Search results

The behaviors of sea surface drag coefficient should be well understood for an accurate hurricane prediction. The speed of wind has been applied to characterize the spray production; however, this could result in inaccurate spray productions compared to the experimental or field data if the influence of wave state is not considered. This paper aims to integrate a new sea spray generation function, described by windsea Reynolds number, into the spray momentum flux formula to calculate the spray momentum.

On the basis of this spray momentum, this study proposes the new formulas of spray stress and drag coefficient when the wind speed is high.

Results of the revised formulas show that wave status had significant effects on the spray stress and sea surface drag coefficient. Also, wave age was found to be an important parameter that affects the drag coefficient. The drag coefficient decreased with the increasing wave age. Comparison between this study’s theoretical and observation values of drag coefficient shows that the study results are close to the measured values.

The research findings can enhance the understanding of the behaviors of sea surface drag for an accurate hurricane prediction.

A new sea spray generation function, described by windsea Reynolds number, is integrated into the spray momentum flux formula to calculate the spray momentum. On the basis of this spray momentum, this study proposes the new formulas of spray stress and drag coefficient when the wind speed is high.

Wave breaking significantly affects the exchange process between ocean and atmosphere. This paper aims to simulate the upper ocean dynamics under the influence of wave breaking, which may help to figure out the transport of energy by these breakers.

The authors use a breaker-LES model to simulate the oceanic boundary layer in hurricane conditions, in which breakers become the main source of momentum and energy instead of traditional wind stress.

The mean horizontal velocities and energy increase rapidly with wind speed, reflecting that input from atmosphere dominates the coherent structure in the upper ocean. The penetration ability of a breaker limits its effective depth and thus the total turbulent kinetic energy (TKE) decreases sharply near the surface. Langmuir circulation is the main source of TKE in deeper water. The authors compared the dissipation rate (e) in the simulations with two estimates and found that the model tends to the scaling of ε∼z^–3.4 at extreme wind speeds.

The probability distribution of breakers is also discussed based on the balance between the input from atmosphere and output by wave breaking. The authors considered the contribution of micro-scale breakers and revaluated the probability density function. The results show stability in hurricane conditions.

Vertical take-off is commonly adopted in most insect-mimicking flapping-wing micro air vehicles (FMAV) while insects also adopt horizontal take-off from the ground. The purpose of this paper is to study how insects adjust their attitude in such a short time during horizontal take-off by means of designing and testing an FMAV based on stroke plane modulation.

An FMAV prototype based on stroke plane rotating modulation is built to test the flight performance during horizontal take-off. Dynamic gain and decoupling mixer is added to compensate for the nonlinearity during the rotation angle of the stroke plane getting too large at the beginning of take-off. Force/torque test based on a six-axis sensor validates the change of aerodynamic force and torque at different rotation angles. High-speed camera and motion capture system test the flight performance of horizontal take-off.

Stroke plane modulation can provide a great initial pitch toque for FMAV to realize horizontal take-off. But the large range of rotation angles causes nonlinearity and coupling of roll and yaw. A dynamic gain and a mixer are added in the controller, and the FMAV successfully achieves horizontally taking off in less than 1 s.

The research in this paper shows stroke plane modulation is suitable for insect’s horizontal take-off

Endurance time is an important factor limiting the progress of flapping-wing aircraft. In this study, this paper developed a prototype of a double-wing flapping-wing micro air vehicle (FMAV) that mimics insect-scale flapping wing for flight. Besides, novel methods for optimal selection of motor, wing length and battery to achieve prolonged endurance are proposed. The purpose of this study is increasing the flight time of double-wing FMAV by optimizing the flapping mechanism, wings, power sources, and energy sources.

The 20.4 g FMAV prototype with wingspan of 21.5 cm used an incomplete gear flapping wing mechanism. The motor parameters related to the lift-to-power ratio of the prototype were first identified and analyzed, then theoretical analysis was conducted to analyze the impact of wing length and flapping frequency on the lift-to-power ratio, followed by practical testing to validate the theoretical findings. After that, analysis and testing examined the impact of battery energy density and efficiency on endurance. Finally, the prototype’s endurance duration was calculated and tested.

The incomplete gear facilitated 180° symmetric flapping. The motor torque constant showed a positive correlation with the prototype’s lift-to-power ratio. It was also found that the prototype achieved the best lift-to-power ratio when using 100 mm wings.

A gear-driven flapping mechanism was designed, capable of smoothly achieving 180° symmetric flapping. Besides, factors affecting long-duration flight – motor, wings and battery – were identified and a theoretical flight duration analysis method was developed. The experimental result proves that the FMAV could achieve the longest hovering time of 705 s, outperforming other existing research on double-wing FMAV for improving endurance.

The purpose of the study is to quickly identify significant heterogeneity of surrounding rock of tunnel face that generally occurs during the construction of large-section rock tunnels of high-speed railways.

Relying on the support vector machine (SVM)-based classification model, the nominal classification of blastholes and nominal zoning and classification terms were used to demonstrate the heterogeneity identification method for the surrounding rock of tunnel face, and the identification calculation was carried out for the five test tunnels. Then, the suggestions for local optimization of the support structures of large-section rock tunnels were put forward.

