Significant pressure drops in the regenerator are typical in pulse-tube cryocoolers, with significant impact on performance. Irreversibilities due to viscous friction obviously lower efficiency, but in the pulse tube, this is not necessarily the most crucial issue. Indeed, by virtue of having only one driven element (the compressor), the pulse tube is-a rather inflexible device from a design standpoint. Pressure and velocity amplitudes and phases determine energy fluxes. Impedances ultimately determine how large these fluxes are, hence how good a refrigerator a given design will produce. Impedance values are determined by the volume distribution, the orifice resistance, and the effect of viscous friction in the regenerator. The focus is on friction, which is difficult to deal with, especially if the device includes a bypass. An asymptotically consistent analysis has been developed, in which the regenerator is represented as an arbitrary porous medium. In contrast with most models, the analysis initially assumes arbitrary large pressure gradients and, of course, arbitrarily large temporal pressure fluctuations. The model thus obtained shows that when pressure differences due to viscous friction are comparable with the amplitude of temporal variations, viscous irreversibilities are much larger than the thermal ones. The regenerator formulation is then incorporated within a small-amplitude, harmonic model of the overall device, including the bypass, if any. for simple assumptions with respect to the temperature profile along the regenerator, such as linear and exponential profiles, closed-form solutions are obtained. Finally, the results are analyzed and their relevance is discussed.

Orifice pulse-tube refrigerators show promise as potentially low cost, reliable and efficient small cryocoolers. This paper presents results from numerical simulation of the device, together with a discussion of some of the challenges involved. The physical model includes a one-dimensional representation of the cryocooler geometry, including compressor, heat exchangers, regenerator, tube, orifice and reservoir. Since the one-dimensional model does not allow for proper simulation of transverse diffusion, there is no alternative to empirical models for viscous losses and convective heat transfer with the heat exchanger walls and the regenerator matrix. The numerical solution is based upon a Godunov scheme, consisting of a Lagrangian step followed by reconstruction step on an Eulerian grid. Some global performance prediction results are presented, and, more importantly, the crucial issue of pressure drop and pressure phase shift across the regenerator is analyzed in detail. A consistent physical explanation of the phenomenon is presented, showing that the pressure drop and phase shift is due to strong viscous friction in the regenerator.

A pulse-tube cryocooler prototype is being built as a proof-of-principle for the Square Kilometer Array radio telescope project. In this paper, the cryocooler design code is described. The pulse-tube cryocooler model formulation, including the machine description with orifice and reservoir, and the approximations made to the conservation equations are discussed. A one-dimensional model is adopted making use of empirical models for viscous losses and convective heat transfer with the heat exchanger walls and the regenerator matrix. The numerical solution is based upon a Godunov-like algorithm, consisting of a Lagrangian half step followed by reconstruction on an Eulerian grid. The need for such an algorithm suitable for rapid changes results from the presence of sudden changes in cross section in the machine and a discretisation including relatively large volumes and also much smaller ones. Some simulation results are presented.

The selection and design of a power system for any form of underwater vehicle is an extremely complex and difficult task. The system must be capable of providing the vehicle with the required mission performance in terms of power and energy and also be volumetrically and gravimetrically compact. When the vehicle to be used is a newly designed US Navy Diver Propulsion Vehicle (DPV), other power system constraints are highlighted. These constraints include limited vehicle diameter, high performance operation, low power requirements, safety and a nonmagnetic signature. Of the many power systems available, very few can fulfil the design criteria for the DPV. One system that can is the hydrocarbon fuelled Stirling engine-a dynamic heat engine using an external combustion system. This paper describes the application of the Stirling engine for underwater duties, and in particular the selection, design and development of a Stirling engine powered DPV. Details are given of the specialist vehicle requirements, engine selection and design and the development of a combustion gas recirculation system to enable pure gaseous oxygen to be used as the combustion oxidant. In addition, details are given of the restrictions imposed on component design and manufacture by the low vehicle power requirements

