imposed on the corner gusset and the generalized uniform force method is good for the corner gusset at the base. In addition, existing stability evaluation methods for BRBs and gussets are applied to investigate the out‐of‐plane (OOP) buckling of the first‐story BRB observed at the end of tests. The proposed stability model incorporates the BRB restrainer's flexural effects and 4 rotational springs in assessing the BRB's buckling. This model confirms that the BRB and the gusset's OOP buckling limit states could be coupled and must be evaluated together. By incorporating the flexural effects of the steel casing and the infilled grout, the proposed model satisfactorily predicts the OOP buckling of the first‐story BRB and gussets. These research results can be used for the implementation of BRBs in new RC frame constructions.

Stability Prediction and Step Optimization of Trochoidal Milling

When machining narrow grooves, corners, and other complex cavities with trochoidal milling, the irrationally large trochoidal step usually leads to chatter, while the conservative trochoidal step constrains the machining efficiency. In this paper, a stability prediction model of trochoidal milling is established to solve these problems. An approach considering trochoidal steps and spindle speeds is presented to predict stability boundary of trochoidal milling. With considering the varying cutter-workpiece engagements, the stability of trochoidal milling process is predicted by obtaining the stability lobes of different cutter location (CL) points along the trochoidal milling tool paths. Based on the proposed stability model, a trochoidal step optimization strategy is developed to improve the machining efficiency of trochoidal milling under other parameters in a given situation. Cutting experiments are performed on the machining center GMC 1600H/2 to show the effectiveness of the proposed trochoidal milling stability model. Finally, simulations are adopted to illustrate the optimization strategy.

Stability of Milling Operations With Asymmetric Cutter Dynamics in Rotating Coordinates

High-speed machine tools have parts with both stationary and rotating dynamics. While spindle housing, column, and table have stationary dynamics, rotating parts may have both symmetric (i.e., spindle shaft and tool holder) and asymmetric dynamics (i.e., two-fluted end mill) due to uneven geometry in two principal directions. This paper presents a stability model of dynamic milling operations with combined stationary and rotating dynamics. The stationary modes are superposed to two orthogonal directions in rotating frame by considering the time- and speed-dependent, periodic dynamic milling system. The stability of the system is solved in both frequency and semidiscrete time domain. It is shown that the stability pockets differ significantly when the rotating dynamics of the asymmetric tools are considered. The proposed stability model has been experimentally validated in high-speed milling of an aluminum alloy with a two-fluted, asymmetric helical end mill.

Modeling the stability of terraced slopes: an approach from Valtellina (Northern Italy)

This study focuses on the relationships between hydrological processes and the stability of terraced slopes. Emphasis is given to the presence of dry-stone retaining walls and how to explicitly consider them when performing a distributed stability analysis. Valtellina, an Alpine valley of Northern Italy, is selected as study area. In detail, the slope uphill the village of Tresenda, affected by several superficial landslides since 1983, is studied. Dry-stone walls heavily influence the hydrological and geotechnical processes at the slope scale, and it is therefore crucial to consider them when performing a stability analysis on mountainous terraced areas. Walls are usually 0.60–1.00 m wide, and therefore, base maps (Digital Elevation Models and soil depth map) with a horizontal resolution of 1 m have been appositely derived. Working at this horizontal resolution leads to the failure of some basic assumptions of the infinite slope method, usually applied for distributed stability analysis. In this study, we propose an alternative approach based on the global method of equilibrium applied to sections of single terraces one cell wide. A specific sensitivity analysis allowed to fix some constrains to the model, in order to improve the reliability of the results under different mechanical and hydrological conditions. The proposed stability model was calibrated and evaluated on recorded past rainfall events. It resulted to be a good instrument for the identification of the most unstable areas when stressed with high pore-water pressure conditions.

Partial Variable Stabilization of a Class of Uncertain Systems with Uncertain Equilibrium Point

Partial variable stability is studied for a class of uncertain systems with uncertain equilibrium point. A stability model combining the ultimate boundedness and asymptotic stability is proposed, and the conditions of the stability model are given. According to the proposed stability model, a damping assignment control scheme is presented such that partial variables of the systems are stable in a given area and at the origin in different stages. The work of this paper develops the study on stability of uncertain systems and solves the control problem of a class of uncertain systems with uncertain equilibrium point existing widely in industrial applications. The effectiveness and practicability of the research results are verified by the simulation experiment of a permanent magnet synchronous motor.

