Letteratura scientifica selezionata sul tema "Enhanced FEM stability simulations"
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Articoli di riviste sul tema "Enhanced FEM stability simulations":
1
Zheng, Zumei, Shasha Zhou, Jun Chen, Naoto Mitsume e Shunhua Chen. "A Multi-Resolution MPS/FEM Coupling Method for Three-Dimensional Fluid–Structure Interaction Analysis". Journal of Marine Science and Engineering 11, n. 8 (25 luglio 2023): 1483. http://dx.doi.org/10.3390/jmse11081483.
Abstract (sommario):
This work aims to propose an efficient MPS/FEM coupling method for the simulation of fluid–structure interaction (FSI), where the MPS and FEM are respectively employed to account for fluid flows and structural deformation. The main idea of our method is to develop a multi-scale multi-resolution MPS method for efficient fluid simulations in the context of MPS/FEM coupling. In the developed multi-scale MPS method, the fluid domain is discretized into particles of different resolutions before calculation, where particles close to the interest domain will be discretized into high resolution, while the rest are discretized into low resolution. A large particle interacting with small particles is divided into several small particles virtually, and weight functions are redefined to maintain the simulation stability. A bucket-sort-based algorithm is developed for the fast search of multi-resolution neighboring particles. The capacity of a newly proposed ghost cell boundary model is further enhanced, so as to accurately treat wall boundary problems with particles of different resolutions. On this basis, the multi-resolution MPS method is coupled with the FEM for FSI simulations. Finally, several numerical examples are conducted to demonstrate the accuracy and efficiency of the development method.
2
Song, Eun Jeong, Jung Soo Lee, Hyungpil Moon, Hyouk Ryeol Choi e Ja Choon Koo. "A Multi-Curvature, Variable Stiffness Soft Gripper for Enhanced Grasping Operations". Actuators 10, n. 12 (29 novembre 2021): 316. http://dx.doi.org/10.3390/act10120316.
Abstract (sommario):
For soft grippers to be applied in atypical industrial environments, they must conform to an object’s exterior shape and momentarily change their stiffness. However, many of the existing grippers have limitations with respect to these functions: they grasp an object with only a single curvature and a fixed stiffness. Consequently, those constraints limit the stability of grasping and the applications. This paper introduces a new multicurvature, variable-stiffness soft gripper. Inspired by the human phalanx and combining the phalanx structure and particle jamming, this work guarantees the required grasping functions. Unlike the existing soft pneumatic grippers with one curvature and one stiffness, this work tries to divide the pressurized actuating region into three parts to generate multiple curvatures for a gripper finger, enabling the gripper to increase its degrees of freedom. Furthermore, to prevent stiffness loss at an unpressurized segment, this work combines divided actuation and the variable-stiffness capability, which guarantee successful grasping actions. In summary, this gripper generates multiple grasping curvatures with the proper stiffness, enhancing its dexterity. This work introduces the new soft gripper’s design, analytical modeling, and fabrication method and verifies the analytic model by comparing it with FEM simulations and experimental results.
3
Wei, Wei, Songjian Yu e Baozuo Li. "Research on Magnetic Characteristics and Fuzzy PID Control of Electromagnetic Suspension". Actuators 12, n. 5 (17 maggio 2023): 203. http://dx.doi.org/10.3390/act12050203.
Abstract (sommario):
This paper proposes an electromagnetic suspension with an electromagnetic actuator, which can improve the riding comfort and stability of the vehicle without changing the safety of traditional MacPherson suspension. First, the electromagnetic suspension structure is introduced, and the principle of the proposed actuator is described in detail. Second, a magnetic flux density model of a single PM ring (permanent magnetic ring) and a magnet assembly are built, and a theoretical analysis of the magnetic flux density is carried out for comparison. Then, the magnetic flux distribution of the magnetic field is simulated and analyzed using the finite element method (FEM), and is compared with theoretical and other experimental data. Finally, a vehicle dynamics model with 7 DOF is built, and vehicle simulations based on the fuzzy PID algorithm are carried out on a C-grade road surface and a deceleration strip. The theoretical results and simulation analyses of the FEM indicate that compared with the MacPherson suspension, the root mean square values of the acceleration of centroid acceleration for the electromagnetic suspension are increased by 59.08% and 33.34%, respectively, on a C-grade road surface and a deceleration strip, and other physical quantities have also been improved. The structure and characteristics of the proposed electromagnetic suspension that improve the riding comfort of the suspension and enhance the stability of the MacPherson suspension are feasible.
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Kien, Dang Van, Do Ngoc Anh e Do Ngoc Thai. "Numerical Simulation of the Stability of Rock Mass around Large Underground Cavern". Civil Engineering Journal 8, n. 1 (1 gennaio 2022): 81–91. http://dx.doi.org/10.28991/cej-2022-08-01-06.
Abstract (sommario):
Geotechnical problems are complicated to the extent and cannot be expected in other areas since non-uniformities of existing discontinuous, pores in materials and various properties of the components. At present, it is extremely difficult to develop a program for tunnel analysis that considers all complicated factors. However, tunnel analysis has made remarkable growth for the past several years due to the development of numerical analysis method and computer development, given the situation that it was difficult to solve formula of elasticity, viscoelasticity, and plasticity for the dynamic feature of the ground when the constituent laws, yielding conditions of ground materials, geometrical shape and boundary conditions of the structure were simulated in the past. The stability of rock mass around an underground large cavern is the key to the construction of large-scale underground projects. In this paper, the stability analysis was carried out based on those parameters by using 2D FEM RS2 program. The calculated stress and displacements of surrounding rock and rock support by FEM analysis were compared with those allowable values. The pattern of deformation, stress state, and the distribution of plastic areas are analyzed. Finally, the whole stability of surrounding rock mass of underground caverns was evaluated by Rock Science - RS2 software. The calculated axial forces were far below design capacity of rock bolts. The strong rock mass strength and high horizontal to vertical stress ratio enhanced safe working conditions throughout the excavation period. Thus wide span caverns and the system of caverns could be stability excavated sedimentary rock during the underground cavern and the system of caverns excavation by blasting method. The new method provides a reliable way to analyze the stability of the caverns and the system of caverns and also will help to design or optimize the subsequent support. Doi: 10.28991/CEJ-2022-08-01-06 Full Text: PDF
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Xiao, Enzhao, Shengquan Li, Ali Matin Nazar, Ronghua Zhu e Yihe Wang. "Antarctic Snow Failure Mechanics: Analysis, Simulations, and Applications". Materials 17, n. 7 (25 marzo 2024): 1490. http://dx.doi.org/10.3390/ma17071490.