The selection of an engine and power source for a small, one-man, diver propulsion vehicle (DPV) for potential use in a minefield is the topic of this paper. The stringent requirements of minimal magnetic and acoustic signatures, low detectability, diver safety, and operation in a wide range of environmental conditions prevented the use of standard engine configurations. Other system requirements include two man portability, 10 mile range, 2 knot minimum speed, variable speed control, multiple start/stop capability, 0–300 fsw depth range, 29 °F to 95 °F operating temperature range, and −40°F to 140°F storage temperature range. Several different engine technologies were considered, including electric motors, internal combustion engines, external combustion engines, piezoelectric motors, magneto hydrodynamic engines, and pneumatic engines. Most contenders were quickly eliminated because of their magnetic and/or acoustic signatures. Diesel, Rankine, and Stirling engines were determined to be the best candidates. Candidate power sources were also evaluated. These included batteries, fuel cells, nuclear, and chemical power. Many of these were eliminated because of the safety consideration and others were eliminated because of the incompatibility with the engine. Hydrocarbon combustion was chosen because of its high specific energy and compatibility with candidate engines. Candidate engine and power source technologies were evaluated for their ability to meet system requirements. The Stirling engine and the hydrocarbon combustor were selected as the most promising technologies for engine and power source prototype development This paper discusses the reason for the selection of these technologies.

Economically effective and timely product manufacture requires that appropriate decisions are taken during the design of the product. Recent years have seen very considerable growth in the study and communication of knowledge in the area of design for manufacture (DFM). At the same time there have appeared many additional pressures on the design process: rapid changes in market requirements, evolution and revolution in product and process technologies, legislated strictures and liabilities, and quality and cost issues which must increasingly be addressed earlier in the course of product design. As a consequence there is a strongly perceived need to enhance design methods in order to address the many disparate aspects of design in an efficient manner. In this paper the DFM problem is addressed within this larger context. The approach described in the paper begins with the hypothesis that the concept of manufacturability can be established as one of a number of required attributes of a part which is to be designed and manufactured. An information model is then proposed which provides the potential to allow determination of manufactur-ability to be made in an ongoing fashion in parallel with other design activities. The nature of the information model is shown to be in harmony with object-oriented programming environments. Finally, the information model is used to illustrate the potential to embody the large body of DFM knowledge which is already in existence but which has yet to be systematically encoded.

Abstract The working of the design process has been described as a process of mapping Functional Requirements into Design Parameters. The definitions of these two types of information appear to be based upon intuitive differences. It is posited that by generating an operational distinction between the attributes in these two information domains, useful information patterns can be described for use in the design process. The following distinction is observed: whereas Design Parameters are deemed to have meaning which is insensitive to context, Functional Requirements and attributes can only be assessed with reference to the operative context or environment within which the designed object exists. Functional attributes such as usability, manufacturability, serviceability, safety, and affordability are seen not as intrinsic properties of a designed object but rather as measures of the interaction between the designed object and the relevant context; for the attributes cited, it would be necessary to characterize in turn the user environment, the manufacturing infrastructure, the servicing facilities and skills, the operational/legal environment, and the economic situation. The distinction as outlined serves as a premise upon which a fundamental information structure can be based. The proposed structure involves the categorization of design information into not only the Function Domain and the Design Parameter domain but also embraces a third - contextual - domain identified herein as the Environment Domain. Operational definitions have been devised for each type of information. These definitions also point to the nature of the interactions between the three types of information which take place during the process of design. It is suggested that what is presented here is not a new design paradigm but rather a new way to describe in a clear and explicit fashion the information and information transactions which are known to constitute the design processes. As such, it is seen to be of particular value in design education. However, it may also prove to be useful in organizing information systems for concurrent design activities. This view of design information has emerged through efforts to improve the effectiveness of teaching both design and manufacturing courses as well as the desire to improve the management of graduate design projects. Additionally, it has been influenced through ongoing research and development in the design of specific mechanical systems. As such, it is firmly rooted in the practicalities of design and design teaching and is constantly being put to the tests of utility, practicality, and veracity. For example, assessment of the attribute “manufacturability” has led to a systematic structuring of knowledge and information about manufacturing infrastructure in a way which facilitates decision-making as well as explanation and justification of the decision-making process. Some progress is also being made in developing information patterns which embrace all three information domains by way of providing pre-packaged design solutions for well-established types of design problem. The “bolted-joint”, for example, represents an extremely common design element about which much can be determined analytically but about which many other functional aspects are less accessible. Manufacturability, serviceability, reliability are attributes which can be assessed when due consideration is given to context regarding manufacture, use, placement, etc. The use of this information structure has also been useful in examining various models of the design process whether along traditional problem-solving lines or using artificial intelligence oriented systems. This approach has been used in examining the design process at the graduate level but student feedback has been sufficiently strong to suggest that it would be useful at the undergraduate level. In particular, while the traditional approach to teaching design provides an “activity map”, the addition of an “information map” is seen to be highly complementary. The notion of the information map is also seen to be useful for the management of concurrent design endeavours. It would be expected to provide a picture of both communication pathways and indicate the nature of the communications required. For example, the attribute “affordability” will usually be of particular importance for most designed things. Assessment of this attribute requires knowledge of the marketplace as well as the cost of the article and its performance capability. The cost attribute will require knowledge of the manufacturability of the article and hence the capability of the manufacturing infrastructure. In this way diverse interests can be visibly linked. And of course the map need not be a static one but would be expected to reflect the dynamics of the design process. If the distinction between attribute types continues to prove a useful and valid one, the door is opened to a new generation of parameterized design within which not only geometric relationships are programmed but more fuzzily-defined functions are determined by propagation of information along function-oriented pathways. The language for communication between disparate role-players in the design process has far to grow but the form of the communication can start to take on shape. Finally, the proposed information map will provide an explicit history of a design project thereby facilitating such activities as design audits and accident investigations. Perhaps as important is the role of the information map in recording the knowledge of expert designers and the generation of case histories which more explicitly illustrate the role of specific pieces of information in the generation of design solutions.

