A Combined Approximation Based MATLAB Code for Dynamic Re-Analysis of Aerospace Structures

2009 ◽  
Author(s):  
Hesham A. Afifi ◽  
Efstratios Nikolaidis ◽  
Emily K. Afifi ◽  
Sathya N. Gangadharan
Keyword(s):  
Large Scale ◽  
Dynamic Stiffness ◽  
Excitation Frequency ◽  
Weight Ratio ◽  
Global Approximation ◽  
Reduced Basis ◽  
Aerospace Structures ◽  
Baseline Design ◽  
Matlab Code ◽  
Dynamic Reanalysis

Achieving a high strength-to-weight ratio is one of the most important goals in the design of aerospace structures. Designers are continuously striving to find the optimum solutions that will make aerospace vehicles simultaneously strong and light. During the design process, the structure experiences several changes to reach this goal. Any change to the geometry and/or material property directly influences the global stiffness of the structure. Modification of the applied loading or stiffness impacts the solution of displacements. Each design change requires the implicit analysis equation to be resolved. In large scale models with thousands of degrees of freedom, the cost and time of repeated reanalysis, even for a small change, is significant. A combined approximation approach (CA) was previously developed to provide an efficient and accurate reanalysis of large structures, even with great changes in the design. High quality results have also been obtained through utilizing the CA method for dynamic reanalysis. This approach involves the combination of local and global approximation methods including series expansion, reduced basis vector, matrix factorization, and Gram-Schmidt orthonormalization. In this study, a combined approximation based MATLAB code for dynamic reanalysis has been developed. Changes in both baseline design properties and excitation frequency range have been introduced. The response of the modified system is calculated as a function of these changes, directly via inversion of the dynamic stiffness matrix and approximately via combined approximation method. A reanalysis example of a simplified aircraft wing spar model using this code is presented. Both methods are compared for solution accuracy.

Concrete Strength and Deformation Property under Sea Water Erosion Environment

2012 ◽  
Vol 446-449 ◽  
pp. 2554-2559 ◽  
Author(s):  
Jian Jun Cai ◽  
Feng Zhang ◽  
Wei Cui ◽  
Shou Shan Chen ◽  
Pu Lun Liu
Keyword(s):  
Large Scale ◽  
Failure Modes ◽  
Deformation Property ◽  
Sea Water ◽  
Dynamic Stiffness ◽  
Concrete Strength ◽  
Strain Curve ◽  
Water Erosion ◽  
Strength And Deformation ◽  
Erosion Environment

In order to effectively assess the concrete strength and deformation property under sea water erosion environment, concrete stress and strain curve was researched with the number of wet and dry cycle of 0 times, 10 times , 20 times, 30 times, 40 times, 50 times and 60 times based on the large-scale static and dynamic stiffness servo test set. The stress - strain curves of concrete was tested for the lateral pressure 10.8MPa, 14.4MPa, and 18.8MPa at different dry-wet cycles, The failure modes and superficial cracking characteristics of specimens are reported at different dry-wet cycles. Concrete elastic modulus and compressive strength were researched. Based on concrete mechanical theory , the classic Kufer-Gerstle strength criteria of concrete was used, a large number of test samples of multivariate data were nonlinear regressed, a biaxial concrete strength criterion was established taking into account the stress ratio and the number of dry-wet cycles.

Design and structural performance measurements of a novel multi-cantilever foil bearing

2014 ◽  
Vol 229 (10) ◽  
pp. 1830-1838 ◽  
Author(s):  
Kai Feng ◽  
Xueyuan Zhao ◽  
Zhiyang Guo
Keyword(s):  
Dynamic Characteristics ◽  
Dynamic Load ◽  
Dynamic Stiffness ◽  
Excitation Frequency ◽  
Viscous Damping ◽  
Equivalent Viscous Damping ◽  
Foil Bearing ◽  
Load Tests ◽  
Stiffness And Damping ◽  
Motion Amplitude

