Usually solid fins are used in industrial heating as well as cooling systems. Installing porous fins in heat exchangers and process cooling equipments like chillers can significantly improve the heat transfer ability of the equipments. This happens due to the increase in effective thermal conductivity as a result of the increase in surface area for convection through pores. The theory of porous media was primarily introduced by Kiwan.1 An approximate solution was given by Vafai and Thiyagaraja2 on porous and fluid zone interface for the velocity and temperature distributions. An exact solution of the same problem was carried out by Vafai and Kim.3 Kiwan and Zeitoun4 studied natural convection in a horizontal cylindrical annulus using porous fins where they used energy equation and Darcy model to formulate the governing equation. Cuce and Cuce5 used this model to analyse the efficiency and effectiveness of longitudinal porous fin. High thermal conductivity porous fins and smaller Darcy numbers can enhance heat transfer rate as reported by Hamdan and Al-Nimr.6 On the other hand, effect of various parameters like Rayleigh number (Ra), Darcy number (Da) and thermal conductivity ratio was investigated by Kundu et al.7 It was noticed that thermal performance of porous fin increased at higher Ra and Da up to a limited conductivity ratio. Similar conclusion was given by Kiwan8 when analysing the thermo-physical properties of porous fin for three different types. It was also found that the heat transfer rate from porous fin can be higher than that of a solid fin.

Usually solid fins are used in industrial heating as well as cooling systems. Installing porous fins in heat exchangers and process cooling equipments like chillers can significantly improve the heat transfer ability of the equipments. This happens due to the increase in effective thermal conductivity as a result of the increase in surface area for convection through pores. The theory of porous media was primarily introduced by Kiwan.1 An approximate solution was given by Vafai and Thiyagaraja2 on porous and fluid zone interface for the velocity and temperature distributions. An exact solution of the same problem was carried out by Vafai and Kim.3 Kiwan and Zeitoun4 studied natural convection in a horizontal cylindrical annulus using porous fins where they used energy equation and Darcy model to formulate the governing equation. Cuce and Cuce5 used this model to analyse the efficiency and effectiveness of longitudinal porous fin. High thermal conductivity porous fins and smaller Darcy numbers can enhance heat transfer rate as reported by Hamdan and Al-Nimr.6 On the other hand, effect of various parameters like Rayleigh number (Ra), Darcy number (Da) and thermal conductivity ratio was investigated by Kundu et al.7 It was noticed that thermal performance of porous fin increased at higher Ra and Da up to a limited conductivity ratio. Similar conclusion was given by Kiwan8 when analysing the thermo-physical properties of porous fin for three different types. It was also found that the heat transfer rate from porous fin can be higher than that of a solid fin.

As the core component of screw compressors, the rotor profile projected by a screw rotor on the rotor's end face is one of the most important parts of twin-screw compressors to study. The performance of the designed rotor profile directly affects the efficiency, accuracy, and service life of twin-screw compressors. The key to design and machine the rotors is to efficiently and highly accurately overcome problems in the mutual solution of male and female rotors. As for the design of the rotor profile, according to the principle of gear meshing, the meshing of any graph conforms to the Willis principle,1 that is, at any moment during the transmission, the common normal at the contact point must pass through the instantaneous center point of this moment. Litvin2 applied the principle of gear meshing to calculate the profiles of meshing components such as the screw rotor and gear. Since the screw rotor can be regarded as a special helical gear, the principle of gear meshing discussed by Litvin2 became part of the basic theory of the design of the rotor profile. In the nearly half century since the screw compressor was invented, there have been many excellent patents regarding the rotor profile. According to Chen,3 Robert,4 and Yoshimura,5 these successful patents were all generated by the classic envelope method. Stosic et al.6 proposed a method to generate the rotor profile using the meshing line equation of male and female rotors of the twin-screw compressor based on the conjugate principle. According to the conjugate principle, this method determined the corresponding rotor profile based on the distance between the rotor axes, the number of teeth, and the given meshing line equation. Stosic,7 Zaytsev and Ferreira,8 and Fong et al.9 designed the male and female rotor profiles through the defined rack profile and a meshing line equation that can be optimally controlled.10–13