Abstract (sommario):
Snow failure is the process by which the stability of snow or snow-covered slopes is destroyed, resulting in the collapse or release of snow. Heavy snowfall, low temperatures, and volatile weather typically cause consequences in Antarctica, which can occur at different scales, from small, localized collapses to massive avalanches, and result in significant risk to human activities and infrastructures. Understanding snow damage is critical to assessing potential hazards associated with snow-covered terrain and implementing effective risk mitigation strategies. This review discusses the theoretical models and numerical simulation methods commonly used in Antarctic snow failure research. We focus on the various theoretical models proposed in the literature, including the fiber bundle model (FBM), discrete element model (DEM), cellular automata (CA) model, and continuous cavity-expansion penetration (CCEP) model. In addition, we overview some methods to acquire the three-dimensional solid models and the related advantages and disadvantages. Then, we discuss some critical numerical techniques used to simulate the snow failure process, such as the finite element method (FEM) and three-dimensional (3D) material point method (MPM), highlighting their features in capturing the complex behavior of snow failure. Eventually, different case studies and the experimental validation of these models and simulation methods in the context of Antarctic snow failure are presented, as well as the application of snow failure research to facility construction. This review provides a comprehensive analysis of snow properties, essential numerical simulation methods, and related applications to enhance our understanding of Antarctic snow failure, which offer valuable resources for designing and managing potential infrastructure in Antarctica.
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Chen, Peng, Xiaorong Cai, Na Min, Yunfan Liu, Zhengxiong Wang, Mingjiang Jin e Xuejun Jin. "Enhanced Fatigue Resistance of Nanocrystalline Ni50.8Ti49.2 Wires by Mechanical Training". Metals 13, n. 2 (10 febbraio 2023): 361. http://dx.doi.org/10.3390/met13020361.
Abstract (sommario):
In this paper, the fatigue resistance of superelastic NiTi shape memory alloy (SMA) wires was improved by combining mechanical training and nanocrystallization. Fatigue tests were performed after mechanical training with a peak stress of 600 MPa for 60 cycles of nanocrystalline (NC) NiTi wires, and the associated microscopic mechanism was investigated by using transmission electron microscopy (TEM) and transmission Kikuchi diffraction (TKD). The results showed that stress-controlled training effectively improved the functional stability (the accumulated residual strain decreased by 83.8% in the first 5000 cycles) of NC NiTi SMA wires, as well as increased the average structural fatigue life by 187.4% (from 4538 cycles to 13,040 cycles). TEM observations and TKD results revealed that training-induced dislocations resulted in lattice rotation and preferential grain orientation. The finite element method (FEM) simulation results indicated that the training-induced preferential grain orientation tended to decrease the local stress concentration and strain energy density. Combined with fractography analysis, the uniform deformation caused by mechanical training changed the crack growth mode from multi-regional propagation to single-regional propagation, improving the structural fatigue life.
7
Gil, Javier, Clara Sandino, Miguel Cerrolaza, Román Pérez, Mariano Herrero-Climent, Blanca Rios-Carrasco, Jose Vicente Rios-Santos e Aritza Brizuela. "Influence of Bone-Level Dental Implants Placement and of Cortical Thickness on Osseointegration: In Silico and In Vivo Analyses". Journal of Clinical Medicine 11, n. 4 (16 febbraio 2022): 1027. http://dx.doi.org/10.3390/jcm11041027.
Abstract (sommario):
The purpose of this research is to study the biomechanical response of dental implants in bone-level type locations, 0.5 mm above and below the bone level. In addition, the influence of the thickness of the cortical bone on osseointegration is determined due to the mechanical loads transfer from the dental implant to the cortical and trabecular bone. The thicknesses studied were 1.5 mm and 2.5 mm. Numerical simulations were performed using a finite element method (FEM)-based model. In order to verify the FEM model, the in silico results were compared with the results obtained from a histological analysis performed in an in vivo study with 30 New Zealand rabbits. FEM was performed using a computerized 3D model of bone-level dental implants inserted in the lower jawbone with an applied axial load of 100 N. The analysis was performed using different distances from the bone level and different thicknesses of cortical bone. The interface area of bone growth was evaluated by analyzing the bone–implant contact (BIC), region of interest (ROI) and total bone area (BAT) parameters obtained through an in vivo histological process and analyzed by scanning electron microscopy (SEM). Bone-level implants were inserted in the rabbit tibiae, with two implants placed per tibia. These parameters were evaluated after three or six weeks of implantation. FEM studies showed that placements 0.5 mm below the bone level presented lower values of stress distribution compared to the other studied placements. The lower levels of mechanical stress were then correlated with the in vivo studies, showing that this position presented the highest BIC value after three or six weeks of implantation. In this placement, vertical bone growth could be observed up the bone level. The smallest thickness of the study showed a better transfer of mechanical loads, which leads to a better osseointegration. In silico and in vivo results both concluded that the implants placed 0.5 mm below the cortical bone and with lower thicknesses presented the best biomechanical and histological behavior in terms of new bone formation, enhanced mechanical stability and optimum osseointegration.
8
Ren, Qinghua, Junhong Chen, Xin Liu, Songsong Zhang e Yuandong Gu. "Design and 3D FEM Analysis of a Flexible Piezoelectric Micromechanical Ultrasonic Transducer Based on Sc-Doped AlN Film". Sensors 22, n. 21 (22 ottobre 2022): 8100. http://dx.doi.org/10.3390/s22218100.