With increasing need for high-speed, high-temperature, and oil-free turbomachinery, gas foil bearings (GFBs) have been considered to be the best substitutes for traditional oil-lubricated bearings. A multi-cantilever foil bearing (MCFB), a novel GFB with multi-cantilever foil strips serving as the compliant underlying structure, was designed, fabricated, and tested. A series of static and dynamic load tests were conducted to measure the structural stiffness and equivalent viscous damping of the prototype MCFB. Experiments of static load versus deflection showed that the proposed bearing has a large mechanical energy dissipation capability and a pronounced nonlinear static stiffness that can prevents overly large motion amplitude of journal. Dynamic load tests evaluated the influence of motion amplitude, loading orientation and misalignment on the dynamic stiffness and equivalent viscous damping with respect to excitation frequency. The test results demonstrated that the dynamic stiffness and damping are strongly dependent on the excitation frequency. Three motion amplitudes were applied to the bearing housing to investigate the effects of motion amplitude on the dynamic characteristics. It is noted that the bearing dynamic stiffness and damping decreases with incrementally increasing motion amplitudes. A high level of misalignment can lead to larger static and dynamic bearing stiffness as well as to larger equivalent viscous damping. With dynamic loads applied to two orientations in the bearing midplane separately, the dynamic stiffness increases rapidly and the equivalent viscous damping declines slightly. These results indicate that the loading orientation is a non-negligible factor on the dynamic characteristics of MCFBs.

Measured Static and Rotordynamic Coefficient Results for a Rocker-Pivot, Tilting-Pad Bearing With 50 and 60% Offsets

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Chris D. Kulhanek ◽  
Dara W. Childs
Keyword(s):  
Dynamic Stiffness ◽  
Mass Matrix ◽  
Excitation Frequency ◽  
Quadratic Function ◽  
Added Mass ◽  
Damping Coefficients ◽  
Stiffness Coefficients ◽  
Tilting Pad ◽  
Frequency Independent ◽  
Direct Stiffness

Static and rotordynamic coefficients are measured for a rocker-pivot, tilting-pad journal bearing (TPJB) with 50 and 60% offset pads in a load-between-pad (LBP) configuration. The bearing uses leading-edge-groove direct lubrication and has the following characteristics: 5-pads, 101.6 mm (4.0 in) nominal diameter,0.0814 -0.0837 mm (0.0032–0.0033 in) radial bearing clearance, 0.25 to 0.27 preload, and 60.325 mm (2.375 in) axial pad length. Tests were performed on a floating bearing test rig with unit loads from 0 to 3101 kPa (450 psi) and speeds from 7 to 16 krpm. Dynamic tests were conducted over a range of frequencies (20 to 320 Hz) to obtain complex dynamic stiffness coefficients as functions of excitation frequency. For most test conditions, the real dynamic stiffness functions were well fitted with a quadratic function with respect to frequency. This curve fit allowed for the stiffness frequency dependency to be captured by including an added mass matrix [M] to a conventional [K][C] model, yielding a frequency independent [K][C][M] model. The imaginary dynamic stiffness coefficients increased linearly with frequency, producing frequency-independent direct damping coefficients. Direct stiffness coefficients were larger for the 60% offset bearing at light unit loads. At high loads, the 50% offset configuration had a larger stiffness in the loaded direction, while the unloaded direct stiffness was approximately the same for both pivot offsets. Cross-coupled stiffness coefficients were positive and significantly smaller than direct stiffness coefficients. Negative direct added-mass coefficients were obtained for both offsets, especially in the unloaded direction. Cross-coupled added-mass coefficients are generally positive and of the same sign. Direct damping coefficients were mostly independent of load and speed, showing no appreciable difference between pivot offsets. Cross-coupled damping coefficients had the same sign and were much smaller than direct coefficients. Measured static eccentricities suggested cross coupling stiffness exists for both pivot offsets, agreeing with dynamic measurements. Static stiffness measurements showed good agreement with the loaded, direct dynamic stiffness coefficients.

scholarly journals Efficiency factor and modulus of elasticity of lightweight concrete with expanded clay aggregate

2010 ◽  
Vol 3 (2) ◽  
pp. 195-204 ◽  
Author(s):  
W.G Moravia ◽  
A. G. Gumieri ◽  
W. L. Vasconcelos
Keyword(s):  
Compressive Strength ◽  
Modulus Of Elasticity ◽  
Large Scale ◽  
Lightweight Concrete ◽  
Weight Ratio ◽  
Lightweight Aggregate ◽  
Normal Weight ◽  
Lightweight Aggregate Concrete ◽  
Empirical Methods ◽  
Normal Weight Concrete

Nowadays lightweight concrete is used on a large scale for structural purposes and to reduce the self-weight of structures. Specific grav- ity, compressive strength, strength/weight ratio and modulus of elasticity are important factors in the mechanical behavior of structures. This work studies these properties in lightweight aggregate concrete (LWAC) and normal-weight concrete (NWC), comparing them. Spe- cific gravity was evaluated in the fresh and hardened states. Four mixture proportions were adopted to evaluate compressive strength. For each proposed mixture proportion of the two concretes, cylindrical specimens were molded and tested at ages of 3, 7 and 28 days. The modulus of elasticity of the NWC and LWAC was analyzed by static, dynamic and empirical methods. The results show a larger strength/ weight ratio for LWAC, although this concrete presented lower compressive strength.

