Search results

The purpose of this paper is to investigate the dynamic stability of liquid hydrogen turbopump rotor system in rocket engine under the effects of seal and internal rotor damping.

The dynamic modeling of a liquid hydrogen turbopump rotor system in rocket engine is presented in this paper with the aid of the finite element technique. The mathematical model takes into account the seal hydrodynamic forces described by Muszynska model and the internal rotor damping, viscous damping, and hysteretic damping. The shooting method and Floquet theory are employed to investigate the effects of seal and internal rotor damping on the nonlinear dynamic stability of two turbopump designs, the original and the modified design with a flexible bearing support.

The numerical results, which are in good agreement with test data, show that the destabilizing effect of internal rotor damping play a key role in the original design. In the modified design, the stability margins are enhanced and the vibration response levels are minimized. The onset speed of instability increases in original design and decreases in modified design as the effects of seal nonlinearities are considered. The predicted results indicate that the seals have a great destabilizing effect in the modified design and the turbine end bearing is the most dangerous hardware in both designs. The system stability analysis shows that the effect of seal length on the system stability is significant comparing with that of seal radius.

The results can be used in the design and operation of a liquid hydrogen turbopump rotor system to improve its stability performance and eliminate its subsynchronous problem.

Since seal and internal damping are two key destabilizing factors in liquid hydrogen turbopumps and the seal nonlinearities are inevitable, the use of nonlinear theory to study their effects on nonlinear stability and dynamic performance can lead to accurate prediction and explain the nature of the subsynchronous motion.

This research explores the influence of authoritarian leadership on employee creativity as mediated by employee creative self-efficacy, moderated by benevolent leadership and power distance.

A survey sample of 325 employees was collected from Chinese companies in different industries. The hypotheses were tested adopting a hierarchical regression and a bootstrapping test.

Employee creative self-efficacy partially mediated the association between authoritarian leadership and employee creativity. The negative impacts of authoritarian leadership on employee creative self-efficacy can be moderated by benevolent leadership. Additionally, the moderation effects of benevolent leadership can be moderated by power distance, which means that these moderation effects of benevolent leadership are significant only in subordinates with low levels of power distance.

An organization should be conscious of the perniciousness of an authoritarian leader and is better for leaders not to show contradictory behaviors to employees. Moreover, when leaders exhibit inconsistent behaviors, they should be sensitive to employee power distance.

Previous studies have been done to explore the predictors of employee creativity. Yet, studies for the impacts of destructive leadership styles on employee creativity are lacking. This study introduces employee creative self-efficacy as a mediator of the relationship between authoritarian leadership and employee creativity. In addition, benevolent leadership and power distance are identified as two boundary conditions to explore the impacts of authoritarian leadership.

This paper aims to investigate the high-temperature mechanical properties of HS110S steel and its corrosion behaviors in harsh downhole environment.

In this work, mechanical property measurements were carried out from 25°C to 350°C and the scanning electron microscopy was used to observe the fracture morphology. The weight-loss measurements and surface characterization were used to evaluate the corrosion resistance of HS110S steel in harsh downhole environment.

Results show that the yield strength and tensile strength of HS110S steel at 350 °C are 779 and 861 MPa, respectively. Compared with room temperature, the reduction rate values are both less than 20%. At the high-temperature corrosion environment (350 °C), the static and dynamic corrosion rates are 0.9668 and 1.9236 mm/a, respectively. The generated corrosion products are mainly composed of FeSx, FeCO₃ and Fe₃O₄. Therefore, the HS110S steel applied under such conditions needs to take suitable protective measures.

In general, the HS110 steel has widely used in conventional development conditions (e.g. low H₂S or high CO₂ environments). However, to the best of the authors’ knowledge, no studies have reported on its application at more than 250°C. Therefore, this work can be a reference to the application of HS110S steel in high-temperature corrosion conditions.

System dynamics is a whole-system modelling and learning approach, useful for tackling non-linear problems, such as sustainable urban development. The purpose of this paper is to review system dynamics applications in the simulation of sustainable urban development over a period from 2005 to 2017.

The analysis reveals that the number of applications of system dynamics modelling in the area of urban sustainable development increased in the analysed period. Research has changed its focus from the modelling of environmental problems to more complex models, portraying the multidimensional socio-economic processes that have an impact on the sustainability of urban development. Analysed case studies most often use the behaviour reproduction test for model validation, but without a unified approach. In most cases, modelling has been done in China, Germany and the USA, while urban development in the Eastern European countries, Africa and Latin America has not often been investigated. This paper indicates the knowledge gaps and suggests future research directions.

Papers that report the use of system dynamics modelling reveal a wide range of applications in urban sustainability. The analysis shows significant emphasis on environmental problems, while the interest for modelling social problems has been increasing during the last several years. Most of the modelled problems examine the sustainability of resources (land, water) and waste management, which are used for insights into the reasons for the system behaviour, forecasting future behaviour and policy testing.

The presented models were developed in most cases for the purpose of understanding the phenomena examined, as well as the future use of the models in policy planning. This brings us back to the need for greater stakeholder involvement, not only in the initial phase, but also during the whole modelling process, which could increase understanding, use and ownership of the models in the future, and thus increase their practical application.