Chatter Stability of General Turning Operations With Process Damping

The accurate prediction of chatter stability in general turning operations requires the inclusion of tool geometry and cutting conditions. This paper presents regenerative chip and regenerative chip area/cutting edge contact length based dynamic cutting force models, which consider cutting conditions and turning tool geometry. The cutting process is modeled as it takes place along the equivalent chord length between the two end points of the cutting edge. The regenerative chip model is simple, and the stability can be solved directly. However, the three-dimensional model considers the effect of tool vibrations at the present and previous spindle revolutions on the chip area, chord length, and force directions and is solved using Nyquist stability criterion. The penetration of worn tool flank into the finish surface is considered as a source of process damping. The effects of the nose radius, approach angle of the tool, and feedrate are investigated. The proposed stability model is compared favorably against the experimental results.

Stability analysis of turning process with tailstock-supported workpiece

This paper proposes an analytical scheme for stability analysis in turning process by considering the motion of tailstock-supported workpiece using a compliance model of tool and work. A dynamic cutting force model based on relative motion between the cutting tool and workpiece is developed to study the chatter stability. Linear stability analysis is carried out in the frequency domain and the stability charts are obtained with and without considering workpiece flexibility. Variations of stability limits with workpiece dimensions and cutter position as well as the effects of cutting tool dynamics are studied and wherever possible results are compared with existing models. Experimental analysis is conducted on tailstock-supported workpiece to examine the correctness of the proposed stability model.

Modal stability of inclined cables subjected to vertical support excitation

In this paper the out-of-plane dynamic stability of inclined cables subjected to in-plane vertical support excitation is investigated. We compute stability boundaries for the out-of-plane modes using rescaling and averaging methods. Our study focuses on the 2:1 internal resonance phenomenon between modes that occurs when the excitation frequency is twice the first out-of-plane natural frequency of the cable. The second in-plane mode is excited directly, while the out-of-plane modes can be excited parametrically. An analytical model is developed in order to study the stability regions in parameter space. In this model we include nonlinear coupling effects with other modes, which have thus far been omitted from previous models of parametric excitation of inclined cables. Our study reflects the importance of such effects. Unstable parameter regions are defined for the selected cable configuration. The validity of the proposed stability model was tested experimentally using a small-scale cable actuator rig. A comparison between experimental and analytical results is presented in which very good agreement with model predictions was obtained.

On the prediction of internal particle morphology in suspension polymerization of vinyl chloride. Part I:: The effect of primary particle size distribution

The present study provides a comprehensive investigation on the determination of the primary particle size distribution in the suspension “powder” polymerization of vinyl chloride. The primary particle size distribution inside the polymerizing monomer droplets is determined by the solution of a population balance equation governing the nucleation, growth, and aggregation of the primary particles. The stability of the colloidal primary particles is expressed in terms of the electrostatic and steric stabilization forces. The primary particle stability model includes the effects of agitation, temperature, electrolyte as well as primary and secondary stabilizer concentrations. It also includes both diffusive and shear-induced particle destabilization mechanisms. The proposed stability model is shown to accurately describe existing experimental data on particle number, mean particle size and particle size distribution for both bulk and suspension vinyl chloride polymerizations. The primary particle population balance model can predict the critical monomer conversion at which massive particle aggregation occurs leading to the formation of a continuous network of primary polymer particles inside the polymerizing monomer droplets. A detailed investigation on the predicted critical monomer conversion is carried out including its dependence on the rate of agitation, temperature, electrolyte concentration, as well as the concentrations of the primary and secondary stabilizers.

Analytical Modeling of Chatter Stability in Turning and Boring Operations: A Multi-Dimensional Approach

In this study, an analytical model for the stability of turning and boring processes is proposed. The proposed model is a step ahead from the previous studies as it includes the dynamics of the system in a multi-dimensional form, uses the true process geometry and models the insert nose radius in a precise manner. Simulations are conducted in order to compare the results with the traditional oriented transfer function stability model, and to show the effects of the insert nose radius on the stability limit. It is shown that very high errors in stability, which limit predictions can be caused when the true process geometry is not considered in the calculations. The proposed stability model predictions are compared with experimental results and an acceptable agreement is observed.

Nucleate Boiling Instability of Alkali Metals

A simplified theoretical model for bubble nucleation stability has been proposed, and an approximate stability criterion has been developed. This criterion contains both fluid and surface properties, and it predicts that nucleation for sodium should be unstable. Commercial-grade sodium was boiled from a horizontal disk at pressures near 60 mm Hg absolute, with sodium temperatures near 1200 F. Heat fluxes as high as 236,000 Btu/hr ft2 were attained. Boiler surface finishes ranged from highly polished mirror finishes to coarse, porous coatings. The effects of surface material, chemical treatment, heat flux, and cavity geometry on nucleation stability were measured, and the experimental results agreed with the predictions of the proposed stability model.