Modeling and Identification of Elastomeric Bearing Characteristics for Large-Scale Simulations

1998 ◽  
Vol 120 (1) ◽  
pp. 63-73 ◽  
Author(s):  
K. N. Morman ◽  
E. Nikolaidis ◽  
J. Rakowska ◽  
S. Seth
Keyword(s):  
Large Scale ◽  
Dynamic Stiffness ◽  
Testing Procedure ◽  
Nonlinear Dependence ◽  
Model Parameters ◽  
Elastomeric Bearing ◽  
Nonlinear Viscoelastic ◽  
Component Test ◽  
Differential Type ◽  
Stiffness And Damping

A constitutive equation of the differential type is introduced to model the nonlinear viscoelastic response behavior of elastomeric bearings in large-scale system simulations for vibration assessment and component loads prediction. The model accounts for the nonlinear dependence of dynamic stiffness and damping on vibration amplitude commonly observed in the behavior of bearings made of particle-reinforced elastomers. A testing procedure for the identification of the model parameters from bearing component test data is described. The experimental and analytical results for predicting the behavior of four (4) different car bushings are presented. In an example application, the model is incorporated in an ADAMS simulation to study the dynamic behavior of a car rear suspension.

Dynamic Property Analysis of Damping Rubber in Rail Fastenings under Different Deformation Condition

2014 ◽  
Vol 494-495 ◽  
pp. 706-710
Author(s):  
Bin Zhang ◽  
Yan Yun Luo ◽  
Zhi Nan Shi
Keyword(s):  
Mechanical Model ◽  
Dynamic Stiffness ◽  
Excitation Frequency ◽  
Nonlinear Damping ◽  
Deformation Condition ◽  
Damping Force ◽  
Restoring Force ◽  
Dynamic Mechanical ◽  
Large Distortion ◽  
Hydraulic Servo

This paper studies the experimental research on dynamic characteristics of the damping rubber in high elastic fastening by the electro-hydraulic servo movement tester. Based on a hypothesis superposition theory of nonlinear elastic restoring force and nonlinear damping force, a non-linear dynamic mechanical model is proposed. The dynamic stiffness and damping parameters of the rubber are obtained in different deformation conditions based on the dynamic mechanical model. The dynamic stiffness is analyzed, and the results show that dynamic stiffness is closely related to excitation frequency and amplitude. Furthermore the dynamic stiffness is analyzed under different free surface of rubber components by using FEM. That also reveals the changeable characteristics and affected factors of the damping rubber of the high elastic fastenings in large distortion condition.

Analysis of Modal Emissions From Diverse In-Use Vehicle Fleet

1997 ◽  
Vol 1587 (1) ◽  
pp. 73-84 ◽  
Author(s):  
Matthew Barth ◽  
Theodore Younglove ◽  
Tom Wenzel ◽  
George Scora ◽  
Feng An ◽  
...  
Keyword(s):  
Large Scale ◽  
Weight Ratio ◽  
Emission Model ◽  
Air Conditioner ◽  
Emission Standard ◽  
Vehicle Class ◽  
Testing Protocol ◽  
Vehicle Technology ◽  
Vehicle Fleet ◽  
Emissions Testing

The initial phase of a long-term project with national implications for the improvement of transportation and air quality is described. The overall objective of the research is to develop and verify a computer model that accurately estimates the impacts of a vehicle’s operating mode on emissions. This model improves on current emission models by allowing for the prediction of how traffic changes affect vehicle emissions. Results are presented that address the following points: vehicle recruitment, preliminary estimates of reproducibility, preliminary estimates of air conditioner effects, and preliminary estimates of changes in emissions relative to speed. As part of the development of a comprehensive modal emission model for light-duty vehicles, 28 distinct vehicle/technology categories have been identified based on vehicle class, emission control technology, fuel system, emission standard level, power-to-weight ratio, and emitter level (i.e., normal versus high emitter). These categories and the sampling proportions in a large-scale emissions testing program (over 300 vehicles to be tested) have been chosen in part based on emissions contribution. As part of the initial model development, a specific modal emissions testing protocol has been developed that reflects both real-world and specific modal events associated with different levels of emissions. This testing protocol has thus far been applied to an initial fleet of 30 vehicles, where at least 1 vehicle falls into each defined vehicle/technology category. The different vehicle/technology categories, the emissions testing protocol, and preliminary analysis that has been performed on the initial vehicle fleet are described.