Abstract (sommario):
In this paper, a flexible piezoelectric micromachined ultrasonic transducer (PMUT) based on Scandium (Sc)-doped Aluminum Nitride (AlN) film was designed and modeled by the three-dimensional finite element method (3D-FEM). The resonant frequency of 218.1 kHz was reported. It was noticeable that a high effective electromechanical coupling coefficient (k2eff) of 1.45% was obtained when a combination of a flexible PI and a thin Si layer was used as the PMUT supporting structure layer. Compared with a pure Si supporting layer counterpart, the coupling coefficient had been improved by 110.68%. Additionally, the increase of Sc doping concentration in AlN film further enhanced the device electromechanical coupling coefficient and resulted in an improvement for transmitting/receiving sensitivity of the proposed flexible PMUT. When the doping concentration of Sc reached 30%, the emission sensitivity was as large as 1.721 μm/V, which was 2.86 times greater than that of conventional AlN film-based PMUT. The receiving sensitivity was found to be 2.11 V/KPa, which was as high as 1.23 times the performance of an undoped device. Furthermore, the bending simulation result showed that the proposed flexible PMUT device can maintain a good mechanical stability when the bending radius is greater than 1.5 mm. The simulation of sound field characteristics demonstrated that the flexible PMUT based on AlScN could receive stable sound pressure signals under the bending radius of 1.5 cm.
9
Sanchaniya, Jaymin Vrajlal, Inga Lasenko, Vishnu Vijayan, Hilary Smogor, Valters Gobins, Alaa Kobeissi e Dmitri Goljandin. "A Novel Method to Enhance the Mechanical Properties of Polyacrylonitrile Nanofiber Mats: An Experimental and Numerical Investigation". Polymers 16, n. 7 (4 aprile 2024): 992. http://dx.doi.org/10.3390/polym16070992.
Abstract (sommario):
This study addresses the challenge of enhancing the transverse mechanical properties of oriented polyacrylonitrile (PAN) nanofibers, which are known for their excellent longitudinal tensile strength, without significantly compromising their inherent porosity, which is essential for effective filtration. This study explores the effects of doping PAN nanofiber composites with varying concentrations of polyvinyl alcohol (PVA) (0.5%, 1%, and 2%), introduced into the PAN matrix via a dip-coating method. This approach ensured a random distribution of PVA within the nanofiber mat, aiming to leverage the synergistic interactions between PAN fibers and PVA to improve the composite’s overall performance. This synergy is primarily manifested in the structural and functional augmentation of the PAN nanofiber mats through localized PVA agglomerations, thin films between fibers, and coatings on the fibers themselves. Comprehensive evaluation techniques were employed, including scanning electron microscopy (SEM) for morphological insights; transverse and longitudinal mechanical testing; a thermogravimetric analysis (TGA) for thermal stability; and differential scanning calorimetry (DSC) for thermal behavior analyses. Additionally, a finite element method (FEM) analysis was conducted on a numerical simulation of the composite. Using our novel method, the results demonstrated that a minimal concentration of the PVA solution effectively preserved the porosity of the PAN matrix while significantly enhancing its mechanical strength. Moreover, the numerical simulations showed strong agreement with the experimental results, validating the effectiveness of PVA doping in enhancing the mechanical properties of PAN nanofiber mats without sacrificing their functional porosity.
10
Hatipoglu, Kenan, Mohammed Olama e Yaosuo Xue. "Model-Free Dynamic Voltage Control of Distributed Energy Resource (DER)-Based Microgrids". Energies 13, n. 15 (27 luglio 2020): 3838. http://dx.doi.org/10.3390/en13153838.
Abstract (sommario):
In this paper, we present a new control technique for sustaining dynamic voltage stability by effective reactive power control and coordination of distributed energy resources (DERs) in microgrids. The proposed control technique is based on model-free control (MFC), which has shown successful operation and improved performance in different domains and applications. This paper presents its first use in the voltage stability of a microgrid setting employing multiple synchronous generator (SG)-based and power electronic (PE)-based DERs. MFC is a computationally efficient, data-driven control technique that does not require modelling of the different components and disturbances in the power system. It is utilized as an online controller to achieve the dynamic voltage stability of a microgrid system under different disturbances and fault conditions. A 21-bus microgrid system fed by multiple DERs is considered as a case study and the overall dynamic voltage stability is investigated using time-domain dynamic simulations. Numerical results show that the proposed MFC provides improvements on the dynamic load bus voltage profiles and requires less computational time as compared to the traditional enhanced microgrid voltage stabilizer (EMGVS) scheme. Due to its simplicity and low computational requirement, MFC can be easily implemented in resource-constrained computing devices such as smart inverters.
Tesi sul tema "Enhanced FEM stability simulations":
1
Strubel, Nicolas. "Brake squeal : identification and influence of frictional contact localizations". Electronic Thesis or Diss., Université de Lille (2022-....), 2023. http://www.theses.fr/2023ULILN059.
Abstract (sommario):
En tant que radiations acoustiques intenses impliquant de conséquentes nuisances environnementales ainsi que de nombreux retours clients, le crissement des systèmes de freinage est un problème de vibration induite par frottement dépendant indubitablement de problématiques multi-physiques et multi-échelles. Parmi ces dernières, la structure du système, les paramètres opérationnels de freinage, les interfaces de contact frottant, couplés à une dépendance en température, ainsi que les non-linéarités de contact ou les aspects tribologiques, sont des éléments affectant considérablement le crissement, faisant de ce déplaisant bruit un sujet complexe à appréhender. Au sein de ce travail, le système complet de freinage est considéré, et plusieurs tendances principales sont identifiées au regard de l'influence des localisations de contact sur les émissions acoustiques.Des essais NVH sont réalisés, cette analyse implique différentes échelles d'intérêt visant à changer les caractéristiques de contact : les plaquettes de freinage sont modifiées d'une part à l'échelle macroscopique -avec la volonté de varier implicitement les zones de portance-, d'autre part à l'échelle mésoscopique -tendant à impacter l'évolution du circuit tribologique-. Le but inhérent est d'identifier les paramètres patins influençant le crissement, en affectant l'interface tribologique et engageant des différences de signatures acoustiques entre les expériences conduites.Des tests fortement instrumentés sont réalisés à l'échelle du système de frein complet, se focalisant sur différentes formes patins : le développement d'une instrumentation enrichie au travers d'un suivi in-operando des surfaces de contact via mesures thermiques, autorise l'accès à des informations de sollicitation supplémentaires, permettant le suivi des zones de portance supposées. L'emploi de méthodes de clustering est considéré afin d'analyser les données thermiques.Des simulations en stabilité impliquant corrélations expérimental / numérique sont effectuées. Des analyses sous-jacentes sont réalisées, en investiguant l'impact de caractéristiques de chanfreins sur le crissement, l'influence du coefficient de frottement, ou l'implémentation de formes globales d'usures. Qui plus-est, les simulations thermomécaniques