scholarly journals SPATIAL PROBLEMS OF DYNAMIC STABILITY OF FRAME STRUCTURES

2021 ◽  
Vol 3 (2) ◽  
pp. 40-51
Author(s):  
V. Fomin ◽  
◽  
I. Fomina ◽  
Keyword(s):  
Dynamic Stability ◽  
Dynamic Instability ◽  
Difficult Problem ◽  
Frame Structures ◽  
Spatial Problem ◽  
Deformation Method ◽  
Destructive Effect ◽  
Modified Method ◽  
Unlimited Growth ◽  
Transverse Oscillations

Periodic longitudinal forces in structural elements caused by operational or seismic influences, at certain values of the parameters of these forces can cause the occurrence and growing of transverse oscillations of these elements. This phenomenon is called parametric resonance or loss of dynamic stability. In the works of N. M. Belyaev, N. M. Krylov, М. М. Bogolyubov, E. Mettler, V. N. Chelomey, V. V. Bolotin flat problems of dynamic stability of frame structures were investigated. In this paper the modified Bolotin’s method, proposed to solve flat problems of dynamic stability of frames, is used. Instead of the deformation method used by V. V. Bolotin to construct analytical expressions of deflections of frame rods, in the modified method the numerical-analytical method of boundary elements is used. The article proposes a method for constructing domains of dynamic instability of frames in the space of parameters (frequency and amplitude) of seismic and operational dynamic influences that cause longitudinal forces in the rods, which periodically change over time and lead to unlimited growth of transverse oscillations amplitudes in the domains of instability. The proposed method is demonstrated in example, which considers the spatial problem of dynamic stability of a П-shaped frame with two concentrated masses located on it, which are under the action of vertical periodic forces. These forces create periodic longitudinal forces in the vertical rods of the frame. Areas of dynamic instability of the frame were constructed. Taking into account the destructive effect of oscillations is important for practical application. The most dangerous destructive effect of oscillations is observed in earthquakes and explosions. The study of this action makes it possible to avoid undesirable consequences of oscillations by limiting their level and to solve important practical problems of the dynamics of structures. Solving dynamics problems is a difficult problem. Dynamic calculation of structures provides their bearing capacity under the combined action of static and dynamic loads.

scholarly journals STUDY OF SPATIAL PROBLEMS OF DYNAMIC STABILITY OF REINFORCED CONCRETE FRAMES

2021 ◽  
pp. 62-70
Author(s):  
V.М. Fomin ◽  
◽  
І.P. Fomina ◽  
Keyword(s):  
Reinforced Concrete ◽  
Dynamic Stability ◽  
Degrees Of Freedom ◽  
Dynamic Instability ◽  
Practical Importance ◽  
Harmful Effect ◽  
Spatial Problem ◽  
Concrete Frames ◽  
Destructive Effect ◽  
Reinforced Concrete Frames

Abstract. The article proposes a method for constructing areas of dynamic instability of reinforced concrete frames in the space of parameters (frequency and amplitude) of seismic and operational dynamic impacts that cause the appearance of longitudinal forces in the bars of structures, which periodically change in time and lead to an unlimited increase in amplitudes of transverse vibrations when the values of these parameters are in the areas of instability. The proposed method is demonstrated by a specific example, which considers the spatial problem of dynamic stability of a П-shaped frame with two concentrated masses located on it, which are under the action of vertical periodic forces. These forces create periodic longitudinal forces in the vertical rods of the frame. Areas of dynamic instability of the frame are constructed. From the point of view of human activity, fluctuations can be both beneficial and harmful. We can observe vibrations of various buildings, structures, bridges, which cause additional stresses and deformations of these structures, have a harmful effect on their safe functioning. Too intense fluctuations lead to serious consequences. This leads to the destruction of individual elements of the structure and, as a result, to accidents. The most destructive effect of vibrations is observed during earthquakes and explosions. The study of vibrations is of great practical importance. This avoids the unwanted effects of fluctuations by limiting their level. Only on the basis of a deep study of various types of vibrations can important practical problems of the dynamics of structures be solved. Solving dynamics problems is a complex problem. In contrast to static calculation, when studying oscillations, one has to take into account an additional factor – time. The dynamic design of structures provides them with bearing capacity under the combined action of static and dynamic loads. A construction will be considered as a system with an infinite number of elementary masses distributed over it with an infinitely large number of dynamic degrees of freedom.