Hydrogen may be stored compactly as a cryogenic liquid at low pressure and temperature, i.e. 20 K at atmospheric pressure. Gaseous hydrogen at normal temperature may be liquefied on a small scale using a cryogenic refrigerator (cryocooler). Stirling refrigerators are well suited to this duty. These machines operate on a closed thermodynamic regenerative cycle with compression and expansion of the working fluid (helium) at different temperature levels. Very low temperature Stirling refrigerators have several stages of expansion, typically two or three for a hydrogen liquefier. A concept for an electrically driven Stirling hydrogen liquefier of low capacity is described. Stirling machines can also be used as power systems converting heat to work. A second concept is described for a combustion heated Stirling-Stirling hydrogen liquefier. Conceptual design studies for both units have been carried out including computer simulation of the power system and cryocooler systems. These indicate the net energy flow and principal dimensional parameters permitting first order estimates of costs for prototype manufacture and the unit costs in series production.

The fluidyne, or liquid piston Stirling engine, incorporates liquid columns as displacers and pistons in a heat engine type which can be used in conjunction with low-grade heat sources to provide useful work in the form of liquid pumped over a modest head. The liquid feedback type of fluidyne offers particular advantages including the absence of moving mechanical parts; this type of machine incorporates a liquid column to divert a small quantity of cycle work which is then used to re energise the displacer of the engine which must supply all of the pumping work of the engine. Previous research has demonstrated the import ance of correct design of the mixing of the liquid of the tuning line and the displacer. In this paper the results of an exDeriment are reported which demonstrate the response of the two liquid columns to tho varying system pressure which is both the consequence of engine operation as well as the means bv which the svstem is actuated.

In the most common design of liquid piston Stirling engines, an oscillating water column in a U-tube serves as the displacer. The motion of the water is maintained despite viscous and other flow losses by means of a second water column (usually referred to as the tuning line) that is connected to the displacer U-tube near to the expansion space. This second column, driven by the gas pressure changes in the working gas space, feeds energy into the oscillating displacer column by adding water to it when the water level, and therefore the potential energy, is high, and removing water when the level is lower. Several authors have published theoretical papers describing this process; most of the theories are mathematically equivalent. This paper describes some actual experimental results obtained with a large water-filled U-tube (representing a fluidyne displacer) excited by a second, piston-driven water column. The results are in good agreement with the predictions of a simple theory whose equations are illustrated by the vector, or phasor, method of representing the motions of coupled systems.

Multi-axis CNC machine tools, in which spindle orientation may be varied while cutting, are commonly programmed using APT or a closely-related system in order to generate machine control programs economically. In the consecutive passes through the APT processor and the subsequent post-processing in which generalized data is translated into machine-specific code, a particular type of machining error can develop. Such 'linearization' errors can cause the surface being produced to be partly or wholly outside the specified tolerances.This paper analyzes the sources of linearization error to find the range of possible deviations from the required system performance. This indicates that higher-order interpolation and contextual processors could reduce the severity of these errors and the associated cost of maintaining tolerances.