As the core component of screw compressors, the rotor profile projected by a screw rotor on the rotor's end face is one of the most important parts of twin-screw compressors to study. The performance of the designed rotor profile directly affects the efficiency, accuracy, and service life of twin-screw compressors. The key to design and machine the rotors is to efficiently and highly accurately overcome problems in the mutual solution of male and female rotors. As for the design of the rotor profile, according to the principle of gear meshing, the meshing of any graph conforms to the Willis principle,1 that is, at any moment during the transmission, the common normal at the contact point must pass through the instantaneous center point of this moment. Litvin2 applied the principle of gear meshing to calculate the profiles of meshing components such as the screw rotor and gear. Since the screw rotor can be regarded as a special helical gear, the principle of gear meshing discussed by Litvin2 became part of the basic theory of the design of the rotor profile. In the nearly half century since the screw compressor was invented, there have been many excellent patents regarding the rotor profile. According to Chen,3 Robert,4 and Yoshimura,5 these successful patents were all generated by the classic envelope method. Stosic et al.6 proposed a method to generate the rotor profile using the meshing line equation of male and female rotors of the twin-screw compressor based on the conjugate principle. According to the conjugate principle, this method determined the corresponding rotor profile based on the distance between the rotor axes, the number of teeth, and the given meshing line equation. Stosic,7 Zaytsev and Ferreira,8 and Fong et al.9 designed the male and female rotor profiles through the defined rack profile and a meshing line equation that can be optimally controlled.10–13

The complexity and importance of an efficient maintenance strategy is widely recognized in today's competitive market. Industrial organizations are continuously seeking new maintenance strategies to improve the effectiveness of their operations.1 Maintenance has evolved over time as advancement in technology and fast growing research has been put into building more efficient and reliable systems.2

The complexity and importance of an efficient maintenance strategy is widely recognized in today's competitive market. Industrial organizations are continuously seeking new maintenance strategies to improve the effectiveness of their operations.1 Maintenance has evolved over time as advancement in technology and fast growing research has been put into building more efficient and reliable systems.2

In construction and mining equipment that are subjected to large variation in load, the valve controlled hydro-motor drives are commonly used. The said drive is usually in open-loop configuration where by controlling the valve, the variable flow is supplied to the actuator to regulate its rotational speed. The performance of such valve is almost same as that of the servo-valve; however, it is less expensive and high responsiveness.

In construction and mining equipment that are subjected to large variation in load, the valve controlled hydro-motor drives are commonly used. The said drive is usually in open-loop configuration where by controlling the valve, the variable flow is supplied to the actuator to regulate its rotational speed. The performance of such valve is almost same as that of the servo-valve; however, it is less expensive and high responsiveness.

Claw couplings generally connect two axes and facilitate torque transmission using gear teeth, and are available with a variety of gear teeth shapes. Among these, Curvic couplings are widely used in heavy-duty gas turbines and the aeroengine industry because of the special shape of their teeth and attributes such as reliable positioning, precise centering, excellent structural stability, strong load bearing ability, and adequate strength, vibration, and fatigue life.1 Because the contact stiffness of these joint surfaces greatly affects the static and dynamic characteristics of mechanical systems, it is necessary to predict dynamic characteristics accurately and secure stability in the rotor system rotating at high speed where Curvic couplings are primarily applied. For this prediction, contact and bending stiffness must be evaluated, which are closely related to the contact surface roughness.

Claw couplings generally connect two axes and facilitate torque transmission using gear teeth, and are available with a variety of gear teeth shapes. Among these, Curvic couplings are widely used in heavy-duty gas turbines and the aeroengine industry because of the special shape of their teeth and attributes such as reliable positioning, precise centering, excellent structural stability, strong load bearing ability, and adequate strength, vibration, and fatigue life.1 Because the contact stiffness of these joint surfaces greatly affects the static and dynamic characteristics of mechanical systems, it is necessary to predict dynamic characteristics accurately and secure stability in the rotor system rotating at high speed where Curvic couplings are primarily applied. For this prediction, contact and bending stiffness must be evaluated, which are closely related to the contact surface roughness.