sont ici d'intérêt, et l'introduction des zones de contact issues des méthodes de clustering est discutée.Bien que la considération du frein complet puisse impliquer de sévères dispersions expérimentales, des corrélations initiales entre les patins modifiés à différentes échelles -via des formes de patins à l'échelle macroscopique et des traitements thermiques à l'échelle mésoscopique- et les caractéristiques de bruit sont observées. Les essais avec instrumentation enrichie concluent que les localisations de contact peuvent varier pendant les tests NVH, dépendant des paramètres de sollicitation. Un lien particulier entre les conditions opérationnelles de freinage (pression, température), les localisations de contact, et le crissement est établi au travers des méthodes de clustering. Également, les tendances observées en simulation tendent à suivre celles expérimentales, et l'enrichissement des modèles via une description plus précise du contact peut présenter des améliorations quant à la capacité de prédiction du crissement de telles simulationsAs intense acoustic radiations implying consequent environmental nuisances and customer complaints, squeal noises in brake systems are friction-induced vibration issues indubitably depending on multiphysics and multiscales problematics. Among these latter, system structure, braking operational parameters, frictional contact interfaces, coupled to temperature dependency, as well as contact non-linearities or tribological aspects, are elements considerably affecting squeal, making from this unpleasant noise a complex problem to apprehend. In this work, the full scale system is considered, and several principal tendencies are identified regarding the influence of contact localizations on acoustic emissions.NVH tests are conducted, this analysis involves several scales of interest aiming at changing contact characteristics: pads are modified either at the macroscopic scale -with the will of implicitly varying load bearing areas-, or at the mesoscopic one -tending to impact evolution of the tribological circuit-. The inherent purpose is to identify pads parameters influencing squeal, by affecting tribolayer as well as engaging noise signature differences between conducted experiments.Heavily instrumented tests are realized on a full scale brake system, focusing on different pad shapes: the development of an enriched instrumentation through in-operando thermal surface tracking allows to access to supplementary solicitation informations, permitting to follow the assumed load bearing area. The employment of clustering methods is considered to manage the analysis of thermal datas.Experimental / numerical correlated stability simulations are conducted. Subsequent analyses are realized, by investigating pads chamfer characteristic impact on squeal, influence of coefficient of friction, or implementation of global pads wear shapes. Furthermore, thermomechanical simulations are of interest, and the introduction of previously clustered-defined contact areas into models is realized.Although the full brake system consideration can involve severe experimental dispersions, initial correlations between modified pads at different scales -via pad shapes for the macroscopic one, and thermal treatments of friction material focusing on the mesoscopic level- and noise characteristics are observed. Enriched instrumented tests lead to the conclusion that contact localizations can evolve during NVH tests, depending on solicitation variables. A particular link between braking operational parameters (pressure, temperature), contact localizations, and squeal features is established through clustering. Finally, observed simulated tendencies tend to follow experimental ones, and model enrichment via a more accurate contact description could present improvements regarding squeal prediction capability of such simulation
2
Griffiths, Thomas Richard. "An Enhanced Data Model and Tools for Analysis and Visualization of Levee Simulations". Diss., CLICK HERE for online access, 2010. http://contentdm.lib.byu.edu/ETD/image/etd3477.pdf.
Capitoli di libri sul tema "Enhanced FEM stability simulations":
1
Feil, Jan-Henning, Reimund P. Rötter, Sara Yazdan Bakhsh, William C. D. Nelson, Bernhard Dalheimer, Quang Dung Lam, Nicole Costa Resende Ferreira et al. "Potential of Improved Technologies to Enhance Land Management Practices of Small-Scale Farmers in Limpopo Province, South Africa". In Sustainability of Southern African Ecosystems under Global Change, 653–85. Cham: Springer International Publishing, 2024. http://dx.doi.org/10.1007/978-3-031-10948-5_23.
Abstract (sommario):
AbstractIn this chapter, we explore how, in the face of increasing climatic risks and resource limitations, improved agro-technologies can support sustainable intensification (SI) in small-scale farming systems in Limpopo province, South Africa. Limpopo exhibits high agro-ecological diversity and, at the same time, is one of the regions with the highest degree of poverty and food insecurity in South Africa. In this setting, we analyze the effects of different technology changes on both food security dimensions (i.e., supply, stability, and access) and quality of ecosystem service provision. This is conducted by applying a mixed-method approach combining small-scale farmer survey data, on-farm agronomic sampling, crop growth simulations, and socioeconomic modeling. Results for a few simple technology changes show that both food security and ecosystem service provision can be considerably improved when combining specific technologies in a proper way. Furthermore, such new “technology packages” tailored to local conditions are economically beneficial at farm level as compared to the status quo. One example is the combination of judicious fertilizer application with deficit or full irrigation in small-scale maize-based farming systems. Provided comparable conditions, the results could be also beneficial for decision-makers in other southern African countries.
2
T, Yuvapriya, e Lakshmi P. "Active Suspension Control of Full Car Model Using Bat Optimized PID Controller". In Artificial Intelligence Applications in Battery Management Systems and Routing Problems in Electric Vehicles, 150–90. IGI Global, 2023. http://dx.doi.org/10.4018/978-1-6684-6631-5.ch008.
Abstract (sommario):
Long drives on bumpy roads and configuration issues like discomfort in seating arrangements have a harmful impact on the human body. The passengers experience severe health problems and stress-related issues. The full car model (FCM) with seven degrees of freedom (DOF) is considered for vibration control analysis. The aim of this work is to optimize the parameters of proportional integral and derivative (PID) controller by grey wolf optimization (GWO) and bat algorithm for betterment in the ride comfort of the passengers. A comparative analysis between the most commonly used PID controller and proposed optimized PID controller was executed over bump input (BI), ISO standard random input (RI), and sinusoidal input (SI) road profiles in MATLAB. Simulation results demonstrate that bat tuned PID (Bat-PID) controller enhances the ride comfort by decreasing the root mean square (RMS), frequency weighted RMS (FWRMS), and vibration dose values (VDV) of the body acceleration (BA) of the vehicle passing over BI, RI, and SI road profiles, which ensures the stability of the vehicle.
Atti di convegni sul tema "Enhanced FEM stability simulations":
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Gerenda´s, Miklo´s, Yannick Cadoret, Christian Wilhelmi, Thays Machry, Ralf Knoche, Thomas Behrendt, Thomas Aumeier et al. "Improvement of Oxide/Oxide CMC and Development of Combustor and Turbine Components in the HiPOC Program". In ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/gt2011-45460.