Study on Wear-Preventing of Needle Valve in Fuel Injection System Mounted on DME Engine

2011 ◽  
Vol 228-229 ◽  
pp. 1057-1062
Author(s):  
Xin Rong Wen ◽  
Guang De Zhang ◽  
Wei Hua Wang ◽  
Xie Lu ◽  
Sun Jing
Keyword(s):  
Dynamic Stability ◽  
Structural Design ◽  
Fuel Injection ◽  
Dynamic Instability ◽  
Calculation Model ◽  
The Other ◽  
Injection System ◽  
Needle Valve ◽  
Fuel Injection System ◽  
Theoretical Support

The purpose of this paper is to provide theoretical support for the structural design to prevent the wear of needle. The actual wear of the orientation part of the needle in scrapped needles was researched. The presented results showed that the main reason to the wear of the orientation part of needle was the dynamic instability and the abrasives enter into the surface of orientation part which increases the wear, and that the calculation model of dynamic stability was proposed to prevent the wear of needle. This model was a pressure rod, one end of which was fixed, the other was free, and the two ends were pressed on axial force which changes with time. Besides, the classic formula of dynamic stability of pressure rod was changed rationally, so as to correspond with the calculation model. It will play a part in preventing the wear of needle.

Dynamic Instability of a High-Speed Planing Boat Model

2000 ◽  
Vol 37 (03) ◽  
pp. 146-152
Author(s):  
Eric Thornhill ◽  
Brian Veitch ◽  
Neil Bose
Keyword(s):  
Dynamic Stability ◽  
High Speed ◽  
Research Council ◽  
Dynamic Instability ◽  
National Research Council ◽  
Scale Model ◽  
Clear Water ◽  
Towing Tank ◽  
Stability Limits ◽  
Resistance Tests

A series of bare-hull resistance and self-propulsion tests were carried out on a 1/8 scale model of a 11.8 m long, waterjet-propelled planing hull in the clear water towing tank at the National Research Council of Canada's Institute for Marine Dynamics. The bare-hull resistance tests, performed with the waterjet inlets closed, spanned a range of eight model velocities and nine ballast conditions consisting of three displacements each with three positions of the longitudinal center of gravity. The hull was then fitted with two model waterjet thrusters and tested over the same speeds and ballast conditions. Dynamic instability, or porpoising, was seen during certain high-speed tests. A discussion of this behavior and its relation to published dynamic stability limits is given.

scholarly journals Dynamic Stability Discrimination Method for Concrete Dam under Complex Geological Conditions

2019 ◽  
Vol 2019 ◽  
pp. 1-16
Author(s):  
Liaojun Zhang ◽  
Tianxiao Ma ◽  
Hanyun Zhang ◽  
Dongsheng Chen
Keyword(s):  
Stability Analysis ◽  
Dynamic Stability ◽  
Dynamic Instability ◽  
Limit Equilibrium ◽  
Element Model ◽  
Safety Factors ◽  
Stability Calculation ◽  
Dam Foundation ◽  
Geological Conditions ◽  
Dam Foundations

The instability of dams will bring immeasurable personal and property losses to the downstream, so it has always been a trendy topic worthy of investigation. Currently, the rigid body limit equilibrium method is the most commonly used method for the dynamic stability analysis of dams. However, under the action of earthquakes, the instability of the integral dam-foundation system threatens the safety of the dams and is of great concern. In this paper, a stability analysis method that can reflect the complex geological structural forms of dam foundations is proposed in this paper. The advantages are that this method deals with the difficulty in assuming sliding surfaces and the lack of quantitative criteria for the dynamic instability analysis of dams with complex geological structural forms of dam foundations. In addition, through the method, the sliding channels that may appear in the dam foundations can be automatically searched under random earthquake action, and the safety factors of the dynamic instability of dams be quantitatively obtained. Taking a high RCC gravity dam under construction in China as an example, the proposed method is applied to the three-dimensional finite element model of the dam-foundation system of this dam, and then the dynamic stability calculation is carried out. Through this method, the formation process of the dam foundation’s plastic zone and the failure of sliding channels with different strength reduction coefficients are studied on and analyzed detailedly, and the quantitative acquisition of the safety factors is realized. The results show that the method is reasonable and feasible, and helps provide a new idea and method for the dynamic stability analysis of dams.