With the increasing number of global automobiles, energy crisis and environmental pollution have become the bottleneck issues restricting the development of global automobile industry. The “Made in China 2025” plan clearly points out that “new energy vehicle” – the automobile with electric propulsion link – is one of the 10 key development industries in the future. Therefore, the research and development of clean hybrid vehicle with low-energy consumption has aroused wide concern by various countries in the world. TOYOTA creatively proposed in the first generation of the PRIUS the use of the THS power shunt system (PSS) in achieving hybrid and electronic continuously variable functions, and has insisted on upgrading. At present, the research of power shunt hybrid systems in foreign countries mainly focuses on single-system THS represented by PRIUS series and dual-system AHS represented by general Allison,1,2 but both of them cannot adapt to the switching of modes under different cycle conditions. Research on power shunt hybrid systems in major domestic universities is mainly focused on structure design. For example, Lee et al.3 conducted an in-depth study on the parameter matching and optimization of power shunt hybrid vehicles. Santucci et al.4 studied the parameter optimization of the input shunt hybrid vehicle. Kim et al.5 proposed a single-mode PSS configuration that uses the double-row planetary gear structure. Most of these studies were simply based on empirical formulae for parameter design and have not proposed any systematic parameter optimization methods.

With the increasing number of global automobiles, energy crisis and environmental pollution have become the bottleneck issues restricting the development of global automobile industry. The “Made in China 2025” plan clearly points out that “new energy vehicle” – the automobile with electric propulsion link – is one of the 10 key development industries in the future. Therefore, the research and development of clean hybrid vehicle with low-energy consumption has aroused wide concern by various countries in the world. TOYOTA creatively proposed in the first generation of the PRIUS the use of the THS power shunt system (PSS) in achieving hybrid and electronic continuously variable functions, and has insisted on upgrading. At present, the research of power shunt hybrid systems in foreign countries mainly focuses on single-system THS represented by PRIUS series and dual-system AHS represented by general Allison,1,2 but both of them cannot adapt to the switching of modes under different cycle conditions. Research on power shunt hybrid systems in major domestic universities is mainly focused on structure design. For example, Lee et al.3 conducted an in-depth study on the parameter matching and optimization of power shunt hybrid vehicles. Santucci et al.4 studied the parameter optimization of the input shunt hybrid vehicle. Kim et al.5 proposed a single-mode PSS configuration that uses the double-row planetary gear structure. Most of these studies were simply based on empirical formulae for parameter design and have not proposed any systematic parameter optimization methods.

Reciprocating compressors are widely used in the fields of petrochemistry and metallurgy. The design scheme for the compressor system must meet the demands of the highest operational power and flow; however, most of the actual operational states of the compressor are lower than the design state. Therefore, a stepless capacity method that functions through delayed closure of the suction valve has been proposed in engineering. The suction valve unloader can not only provide stepless changes in flow but can also save energy. Thus, it plays an important role in the industries under the global energy scarcity. However, this method can cause serious vibration and noise in practical applications.1

Reciprocating compressors are widely used in the fields of petrochemistry and metallurgy. The design scheme for the compressor system must meet the demands of the highest operational power and flow; however, most of the actual operational states of the compressor are lower than the design state. Therefore, a stepless capacity method that functions through delayed closure of the suction valve has been proposed in engineering. The suction valve unloader can not only provide stepless changes in flow but can also save energy. Thus, it plays an important role in the industries under the global energy scarcity. However, this method can cause serious vibration and noise in practical applications.1

Microfluidics technology has been applied to different chemical and biological applications of lab-on-a-chip (LOC) devices including medical diagnostics, drug development etc. A LOC device needs to be compact, miniatured requiring a small concentration of reagents for analysis. Microfluidic devices range from ten to several hundred micrometers in characteristic dimension. These devices are formed by the integration of micropumps, microvalves, micromixer, micro-separator and micro-reactors.1 In most processes there is need of two or more fluids mixing for example blood solution with the biomarkers that are immersed in a buffer solution. Therefore, micromixer is an essential component of the LOC. Due to very wide range of micromixers applications in chemical reactions, dispersions, and emulsification, it is important for the mixer to have superior mixing efficiency. The difficulty in achieving sufficient mixing in a microfluidic device results from laminar flows that can be explained by low Reynolds number; sometimes its value is less than 1.2,3 The flow is laminar and there is lack of turbulence which makes molecular diffusion the primary mechanism for mixing. High mixing efficiency cannot be achieved with the help of only diffusion. During the process of mixing by diffusion, low molecular weight molecules mix in a shorter duration whereas, molecules with high molecular weights such as nucleic acids, proteins not only require a greater length of microchannel but also more time duration (minutes to hours) to ensure complete mixing.4 Thus mixing of fluids in these devices at low Reynolds number is a challenge because of very short channels or chamber for fluid flow and controlled time for mixing process to take place. Mixing performance can be enhanced with the help of designs structure modification or applying some external force.5