Abstract (sommario):
Three different oxide/oxide ceramic matrix composite (CMC) materials are described. Design concepts for the attachment of the CMC component to the metal structure of the gas turbine are developed in a first work stream focused on the combustion chamber and the turbine seal segment. Issues like environmental barrier coating (EBC)/thermal barrier coatings (TBC), application and volatilization, allowance for the different thermal expansion and the mechanical fixation are addressed. The design work is accompanied by CFD and FEM simulations. A variation of the microstructural design of the three oxide/oxide CMC materials in terms of different fiber architecture and processing of matrix are considered. Also, mechanical properties of these variations are evaluated. The material concepts are developed further in a second work stream. The CMCs are tested in various loading modes (tension, compression, shear, off-axis loading) from room temperature to maximum application temperature focusing on tensile creep behavior. By modification of the matrix and the fiber-matrix interface as well as EBC coatings, the high temperature stability and the insulation performance are enhanced. An outline of the “High Performance Oxide Ceramic”-program HiPOC for the following years is given, including manufacturing of a high-pressure tubular combustor and turbine seal segments from the improved materials as technology samples, for which validation testing up to technology readiness level 4 is scheduled for 2011.
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Franca Somers, Miss, Clément Roos, Francesco Sanfedino, Samir Bennani e Valentin Preda. "Probabilistic stability margins and their application to AOCS validation". In ESA 12th International Conference on Guidance Navigation and Control and 9th International Conference on Astrodynamics Tools and Techniques. ESA, 2023. http://dx.doi.org/10.5270/esa-gnc-icatt-2023-089.
Abstract (sommario):
Current validation and verification (V&V) activities in aerospace industry mostly rely on time-consuming simulation-based tools. These tools can give a measure of probability for sufficiently frequent phenomena, but they may fail in detecting rare but critical combinations of parameters. As the complexity of modern space systems increases, this limitation plays an ever-increasing role. In recent years, model-based worst-case analysis methods have reached a good level of maturity. Without the need of simulations, these tools can fully explore the space of all possible combinations of uncertain parameters and provide guaranteed mathematical bounds on robust stability and worst-case performance levels. However, they give no measure of probability and can therefore be overly conservative. Introduced more recently probabilistic μ-analysis combines worst-case information with probability measure. As such, it tempts to bridge the analysis gap between Monte Carlo simulations and deterministic μ-analysis [4]. The STOchastic Worst-case Analysis Toolbox (STOWAT), is a toolbox dedicated to probabilistic μ-analysis, developed by ONERA, The French Aerospace Lab. The original version of the toolbox, released by [9] and [1], only allowed for probabilistic robust stability and H∞ performance analysis. However, for the STOWAT to be fully convincing for industry, it should be as efficient and versatile as possible. For this purpose, focus has been on efficiency improvement ever since [3]. Furthermore, the toolbox was recently equipped with four probabilistic stability margin algorithms, devoted to probabilistic gain, phase, disk and delay margin analysis [8], [2], [7]. All four can be classified as μ-analysis based Branch-and-Bound (B&B) algorithms. At each iteration sufficient μ-analysis based conditions are evaluated to ascertain if the considered margin is guaranteed to be below (violation test) or above (satisfaction test) a desired threshold on a given set of uncertainties. If no conclusions can be drawn, the uncertainty set is split into two subsets and the analysis is repeated on each of them. These tools are limited to Single-Input Single-Output (SISO) system analysis. But since most industrial problems involve Multiple-Input Multiple-Output (MIMO) systems, this contribution first focuses on extending the algorithms to MIMO system analysis. Only adjustments need to be made to the conditions used to determine whether the satisfaction test or violation test should be applied. For SISO systems these conditions mostly rely on grid-based methods. However, in [8] it was already shown that gridding is usually very efficient for SISO and loop-at-a-time margin analysis, but gets quickly slower as the number of input/output channels increases. An alternative approach for MIMO systems, using μ-based tools was already proposed for disk margin analysis in [8]. This approach is used again here for MIMO phase, gain and delay margin analysis. However, it should be noted that the μ-based algorithm used should be adapted to the type of uncertainties (real/complex) in the studied stability margin problem. The developed MIMO analysis algorithms are all implemented in the STOWAT. Besides MIMO analysis, there is also an increased interest in multivariable margin analysis. This is because most realistic systems are subject to multiple perturbations at the same time. Multivariable analysis can for instance be an alternative to disk margin analysis [6], [8] in the case of simultaneous analysis of gain and phase perturbations. A probabilistic multivariable margin analysis algorithm is proposed in this contribution and implemented in the STOWAT. It was developed to overcome the conservatism provided by the deterministic worst-case equivalent at the end of the distribution tail. The STOWAT implementation allows users to specify multiple desired stability margins and determine the probability of multivariable margin violation. Analysis can be performed for both SISO and MIMO systems, where for MIMO systems different margin requirements can be set for each input and/or output. The heart of the existing algorithms remains the same, but two main modifications are needed. First a few additional matrix operations to construct the perturbed system used by the B&B algorithm should be included. Then new μ-analysis based conditions involving multiple real and complex uncertainties should be defined to determine whether the satisfaction or violation test should be performed. To demonstrate the added value of the developed tools, they are applied to analyse two satellite models: an academic model and a realistic benchmark. The academic model represents the spinning satellite adapted from [10] and the realistic one concerns the satellite with two flexible solar panels, previously introduced in [5]. References [1] J.-M. Biannic, C. Roos, S. Bennani, F. Boquet, V. Preda, and B. Girouart, “Advanced probabilistic μ-analysis techniques for AOCS validation,” European Journal of Control, vol. 62, pp. 120–129, 2021. [2] F. Somers, C. Roos, F. Sanfedino, S. Bennani, and V. Preda, “Probabilistic delay margin analysis,” Submitted to the American Control Conference, 2023. [3] C. Roos, J.-M. Biannic, and H. Evain, “A new step towards the integration of probabilistic μ in the aerospace V&V process,” in Proceedings of the 6th CEAS Conference on Guidance, Navigation and Control, 2022. [4] C. Roos, F. Sanfedino, V. Preda, and S. Bennani, “Phd position in analysis of aerospace control systems: Enhanced probabilistic tools to improve verification and validation of space control systems,” 2021. [5] F. Sanfedino, D. Alazard, E. Kassarian, and F. Somers, “Satellite dynamics toolbox library: a tool to model multi body space systems for robust control synthesis and analysis,” Submitted to the IFAC World Congress, 2023. [6] P. Seiler, A. Packard, and P. Gahinet, “An introduction to disk margins [lecture notes],” IEEE Control Systems Magazine, vol. 40, no. 5, pp. 78–95, 2020. [7] F. Somers, C. Roos, F. Sanfedino, S. Bennani, and V. Preda, “Comparative study of new probabilistic delay margin analysis techniques,” Submitted to International Journal of Robust and Nonlinear Control, 2023. [8] F. Somers, S. Thai, C. Roos, J.-M. Biannic, S. Bennani, V. Preda, and F. Sanfedino, “Probabilistic gain, phase and disk margins with application to AOCS validation,” in Proceedings of the 10th IFAC Symposium on Robust Control Design, 2022. [9] S. Thai, C. Roos, and J.-M. Biannic, “Probabilistic μ-analysis for stability and H∞ performance verification,” in Proceedings of the American Control Conference, 2019. [10] K. Zhou, J. Doyle, and K. Glover, Robust and optimal control. Prentice-Hall, New Jersey, 1996.