Modeling and Experimental Investigation of Micro-Hydrostatic Gas Thrust Bearings for Micro-Turbomachines

2005 ◽  
Author(s):  
C. J. Teo ◽  
Z. S. Spakovszky
Keyword(s):  
Dynamic Stability ◽  
High Speed ◽  
Thrust Bearing ◽  
Dynamic Instability ◽  
Axial Stiffness ◽  
Stable Operation ◽  
Essential Information ◽  
Flow Choking ◽  
Thrust Bearings

One of the major challenges for the successful operation of high-power-density micro-devices lies in the stable operation of the bearings supporting the high-speed rotating turbomachinery. Previous modeling efforts by Piekos [1], Liu et al. [2] and Spakovszky and Liu [3] have mainly focused on the operation and stability of journal bearings. However, since thrust bearings play the vital role of providing axial support and stiffness, there is a need to gain a fuller understanding of their behavior. In this work, a rigorous theory is presented to analyze the effects of compressibility in micro-flows (characterized by low Reynolds numbers and high Mach numbers) through hydrostatic thrust bearings for application to microturbomachines. The analytical model, which combines a 1-D compressible flow model with Finite-Element Analysis, serves as a useful tool for establishing operating protocols and assessing the stability characteristics of hydrostatic thrust bearings. The model is capable of predicting key steady-state performance indicators, such as bearing mass flow, axial stiffness and natural frequency as a function of the hydrostatic supply pressure and thrust bearing geometry. The model has been applied to investigate the static stability of hydrostatic thrust bearings in micro-turbine-generators, where the electrostatic attraction between the stator and rotor gives rise to a negative axial stiffness contribution and may lead to device failure. Thrust bearing operating protocols have been established for a micro-turbopump, where the bearings also serve as an annular seal preventing the leakage of pressurized liquid from the pump to the gaseous flow in the turbine. The dual role of the annular pad poses challenges in the operation of both the device and the thrust bearing. The operating protocols provide essential information for the required thrust bearing supply pressures and axial gaps required to prevent the leakage of water into the thrust bearings for various pump outlet pressures. Good agreement is observed between the model predictions and experimental results. In addition, a dynamic stability analysis is also performed, which indicates the occurrence of unstable axial oscillations due to flow choking effects in both forward and aft thrust bearings. These a-priori dynamic stability predictions were subsequently verified experimentally on a micro-turbocharger. The frequencies of unstable axial oscillations predicted using the model compare favorably to those determined experimentally, thus vindicating the validity of the model. A simple and useful dynamic stability criterion is established, where the occurrence of flow choking in both thrust bearings give rise to dynamic instability.

Dynamic Stability of a Cantilever Shaft-Disk System

1992 ◽  
Vol 114 (3) ◽  
pp. 326-329 ◽  
Author(s):  
Lien-Wen Chen ◽  
Der-Ming Ku
Keyword(s):  
Dynamic Stability ◽  
Dynamic Instability ◽  
Equations Of Motion ◽  
Beam Theory ◽  
The Finite Element Method ◽  
Disk System ◽  
Stability Behavior ◽  
Gyroscopic Moment ◽  
The Mathematical Model ◽  
Cantilever Shaft

The dynamic stability behavior of a cantilever shaft-disk system subjected to axial periodic forces varying with time is studied by the finite element method. The equations of motion for such a system are formulated using deformation shape functions developed from Timoshenko beam theory. The effects of translational and rotatory inertia, gyroscopic moment, bending and shear deformation are included in the mathematical model. Numerical results show that the effect of the gyroscopic term is to shift the boundaries of the regions of dynamic instability outwardly and, therefore, the sizes of these regions are enlarged as the rotational speed increases.