Microfluidics technology has been applied to different chemical and biological applications of lab-on-a-chip (LOC) devices including medical diagnostics, drug development etc. A LOC device needs to be compact, miniatured requiring a small concentration of reagents for analysis. Microfluidic devices range from ten to several hundred micrometers in characteristic dimension. These devices are formed by the integration of micropumps, microvalves, micromixer, micro-separator and micro-reactors.1 In most processes there is need of two or more fluids mixing for example blood solution with the biomarkers that are immersed in a buffer solution. Therefore, micromixer is an essential component of the LOC. Due to very wide range of micromixers applications in chemical reactions, dispersions, and emulsification, it is important for the mixer to have superior mixing efficiency. The difficulty in achieving sufficient mixing in a microfluidic device results from laminar flows that can be explained by low Reynolds number; sometimes its value is less than 1.2,3 The flow is laminar and there is lack of turbulence which makes molecular diffusion the primary mechanism for mixing. High mixing efficiency cannot be achieved with the help of only diffusion. During the process of mixing by diffusion, low molecular weight molecules mix in a shorter duration whereas, molecules with high molecular weights such as nucleic acids, proteins not only require a greater length of microchannel but also more time duration (minutes to hours) to ensure complete mixing.4 Thus mixing of fluids in these devices at low Reynolds number is a challenge because of very short channels or chamber for fluid flow and controlled time for mixing process to take place. Mixing performance can be enhanced with the help of designs structure modification or applying some external force.5

Electronic devices have become a crucial part of our life. From huge prime movers to small gadgets, everything is electronically driven. The trend from quite some time has been on the miniaturization of these devices and the increase of their power density. Along with that, we also have to keep their temperature below some critical value or else they would become inefficient and unreliable. Fluctuating temperature values, the presence of hotspots, etc. will cause thermal stresses and hence, shorten their life and may even lead to a sudden failure.1 Due to the rapid development of technology and the miniaturization of electronic devices, various traditional cooling technologies are unable to meet their required cooling effect. Thermal management of these electronic devices plays a major role in their effective working. For the thermal management of these electronic devices, an innovative cooling technology i.e. microchannel heat sink cooling technology was first proposed and developed by Tuckerman and Pease2 in 1981. To overcome this difficulty, several other cooling technologies were suggested.3,4 Among those, liquid cooling technology5,6 has major benefits with respect to other technologies. One of these is its high heat transfer rate. Hassan et al.7 reviewed the heat transfer and fluid flow characteristics in single and two-phase flows in microchannels. They noticed that water was used as a working fluid in most of the studies. It is due to its high thermal conductivity and is compatible with most of the channel materials. Jang et al.8 numerically compared the working performances of liquid cooling technologies and air cooling technologies which adopted to cool the three-dimensional multicore processor. They observed that liquid cooling technologies decrease its temperature by 45 ℃.

Electronic devices have become a crucial part of our life. From huge prime movers to small gadgets, everything is electronically driven. The trend from quite some time has been on the miniaturization of these devices and the increase of their power density. Along with that, we also have to keep their temperature below some critical value or else they would become inefficient and unreliable. Fluctuating temperature values, the presence of hotspots, etc. will cause thermal stresses and hence, shorten their life and may even lead to a sudden failure.1 Due to the rapid development of technology and the miniaturization of electronic devices, various traditional cooling technologies are unable to meet their required cooling effect. Thermal management of these electronic devices plays a major role in their effective working. For the thermal management of these electronic devices, an innovative cooling technology i.e. microchannel heat sink cooling technology was first proposed and developed by Tuckerman and Pease2 in 1981. To overcome this difficulty, several other cooling technologies were suggested.3,4 Among those, liquid cooling technology5,6 has major benefits with respect to other technologies. One of these is its high heat transfer rate. Hassan et al.7 reviewed the heat transfer and fluid flow characteristics in single and two-phase flows in microchannels. They noticed that water was used as a working fluid in most of the studies. It is due to its high thermal conductivity and is compatible with most of the channel materials. Jang et al.8 numerically compared the working performances of liquid cooling technologies and air cooling technologies which adopted to cool the three-dimensional multicore processor. They observed that liquid cooling technologies decrease its temperature by 45 ℃.