The above quotations highlight the adverse consequences of corruption in many countries around the world today. Indeed, the research taboo on corruption, which Gunnar Myrdal identified in 1968, no longer exists, and the silence on the “C” word (corruption) in the World Bank was broken by James Wolfensohn in his famous October 1996 speech, which focused on the negative consequences of the “cancer of corruption” on the World Bank's aid programs.

With the analysis of the causes of corruption, this study aims to investigate specific anti-corruption measures that can be implemented to reform the political system and the social climate of China.

This study examines 97 severe corruption cases of high-ranking officials in China, which occurred between 2012 and 2015. As this insinuates that both institutional and social corruption are major problems in China, the analysis delves into multiple facts of corruption, including different types, four primary underlying causes, and suggestions regarding the implementation of three significant governmental shifts that focus on investigation, prevention tactics and legal regulations.

China’s corruption is not only individual-based but also it has developed into institutional corruption and social corruption. Besides human nature and instinct, the causes of corruption can be organised into four categories, namely, social customs, social transitions, institutional designs and institutional operations. For the removed high-ranking officials, the formation of interest chains was an important underlying cause behind their corruption.

This study makes a significant contribution to the literature because this study provides a well-rounded approach to a complex issue by highlighting the significance of democracy and the rule of law as ways to regulate human behaviour to combat future corruption.

It is shown in natural gas proportion mixing experiments that a mixed-source natural gas is the physical combination of end member gas. Both the carbon and hydrogen isotopes in the mixed-source natural gas can be expressed by the weighted average of corresponding components content and isotopes of end member gas. Under certain geological setting, the selection of end member gas is the key to mixed-source ratio calculation. Then, it's better to estimate the mixed-source ratio with δ¹³C₁ and component data according to the weighted average calculation formula. The analysis on natural gas geochemistry characteristics show that the natural gas extracted from Jingbian Gas Field in the Ordos Basin is mainly an upper Paleozoic coal-derived gas. In the analysis of geological conditions for reservoir forming and characteristics of natural gas, natural gas from Longtan 1 Well and Tao 6 Well were selected as the end member gases of lower Paleozoic oil-type gas and upper Paleozoic coal-type gas respectively to calculate the mixed-source ratio of natural gas in Jingbian Gas Field. The ratio of upper Paleozoic coal-derived gas mostly accounts for over 70% and its average ratio reaches 81%. Therefore, the exploration of natural gas of Ordos Basin should be focused on the upper palaeozoic coal source rock, and attention should be paid to the matching of coal source rock in the exploration of weathered crust gas deposit.

Four decades ago, the Swedish economist, Gunnar Myrdal (1970, p. 230) attributed the paucity of research on corruption in South Asia to the research taboo on this topic. Fortunately, this taboo has been gradually eroded since the 1990s as reflected in the tremendous amount of research that has been done on corruption in the Asia-Pacific countries. Corruption has emerged in the 1990s as “a truly global political issue eliciting a global political response” (Glynn, Kobrin, & Naim, 1997, p. 7). Indeed, the globalization of corruption has given rise to an overriding concern with how to combat corruption in many countries among their governments and many international agencies. Consequently, many international organizations like the Asian Development Bank, Commonwealth Association for Public Administration and Management, Eastern Regional Organization for Public Administration, International Institute for Administrative Sciences, Organization of American States, Organization for Economic Co-operation and Development, Transparency International, United Nations Development Programme, World Bank, and World Economic Forum have organized numerous conferences, symposia and workshops on various aspects of corruption.

This paper aims to discuss opportunities for pairing the carbon dioxide (CO₂) points of supply from stationary sources such as power plants, steel and cement production, coal to liquid plants and refineries, with potential oil reservoirs in China.

This study builds a linear optimization model to analyze the tradeoffs in developing CO₂-enhance oil recovery (EOR) projects in China for a range of policy options to match points of supply with the points of demand (oil fields). The model works on optimizing CO₂ application costs by meeting four principal components; CO₂ storage, CO₂ capture, transport costs and additional oil recovery.

This study reveals new opportunities and economic sources to feed CO₂-EOR applications and offers reasonable options to supply CO₂ for potential points of demand. Furthermore, power plants and coal to liquid industries had the most significant and economic contributions to potential CO₂-EOR projects in China. Total annual emission reduction is expected to be 10% (based on 10 Gton annual emissions). The emission reductions and potential CO₂ storage from the different industries as follow; 94% from power plants, 4% from biofuel and 2% from coal to liquid plants.

Carbon capture and storage (CCS) is one practice aiming to reduce the amounts of anthropogenic emissions of carbon dioxide emitted into the atmosphere and reduce the related social costs. However, given the relatively high cost associated with this practice, coupling it with EOR could offer a significant financial incentive to facilitate the development of CCS projects and meet climate change objectives.

The model used in this study can be straightforwardly adapted to any geographic location where industry and policymakers are looking to simultaneously reduce CO₂ emissions while increasing hydrocarbon recovery. The model is highly adaptable to local values in the parameters considered and to include additional local considerations such as geographic variation in capture costs, taxes and premiums to be placed on CO₂ capture in so-called “non-attainment zones” where pollution capture make could make a project politically and economically viable. Regardless of how and where this model is applied, it is apparent that CO₂ from industrial sources has substantial potential value as a coproduct that offsets its sequestration costs using existing, commercially available CO₂-EOR technology, once sources and sinks are optimally paired.