Dynamic Stability of Timoshenko Beams by Finite Element Method

1976 ◽  
Vol 98 (4) ◽  
pp. 1145-1149 ◽  
Author(s):  
J. Thomas ◽  
B. A. H. Abbas
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Stability Analysis ◽  
Shear Deformation ◽  
Dynamic Stability ◽  
Timoshenko Beam ◽  
Dynamic Instability ◽  
Rotary Inertia ◽  
Timoshenko Beams ◽  
Buckling Loads

A Finite Element model is developed for the stability analysis of Timoshenko beam subjected to periodic axial loads. The effect of the shear deformation on the static buckling loads is studied by finite element method. The results obtained show excellent agreement with those obtained by other analytical methods for the first three buckling loads. The effect of shear deformation and for the first time the effect of rotary inertia on the regions of dynamic instability are investigated. The elastic stiffness, geometric stiffness, and inertia matrices are developed and presented in this paper for a Timoshenko beam. The matrix equation for the dynamic stability analysis is derived and solved for hinged-hinged and cantilevered Timoshenko beams and the results are presented. Values of critical loads for beams with various shear parameters are presented in a graphical form. First four regions of dynamic instability for different values of rotary inertia parameters are presented. As the rotary inertia parameter increases the regions of instability get closer to each other and the width of the regions increases thus making the beam more sensitive to periodic forces.

Dynamic Stability and Failure Probability Analysis of Dome Structures Under Stochastic Seismic Excitation

2014 ◽  
Vol 14 (05) ◽  
pp. 1440001 ◽  
Author(s):  
Jie Li ◽  
Jun Xu
Keyword(s):  
Dynamic Stability ◽  
Failure Probability ◽  
Stochastic System ◽  
Dynamic Instability ◽  
Seismic Excitation ◽  
Stochastic Dynamic ◽  
Deterministic System ◽  
Density Evolution ◽  
Stochastic Response ◽  
Strength Failure

The intrinsic relationship between deterministic system and stochastic system is profoundly revealed by the probability density evolution method (PDEM) with introduction of physical law into the stochastic system. On this basis, stochastic dynamic stability analysis of single-layer dome structures under stochastic seismic excitation is firstly studied via incorporating an energetic physical criterion for identification of dynamic instability of dome structures into PDEM, which yields to sample stability (stable reliability). However, dynamic instability is not identical to structural failure definitely, where strength failure can be experienced not only in the stable structure but also when the structure is out of dynamic stability. It is practically feasible to decouple the stochastic dynamic response of dome structures to be a stable one and an unstable one according to the generalized density evolution equation (GDEE). Consequently, the global failure probability can be investigated separately based on the corresponding independent stochastic response. For unstable failure probability assessment, the failure probability is the unstable probability if the dome's failure is attributed to instability, whereas inverse absorbing is firstly implemented to get rid of the stochastic response before instability and a complementary process is filled in the safe domain immediately to finally assess the probability of strength failure after dynamic instability.

Dynamic Stability of Woven Fiber Laminated Composite Shallow Shells in Hygrothermal Environment

2017 ◽  
Vol 17 (08) ◽  
pp. 1750084 ◽  
Author(s):  
M. Biswal ◽  
S. K. Sahu ◽  
A. V. Asha
Keyword(s):  
Dynamic Stability ◽  
Degrees Of Freedom ◽  
Dynamic Instability ◽  
Shear Deformation Theory ◽  
Shell Element ◽  
Load Factor ◽  
Element Formulation ◽  
Shallow Shells ◽  
Instability Regions ◽  
Hygrothermal Environment

The dynamic stability of bidirectional woven fiber laminated glass/epoxy composite shallow shells subjected to harmonic in-plane loading in hygrothermal environment is considered. An eight-noded isoparametric shell element with five degrees of freedom is used in the analysis. In the present finite element formulation, a composite doubly curved shell model based on first-order shear deformation theory (FSDT) is used for the dynamic stability analysis of shell panels subjected to hygrothermal loading. A program is developed using MATLAB for the parametric study on the dynamic stability of shell panels under the hygrothermal field. The effects of various parameters like static load factor, curvature, shallowness, temperature, moisture, stacking sequence and boundary conditions on the dynamic instability regions of woven fiber glass/epoxy shell panels are investigated. The location of dynamic instability regions is shown to affect significantly due to presence of the hygrothermal field.

Dynamic Stability of Off-Shore Structures

1980 ◽  
Vol 22 (1) ◽  
pp. 37-39
Author(s):  
J. Thomas ◽  
B. A. H. Abbas
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Computer Program ◽  
Dynamic Stability ◽  
Dynamic Instability ◽  
Buckling Load ◽  
The Finite Element Method ◽  
Shore Platforms ◽  
Element Method

This paper presents the results of an investigation of the dynamic stability of steel off-shore platforms subjected to vertical and horizontal forces. A computer program based on the finite-element method was developed to calculate the frequencies of vibration, the buckling load, and the regions of dynamic instability.

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