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Wu, Huanyu, Qi Zhao, Jiayi Shen e Hanze Li. "Numerical Simulation of the Underground Storage Cavern Using FDEM". In 57th U.S. Rock Mechanics/Geomechanics Symposium. ARMA, 2023. http://dx.doi.org/10.56952/arma-2023-0282.
Abstract (sommario):
ABSTRACT Underground storage cavern has been increasingly exploited as it has many advantages such as reducing investment, economizing land use and improving safety compared with storage above the ground surface. We employ the hydromechanical coupled FDEM to simulate the excavation and operation phases of the underground storage cavern with a water curtain system (WCS), taking into consideration the natural discrete fracture network (DFN). The simulation results captured the propagation and slipping of the pre-existing DFN during the excavation and operation process. We quantitatively evaluate the containment performance based on the water inflow and pore pressure distribution. This study provides new insights into evaluating the stability of cavern-surrounding rock masses and containment performance of underground storage caverns. INTRODUCTION Underground storage caverns have better performance on safety, security, economy, and greater environmental acceptance compared with traditional storage infrastructures such as storage tanks and pipelines. Several large underground storage caverns have been constructed, for example, Jurong rock caverns in Singapore (Zhou & Zhao, 2016) and Huangdao underground oil storage caverns in China (Wang et al., 2015). Underground storage caverns are constructed in fractured rock masses, confining the storage medium (such as oil and gas) by maintaining groundwater pressure around caverns which is also called hydraulic confinement (Aberg, 1978; Froise, 1987; Lindblom, 1997). The basic principle of underground containment the cavern is that no gas could leak as long as the water pressure increases along all possible gas leakage paths away from the cavern (Goodall et al., 1988). To enhance the sealing performance, water curtain systems (WCS) are constructed to manually control the pore pressure distribution by regulating the water curtain pressure. (Shi et al., 2018). Previous studies has evaluated the stability of excavated rock masses (Mohanty & Vandergrift, 2012; Ma et al., 2016; Zhuang et al., 2017) and containment performance (Xu et al., 2018; Liu et al., 2021) by using in-situ monitoring methods and numerical simulation. However, the fracture propagation and slip induced by the excavation and operation of the storage cavern, as well as the resultant fluid pressure variation, have not been illustrated.
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Elhassan, Azza, Patrick Manga, Mohamed S. Abdellatif, Ahmedagha Hamidzada, Kerron Andrews, Takahiro Takahiro e M. Sherif. "Impact of Change in Mud Weight & Offset Well Injection Pressure on Cement Sheath Integrity; Case Study for UAE Offshore Field." In ADIPEC. SPE, 2023. http://dx.doi.org/10.2118/216852-ms.
Abstract (sommario):
Abstract As drilling horizontal wells became more complex with multiple production drains from various reservoirs, zonal isolation has become a key challenge to be achieved. Many studies have shown the impact of change in mud weight during drilling activities on wellbore stability, without considering the consequences on the set cement. This case study will be focusing on drilling activities on offset wells, evaluating & exploring how mud weight changes can affect wellbore instability and damage the cement sheath despite the fact that the cement evaluation logs showed good results days after the cement job and before the mud weight reduction. The wells being studied have been analyzed using Finite Element Analysis (FEA) modeling after the cement was set and exposed to a change in mud weight as well as being exposed to the offset injection well. FEA computer simulations have enabled this modelling to determine the optimal mechanical properties required for the cement slurries to withstand those load limits (pressure testing, pressure reduction due to change of mud weight or an increase of the pore pressure due to an offset injection well). After opening the window and drilling ahead through the production drain wellbore, the wells have the same tendency of instability and require an increase in mud weight to control the inflow. This paper presents the impacts of the offset wells and the change of mud weight on the cement sheath failure in debonding, cracking, or sheath deterioration leading to gas channeling due to a micro annulus. The considered wells present the same behavior that has been highlighted above. The question to ask is why did a well that has been cemented and recorded a good cement bond fail to provide proper zonal isolation? The injection pressure of the offset well was evaluated and then used in the simulations, considering the conventional cement used during the primary cement job. The analysis has shown a complete failure of the cement integrity: cement debonding from the casing or from the formation; cement cracking and sheath failure. The cement slurry with improved mechanical properties was employed for the study under the same pressure conditions from an offset well and mud weight change. The model results demonstrate that the new cement's ability to withstand stresses has improved on the wells cemented after this study. The modelling effort presented in this paper allows for a barrier to be designed that has enhanced mechanical properties compared to the already placed barrier on the offset wells in the same field. Aside from improving the set cement mechanical properties, the mud weight change design has been improved in such a way that the mud weight must be anticipated, decreasing its impact on the barrier.
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Shah, Sameer Rafiq, Dilip Kumar e Nishant Tiwari. "Design and Development Of An In-Wheel Suspension With Novel Automatic Camber Control Strategy For Improved Handling". In FISITA World Congress 2021. FISITA, 2021. http://dx.doi.org/10.46720/f2020-vdc-081.