The results show that compared with the two classification models based on neural networks, the SVM-based classification model has a higher classification accuracy when the sample size is small, and the average accuracy can reach 87.9%. After the samples are replaced, the SVM-based classification model can still reach the same accuracy, whose generalization ability is stronger.

By applying the identification method described in this paper, the significant heterogeneity characteristics of the surrounding rock in the process of two times of blasting were identified, and the identification results are basically consistent with the actual situation of the tunnel face at the end of blasting, and can provide a basis for local optimization of support parameters.

Due to greater returns to high skill and desirable amenities, high-skilled workers are increasingly agglomerating in metropolitan areas and form path dependence. This chapter explores whether the land supply policy of China constraining big cities' urban construction land quota strengthens the spatial divergence of human capital. Using city-level land supply data, population census data, and land transaction micro data, we find that the higher the degree of a city's land supply lagging behind land demand, the greater the enlargement effect of the initial share of population with college degrees on the increase in share of population with college degrees. Further research reveals that the main mechanism causing this phenomenon is the rapidly rising housing prices hindering low-skill labor flows to big cities.

This paper aims to provide an elucidative and explanatory overview of decision-making theory that human resource management and development (HR) researchers and practitioners can use to explore the impact of heuristics and biases on organizational decisions, particularly within HR contexts.

This paper draws upon three theoretical resources anchored in decision-making research: the theory of bounded rationality, the heuristics and biases program, and cognitive-experiential self-theory (CEST). A selective narrative review approach was adopted to identify, translate, and contextualize research findings that provide immense applicability, connection, and significance to the field and study of HR.

The authors extract key insights from the theoretical resources surveyed and illustrate the linkages between HR and decision-making research, presenting a theoretical framework to guide future research endeavors.

Decades of decision-making research have been distilled into a digestible and accessible framework that offers both theoretical and practical implications.

Heuristics are mental shortcuts that facilitate quick decisions by simplifying complexity and reducing effort needed to solve problems. Heuristic strategies can yield favorable outcomes, especially amid time and information constraints. However, heuristics can also introduce systematic judgment errors known as biases. Biases are pervasive within organizational settings and can lead to disastrous decisions. This paper provides HR scholars and professionals with a balanced, nuanced, and integrative framework to better understand heuristics and biases and explore their organizational impact. To that end, a forward-looking and direction-setting research agenda is presented.

In a rapidly shifting market, organizations seek more diverse and innovative employee development interventions. Yet, these initiatives may have limited impact without employees’ engagement. This conceptual paper aims to propose self-leadership as a value-added strategy for promoting both individual and organizational development.

The authors conducted a conceptual analysis with three case examples. The cases were purposefully selected, aiming to comprehend how the concept of self-leadership has been applied within organizations and to identify real-life examples where self-leadership has been adopted as an organizational strategy.

This study demonstrates that self-leadership plays a significant role in facilitating human resource development (HRD) initiatives. Specifically, the authors illustrate how self-leadership interventions in companies empower individuals to take charge of their development, aligning personal and organizational goals. When effectively applied, self-leadership strategies positively impact HRD practices in the areas of training and development, organization development and career development, yielding benefits for both employees and employers.

This study addresses knowledge gaps in the emerging field of self-leadership in HRD by providing three companies’ examples of how self-leadership can add value to HRD. The findings offer unique insights into the synergy between self-leadership and HRD, benefiting academics interested in this line of inquiry and HRD practitioners seeking innovative approaches to employee and organizational development.

Land use changes significantly impacts ecosystem services and functions. The estimation of ecosystem services value is conducive to clarifying the ecological changes in response to LULC changes due to urbanization. Chengde was the upper water source of Beijing and Tianjin, the ecosystem is very fragile. After a series of ecology conservation projects like "returning cropland to forestry", the ecosystem service value increased from 5100.17 x 10⁷ Yuan in 1990 to 5104.08 x 10⁷ Yuan in 2008 respectively, with the average increase of 2.3 x 10⁶ Yuan per year. It is indicated that ecosystem service value has the potential to inform policy decisions by emphasizing the benefits of sustainable ecosystem management. So plans on land use management should be made to maintain a balance between urbanization and ecosystem health.

This study aims to explore the phenomenon of training engagement from the trainers’ perspective. Specifically, two questions guided this inquiry. First, how do trainers define engagement in the training context? and What strategies do trainers use to engage trainees?

The collective case study approach was adopted for this qualitative study. Seven cases were selected for in-depth analyses. Data were collected through individual, face-to-face interviews and analyzed using the constant comparative analysis method.

Major findings suggest that engaging training practices take various forms. They include being trainee-centered, maximizing learning through entertaining and interesting instruction, accommodating different learning styles, eliciting trainee participation by creating an encouraging learning environment and connecting with trainees by building rapport early in a training session.

The small sample limits the generalizability of the findings. However, this study expands training literature by focusing on an under-explored research area, the role of engaging trainees in maximizing learning outcomes.

For trainers, this study offered some specific strategies they can use to engage learners in the training context to achieve desired learning outcomes. In addition, the seven cases selected for this study may be used as a benchmark against which both experienced and novice trainers compared their own practices.

This is one of very few qualitative studies with a focus on emotional aspects involved in training. The rich data from this study shed light on areas for future improvement, particularly regarding how to effectively engage trainees to maximize learning outcomes.