The first issue of the Journal of Mechanical Engineering Science (JMES) was published in June 1959 to provide a forum for specialised and scientific contributions in mechanical engineering. The development of the journal over its first 50 years was described in an editorial by Professor Duncan Dowson in 2009. In January 2019, I introduced our 60th anniversary with an editorial describing more recent developments of the JMES. To further mark the 60th anniversary, the present editorial board have organised this special edition. The authors of the papers included are either editorial board members or have been invited by the board. The intention is to illustrate some recent and current areas of international research, giving an opportunity to reflect on developments in these areas and on the discipline of Mechanical Engineering Science as a whole.

The growing demand for higher power generation brings the request for increased reliability and efficiency of turbines. The last stage blades in the low-pressure steam turbine parts (LP) are, from this point of view, a key element of the turbine design defining the overall power, dimensions and design of the machine. Therefore, longer and bigger blades are designed.1 However, these large blades are concurrently subject to strong dynamic loads. Therefore, crack detection and inspection is regularly performed during turbine overhauls. However, each outage and opening of the low-pressure part is associated with increased costs, often with an extension of the planned shutdown harmonogram and operators logically try to avoid it. The systems installed for the purpose of long-term monitoring of the rotating blades during operation can assist in deciding whether a blade inspection is necessary. These systems allow to monitor the vibratory behavior of the blades during turbine operation and to detect operation with blade excessive strain.

Gas turbine bladed disks are subjected to high levels of periodic excitation, which can lead to resonant vibration of blades within the operating range, resulting in large stresses that may cause high cycle fatigue (HCF).1 To accurately predict the vibration amplitude, and therefore the fatigue life of the components, the damping effect of friction forces at contact interfaces such as blade roots, shrouds, flanges, and friction dampers2 must be taken into account.3

Stochastic resonance is the nonmonotonic response of a system to stochastic excitation. Although this phenomenon is well known in signal processing technology, it is often perceived as paradoxical, because it contradicts the intuition that has been developed by the analysis of conventional linear systems where the ratio of the output signal-to-noise is the maximum in the absence of noise. Numerous manifestations and applications of stochastic resonance are known in physics, biology, medicine, mechanics and other fields.1–21 For the first time, this phenomenon was mentioned by Benzi et al.13–15 for the description of cyclically recurring glacial periods. In the 1980s, this phenomenon was considered as applicable to bistable systems with a periodic input signal and random noise. Later, it was discussed and used when studying a wider class of systems.16–21

Superharmonic resonances of the periodic vibrations are observed in many nonlinear dynamical systems. The multiple scales method is used to analyze the superharmonic forced vibrations of nonlinear systems in asymptotic limit.1 The superharmonic resonances of the circular plate forced vibrations are analyzed by Srirangarajan.2 The longitudinal-transverse superharmonic shaft vibrations are described by the system of the ordinary differential equations with small parameter in Zou et al.3 The multiple scales method is used to analyze these resonance vibrations. The effect of the non-linear magnetic forces on the non-linear response of the shaft is examined for the case of the superharmonic resonance by multiple scales method in Ji and Leung.4 It is shown that the periodic superharmonic motions undergo the saddle-node and the Hopf bifurcations. The third-order superharmonic resonance in the harmonically excited Duffing oscillator is analyzed by Hassan.5 The recurrent bifurcation behavior of the superharmonic vibrations is treated in Parlitz and Lauterborn and Parlitz.6,7

The analysis of the propagation of waves in structures is a fundamental task in many engineering applications. The knowledge of dispersion relations, providing information on the type and nature of propagating waves is of interest for the prediction of forced response, acoustic radiation, nondestructive testing, and transmission of structure-borne sound. All these themes are nowadays the subject of many studies in order to improve the vibro-acoustic comfort of passenger carries, bridges, pipelines, and space vehicles.