Abstract (sommario):
In this era of electrification, HEVs are mainly focused on weight and space saving. This is done to ensure the maximum size of the battery package on the vehicle. This situation demands for a drive by wire systems which makes the vehicle lighter as well as more spacious. This paper introduces a new type of In-Wheel suspension has been introduced in this paper. The problem of large suspension systems and its bulkiness were studied. Vehicle instability while driving and cornering was also stated. And the suspension's capability to handle uneven tyre wear which is caused due to improper or fixed camber angle was also addressed. The Novel In-Wheel Suspension is introduced in this paper which houses all the crucial parts of the suspension inside the rim of the wheel thus making it compact, lighter and sturdy. Parts were first designed by the principles of Machine Design, Kinematics and Mechanics of Materials. They were later modelled on Solid Edge ST7. Structural simulations was carried out on FEA Solver under highly strained conditions and also under dynamic loading and the results were satisfactory. A scaled prototype was made by manufacturing the parts on CNC machine. Later the suspension was assembled by brazing the parts together. The Impulse hammer technique was used to carry out the modal analysis which was used to study the damping characteristics of the suspension. Another innovation is introduced in this suspension which the Novel concept of Automatic Camber Control strategy which calibrates the camber angle of the wheel in real-time and greatly improves the performance as well as stability of the vehicle. The design process involved understanding the scaling down the size of the suspension without compensating the functionality of the suspension. The working prototype of the suspension was constructed and after rigorous testing which were carried out. It was found that the performance of suspension under low traction conditions was enhanced.
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Yan, Dingbang, Shuangxi Guo, Yilun Li, Jixiang Song, Min Li e Weimin Chen. "Dynamic Characteristics and Stability of Flexible Riser Under Consideration of Non-Uniform Tension and Internal Flow". In ASME 2020 39th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/omae2020-18347.
Abstract (sommario):
Abstract As oil and gas industry is developing towards deeper ocean area, the length and flexibility of ocean risers become larger, which may induce larger-amplitude displacement of flexible riser response due to lower structural stiffness against environmental and operational loads. Moreover, suffering not only the external fluid loads coming from environmental ocean wave and current, these risers also convey internal flow. In other words, the dynamic characteristics and response of the flow-conveying riser face great challenge, such as bucking, divergence and flutter, because of the fluid-solid coupling of the internal hydrodynamics and riser structural dynamics. In this study the dynamic characteristics and stability of a flexible riser, under consideration of its internal flow and, particularly, non-uniform axial tension, are examined through our FEM numerical simulations. First, the governing equations and FEM models of a flexible riser with axially-varying tension and internal flow are developed. Then the dynamic characteristics, including the coupled frequency and modal shape, are presented, as considering the speed of internal speed changes. At last, the dynamic response and corresponding stability behaviors are discussed and compared with the cases of riser with uniform tension. Our FEM results show that the stability and response are quite different from riser with uniform tension. And, the time-spatial evolution of riser displacement exhibit a strong wave propagation phenomenon where travelling wave are observed.
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Pinelli, Lorenzo, Federico Vanti, Andrea Arnone, Benjamin Beßling e Damian M. Vogt. "Influence of Tip Shroud Modeling on the Flutter Stability of a Low Pressure Turbine Rotor". In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-91204.
Abstract (sommario):
Abstract Since the modern design trend of low pressure turbine blades for aeronautical propulsion leads to lighter and more loaded blades, thus prone to flutter induced vibrations; flutter assessment is now a standard verification within the design loop of these components. Flutter stability assessment requires FEM and CFD tools able to predict the pressure response of fluid flow due to blade oscillation in order to compute the aerodynamic damping. Such tools are mature and validated, yet some geometrical aspects of the blade-row as contact interfaces at the blade tip shroud have to be carefully simulated to obtain accurate flutter results. The aim of this paper is to demonstrate the capability of the Open Source FEM tool (CalculiX) to deal with complex interlocked rotor geometries when performing modal analysis and to show the influence of different contact interface modeling on flutter stability. The solid mesh of a single-pitch row sector has been generated by using the Open Source suite Salome and the modal analysis has been carried out with CalculiX with cyclic symmetry conditions. The following uncoupled flutter simulations have been performed with the CFD TRAF code, an in-house solver developed at the University of Florence, which implements a non-linear method for flutter evaluation. An in-depth comparison among the FEM models with different boundary conditions in terms of mode shape frequency and aerodynamic damping curves are reported. These results show the effect of different contact interface models, especially on the first bending mode family, and confirm the overall row stability detected during a dedicated experimental flutter campaign.
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Kar, Sauradeep, Sridhar Singhal e Shailendra Kr Varshney. "Free-carrier assisted enhanced stability of mid-infrared Kerr Frequency Comb in a Silicon microring resonator". In Frontiers in Optics. Washington, D.C.: Optica Publishing Group, 2022. http://dx.doi.org/10.1364/fio.2022.jw4a.16.
Abstract (sommario):
The stability of Kerr frequency combs due to the combined effect of Kerr nonlinearity and the free-carrier effects in a Silicon racetrack microring resonator has been studied through numerical simulations at low temperatures.
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Liu, Yu, e Andrew J. Dick. "Numerical Analysis of Lateral Wave Propagation in Drill-String for Stability Monitoring". In ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-38597.
Abstract (sommario):
In this paper, the propagation of lateral waves in a drill-string are studied by using a new numerical method and a stability monitoring scheme is proposed. The drill-string is modeled as a linear beam structure under gravitational field effects. An iterative wavelet-based spectral finite element method (WS-FEM) model is developed to obtain a high fidelity response. Numerical simulations of the lateral impact wave propagation at the bottom-hole-assembly (BHA) are conducted and a time-frequency analysis technique is applied to the response in order to identify the relationship between the position of the transition point between positive and negative strain and the dispersive properties of the lateral wave. Based on the results, a new monitoring scheme is proposed to monitor the stability of the drill-string based on a combination of lateral impact wave analysis at the BHA and the axial acoustic telemetry technique.
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Leu, Jessica, e Masayoshi Tomizuka. "Motion Planning for Industrial Mobile Robots With Closed-Loop Stability Enhanced Prediction". In ASME 2019 Dynamic Systems and Control Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/dscc2019-9208.