scholarly journals Tribological Investigations of PVD Coated Multi-Layer Constructions

2015 ◽  
Vol 5 (1) ◽  
pp. 97 ◽  
Author(s):  
Marcus Schulze ◽  
Holger Seidlitz ◽  
Franziska Konig ◽  
Sabine WeiB
Keyword(s):  
Carbon Fibre ◽  
Physical Vapor Deposition ◽  
Large Scale ◽  
Metal Cutting ◽  
Wear Behavior ◽  
Cutting Tools ◽  
Weight Ratio ◽  
High Strength ◽  
Coating System ◽  
Wear Rates

<p class="1Body">Multi-layer constructions become more and more relevant in lightweight applications due to their high strength to weight ratio. They offer excellent crash, damping and recycling properties. Also, the morphology of thermoplastic carbon fibre reinforced plastics (CFRP) render them interesting for large scale manufacturing processes. Nevertheless, a major disadvantage results in a poor resistance against wear and tear, e.g. erosion, which is attributed to weak hardness properties. Hence, this work deals with tribological investigations on orthotropic carbon fibre reinforced polymers (PA 6) either with protective ceramic coating or without. The chosen coating system is a well-known protective covering of metal components, e.g. metal cutting tools, produced by physical vapor deposition (PVD). To characterize the coating system on thermoplastic CFRP, standard analyzing methods are utilized, like optical and scanning electron microscopy (SEM). The tribological investigations are conducted by the tribological ball on disk method to generate wear tracks on the sample surfaces and hence to calculate the wear rates. These results are compared to literature findings with respect to a certain protective coating system (TiN) and a second nano-structured gel coating system, where both systems are deposited on a thermosetting material, i.e. carbon fibre reinforced epoxy resin, respectively. For this purpose the feasibility of depositing a protective ceramic layer on thermoplastic CFRP is demonstrated. First results on suitable surface pre-treatments have shown a significant influence on the coating quality. The improved performance regarding the wear behavior with respect to tribology compared to the poor substrate and existing technologies is shown additionally.</p>

Leakage and Force Coefficients of a Grooved Wet (Bubbly Liquid) Seal for Multiphase Pumps and Comparisons With Prior Test Results for a Three Wave Seal

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Xueliang Lu ◽  
Luis San Andrés ◽  
Tingcheng Wu
Keyword(s):  
Pressure Drop ◽  
Volume Fraction ◽  
Dynamic Stiffness ◽  
Pressure Ratio ◽  
Excitation Frequency ◽  
Gas Content ◽  
Bubbly Liquid ◽  
Dynamic Force ◽  
Force Coefficients ◽  
Ring Seal

Abstract In the subsea oil and gas industry, multiphase pumps and wet gas compressors are engineered choices saving transportation and separation facility costs. In these machines, seals handling multiple phase components must be able to operate without affecting the system efficiency and its dynamic stability. This paper, extending prior work conducted with uniform clearance and wavy surface annular seals, presents measurements of leakage and dynamic force coefficients in a grooved seal whose dimensions are scaled from an impeller wear ring seal in a boiler feed pump. The 14-grooves seal has diameter D = 127 mm, length L = 0.34 D, and clearance c = 0.211 mm; each groove has shallow depth dg ∼2.6 c and length Lg ∼ 3.4% L. At a shaft speed of 3.5 krpm (surface speed = 23.3 m/s), a mixture of air in ISO VG 10 oil with inlet gas volume fraction (GVF) ranging from 0 (just oil) to 0.7 (mostly air) lubricates the seal. The pressure ratio (inlet/exit) is 2.9. The flow is laminar since the liquid is viscous and the pressure drop is low. The measured mixture mass flow decreases continuously with an increase in inlet GVF. The seal stiffnesses (direct K and cross coupled k), added mass (M), and direct damping (C) coefficients are constant when the supplied mixture is low in gas content, GVF ≤ 0.1. As the gas content increases, 0.2 ≤  GVF ≤ 0.5, the seal direct dynamic stiffness becomes nil with an increase in excitation frequency, whereas k and C reduce steadily with GVF. In general, for GVF ≤ 0.5, the direct damping is invariant with frequency; variations appearing for GVF = 0.7. Compared against a three wave annular seal, the grooved seal offers much lower force coefficients, in particular the viscous damping. Thus, for laminar flow operation (heavy oil) with a low pressure drop as in a wear ring seal, a three wave seal is recommended as it also offers a significant centering stiffness.

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