Free cutting steels, which are commonly used in many mass production fields, such as the automotive industry and household appliances, contain sulfur, lead, and some other elements, which promote machinability. For this reason, this class of materials is widely used in lock industries, which are characterized by very large production batches in order to cut production costs. It must be observed that, in some cases, free-cutting steel components must withstand remarkably high fatigue loads, even in harsh environment. For example, as indicated by Standard,1 the lock shall be mounted in a fixture being similar to a door application. Afterwards, it is sprayed by neutral salt for a defined duration: in this particular condition, it is required to comply with some standard requirements and to pass specific tests to ensure its ability to operate after environmental exposure. To achieve acceptable material properties, thus improving wear resistance, even in harsh environments, considering as well cost issues, the widespread procedure in the lock industries is to use electrodeposited coatings over free-cutting steel materials. This is a very serious issue, as the failure of the locking devices may arise both from too high wear, which is no longer compliant with the standard requirement, and from fatigue damage. In particular, some authors indicate that coatings may have a detrimental effect on the fatigue strength of the materials.2–6 Therefore, it is important to clarify this point, depending on the involved materials and coatings, and, in case, to search a compromise. For these reasons, some free-cutting steels have been investigated in the last years.7–13 However, a literature survey still indicates a lack of knowledge in this field, in particular regarding the interaction between the material properties and the coating alloy components and the related combined effect on the mechanical response with particular reference to fatigue.

Stationary ergodic Gaussian random data have been the convenient basis of many of the data used for the development of models for the analysis of random vibration fatigue problems especially using spectral-based methods.1–5 It is, however, known that non-Gaussian excitations occur due to road irregularities in automobiles and turbulent pressure flections in the aerospace sector.6,7 Highly non-Gaussian excitations occur on rail vehicles caused by wheel–rail contact.8 Wind loading effects are also known to be non-Gaussian with high uncertainties and peak values.9 The main consequence of non-Gaussian data effect is that its peakedness effect can be overlooked in analysis and may lead to failure. There have, therefore, been a lot of interest in non-Gaussian fatigue loading analysis.7,10 A number of researchers have attempted to use higher order statistical properties such as signal Kurtosis as an additional parameter to resolve issues associated with inaccuracies encountered in fatigue life prediction under non-Gaussian loading condition.11 A lot of effort has also been going on towards the modelling simulation of non-Gaussian data for fatigue analysis.7,10,12,13

Damage identification attracts wide attention and in-depth research in numerous engineering fields for its paramount importance for systems safety and operational assessment. Among the proposed techniques, structural vibration-based ones are increasingly considered. There are two main reasons behind this progression: a practical motivation, related to the aptitude of dynamic tests in capturing the real behaviour of structural systems,1,2 and a technological reason, related to the reduction of costs and the miniaturisation of the electronic acquisition devices.3 Vibration-based structural health monitoring systems are nowadays widespread, for both new and existing structural systems, and dynamic structural damage identification is a new target of a wide scientific community.4 However, this task is intrinsically more complicated than the ‘mere’ structural identification one, since it calls for extracting damage-sensitive features over time from periodically spaced response measurements. Mathematical models derived from physical basis are used for modelling mechanical systems, often resorting to output-only modal parameter estimation methods5,6; alternatively, data-driven models describing the systems input–output relation are adopted. A trade-off between the two approaches is based on the combination of both, physical insights and experimental data. As reported in the comprehensive reviews published in the last two decades,7–9 the variety of proposed identification strategies are devised to detect, localise, quantify damage and, ultimately, to estimate the remaining service life of the structure. These goals are pursued by relying on different quantities, i.e. physical properties (mass, stiffness, damping), modal properties (natural frequencies, mode shapes, modal damping) and structural response signal features (e.g. Fourier, Wavelet or Hilbert transform). In essence, all the identification strategies aim at extracting reliable signs for early diagnosis of structural damage from the least amount of data. For most real structural systems, direct measurement of global physical properties and their variations, possibly ascribable to damage, is unfeasible; therefore, local, albeit numerous, dynamic response quantities are usually relied upon. Modal property-based approaches seek after dynamic response alteration due to damage, which is usually expected to cause a change in stiffness. Predictive models and physically sound interpretations can be provided by these approaches. However, some difficulties may arise, such as the need to rely on accurate structural modelling and to select proper response signals, not to mention the lack of solution uniqueness of the inverse problem. Differently, signal processing-based techniques seek after signals changes, in time and frequency, between undamaged and damaged states. Direct evidence of signals alteration can be readily detected; however, its physical interpretation is often cumbersome.