Abstract (sommario):
Abstract Real-time, safe, and stable motion planning in co-robot systems involving dynamic human robot interaction (HRI) remains challenging due to the time varying nature of the problem. One of the biggest challenges is to guarantee closed-loop stability of the planning algorithm in dynamic environments. Typically, this can be addressed if there exists a perfect predictor that precisely predicts the future motions of the obstacles. Unfortunately, a perfect predictor is not possible to achieve. In HRI environments in this paper, human workers and other robots are the obstacles to the ego robot. We discuss necessary conditions for the closed-loop stability of a planning problem using the framework of model predictive control (MPC). It is concluded that the predictor needs to be able to detect the obstacles’ movement mode change within a time delay allowance and the MPC needs to have a sufficient prediction horizon and a proper cost function. These allow MPC to have an uncertainty tolerance for closed-loop stability, and still avoid collision when the obstacles’ movement is not within the tolerance. Also, the closed-loop performance is investigated using a notion of M-convergence, which guarantees finite local convergence (at least M steps ahead) of the open-loop trajectories toward the closed-loop trajectory. With this notion, we verify the performance of the proposed MPC with stability enhanced prediction through simulations and experiments. With the proposed method, the robot can better deal with dynamic environments and the closed-loop cost is reduced.
Rapporti di organizzazioni sul tema "Enhanced FEM stability simulations":
1
Arduino, Pedro, Long Chen e Christopher McGann. Estimation of Shear Demands on Rock Socketed Drilled Shafts subjected to Lateral Loading. Pacific Earthquake Engineering Research Center, University of California, Berkeley, CA, dicembre 2018. http://dx.doi.org/10.55461/nsos1322.
Abstract (sommario):
This report presents results of an evaluation study on the applicability of current design procedures (based on p-y curves) to the analysis of large-diameter shafts socketed in rock, and the identification of enhanced moment transfer mechanisms not considered in current design methodologies. For this purpose simplified models, and possible three-dimensional (3D) finite-element method (FEM) models are studied to shed some light on the response of drilled shafts socketed in rock. A parametric study using p-y and considering a wide range of rock properties and rock-socket depths, different criteria to define the soil and rock p-y curves, different beam theories, and different interface frictional resistances are presented and compared with 3D FEM simulations. A new element is discussed to account for the shaft toe and underlain rock interaction, which could provide benefit to reduce shear demands when the socket is shallow.
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Heinz, Kevin, Itamar Glazer, Moshe Coll, Amanda Chau e Andrew Chow. Use of multiple biological control agents for control of western flower thrips. United States Department of Agriculture, 2004. http://dx.doi.org/10.32747/2004.7613875.bard.
Abstract (sommario):
The western flower thrips (WFT), Frankliniella occidentalis (Pergande), is a serious widespread pest of vegetable and ornamental crops worldwide. Chemical control for Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) on floriculture or vegetable crops can be difficult because this pest has developed resistance to many insecticides and also tends to hide within flowers, buds, and apical meristems. Predatory bugs, predatory mites, and entomopathogenic nematodes are commercially available in both the US and Israel for control of WFT. Predatory bugs, such as Orius species, can suppress high WFT densities but have limited ability to attack thrips within confined plant parts. Predatory mites can reach more confined habitats than predatory bugs, but kill primarily first-instar larvae of thrips. Entomopathogenic nematodes can directly kill or sterilize most thrips stages, but have limited mobility and are vulnerable to desiccation in certain parts of the crop canopy. However, simultaneous use of two or more agents may provide both effective and cost efficient control of WFT through complimentary predation and/or parasitism. The general goal of our project was to evaluate whether suppression of WFT could be enhanced by inundative or inoculative releases of Orius predators with either predatory mites or entomopathogenic nematodes. Whether pest suppression is best when single or multiple biological control agents are used, is an issue of importance to the practice of biological control. For our investigations in Texas, we used Orius insidiosus(Say), the predatory mite, Amblyseius degeneransBerlese, and the predatory mite, Amblyseius swirskii(Athias-Henriot). In Israel, the research focused on Orius laevigatus (Fieber) and the entomopathogenic nematode, Steinernema felpiae. Our specific objectives were to: (1) quantify the spatial distribution and population growth of WFT and WFT natural enemies on greenhouse roses (Texas) and peppers (Israel), (2) assess interspecific interactions among WFT natural enemies, (3) measure WFT population suppression resulting from single or multiple species releases. Revisions to our project after the first year were: (1) use of A. swirskiiin place of A. degeneransfor the majority of our predatory mite and Orius studies, (2) use of S. felpiaein place of Thripinema nicklewoodi for all of the nematode and Orius studies. We utilized laboratory experiments, greenhouse studies, field trials and mathematical modeling to achieve our objectives. In greenhouse trials, we found that concurrent releases of A.degeneranswith O. insidiosusdid not improve control of F. occidentalis on cut roses over releases of only O. insidiosus. Suppression of WFT by augmentative releases A. swirskiialone was superior to augmentative releases of O. insidiosusalone and similar to concurrent releases of both predator species on cut roses. In laboratory studies, we discovered that O. insidiosusis a generalist predator that ‘switches’ to the most abundant prey and will kill significant numbers of A. swirskiior A. degeneransif WFTbecome relatively less abundant. Our findings indicate that intraguild interactions between Orius and Amblyseius species could hinder suppression of thrips populations and combinations of these natural enemies may not enhance biological control on certain crops. Intraguild interactions between S. felpiaeand O. laevigatus were found to be more complex than those between O. insidiosusand predatory mites. In laboratory studies, we found that S. felpiaecould infect and kill either adult or immature O. laevigatus. Although adult O. laevigatus tended to avoid areas infested by S. felpiaein Petri dish arenas, they did not show preference between healthy WFT and WFT infected with S. felpiaein choice tests. In field cage trials, suppression of WFT on sweet-pepper was similar in treatments with only O. laevigatus or both O. laevigatus and S. felpiae. Distribution and numbers of O. laevigatus on pepper plants also did not differ between cages with or without S. felpiae. Low survivorship of S. felpiaeafter foliar applications to sweet-pepper may explain, in part, the absence of effects in the field trials. Finally, we were interested in how differential predation on different developmental stages of WFT (Orius feeding on WFT nymphs inhabiting foliage and flowers, nematodes that attack prepupae and pupae in the soil) affects community dynamics. To better understand these interactions, we constructed a model based on Lotka-Volterra predator-prey theory and our simulations showed that differential predation, where predators tend to concentrate on one WFT stage contribute to system stability and permanence while predators that tend to mix different WFT stages reduce system stability and permanence.