Due to outdoor exposure, photovoltaic (PV) modules are subjected to degradation phenomena during their expected lifetime (20–25 years). Producer warranties claim power losses lower than 10% of the initial nominal power during the first 10–12 years, and up to 20% after 20–25 years of operation, with different power loss rates.1 Many external sources of stress, like solar radiation, wind, high temperature excursions, moisture, hail impacts, vibrations, fatigue, etc. contribute to PV damage.1–7 PV degradation manifests itself as a gradual deterioration of materials and components, affecting the optimal working conditions.8,9 As a result of that, electrical performances might decrease over time. In addition to this, safety issues are also related to material and component degradation. Conventionally, a relevant degradation occurs when the PV power output drops below 80% of its initial value,2 while the excess of degradation over a threshold specified for each failure mode could be critical for PV operation.10

Aerodynamic development and testing have become fundamental to successful motorsport and road vehicle programs. The aerodynamic development of the vehicle is fully integrated within the complete design cycle. A mix of development techniques are used throughout the process, where the exact selection of the development tool depends on many factors ranging from performance to accessibility and economics. For example, the wind tunnel provides efficient and fast results of the full vehicle design concept. Computational fluid dynamics (CFD) provides insightful iterations and optimizations of vehicle sub-systems, and provides visual cues that resonate well with production car stylists. However, recent advances bring more capabilities to each of the tools, and provide aerodynamicists with enhanced options to optimize aerodynamic performance parameters. For example, advancements in robotic particle image velocimetry (PIV) and pressure probe measurements provide detailed flow field visualizations. Advancements in computational power and algorithms allow for more advanced full vehicle analysis.

As the world economy continues to grow, energy demand is likely to increase despite efforts to increase the efficiency of energy use. The urgent need to meet this increasing demand and to reduce greenhouse gas emissions is being met, at least in part, by the development of large-scale wind turbines, both onshore and offshore. Nevertheless, for some situations including urban centres and off-grid locations there is an argument for the development of local, decentralized production of electric power to complement large-scale electric power plants which are located in just a few specific strategic locations. One of the most promising local production sources of clean electricity, for example in the built environment, is the small-scale wind turbine and, in particular, vertical axis machines that can tolerate large, rapid changes of wind direction. Although the small size of these turbines inevitably leads to a low power rating, in large numbers they can still contribute significantly to renewable energy production, improve building energy efficiency and make a considerable contribution to the future electricity generation mix.

The immersed boundary method (IBM), first developed by Professor Peskin,1 is a methodology for dealing with boundary conditions at interfaces (including fluid–fluid and fluid–solid ones) based on meshes that do not conform to the shapes of the immersed boundaries or interfaces. The advantages of the IBM are manifold: the mesh generation is very easy even for complicated geometries; mesh movement and mesh regeneration are avoided for flows involving moving boundaries and fluid–structure interactions (FSIs); it is easy to handle the cases where the topology of the computational domain changes; and thus the computational efficiency could be higher than that of the traditional body-conformal grid approaches for the cases involving complicated geometries and large boundary movement.2–6 Due to its simplicity in mesh processing, the IBM has been attracting growing attention in the recent years with effort in developing new features and promoting its applications.7–26

For every complex problem there is a solution that is simple, neat and wrong. – H. L. Mencken

In recent years, continuum robots mimicking biological structures such as octopus tentacles and elephant trunks have gained increasing attention due to their unique structural advantages of inherent compliance and adaptability. This enables them to be suitable for operations in narrow, complex, and unconstructed environments such as detection, rescue, and medical fields.1

The origin and early evolution of birds and avian flight is one of the most discussed topics in palaeontology. Two years after Darwin’s celebrated book On the Origin of Species, one of the major clues for understanding the origin of birds was already discovered in Upper Jurassic limestones from Bavaria in Germany.1,2 The skeleton of Archaeopteryx is characterized by a mosaic of “reptilian” (teeth, claws, bony tail, unfused hand fingers) and avian (feathers, furcular, perching feet).3 Recent discoveries of hundreds of incredibly preserved specimens of feathered dinosaurs and early birds from Middle Jurassic to Early Cretaceous deposits in north eastern China definitely proved that birds are closely related to small carnivorous dinosaurs. Dinosaurs did not completely disappear 65 million years ago, as often depicted, but some of them, known as “birds”, survived and even flourished until today.